Powder conveying system for conveying raw material powder to device for manufacturing three-dimensional workpieces

Abstract

The invention relates to a powder delivery system for delivering a raw material powder to a device for producing a three-dimensional workpiece by irradiating a layer of the raw material powder by means of electromagnetic radiation or particle radiation. The powder delivery system comprises: a conveyor line designed to convey a flow of gas at least along a section and a flow of powder driven by the flow of gas at least along the section; and a conveying device designed to convey the gas flow through the conveying line. The powder delivery system further includes a first tank connected to the conveyor line for supplying the powder for the additive manufacturing process to the device; and at least one overflow vessel connected to the conveyor line for receiving excess powder accumulated during the additive manufacturing process. The powder conveying system further comprises a buffer container connected to the conveying line and used for supplying the powder to be screened to the screening equipment; and the screening equipment is used for screening the powder to be screened and distributing the screened powder. The powder delivery system includes an interface for an external tank connected to the conveyor line for introducing fresh or impure powder into the powder delivery system. The powder delivery system further comprises a controller for controlling the powder delivery system such that the system performs at least one of the following delivery processes: a. Delivering the screened powder into the first tank; b. Conveying the powder from the at least one overflow container into a buffer container; and c. Conveying the powder from the outer tank into the buffer container.

Description

Technical Field

[0001] The present invention relates to a powder conveying system for conveying raw material powder to an apparatus for producing three-dimensional workpieces by irradiating a layer of raw material powder with electromagnetic radiation or particle radiation (e.g., an apparatus for selective laser melting or sintering). Background Technology

[0002] In additive manufacturing (or generation) processes for producing three-dimensional workpieces, particularly in the process of building layers, it is known to apply a molding compound, initially shapeless or neutral in shape, of a raw material (e.g., raw material powder) layer by layer onto a carrier, and to solidify the molding compound by site-specific irradiation (e.g., by melting or sintering) to ultimately obtain a workpiece of the desired shape. Irradiation can be performed by electromagnetic radiation (e.g., in the form of laser radiation) or by particle radiation (e.g., in the form of electron radiation). In its initial state, the molding compound may initially be in the form of particles, powder, or liquid, and can be selectively solidified as a result of irradiation, or in other words, can be solidified site-specifically. In particular, the molding compound can be a bulk material, such as raw material powder. The molding compound may include, for example, ceramic, metallic, or plastic materials, and mixtures of these materials. A variation of the building layer method involves so-called laser beam melting (also known as selective laser melting) in a powder bed, wherein, in particular, metallic and / or ceramic raw material powder materials are solidified into a three-dimensional workpiece by irradiation with a laser beam.

[0003] To produce individual workpiece layers in selective laser melting, it is also known to apply a raw material powder material in the form of a raw material powder layer onto a carrier and selectively irradiate the raw material powder material according to the geometry of the workpiece layer to be produced. Laser radiation penetrates the raw material powder and solidifies it, for example, due to melting or sintering caused by heating. Once the workpiece layer has solidified, a new, unprocessed raw material powder layer is applied onto the produced workpiece layer. This can be done using known coating arrangements or powder application equipment. The currently topped, still unprocessed raw material powder layer is then irradiated again. Thus, the workpiece is built layer by layer, where each layer defines the cross-sectional area and / or contour of the workpiece. In this context, it is also known to manufacture workpieces substantially automatically using CAD or similar workpiece data.

[0004] In order to perform a three-dimensional manufacturing process in the processing chamber of the apparatus, fresh, uncontaminated raw material powder needs to be supplied to the coating machine (i.e., powder application equipment) of the apparatus. In addition, it is known that the raw material powder already located in the processing chamber is collected in one or more overflow tanks, then sieved, and finally used again as sieved raw material powder for processing.

[0005] In known devices, powder is manually conveyed at least in sections, and / or powder handling requires manual intervention from operators of the powder conveying system. However, this poses health risks, such as those from inhaling powder, and increases the risk of powder contamination, for example, through contact with ambient air. Therefore, it is desirable to provide a powder conveying system that can convey powder as automatically as possible, particularly between several source and target tanks, and / or requires minimal maintenance and / or minimal user intervention, and / or enables powder conveying in which the powder does not come into contact with the ambient atmosphere or has minimal contact with the ambient atmosphere. Summary of the Invention

[0006] Therefore, the object of the present invention is to provide an improved powder conveying system that solves at least one of the above-mentioned problems or related problems.

[0007] This objective is achieved by a powder delivery system having the features of the independent claim. Further embodiments are detailed in the dependent claims.

[0008] Therefore, according to a first aspect, the present invention relates to a powder conveying system for conveying raw material powder to an apparatus for producing a three-dimensional workpiece by irradiating a layer of raw material powder with electromagnetic radiation or particle radiation. The powder conveying system includes: a conveyor line configured to convey a gas flow and a powder flow driven by the gas flow in at least a section; and a conveying device configured to convey the gas flow through the conveyor line. The powder conveying system further includes: a first tank connected to the conveyor line for supplying powder to the apparatus for an additive manufacturing process; and at least one overflow container connected to the conveyor line for receiving excess powder from the additive manufacturing process. Furthermore, the powder conveying system includes: a buffer container connected to the conveyor line for supplying powder to be sieved to a sieving device; and a sieving device for sieving the powder to be sieved and for distributing sieved powder. The powder conveying system includes an interface connected to the conveyor line for introducing fresh or contaminated powder into the powder conveying system. In addition, the powder conveying system includes a control device for controlling the powder conveying system such that the powder conveying system performs at least one of the following conveying processes: a. conveying sieved powder into a first tank; b. conveying powder from at least one overflow container into a buffer container; and c. conveying powder from an outer tank into a buffer container.

[0009] The powder conveying system can be configured to perform pneumatic conveying of powder at least in sections, or to perform pneumatic conveying of powder entirely. Therefore, one or more conveying sections can also be designed, for example, mechanically (e.g., in the form of a screw conveyor) or as a gravity conveyor. The device can be particularly suitable for selective laser melting or sintering, for example having one or more of the features described above. Alternatively, the device can be suitable for selective electron beam melting.

[0010] The conveyor line may include, for example, one or more pipes and / or one or more hoses and / or one or more connectors. The conveyor line may be powder-sealed, particularly gas- and powder-sealed, such that gas or powder cannot (laterally) enter or leave the conveyor line except through openings in the conveyor line.

[0011] The fact that the conveyor line is configured to transport gas-driven powder flows in sections means that only one section of the entire conveyor loop formed by the conveyor line is configured to transport a gas-powder mixture. The rest of the conveyor loop essentially only transports gases (transport gases), such as air, protective gases, or air-protective gas mixtures.

[0012] The control device may include, for example, a computer. The control device may include a processor and memory, wherein a program is stored in the memory, and when the program is run, the program causes the processor to perform methods according to the details described below. In particular, it should be noted that the method steps described below can all be performed by a control unit. Thus, for example, if stopping the conveyor is described below, this could mean that the control device is configured to control the conveyor in a manner that causes it to stop. As another example, it could be described that measurements from sensors are taken into account. This could mean that the control unit is configured to receive values ​​from the respective sensors and, if necessary, react according to the control values.

[0013] The terms “can,” “storage vessel,” and “container” are used as synonyms herein. In particular, the terms “overflow container” and “overflow can” have the same meaning herein. All the foregoing terms (“can,” “storage vessel,” and “container”) refer to a container constructed to hold a predetermined maximum amount of powder, wherein the use of the corresponding terms does not make any (limiting) statement regarding the size of that maximum amount of powder in the corresponding container. However, specific terms are used to refer to different containers, such as “first can,” “buffer container,” “main storage vessel,” and “outer can.” However, the individual terms should not be construed as limiting, but are only used to distinguish different containers from one another. For example, a “buffer container” may also be referred to as a “second can.” Thus, for example, no structural difference is intended between “can” and “container.” In particular, the corresponding can may also be formed by a section of a conveyor line or a section of a cyclone separator, if that section is constructed to hold a predetermined amount of powder.

[0014] An associated segment of the conveyor line can be provided to each of conveying processes a, b, and c. In other words, an associated segment of the conveyor line can be assigned to each of conveying processes a, b, and c through which the conveying gas flows during the corresponding conveying process. Therefore, in relation to conveying processes a, b, and c, corresponding conveying loops a, b, and c can also be mentioned. Conveying loops a, b, and c may share segments of the conveyor line. In other words, at least one segment of the conveyor line may be used by at least two of conveying processes a, b, and c.

[0015] Therefore, the following applies: Each of the conveying processes a, b, and c can be assigned a corresponding conveying loop a, b, and c. Each conveying loop corresponds to a closed section of the conveyor line. At least two conveying loops can share one or more sections of the conveyor line; that is, at least two conveying loops can use that section or these sections together.

[0016] Based on the above understanding, the terms "transportation loop" and "transportation process" are used as synonyms in some parts of this disclosure. When referring to a defined transport process, a corresponding transport loop is obviously implied, and vice versa.

[0017] Conveying processes a, b, and c can be initiated or implemented by opening and / or closing corresponding valves. For this purpose, corresponding valves can be installed at appropriate locations along the conveyor line. For example, if conveying gas is to be transported through a defined conveying loop, a valve located along the conveyor line along that loop can be opened. Simultaneously, valves separating the defined conveying loop from other conveying loops can be closed, preventing the conveying gas from flowing through one or more conveying loops that do not transport powder. Additionally or alternatively, sections of conveying processes a, b, and c, or one or more of conveying processes a, b, and c, can be designed entirely as non-pneumatic conveying processes. In this case, for example, conveying via the conveyor screw can be started by starting the motor of the conveyor screw and terminated by stopping the motor. For example, gravity conveying can be started by opening a baffle or valve and terminated by closing the baffle or valve.

[0018] The first container may be located above the processing chamber of the device. The first container may be located inside or outside the housing of the device. In addition to the first container, another container (hereinafter also referred to as an intermediate container) may be located above the processing chamber, wherein powder from the first container may be supplied to the intermediate container. Specifically, the first container may be located above the intermediate container. The first container may be located outside the housing of the device, and the intermediate container may be located inside the housing.

[0019] (a) All of the conveying processes a to c may include a pneumatic conveying process in which the powder being conveyed is transported by a gas flow, or (b) at least one of the conveying processes a to c may not include a pneumatic conveying process, in particular conveying process b may not include a pneumatic conveying process.

[0020] In case (b), the conveying process, which does not include pneumatic conveying, may include conveying by conveyor screw and / or conveying by gravity.

[0021] Therefore, there is at least one embodiment in which all conveying processes a to c are designed as pneumatic conveyor lines, configured to convey gas flows and, at least in sections, powder flows driven by the gas flows. However, powder can be supplied (particularly metered) to the respective conveying processes a to c via a conveyor screw. Furthermore, one of the conveying processes a to c, such as process b, can be performed entirely non-pneumatically, for example, by a suitably designed conveyor screw and / or by gravity conveying.

[0022] The powder conveying system may also include a main storage tank connected to the conveyor line for receiving sieved powder. Conveying process a can transfer the sieved powder from the main storage tank to a first container.

[0023] If a main storage tank is not present, the conveying process a can, for example, directly remove the sieved powder from the sieve and convey the sieved powder to the first tank, particularly by pneumatic conveying. For removing powder from the sieve, the sieve may have a corresponding container for the sieved powder.

[0024] The following description applies in particular to powder conveying systems in which all conveying processes a through c are designed as pneumatic conveying processes. However, if technically feasible, the following description may also apply to powder conveying systems in which at least one of the conveying processes a through c is designed as a non-pneumatic conveying process (e.g., screw conveyor).

[0025] The powder conveying system enables closed-loop powder conveying. Specifically, it achieves powder conveying in which the conveyed powder does not leave the system during multiple consecutive additive manufacturing processes of the apparatus. Therefore, the term "closed-loop powder conveying" can be understood as describing and replacing "powder conveying" in which the conveyed powder does not leave the system during multiple consecutive additive manufacturing processes of the apparatus. This minimizes operator intervention.

[0026] Powder conveying systems can be configured to maintain an inert gas atmosphere within the conveying line, particularly during one of the conveying processes a to c. The inert gas can be nitrogen or argon. Therefore, the conveying line can be suitably sealed to inert gas, and one or more inert gas sources can be provided to fill the conveying line with inert gas.

[0027] The powder conveying system may also include a pressure balancing tank connected to the conveyor line. The pressure balancing tank reduces the positive pressure within the conveyor line. The pressure balancing tank may be connected to the conveyor line downstream of the conveying equipment and upstream of the connection between the first tank, at least one overflow tank, buffer tank, main storage tank, and external tank.

[0028] The powder conveying system may also include at least one metering feeder, which in particular includes a conveyor screw for metering the powder to be conveyed from at least one overflow tank, from a main storage tank and / or from an external tank into the conveying line.

[0029] For example, as an alternative to a conveyor screw, a metering feeder may include a metering screw, a vibrating conveyor, or a tubular chain conveyor.

[0030] The powder conveying system may also include at least one separation device, particularly including a cyclone separator, for separating the conveyed powder from the conveying line and for supplying the powder to a first tank and / or a buffer container.

[0031] As an alternative to cyclone separators, separation devices may include, for example, centrifugal separators, filter separators, or electrostatic separators.

[0032] At least one of the following containers may be connected to the pressure balance line: a first tank, at least one overflow tank, a buffer container, a main storage tank, and an external tank.

[0033] The method described below, particularly for controlling a powder conveying system according to the first aspect, can also be used independently of the system of the first aspect. In particular, one or more aspects of the following can be used in a powder conveying system capable of conveying powder from a source tank to a target tank by pneumatic conveying.

[0034] The control device can be configured to perform flow tests, which include testing the flow rate through the conveyor line.

[0035] The powder conveying system may also include a speedometer for measuring the velocity of the gas flow in the conveying line. Flow testing includes: opening a valve in the powder conveying system to allow flow through at least one conveying loop associated with one of the conveying processes a, b, and c. Flow testing also includes: setting the conveying velocity of the gas flow to a value or a predetermined range; and determining whether the velocity value of the gas flow measured by the speed sensor is greater than a predetermined threshold.

[0036] Setting the conveying speed may include: determining whether the speed value measured by the speed sensor is within a predetermined range; if not, determining whether the speed value is below the predetermined range; if the speed value is below the predetermined range, increasing the power of the conveying equipment; and if the speed value is not below the predetermined range, decreasing the power of the conveying equipment.

[0037] The powder conveying system may also include: a pressure sensor for measuring the pressure of the gas flow; and a filter for filtering residual powder particles from the gas flow. Flow testing may include: determining the total pressure loss based on sensor data from the pressure sensor; if the total pressure loss is determined to exceed a predetermined limit, performing filter cleaning of the filter and determining the total pressure loss again; and if the total pressure loss is determined not to exceed the predetermined limit, conveying powder in at least one of conveying processes a, b, and c.

[0038] The flow test performed by the control device may also include: if it is determined that the total pressure loss exceeds a predetermined limit, an error is output before performing filter cleaning.

[0039] The powder conveying system may include at least one oxygen sensor for measuring the oxygen content of the gas stream. The control device may be configured to perform an oxygen content test, which may include measuring the oxygen content using at least one oxygen sensor.

[0040] The powder conveying system may include a first oxygen sensor and a second oxygen sensor. The first oxygen sensor is used to measure the oxygen content of the gas flow, and the second oxygen sensor serves as a redundancy for the first oxygen sensor and is used to measure the oxygen content of the gas flow.

[0041] The control device can be configured to perform pipeline inertization of the conveyor line if a measurement of the oxygen content of the gas flow indicates that the oxygen content is higher than a predetermined limit value.

[0042] Alternatively or additionally, refilling can be performed using a protective gas.

[0043] The powder conveying system may also include a safety valve for releasing gas from the conveying line into the environment or an external volume. Pipeline inertization may include opening the safety valve.

[0044] The filter can be installed downstream of the safety valve (i.e., located downstream of the safety valve).

[0045] Pipeline inertization may also include: evacuating at least a portion of the conveyor line; performing a leak test on the conveyor line; normalizing the conveyor line; and testing the oxygen content in the conveyor line.

[0046] Draining may include: testing whether the measured pressure within the conveyor line is lower than the predetermined draining pressure.

[0047] The powder conveying system may also include a speedometer for measuring the velocity of the gas flow in the conveying line. Evacuation may include: determining whether the velocity value measured by the speed sensor is within a predetermined range; if not, determining whether the velocity value is below the predetermined range; if the velocity value is below the predetermined range, increasing the power of the conveying equipment; and if the velocity value is not below the predetermined range, decreasing the power of the conveying equipment.

[0048] Leakage testing may include: closing safety valves; stopping the conveyor; determining whether each increase in system pressure exceeds a predetermined limit; outputting an error message if each increase in system pressure exceeds the predetermined limit; and continuing to normalize the conveyor line if each increase in system pressure does not exceed the predetermined limit.

[0049] A powder conveying system may include a first pressure sensor located at the inlet side of the conveying device and a second pressure sensor located at the outlet side of the conveying device. Determining the increase in system pressure may include considering the sum of the measurements from the first and second pressure sensors.

[0050] Normalizing a conveyor line may include: filling the conveyor line with an inert gas; and measuring the oxygen content in the conveyor line.

[0051] The powder conveying system may further include: restarting pipeline inerting if the oxygen content measured in the conveying line exceeds a predetermined limit. Optionally, inert gas may be refilled before restarting pipeline inerting. If the predetermined limit is still exceeded, pipeline inerting is restarted. If the limit is no longer exceeded, conveying may, for example, begin, or restarting pipeline inerting may be omitted.

[0052] Testing the oxygen content in the delivery line may include restarting the pipeline inertization process if the measured oxygen content exceeds a predetermined limit for a predetermined number of times.

[0053] The control device can be configured to perform conveying according to at least one of conveying processes a, b, and c, wherein conveying includes: opening at least one valve arranged in a conveying loop assigned to the corresponding conveying process.

[0054] The control device can be configured to perform conveying control during conveying, including: monitoring the oxygen content in the conveying line; monitoring the pressure in the conveying line; monitoring the conveying speed of the gas flow; monitoring at least one measurement parameter of the powder conveying system; and testing termination conditions for terminating the conveying.

[0055] Monitoring the oxygen content in the conveyor line may include: determining whether the measured oxygen content exceeds a predetermined limit; and if the measured oxygen content exceeds the predetermined limit, opening a valve to supply inert gas to the conveyor line.

[0056] Monitoring the pressure in the conveyor line may include: determining whether the measured pressure in the conveyor line is within a predetermined range; if the measured pressure in the conveyor line is below the predetermined range, opening a valve to supply inert gas; and if the measured pressure in the conveyor line is above the predetermined range, opening a safety valve to release gas from the conveyor line.

[0057] Monitoring the conveying speed of a gas flow may include: determining the gas density of the gas flow based on at least one measured parameter of the gas flow; determining the mass flow rate of powder conveyed by the conveyor line based on control values ​​of a metering device applied to the source tank of the conveying system; determining a target speed of the gas flow based on the gas density and the mass flow rate of the bulk material; and controlling the conveying equipment to convey the gas flow at the determined target speed.

[0058] Monitoring at least one measurement parameter of the powder conveying system may include: a metering device that controls the conveying of the source tank with a predetermined control value; determining whether at least one measurement parameter of the powder conveying system is higher than a predetermined maximum value of the corresponding parameter; and if at least one measurement parameter is higher than the predetermined maximum value, reducing the control value of the metering device by a predetermined value, such that the metering device dispenses a lower dose of powder into the gas stream each time.

[0059] The control device can also be configured to increase the control value of the metering device by a predetermined value if at least one measured parameter is below a predetermined maximum value, so that the metering device dispenses a higher dose of powder into the gas stream each time.

[0060] At least one parameter may include at least one of the following parameters: delivery speed, pump outlet pressure, pump power, and powder dosage per batch.

[0061] The termination conditions for testing to stop the delivery may include stopping the delivery equipment when at least one of the following events is detected: the filling level of the source tank from which the powder to be delivered is below a predetermined limit; the filling level of the target tank to which the powder is delivered exceeds a predetermined limit; a predetermined maximum delivery time is exceeded; and the total pressure loss of the delivery gas exceeds a predetermined limit.

[0062] The control device can be configured to perform pipeline cleaning and filter cleaning after the termination of conveying according to conveying processes a, b and / or c, wherein pipeline cleaning includes: allowing gas to flow through the conveying line, and wherein filter cleaning includes: purging the filters installed in the conveying line using compressed air.

[0063] The powder conveying system may also include at least one dew point sensor for measuring the relative humidity within the conveying line and / or the relative humidity inside the tank of the powder conveying system. The control unit may be configured to initiate automatic powder drying when the measured relative humidity exceeds a predetermined limit.

[0064] Powder drying can be performed using a drying unit within a powder conveying system. For this purpose, the drying unit may include a heating unit and / or a desiccant. Additionally, a vacuum generating unit can be used as the drying unit. Then, powder drying can be stopped when a dew point sensor measures a predetermined residual moisture content, i.e., when the measured moisture value is below a predetermined threshold.

[0065] A dew point sensor may be installed on at least one of the following components of a powder conveying system: the main storage tank, the external tank, and the conveying equipment.

[0066] At least one oxygen sensor for measuring oxygen concentration may be installed on at least one of the following components of the powder conveying system: a first tank, an overflow tank, a buffer container, a main storage tank, an external tank, and a screening device. The control device may be configured to initiate the filling of the conveying line with inert gas when it is determined that at least one of the installed oxygen sensors has measured an oxygen concentration above a predetermined limit value.

[0067] At least one pressure sensor for measuring pressure may be installed on at least one of the following components of the powder conveying system: a first tank, an overflow tank, a buffer container, a main storage tank, an external tank, and a screening device. The control device may be configured to, when it is determined that at least one of the installed pressure sensors measures a pressure increase exceeding a predetermined limit value per specified time unit, perform at least one of the following steps: output a warning message; fill the conveyor line or affected section of the powder conveying system with inert gas; measure the oxygen content in the affected section of the powder conveying system; and perform filter cleaning.

[0068] At least one temperature sensor for measuring temperature may be installed on at least one motor in the powder conveying system, particularly on the motor of the conveying device and / or the conveyor screw. The control device may be configured to shut down the conveying device if it is determined that at least one of the installed temperature sensors measures a temperature value higher than a predetermined limit value.

[0069] The control device can be configured to initiate the shutdown of the conveying device if at least one of the following events is detected: the torque of the motor of the metering feeder exceeds a predetermined limit; the valve of the powder conveying system is in an actual position that does not correspond to its set position; and a fault is detected in the sensor.

[0070] A level sensor for measuring the fill level of at least one overflow container may be provided on at least one overflow container. The level sensor is particularly in the form of one or more weighing units. A level sensor for measuring the level of an intermediate container is provided on an intermediate container, which is arranged above a processing chamber and configured to supply powder to the processing chamber and to supply powder from a first container to the intermediate container. The level sensor is particularly in the form of one or more weighing units. In the event of a failure to convey powder by the conveying equipment, the control equipment may be configured to continue the additive manufacturing process of the device until at least one of the following events occurs: the fill level sensor of the overflow container detects that the fill level of the overflow container exceeds a predetermined limit value; and the fill level sensor of the intermediate container detects that the fill level of the intermediate container is below a predetermined limit value.

[0071] The control device can be configured to deliver a predetermined amount of powder according to one of the conveying processes a, b, or c, and then stop the conveying.

[0072] The control device can be configured to determine a priority value for each conveying process after each conveying operation according to one of the conveying processes a, b, and c, based on a predetermined fill level limit for the source tank and a predetermined fill level limit for the target tank. The control device can then be configured to execute conveying according to the conveying process with the highest priority value.

[0073] For example, the apparatus described herein for producing three-dimensional workpieces by irradiating a layer of raw material powder with electromagnetic radiation or particle radiation may include a carrier device for applying powder in multiple layers to form a powder bed. Furthermore, one or more powder application devices may be provided for applying powder, and, if desired, powder of different materials. A separate powder application device may be provided for each material. The carrier device may be moved vertically downwards by a lifting device so that the top powder layer remains at the same height relative to the build chamber of the apparatus. Additionally, the apparatus may include one or more irradiation units. Each irradiation unit includes a beam source (particularly a laser beam source) and an optical system having one or more optical components (e.g., beam expander, focusing unit, scanner device, F-θ lens) for shaping and deflecting the beam. Alternatively, the beam source may be located outside the respective irradiation unit, wherein the beam is guided to the irradiation unit by a light guide (e.g., glass fiber). Attached Figure Description

[0074] The invention will be explained below with reference to the accompanying drawings. These drawings show: Figure 1 A schematic overview of a powder conveying system used to transport raw material powder to an apparatus for producing three-dimensional workpieces; Figure 2 Flowchart of advanced functions of the powder conveying system; Figure 3 : Flow test of conveying loop a or conveying in conveying loop a, wherein, according to Figure 1 The functional components of the powder conveying system are highlighted in bold. Figure 4 : Flow test of conveying loop b or conveying in conveying loop b, wherein, according to Figure 1 The functional components of the powder conveying system are highlighted in bold. Figure 5 : Flow test of conveying loop c or conveying in conveying loop c, wherein, according to Figure 1 The functional components of the powder conveying system are highlighted in bold. Figure 5a A schematic overview of alternative designs for powder conveying systems used to transport raw material powder to apparatus for producing three-dimensional workpieces; Figure 6 Flowchart of leak testing; Figure 7 Pipeline emptying, among which, according to Figure 1 The functional components of the powder conveying system are highlighted in bold. Figure 8 Flowchart for oxygen content testing; Figure 9 Flowchart for adjusting the speed of the conveyed gas; Figure 10 Flowchart for limit value control; Figure 11 : An apparatus for producing three-dimensional workpieces by irradiating a layer of raw material powder with electromagnetic radiation or particle radiation, the apparatus being equipped with a bulk material conveying system; Figure 12 : A schematic representation of a quantitative feeding device in the form of a conveyor screw, wherein the parameters of the conveyor screw are specified for calculating the mass flow rate conveyed by the conveyor screw; Figure 13 Flowchart of the limit value control process; Figure 14 The apparatus shown is for producing three-dimensional workpieces by irradiating a layer of raw material powder with electromagnetic radiation or particle radiation, the apparatus being equipped with a powder handling system including a sieving device. Figure 15 : Shown according to Figure 14 Detailed view of the screening equipment used in the powder handling system; Figure 16 This shows loose powder clumps on a flat surface; Figure 17 This illustrates that when the sieve is continuously driven at a lower (second) driving power, according to Figure 15 Screening equipment; Figure 18 This illustrates that when the sieve is continuously driven at a higher (first) driving power, according to Figure 15 Screening equipment; Figure 19 : Shows the running data Figure 15 The screening equipment, wherein the screening equipment is periodically driven alternately with a first driving power and a second driving power; Figure 20 This shows the changes in drive power (top) and feed mass flow rate (bottom) over time when the feed mass flow rate is controlled based on drive power. Figure 21 This illustrates the change in the step response of the sum of the mass flow rates of the sieved powder and the oversized particles to the metered feed mass flow rate in the presence of defects in the sieve; and Figure 22 An alternative embodiment of the screening equipment is shown, in which the screening equipment includes a housing and a sieve mounted so as to be tiltable relative to the housing, and the tilt angle of the sieve relative to the horizontal plane is adjustable. Detailed Implementation

[0075] Figure 1 A schematic representation of a powder conveying system is shown, which is used to convey raw material powder into an apparatus 1100 for producing three-dimensional workpieces by irradiating the raw material powder layer with electromagnetic radiation or particle radiation.

[0076] exist Figure 1 The system shown can perform several conveying processes within the system, namely, conveying processes from different source tanks to different target tanks. The exact structure and operating mode of the powder conveying system are described below.

[0077] Not in Figure 1 The control equipment shown (but as part of the system) is the control device for the powder conveying system. This control equipment controls... Figure 1 The system is illustrated with various components, particularly the valves, metering devices, and conveying devices described below. Additionally, the control equipment receives and processes data from sensors described below.

[0078] Apparatus 1100 corresponds, for example, to an apparatus commonly known for additive manufacturing by selective laser melting or selective laser sintering. Figure 1 Only the processing chamber of the apparatus 1100 is shown. Raw material powder is supplied from the intermediate tank 2102 (also referred to as the hopper) of the apparatus 1100 to the processing chamber (more precisely, to the powder application device or coater in the processing chamber 1011) via the loader 2104.

[0079] Excess powder from the additive manufacturing process can be collected in either the front overflow tank 2 or the rear overflow tank 3. This excess powder is primarily unwanted powder when applying a new powder layer, and is therefore pushed into one of the overflow tanks 2 or 3 by the powder application equipment. An inlet valve 19 or 17 is located at the inlet of the respective powder tank 2 or 3.

[0080] Overflow tanks 2 and 3 each include an outlet valve 34 or 25. Furthermore, powder sensors 35 or 26 are provided in the respective outlet areas of overflow tanks 2 and 3. This monitors the inlet of the associated metering device, which takes the form of a metering screw (or also referred to as a conveyor screw) 36 or 27. Powder sensors 37 or 28 are also provided at the outlet of the respective metering screw 36 or 27.

[0081] Overflow tanks 2 and 3 each include upper powder sensors 31 and 22 and lower powder sensors 32 and 23 for monitoring the filling level of the respective overflow tanks 2 and 3. Additionally, weighing units 33 and 24 are provided on the respective overflow tanks 2 and 3. For pressure balancing, valves 30 and 21 are located on the respective upper sides of overflow tanks 2 and 3. The respective overflow tanks 2 and 3 are connected to the conveyor line via valves 30 and 21. For this purpose, additional valves 38 and 29 are located at the respective connection points of the conveyor line.

[0082] The processing chamber is connected to the lines that connect valves 30 and 21 to valves 38 and 29 via valves 20 and 18, which are used for pressure balancing.

[0083] Powder is conveyed from overflow tanks 2 and 3 to buffer container 4 via conveyor lines. Cyclone separator 42 is located above buffer container 4 to separate the powder.

[0084] After the powder has been separated in the cyclone separator 42, the delivery gas flows through a conveyor line into the filter 41, where any remaining powder particles are filtered out. To clean the filter, a compressed gas supply 39 contacts the filter 41 and can be switched on via a control device. A valve 40 is located downstream of the filter 41. The delivery circuit leads to a delivery device 79, which is provided in the form of a pump 79. The path of the delivery gas from valve 40 proceeds sequentially through a pump protection filter 74, a dew point sensor 75, an oxygen sensor 76, a redundant oxygen sensor 77, and a pressure sensor 78, more specifically, the pressure sensor 78 located on the pump suction side.

[0085] Starting from pump 79, the delivered gas flows further through pressure sensor 80 located on the pump pressure side (in... Figure 1 (Not shown separately on the pump pressure side in the schematic representation). A pressure compensation tank 84 is provided downstream of the pressure sensor 80. The pressure compensation tank 84 is equipped with an inert gas supply 82 and a safety valve 83. The pressure compensation tank 84 is used to prevent excessive positive pressure on the pump pressure side (i.e., downstream of pump 79).

[0086] An exhaust valve 81 is located between the pressure sensor 80 and the pressure compensation tank 84, through which gas can be discharged from the delivery line. Further downstream of the pressure compensation tank 84 are speed and temperature sensors 86. After passing through the exhaust ports of valves 88 and 87, powder can be delivered from the main storage tank 6 by opening valve 72, and / or powder can be delivered from the external tank 8 and / or from one or both of the overflow tanks 2 and 3 by opening valve 73.

[0087] When valve 72 is opened, after powder from main storage tank 6 is introduced into the gas stream via valve 60, the delivery gas flows to cyclone separator 9 located above first tank 1. At cyclone separator 9, the powder is separated and delivered to first tank 1. The delivery gas flows along the aforementioned path through cyclone separator 42 and through filter 41 back to pump 79 (including passing through several sensors).

[0088] When valve 73 is open, powder from external tank 8 can be added to the conveying gas stream via metering feeder 70 (conveyor screw 70). Additionally, powder can be added from overflow tank 3 via conveyor screw 27, and / or from overflow tank 2 via conveyor screw 36. Then, as described above, the conveying gas-powder mixture flows to cyclone separator 42, where it can be conveyed to buffer container 4.

[0089] Powder leaving the conveyor screw 58 of the main storage tank 6 can be supplied to the conveying gas of the conveying line associated with valve 72 via valve 60, or alternatively or additionally, to the conveying gas of the conveying line associated with valve 73 via valve 61.

[0090] The powder separated by the cyclone separator 9 enters the first tank 1 through the inlet valve 12. The powder is then conveyed from the first tank 1 to the intermediate tank 2102 (also referred to as the hopper) through the outlet valve 16, for example, by gravity conveying. The powder can then be supplied from the intermediate tank 2102 to the processing chamber 1011 of the device 1100 via the loader 2104 for use in the additive manufacturing process.

[0091] The powder separated by cyclone separator 42 enters buffer container 4 through inlet valve 44. The powder can then be supplied from buffer container 4 to screening device 5 (by gravity) through outlet valve 48. Screening device 5 is used to filter out larger particles and impurities from the powder, especially if the powder supplied to screening device 5 has been used in the additive manufacturing process and originates, for example, from one or both of overflow tanks 2 and 3.

[0092] The screening equipment 5 includes a quantitative feeding device 49, which is in the form of a conveyor screw 49, used to feed the powder to be screened to the ultrasonic sieve 50 of the screening equipment 5 in a quantitative manner. The screened powder or screened particles are supplied to the oversized particle container 7 through pipelines.

[0093] The sieved powder enters the main storage tank 6 through the inlet valve 52. As described above, the powder can be supplied from the main storage tank 6 to the first tank 1 through the outlet valve 56 of the conveyor line for pneumatic conveying and the conveyor screw 58.

[0094] Furthermore, the outer tank 8 can be connected to a conveyor line, and the outer tank 8 can be, for example, a movable tank that can be connected to the conveyor line via a suitable interface. Alternatively, the movable tank can be connected to the outer tank 8 via an inlet valve 63, so that, for example, fresh powder can be supplied to the system.

[0095] Powder from external tank 8 is supplied to conveyor screw 70 through outlet valve 67 of external tank 8 and inlet valve 68 of conveyor screw 70. Powder enters the conveyor line from conveyor screw 70 and is conveyed by gas flow when valve 73 is open.

[0096] Powder containers 1, 2, 3, 4, 6, and 8 each have inlet valves 12, 19, 17, 44, 52, and 63, and outlet valves 14, 34, 25, 48, 56, and 67. For pressure balancing, powder containers 1, 2, 3, 4, 6, and 8 also have valves 10 or 11, 30, 21, 43, 51, and 62. Through these pressure balancing valves, the respective powder containers are connected to the conveying lines through which the gas flows via their respective pressure balancing lines, except in the case of container 1, where the pressure balancing line of container 1 is connected to the intermediate container.

[0097] The pressure balance lines of powder containers 2, 3, 4, 6, and 8 are connected to the conveyor line via associated valves 38, 29, 8 (valve 8 is the same for containers 4 and 6) and 87.

[0098] To measure the filling level of powder containers 1, 2, 3, 4, 6, and 8, each of these powder containers includes upper powder sensors 13, 31, 22, 45, 53, and 64 and lower powder sensors 14, 32, 23, 46, 54, and 65.

[0099] In addition, powder containers 1, 2, 3, 4, 6, and 8 are each equipped with weighing units 15, 33, 24, 47, 55, and 66, respectively. These weighing units are used to weigh the corresponding containers and therefore also to determine the filling level of the corresponding containers.

[0100] Specifically, in order to prevent and / or detect blockages, powder sensors 35, 26, 57, and 69 are installed at the inlets of conveyor screws 36, 27, 58, and 70, and powder sensors 37, 28, 59, and 71 are installed at the outlets of conveyor screws 36, 27, 58, and 70.

[0101] Figure 1 The various components of the bulk material conveying system shown are listed again below by their reference numerals, wherein the list is not exhaustive.

[0102] 1-First can 2-Front Overflow Tank 3-Rear Overflow Tank 4-lock 5-sieve 6-Main Storage 7-Extra Large Particle Bucket (Extra Large Particle Container) 8-External Tank Module (External Tank) 9-Cyclone Separator 10-Valve pressure balance, first tank 11-Valve pressure balance, first tank, machine side 12-Valve inlet, first tank 13-Upper powder sensor, first can 14-Lower powder sensor, first can 15 - Weighing Unit, First Tank 16-valve outlet, first tank 17-Valve inlet, rear overflow tank 18-valve pressure balance, rear overflow tank, machine side 19-Valve inlet, front overflow tank 20-valve pressure balance, front overflow tank, machine side 21-Valve pressure balance, rear overflow tank 22-Upper powder sensor, rear overflow tank 23-Lower powder sensor, rear overflow tank 24-Weighing unit, rear overflow tank 25-Valve outlet, rear overflow tank 26 - Powder sensor inlet, metering screw, rear overflow tank 27-Quantitative feed screw, rear overflow tank 28 - Powder sensor outlet, metering feed screw, rear overflow tank 29-Valve pressure balancing conveyor line, rear overflow tank 30-valve pressure balance, front overflow tank 31-Upper powder sensor, front overflow tank 32-Lower powder sensor, front overflow tank 33-Weighing unit, front overflow tank 34-Valve outlet, front overflow tank 35 - Powder sensor inlet, metering screw, front overflow tank 36-Quantitative feed screw, front overflow tank 37-Powder sensor outlet, metering feed screw, front overflow tank 38-valve pressure balancing conveyor line, front overflow tank 39- Compressed gas supply, filter cleaning 40-valve suction side filter 41-Filter 42-Cyclone Separator 43-Valve Pressure Balance Lock 44-Valve Inlet Lock 45-Upper Powder Sensor Lock 46-Lower Powder Sensor Lock 47-Weighing Unit Lock 48-Valve Outlet Lock 49-Quantitative Feeding Screw Screen 50-Ultrasonic sieve 51-Valve Pressure Balance Main Storage 52-Valve Inlet Main Storage 53-Upper Powder Sensor Main Storage 54-Lower Powder Sensor Main Storage 55-Weighing Unit Main Storage 56-valve outlet main storage 57 - Powder sensor inlet, metering screw main storage 58-Quantitative feed screw main storage unit 59 - Powder sensor outlet, metering screw main storage 60-Valve Powder Outlet “a” 61-Valve Powder Outlet “b” 62-Valve Pressure Balancing External Tank Module 63-Valve Inlet External Tank Module 64-Upper Powder Sensor External Can Module 65-Lower Powder Sensor External Can Module 66-Weighing Unit External Tank Module 67-Valve Outlet External Tank Module 68-Valve Inlet Metering Feed Screw External Tank Module 69-Powder sensor inlet, external tank module for metering feed screw 70-Quantitative Feeding Screw External Tank Module 71-Powder sensor outlet, external tank module for metering feed screw 72-Valve Gas Supply “a” 73-Valve gas supply “b” and “c” 74-Pump Protection Filter 75-Dew Point Sensor 76-Oxygen Sensor 77-Redundant Oxygen Sensor 78 - Pressure sensor, pump suction side 79-Pump 80-Pressure sensor, pump pressure side 81-Exhaust Valve 82-Inert gas supply pressure compensation tank 83-Safety Valve Pressure Compensation Tank 84-Pressure Compensation Tank 85-Inert Gas Supply and Conveying Line 86-Speed ​​and Temperature Sensor 87-Valve Pressure Balance Conveyor Line External Tank Module 88-valve pressure balance, main storage tank of the conveyor line Combining the above description and Figure 1The arrangement of the bulk material conveying system shown allows for at least three conveying processes a to c. In other words, the bulk material conveying system includes at least three conveying loops a to c. Here, the conveying loops share a conveying line through which the conveying gas flows, at least in sections. Furthermore, two conveying processes can operate in parallel, particularly conveying processes b and c, described below. This enables the mixing of powders from overflow tanks 2 and 3 and external tank 8, wherein the powders are mixed in buffer container 4.

[0103] The various conveying processes and conveying loops are explained below. Figures 3 to 5 As shown in the image. Here, Figure 3 The conveying process a is shown. Figure 4 The conveying process b is shown. Figure 5 The conveying process c is shown. The components in operation are shown in bold so that the powder or gas flow can be tracked.

[0104] Conveying process a ( Figure 3 ): In conveying process a, powder is conveyed from the main storage tank 6 (source tank) to the first tank 1 (target tank). The conveying in process a includes first opening valves 56 and 60. The powder in the main storage tank 6 is pre-screened by the screening device 5. The powder can then be supplied from the first tank 1 to the additive manufacturing process in the processing chamber. The powder is fed into the conveyor line via the conveyor screw 58 and separated in the cyclone separator 9. The conveying gas flows back to the pump 79 through the filter 41.

[0105] Transport process b ( Figure 4 ): In conveying process b, powder is conveyed from overflow tank 2 (source tank) and / or overflow tank 3 (source tank) to buffer container 4 (target tank). The conveying in process b includes first opening valves 25 and 34. The powder in the overflow tank is contaminated powder that has not yet solidified during the additive manufacturing process. The contaminated powder is supplied from buffer container 4 to screening equipment 5. The powder is fed into the conveyor line via conveyor screws 36 and 27 and separated in cyclone separator 42. The conveying gas flows back to pump 79 through filter 41.

[0106] Conveying process c ( Figure 5 ): In conveying process c, powder is conveyed from external tank 8 (source tank) to buffer container 4 (target tank). The conveying process c includes first opening valves 67 and 68. The powder in external tank 8 can be contaminated powder supplied from outside the process. However, the powder in external tank 8 can also be uncontaminated, fresh powder. The powder conveyed to buffer container 4 is fed to screening equipment 5. The powder is fed into the conveyor line via conveyor screw 69 and separated in cyclone separator 42. The conveying gas flows back to pump 79 through filter 41.

[0107] Figure 5a A schematic representation of an alternative powder conveying system is shown, used to convey raw material powder into an apparatus 1100 for producing three-dimensional workpieces by irradiating a layer of raw material powder with electromagnetic radiation or particle radiation. Because... Figure 5a The powder conveying system is similar in design to Figure 1 The powder conveying system is described below, therefore the following description focuses particularly on the differences between the two embodiments. Unless otherwise stated, Figure 5a The unexplained aspects of the powder conveying system may correspond to Figure 1 Those aspects of the system. In particular, Figure 5 The same or equivalent components of the powder conveying system are made of the same material as those in the powder conveying system. Figure 1 The same reference numerals are used in the accompanying drawings.

[0108] exist Figure 5a The system shown can perform several conveying processes within the system, namely, conveying processes from different source tanks to different target tanks. The exact structure and operating mode of the powder conveying system are described below.

[0109] Not in Figure 5a The control equipment shown (but as part of the system) is the control device for the powder conveying system. This control equipment controls... Figure 5a The system comprises various components, particularly the valves, metering feeders, conveyor screws, and conveying devices described below. Additionally, the control equipment receives and processes data from... Figure 5a The system shown contains sensor data, which correspond to the data in the above-described combination. Figure 1 The sensors described above will not be described again to avoid repetition.

[0110] Apparatus 1100 corresponds, for example, to an apparatus commonly known for additive manufacturing by selective laser melting or selective laser sintering. Figure 5a Only the processing chamber 1011 of the apparatus 1100 is shown. Raw material powder is supplied from the first tank 1 of the apparatus 1100 to the processing chamber 1011 (more precisely, to a powder application device or coater within the processing chamber 1011) via a loader. Alternatively, it can be described according to the above... Figure 1 The description states that an additional intermediate tank is provided between the first tank 1 and the processing chamber 1011.

[0111] Excess powder from the additive manufacturing process can be collected in either the front overflow tank 2 or the rear overflow tank 3, wherein overflow tanks 2 and 3 are... Figure 5a The excess powder is mainly unwanted powder when applying a new powder layer, so the powder is pushed into one of the overflow tanks 2 or 3 by the powder application device.

[0112] Powder is conveyed from overflow tanks 2 and 3 to buffer container 4 via conveyor screws 991, which are part of a conveyor line. Specifically, two conveyor screws 991 may be provided—one of these screws is used for each of the overflow tanks 2 and 3. A valve 992 is provided at the inlet of buffer container 4. In the area of ​​valve 992, powder can fall into buffer container 4 by gravity.

[0113] The powder received in the buffer container 4 can be supplied from the buffer container 4 to the screening equipment 5 via the conveyor screw 49. A valve 993 is provided at the inlet of the screening equipment 5, and the valve 993 must be opened in order to supply powder to the screening equipment. The powder is supplied to the screening equipment 5 by gravity conveying starting from one end of the conveyor screw 49.

[0114] The sieved oversized particles are pneumatically conveyed to the oversized particle container 7 via a cyclone separator 994. A valve 995 is installed at the inlet of the oversized particle container. The sieved powder is collected in a designated volume at the bottom of the sieving equipment and conveyed out from the bottom of the sieving equipment via pneumatic conveying. The powder is separated in the cyclone separator 9 and supplied to the first tank 1.

[0115] The gas flow in the pneumatic conveying circuit is driven by a conveying device 79, which is provided in the form of a pump 79. An exhaust valve 81 is provided downstream of the pump 79, through which gas can be discharged from the conveying line.

[0116] When valve 996 is open, powder from external tank 8 can be mixed into the conveying gas stream via metering feeder 70 (conveyor screw 70). The conveying gas-powder mixture then flows to cyclone separator 997, where it can be conveyed to buffer container 4. This allows new powder (i.e., powder newly supplied to the system) to be first screened by screening device 5 and then processed in processing chamber 1011.

[0117] The powder separated by the cyclone separator 9 enters the first tank 1 through the inlet valve 12. The powder can then be supplied from the first tank 1 to the loader of the processing chamber 1011 of the device 1100 and used in the additive manufacturing process.

[0118] The powder separated by the cyclone separator 997 enters the buffer container 4 through the inlet valve 998. The powder can then be fed from the buffer container 4 to the screening equipment 5 via the conveyor screw 49.

[0119] Furthermore, the powder conveying system can be emptied by controlling the corresponding valves, particularly by the powder screw conveyor 49 and the cyclone separator 994.

[0120] A valve 9911 is provided at the inlet of cyclone separator 9. A valve 9910 is provided at the inlet of cyclone separator 997. A valve 999 is provided at the inlet of cyclone separator 994. By opening these valves 999, 9910, and 9911, separation through the corresponding cyclone separator can be initiated. Therefore, in particular, the corresponding conveying process can be opened and closed by these valves 999, 9910, and 9911.

[0121] Combining the above description and Figure 5a The powder conveying system arrangement shown allows for at least three conveying processes a to c. In other words, the bulk material conveying system includes at least three conveying loops a to c. Here, the conveying loops share a conveying line through which the conveying gas flows, at least in sections. Furthermore, two conveying processes can operate in parallel, particularly conveying processes b and c, described below. This enables the mixing of powder from overflow tanks 2 and 3 and external tank 8, wherein the powder is mixed in buffer container 4. Figure 5a In the example shown, the conveying process b is implemented as a non-pneumatic conveying process.

[0122] The various conveying processes and conveying loops are explained below.

[0123] Conveying process a: In conveying process a, the sieved powder is conveyed from the bottom volume of the sieving device 5 (source tank) to the first tank 1 (target tank). The conveying in conveying process a includes at least opening valve 9911. The sieved powder is powder that has been pre-sieved by the sieving device 5. The powder can then be supplied from the first tank 1 to the additive manufacturing process in the processing chamber 1011. The conveying gas flows back to pump 79 through valve 9911.

[0124] Conveying process b: In conveying process b, powder is conveyed from overflow tank 2 (source tank) and / or overflow tank 3 (source tank) to buffer container 4 (target tank). For this purpose, conveyor screw 991 is activated, and conveying is performed mechanically rather than pneumatically. At one end of conveyor screw 991, powder falls into buffer container 4 by gravity through an open valve 992. The conveying in conveying process b may include opening valve 992 first. The powder in overflow tanks 2 and 3 is contaminated powder that has not yet solidified during the additive manufacturing process. The contaminated powder is supplied from buffer container 4 to screening equipment 5 via conveyor screw 49.

[0125] Conveying process c: In conveying process c, powder is conveyed from external tank 8 (source tank) to buffer container 4 (target tank). The conveying process c includes first opening valves 996 and 9910. The powder in external tank 8 can be contaminated powder supplied from outside the process. However, the powder in external tank 8 can also be uncontaminated, fresh powder. The powder conveyed to buffer container 4 is fed to screening equipment 5. The powder is fed into the conveyor line via conveyor screw 70 and separated in cyclone separator 997. The conveying gas flows back to pump 79 through valve 9910.

[0126] Figure 1 Further details of the powder conveying system shown are explained below, particularly describing the processes and methods that can be performed in conjunction with the powder conveying system. The described methods are performed by a control unit (not shown) of the powder conveying system. For this purpose, the control device includes a processor and a memory, in which corresponding commands for executing the various methods are stored. Furthermore, the control device includes one or more interfaces for receiving sensor data and a human-machine interface. Finally, the control device includes one or more interfaces for (electrically) controlling the various components of the powder conveying system (e.g., valves, metering devices, etc.).

[0127] Although the explanation below specifically addresses Figure 1 The powder conveying system, but the explanation below also applies to powder conveying systems. Figure 5a The powder conveying system. Even in Figure 5a It is not explicitly stated in the document that, Figure 5a The container shown and described above also includes corresponding sensors and / or valves for performing the processes described below.

[0128] Exemplary embodiments of the technology proposed herein are particularly capable of conveying inert metal powders, which generally approximate the optimal conveying point (i.e., conveying gas velocity) for common powder types by inputting specific powder parameters (particle size, bulk density, etc.) and respond to varying system effects (clogged filters, leaks, increased O2, etc.).

[0129] The powder conveying system features an HMI (Human-Machine Interface) and a PLC (Programmable Logic Controller), enabling the storage of formulations for different types of powders, particularly metal powders. These formulations contain material-specific parameters, such as: -Solid density -Bulk density - Particle size distribution and average particle size.

[0130] Leveraging these material properties, the system's conveying control can approach the near-optimal conveying point. This is limited by the jump speed plus a safety margin. See also Figure 9 The phrase "adjusting the gas delivery speed" appears in the text.

[0131] In addition to Figure 9 In addition to regulating the gas delivery rate, several processes are presented here and in particular below, each of which can operate independently of the others and offer independent advantages. Specifically, regulating the gas delivery rate is only optional, depending on... Figure 1 The arrangement of several transmission loops and the setting of different control processes each offer independent advantages.

[0132] Furthermore, it should be noted that the various control processes described below (e.g., the process of regulating the delivery gas rate) can also be independent of the control processes described below. Figure 1 It is used in pneumatic conveying systems with a specific arrangement.

[0133] Figure 1 The system has three transport processes: a- Transports the powder from main tank 6 to first tank 1. b- The powder is conveyed from the front overflow tank 2 and the rear overflow tank 3 to the lock 4 (buffer container 4). c- The powder is conveyed from the outer tank 8 to the lock 4.

[0134] Conveying processes b and c can also be run in parallel, referred to as "mixing" (mixing of powders from tanks 2 or 3 and 8).

[0135] Each container (i.e., in particular containers 1, 2, 3, 4, 6, and 8) has a pressure balance line leading to the conveying system to ensure optimal powder discharge.

[0136] Figure 1 The advanced functions of the powder conveying system shown are in Figure 2 As shown in the image.

[0137] In each delivery cycle ( Figure 2Before the "delivery" step, an attempt is made to establish a gas flow in the corresponding target piping system and determine the total pressure loss. If the total pressure loss exceeds a defined limit, automatic filter cleaning is triggered, and another attempt is made to establish a gas flow. If this attempt fails again under the defined operating conditions, an error is output indicating a system blockage.

[0138] If the system pressure difference is below the defined limit, then determine the oxygen content of the gas flow. Figure 2 The "Initial O2 Test" in the document states that if the oxygen content is below the specified limit, metal powder delivery can begin. Figure 2 (The "transportation" part). If the oxygen level exceeds the defined limit, initial pipeline inertization is triggered.

[0139] During the initial pipeline inertization, the pipeline loop is interrupted at valves 72 and 73, and safety valve 81 is opened. The pipeline can be purged separately (“a” and “b”) or together. If the pressure at sensor 78 falls below the defined limit, the system continues with a pipeline leak test (see [link to relevant documentation]). Figure 6 ).

[0140] During leak testing ( Figure 6 Evaluate pressure sensors 78 and 80. Each increase in system pressure must not exceed a predetermined limit. If the pressure falls below the limit, normalization can continue. If the limit is exceeded, an error message is displayed on the HMI.

[0141] During normalization, safety valve 81 is closed, shut-off valves 72 and 73 are opened, and the inert gas supply 82 is opened. The pressure in the piping system is increased to the defined total system pressure using inert gas, and then valve 82 is closed. During this process, the oxygen content of the piping system 76 and 77 is monitored. If the oxygen content repeatedly exceeds the defined limit, the initial piping inerting is repeated. After a defined number of repetitions, the piping inerting is considered to have failed. An error message is displayed on the HMI.

[0142] If the oxygen content is below the specified limit, the metal powder can continue to be transported. Figure 2 (The word "transportation" in the text).

[0143] In the metal powder conveying cycle, open the corresponding valves of the required conveying loops. These valves include the powder outlet valve of the source tank, the inlet valve of the target tank, and the internal mechanical lock 4. Also open the pressure balance line from the source tank to the conveying line. Activate the motor of the corresponding metering feeder and adjust the motor speed through the conveying control system.

[0144] The transport control has a multi-level structure and operates in a loop until the defined termination criteria are met.

[0145] The first step is an oxygen test. If the oxygen content measured at sensors 76 and 77 exceeds a predetermined limit, valve 85 is opened and inert gas is supplied. If the oxygen level is below the limit, valve 85 is closed. However, if a predetermined time value is exceeded by then, valve 85 remains open and the next pressure control step begins.

[0146] During pressure control, sensors 78 and 80 test whether the total system pressure is within a defined range. If the total system pressure is below this range, valve 85 is opened and inert gas is supplied. If it exceeds this range, valve 81 is opened and the supplied gas is discharged. Once the defined range for the total system pressure is reached, the set velocity of the gas flow continues to be calculated (see also...). Figure 9 ).

[0147] The calculation of the set velocity of the gas flow is carried out in three stages (see...). Figure 9 The first sub-calculation determines the density of the conveyed gas (“Gas Density Calculation”). This depends on the mixing ratio of the inert gas, residual air, and moisture content, as well as their standard parameters (e.g., density). The mixing ratio is determined using oxygen sensors 76, 77 and dew point sensor 75. The gas density at the pump outlet can be determined using the mixing ratio of the gas pressure at sensor 80 and the gas temperature at sensor 86. For the powder supply points further along the pipeline, additional pressure sensors should preferably be installed at the supply points; alternatively, determined correction coefficients can be used. The second sub-calculation determines the metal powder mass flow rate (“Mass Flow Rate Calculation”) using the motor speed of the corresponding metering device, the metal powder parameters from the formulation, the geometry of the metering device, and the determined efficiency. The third sub-calculation (“Jump Speed ​​Calculation”) combines all the results and determines the set velocity of the gas flow for the corresponding metal powder mass flow rate by using additional geometric parameters (e.g., pipeline cross-section) and metal powder characteristics (e.g., average particle size).

[0148] The set speed is controlled using PID pump control and speed sensor 86.

[0149] The final part of conveyor control is limit control for machine protection purposes (see [link]). Figure 10 The result is the adjustment of the metal powder mass flow rate. Test the limits for the following: - Maximum delivery speed (wear protection for pipeline systems); - Maximum pump outlet pressure (pump protection, component specific); - Maximum pump capacity (service life); and - Maximum metering capacity (service life).

[0150] If all limit values ​​are weakened, the motor speed of the corresponding metering feeder (i.e., the corresponding conveyor screw) is increased by a specified limit. If at least one limit value is exceeded, the motor speed of the corresponding metering feeder is decreased by a specified limit. Once limit control is complete, the termination conditions for metal powder conveying are checked. If these termination conditions are not met, the conveying control loop restarts from the beginning.

[0151] The delivery cycle terminates under the following conditions: -The source tank is empty, or - The target tank is full, or - The maximum delivery time has been exceeded, or - The total pressure loss exceeds the limit value.

[0152] An empty source tank indicates that the level sensor in the source tank for the corresponding transport process is reporting a level below a predetermined limit. A full target tank indicates that the level sensor in the target tank for the corresponding transport process is reporting a level above a predetermined limit.

[0153] When the conveying cycle ends, a gas flow cleans the corresponding piping system to prevent blockages in vertical sections caused by powder falling as the gas flow stops (see [link]). Figure 2 (Referring to "pipeline cleaning" in the text). The cleaning of the pipeline system terminates when the weighing unit of the target tank detects a defined limit for weight change after that time.

[0154] Once the pipe cleaning cycle terminates, automatic filter cleaning is eventually triggered (39, 40) (see also...) Figure 2 (Refrigerator cleaning).

[0155] The system includes a pressure compensation tank 84, which is used to reduce the positive pressure at the pump outlet. When using a conventional vacuum pump, the maximum positive pressure is predetermined by the manufacturer and must not be exceeded to protect components. This is ensured through limit value control (see above). The pressure compensation tank is used to increase delivery speed.

[0156] Exemplary embodiments of the powder conveying system described herein can adapt to changing equipment conditions (e.g., filter wear), changing materials (e.g., material properties), and / or changing environmental conditions without requiring a different set of conveying parameters determined empirically. This also implies optimal performance for the corresponding machine, material, and environmental conditions.

[0157] In addition to the above process, especially Figure 2 In addition to the advanced functions and their subroutines shown, or as described above, particularly Figure 2By replacing the advanced functions and subroutines shown, the powder conveying system of this disclosure may have the following advantageous features or perform the following advantageous processes.

[0158] The following describes, in particular, the combinability. Figure 1 The powder conveying system utilizes multiple aspects of automated condition monitoring.

[0159] A dew point sensor is installed on at least one of the following components of the powder conveying system: main tank 6, outer tank 8, and conveying device 79. The dew point sensor is used to measure humidity during vacuum conveying and to measure humidity inside tanks 6 and 8 via the exhaust unit. If a defined limit value is exceeded (>5% according to one embodiment), automatic powder drying is initiated.

[0160] An oxygen sensor for measuring oxygen concentration is installed on at least one of the following components of the powder conveying system: a first tank 1, an overflow tank 2 or 3, a buffer container 4, a main storage tank 6, an external tank 8, and a sieving device 5. The oxygen sensor monitors the oxygen concentration during vacuum conveying as well as the oxygen concentration in all tanks and sieves. Automatic inertia is initiated if the corresponding limit value is exceeded. Measurements during conveying are performed continuously, while measurements in the tanks and sieves are performed discontinuously at specified intervals.

[0161] Pressure sensors for measuring pressure are installed on at least one of the following components of the powder conveying system: first tank 1, overflow tank 2 or 3, buffer container 4, main storage tank 6, external tank 8, and screening equipment 5. Pressure sensors in the tanks and screening equipment are used for leak control. If a pressure loss / increase limit is measured each time, a warning message is output, and inertization / O2 measurements of the corresponding device component are performed to compensate for any lack of inertization. Additionally, pressure sensors in the conveying system can be used for filter monitoring. If the differential pressure rises above a defined limit, automatic filter cleaning is triggered. If the increased differential pressure is not corrected by filter cleaning, a blockage may exist in the piping system, and a warning message is output.

[0162] The motors of the vacuum pump (conveyor equipment) and the metering feeder (conveyor screw) are subject to temperature monitoring (using appropriate temperature sensors). If the temperature limit is exceeded, a shutdown is executed to protect the components. Temperature sensors are also present in the conveyor line.

[0163] The motor of the metering feeder is monitored for torque. If the torque exceeds the specified limit, the device will shut down and output a warning message.

[0164] All pipeline valves have position feedback. If there is a difference between the set position and the actual position, the machine enters a safe state and outputs a warning message related to the corresponding component.

[0165] Check the functionality of all sensors / monitor all sensors. If an error occurs, the machine enters a safe state and outputs a warning message related to the corresponding component.

[0166] The following describes, in particular, the combinability. Figure 1 Prioritize aspects of optimizing the remaining runtime of the powder conveying system.

[0167] At least one or more containers, particularly all containers (1, 2, 10, 2, 3, 4, 6, 7, 8), are equipped with weighing units that ensure continuous horizontal measurement of the respective containers.

[0168] If an interruption occurs in the closed-loop operation, tanks (2102, 2, 3) form a safety reserve for the additive manufacturing process. Intermediate tank 2102 (hopper) stores powder for the additive manufacturing process. If intermediate tank 2102 is empty, the process is interrupted. Overflow tanks (2, 3) collect excess process powder. Empty volumes form a reserve here. If at least one overflow tank is full, the process is interrupted.

[0169] The goal is to optimize the remaining runtime related to hopper fill levels and overflow reserves. It should be noted that the amount emptied from the hopper each time is variable and depends on irradiation time, layer thickness, and excess coefficient. The same applies to the amount of material filled for each overflow. Therefore, the change in weight measured at the weighing unit over time is a dynamic input to the algorithm.

[0170] There are three different transport loops or transport processes: a. The material is conveyed from tank 6 to hopper 2102 via lock 1. b. The contents are conveyed from overflow outlets 2 and 3 through lock 4 to the sieve 50 in tank 6. c. The material is conveyed from the external tank 8 to the sieve 50 in the tank 6 via the lock 4.

[0171] The conveying cycle delivers a predetermined amount of powder (e.g., 25L) to lock 1 or lock 4, and then the conveying cycle terminates.

[0172] After each transport cycle, the algorithm calculates the priorities of transport loops a, b, and c. The transport process with the highest priority is executed.

[0173] Each tank has a fixed minimum and maximum limit. Tank 6 forms the node between all loops. According to the embodiment, tank 6 must not be filled to its maximum capacity via "c", otherwise the volume required to convey the overflow "b" will be lost. According to the embodiment, conveying loop "b" always takes precedence over conveying loop "c".

[0174] The powder conveying system disclosed herein (in particular) Figure 1The powder conveying system described herein can also be a special case of the bulk material conveying system described below. The various aspects of the powder conveying system described herein can be combined with and / or supplemented by the aspects of the bulk material conveying system described below in any way. In particular, in conjunction with the powder conveying system of this disclosure, the adjustment of the conveying speed can be performed according to the description below.

[0175] However, the aspects of the bulk material conveying system described below can also be advantageous in themselves and can constitute one or more inventions. Therefore, the bulk material conveying system described below can also be used independently (i.e., independently of the powder conveying system described above).

[0176] The following disclosure relates to a bulk material conveying system and a method for conveying bulk materials. In particular, the following disclosure relates to conveying raw material powder in an apparatus for producing three-dimensional workpieces by irradiating a layer of raw material powder with electromagnetic radiation or particle radiation (e.g., an apparatus for selective laser melting).

[0177] In additive manufacturing (or generation) processes for producing three-dimensional workpieces, particularly in the process of building layers, it is known to apply a molding compound, initially shapeless or neutral in shape, of a raw material (e.g., raw material powder) layer by layer onto a carrier, and to solidify the molding compound by site-specific irradiation (e.g., by melting or sintering) to ultimately obtain a workpiece of the desired shape. Irradiation can be performed by electromagnetic radiation (e.g., in the form of laser radiation) or by particle radiation (e.g., in the form of electron radiation). In its initial state, the molding compound may initially be in the form of particles, powder, or liquid, and can be selectively solidified as a result of irradiation, or in other words, can be solidified site-specifically. In particular, the molding compound can be a bulk material, such as raw material powder. The molding compound may include, for example, ceramic, metallic, or plastic materials, and mixtures of these materials. A variation of the building layer method involves so-called laser beam melting (also known as selective laser melting) in a powder bed, wherein, in particular, metallic and / or ceramic raw material powder materials are solidified into a three-dimensional workpiece by irradiation with a laser beam.

[0178] To produce individual workpiece layers in selective laser melting, it is also known to apply a raw material powder material in the form of a raw material powder layer onto a carrier and selectively irradiate the raw material powder material according to the geometry of the workpiece layer to be produced. Laser radiation penetrates the raw material powder and solidifies it, for example, due to melting or sintering caused by heating. Once the workpiece layer has solidified, a new, unprocessed raw material powder layer is applied onto the produced workpiece layer. This can be done using known coating arrangements or powder application equipment. The currently topped, still unprocessed raw material powder layer is then irradiated again. Thus, the workpiece is built layer by layer, where each layer defines the cross-sectional area and / or contour of the workpiece. In this context, it is also known to manufacture workpieces substantially automatically using CAD or similar workpiece data.

[0179] This disclosure generally relates to a bulk material conveying system for conveying bulk materials. In particular, the bulk material may be raw material powder used in one of the aforementioned apparatuses for producing three-dimensional workpieces.

[0180] It may be necessary to transport bulk materials from the source tank to the target tank, especially for providing raw material powders in the additive manufacturing process described above, but also for other applications.

[0181] For this purpose, so-called pneumatic conveying is commonly used. In this process, conveying equipment (e.g., pumps or blowers) generates a flow of conveying gas (e.g., air, or a protective gas such as argon, or an air-protective gas mixture) through the conveying line, wherein the conveying line can, in particular, form a closed loop, such that the gas flow is conveyed in a loop (so-called conveying loop). For example, a predetermined dose of bulk material is supplied from a source tank to the gas flow each time by a metering device. Bulk material from several source tanks can also be supplied to the gas flow simultaneously. From the point of supply of bulk material, the gas-bulk material mixture is conveyed via the conveying line to the point in the conveying loop where a separation device (e.g., a cyclone separator) is located. By means of the separation device, the bulk material is separated from the gas-bulk material mixture as completely as possible and supplied to the target tank. For example, a cyclone separator can be located above the target tank, wherein the separated bulk material falls into the target tank due to gravity (so-called gravity conveying).

[0182] One problem with pneumatic bulk material conveying is that the operating parameters of the apparatus and / or the properties of the bulk material (e.g., the bulk powder material used and its associated conveying properties) may change during operation or between individual conveying processes. In such cases, certain operating parameters of the bulk material conveying system must be readjusted, particularly the gas flow rate determined by the conveying equipment. Another operating parameter of the bulk material conveying system that may need to be readjusted is the dosage of bulk material delivered to the gas flow each time.

[0183] In particular, determining the appropriate gas flow velocity for pneumatic bulk material transport under variable conditions (e.g., operating parameters of the device and / or the properties of the bulk material) becomes a problem.

[0184] Therefore, the purpose of the following disclosure is to provide a bulk material conveying system and a corresponding method for conveying bulk materials, which solves at least one of the aforementioned problems or related problems. In particular, it is desirable that the setpoint for the gas velocity, which can respond to changes in one or more operating parameters, can be reliably and easily set.

[0185] This objective is achieved by a bulk material conveying system having the features of the independent aspects listed below and a method for conveying bulk materials. Further embodiments are specified in the dependent aspects.

[0186] According to a first aspect, this disclosure relates to a bulk material conveying system, particularly for conveying raw material powder in an apparatus for producing three-dimensional workpieces by irradiating a layer of raw material powder with electromagnetic radiation or particle radiation. The bulk material conveying system includes: a conveyor line configured to convey a gas flow and, at least in sections, a bulk material flow driven by the gas flow; and a metering device configured to supply a predetermined dose of bulk material to the gas flow each time. The dose is determined by a control value applied to the metering device. The bulk material conveying system further includes: a conveying device configured to convey the gas flow through the conveyor line; and at least one measuring device for measuring at least one parameter of the gas flow. Furthermore, the bulk material conveying system includes a control device configured to: determine a gas density of the gas flow based on at least one measured parameter of the gas flow; determine a bulk material mass flow rate of the bulk material flow based on the control value applied to the metering device; determine a set velocity of the gas flow based on the gas density and the bulk material mass flow rate; and control the conveying device to convey the gas flow at the determined set velocity.

[0187] Bulk material conveying systems can be configured to perform pneumatic conveying of bulk materials. The apparatus can be, in particular, for selective laser melting or sintering, for example, having one or more of the features described above. Alternatively, the apparatus can be for selective electron beam melting.

[0188] The conveyor line may include, for example, one or more pipes and / or one or more hoses and / or one or more connectors. The conveyor line may be sealed for powder, and in particular for gas and powder, such that gas or powder cannot enter or leave the conveyor line (laterally) except through openings in the conveyor line.

[0189] The fact that a conveyor line is constructed to transport a gas-driven flow of bulk material in sections means that only one section of the entire conveyor loop formed by the conveyor line is configured to transport a gas-bulk material mixture. The rest of the conveyor loop essentially transports only gas (conveyor gas), such as air, protective gas, or an air-protective gas mixture.

[0190] The control value can be voltage, current, pulse, or another suitable signal (especially an electrical signal), and changing the control value can alter the dosage delivered by the metering device. The conveying device can be a pump or a blower. Furthermore, one or more filter devices can be installed in the conveying loop formed by the conveying line, particularly for filtering bulk material or bulk material residues remaining in the gas stream.

[0191] The control device may include, for example, a computer. The control device may include a processor and memory, wherein a program is stored in the memory, and when the program is run, the program causes the processor to perform the method according to the second aspect.

[0192] The term “bulk material mass flow rate” is used herein to indicate the physically quantifiable mass flow rate (in kg / s) of the bulk material being conveyed. Conversely, the term “bulk material flow” (only) describes the presence of bulk material being conveyed via a conveyor line.

[0193] Each of the above-described determining steps may include one or more calculations. Measured values ​​and stored values ​​(e.g., standard values) may be included in the corresponding calculations. The conveying equipment can be controlled to decrease or increase the speed of the conveyed gas flow. In particular, increasing the voltage applied to the conveying equipment may, for example, increase the speed of the gas flow. Since the gas flow conveys bulk materials, the speed of the gas flow also determines the speed of the conveyed bulk materials.

[0194] Determining gas density can be done based on at least one of the following parameters of the gas flow: oxygen content, pressure, temperature, dew point, and humidity.

[0195] For each of the parameters mentioned, a corresponding sensor can be set in the gas flow, and the sensor is configured to measure the corresponding parameter.

[0196] Determine gas density The following formula can be used to perform this action: , in It is the measured pressure of the gas flow. It is the measured temperature of the gas flow. It is a predetermined atmospheric pressure. It is scheduled for room temperature. It is given by the following formula: , in It is the known density of air, which is a component of the gas stream. It is the known density of the protective gas, which is a component of the gas flow. It is the known oxygen content of the air. It is the oxygen content of the measured gas stream.

[0197] and Each can be measured by suitable sensors arranged in the gas flow. At least one or two of the sensors required for this purpose can be arranged downstream of the conveying equipment, particularly between the conveying equipment and the source tank from which the bulk material is conveyed. Specifically, at least one or two of the sensors can be arranged directly downstream of the conveying equipment. Atmospheric pressure and ambient temperature can be predetermined standard values; for example, atmospheric pressure can be 1013.25 mbar and ambient temperature can be 293.15 K. However, atmospheric pressure and / or ambient temperature can also be measurements of ambient pressure or ambient temperature.

[0198] For example, the protective gas could be argon, where the density is... The density corresponds to that of argon. The density of air, the density of the protective gas used, and the oxygen content of the air can be found in corresponding tables in the technical literature. The oxygen content of the air can also be the measured oxygen content of the ambient air.

[0199] Measurements can be taken using suitable sensors positioned within the gas flow. The necessary sensors can be positioned upstream of the conveying equipment, between the target tank to which the bulk material is being conveyed and the conveying equipment. Specifically, the sensors can be positioned directly upstream of the conveying equipment.

[0200] The control value applied to a quantitative feeding device can be the motor speed of the motor of the quantitative feeding device, especially the motor speed of the motor used to drive the conveyor screw of the quantitative feeding device.

[0201] However, the control value can also be the current or voltage applied to the motor. Generally, the control value can represent any (e.g., electrical) signal suitable for changing the dosage (more precisely, the dosage each time) dispensed by the metering device, particularly suitable for setting the dosage to a predetermined value. As mentioned above, the metering device may include a conveyor screw configured to convey bulk material from a source tank. Furthermore, the metering device may include at least one of the following elements: a rotary valve, a metering slider, and a valve, particularly a valve with a variable opening diameter.

[0202] Determine the set velocity of the gas flow. This may include: calculating the jump velocity based on the determined gas density and the determined mass flow rate of the bulk material; and determining the set velocity. The following formula can be used to perform this action: , in It is the calculated jump speed of the bulk material being transported. This is the predetermined safe speed.

[0203] The jump speed can be a speed below which particles of the conveyed bulk material (e.g., powder) begin to fall and accumulate at the bottom of the conveyor line. To ensure this does not occur, a predetermined safety speed can be added to the calculated jump speed. This creates a safety margin from the jump speed, ensuring no bulk material settles in the conveyor line. Alternatively, the jump speed can be multiplied by a safety factor.

[0204] The jump velocity can be calculated using the following formula: , in It is the determined mass flow rate of bulk materials, in kg / s; It is the predetermined gravitational acceleration, in m / s² 2 The unit is D; D is the diameter of the conveyor line, in meters (m). It is the gas density of the determined gas flow, expressed in kg / m³. 3 The unit is d; and a and b are parameters that depend on the particle size d of the bulk material.

[0205] The predetermined gravitational acceleration corresponds to the gravitational acceleration at the Earth's surface, which is 9.81 m / s². 2 Parameters a and b can each be predetermined and / or pre-stored constants for the corresponding bulk materials. Furthermore, parameters a and / or b can be determined based on the particle size d of the bulk material used. In other words, the formulas for calculating parameter a and / or parameter b can depend on the particle size d. The particle size d can be taken from the specifications of the bulk material used. For example, the particle size d can be stored in the memory of the control device. Specifically, a table can be stored in the memory of the control device, where corresponding values ​​of the particle size d for different powder materials are stored. Thus, when calculating the set speed, the corresponding particle size d can be used.

[0206] A speed sensor and a control loop for measuring the speed of a gas flow can be used to control a conveying device for conveying a gas flow at a determined set speed. The control loop specifically includes a PID controller.

[0207] A PID controller is a "proportional-integral-derivative controller". It is well known in control engineering to set and maintain a predetermined value (in this example, gas velocity).

[0208] The control device can also be configured to: determine whether at least one measured parameter of the bulk material conveying system is higher than a predetermined maximum value of the corresponding parameter; and if at least one measured parameter is higher than the predetermined maximum value, reduce the control value of the quantitative feeding device by a predetermined value.

[0209] Several parameters can be determined (especially measured), and if at least one of the determined parameters is higher than a predetermined maximum value for that parameter, the control value is reduced by the predetermined value.

[0210] Bulk material conveying systems may include one or more sensors for measuring relevant parameters. Determining whether at least one measured parameter is above a predetermined maximum value and adjusting the control value accordingly can be performed after the steps of determining the gas density, determining the bulk material mass flow rate, determining the set speed, and controlling the conveying equipment. These steps can be performed again with a new control value after adjustment. Therefore, determining the set speed (and adjusting it if necessary) and adjusting the control value (if needed) can be performed alternately. Decreasing the control value means that the metering device dispenses a smaller dose of bulk material each time.

[0211] The control device can also be configured to increase the control value of the quantitative feeder by a predetermined value if at least one measured parameter is below a predetermined maximum value.

[0212] Several parameters can be determined (especially measured), and if all of the determined parameters are below their respective predetermined maximum values, the control value is increased by the predetermined value. Therefore, the control value can only be increased if all determined parameters do not exceed their associated maximum values. Increasing the control value means that the metering device dispenses a higher dose of bulk material each time.

[0213] At least one parameter may include at least one of the following parameters: delivery speed, pump outlet pressure, pump capacity, and the amount of bulk material per batch.

[0214] For example, the relevant parameters can be measured using sensors designed for this purpose, or determined in other ways. For example, parameters can be calculated based on at least one input value (e.g., the applied voltage) of a component (e.g., a conveying device) applied to a powder conveying system.

[0215] The control device can be configured to terminate the conveying process by stopping the conveying equipment when at least one of the following events is detected: the source tank from which the bulk material is discharged via the metering device is empty; the target tank to which the bulk material is being conveyed is full; a predetermined maximum conveying time is exceeded; and the total pressure loss of the conveyed gas exceeds a predetermined limit value.

[0216] For example, corresponding events can be detected using appropriate sensors. Specifically, events can be detected as follows: A source tank from which bulk material is being discharged via a metering device can be determined to be empty using a corresponding level sensor (e.g., a capacitive sensor, radar sensor, ultrasonic sensor, or optical sensor). A target tank reached by the conveyed bulk material can be determined to be full using a corresponding level sensor (e.g., a capacitive sensor, radar sensor, ultrasonic sensor, or optical sensor). A predetermined maximum conveying time can be determined by a corresponding timer started at the start of conveying. The total pressure loss of the conveyed gas can be determined to exceed a predetermined limit using one or more pressure sensors in the conveyor line.

[0217] The bulk material conveying system may also include a pressure balancing tank, which is connected to the conveying line downstream of the conveying equipment and upstream of the metering feeder.

[0218] Pressure balancing tanks can be configured to reduce the positive pressure at the outlet of a conveying device (e.g., a pump). Therefore, a positive pressure tank can be installed at the outlet of the conveying device.

[0219] The bulk material conveying system may include at least one first conveying loop for conveying raw material powder from a main storage tank to a first tank of an apparatus for producing three-dimensional workpieces by irradiating the raw material powder layer with electromagnetic radiation or particle radiation. The lower outlet of the first tank may be connected to the upper inlet of an intermediate tank of the apparatus, wherein powder from the intermediate tank is supplied to the manufacturing process in the processing chamber of the apparatus. The upper inlet of the main storage tank may be connected to the outlet of a sieve for screening the raw material powder.

[0220] For example, the main storage unit may be a storage unit or tank permanently installed in the bulk material conveying system. The main storage unit may be located at a lower height than the first tank. The first conveying circuit can be activated by a control device by opening at least one valve, allowing the conveying equipment to deliver gas through this circuit. The bulk material conveying system may be designed to supply powder from a buffer container located above the sieve into the sieve. For example, powder may be conveyed from the device's overflow tank and / or from an external tank to the buffer container via a second conveying circuit.

[0221] The terms “tank,” “storage container,” and “container” are used as synonyms in this document. However, specific terms are used to refer to different containers, such as “tank,” “buffer container,” “main storage container,” and “external tank.” These terms should not be construed as restrictive, but are merely used to distinguish different containers from one another. For example, a “buffer container” can also be referred to as a “secondary tank.”

[0222] The bulk material conveying system may include at least one second conveying loop for conveying raw material powder from an overflow tank to a buffer container. The overflow tank may be configured to receive excess powder from a processing chamber of an apparatus for producing three-dimensional workpieces by irradiating a layer of raw material powder with electromagnetic radiation or particle radiation. The lower outlet of the buffer container may be connected to the inlet of a sieve for sieving the raw material powder.

[0223] The second delivery circuit can be activated by a control device by opening at least one valve, allowing the delivery device to deliver gas through this second delivery circuit. For example, an overflow tank can be arranged in a lateral region next to the construction cylinder of the device, wherein the overflow tank is open at the top, allowing excess powder to be pushed into the overflow tank, for example, by a powder application device.

[0224] The bulk material conveying system may include at least one third conveying loop for conveying raw material powder from an external tank to a buffer container. The external tank may be detachably connected to the bulk material conveying system, or may be connected to the bulk material conveying system. The lower outlet of the buffer container may be connected to the inlet of a sieve used for screening the raw material powder.

[0225] The third delivery circuit can be activated by a control device by opening at least one valve, allowing the delivery device to deliver gas through this third delivery circuit. The third delivery circuit can operate simultaneously with the second delivery circuit, allowing powder from the outer tank and powder from the overflow tank to be mixed together at an adjustable mixing ratio. For example, the mixing ratio can be adjusted via the corresponding metering device of the respective container (outer tank, overflow tank).

[0226] The quantitative feeding device can be located at the outlet of the corresponding source tank, and the cyclone separator can be located at the inlet of the corresponding target tank. The cyclone separator is used to separate the raw material powder from the gas stream and to supply the raw material powder to the target tank.

[0227] Bulk material can be introduced into the gas stream through a quantitative feeding device, and the bulk material can be removed from the gas stream again through a cyclone separator.

[0228] According to a second aspect, this disclosure relates to a method for conveying bulk materials, particularly a method for conveying raw material powder into an apparatus for producing a three-dimensional workpiece by irradiating a layer of raw material powder with electromagnetic radiation or particle radiation. The method includes: conveying a gas stream and a bulk material stream driven by the gas stream via a conveyor line; and supplying a predetermined dose of bulk material at a time via a metering device. The dose can be determined by a control value applied to the metering device. The method further includes: conveying the gas stream via the conveyor line using a conveying device; and measuring at least one parameter of the gas stream using a measuring device. The method further includes: determining a gas density of the gas stream based on the measured at least one parameter of the gas stream; and determining a bulk material mass flow rate of the bulk material stream based on the control value applied to the metering device. The method further includes: determining a set velocity of the gas stream based on the gas density and based on the bulk material mass flow rate; and controlling the conveying device to convey the gas stream at the determined set velocity.

[0229] All the foregoing details and features of the first aspect (bulk material conveying system) can be applied in conjunction with the method for conveying bulk materials according to the second aspect (applied independently or in arbitrary combination with each other). The bulk material conveying system according to the first aspect can be configured to perform the method for conveying bulk materials according to the second aspect.

[0230] Determining gas density can be done based on at least one of the following parameters of the gas flow: oxygen content, pressure, temperature, dew point, and humidity.

[0231] The following formula can be used to determine the density of a gas: , in It is the measured pressure of the gas flow. It is the measured temperature of the gas flow. It is a predetermined atmospheric pressure. It is scheduled for room temperature. It is given by the following formula: , in It is the known density of air, which is a component of the gas stream. It is the known density of the protective gas, which is a component of the gas flow. It is the known oxygen content of the air. It is the oxygen content of the measured gas stream.

[0232] The control value applied to a quantitative feeding device can be the motor speed of the motor of the quantitative feeding device, especially the motor speed of the motor used to drive the conveyor screw of the quantitative feeding device.

[0233] Determine the set velocity of the gas flow. This may include: calculating the jump velocity based on the determined gas density and the determined mass flow rate of the bulk material; and determining the set velocity. The following formula can be used to perform this action: , in It is the calculated jump speed of the bulk material being transported. This is the predetermined safe speed.

[0234] The jump velocity can be calculated using the following formula: , in It is the determined mass flow rate of bulk materials, in kg / s; It is the predetermined gravitational acceleration, in m / s² 2 The unit is D; D is the diameter of the conveyor line, in meters (m). It is the gas density of the determined gas flow, expressed in kg / m³. 3 The unit is d; and a and b are parameters that depend on the particle size d of the bulk material.

[0235] A speed sensor and a control loop for measuring the speed of a gas flow can be used to control a conveying device for conveying a gas flow at a determined set speed. The control loop specifically includes a PID controller.

[0236] The method may further include: determining whether at least one measured parameter of the bulk material conveying system is higher than a predetermined maximum value of the corresponding parameter; and if at least one measured parameter is higher than the predetermined maximum value, reducing the control value of the quantitative feeding device by a predetermined value.

[0237] The method may further include: if at least one measured parameter is below a predetermined maximum value, increasing the control value of the quantitative feeding device by a predetermined value.

[0238] At least one parameter may include at least one of the following parameters: delivery speed, pump outlet pressure, pump capacity, and the amount of bulk material per batch.

[0239] The method may further include terminating the conveying process by stopping the conveying equipment when at least one of the following events is detected: the source tank from which bulk material is discharged via a metering feeder is empty; the target tank to which the bulk material is being conveyed is full; a predetermined maximum conveying time has been exceeded; and the total pressure loss of the conveyed gas has exceeded a predetermined limit.

[0240] The method may include: conveying raw material powder from a main reservoir to a first tank of an apparatus for producing a three-dimensional workpiece by irradiating a layer of raw material powder with electromagnetic radiation or particle radiation via at least one first conveying loop. The lower outlet of the first tank may be connected to the upper inlet of an intermediate tank of the apparatus, wherein powder from the intermediate tank is supplied to the manufacturing process in the processing chamber of the apparatus. The upper inlet of the main reservoir may be connected to the outlet of a sieve for sieving the raw material powder.

[0241] The method may include conveying raw material powder from an overflow tank to a buffer container via at least one second conveying loop. The overflow tank may be configured to receive excess powder from a processing chamber of an apparatus for producing three-dimensional workpieces by irradiating a layer of raw material powder with electromagnetic radiation or particle radiation. The lower outlet of the buffer container may be connected to the inlet of a sieve for sieving the raw material powder.

[0242] The method may include conveying raw material powder from an external tank to a buffer container via at least one third conveying loop. The external tank may be detachably connected to, or may be connected to, a bulk material conveying system. The lower outlet of the buffer container may be connected to the inlet of a sieve used for screening the raw material powder.

[0243] The metering feeder can be located at the outlet of the corresponding source tank. The cyclone separator can be located at the inlet of the corresponding target tank; the cyclone separator is used to separate the raw material powder from the gas stream and to supply the raw material powder to the target tank.

[0244] For example, the apparatus described herein for producing three-dimensional workpieces by irradiating a layer of raw material powder with electromagnetic radiation or particle radiation may include a carrier device for applying powder in multiple layers to form a powder bed. Furthermore, one or more powder application devices may be provided for applying powder, and, if desired, powder of different materials. A separate powder application device may be provided for each material. The carrier device may be moved vertically downwards by a lifting mechanism so that the top powder layer remains at the same height relative to the build chamber of the apparatus. Additionally, the apparatus may include one or more irradiation units. Each irradiation unit includes a beam source (particularly a laser beam source) and an optical system having one or more optical components (e.g., beam expander, focusing unit, scanner device, F-θ lens) for shaping and deflecting the beam. Alternatively, the beam source may be located outside the respective irradiation unit, wherein the beam is guided to the irradiation unit by a light guide (e.g., glass fiber).

[0245] Figure 11An apparatus 1100 is shown for producing a three-dimensional workpiece by irradiating a layer of raw material powder with electromagnetic radiation or particle radiation. In other words, apparatus 1100 is an apparatus for producing a three-dimensional workpiece by an additive manufacturing process (e.g., selective laser melting or selective laser sintering), wherein raw material powder is used in the additive manufacturing process.

[0246] Although the bulk material conveying system of this disclosure is described below in conjunction with the aforementioned apparatus, the bulk material conveying system or method for conveying bulk materials is not limited to use in conjunction with additive manufacturing apparatus. The advantages arising from the bulk material conveying system and associated methods presented herein generally apply to the conveying of bulk materials by pneumatic conveying.

[0247] The apparatus 1100 includes a carrier 1002 and a powder application device 1003 for applying raw material powder 1004 onto the carrier 1002. The carrier 1002 and the powder application device 1003 are located within a processing chamber 1011, which is sealable and isolated from the ambient atmosphere, i.e., isolated from the environment surrounding the processing chamber 1011. The apparatus 1100 also includes an irradiation device 1005 for selectively irradiating the raw material powder 1004 applied to the carrier 1002 with electromagnetic radiation or particle radiation.

[0248] Raw material powder 1004 is supplied to the processing chamber 1011 (i.e., powder application device 1003) via a bulk material conveying system 1001, which is described in detail below. In the current powder conveying configuration, the bulk material conveying system 1001 is a powder conveying system. The bulk material conveying system 1001 includes a powder storage tank 1006 in which the raw material powder 1004 to be supplied to the processing chamber 1011 is stored. The powder storage tank 1006 is connected to the conveyor line 1007 via a metering feeder 1008. The powder is then conveyed along the conveyor line 1007 via a conveyor 1019. Figure 11 The arrow in the diagram indicates the direction in which gas flow 1009 is conveyed via conveyor line 1007. Figure 11 In the exemplary powder conveying system 1001 shown, the conveying device 1009 is designed as a vacuum pump.

[0249] The metering feeder 1008 is configured to deliver a desired dose of raw material powder 1004 into a gas flow 1009 passing through a conveyor line 1007. Specifically, the metering feeder 1008 includes a first powder valve 1021 with a continuously variable flow cross-section, such that the amount of powder 1004 introduced into the gas flow 1009 through the metering feed opening 1023 of the metering feeder 1008 per unit time can be continuously varied. In other words, a control value can be applied to the metering feeder 1008 by a control device 1040 described below, which determines the dose dispensed each time. In the case of the valve 1021 with a variable cross-section described above, the control value determines the cross-section and thus the dose. Alternatively, the valve 1021 can be replaced by a conveyor screw and an associated motor for driving the conveyor screw. In this case, the control value determines the speed of the motor and thus the dispensed dose. Therefore, the desired dose of powder delivered per unit time can be specified by applying a predetermined control value.

[0250] The raw material powder-gas mixture flowing downstream of the metering feeder 1008 via the conveyor line 1007 is fed to a cyclone separator 1010, which serves as a separation device. The cyclone separator 1010 includes an inlet 1020 that allows the raw material powder-gas mixture to flow tangentially into a conical separation chamber 1022. Powder particles 1004 detached from the rotating flow of the raw material powder-gas mixture formed within the conical separation chamber 1022 are discharged from the cyclone separator 1010 through a powder outlet 1024 located in the lower region of the cyclone separator 1010. These powder particles 1004 are supplied to the processing chamber 1011, i.e., to the powder application device 1003, via a connecting line 1026 connecting the powder outlet 1024 of the cyclone separator 1010 to the powder inlet 1028 of the processing chamber 1011.

[0251] A second powder valve 1030 is provided in the connecting line 1026. Similar to the first powder valve 1021 of the metering feeder 1008, the second powder valve 1030 is also equipped with a continuously variable flow cross section, so that the amount of powder 1004 supplied from the powder outlet 1024 of the cyclone separator 1010 to the processing chamber 1011 can be continuously varied. The second powder valve 1030 can also be replaced by a conveyor screw and an associated motor (similar to the first powder valve).

[0252] Therefore, in Figure 11 In the case shown, powder is conveyed from a source container formed by a powder storage unit 1006 to a target container, wherein the target container can be considered, for example, the volume of the connecting line 1026 below the powder valve 1030. Figure 11In the schematic representation, the volume represents a powder container for the powder application apparatus 1003 from which powder for applying various layers is supplied to the powder application apparatus 1003. Alternatively, the powder reservoir (and therefore the target container) may be integrated into the powder application apparatus 1003.

[0253] The gas separated from the powder particles 1004 in the cyclone separator 1010 is guided back to the conveyor line 1007 through the gas outlet 1032 of the cyclone separator 1010. The gas outlet 1032 is located at the top of the cyclone separator 1010.

[0254] Since the gas stream 1009 exiting the gas outlet 1032 of the cyclone separator 1010 may contain residual raw material powder particles 1004, a filter unit 1014 is arranged in the conveyor line 1007 downstream of the cyclone separator 1010. The filter unit 1014 includes a replaceable filter 1013, which is configured to filter out any remaining raw material powder particles 1004 present in the gas stream 1009 exiting the gas outlet 1032.

[0255] The bulk material conveying system 1001 also includes a measuring device 1050, which is used to measure parameters of the gas flow conveyed in the conveyor line 1007. Figure 11 In the illustrated embodiment, measuring device 1050 is directly arranged downstream of conveyor 1019, and measuring device 1050 is a pressure sensor for measuring the pressure (gas pressure) within conveyor line 1007. In addition to measuring device 1050, other measuring devices 1015, 1016, 1017, and 1018 are also provided along conveyor line 1007. Measuring device 1018 is a temperature sensor for measuring the temperature of the gas flow. Measuring device 1015 is an oxygen sensor for measuring the oxygen content of the gas flow. Measuring devices 1016 and 1017 can each be additional sensors for measuring one of the aforementioned properties (pressure, temperature, oxygen content). Furthermore, measuring devices 1016 and 1017 can each be sensors independently used to measure flow rate, the presence of bulk material (e.g., capacitive or ultrasonic sensors), dew point, etc. In addition to measuring devices 1050 and 1015 to 1018, fewer or more sensors may be provided. Furthermore, measuring devices may be located at another location within the conveyor line.

[0256] Pressure sensor 1050, temperature sensor 1018 and oxygen sensor 1015 are particularly relevant to the function of control device 1040 (see below) described herein.

[0257] Finally, the bulk material conveying system 1001 includes a control device 1040. The control device 1040 controls the operation of the components of the bulk material conveying system, particularly the operation of all controllable components. For example, the control device 1040 controls the conveying device 1019, and specifically controls the conveying device 1019 such that a predetermined flow rate of the conveying gas is set, for example, by applying a voltage value set by the control device 1040. Furthermore, the control device 1040 can increase or decrease the flow rate by a predetermined value. The control device 1040 also controls the metering feeder 1008. Specifically, the control device 1040 applies a predetermined control value to the metering feeder 1008, causing the metering feeder to dispense a predetermined dose of raw material powder into the gas stream per unit time. Furthermore, the control device 1040 can increase or decrease the currently dispensed dose by a predetermined value. The control device 1040 also receives measurement data from all measuring devices. Additionally, the control device 1040 controls valve 1030.

[0258] The control device 1040 can also be configured to control the entire operation of the device 1010, namely, irradiation by the irradiation device 1005, powder application by the powder application device 1003, and lowering the carrier 1002.

[0259] In order to determine a suitable setpoint for the gas velocity in the conveyor line 1007 and set a velocity corresponding to that setpoint, the control device 1040 performs the following steps: A. Determine the gas density of the gas flow based on at least one parameter of the measured gas flow; B. Determine the bulk material mass flow rate based on the control values ​​applied to the quantitative feeding equipment; C. Determine the set velocity of the gas flow based on gas density and the mass flow rate of the bulk material; and D. Control the conveying equipment to deliver the gas stream at a predetermined set speed.

[0260] Regarding each step: Step A: Control device 1040 calculates the gas density of the gas flow based on measured parameters of the gas flow. Several methods exist for determining (e.g., calculating or estimating) the gas density of the gas flow based on one or more measured parameters. An example is shown below. Here, control device 1040 uses measured pressure (measured by pressure sensor 1050), measured temperature (measured by temperature sensor 1018), and measured oxygen content (measured by oxygen sensor 1015).

[0261] The following formula is used to determine the gas density: , in It is the measured pressure of the gas flow. It is the measured temperature of the gas flow. It is a predetermined atmospheric pressure (in the example, atmospheric pressure). =1013.25 millibars), It is the predetermined room temperature (in the example, room temperature is 293.15K). It is given by the following formula: , in It is the known density of air, which is a component of the gas stream. It is the known density of the protective gas, which is a component of the gas flow. It is the known oxygen content of the air. This is the oxygen content of the gas stream measured by oxygen sensor 1015. For example, =1.225kg / m 3 It can be used as the density of air; if argon is used as a protective gas, then =1.784kg / m 3 The density of the protective gas. The oxygen content of the air can be set to... =20.94%. Alternatively, the oxygen content of the ambient atmosphere can be measured and used.

[0262] Step B: The control device 1040 determines the bulk material mass flow rate of the bulk material stream based on control values ​​applied to the quantitative feeding device 1008. In the case of the described powder conveying, the bulk material mass flow rate is the powder mass flow rate. For example, the mass flow rate is expressed in kg / s.

[0263] The determination of the mass flow rate of the bulk material depends on the metering device 1009 used, and particularly the geometry of the metering device 1009. For example, in the case of a calibrated metering device 1009, the associated volumetric flow rate of the conveyed bulk material can be calculated or read from a table based on the applied control values ​​(e.g., the rotational speed of the conveyor screw). In particular, a linear relationship may exist between the control values ​​and the volumetric flow rate, wherein the factor characterizing the linear relationship may have been determined in advance through calibration. The known density (kg / m³) of the conveyed bulk material can be used. 3 From the determined volumetric flow rate (m³) 3 Calculate the desired mass flow rate (in kg / s). For example, methods or calibration tables for calculating volumetric flow rates based on given control values ​​can be found in the manual or instruction manual for the quantitative feeder 1009.

[0264] If no corresponding calibration data is available, the metering feeder 1009 can be calibrated to determine the relationship between the control value and the volumetric flow rate.

[0265] In addition, the mass flow rate of bulk materials can be calculated. The following example using a conveyor screw illustrates the corresponding calculation.

[0266] The mass flow rate of bulk materials is calculated using the following formula: , here, It is the mass flow rate of bulk materials. It is the outer diameter of the conveyor screw. It is the height of the screw wall. 'e' is the first pitch, and 'e' is the thickness of the screw wall. is the rotational speed of the conveyor screw, and i is the transmission ratio. It is the bulk density.

[0267] In the context of the conveyor screw, further details relating to the above parameters come from... Figure 12 , Figure 12 The conveyor screw and associated parameters are shown.

[0268] Step C: The control device 1040 determines the set velocity of the gas flow based on the gas density determined in step A and the bulk material mass flow rate determined in step B.

[0269] Determine the set velocity of the gas flow. This may include calculating the jump speed based on the determined gas density and the determined mass flow rate of the bulk material. According to an embodiment, a set speed is determined. Use the following formula to perform the operation: , in It is the calculated jump speed of the bulk material being transported. This is the predetermined safe speed.

[0270] The jump speed is a speed below which particles of the conveyed bulk material (e.g., powder) begin to fall and accumulate at the bottom of conveyor line 1007. To ensure this does not occur, a predetermined safety speed is added to the calculated jump speed. This creates a safety margin from the jump speed to ensure that bulk material deposition does not occur in conveyor line 1007. Alternatively, the jump speed can be multiplied by a predetermined safety factor (e.g., 1.1 or 1.2).

[0271] The jump speed is calculated using the following formula: , here, It is the determined mass flow rate of bulk materials, in kg / s; It is the predetermined gravitational acceleration, in m / s² 2 The unit is D; D is the diameter of the conveyor line, in meters (m). It is the gas density of the determined gas flow, expressed in kg / m³. 3 The units are d and a and b are parameters that depend on the particle size d of the bulk material. For example, parameters a and b can be stored as constants in the memory of the control device for use with the bulk material. Furthermore, at least one of the two parameters a and b can be calculated, where the corresponding calculation depends on the particle size d of the bulk material used.

[0272] The particle size d is taken from the specifications of the bulk material used, such as the data sheet of the powder used. For example, the particle size d can also be stored in the memory of the control device 1040. Specifically, a table can be stored in the memory of the control device 1040, storing the corresponding values ​​of the particle size d for different powder materials. Thus, when calculating the set speed, the corresponding particle size d can be used by inputting or selecting the powder used through the user interface of the control device 1040.

[0273] Step D: The control device 1040 controls the conveying device 1019 to convey the gas stream at the set speed determined in step C. Here, for example, a signal with a predetermined voltage value or a predetermined frequency is applied to the conveying device 1019, wherein it is known that the voltage value or frequency can achieve the desired conveying speed of the conveying device 1019.

[0274] If the conveying device 1019 is not calibrated accordingly, a control loop can be used that takes into account the gas velocity value measured from the velocity sensor. For example, sensor 1016 or 1017 could be a corresponding velocity sensor. For example, PID control can be used to adjust the desired value of the set velocity.

[0275] The aforementioned technology allows for the rapid, easy, and uncomplicated setting of operating points for conveying bulk materials (i.e., setting the conveying speed of the conveying gas, and thus the conveying speed of the conveyed bulk material). On one hand, data for different types of powders (e.g., particle size and bulk density of the powder) stored in the memory of the control device 1040 is used. On the other hand, it can respond to changes in operating parameters, particularly changes in measurements within the conveying line 1007 (e.g., oxygen content, pressure, and / or temperature). Changes in the mass flow rate of the conveyed bulk material can also be responded to by adjusting the gas flow rate.

[0276] According to an exemplary embodiment, the steps A to D performed by the control device 1040 may follow so-called limit value control. However, this is optional, and only the set speed determined according to steps A to D may be performed.

[0277] The details of limit value control are in Figure 13 As shown in the image. Figure 13 The limit value control corresponds to the combination mentioned above. Figure 10 The description is aimed at Figure 1 Limit control of the powder conveying system. In this regard, the control device 1040 is configured to determine whether at least one measured parameter of the bulk material conveying system 1001 is higher than a predetermined maximum value of the corresponding parameter. If at least one measured parameter is higher than the predetermined maximum value, the control device 1040 reduces the control value of the metering feeder 1008 by a predetermined value, such that the metering feeder 1008 distributes a lower dose of bulk material into the gas stream per unit time.

[0278] An example of using limit values ​​for specific parameters is shown in Figure 13 As shown in the image. Figure 13 A flowchart is shown of the process executed by the control device 1040 after the set speed is determined and the conveying device is controlled.

[0279] The process begins at step 1202, where it is checked whether the measured conveying speed is below a predetermined maximum value. To measure the conveying speed, a speed sensor in a gas flow or gas-powder mixture flow is used, for example... Figure 11 The sensor in the middle is 1016 or 1017.

[0280] If "yes", the process proceeds to step 1204, where it is checked whether the measured pump outlet pressure is lower than a predetermined maximum value. To measure the pump outlet pressure, a pressure sensor in the gas flow downstream of pump 1019 is used, for example... Figure 11 The sensor in the 1050.

[0281] If "yes", the process proceeds to step 1206, where it is checked whether the pump power consumed by pump 1019 is lower than a predetermined maximum value.

[0282] If “yes”, the process proceeds to step 1208, where it is checked whether the dose of bulk material dispensed by the quantitative feeding device 1008 per unit time is within a predetermined maximum range.

[0283] If "yes", the process is complete. You can then check whether the conveying should be stopped. If not, repeat steps A through D discussed above, and readjust the conveying speed (if necessary).

[0284] If it is determined in step 1208 that the dose of bulk material allocated per unit time is not within the predetermined maximum range ("No" after step 1208), then in step 1210, it is checked whether the dose is below the predetermined maximum range. If this is the case ("Yes"), then in step 1212, the dose is increased by a predetermined value. If this is not the case ("No" after step 1210), then in step 1214, the dose is decreased by a predetermined value.

[0285] After step 1214, in step 1216, it is checked whether the dose is less than a predetermined minimum. If this is not the case ("No"), the process terminates. However, if this is the case ("Yes" after step 1216), filter cleaning is performed in step 1218.

[0286] If the result of at least one of queries 1202, 1204 and 1206 is "no" and therefore the corresponding maximum value has been reached or exceeded, the process proceeds further to reduce the dose of the metering device 1008 according to step 1214.

[0287] exist Figure 13 After the process, an inspection is conducted to check whether the conveying process has been terminated, especially whether the conveying equipment 1019 has been stopped.

[0288] The above situation is determined if at least one of the following events is detected: the source tank 1006 from which bulk material is discharged via the metering feeder 1008 is empty; the target tank (or corresponding cyclone separator 1010) to which the bulk material is conveyed is full; the predetermined maximum conveying time has been exceeded; and the total pressure loss of the conveyed gas exceeds a predetermined limit.

[0289] If the conveying process is not terminated, the method executed by the control device 1040 returns to step A (see above).

[0290] Figure 1 A schematic representation of a bulk material conveying system is shown, which is used to convey raw material powder into an apparatus 1100 for producing three-dimensional workpieces by irradiating the raw material powder layer with electromagnetic radiation or particle radiation.

[0291] and Figure 11 compared to, Figure 1 The following is a more detailed representation of a bulk material conveying system, in which specific components are shown, and these components are marked with reference numerals. Reference numerals may also be present in... Figure 11 It exists in the system, but is not explicitly described.

[0292] However, in addition, Figure 1The system also represents a more complex design for the type of bulk material conveying system described in this paper, particularly because several conveying processes can be performed within the system, i.e., conveying processes from different source tanks to different destination tanks. The exact structure and operating mode of the bulk material conveying system have been combined above. Figure 1 (Described in the context of a powder conveying system).

[0293] In particular, it can also be combined with Figure 1 The system is used to execute methods including steps A through D for adjusting the conveying speed. This also applies to... Figure 13 Limit value control. Therefore, Figure 1 Bulk material conveying systems also include controls Figure 1 The control devices (not shown) for each component of the system.

[0294] For example, device 1100 corresponds to Figure 11 The apparatus 1100, generally speaking, corresponds to the apparatus commonly known for additive manufacturing by selective laser melting or selective laser sintering.

[0295] In combination Figure 1 During the operation (i.e., the conveying operation) of at least one of the described conveying processes a to c, a method may be performed to determine a gas velocity (set velocity) and adjust pump 79 such that pump 79 conveys the gas at the determined set velocity. Steps A to D described above may be performed by the control equipment of the bulk material conveying system.

[0296] In one embodiment, sensor data from pressure sensor 80, temperature sensor 86, and oxygen sensor 76 are used to determine the gas density of the gas flow. To determine the mass flow rate of the bulk material, the geometry of the corresponding conveyor screw located at the outlet of the respective source tank is taken into account. Speed ​​sensor 86 is used, for example, by PID control to regulate the speed of the gas delivered by pump 79.

[0297] In addition, according to Figure 13 Limit control can be implemented in conjunction with each of the conveying processes a through c (see description above).

[0298] The closed powder loop of conveying processes a to c offers particular advantages: operators can minimize manual intervention and contact with the powder during the process, as contact with the powder poses health risks and may represent the risk of ignition or explosion for the identified powder type. Automatic adjustment of the conveying speed offers the advantage of quickly and easily setting the optimal operating point (i.e., optimal conveying speed) for different powder types and / or different process conditions.

[0299] It can be used independently and / or with a powder conveying system or Figure 1 The following aspects can be combined for application: 1. A bulk material conveying system, particularly for conveying raw material powder into an apparatus for producing three-dimensional workpieces by irradiating a layer of raw material powder with electromagnetic radiation or particle radiation, wherein the bulk material conveying system comprises: A conveyor line, configured to transport a gas flow and, at least in sections, a flow of bulk material driven by the gas flow; A metering feeder is configured to supply a predetermined dose of bulk material to a gas stream each time, wherein the dose is determined by a control value applied to the metering feeder; Conveying equipment, which is constructed to transport gas streams via conveyor lines; At least one measuring device, the at least one measuring device being used to measure at least one parameter of a gas flow; and The control device is configured to: The gas density of the gas flow is determined based on at least one parameter of the measured gas flow. Based on the control values ​​applied to the quantitative feeding equipment, the bulk material mass flow rate is determined; The set velocity of the gas flow is determined based on gas density and the mass flow rate of the bulk material; and Control the conveying equipment to deliver the gas stream at a predetermined set speed.

[0300] 2. The bulk material conveying system according to aspect 1, wherein determining the gas density is performed based on at least one of the following parameters of the gas flow: oxygen content, pressure, temperature, dew point, and humidity.

[0301] 3. The bulk material conveying system according to aspect 2, wherein the gas density is determined using the following formula: , in It is the measured pressure of the gas flow. It is the measured temperature of the gas flow. It is a predetermined atmospheric pressure. It is scheduled for room temperature. It is given by the following formula: , in It is the known density of air, which is a component of the gas stream. It is the known density of the protective gas, which is a component of the gas flow. It is the known oxygen content of the air. It is the oxygen content of the measured gas stream.

[0302] 4. The bulk material conveying system according to any one of aspects 1 to 3, wherein the control value applied to the metering feeder is the motor speed of the motor of the metering feeder, and in particular the motor speed of the motor used to drive the conveyor screw of the metering feeder.

[0303] 5. The bulk material conveying system according to any one of aspects 1 to 4, wherein a set velocity of the gas flow is determined. This includes: calculating the jump velocity based on the determined gas density and the determined mass flow rate of the bulk material, wherein a set velocity is determined. Use the following formula to perform the operation: , in It is the calculated jump speed of the bulk material being transported. This is the predetermined safe speed.

[0304] 6. The bulk material conveying system according to aspect 5, wherein the jump speed is calculated using the following formula: , in It is the determined mass flow rate of bulk materials, in kg / s; It is the predetermined gravitational acceleration, in m / s² 2 The unit is D; D is the diameter of the conveyor line, in meters (m). It is the gas density of the determined gas flow, expressed in kg / m³. 3 The unit is d; and a and b are parameters that depend on the particle size d of the bulk material.

[0305] 7. A bulk material conveying system according to any one of aspects 1 to 6, wherein a speed sensor for measuring the speed of a gas flow and a control loop are used to perform control of a conveying device for conveying the gas flow at a determined set speed, the control loop particularly including a PID controller.

[0306] 8. The bulk material conveying system according to any one of aspects 1 to 7, wherein the control equipment is further configured to: Determine whether at least one measured parameter of the bulk material conveying system is higher than a predetermined maximum value for the corresponding parameter; and If at least one measured parameter is higher than a predetermined maximum value, the control value of the quantitative feeding device is reduced by the predetermined value.

[0307] 9. The bulk material conveying system according to aspect 8, wherein the control equipment is further configured to: If at least one measured parameter is below a predetermined maximum value, the control value of the quantitative feeding device is increased by the predetermined value.

[0308] 10. The bulk material conveying system according to aspect 8 or 9, wherein at least one parameter includes at least one of the following parameters: Conveying speed, pump outlet pressure, pump capacity, and the amount of bulk material per batch.

[0309] 11. The bulk material conveying system according to any one of aspects 1 to 10, wherein the control equipment is configured to: The conveying process is terminated by stopping the conveying equipment when at least one of the following events is detected: The source tank from which bulk material is discharged by the quantitative feeding device is empty; the target tank to which the bulk material is being transported is full; the predetermined maximum transport time has been exceeded; and the total pressure loss of the transported gas has exceeded the predetermined limit.

[0310] 12. The bulk material conveying system according to any one of aspects 1 to 11 further includes: a pressure balancing tank, which is connected to the conveying line downstream of the conveying equipment and upstream of the metering feeder.

[0311] 13. The bulk material conveying system according to any one of aspects 1 to 12, comprising: at least one first conveying loop for conveying raw material powder from a main storage tank to a first tank of an apparatus for producing a three-dimensional workpiece by irradiating the raw material powder layer with electromagnetic radiation or particle radiation. The lower outlet of the first tank is connected to the upper inlet of the intermediate tank of the apparatus, wherein powder from the intermediate tank is supplied to the manufacturing process in the processing chamber of the apparatus, and The upper inlet of the main storage tank is connected to the outlet of a sieve used to screen the raw material powder.

[0312] 14. The bulk material conveying system according to any one of aspects 1 to 13, comprising: at least one second conveying circuit for conveying raw material powder from an overflow tank to a buffer container, The overflow tank is configured to receive excess powder from the processing chamber of a device used to produce three-dimensional workpieces by irradiating a layer of raw material powder with electromagnetic radiation or particle radiation. The lower outlet of the buffer container is connected to the inlet of a sieve used for screening the raw material powder.

[0313] 15. The bulk material conveying system according to any one of aspects 1 to 14, comprising: at least one third conveying circuit for conveying raw material powder from an outer tank to a buffer container, The outer tank is detachably connected to the bulk material conveying system, or connected to the bulk material conveying system, and The lower outlet of the buffer container is connected to the inlet of a sieve used for screening the raw material powder.

[0314] 16. The bulk material conveying system according to any one of aspects 1 to 15, wherein a metering feeder is located at the outlet of the respective source tank, and wherein a cyclone separator is located at the inlet of the respective target tank, the cyclone separator being used to separate the raw material powder from the gas stream and to supply the raw material powder to the target tank.

[0315] 17. A method for conveying bulk materials, particularly for conveying raw material powder into an apparatus for producing a three-dimensional workpiece by irradiating a layer of raw material powder with electromagnetic radiation or particle radiation, wherein the method comprises: Gas flow and bulk material flow driven by gas flow are transported via conveyor lines; A predetermined dose of bulk material is supplied each time by a quantitative feeding device, wherein the dose is determined by a control value applied to the quantitative feeding device; Gas flow is transported via conveyor lines using conveyor equipment; Use measuring equipment to measure at least one parameter of the gas flow; The gas density of the gas flow is determined based on at least one parameter of the measured gas flow. Based on the control values ​​applied to the quantitative feeding equipment, the bulk material mass flow rate is determined; The set velocity of the gas flow is determined based on gas density and the mass flow rate of the bulk material; and Control the conveying equipment to deliver the gas stream at a predetermined set speed.

[0316] 18. The method according to aspect 17, wherein determining the gas density is performed based on at least one of the following parameters of the gas flow: oxygen content, pressure, temperature, dew point, and humidity.

[0317] 19. The method according to aspect 18, wherein the gas density is determined using the following formula: , in It is the measured pressure of the gas flow. It is the measured temperature of the gas flow. It is a predetermined atmospheric pressure. It is scheduled for room temperature. It is given by the following formula: , in It is the known density of air, which is a component of the gas stream. It is the known density of the protective gas, which is a component of the gas flow. It is the known oxygen content of the air. It is the oxygen content of the measured gas stream.

[0318] 20. The method according to any one of aspects 17 to 19, wherein the control value applied to the quantitative feeding device is the motor speed of the motor of the quantitative feeding device, particularly the motor speed of the motor used to drive the conveyor screw of the quantitative feeding device.

[0319] 21. The method according to any one of aspects 17 to 20, wherein the set velocity of the gas flow is determined. This includes: calculating the jump velocity based on the determined gas density and the determined mass flow rate of the bulk material, wherein a set velocity is determined. Use the following formula to perform the operation: , in It is the calculated jump speed of the bulk material being transported. This is the predetermined safe speed.

[0320] 22. According to the method of aspect 21, the jump speed is calculated using the following formula: , in It is the determined mass flow rate of bulk materials, in kg / s; It is the predetermined gravitational acceleration, in m / s² 2 The unit is D; D is the diameter of the conveyor line, in meters (m). It is the gas density of the determined gas flow, expressed in kg / m³. 3 The unit is d; and a and b are parameters that depend on the particle size d of the bulk material.

[0321] 23. The method according to any one of aspects 17 to 22, wherein a speed sensor for measuring the speed of the gas flow and a control loop are used to perform control of a conveying device for conveying the gas flow at a determined set speed, the control loop in particular including a PID controller.

[0322] 24. The method according to any one of aspects 17 to 23, further comprising: Determine whether at least one measured parameter of the bulk material conveying system is higher than a predetermined maximum value for the corresponding parameter; and If at least one measured parameter is higher than a predetermined maximum value, the control value of the quantitative feeding device is reduced by the predetermined value.

[0323] 25. The method according to aspect 24 further includes: If at least one measured parameter is below a predetermined maximum value, the control value of the quantitative feeding device is increased by the predetermined value.

[0324] 26. The method according to aspect 24 or 25, wherein at least one parameter includes at least one of the following parameters: Conveying speed, pump outlet pressure, pump capacity, and the amount of bulk material per batch.

[0325] 27. The method according to any one of aspects 17 to 26, further comprising: The conveying process is terminated by stopping the conveying equipment when at least one of the following events is detected: The source tank from which bulk material is discharged by the quantitative feeding device is empty; the target tank to which the bulk material is being transported is full; the predetermined maximum transport time has been exceeded; and the total pressure loss of the transported gas has exceeded the predetermined limit.

[0326] 28. The method according to any one of aspects 17 to 27, comprising: The raw material powder is conveyed from the main storage tank to the first tank of the apparatus for producing three-dimensional workpieces by irradiating the raw material powder layer with electromagnetic radiation or particle radiation via at least one first conveying loop. The lower outlet of the first tank is connected to the upper inlet of the intermediate tank of the apparatus, wherein powder from the intermediate tank is supplied to the manufacturing process in the processing chamber of the apparatus, and The upper inlet of the main storage unit is connected to the outlet of a sieve used for screening the raw material powder.

[0327] 29. The method according to any one of aspects 17 to 28, comprising: The raw material powder is conveyed from the overflow tank to the buffer container via at least one second conveying circuit. The overflow tank is configured to receive excess powder from the processing chamber of a device used to produce three-dimensional workpieces by irradiating a layer of raw material powder with electromagnetic radiation or particle radiation. The lower outlet of the buffer container is connected to the inlet of a sieve used for screening the raw material powder.

[0328] 30. The method according to any one of aspects 17 to 29, comprising: The raw material powder is transported from the external tank to the buffer container via at least one third conveying loop. The outer tank is detachably connected to the bulk material conveying system, or connected to the bulk material conveying system, and The lower outlet of the buffer container is connected to the inlet of a sieve used for screening the raw material powder.

[0329] 31. The method according to any one of aspects 17 to 30, wherein the metering feeder is located at the outlet of the respective source tank, and wherein the cyclone separator is located at the inlet of the respective target tank, the cyclone separator being used to separate the raw material powder from the gas stream and to supply the raw material powder to the target tank.

[0330] The screening equipment disclosed herein (especially) Figure 1 The screening equipment 5) can also be constructed according to the screening equipment disclosed below. Figure 1 The method performed by the screening equipment 5 may correspond to one of the methods disclosed below.

[0331] The various aspects of the screening equipment and / or methods described below can be applied to the screening equipment 5 described above.

[0332] However, various aspects of the screening equipment or associated methods described below may also be advantageous individually and may constitute one or more inventions. Therefore, the screening equipment and / or methods described below may also be used independently (i.e., independently of the powder conveying system described above).

[0333] The following disclosure relates to a method for controlling the operation of a screening device and the screening device itself, which is suitable for use, for example, in a powder conveying system of an apparatus for producing three-dimensional workpieces using a layer-building process. The following disclosure also relates to an apparatus for producing three-dimensional workpieces using a layer-building process, the apparatus being equipped with such screening equipment.

[0334] In the generative layer construction process for manufacturing three-dimensional workpieces, particularly in so-called powder bed melting, raw material powders or particles are applied layer by layer onto a carrier, and selectively exposed to electromagnetic radiation, such as laser radiation or particle radiation, depending on the desired geometry of the workpiece to be produced. Radiation penetrating into the powder layer causes heating, thus causing the raw material powder particles to melt or sinter. Subsequently, another layer of raw material powder is sequentially applied onto the radiation-treated and cured layer on the carrier until the workpiece has the desired shape and size. The raw material powder may include ceramics, metals, or plastic materials, but may also include mixtures of these materials. For example, generative layer construction processes, particularly powder bed melting processes, can be used to manufacture prototypes, tools, spare parts, or medical prostheses (such as dental or orthopedic prostheses) and for repairing components based on CAD data.

[0335] An apparatus for producing three-dimensional workpieces by selectively irradiating a raw material powder is known, for example, from EP 2 335848 B1. The apparatus includes a processing chamber sealed relative to the ambient atmosphere, and a carrier arranged within the processing chamber for receiving the raw material powder to be irradiated. The apparatus also includes an irradiation device and an optical unit, the irradiation device being equipped with a radiation source, particularly a laser source. The optical unit is used to selectively guide an irradiation beam generated by the radiation source onto a layer of raw material powder applied to the carrier, according to the geometry of the workpiece to be produced. When a three-dimensional workpiece is constructed by selectively irradiating the powder layer applied to the carrier, the radiative energy introduced into the raw material powder causes the powder particles to melt and / or sinter.

[0336] In additive manufacturing of three-dimensional components in a powder bed (particularly via selective laser melting and / or selective laser sintering), excess powder is generated when individual powder layers are applied. This excess powder can be collected in one or more collection containers. Furthermore, excess cured powder can be recovered during workpiece unpacking. The excess powder can be reused in the additive manufacturing process after appropriate reprocessing. For example, the reprocessed powder can be used again as feedstock powder for selective laser melting or laser sintering processes, or it can be mixed with fresh feedstock powder used in those processes. However, if the excess powder is reused in the additive manufacturing process, particulate impurities in the excess powder, as well as adhered or sintered powder agglomerates, can contaminate the powder bed and thus reduce workpiece quality.

[0337] Therefore, sieving is a necessary step in the reprocessing of excess powder, used to remove unwanted particulate impurities with a particle size larger than that of the powder. Furthermore, excess powder can undergo further powder reprocessing steps, such as drying, cleaning, and component separation, which can be performed before and / or after sieving.

[0338] An apparatus for sieving powder is described in DE 20 2021 102 494. This apparatus is suitable for use in devices for producing three-dimensional workpieces by selective electron beam melting, selective laser melting, laser deposition welding, laser metal deposition, or selective laser sintering. The apparatus includes a base unit and a control unit. The base unit has a vibration generator, and the control unit controls the vibration generator. The base unit has an interface for connecting a replacement module, which includes a sieve and a housing for receiving the sieve. The replacement module can be connected to the base unit via the interface.

[0339] The purpose of the following disclosure is to provide a method and a screening device for controlling the operation of a screening apparatus, which can efficiently screen powder and is therefore particularly suitable for use in powder conveying systems of apparatuses used to produce three-dimensional workpieces using a layer-building process. Furthermore, the purpose of the following disclosure is to provide an apparatus for producing three-dimensional workpieces using a layer-building process, which can efficiently produce high-quality workpieces.

[0340] This objective is achieved by a method for controlling the operation of a screening device having the features of aspect 1, a screening device having the features of aspect 13, and an apparatus for producing three-dimensional workpieces using a generation layer construction process having the features of aspect 21.

[0341] In a method for controlling the operation of a sieving device, in step (i), powder to be sieved is supplied to a sieve through a powder inlet. The sieve may include a sieve frame on which a screen defining the sieve surface extends. The sieve frame may be attached to or placed on a sieve container. The sieved powder may then be collected in the sieve container after passing through the screen. The sieve container may have a downwardly tapered cross section such that the sieved powder collected in the sieve container may be discharged from the sieve container by gravity through a sieved powder outlet located in the lower section of the sieve container. The sieving device may have an oversized particle outlet for discharging oversized particles that are too coarse to pass through the screen towards the sieve container. Preferably, the powder inlet and the oversized particle outlet are located in regions of opposite side edges of the sieving surface.

[0342] Preferably, the screening equipment is equipped with a drive device for driving the sieve. Preferably, the drive device is engaged with the sieve frame such that during operation of the screening equipment, the sieve frame is set to vibrate by the drive device, and thus the sieve mesh is set to vibrate by the drive device. The drive device can be a mechanical drive device that vibrates and excites the sieve. However, preferably, the drive device is designed as an ultrasonic drive device and configured to apply ultrasonic vibrations to the sieve. Using an ultrasonic drive device instead of a mechanical drive device increases the powder throughput of the sieve, i.e., achieves higher screening performance, thereby improving the efficiency of the screening equipment. In particular, equipping the screening equipment with an ultrasonic drive device can increase the powder throughput of the sieve by approximately four times compared to a mechanically driven screening equipment.

[0343] In ultrasonic driven equipment, frequency is the most important factor, as it determines the drive power. Although amplitude also affects the power consumption of the drive motor, frequency is the most critical parameter for drive power because it influences the vibration of the screen, thereby affecting the screen's separation efficiency. Higher frequencies typically result in improved separation, leading to higher powder throughput, or higher sieving performance.

[0344] In a loose mass of powder on a flat surface, a mass angle is formed. The mass angle is the angle between the horizontal plane and the maximum angle the mass can exhibit without further irritation; that is, the angle at which the mass begins to flow when poured onto an inclined surface. The mass angle depends on various factors, such as the size and shape of the powder particles. Furthermore, the mass angle is affected by process parameters (e.g., relative humidity). For example, the powder mass to be sieved by a sieving device may have a mass angle between about 20° and about 40°, preferably between about 25° and about 35°, and particularly preferably about 30°.

[0345] On the other hand, the wall friction angle is defined as the angle between the horizontal plane and the inclination of the powder when it adheres to the wall and no longer flows further. The wall friction angle depends on the type and properties of the wall and the surface properties of the powder particles. For example, the powder mass to be sieved by a sieving device may have a wall friction angle between about 10° and about 30°, preferably between about 15° and about 25°, and particularly preferably about 20°.

[0346] When powder is supplied through the powder inlet of the screening equipment, blocky cones are formed on the sieve, i.e., on the screen mesh. The shape and angle of these blocky cones are affected by vibrations acting on them, and therefore by the drive power of the equipment driving the sieve. Specifically, the angle of the blocky cones decreases as the drive power increases. Simultaneously, the vibrations caused by the drive equipment reduce wall friction, which facilitates the sliding of powder blocks on the screening surface. When the sieve is driven with low drive power, the blocky cones formed below the powder inlet on the sieve resemble those formed on a stationary plane, with the base region of these cones occupying only a small segment of the screening surface. In this operating state of the screening equipment, the utilization rate of the screening area is low because only a small segment of the screening surface adjacent to the powder outlet is actually exposed to powder.

[0347] On the other hand, if the sieve is driven with high power, the powder spreads out on the sieving surface. That is, the angle of the blocky cone formed by the powder supplied to the sieve through the powder inlet decreases with increasing drive power of the drive device, and the wall friction angle decreases similarly. This increases the base area of ​​the blocky cone, increasing the utilization rate of the sieve area, and sections of the sieve surface further away from the powder inlet and closer to the oversized particle outlet are also covered by powder. However, if the base area of ​​the blocky cone becomes too large, especially so large that the powder flows across the entire sieve surface, thus exposing the entire sieve surface to powder, there is a risk that powder will flow unscreened into the oversized particle outlet. As a result, powder that is actually fine enough to pass through the sieve is lost unused, leading to reduced sieving efficiency.

[0348] Therefore, in the method for controlling the operation of a screening device, in step (ii), the sieve is driven with a first drive power for a first time interval, the size of which is set such that when the sieve is continuously driven with the first drive power, the powder to be screened flows across the entire screening surface of the sieve and / or flows into the oversized particle outlet. Thus, driving the screening device with such a high drive power during the first time interval ensures, on the one hand, maximum utilization of the screening area if the screening device is continuously driven with such a high drive power, but on the other hand, it at least involves a high risk of unscreened powder being lost through the oversized particle outlet.

[0349] Therefore, after the first time interval has elapsed, in step (iii), the sieve is driven at a second driving power lower than the first driving power for a second time interval. After the second time interval has elapsed, steps (ii) and (iii) are repeated, that is, the sieve is driven periodically alternately at a first higher driving power and a second lower driving power.

[0350] The first driving power can have different values ​​depending on the type of powder and the process parameters (e.g., temperature, particle size distribution, moisture content, etc.). Therefore, the first driving power can be determined empirically before the sieving process, or obtained from a previously created table of driving power values ​​for different powder types and process parameters. Alternatively, the first driving power can be selected based on empirical values.

[0351] During the first time interval, high sieve area utilization, generated by high drive power, is achieved, thus utilizing high screening performance. Furthermore, during the first time interval, extra-large particles are specifically conveyed towards the extra-large particle outlet. In particular, the "spreading" of the block cone across the entire screening surface during the periodically repeated first time interval allows extra-large particles collected inside the block cone and "accumulated" in a columnar manner during the second time interval to pass through the extra-large particle outlet and be removed from the screening surface. This counteracts the formation of so-called clogging particles caused by powder particles pressed into the screen and clogging it due to back pressure and screen vibration. On the other hand, the reduction in drive power during the second time interval ensures that losses due to unscreened powder passing through the extra-large particle outlet are minimized.

[0352] Therefore, the method for controlling the operation of the screening equipment described herein enables highly efficient powder screening, making it particularly suitable for use in powder conveying systems for devices used in the production of three-dimensional workpieces using a layer-building process, where large quantities of relatively expensive (metallic) powders may also need to be screened during the layer-building process. Furthermore, the periodically varying drive power means that the screen mesh bears a smaller total powder mass, and therefore experiences less stress. The result is less wear and thus a longer screen lifespan.

[0353] Preferably, the second driving power is set such that when the sieve is continuously driven with the second driving power, the powder to be sieved forms blocky cones in the powder inlet region of the sieve's sieving surface, which substantially correspond to the blocky cones formed on the stationary plane. When the sieve is driven with the second driving power, the blocky cones formed on the sieve surface have, in particular, a block angle that is at most 30%, preferably at most 20%, and particularly preferably at most 10% larger than the block angle of the blocky cones formed on the stationary plane. When the sieve is continuously driven with the second driving power, the base region of the blocky cones formed on the sieve surface occupies only a small segment of the sieve's sieving surface located in the powder inlet region. Therefore, during the second time interval, the sieving device can be driven with such a low driving power that if the sieving device is continuously driven with such a low driving power, it can be ensured that no or almost no powder flows into the oversized particle outlet without being sieved. However, on the other hand, due to the low utilization rate of the sieve area, the sieve throughput is low, resulting in low sieving performance. Therefore, the second driving power can be lower than the first driving power, but greater than zero.

[0354] However, in one or more embodiments, the second drive power may also be zero. In this case, the sieve is not driven during the second time interval.

[0355] The second driving power can have different values ​​depending on the powder type and process parameters (e.g., temperature, particle size distribution, moisture content, etc.). Therefore, the second driving power can be determined empirically before the sieving process, or obtained from a previously created table of driving power values ​​for different powder types and process parameters. Alternatively, the second driving power can be selected based on empirical values.

[0356] In principle, the sieving surface of the sieve can be aligned with a horizontal plane. However, alternatively, it is conceivable that the sieving surface of the sieve is inclined relative to a horizontal plane. Preferably, when the sieve is driven with a second driving power, the block angle of the block cone formed in the powder inlet region on the sieve's sieving surface is adapted to the alignment of the sieve surface. This means that when the sieve's sieving surface is aligned with a horizontal plane, the powder supplied to the sieve through the powder inlet preferably forms symmetrical block cones with a constant block angle along the circumference of the block cone. On the other hand, if the sieve's sieving surface is inclined relative to a horizontal plane, the powder supplied to the sieve through the powder inlet preferably forms block cones whose block angle varies along the circumference of the block cone depending on the inclination direction and angle of the sieve surface.

[0357] Preferably, the sieving surface of the sieve is inclined relative to the horizontal plane, such that the flow of powder supplied through the powder inlet along the direction of the oversized particle outlet is supported by gravity. In other words, preferably, the sieving surface of the sieve is inclined from the region below the powder inlet toward the oversized particle outlet. This not only promotes the spreading of powder on the sieving surface but also moves oversized particles from the sieving surface to the oversized particle outlet. Therefore, preferably, the block angle of the block cone formed on the sieving surface when the sieve is driven with the second driving power is smaller in the circumferential section of the block cone facing the oversized particle outlet than in the circumferential section of the block cone away from the oversized particle outlet.

[0358] However, preferably, the angle of inclination of the sieve's screening surface relative to the horizontal plane is smaller than the block angle of the blocky cone formed by the powder to be screened on the horizontal plane. This ensures that, at least when the sieve is driven with a second drive power, a stable blocky cone is still formed in the region of the powder inlet, and the powder does not flow uncontrollably on the screening surface. For example, the angle of inclination of the sieve's screening surface relative to the horizontal plane can be from about 10° to about 25°, preferably from about 15° to about 20°, and particularly preferably about 17°.

[0359] Similar to the first drive power, the first time interval can also take different values ​​for different powder types and different process parameters (e.g., temperature, powder particle size distribution, powder moisture content, etc.). Therefore, preferably, the first time interval is a value determined empirically before the sieving process of the powder to be sieved. However, the first time interval can also be obtained from a value table previously created for different powder types and process parameters, which contains different values ​​for the first time interval; or, the first time interval can be selected based on empirical values.

[0360] When the first time interval is determined, it preferably terminates no later than when the powder to be screened flows into the ultra-large particle outlet. The inflow of the powder to be screened into the ultra-large particle outlet can be detected by an ultra-large particle sensor. Preferably, the ultra-large particle sensor is located in the region of the ultra-large particle outlet.

[0361] Preferably, the first time interval is set such that at the end of the first time interval, the utilization rate of the sieve area does not exceed about 70% to about 90% of the total sieve area, preferably about 75% to about 85%, and particularly preferably about 80%. In other words, preferably, the first time interval provides a "time safety reserve" so that powder does not spread across the entire sieving surface during the first time interval. This reliably prevents unsieving powder from being lost through the oversized particle outlet.

[0362] The second time interval can take different values ​​depending on the type of powder and the process parameters (e.g., temperature, particle size distribution, moisture content). Therefore, preferably, the second time interval is also a value determined empirically before the sieving process of the powder to be sieved. However, the second time interval can also be obtained from a table of values ​​previously created for different powder types and process parameters, which contains different values ​​for the second time interval; or, the second time interval can be selected based on empirical values.

[0363] When determining the second time interval, it preferably terminates no later than when the powder to be screened forms blocky cones of a defined size on the screening surface of the sieve located in the powder inlet region. This prevents the blocky cones from becoming too large and clogging the powder inlet. On the other hand, the transition to the first time interval improves the efficiency of the screening process, during which the sieve is driven with increased drive power, thus increasing the sieve throughput. For example, the formation of blocky cones of a defined size can be detected by a metering sensor. Preferably, the metering sensor is located in the powder inlet region.

[0364] The following section explains the control of the powder supply through the powder inlet of the sieve, which can also request protection independently of the aforementioned drive control.

[0365] In a method for controlling the operation of a screening device that can be protected independently, the powder to be screened is supplied to the screen at a quantitative feed mass flow rate, at least temporarily and continuously, through the powder inlet: , For example, the metering feed mass flow rate can be adjusted by correspondingly controlling a metering feed device (which may include, for example, a metering feed screw) associated with the powder inlet and / or by controlling a valve associated with the powder inlet. Parameters and The sieve area utilization and sieve throughput are limited when the sieve is driven with a first driving power. The magnitude of the first driving power is set such that when the sieve is continuously driven with the first driving power, the powder to be sieved flows across the entire sieve area and / or flows into the oversized particle outlet. On the other hand, parameters and The screen area utilization and screen throughput are defined when the screen is driven at a second drive power lower than the first drive power. Therefore, the continuous metering feed mass flow rate can be determined by averaging the screen throughput when the screen is driven at the first drive power and the screen throughput when the screen is driven at the second drive power.

[0366] Preferably, the sieve throughput when the sieve is driven with the second driving power is determined by increasing the metered feed mass flow rate of the powder to be sieved through the powder inlet when the sieve is driven with the second driving power, until the powder to be sieved has formed blocky cones of a defined size on the sieve surface located in the powder inlet region. For example, the formation of blocky cones of a defined size can be detected by a metering sensor arranged in the area of ​​the powder inlet. In other words, the sieve throughput when the sieve is driven with a second drive power is determined. In this case, it is preferable to increase the quantitative feed mass flow rate of the powder to be screened through the powder inlet until the quantitative feed sensor is triggered.

[0367] Preferably, the sieve throughput when the sieve is driven with the first driving power is determined by increasing the metered feed mass flow rate of the powder to be sieved through the powder inlet when the sieve is driven with the first driving power, until the powder to be sieved has formed blocky cones of a defined size on the sieve surface located in the powder inlet area and the powder to be sieved flows into the oversized particle outlet. For example, the formation of blocky cones of a defined size can be detected again by a metering sensor arranged in the powder inlet area. On the other hand, the inflow of powder to be screened into the oversized particle outlet can be detected by an oversized particle sensor arranged in the oversized particle outlet area. In other words, the sieve throughput when the sieve is driven with a first drive power is determined. When this is done, it is preferable to increase the quantitative feed mass flow rate of the powder to be screened through the powder inlet until the quantitative feed sensor and the large particle sensor are triggered.

[0368] Preferably, the result obtained therefrom The value is multiplied by a safety factor to offset unintentional overfeeding of powder. For example, the safety factor could be 0.8, 0.7, 0.6, or 0.5.

[0369] During the screening process, the screen can become clogged, for example, due to clogging particles formed by powder particles being pressed into the screen or due to cold welding. This reduces the screen throughput. To mitigate this phenomenon, the metered feed mass flow rate can be reduced by forming defined-sized blocky cones on the screening surface in the powder inlet area. For example, the formation of blocky cones of a defined size can again be detected by a metering sensor located in the area where the powder enters. In other words, when the metering sensor is triggered during an ongoing sieving process, this can be interpreted as a sign of screen clogging and the resulting reduction in screen throughput, and the metering mass flow rate can be reduced accordingly.

[0370] Additionally or alternatively, when the powder to be screened forms blocky cones of a defined size on the screening surface of the sieve located in the powder inlet area and / or when the metered feed mass flow rate... When the flow rate is below the limit, sieve cleaning can be initiated. In other words, if even when the metered feed mass flow rate is low and below the limit, the formation of blocky cones of a defined size on the sieving surface of the sieve in the powder inlet area can be interpreted as an indication that the sieve is so clogged that sieve cleaning is necessary.

[0371] Additionally or alternatively, sieve cleaning can be initiated at the end of each sieving process. For example, the sieving process can be terminated when the powder supply container (which can be connected to the powder inlet of the sieving equipment) for the powder to be sieved is empty.

[0372] In addition to or as an alternative to the options mentioned above, screen cleaning can also be triggered manually, i.e., initiated by user input. Additionally or alternatively, screen cleaning can be initiated based on time control, for example, whenever a predetermined time (i.e., absolute time) or a predetermined operating time of the screening equipment (i.e., the time the screening equipment is in operation) has elapsed since the last screen cleaning.

[0373] When initiating sieve cleaning, it is preferable to stop supplying powder through the powder inlet. Additionally, powder remaining in the sieve can be sieved before sieve cleaning begins. After sieve cleaning begins, the sieve can be driven at maximum drive power. Alternatively or additionally, a vibrator can be activated after sieve cleaning begins, driving the sieve independently of the drive mechanism of the sieving device. Preferably, the contact angle between the vibrator and the sieve, the drive amplitude of the vibrator, and / or the drive frequency of the vibrator are variablely adjustable.

[0374] In addition to, or as an alternative to, continuous powder feeding, the powder to be sieved can be supplied to the sieve through the powder inlet at least temporarily and intermittently. In the case of intermittent powder supply, the powder to be sieved can first be supplied to the sieve through the powder inlet without driving the sieve, until the powder to be sieved has formed blocky cones of a defined size on the sieve surface located in the powder inlet area. The formation of these blocky cones can then be detected using a metering sensor located in the powder inlet area. After the powder supply is terminated, the sieve can be driven, and the powder supplied to the sieve surface can be sieved.

[0375] The screening process can be terminated under the following conditions: , in It refers to the quality of the supplied powder. It refers to the mass of the ultra-large particles flowing into the ultra-large particle outlet, and This refers to the mass of the sieved powder. For example, the mass of the supplied powder can be determined by a first measuring device installed in the powder supply container. The powder supply container can be connected to the powder inlet of the screening equipment. The mass of the powder that has passed through the ultra-large particle outlet and flowed into the ultra-large particle container can be determined by a second measuring device installed in the ultra-large particle container. The oversized particle container can be connected to the oversized particle outlet of the screening equipment. Finally, the mass of the screened powder can be determined by a third measuring device installed in the screened powder container. The sieved powder container can be connected to the sieved powder outlet of the sieving equipment.

[0376] In methods for controlling the operation of screening equipment, powder can be supplied continuously or discontinuously. However, it is also conceivable that the powder supply can be temporarily continuous or temporarily discontinuous.

[0377] In addition to, or as an alternative to, the continuous or discontinuous metered powder feeding described above, the powder to be screened can be supplied to the sieve, at least temporarily, through the powder inlet at a metered feed mass flow rate determined based on the drive power used to drive the sieve. Preferably, the first metered feed mass flow rate during a first time interval when the powder to be screened is supplied to the sieve through the powder inlet is greater than the second metered feed mass flow rate during a second time interval. In other words, when the sieve is driven with a higher drive power during the first time interval, more powder is directed onto the sieve through the powder inlet compared to during the second time interval (during which the sieve is driven with a lower drive power). This prevents powder buildup and / or a large amount of powder remaining on the screen, thus reducing screening performance. This increases powder throughput.

[0378] The first and / or second quantitative feed mass flow rates can be adjusted according to the properties of the powder to be screened, as well as the lengths of the first and second time intervals, and the first and second drive powers. The first and second quantitative feed mass flow rates can each have a positive value >0. However, it is also conceivable that the value of the second quantitative feed mass flow rate = 0, i.e., during the second time interval (during which the sieve is driven with a lower second drive power), no powder is supplied to the sieve through the powder inlet.

[0379] The oversized particle ratio is a parameter indicating the ratio of the mass of oversized particles flowing into the oversized particle outlet within a defined time unit to the mass of all powder processed within the screening equipment within the defined time unit. Specifically, the oversized particle ratio... It can be calculated using the following formula: , in It is the mass flow rate of sieved powder flowing into the sieved powder container during the sieving process, wherein the sieved powder container can be connected to the sieved powder outlet of the sieving equipment; This refers to the mass flow rate of oversized particles flowing into an oversized container during the screening process, where the oversized container can be connected to the oversized particle outlet of the screening equipment. For example, during the screening process, parameters can be continuously monitored using a second measuring device located in the oversized particle container and a third measuring device located in the container containing the screened powder. and Therefore, the ratio of ultra-large particles can also be continuously measured. .

[0380] Preferably, in the method for controlling the operation of the screening equipment, a warning signal is output when the oversized particle rate exceeds a limit value. When using screening equipment to process raw material powder (the raw material powder is intended for processing in an apparatus used to produce three-dimensional workpieces using a layer-building process), an excessively high oversized particle rate can be an indication of an unfavorable process parameter of the apparatus. For example, an excessively high oversized particle rate can indicate the generation of large weld spatter during powder irradiation, which remains in the powder bed and can therefore impair the quality of the workpiece to be produced. Therefore, monitoring the oversized particle rate can be used to monitor process parameters in an apparatus used to produce three-dimensional workpieces using a layer-building process.

[0381] In a preferred embodiment of the method for controlling the operation of a screening device, the screening device is sealed relative to the ambient atmosphere and filled with a protective gas during operation. This prevents undesirable oxidation of the powder to be screened by the screening device. Preferably, additional protective gas can be supplied to the screening device when the inert gas pressure in the screening device is below a threshold. This makes it possible to detect and compensate for leaks in the screening device.

[0382] Furthermore, during the sieving process, the step response of the sum of the sieved powder mass flow rate and the oversized particle mass flow rate to the metered feed mass flow rate can be monitored. The “step response” of the sum of the sieved powder mass flow rate and the oversized particle mass flow rate to the metered feed mass flow rate should be understood as the time difference between the point in time when the defined metered feed mass flow rate is supplied to the sieving equipment and the point in time when the corresponding sieved powder mass flow rate passes through the screen. Therefore, the step response is a time parameter indicating the duration of the sieving process for a specific powder mass flow rate. For example, the metered feed mass flow rate can be measured using a first measuring device located in a powder supply container, which can be connected to the powder inlet of the sieving equipment. Similarly, the sum of the sieved powder mass flow rate and the oversized particle mass flow rate can be detected using a second measuring device located in an oversized particle container and a third measuring device located in a sieved powder container, which can be connected to the oversized particle outlet of the sieving equipment, and the sieved powder container can be connected to the sieved powder outlet of the sieving equipment. It can continuously measure the mass flow rate of the metered feed, as well as the sum of the mass flow rates of the sieved powder and the oversized particles. Therefore, it can also continuously monitor the step response of the sum of the mass flow rates of the sieved powder and the oversized particles to the mass flow rate of the metered feed.

[0383] If the screen becomes clogged during the sieving process, the step response of the sum of the sieved powder mass flow rate and the oversized particle mass flow rate to the metered feed mass flow rate is prolonged. Conversely, a shortened step response, particularly below a certain limit, is an indication of a defect (e.g., tearing in the screen). Therefore, preferably, a warning signal is output when the step response of the sum of the sieved powder mass flow rate and the oversized particle mass flow rate to the metered feed mass flow rate is below a first limit. Additionally or alternatively, if the step response of the sum of the sieved powder mass flow rate and the oversized particle mass flow rate to the metered feed mass flow rate exceeds a second limit, screen cleaning can be initiated. This allows for additional monitoring of screen throughput, which is redundant (if necessary) for monitoring the formation of blocky cones exceeding a certain size in the powder inlet area and the subsequent initiation of screen cleaning.

[0384] Methods for controlling the operation of screening equipment may also include: changing the tilt angle of the screening surface of the sieve relative to the horizontal plane.

[0385] This aspect, as well as all aspects described below in conjunction with changes in the tilt angle, can be applied, on the one hand, to one of the methods described above, and / or on the other hand, independently of the methods described above, to methods for controlling the operation of screening equipment.

[0386] Therefore, a method for controlling the operation of a screening device, particularly for screening powder from an additive manufacturing device (such as a device for producing three-dimensional workpieces by selective electron beam melting, selective laser melting, laser deposition welding, laser metal deposition, or selective laser sintering), may include the steps of: feeding powder to be screened onto a sieve through a powder inlet; driving the sieve; and changing the inclination angle of the screening surface of the sieve relative to a horizontal plane.

[0387] For example, changing the tilt angle may include initially changing and thus setting the tilt angle, particularly before the step of feeding the powder to be sieved. Additionally or alternatively, the change of tilt angle may also be performed during operation of the sieving equipment, for example, at the beginning of a first time interval and / or a second time interval.

[0388] The sieve can be arranged within an airtight sealed housing, and the sieve can rotate relative to the housing to change its tilt angle. The airtight sealed housing can be closed airtightly via a baffle. The sieve can be inserted into the housing via the baffle.

[0389] A first tilt angle may be set during a first time interval, and a second tilt angle may be set during a second time interval. (a) The first tilt angle is less than the second tilt angle, or (b) The first tilt angle is greater than the second tilt angle.

[0390] The tilt angle can be changed during the first time interval and / or the second time interval.

[0391] The method may further include: detecting the spreading speed of the powder to be sieved on the sieve and / or the position of the powder leading edge of the powder to be sieved on the sieve. The tilt angle of the sieve surface relative to the horizontal plane may be changed according to the detected spreading speed and / or according to the detected position.

[0392] For example, sensors can be used to perform the detection, which may include, in particular, cameras, inductive sensors, and / or light barriers. The sensors may be attached to the housing, particularly to the upper wall of the housing. Detection can also be performed via a control unit. The spreading rate of the powder to be sieved can be the spreading rate of the powder front.

[0393] When the detected spreading speed of the powder to be sieved and / or the detected position of the powder leading edge exceed a predetermined threshold, the tilt angle can be changed to decrease the tilt angle. Conversely, when the detected spreading speed of the powder to be sieved and / or the detected position of the powder leading edge are below a predetermined threshold, the tilt angle can be changed to increase the tilt angle. The tilt angle can also be permanently adjusted, for example, within a closed control loop, to set a constant spreading speed for the powder to be sieved.

[0394] A sieving apparatus includes a powder inlet and a drive device configured to drive a sieve. The sieving apparatus also includes a control unit configured to control the powder inlet and the drive device such that, in step (i), powder to be sieved is supplied to the sieve through the powder inlet, and in step (ii), the sieve is driven at a first drive power for a first time interval, wherein the magnitude of the first drive power is set such that when the sieve is continuously driven at the first drive power, the powder to be sieved flows across the entire sieving surface of the sieve and / or flows into an oversized particle outlet. Furthermore, the control unit is configured to control the powder inlet and the drive device such that, in step (iii), after the first time interval has elapsed, the sieve is driven at a second drive power lower than the first drive power for a second time interval; and in step (iv), after the second time interval has elapsed, steps (ii) and (iii) are repeated.

[0395] Preferably, the magnitude of the second driving power is set such that when the sieve is continuously driven with the second driving power, the powder to be sieved forms a blocky cone in the region of the powder inlet on the sieve's sieving surface. This blocky cone substantially corresponds to a blocky cone formed on a stationary plane, wherein the block angle of the blocky cone is particularly adapted to the orientation of the sieve surface.

[0396] Additionally or alternatively, the sieving surface of the sieve may be inclined relative to the horizontal plane, such that the flow of powder supplied through the powder inlet along the direction of the oversized particle outlet is supported by gravity, wherein, preferably, the inclination angle of the sieving surface of the sieve relative to the horizontal plane is smaller than the block angle of the block cone formed by the powder to be sieved on the horizontal plane.

[0397] The first time interval can be a value determined empirically for the powder to be screened. Additionally or alternatively, the control unit can be configured to terminate the first time interval no later than when the powder to be screened flows into the oversized particle outlet. The screening equipment may include an oversized particle sensor disposed in the area of ​​the oversized particle outlet for monitoring the flow of powder to be screened into the oversized particle outlet. The control unit can be configured to set the size of the first time interval such that at the end of the first time interval, the utilization rate of the sieve area does not exceed about 70% to about 90% of the total sieve area, preferably about 75% to about 85%, and particularly preferably about 80%.

[0398] The second time interval can be a value determined empirically for the powder to be screened. Additionally or alternatively, the control unit can be configured to terminate the second time interval no later than when the powder to be screened forms blocky cones of a defined size on the screening surface of the sieve located in the powder inlet region, at the latest when the second time interval is determined. The screening equipment may include a metering sensor disposed in the powder inlet region for detecting the formation of blocky cones of a defined size.

[0399] The following describes an embodiment of a screening device equipped with a control unit for controlling the supply of powder through the powder inlet of the sieve, and the screening device can also request protection independently of the aforementioned screening device with a control unit for performing drive control.

[0400] A screening device that can be independently claimed for protection includes a powder inlet and a control unit, the control unit being configured to control the powder inlet such that the powder to be screened is supplied to the screen at a quantitative feed mass flow rate through the powder inlet at least intermittently and at least temporarily continuously: , For example, to set the metered feed mass flow rate, the control unit can be configured to correspondingly control the metering device (which may include, for example, a metering screw) associated with the powder inlet and / or control the valve associated with the powder inlet. Parameters and The sieve area utilization and sieve throughput are limited when the sieve is driven with a first driving power. The magnitude of the first driving power is set such that when the sieve is continuously driven with the first driving power, the powder to be sieved flows across the entire sieve area and / or flows into the oversized particle outlet. On the other hand, parameters and The screen area utilization and screen throughput are limited when the screen is driven with a second driving power lower than the first driving power.

[0401] The control unit can also be configured to, when the sieve is driven with a second drive power, determine the amount of powder to be sieved by increasing the metered feed mass flow rate of the powder to be sieved through the powder inlet until the powder to be sieved has formed blocky cones of a defined size on the sieve surface located in the powder inlet area. .

[0402] Alternatively or additionally, the control unit may be configured to: when the sieve is driven with a first drive power, determine the presence of a fixed feed mass flow rate of the powder to be sieved through the powder inlet until the powder to be sieved has formed blocky cones of a defined size on the sieve surface located in the powder inlet region and the powder to be sieved flows into the oversized particle outlet. Preferably, the result obtained therefrom The value is multiplied by a safety factor of 0.8, 0.7, 0.6, or 0.5. The control unit can also be configured to reduce the metered feed mass flow rate when the powder to be screened forms blocky cones of a defined size on the screening surface of the sieve located in the powder inlet area. Furthermore, the control unit can be configured to: form blocky cones of a defined size on the screening surface of the sieve located in the powder inlet region when the powder to be screened forms such cones and / or when the metered feed mass flow rate... When the value falls below the limit, the sieve cleaning process is initiated.

[0403] The control unit can be configured to, upon initiation of sieve cleaning,: control the powder inlet to stop supplying powder through it; and / or control the drive device to sieve the powder still present in the sieve before sieve cleaning begins; and / or control the drive device to drive the sieve at maximum drive power after sieve cleaning begins; and / or activate the vibrator after sieve cleaning begins, the vibrator being configured to drive the sieve independently of the sieving device. Preferably, the contact angle between the vibrator and the sieve, the drive amplitude of the vibrator, and / or the drive frequency of the vibrator are variablely adjustable.

[0404] The control unit can also be configured to control the powder inlet, such that the powder to be sieved is supplied to the sieve at least temporarily and discontinuously through the powder inlet. Specifically, the control unit can be configured to control the drive device and the powder inlet, such that: initially, in a non-driven state of the sieve, the powder to be sieved is supplied to the sieve through the powder inlet until the powder to be sieved has formed blocky cones of a defined size on the sieve surface located in the area of ​​the powder inlet; and after the powder supply is terminated, the sieve is driven to sieve the powder supplied to the sieve surface. Furthermore, the control unit can be configured to control the drive device and the powder inlet, such that the sieving process is terminated under the following conditions: , in It refers to the quality of the supplied powder. It refers to the mass of the ultra-large particles flowing into the ultra-large particle outlet, and This refers to the mass of the sieved powder.

[0405] Screening equipment may include: for determining A first measuring device, disposed in a powder supply container, which is connectable to the powder inlet of a sieving device; used to determine... A second measuring device, disposed within an ultra-large particle container, which may be connected to the ultra-large particle outlet of the screening equipment; and / or used to determine The third measuring device is set in the sieved powder container, which can be connected to the sieved powder outlet of the sieving equipment.

[0406] The control unit can also be configured to control the powder inlet such that the powder to be screened is supplied to the sieve, at least temporarily, through the powder inlet at a quantitative feed mass flow rate determined based on the drive power used to drive the sieve, wherein, in particular, the first quantitative feed mass flow rate when the powder to be screened is supplied to the sieve through the powder inlet during a first time interval is greater than the second quantitative feed mass flow rate when the powder to be screened is supplied to the sieve through the powder inlet during a second time interval.

[0407] The control unit can be configured to output a warning signal when, in particular, the continuously measured rate of ultra-large particles exceeds a limit.

[0408] Preferably, the screening equipment is sealed relative to the ambient atmosphere and filled with a protective gas during operation. Additionally or alternatively, the control unit may be configured to supply additional protective gas to the screening equipment when the inert gas pressure in the screening equipment falls below a threshold. For this purpose, for example, the control unit may activate a valve that controls the supply of inert gas to the screening equipment.

[0409] Preferably, the control unit is further configured to monitor the step response of the sum of the mass flow rates of the screened powder and the oversized particles to the mass flow rate of the metered feed during the screening process. Furthermore, the control unit may be configured to output a warning signal when the step response of the sum of the mass flow rates of the screened powder and the oversized particles to the mass flow rate of the metered feed is below a first limit value. Finally, the control unit may be configured to initiate screen cleaning when the step response of the sum of the mass flow rates of the screened powder and the oversized particles to the mass flow rate of the metered feed exceeds a second limit value.

[0410] The screening equipment may also include a lid removable from the screen container. A seal may be disposed within the lid. For example, the seal may be disposed in a region of the lid facing the screen container and used to seal the screen container relative to the ambient atmosphere when the lid is closed. Furthermore, the screening equipment may include a clamping device configured to apply a clamping force to the seal, which holds the seal in its position within the lid. For example, the clamping device may include a clamping member that can be pressed against the seal by an adjusting screw. Advantageously, the clamping device prevents the seal from detaching from the lid when it is removed from the screen container.

[0411] Screening equipment may include tilting devices, which are used to change the tilt angle of the screening surface of the screen relative to the horizontal plane.

[0412] This aspect, as well as all aspects described below in conjunction with changes in the tilt angle, can be applied, on the one hand, to one of the screening devices described above, and / or on the other hand, to screening devices independently of the screening devices described above.

[0413] Therefore, a screening device, particularly for screening powders from additive manufacturing equipment (such as equipment for producing three-dimensional workpieces by selective electron beam melting, selective laser melting, laser deposition welding, laser metal deposition, or selective laser sintering), may include: a powder inlet; a drive device configured to drive the sieve; and an tilting device for changing the tilt angle of the screening surface of the sieve relative to a horizontal plane.

[0414] For example, changing the tilt angle may include initially changing and thus adjusting the tilt angle, particularly before the step of feeding the powder to be sieved. Additionally or alternatively, the tilt angle may also be changed during operation of the sieving equipment, for example, at the beginning of a first time interval and / or a second time interval.

[0415] Screening equipment may include a housing, which in particular may be airtight, wherein the screen is arranged inside the housing, and wherein an inclining device is configured to rotate the screen relative to the housing, thereby changing the inclining angle.

[0416] The powder inlet and the oversized particle outlet can be fixedly attached to the housing. The powder inlet can be attached to the upper side of the housing, and the oversized particle outlet can be attached to the lower side of the housing. In addition, the sieve container can be fixedly attached to the lower side of the housing.

[0417] Screening equipment may include a screen retainer for holding the screen, and in particular for inserting the screen. An inclined device may be attached to the screen retainer and configured to rotate the screen retainer.

[0418] The control unit can be configured to set a first tilt angle during a first time interval and a second tilt angle during a second time interval. (a) The first tilt angle is less than the second tilt angle, or (b) The first tilt angle is greater than the second tilt angle. The first tilt angle and the second tilt angle can remain constant during the first time interval and the second time interval, respectively.

[0419] The control unit can be configured to change the tilt angle during a first time interval and / or a second time interval.

[0420] The sieving equipment may also include at least one sensor for detecting the spreading speed of the powder to be sieved on the sieve and / or the position of the powder leading edge of the powder to be sieved on the sieve. The control unit may be configured to perform a change in the tilt angle of the sieving surface of the sieve relative to the horizontal plane based on the detected spreading speed and / or the detected position.

[0421] Sensors may include, in particular, cameras, inductive sensors, and / or light barriers. Sensors may be mounted on the housing, particularly on the upper wall of the housing. Detection may also be performed by a control unit. The spreading speed of the powder to be sieved may be the spreading speed of the powder front.

[0422] The control unit can be configured to decrease the tilt angle when the detected spreading speed of the powder to be sieved and / or the detected position of the powder leading edge exceeds a predetermined threshold. Furthermore, the control unit can be configured to increase the tilt angle when the detected spreading speed of the powder to be sieved and / or the detected position of the powder leading edge is below a predetermined threshold. For example, the control unit can also permanently adjust the tilt angle, for instance, by adjusting the tilt angle within a closed control loop to set a constant spreading speed for the powder to be sieved.

[0423] A powder handling system includes the sieving equipment described above. For example, the powder handling system can be designed as a closed system sealed relative to the ambient atmosphere. Furthermore, the powder handling system can be partially or completely filled with a protective gas during operation. The powder handling system may include: a powder supply container connected to the powder inlet of the sieving equipment; a sieved powder container connected to the sieved powder outlet of the sieving equipment; and a large particle container connected to the large particle outlet of the sieving equipment. The powder handling system is particularly intended for use in apparatuses for producing three-dimensional workpieces by irradiating a layer of raw material powder with electromagnetic radiation or particle radiation.

[0424] An apparatus for producing three-dimensional workpieces by irradiating a layer of raw material powder with electromagnetic radiation or particle radiation, comprising the screening equipment as described above and / or the powder handling system as described above.

[0425] Furthermore, the apparatus may include a processing chamber and a carrier, the processing chamber being sealed, particularly relative to the ambient atmosphere, and the carrier for receiving the raw material powder to be irradiated. Excess powder generated when the individual powder layers are applied to the carrier can be collected in one or more collection containers. The processing chamber may include a gas inlet and a gas outlet, the gas inlet for supplying gas (particulate gas) into the processing chamber, and the gas outlet for removing gas that may carry particulate impurities from the processing chamber. The carrier may be arranged within the processing chamber. However, it is also conceivable that the processing chamber may be movable on the carrier. The carrier may be a rigidly fixed carrier. However, preferably, the carrier may be movable in a vertical direction, such that as the height of the workpieces piled on the carrier increases, the carrier may move progressively downwards in a vertical direction.

[0426] For example, the raw material powder applied to the carrier by a powder application device movable on the carrier is preferably a metal powder, particularly a metal alloy powder. However, the raw material powder can also be a ceramic powder or a powder containing various materials. The powder can have any suitable particle size or particle size distribution. However, it is preferable to process powders with a particle size of less than 100 μm. Preferably, the apparatus also includes an irradiation device for selectively directing electromagnetic radiation or particle radiation onto the powder bed applied to the carrier. Furthermore, the apparatus may include a packaging and unpacking station, to which the workpiece received in the build chamber can be transported after completion. At the packaging and unpacking station, the workpiece can be removed from the build chamber and the uncured powder surrounding the workpiece can be removed, if necessary, after a cooling period.

[0427] Figure 14The apparatus 100s shown for producing a three-dimensional workpiece by irradiating a layer of raw material powder with electromagnetic radiation or particle radiation includes a processing chamber 102s, which is sealed relative to the ambient atmosphere. A powder application device 104s arranged in the processing chamber 102s is used to apply the raw material powder layer onto a carrier 106s. Excess powder accumulated during the application of the individual powder layers onto the carrier 106s is collected in a collection container 107s. The carrier 106s is movable in a vertical direction such that as the height of the workpiece 108s constructed on the carrier 106s increases, the carrier 106s can be progressively moved vertically downwards into a construction chamber 109s.

[0428] The processing chamber 102s is provided with a gas inlet 110s for supplying an inert gas (e.g., argon) into the processing chamber 102s. A gas outlet 112s is also provided, allowing a continuous gas flow to be generated through the processing chamber 102s. This gas flow can be used to remove molten spatter and / or other unwanted contaminant particles, such as welding fumes, from the processing chamber 102s.

[0429] The apparatus 100s also includes an irradiation device 112s, which is used to selectively direct electromagnetic radiation or particle radiation onto a powder bed applied to a carrier 106s according to the location. Figure 14 The exemplary device 100s shown includes only one irradiation device 112s. However, the device 100s may also include multiple irradiation devices 112s.

[0430] The irradiation device 112 includes a radiation source 114s, which is here specifically formed in the form of a laser source. The radiation source 114s can be integrated into the irradiation device 112s, and can include, for example, a diode-pumped ytterbium fiber laser emitting laser light with a wavelength of approximately 1070 nm to 1080 nm. However, in Figure 14 In the device 100s shown, a radiation source 114s is arranged outside the irradiation device 112s, wherein a laser beam 116s emitted by the radiation source 114s is guided into the irradiation device 112s through an optical fiber 118s.

[0431] The illumination unit 112s also includes two lenses 120s and 122s. Figure 14 In the embodiment of the illumination unit 112s shown, both lenses 120s and 122s have positive refractive power. Lens 120s collimates the laser emitted from fiber 118s to produce a collimated or substantially collimated laser beam 116. On the other hand, lens 122s is configured to focus the collimated (or substantially collimated) laser beam 116s to a desired z-position along the z-axis.

[0432] Finally, the irradiation unit 112s includes a scanner system having a scanner mirror 124s pivotable about a pivot axis S. During operation of the device 100s, the scanner system, in particular the scanner mirror 124s, is used to deflect the laser beam 116s emitted by the radiation source 114s, so that the beam 116s strikes the raw material powder layer applied to the carrier 106s at a desired location.

[0433] The apparatus 100s also includes a packaging and unpacking station 126s. When the production of workpiece 108s is completed, the build chamber 109s, in which workpiece 108s is arranged, is transported to the packaging and unpacking station 126s. Then, the irradiation equipment 112s and the processing chamber 102s can be used to produce new workpieces without further delay. In the packaging and unpacking station 126s, workpiece 108s can be cooled if necessary, and then the packaging of workpiece 108s is unpacked, i.e., workpiece 108s is removed from the build chamber 109s. This process generates potentially large amounts of uncured powder, which workpiece 108s is embedded in before unpacking.

[0434] The powder collected in the collection container 107s and the powder recovered in the packaging and unpacking station 126s can both contain particulate impurities and adhered or sintered powder agglomerates. If the aforementioned powder is reused in the additive manufacturing process in the apparatus 100s, these impurities can cause contamination of the powder bed and thus reduce the quality of the workpiece 108s. Therefore, the apparatus 100s includes a powder handling system 128s, which is connected to the collection container 107s and the packaging and unpacking station 126s via a powder line 130s. Blowers, conveyor screws, or other suitable conveying equipment (not included in the process) Figure 14 (As shown in the diagram) This system can be used to transport powder from the collection container 107s and the packaging unpacking station 126s to the powder handling system 128s. The powder handling system is designed to be a closed system relative to the ambient atmosphere and is completely filled with a protective gas, such as argon, during operation.

[0435] The powder handling system 128s includes a powder supply container 132s connected to the powder line 130s. Therefore, the powder supply container 132s receives powder to be processed from the collection container 107s and the packaging unpacking station 126s. Furthermore, the powder handling system 128s includes a sieving device 10s having a sieve formed by a sieve frame 14s and a screen 16s extending from the sieve frame. The sieved powder is collected in a sieve container 18s after passing through the screen 16s.

[0436] A lid 20s is placed on the sieve frame 14s, sealing the sieve container 18s relative to the ambient atmosphere, just like the other components of the powder handling system 128s, and allowing it to be filled with inert gas during operation of the sieving device 10s. For example, argon can be used as an inert protective gas to prevent undesirable oxidation of the powder 56s to be sieved in the sieving device 10s. The inert gas pressure in the sieving device 10s is continuously monitored by a pressure sensor (not shown in the figure). When the inert gas pressure in the sieving device 10s falls below a threshold, additional protective gas is supplied to the sieving device 10s under the control of the control unit 40.

[0437] Detailed view of the 10s screening equipment is available at [link / website / etc.]. Figure 15 As shown in [the image]. Figure 14 The system shown uses Figure 15 The screening device 10s. Alternatively, the screening device 10s can be used as Figure 14 5. Screening equipment in the system.

[0438] The powder inlet 22s of the screening device 10s includes a metering feeder 24s and a valve 26s, allowing powder to be supplied in a controlled manner from the powder supply container 132s to the sieve via the powder inlet 22s. A metering feed sensor 23s is disposed in the region of the powder inlet 22s; the function of the metering feed sensor 23s will be explained in more detail below. The sieve container 18s has a downwardly tapered cross-section. Therefore, the sieved powder received in the sieve container 18s can be discharged from the sieve container by gravity through the sieved powder outlet 28s arranged in the lower section of the sieve container 18s. The sieved powder outlet 28s is connected to the sieved powder container 134s of the powder handling system 128s and includes a valve 30s, allowing the sieved powder outlet 28s to be discharged in a controlled manner from the sieve container 18s into the sieved powder container 134s of the powder handling system 128s.

[0439] Furthermore, the screening device 10s includes an oversized particle outlet 32s, to which a valve 34s is provided. An oversized particle sensor 33s is provided in the region of the oversized particle outlet 32s, which can detect powder particles flowing into the oversized particle outlet 32s. Oversized particles that are too coarse to pass through the oversized particle outlet 24s can be discharged from the screening device 10s through the oversized particle outlet 24s and supplied to the oversized container 136 of the powder processing system 128s. The powder inlet 22s and the oversized particle outlet 32s are arranged in the region of opposite side edges of the screening surface defined by the screen 16s. Furthermore, the screening surface of the screen 16s and thus the sieve defined by the screen 16s is inclined relative to the horizontal plane E, such that the flow of powder supplied through the powder inlet toward the oversized particle outlet 32s is supported by gravity. In other words, the sieving surface of the sieve is inclined from the area below the powder inlet 22s toward the oversized particle outlet 32s, thereby promoting the spreading of the powder supplied through the powder inlet 22s on the sieving surface and moving the oversized particles to the oversized particle outlet 32s. Similar to the removal of sieved powder, the removal of oversized particles from the sieving device 10s is also gravity-driven.

[0440] The screening device 10s is also equipped with a drive device 36s for driving the sieve. The drive device 36s engages with the sieve frame and vibrates the sieve frame 14s during operation of the screening device 10s, thereby causing the screen 16s to vibrate. In a preferred embodiment of the screening device 10s shown here, the drive device 36s is in the form of an ultrasonic drive device configured to apply ultrasonic vibrations to the sieve. Furthermore, a vibrator 38s is provided, which also engages with the sieve frame 14s and is used to set the sieve frame 14s to vibrate, thus setting the screen 16s to vibrate for sieve cleaning.

[0441] The operation of the screening equipment 10s is controlled by the control unit 40s. The control unit 40s may be a control unit specifically assigned to the screening equipment 10s. However, alternatively, it is conceivable that the control unit 40s is integrated into a higher-level control unit, for example, integrated into a control unit for controlling the powder handling system 128s and / or a control unit for controlling the device 100s for producing three-dimensional workpieces.

[0442] Finally, the sieving device 10s includes a first measuring device 42s, a second measuring device 40s, and a third measuring device 46s. The first measuring device 42s is designed as one or more weighing units, arranged in the powder supply container 132s of the powder processing system 28s, and is used to detect the mass of powder supplied from the powder supply container 32s to the powder inlet 22s of the sieving device 10s. The second measuring device 44s is also designed as one or more weighing units, arranged in the oversized particle container 136s of the powder processing system 28s, and is used to determine the mass of oversized particles that have passed through the oversized particle outlet 32s of the sieving device 10s and flow into the oversized particle container 136s. Finally, the third measuring device 46s is again designed as one or more weighing units, arranged in the sieved powder container 134s of the powder processing system 28s, and is used to determine the mass of sieved powder that flows from the sieved powder outlet 28s of the sieving device 10s into the sieved powder container 134s.

[0443] If possible Figure 16 As seen in the diagram, in the loose powder mass 56s on the plane, a mass angle αa is formed. The mass angle αa is affected by various factors (e.g., the shape, density, size distribution and surface properties of the powder particles), as well as by process parameters (e.g., relative humidity and temperature), and by vibration and motion acting on the block cone.

[0444] When the powder to be screened is fed onto the sieve of the screening device 10s through the powder inlet 22s 56s, blocky cones are formed on the sieve, i.e., on the screen mesh 16s. The shape and angle of the blocky cones are affected by the vibrations acting on them, and therefore by the driving power of the drive device 36s that drives the sieve. In addition, the shape and angle of the blocky cones are affected by the inclination angle of the screening surface.

[0445] When the sieve is driven with a low drive power of 36 seconds, such as Figure 17 As shown, the blocky cone formed below the powder inlet 22s on the sieve is similar to a blocky cone formed on a stationary plane, with its base occupying only a small segment a of the sieving surface. Under this operating condition of the sieving device for 10s, the utilization rate of the sieving area is correspondingly low because only the small segment a of the sieving surface adjacent to the powder inlet 22s is actually exposed to the powder for 56s. In contrast, the sieving surface segment b is relatively large and is not exposed to the powder, thus defining a "safe distance" between the powder-exposed sieving surface segment a and the oversized particle outlet 32s.

[0446] The tilting of the screening surface toward the outlet of the oversized particles by 32 seconds has the following effects: Figure 16As shown, the block cone is no longer symmetrical in shape, but rather adapted to the orientation of the screening surface and has a variable block angle. This variable block angle is smaller in the circumferential section of the block cone facing the ultra-large particle outlet 32s than in the circumferential section of the block cone away from the ultra-large particle outlet 32s. However, the tilt angle αa-w of the screening surface of the sieve relative to the horizontal plane E (see...) Figure 15 The angle αa of the block cone formed by the powder 56s to be screened on the horizontal plane is smaller than that of the powder cone, thus ensuring that a stable block cone is still formed in the region of the powder inlet 22s when the sieve is driven with low driving power, and that the powder 56s does not flow uncontrollably on the screening surface.

[0447] On the other hand, such as Figure 18 As shown, if the sieve is driven with high driving power, the powder 56s spreads out on the sieving surface. That is, the block angle αar of the block cone formed by the powder 56s supplied to the sieve surface through the powder inlet decreases as the driving power of the driving device 36s driving the sieve increases. Simultaneously, the base region of the block cone increases, increasing the section a of the sieve surface exposed to the powder 56s, and thus increasing the sieve area utilization rate, until the powder eventually flows across the entire sieve surface, thus exposing the entire sieve surface to powder. Then, the section b of the sieve surface not exposed to powder no longer exists, so that the section a of the sieve surface exposed to powder no longer has a "safe distance" from the outlet 32s of the oversized particles. The result is as follows... Figure 18 As shown, during continuous operation of the sieve at high drive power, powder 56s flowed into the oversized particle outlet 32s without being sieved. As a result, powder 56s that was actually fine enough to pass through the sieve 16s was lost without being used.

[0448] exist Figure 19 In the method for controlling the operation of the screening device 10s, shown in more detail below, firstly in step (i), the powder to be screened is supplied to the sieve 56s through the powder inlet 22s. Then, in step (ii), the sieve is driven with a first drive power for a first time interval (see [reference]). Figure 19 (Top and middle). The magnitude of the first driving power is set such that when the sieve is continuously driven with the first driving power, as... Figure 18 As shown, the powder to be screened 56s can flow across the entire screening surface of the sieve and / or flow into the oversized particle outlet. Therefore, the first drive power is so high that if such a high first drive power is maintained continuously, maximum sieve area utilization can be ensured, but there is at least a high risk that the powder 56s will be lost by passing through the oversized particle outlet 32s unscreened. Therefore, driving the sieve with the first drive power is time-limited.

[0449] Therefore, after the first time interval has elapsed, in step (iii), the sieve is driven at a second driving power lower than the first driving power for the second time interval (see...). Figure 19 (Bottom). The magnitude of the second driving power is specifically set such that when the sieve is continuously driven with the second driving power, as... Figure 17 As shown, the powder 56s to be screened forms a blocky cone in the region of the powder inlet 22s on the screening surface of the sieve. This blocky cone essentially corresponds to the blocky cone formed on the stationary plane, and the base region of this blocky cone occupies only a small segment a of the screening surface of the sieve located in the region of the powder inlet 22s. If the sieve is continuously driven with the second drive power, it can be ensured that no or almost no powder 56s flows into the oversized particle outlet without being screened. However, due to the low utilization rate of the sieve area, the sieve throughput is low, resulting in poor screening performance. Therefore, driving the sieve with the second drive power is also time-limited.

[0450] In the above scenario, the second driving power is greater than zero and less than the first driving power. In a special case, the second driving power can also be zero, so that no active sieving occurs during the second time interval. However, passive sieving can also occur in a non-driven state, where the powder trickles through the sieve due to gravity.

[0451] After the second time interval has elapsed, steps (ii) and (iii) are repeated, i.e., the sieve is periodically driven alternately with a first higher driving power and a second lower driving power. During the first time interval when the sieve is driven with the first (high) driving power, the powder particles of the powder to be sieved 56s (including the ultra-large particles 50s contained in the powder 56s) are distributed on the sieving surface (see...). Figure 19 (Top), allowing the screening process to occur even with high sieve area utilization, wherein oversized particles are transported by gravity towards the oversized particle outlet for 32 seconds and 50 seconds (see top). Figure 19 (Middle section). In contrast, the utilization rate of the sieve area was low during the second time interval. Furthermore, oversized particles "accumulated" in a columnar manner inside the blocky cone for 50 seconds. As a result, powder particles pressed into the sieve by dynamic pressure and sieve vibration for 16 seconds could form clogging particles and clog the sieve.

[0452] Because the first and second time intervals alternate periodically, and thus the sieve is periodically driven with alternating higher and lower drive powers, the advantages of both drive powers can be combined. The time constraint of the first time interval ensures good distribution of powder particles on the sieving surface and efficient removal of oversized particles towards the oversized particle outlet 32s 50s. However, section b of the sieving surface is always kept unexposed to powder, thus maintaining a "safe distance" between section A of the sieving surface exposed to powder and the oversized particle outlet 32s. Furthermore, the sieve is exposed to a lower total powder mass for 16s, and therefore experiences less stress.

[0453] For different powder types and different process parameters (e.g., temperature, powder particle size distribution, powder moisture content, etc.), the first driving power and the second driving power can have different values. Therefore, the first driving power and the second driving power are determined empirically before the sieving process; or obtained from a driving power value table for different powder types and process parameters; or selected based on empirical values. Similarly, for different powder types and different process parameters (e.g., temperature, powder particle size distribution, powder moisture content, etc.), the first time interval and the second time interval can also have different values. Therefore, the first time interval and the second time interval are values ​​determined empirically for the powder to be sieved before sieving; or values ​​obtained from a value table; or values ​​selected based on empirical values.

[0454] When the first time interval is determined, it is terminated no later than 32 seconds after the powder to be screened flows into the oversized particle outlet (56 seconds). That is, the first time interval is selected such that no powder to be screened is lost during the first time interval when the sieve is driven at the first drive power. The inflow of powder to be screened into the oversized particle outlet is detected by the oversized particle sensor for 33 seconds and 32 seconds. Specifically, the size of the first time interval is set such that at the end of the first time interval, the utilization rate of the sieve area does not exceed approximately 70% to approximately 90% of the total sieve area, preferably approximately 75% to approximately 85%, and particularly preferably approximately 80%. Therefore, the first time interval provides a "time safety reserve" so that powder does not spread across the entire screening surface during the first time interval.

[0455] When determining the second time interval, it terminates no later than when the powder to be screened (56s) forms a blocky cone of a defined size on the screening surface of the sieve located in the region of the powder inlet (22s). The formation of the blocky cone is detected by a metering sensor (23s), which is triggered when the tip of the blocky cone protrudes into the detection area of ​​the metering sensor (23s). This limitation of the second time interval prevents the blocky cone from becoming too large and clogging the powder inlet (22s) during the second time interval.

[0456] During the 10s operation of the screening equipment, the powder to be screened is continuously supplied to the sieve through the powder inlet for at least 22s for 56s. The quantitative feed mass flow rate is set by corresponding control of the quantitative feeding device for 24s and / or corresponding control of the valve for 26s via the control unit for 40s. In particular, a continuous quantitative feed mass flow rate is set. It is given by the following formula: , Among them, parameters and The screen area utilization rate and screen throughput are limited when the screen is driven with the first driving power, as well as parameters. and The utilization rate of the screen area and the throughput of the screen are limited when the screen is driven by the second driving power.

[0457] The throughput of the sieve when driven by the second driving power is determined by increasing the metered feed mass flow rate of the powder to be sieved 56s passing through the powder inlet 22s when the sieve is driven by the second driving power, until the powder to be sieved 56s has formed blocky cones of a defined size on the sieve surface located in the region of the powder inlet 22s and thus triggering the metered feed sensor 23s. On the other hand, the throughput of the sieve when the sieve is driven with the first driving power is determined by increasing the metered feed mass flow rate of the powder to be sieved 56s passing through the powder inlet 22s until the powder to be sieved 56s has formed blocky cones of a defined size on the sieve surface located in the area of ​​the powder inlet 22s, and the powder to be sieved 56s flows into the oversized particle outlet. Therefore, when the sieve is driven with the first driving power, the sieve throughput is determined. At that time, the quantitative feed mass flow rate of the powder to be screened is increased after passing through the powder inlet for 22 seconds until the quantitative feed sensor for 23 seconds and the oversized particle sensor for 33 seconds are triggered. This is achieved in this way... The value is multiplied by a safety factor, such as 0.8, 0.7, 0.6, or 0.5, to offset unintentional overfeeding of powder.

[0458] If the screen becomes clogged during the screening process (e.g., due to clogging particles or cold welding), the screen throughput decreases. Therefore, if, during the screening process (e.g., the powder to be screened (e.g., (e.g., (e.g., (e.g., (e.g., (e.g.," ...)" (e.g.)" (e.g.)" (e.g.)" (e.g., the screen becomes clogged), the screen clogging is caused by clogging particles or cold welding), the screen throughput decreases. Thus, if, during the screening process (e.g., (e.g., (e.g., (e.g., (e.g., (e.g.," (e.g.," the screen becomes clogged), the powder to be screened Reduced. However, if the mass flow rate is continuously metered... If the amount of powder to be screened has been reduced to below the limit, and the powder to be screened 56s still forms blocky cones of a defined size on the screening surface of the screen in the area of ​​the powder inlet 22s, thus triggering the quantitative feed sensor 23s, then this is interpreted by the control unit 40s as a blockage of the screen 16s and an indication to initiate screen cleaning.

[0459] When the control unit detects the need to initiate sieve cleaning in 40s, it first stops supplying powder through the powder inlet for 22s. Before sieve cleaning begins, any powder still remaining in the sieve is sieved for 56s. After sieve cleaning begins, the sieve is driven at maximum drive power. Additionally or alternatively, the vibrator 38s can be activated after sieve cleaning begins, wherein the contact angle between the vibrator 38s and the sieve, the drive amplitude of the vibrator 38s, and / or the drive frequency of the vibrator 38s are variablely adjustable. In addition to initiating sieve cleaning due to sieve clogging in 16s, or as an alternative to initiating sieve cleaning due to sieve clogging in 16s, sieve cleaning can also be initiated after each sieving process when the powder supply container 132s is empty.

[0460] In addition to or as an alternative to the continuous powder feeding method described above, the powder to be sieved 56s can also be supplied to the sieve, at least temporarily and discontinuously, through the powder inlet 22s. In the case of discontinuous powder supply, initially, with the sieve in a non-driven state, the powder to be sieved 56s is supplied to the sieve through the powder inlet 22s until the powder to be sieved 56s has formed blocky cones of a defined size on the sieve's sieving surface in the region of the powder inlet 22s, triggering the quantitative feed sensor 23s. Then, the powder supply is stopped and the sieve is driven, thereby sieving the powder 56s supplied to the sieve's sieving surface.

[0461] In addition to, or as an alternative to, the continuous or discontinuous powder feeding described above, the powder to be screened can be supplied to the sieve for at least temporarily through the powder inlet 22s for 56s at a quantitative feed mass flow rate determined based on the drive power used to drive the sieve. Specifically, the first quantitative feed mass flow rate during the first time interval when the powder to be screened is supplied to the sieve through the powder inlet 22s can be greater than the second quantitative feed mass flow rate during the second time interval when the powder to be screened is supplied to the sieve through the powder inlet 22s.

[0462] exist Figure 20 In the diagram, at the top, the drive power L is plotted as dependent on time t, and at the bottom, the metered feed mass flow rate is plotted. The data is plotted as being time-dependent. During the periodically repeating first time interval t1, the sieve is driven with a higher first drive power L1, while during the periodically repeating second time interval t2, the sieve is driven with a lower second drive power L2. Therefore, during the first time interval t1, powder is fed through the powder inlet for 22s and 56s at a higher first metering feed mass flow rate. The powder is fed onto the sieve, and during the second time interval t2, the powder is fed through the powder inlet for 22s and then for 56s at a lower second quantitative feed mass flow rate. It is supplied to the sieve. Specifically, the second quantitative feed mass flow rate... Here, the value is 0, meaning that during the second time interval t2, no powder is supplied to the sieve through the powder inlet.

[0463] Figure 20 The "sine" curve of the metering mass flow rate shown in the lower diagram is generated by the response behavior of the metering device when the movement of the metering device (e.g., a metering screw) is started or stopped. A "rectangular" curve for the metering mass flow rate can also be considered. If the first time interval and the second time interval have equal lengths (e.g., ...), ... Figure 20 As shown in the figure, the average quantitative feeding capacity is achieved. .

[0464] The screening process is terminated under the following conditions: , in It refers to the quality of the supplied powder. It refers to the mass of the ultra-large particles flowing into the ultra-large particle outlet in 32 seconds, and This refers to the mass of the sieved powder. The mass of the supplied powder is determined by the first measuring device over 42 seconds. In this process, the first measuring device detects the outflow of powder from the powder supply container for 132 seconds. The second measuring device for 44 seconds determines the mass of the powder that has passed through the large particle outlet and flowed into the large particle container for 38 seconds. The process involves two measuring devices: a second measuring device detects oversized particles flowing into the oversized particle container for 44 seconds, and a third measuring device determines the mass of the sieved powder for 46 seconds. The third measuring device detects the flow of sieved powder into the sieved powder container in 46 seconds and in 134 seconds.

[0465] The oversized particle ratio is a parameter indicating the ratio of the mass of oversized particles flowing into the oversized particle outlet for 32 seconds within a defined time unit to the mass of all powder processed within 10 seconds in the screening equipment within a defined time unit. Specifically, the oversized particle ratio... It can be calculated using the following formula: , in It is the mass flow rate of the sieved powder that passes through the sieving equipment for 10 seconds, exits for 28 seconds, and flows into the sieved powder container for 134 seconds during the sieving process. It is the mass flow rate of ultra-large particles that pass through the screening equipment for 10 seconds, exit for 32 seconds, and flow into the ultra-large particle container for 136 seconds during the screening process.

[0466] In the process of processing raw material powder (which is intended to be processed in apparatus 100s for producing three-dimensional workpieces using a layer-building process) using the screening device 10s described herein, an excessively high oversized particle ratio can be an indicator of unfavorable process parameters of apparatus 100s. For example, an excessively high oversized particle ratio can indicate the generation of large welding spatter when the powder is irradiated by the irradiation device 112s, which remains in the powder bed and can therefore impair the quality of the workpiece 108s to be produced. Therefore, during the screening process, parameters are continuously monitored by a second measuring device 44s and a third measuring device 46s. and The control unit continuously determines the ultra-large particle ratio based on these values ​​over 40 seconds. Furthermore, under the control of the control unit 40s, if the oversized particle rate exceeds the limit value, a warning signal is output, allowing the process parameters of the device to be checked for 100s (if necessary).

[0467] In addition, the mass flow rate of the sieved powder is monitored during the sieving process. and ultra-large particle mass flow rate The sum of the mass flow rates of the quantitative feed The step response, wherein the mass flow rate of the quantitative feed is continuously detected by the first measuring device for 42 seconds. The mass flow rate of ultra-large particles was continuously detected for 44 seconds using a second measuring device. The mass flow rate of the sieved powder was continuously detected for 46 seconds using a third measuring device. .exist Figure 21 The diagram shown represents the mass flow rate of the sieved powder. and ultra-large particle mass flow rate The sum of these factors changes with time t, represented by a point-like curve, while the quantitative feed mass flow rate... The change over time t is represented by the dashed curve.

[0468] Mass flow rate of sieved powder and ultra-large particle mass flow rate The sum of the mass flow rates of the quantitative feed The "step response" is the response to a defined quantitative feed mass flow rate. The time point t1 when the powder is supplied to the screening equipment for 10 seconds and the mass flow rate of the screened powder and ultra-large particle mass flow rate The sum of these parameters corresponds to the time difference Δt between the time point t2 when the powder has passed through the sieve for 16 seconds. Therefore, the step response is a time parameter indicating the duration of the sieving process at a given powder mass flow rate.

[0469] If the step response is from Figure 21 The value Δt1 shown in the upper part of the diagram is shortened to Figure 21 The value Δt2 shown in the lower part of the diagram, i.e., the curves in the diagram moving closer together, can be interpreted as an indication of a defect (e.g., tearing in the sieve 16s) if the step response is below the first limit value. Therefore, if the mass flow rate of the sieved powder is... and ultra-large particle mass flow rate The sum of the mass flow rates of the quantitative feed If the step response is lower than the first limit value, the control unit will output a warning signal after 40 seconds.

[0470] On the other hand, if the step response is prolonged, this indicates that the sieving process has been prolonged, and can be interpreted as an indication that the screen has become clogged after 16 seconds. Therefore, under the control of the control unit 40 seconds, if the mass flow rate of the sieved powder is... and ultra-large particle mass flow rate The sum of the mass flow rates of the quantitative feed If the step response exceeds the second limit value, then sieve cleaning is initiated.

[0471] Figure 22 A schematic side view of the screening device 10s is shown. Figure 22 Can be regarded as Figure 14 Alternative embodiments or further developments of the screening equipment 10s. The screening equipment 10s can be used in conjunction with all embodiments of the screening equipment 10s described above, the powder handling system 128s, and / or the apparatus 100s for producing three-dimensional workpieces. Components and / or functions of the screening equipment 10s not described below correspond to the components and / or functions of the screening equipment 10s described above, particularly... Figure 15 The screening equipment consists of 10s components and / or functions. Therefore, Figure 22 Some components of the screening equipment 10s are not shown or are only schematically indicated, as these components correspond to those already explained in detail above. Figure 15 The screening equipment has 10s components.

[0472] exist Figure 22 In the upper part (a), the screening device 10s is shown in a state where the sieve (composed of sieve frame 14s and sieve mesh 16s) has not yet been installed in the housing 60s of the screening device 10s. Figure 22The lower part (b) shows the screening equipment equipped with sieves 14s and 16s.

[0473] Figure 22 The screening device 10s includes a housing 60s, which is similar to a cover 20s and is suitable for airtightly sealing the screening device 10s. This allows the screening process to be performed in a closed, inert gas atmosphere. A powder inlet 22s is located on the upper side of the housing 60s. An oversized particle outlet 32s and a sieve container 18 for indication are provided on the lower side of the housing. The aforementioned elements 22, 32, and 18 are attached to the housing 60s and are therefore fixed regardless of any change in the tilt angle αa-w (see below).

[0474] The sieve, consisting of a sieve frame 14s and a sieve mesh 16s, can be inserted into the housing from the side via a baffle 62s. The baffle 62s can be closed, and when closed, it airtightly seals the housing 60s. Furthermore, a sieve retainer 66s is provided, into which the sieves 14s and 16s can be inserted and secured if necessary. This allows for easy removal and reinsertion of the sieves 14s and 16s, or easy replacement of the sieves 14s and 16s (if required).

[0475] The tilt angle αa-w of the sieves 14s and 16s (more precisely, the screen 16s) relative to the horizontal plane E is adjustable. For this purpose, a tilting device 64s is provided, which is configured to change the tilt angle αa-w. The tilting device may include a motor, particularly a servo motor. Figure 22 In the example shown, the tilting device 64s is attached to the sieve retainer 66s and is configured to tilt the sieve retainer 66s relative to the housing 60s. More specifically, according to the example shown, the tilting device is arranged at the center of the sieves 14s and 16s and is configured to rotate the sieves 14s and 16s along a horizontally extending axis of rotation.

[0476] Specifically, the tilting device 64s can be controlled by the control unit 40s, allowing any tilt angle αa-w within a predetermined angle range (e.g., 0° to 45°) to be set. According to some embodiments, the tilt angle αa-w can be changed so rapidly that a first tilt angle is set in a first time interval and a second tilt angle is set in a second time interval. In other words, the angle change can occur in a shorter interval than the shorter of the first and second time intervals, specifically at most half, at most 1 / 4, at most 1 / 8, at most 1 / 10, at most 1 / 50, or at most 1 / 100 of the shorter of the first and second time intervals.

[0477] However, the tilt angle αa-w can also change continuously during the first time interval and / or the second time interval.

[0478] Therefore, control over sieving performance (i.e., different sieving performance in the first and second time intervals) can be supported by different tilt angles αa-w in the corresponding time intervals. Specifically, a larger tilt angle can be set for the first time interval compared to the second time interval. Conversely, a smaller tilt angle can be set for the first time interval compared to the second time interval. Both options are advantageous depending on the situation and purpose. A smaller tilt angle αa-w results in less discharge of oversized particles, and powder may accumulate on the sieve 16s. A larger tilt angle αa-w results in better removal of oversized particles, but also means that "good" powder may pass through the sieve 16s and may end up in the oversized particle outlet 32s.

[0479] In some embodiments, the tilt angle can be adjusted according to the powder used. For example, this can initially be done before the sieving process begins, so that the tilt angle remains constant during the sieving process. For example, a higher tilt angle can be set for heavier materials compared to lighter materials. A higher tilt angle can also be set for powder materials with non-circular and / or splattered powder particles and therefore lower flowability compared to powder materials with rounded powder particles and therefore higher flowability. In this way, the tilt angle can be optimized relative to the flowability properties of the material used.

[0480] In addition, a sensor (not shown) may be provided, configured to detect the spreading speed of the powder to be sieved on the sieve and / or the position of the powder front on the sieve. For this purpose, the sensor may include, for example, a camera, an inductive sensor, and / or a light barrier. For example, the sensor may be attached to the inside of the housing 60s, particularly to the upper wall of the housing 60s.

[0481] The control unit can be configured such that the tilt angle αa-w of the sieving surface of the sieve relative to the horizontal plane changes according to the detected spreading speed and / or the detected position. Specifically, when the detected spreading speed of the powder to be sieved and / or the detected position of the powder leading edge exceeds a predetermined threshold, the tilt angle αa-w can be changed to decrease. Similarly, when the detected spreading speed of the powder to be sieved and / or the detected position of the powder leading edge is below a predetermined threshold, the tilt angle αa-w can be changed to increase.

[0482] This enables automatic control of the tilt angle, thus avoiding time-consuming testing to determine the optimal tilt angle depending on the powder.

[0483] It can be used independently and / or with the powder delivery system described above (e.g., see [link]). Figure 1 The combined applications are as follows: 1. A method for controlling the operation of a screening device (10s), comprising the following steps: (i) The powder to be sieved (56s) is fed onto the sieve through the powder inlet (22s); (ii) The sieve is driven with a first driving power for a first time interval, wherein the magnitude of the first driving power is set such that when the sieve is driven continuously with the first driving power, the powder to be sieved (56s) flows across the entire sieving surface of the sieve and / or flows into the oversized particle outlet (32s). (iii) After the first time interval has elapsed, the sieve is driven at a second driving power lower than the first driving power for a second time interval; and (iv) After the second time interval has elapsed, repeat steps (ii) and (iii).

[0484] 2. The method for controlling a sieving device (10s) according to aspect 1, wherein the magnitude of the second driving power is set such that when the sieve is continuously driven with the second driving power, the powder to be sieved (56s) forms a block cone in the region of the powder inlet (22s) on the sieving surface of the sieve, the block cone substantially corresponding to a block cone formed on a stationary plane, wherein the block angle (αa) of the block cone is particularly adapted to the orientation of the sieving surface.

[0485] 3. The method for controlling the operation of a screening device (10s) according to aspect 1 or 2, wherein the screening surface of the sieve is inclined relative to the horizontal plane (E) such that the flow of powder supplied through the powder inlet (22s) along the direction of the oversized particle outlet (32s) is supported by gravity, wherein, preferably, the angle of inclination (αa-w) of the screening surface of the sieve relative to the horizontal plane (E) is smaller than the block angle (αa) of the block cone formed by the powder to be screened (56s) on the horizontal plane (E).

[0486] 4. A method for controlling the operation of a screening device (10ss) according to any one of aspects 1 to 3, wherein: - The first time interval is a value determined empirically for the powder to be sieved (56); and / or - When the first time interval is determined, the first time interval is terminated no later than when the powder to be screened (56s) flows into the oversized particle outlet (32s), wherein, in particular, the inflow of the powder to be screened (56s) into the oversized particle outlet (32s) is detected by an oversized particle sensor (33s) located in the area of ​​the oversized particle outlet; and / or - The size of the first time interval is set such that at the end of the first time interval, the utilization rate of the sieve area does not exceed about 70% to about 90% of the total sieve area, preferably about 75% to about 85%, particularly preferably about 80%; and / or - The second time interval is a value determined empirically for the powder to be sieved (56s); and / or - When the second time interval is determined, the second time interval is terminated no later than when the powder to be screened (56s) forms a blocky cone of a defined size on the screening surface of the sieve located in the area of ​​the powder inlet (22s), wherein the formation of the blocky cone of the defined size is detected in particular by a metering feed sensor (23s) set in the area of ​​the powder inlet (22s).

[0487] 5. A method for controlling the operation of a screening device (10s) according to any one of aspects 1 to 4, wherein the powder to be screened (56s) is supplied to the screen at least temporarily and continuously through the powder inlet (22s) at the following quantitative feed mass flow rate: , in, and This refers to the utilization rate of the screen area and the screen throughput when the screen is driven by the second driving power, and among them, and The utilization rate of the screen area and the throughput of the screen when the screen is driven by the first driving power.

[0488] 6. The method for controlling the operation of the screening equipment (10s) according to aspect 5, wherein: - When the sieve is driven with the second drive power, the quantitative feed mass flow rate of the powder to be sieved (56s) passing through the powder inlet (22s) is increased until the powder to be sieved (56s) has formed blocky cones of a defined size on the sieve surface located in the area of ​​the powder inlet (22s), thus determining the optimal feed rate. ; and / or - When the sieve is driven with the first driving power, the quantitative feed mass flow rate of the powder to be sieved (56s) passing through the powder inlet (22s) is increased until the powder to be sieved (56s) has formed blocky cones of a defined size on the sieve surface located in the area of ​​the powder inlet (22s) and the powder to be sieved (56s) flows into the oversized particle outlet (32s) to determine Preferably, the result obtained therefrom The value is multiplied by a safety factor of 0.8, 0.7, 0.6, or 0.5.

[0489] 7. The method for controlling the operation of the screening equipment (10s) according to aspect 5 or 6, wherein: - When the powder to be screened (56s) forms blocky cones of a defined size on the screening surface of the sieve located in the area of ​​the powder inlet (22s), reduce the metered feed mass flow rate ( ); and / or - When the powder to be screened (56s) forms blocky cones of a defined size on the screening surface of the sieve located in the area of ​​the powder inlet (22s) and / or when the metered feed mass flow rate When the value is below the limit, start the sieve cleaning process.

[0490] 8. The method for controlling the operation of the screening equipment (10s) according to aspect 7, wherein, when initiating screen cleaning: - Stop supplying powder through the powder inlet (22s); and / or - Before sieve cleaning begins, sieve any powder remaining in the sieve; and / or - Drive the sieve at maximum drive power after sieve cleaning begins; and / or - After the sieve cleaning begins, the vibrator (38s) is activated. The vibrator drives the sieve independently of the drive device (36s) of the screening device (10s). Preferably, the contact angle between the vibrator (38s) and the sieve, the drive amplitude of the vibrator (38s) and / or the drive frequency of the vibrator (38s) are variablely adjustable.

[0491] 9. A method for controlling the operation of a screening device (10s) according to any one of aspects 1 to 8, wherein the powder to be screened (56s) is supplied to the screen at least temporarily and discontinuously through the powder inlet (22s), wherein, in particular, - Initially, in the non-driven state of the sieve, the powder to be sieved (56s) is supplied to the sieve through the powder inlet (22s) until the powder to be sieved (56s) has formed blocky cones of a defined size on the sieve surface located in the area of ​​the powder inlet (22s); - After the powder supply is terminated, the sieve is activated to sieve the powder supplied to the sieve's screening surface; and - The screening process will be terminated under the following conditions: , in It refers to the quality of the supplied powder. It is the mass of the powder flowing into the ultra-large particle outlet (32s), and It is the mass of the sieved powder, and in particular, it is determined by the first measuring device (42s). The first measuring device is set in the powder supply container (132s), which can be connected to the powder inlet (22s) of the sieving device (10s); in particular, the second measuring device (44) determines The second measuring device is set in an ultra-large particle container (136s), which can be connected to the ultra-large particle outlet (32s) of a screening device (10s); and / or, particularly by a third measuring device (46), to determine The third measuring device is set in the sieved powder container (134), which can be connected to the sieved powder outlet (28) of the sieving device (10s).

[0492] 10. A method for controlling the operation of a screening device (10s) according to any one of aspects 1 to 9, wherein the powder to be screened (56s) is supplied to the screen at least temporarily through the powder inlet (22s) at a quantitative feed mass flow rate determined according to the drive power used to drive the screen, wherein, in particular, the first quantitative feed mass flow rate when the powder to be screened (56s) is supplied to the screen through the powder inlet (22s) during a first time interval is greater than the second quantitative feed mass flow rate when the powder to be screened (56s) is supplied to the screen through the powder inlet (22s) during a second time interval.

[0493] 11. A method for controlling the operation of a screening device (10s) according to any one of aspects 1 to 10, wherein a warning signal is output when the particle size distribution of oversized particles exceeds a threshold, wherein the oversized particle size distribution is measured continuously.

[0494] 12. A method for controlling the operation of a screening device (10s) according to any one of aspects 1 to 11, wherein: - The screening equipment (10s) is sealed relative to the ambient atmosphere and filled with a protective gas during operation; and / or - When the inert gas pressure in the screening device (10s) is below the threshold, additional protective gas is supplied to the screening device (10s).

[0495] 13. A method for controlling the operation of a screening device (10s) according to any one of aspects 1 to 12, wherein: - During the sieving process, monitor the mass flow rate of the sieved powder ( ) and ultra-large particle mass flow rate ( The sum of the quantities of feed mass flow rate ( The step response of ) and / or - When the mass flow rate of the sieved powder is ( ) and ultra-large particle mass flow rate ( The sum of the quantities of feed mass flow rate ( When the step response of a device is lower than the first limit value, a warning signal is output; and / or - When the mass flow rate of the sieved powder is ( ) and ultra-large particle mass flow rate ( The sum of the quantities of feed mass flow rate ( When the step response of the sieve exceeds the second limit value, the sieve cleaning is initiated.

[0496] 14. The method for controlling the operation of a screening device (10s) according to any one of aspects 1 to 13, further comprising: - Change the tilt angle (αa-w) of the sieve's screening surface relative to the horizontal plane (E).

[0497] 15. The method for controlling the operation of a screening device (10s) according to aspect 14, wherein the screen is arranged in a housing (60s) that is sealed in an airtight manner, and wherein the screen rotates relative to the housing (60s) to change the tilt angle (αa-w).

[0498] 16. The method for controlling the operation of a screening device (10s) according to aspect 14 or 15, wherein a first tilt angle (αa-w) is set during a first time interval and a second tilt angle (αa-w) is set during a second time interval, and wherein (a) the first tilt angle is less than the second tilt angle, or (b) the first tilt angle is greater than the second tilt angle.

[0499] 17. The method for controlling the operation of a screening device (10s) according to aspect 14 or 15, wherein the tilt angle is changed during a first time interval and / or a second time interval.

[0500] 18. The method for controlling the operation of a screening device (10s) according to any one of aspects 14 to 17, further comprising: - Detect the spreading speed of the powder to be sieved (56s) on the sieve and / or the position of the powder leading edge of the powder to be sieved (56s) on the sieve. The tilt angle (αa-w) of the sieve's sieving surface relative to the horizontal plane (E) is changed based on the detected spreading speed and / or the detected position.

[0501] 19. The method for controlling the operation of a sieving device (10s) according to aspect 18, wherein when the spread rate of the detected powder to be sieved (56s) and / or the position of the detected powder leading edge exceeds a predetermined threshold, a change in tilt angle (αa-w) is performed, such that the tilt angle (αa-w) decreases.

[0502] 20. A screening device (10s), comprising: - Powder inlet (22s); - Drive device (36), the drive device is configured to drive the sieve; and - Control unit (40), configured to control powder inlet (22s) and drive device (36), such that: (i) The powder to be sieved (56s) is fed onto the sieve through the powder inlet (22s); (ii) The sieve is driven with a first driving power for a first time interval, wherein the magnitude of the first driving power is set such that when the sieve is driven continuously with the first driving power, the powder to be sieved (56s) flows across the entire sieving surface of the sieve and / or flows into the oversized particle outlet (32s). (iii) After the first time interval has elapsed, the sieve is driven at a second driving power lower than the first driving power for a second time interval; and (iv) After the second time interval has elapsed, repeat steps (ii) and (iii).

[0503] 21. The screening device (10s) according to aspect 20, wherein: - The magnitude of the second driving power is set such that when the sieve is continuously driven with the second driving power, the powder to be sieved (56s) forms blocky cones in the region of the powder inlet (22s) on the sieve surface, which substantially correspond to blocky cones formed on a stationary plane, wherein the block angle (αa) of the blocky cones is particularly adapted to the orientation of the sieve surface; and / or - The sieving surface of the sieve is inclined relative to the horizontal plane (E), such that the flow of powder supplied through the powder inlet (22s) along the direction of the oversized particle outlet (32s) is supported by gravity, wherein, preferably, the inclination angle (αa-w) of the sieve surface relative to the horizontal plane (E) is smaller than the block angle (αa) of the block cone formed by the powder to be sieved (56s) on the horizontal plane (E); and / or - The first time interval is a value determined empirically for the powder to be sieved (56); and / or - The control unit (40) is configured to terminate the first time interval at the latest when the powder to be screened (56s) flows into the oversized particle outlet (32s) upon determination of the first time interval, wherein the screening device (10s) specifically includes an oversized particle sensor located in the region of the oversized particle outlet for detecting the flow of the powder to be screened (56s) into the oversized particle outlet (32s); and / or - The control unit (40s) is configured to set the size of the first time interval such that at the end of the first time interval, the utilization rate of the sieve area does not exceed about 70% to about 90% of the total sieve area, preferably about 75% to about 85%, particularly preferably about 80%; and / or - The second time interval is a value determined empirically for the powder to be sieved (56s); and / or - The control unit (40) is configured to terminate the second time interval at the latest when the powder to be screened (56s) forms a blocky cone of a defined size on the screening surface of the sieve located in the area of ​​the powder inlet (22s) when the second time interval is determined, wherein the screening device (10s) includes, in particular, a quantitative feed sensor (23s) disposed in the area of ​​the powder inlet (22s) for detecting the formation of the blocky cone of a defined size.

[0504] 22. The screening device (10s) according to aspect 20 or 21, wherein the control unit (40s) is configured to control the powder inlet (22s) such that the powder to be screened (56s) is supplied to the screen at least temporarily and continuously through the powder inlet (22s) at the following quantitative feed mass flow rate: , in, and This refers to the utilization rate of the screen area and the screen throughput when the screen is driven by the second driving power, and among them, and The screen area utilization and screen throughput are measured by the first drive power when the screen is driven, wherein the control unit (40s) is specifically configured to: - When the sieve is driven with the second drive power, the quantitative feed mass flow rate of the powder to be sieved (56s) passing through the powder inlet (22s) is increased until the powder to be sieved (56s) has formed blocky cones of a defined size on the sieve surface located in the area of ​​the powder inlet (22s), thus determining the optimal feed rate. ; and / or - When the sieve is driven with the first driving power, the quantitative feed mass flow rate of the powder to be sieved (56s) passing through the powder inlet (22s) is increased until the powder to be sieved (56s) has formed blocky cones of a defined size on the sieve surface located in the area of ​​the powder inlet (22s) and the powder to be sieved (56s) flows into the oversized particle outlet (22s) to determine Preferably, the result obtained therefrom The value is multiplied by a safety factor of 0.8, 0.7, 0.6, or 0.5; and / or - When the powder to be screened (56s) forms blocky cones of a defined size on the screening surface of the sieve located in the area of ​​the powder inlet (22s), reduce the metered feed mass flow rate ( ); and / or - When the powder to be screened (56s) forms blocky cones of a defined size on the screening surface of the sieve located in the area of ​​the powder inlet (22s) and / or when the metered feed mass flow rate When the value falls below the limit, the sieve cleaning process is initiated.

[0505] 23. The screening device (10s) according to aspect 22, wherein the control unit (40s) is configured to: - Control the powder inlet (22s) to stop supplying powder through the powder inlet (22s); and / or - Control the drive device (36s) to sieve the powder still remaining in the sieve before sieve cleaning begins; and / or - Control the drive device (36s) to drive the sieve at maximum drive power after sieve cleaning begins; and / or - After the sieve cleaning begins, the vibrator (38s) is activated. The vibrator is configured to drive the sieve independently of the sieving device (10s). Preferably, the contact angle between the vibrator (38s) and the sieve, the driving amplitude of the vibrator (38s), and / or the driving frequency of the vibrator (38s) are variablely adjustable.

[0506] 24. The screening device (10s) according to any one of aspects 20 to 23, wherein the control unit (40s) is configured to control the powder inlet (22s) such that the powder to be screened (56s) is supplied to the sieve through the powder inlet (22s) at least temporarily and discontinuously, wherein the control unit (40s) is specifically configured to control the drive device (36s) and the powder inlet (22s) such that: - Initially, in the non-driven state of the sieve, the powder to be sieved (56s) is supplied to the sieve through the powder inlet (22s) until the powder to be sieved (56s) has formed blocky cones of a defined size on the sieve surface located in the area of ​​the powder inlet (22s); - After the powder supply is terminated, the sieve is activated to sieve the powder supplied to the sieve's screening surface; and - The screening process will be terminated under the following conditions: , in It refers to the quality of the supplied powder. It is the mass of the powder flowing into the ultra-large particle outlet (22s), and It refers to the mass of the sieved powder, and the sieving equipment (10s) specifically includes: for determining... The first measuring device (42s) is disposed in a powder supply container (132s), which can be connected to the powder inlet (22s) of a sieving device (10s); used to determine A second measuring device (44), the second measuring device being disposed in an ultra-large particle container (136s), the ultra-large particle container being connectable to the ultra-large particle outlet (32s) of a screening device (10s); and / or and / or used to determine The third measuring device (46) is set in the sieved powder container (134), which can be connected to the sieved powder outlet (28s) of the sieving device (10s).

[0507] 25. The screening device (10s) according to any one of aspects 20 to 24, wherein the control unit (40s) is configured to control the powder inlet (22s) such that the powder to be screened (56s) is supplied to the screen at least temporarily through the powder inlet (22s) at a quantitative feed mass flow rate determined according to the drive power used to drive the screen, wherein, in particular, the first quantitative feed mass flow rate when the powder to be screened (56s) is supplied to the screen through the powder inlet (22s) during a first time interval is greater than the second quantitative feed mass flow rate when the powder to be screened (56s) is supplied to the screen through the powder inlet (22s) during a second time interval.

[0508] 26. The screening device (10s) according to any one of aspects 20 to 25, wherein the control unit (40s) is configured to output a warning signal when, in particular, the continuously measured oversized particle rate exceeds a limit value.

[0509] 27. The screening device (10s) according to any one of aspects 20 to 26, wherein: - The screening equipment (40s) is sealed relative to the ambient atmosphere and filled with a protective gas during operation; and / or - The control unit (40s) is configured to supply additional protective gas to the screening equipment (10s) when the inert gas pressure in the screening equipment (10s) is below a threshold.

[0510] 28. The screening device (10s) according to any one of aspects 20 to 27, wherein the control unit (40s) is configured to: - During the sieving process, monitor the mass flow rate of the sieved powder ( ) and ultra-large particle mass flow rate ( The sum of the quantities of feed mass flow rate ( The step response of ) and / or - When the mass flow rate of the sieved powder is ( ) and ultra-large particle mass flow rate ( The sum of the quantities of feed mass flow rate ( When the step response of a device is lower than the first limit value, a warning signal is output; and / or - When the mass flow rate of the sieved powder is ( ) and ultra-large particle mass flow rate ( The sum of the quantities of feed mass flow rate ( When the step response of the sieve exceeds the second limit value, the sieve cleaning is initiated.

[0511] 29. The screening apparatus (10s) according to any one of aspects 20 to 28, comprising: - Lid (20s), the lid can be removed from the sieve container (18s); - Seal (48s), the seal is set in the cap (20s); and - Clamping device (50s) is configured to apply a clamping force to the seal (48s) to hold the seal (48s) in its position within the cover (20s).

[0512] 30. The screening apparatus (10s) according to any one of aspects 20 to 29, comprising: - Inclining device (64s), the inclination device is used to change the inclination angle (αa-w) of the screening surface of the sieve relative to the horizontal plane (E).

[0513] 31. The screening device (10s) according to aspect 30, comprising: - Housing (60s), the housing can be closed in a hermetically sealed manner. The sieve is arranged inside the housing (60s), and the tilting device (64s) is configured to rotate the sieve relative to the housing (60s), thereby changing the tilt angle (αa-w).

[0514] 32. The screening device according to aspect 30 or 31, wherein the powder inlet (22s) and the oversized particle outlet (32s) are fixedly attached to the housing (60s).

[0515] 33. The screening apparatus according to any one of aspects 30 to 32, comprising: - Screen retainer (66s), the screen retainer is used to hold the screen, especially for inserting the screen, wherein an inclined device (64s) is attached to the screen retainer (66s) and is configured to rotate the screen retainer (66s).

[0516] 34. The screening device (10s) according to any one of aspects 30 to 33, wherein the control unit (40s) is configured to set a first tilt angle (αa-w) during a first time interval and a second tilt angle (αa-w) during a second time interval, and wherein (a) the first tilt angle is less than the second tilt angle, or (b) the first tilt angle is greater than the second tilt angle.

[0517] 35. The screening device (10s) according to any one of aspects 30 to 33, wherein the control unit (40s) is configured to change the tilt angle during a first time interval and / or a second time interval.

[0518] 36. The screening apparatus (10s) according to any one of aspects 30 to 35 further includes: - At least one sensor, the at least one sensor being used to detect the spreading speed of the powder to be sieved (56s) on the sieve and / or the position of the powder leading edge of the powder to be sieved (56s) on the sieve, The control unit (40s) is configured to change the tilt angle (αa-w) of the sieve's sieving surface relative to the horizontal plane (E) based on the detected spreading speed and / or the detected position.

[0519] 37. The screening device (10s) according to aspect 36, wherein the control unit (40s) is configured to: when the spread rate of the detected powder to be screened (56s) and / or the position of the detected powder leading edge exceeds a predetermined threshold, perform a change in tilt angle (αa-w) such that the tilt angle (αa-w) decreases.

[0520] 38. A powder processing system (128s) comprising a sieving device (10s) according to any one of aspects 30 to 37.

[0521] 39. An apparatus (100s) for producing a three-dimensional workpiece by irradiating a layer of raw material powder with electromagnetic radiation or particle radiation, comprising a screening device (10s) according to any one of aspects 30 to 37 and / or a powder processing system (128s) according to aspect 38.

Claims

1. A powder delivery system for delivering a feedstock powder to a device for producing a three-dimensional workpiece by irradiating a layer of feedstock powder with electromagnetic or particle radiation, wherein, The powder conveying system comprises: a conveying line configured to convey a gas stream at least in sections and to convey a powder stream driven by the gas stream at least in sections; a conveying device configured to convey the gas stream through the conveying line; a first tank connected to the conveying line for supplying the device with powder for an additive manufacturing process; at least one overflow container connected to the conveying line for receiving excess powder of the additive manufacturing process; a buffer container connected to the conveying line for supplying a sieving device with powder to be sieved; a sieving device for sieving the powder to be sieved and for dispensing sieved powder; an interface connected to a conveying line for an external tank for introducing fresh or contaminated powder into the powder conveying system; and a control device for controlling the powder conveying system such that the powder conveying system performs at least one of the following conveying processes: a conveying the sieved powder into the first tank; b conveying powder from the at least one overflow container into the buffer container; and c conveying powder from the external tank into the buffer container.

2. The powder delivery system of claim 1, wherein, (a) all of the conveying processes a to c comprise a pneumatic conveying process in which the conveyed powder is conveyed by the gas stream, or (b) at least one of the conveying processes a to c does not comprise a pneumatic conveying process, in particular conveying process b does not comprise a pneumatic conveying process.

3. The powder delivery system of claim 2, wherein, In case (b), the conveying process which does not comprise a pneumatic conveying process comprises conveying by a screw conveyor and / or conveying by gravity.

4. The powder delivery system of any one of claims 1 to 3, further comprising: a main reservoir connected to the conveying line for receiving the sieved powder, wherein the conveying process a conveys the sieved powder from the main reservoir into the first tank.

5. The powder delivery system of any one of claims 1 to 4, wherein, The powder conveying system enables closed powder conveying, in particular powder conveying in which the conveyed powder does not leave the powder conveying system during a plurality of consecutive additive manufacturing processes of the device.

6. The powder delivery system of any one of claims 1 to 5, wherein, The powder conveying system is configured to maintain an inert gas atmosphere within the conveying line, in particular during one of the conveying processes a to c.

7. The powder delivery system of any one of claims 1 to 6 in combination with claim 4, further comprising: a pressure equalization tank coupled to the conveying line, in particular downstream of the conveying device and upstream of the connections of the first tank, the at least one overflow tank, the buffer tank, the main reservoir and the external tank.

8. The powder delivery system of any one of claims 1 to 7 in combination with claim 4, further comprising: at least one dosing device, in particular comprising a conveyor screw, for dosing the powder to be conveyed from the at least one overflow container, from the main reservoir and / or from the external tank into the conveying line.

9. The powder delivery system of any one of claims 1 to 8, further comprising: at least one separation device, in particular comprising a cyclone, for separating the conveyed powder from the conveying line and for feeding the powder into the first tank and / or the buffer vessel.

10. The powder delivery system of any one of claims 1 to 9 in combination with claim 4, wherein, at least one of the following vessels is coupled to a pressure equalization line: the first tank, the at least one overflow vessel, the buffer vessel, the main reservoir and the external tank.

11. The powder delivery system of any one of claims 1 to 10, wherein, The control device is configured to perform a flow test, the flow test comprising testing a flow through the conveying line.

12. The powder delivery system of claim 11, further comprising: a speed sensor for measuring a speed of the gas stream in the conveying line, wherein the flow test comprises: opening a valve of the powder conveying system so that a flow through at least one conveying circuit associated with one of the conveying processes a, b and c is possible; setting a conveying speed of the gas stream to a value or a predetermined value range; and determining whether the speed value of the gas stream measured by the speed sensor is greater than a predetermined threshold value.

13. The powder delivery system of claim 12, wherein, Setting the conveying speed comprises: determining whether the speed value measured by the speed sensor lies within the predetermined value range; if this is not the case, determining whether the speed value is below the predetermined value range; if the speed value is below the predetermined value range, increasing a power of the conveying device; and if the speed value is not below the predetermined value range, decreasing the power of the conveying device.

14. The powder conveying system according to any one of claims 11 to 13, further comprising: a pressure sensor for measuring a pressure of the gas stream; and a filter for filtering remaining powder particles from the gas stream, wherein the flow test comprises: determining a total pressure loss based on sensor data from the pressure sensor; if it is determined that the total pressure loss exceeds a predetermined limit value, performing a filter cleaning of the filter and determining the total pressure loss again; and if it is determined that the total pressure loss does not exceed the predetermined limit value, conveying powder in at least one of the conveying processes a, b and c.

15. The powder delivery system of claim 14, wherein, The flow test performed by the control device further comprises: if it is determined that the total pressure loss exceeds the predetermined limit value, outputting an error before performing the filter cleaning.

16. The powder delivery system of any one of claims 1 to 15, comprising: at least one oxygen sensor for measuring an oxygen content of the gas stream, wherein the control device is configured to perform an oxygen content test, and wherein the oxygen content test comprises: measuring an oxygen content using the at least one oxygen sensor.

17. The powder delivery system of claim 16, wherein, The control device is configured to perform a pipe inerting of the conveying line if the measurement of the oxygen content of the gas stream shows that the oxygen content is above a predetermined limit value.

18. The powder delivery system of claim 17, further comprising: a safety valve for releasing gas from the conveying line into the environment or an external volume, wherein the pipe inerting comprises: opening the safety valve.

19. The powder delivery system of claim 18, wherein, The pipe inerting further comprises: evacuating at least a part of the conveying line; performing a leak test on the conveying line; normalizing the conveying line; and testing the oxygen content in the conveying line.

20. The powder delivery system of claim 19, wherein, The evacuation comprises testing whether a measured pressure in the conveying line is below a predetermined evacuation pressure.

21. The powder delivery system of claim 20, further comprising: a speed meter for measuring a speed of the gas flow in the conveying line, wherein the evacuation comprises: determining whether a speed value measured by the speed sensor lies within a predetermined value range; if this is not the case, determining whether the speed value is below the predetermined value range; if the speed value is below the predetermined value range, increasing the power of the conveying device; and if the speed value is not below the predetermined value range, decreasing the power of the conveying device.

22. The powder delivery system of any one of claims 19-21, wherein, The leak test comprises: closing the safety valve; stopping the conveying device; determining whether each system pressure increase exceeds a predetermined limit value; if each system pressure increase exceeds the predetermined limit value, outputting an error message; and if each system pressure increase does not exceed the predetermined limit value, continuing to normalize the conveying line.

23. The powder delivery system of claim 22, comprising: a first pressure sensor located at an inlet side of the conveying device and a second pressure sensor located at an outlet side of the conveying device, wherein determining the system pressure increase comprises taking the sum of a measured value of the first pressure sensor and a measured value of the second pressure sensor.

24. The powder delivery system of any one of claims 19-23, wherein, normalizing the conveying line comprises: filling the conveying line with an inert gas; and measuring an oxygen content in the conveying line.

25. The powder conveying system according to claim 24, further comprising: if the oxygen content measured in the conveying line exceeds a predetermined limit value, restarting the pipe inerting.

26. The powder delivery system of any one of claims 19 to 25, wherein, testing the oxygen content in the conveying line comprises: if the measured oxygen content exceeds a predetermined limit for a predetermined number of times, restarting the pipe inerting.

27. The powder delivery system of any one of claims 1 to 26, wherein, the control unit is configured to perform a conveying in accordance with at least one of the conveying processes a, b and c, wherein the conveying comprises opening at least one valve arranged in a conveying circuit assigned to the respective conveying process.

28. The powder delivery system of claim 27, wherein, the control unit is configured to perform a conveying control during the conveying, the conveying control comprising: monitoring an oxygen content in the conveying line; monitoring a pressure in the conveying line; monitoring a conveying speed of the gas flow; monitoring at least one measured parameter of the powder conveying system; and testing a termination condition for terminating the conveying.

29. The powder delivery system of claim 28, wherein, monitoring the oxygen content in the conveying line comprises: determining whether the measured oxygen content exceeds a predetermined limit value; and if the measured oxygen content exceeds the predetermined limit value, opening a valve to supply an inert gas into the conveying line.

30. The powder delivery system of claim 28 or 29, wherein, monitoring the pressure in the conveying line comprises: determining whether a measured pressure in the conveying line lies within a predetermined range; if the measured pressure in the conveying line is below the predetermined range, opening a valve to supply an inert gas; and if the measured pressure in the conveying line is above the predetermined range, opening a safety valve to release gas from the conveying line.

31. The powder delivery system of any one of claims 28-30, wherein, monitoring the conveying speed of the gas flow comprises: determining a gas density of the gas flow based on at least one measured parameter of the gas flow; determining a mass flow of powder to be conveyed through the conveying line based on a control value of a dosing device of a source tank applied to the conveying system; determining a set speed of the gas stream based on the gas density and based on the bulk material mass flow; and controlling the conveying device to convey the gas stream at the determined set speed.

32. The powder delivery system of any one of claims 28-31, wherein, monitoring at least one measured parameter of the powder conveying system comprises: controlling a dosing device of a source tank of the conveying at a predetermined control value; determining whether the at least one measured parameter of the powder conveying system is above a predetermined maximum value of the respective parameter; and decreasing the control value of the dosing device by a predetermined value if the at least one measured parameter is above the predetermined maximum value, so that the dosing device dispenses a lower dose of powder into the gas stream each time.

33. The powder delivery system of claim 32, wherein, The control device is further configured to: increase the control value of the dosing device by a predetermined value if the at least one measured parameter is below the predetermined maximum value, so that the dosing device dispenses a higher dose of powder into the gas stream each time.

34. The powder delivery system of claim 32 or 33, wherein, The at least one parameter comprises at least one of the following parameters: conveying speed, pump outlet pressure, pump power, and powder dose per time.

35. The powder delivery system of any one of claims 28-34, wherein, The termination conditions for terminating the conveying comprise: terminating the conveying by stopping the conveying device when at least one of the following events is detected: a fill level of a source tank from which powder for conveying is discharged is below a predetermined limit value; a fill level of a target tank into which powder is conveyed exceeds a predetermined limit value; a predetermined maximum conveying time is exceeded; and a total pressure loss of the conveying gas exceeds a predetermined limit value.

36. The powder delivery system of any one of claims 1 to 35, wherein, The control device is configured to perform a pipe cleaning and a filter cleaning after terminating the conveying according to the conveying processes a, b and / or c, wherein the pipe cleaning comprises: passing a gas stream through the conveying line, and wherein the filter cleaning comprises: purging a filter arranged in the conveying line using compressed air.

37. The powder delivery system of any one of claims 1 to 36, further comprising: at least one dew point sensor for measuring a relative humidity within the conveying line and / or a relative humidity within a tank of the powder conveying system. wherein the control unit is configured to initiate an automatic powder drying when a measured value of the relative humidity exceeds a predetermined limit value.

38. The powder delivery system of claim 37 in combination with claim 4, wherein, A dew point sensor is arranged on at least one of the following components of the powder conveying system: a main reservoir, an external tank, and a conveying device.

39. The powder delivery system of any one of claims 1 to 38 in combination with claim 4, wherein, at least one oxygen sensor for measuring an oxygen concentration is arranged on at least one of the following components of the powder conveying system: a first tank, an overflow container, a buffer container, a main reservoir, an external tank, and a sieving device, wherein the control device is configured to initiate a filling of the conveying line with an inert gas when it is determined that at least one of the arranged oxygen sensors measures an oxygen concentration above a predetermined limit value.

40. The powder delivery system of any one of claims 1 to 39 in combination with claim 4, wherein, at least one pressure sensor for measuring a pressure is arranged on at least one of the following components of the powder conveying system: a first tank, an overflow container, a buffer container, a main reservoir, an external tank, and a sieving device, wherein the control device is configured to initiate a filling of the conveying line with an inert gas when it is determined that at least one of the arranged pressure sensors measures a pressure above a predetermined limit value. wherein the control device is configured to perform at least one of the following steps when it is determined that at least one of the provided pressure sensors measures a pressure increase per specified time unit which is higher than a predetermined limit value: outputting a warning message; filling the affected section of the conveying line or the powder conveying system with an inert gas; measuring the oxygen content in the affected section of the powder conveying system; and performing a filter cleaning.

41. The powder delivery system of any one of claims 1 to 40, wherein, at least one temperature sensor for measuring a temperature is provided on at least one motor of the powder conveying system, in particular on a motor of the conveying device and / or of a conveyor screw, wherein the control device is configured to initiate a shutdown of the conveying device when it is determined that at least one of the provided temperature sensors measures a temperature value which is higher than a predetermined limit value.

42. The powder delivery system of any one of claims 1 to 41, wherein, the control device is configured to initiate a shutdown of the conveying device when at least one of the following events is detected: a torque of a motor of the dosing device exceeds a predetermined limit value; a valve of the powder conveying system is in an actual position which does not correspond to its set position; a fault on a sensor is detected.

43. The powder delivery system of any one of claims 1 to 42, wherein, a level sensor for measuring a filling level of the at least one overflow container is provided on the at least one overflow container, in particular in the form of one or more load cells, wherein a level sensor for measuring a level of the intermediate tank is provided on the intermediate tank, the intermediate tank being arranged above the process chamber, being configured to supply powder to the process chamber and being configured to supply powder from the first tank to the intermediate tank, the level sensor being in particular in the form of one or more load cells, wherein, in case of a failure of the powder conveying by the conveying device, the control device is configured to continue the additive manufacturing process of the apparatus until at least one of the following events occurs: a filling level sensor of the overflow container detects that the filling level of the overflow container exceeds a predetermined limit value; and a filling level sensor of the intermediate tank detects that the filling level of the intermediate tank is below a predetermined limit value.

44. The powder delivery system of any one of claims 1 to 43, wherein, the control device is configured to perform a conveying of a predetermined amount of powder according to one of the conveying processes a, b or c and then to stop the conveying.

45. The powder delivery system of claim 44, wherein, the control device is configured to determine a priority value for each of the conveying processes based on a predetermined filling level limit of the source tank and a predetermined filling level limit of the target tank after each conveying operation according to one of the conveying processes a, b and c, and wherein the control device is configured to subsequently perform a conveying according to the conveying process having the highest priority value.

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