Bulk material transport system and bulk material transport method

Abstract

The present invention relates to a bulk material conveying system, and more particularly to a system for conveying raw material powder in an apparatus for manufacturing a three-dimensional workpiece by irradiating a layer of raw material powder with electromagnetic radiation or particle beams. The bulk material conveying system comprises a conveying line configured to convey a gas flow and, at least partially, a bulk material flow moved by the gas flow, and a supply device configured to supply a predetermined amount of bulk material to the gas flow at time intervals. The supply amount is determined by a control value applied to the supply device. Furthermore, the bulk material conveying system comprises a conveying device configured to convey the gas flow through the conveying line, and at least one measuring device for measuring at least one parameter of the gas flow. The bulk material conveying system further comprises a control device configured to determine the gas density of the gas flow based on the measured parameter of the gas flow, determine the bulk material mass flow rate of the bulk material flow based on a control value applied to the supply device, determine a set speed 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 speed.

Description

[Technical Field]

[0001] The present invention relates to a bulk material transport system and a method for transporting bulk materials. In particular, the present invention relates to the transport of raw material powder in an apparatus (e.g., a selective laser melting apparatus) that manufactures a three-dimensional workpiece by irradiating a layer of raw material powder with electromagnetic radiation or particle radiation.

[0002] In additive (or generative) processes for manufacturing three-dimensional workpieces, particularly generative layering processes, it is known that a workpiece of a desired shape is ultimately obtained by layering a molding material, initially of an undefined or neutral shape, consisting of raw materials (e.g., raw material powder), onto a carrier and solidifying it by irradiation (e.g., melting or sintering) to specific areas. Irradiation can be carried out by electromagnetic radiation (e.g., laser radiation) or particle radiation (e.g., electron radiation). In the initial state, the molding material is in the form of granules, powder, or liquid, and can be selectively, i.e., locally, solidified by irradiation. In particular, the molding material may be a bulk material such as raw material powder. The molding material may consist of, for example, ceramic, metal, or plastic materials, or mixtures of these materials. One variation of the generative layering method involves so-called laser beam melting (also called selective laser melting) in a powder bed, in which raw material powder materials, particularly metal and / or ceramic, are solidified into a three-dimensional workpiece by irradiation with a laser beam.

[0003] In selective laser melting, in order to produce individual workpiece layers, it is also known to apply the raw material powder in the form of a raw material powder layer onto a carrier and irradiate it selectively and in accordance with the shape of the workpiece layer currently being produced. The laser light passes through the raw material powder and solidifies the raw material powder by heating, for example, causing melting or sintering. Once the workpiece layer has solidified, a new layer of untreated raw material powder is applied onto the already formed workpiece layer. For this purpose, known coating devices or powder application devices can be used. Then, the untreated raw material powder layer that is currently on the uppermost layer is irradiated again. In this way, the workpiece is laminated layer by layer, and each layer defines the cross-sectional area and / or contour of the workpiece. In this context, it is also known to manufacture the workpiece substantially automatically using CAD or equivalent workpiece data.

[0004] The present disclosure relates to a bulk material conveying system for conveying bulk materials. In particular, the bulk material may be a raw material powder used in any of the devices for manufacturing the three-dimensional workpieces described above.

[0005] In particular, not only for the supply of raw material powder in the additive manufacturing process of the type described above, but also in other applications, there may be a need to convey bulk materials from a source tank to a target tank.

[0006] For this purpose, so-called pneumatic conveying is typically used. In this process, a conveying device (e.g., a pump or a blower) generates a gas flow of a conveying gas (e.g., air, a protective gas such as argon, or a mixture of air and a protective gas) through a conveying line. The conveying line can in particular form a closed circuit, whereby the gas flow is conveyed cyclically (in a so-called conveying circuit). From a supply tank, a predetermined amount of bulk material is supplied to the gas flow, for example using a supply device. It is also possible to supply the bulk material to the gas flow simultaneously from a plurality of supply tanks. From the point where the bulk material is supplied, the mixture of gas and bulk material is conveyed through the conveying line to the point where a separating device (e.g., a cyclone) of the conveying circuit is installed. By means of the separating device, the bulk material is separated from the mixture of gas and bulk material as completely as possible and supplied to a target tank. For example, the cyclone can be arranged above the target tank and the separated bulk material can be dropped into the target tank by gravity (so-called gravity conveying).

[0007] One of the problems in pneumatic bulk material conveying is that the operating parameters of the device and / or the properties of the bulk material (e.g., the material of the bulk powder used and the associated conveying properties) can change during operation or between individual conveying processes. In this case, it is necessary to readjust certain operating parameters of the bulk material conveying system, in particular the velocity of the gas flow determined by the conveying device. Other operating parameters for which readjustment may be necessary in a bulk material conveying system are the supply rate per unit time of the bulk material conveyed in the gas flow.

[0008] In particular, it is difficult to determine a gas flow velocity suitable for pneumatic bulk material conveying under varying conditions (e.g., the operating parameters of the device and / or the properties of the bulk material).

[0009] Therefore, an object of the present invention is to provide a bulk material conveying system and a corresponding method for conveying bulk material that solves at least one of the above problems or related problems. In particular, it is desirable to be able to easily set a set value of the gas velocity that can react to changes in one or more operating parameters with high reliability.

[0010] This objective is addressed by a bulk material transport system and bulk material transport method having the features of the independent claim. Further embodiments are provided in the dependent claims.

[0011] According to a first aspect, the present invention relates to a bulk material conveying system, and more particularly to a bulk material conveying system for conveying raw material powder in an apparatus for manufacturing a three-dimensional workpiece by irradiating a layer of raw material powder with electromagnetic radiation or particle radiation. The bulk material conveying system comprises a conveying line configured to convey a gas flow and, at least partially, a bulk material flow moved by the gas flow, and a supply device configured to supply a predetermined amount of bulk material to the gas flow at time intervals. The supply amount is determined by a control value applied to the supply device. The bulk material conveying system further comprises a conveying device configured to convey the gas flow through the conveying line, and at least one measuring device for measuring at least one parameter of the gas flow. Furthermore, the bulk material conveying system comprises a control device configured to determine the gas density of the gas flow based on at least one parameter of the measured gas flow, determine the bulk material mass flow rate of the bulk material flow based on a control value applied to the supply device, determine a set speed 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 speed.

[0012] The bulk material transport system can be configured to transport bulk materials pneumatically. The apparatus may, in particular, be an apparatus for selective laser melting or sintering having one or more of the features described above. Alternatively, the apparatus may be an apparatus for selective electron beam melting.

[0013] The conveying line may include, for example, one or more pipes and / or one or more hoses and / or one or more connecting components. The conveying line is powder-sealed, in particular gas-sealed, so that gas or powder cannot enter or leave the conveying line except through openings in the conveying line.

[0014] The fact that a conveyor line is configured to be divided into multiple sections for conveying a bulk material flow moved by a gas flow means that only a portion of the entire conveyor circuit formed by the conveyor line is configured to convey a mixture of gas and bulk material. The rest of the conveyor circuit essentially conveys only gas (conveyor gas), such as air, protective gas, or a mixture of air and protective gas.

[0015] The control value is a voltage, current, pulse, or other appropriate signal (particularly an electrical signal), which can be changed to alter the amount supplied by the supply device. The conveying device may be a pump or a blower. Furthermore, the conveying circuit formed by the conveying line may include one or more filter devices, in particular for filtering out bulk material or residues of bulk material remaining in the gas flow.

[0016] The control device may include, for example, a computer. The control device comprises a processor and memory, the memory which stores a program, and when this program is executed, the processor performs the method according to the second embodiment.

[0017] In this specification, the term "bulk material mass flow rate" is used to refer to the physically quantifiable mass flow rate (kg / s) of the bulk material being conveyed. In contrast, the term "bulk material flow" simply refers to the presence of bulk material being conveyed through a conveyor line.

[0018] Each decision step may involve one or more calculations. Each calculation may include not only measured values ​​but also stored values ​​(e.g., standard values). The conveying device can be controlled to decrease or increase the velocity of the conveyed gas flow. In particular, the velocity of the gas flow can be increased, for example, by increasing the voltage applied to the conveying device. Since the gas flow conveys bulk material, the velocity of the gas flow also determines the velocity of the conveyed bulk material.

[0019] The determination of the gas density can be carried out based on at least one of the following parameters of the gas flow, namely oxygen content, pressure, temperature, dew point and humidity.

[0020] For each of the above parameters, a corresponding sensor can be installed in the gas flow, and the sensor is configured to measure the respective parameter.

[0021] The gas density ρ can be determined using the following formula. JPEG2026522228000002.jpg10150 Here, p meas is the measured pressure of the gas flow, T meas is the measured temperature of the gas flow, p n is a predetermined normal pressure, T n is a predetermined normal temperature, ρ mixture is given by the following formula. JPEG2026522228000003.jpg10155 Here, ρ air is the known density of air which is a component of the gas flow, ρ protective gas is the known density of the protective gas which is a component of the gas flow, oxygen content air is the known oxygen content of air, oxygen content measured is the measured oxygen content of the gas flow.

[0022] p meas and T meas can be measured respectively by appropriate sensors arranged in the gas flow. At least one or both of the sensors required for this purpose can be arranged downstream of the conveying device, particularly between the conveying device and the raw material tank where the bulk material is conveyed. In particular, at least one or both of the sensors can be arranged immediately downstream of the conveying device. The normal pressure and the normal temperature can be set as predefined standard values. For example, the normal pressure can be set as 1013.25 mbar and the normal temperature can be set as 293.15 K. However, the normal pressure and / or the normal temperature can also be set as the measured values of the ambient pressure or the ambient temperature.

[0023] The protective gas can be, for example, argon, with density ρ protective gas This corresponds to the density of known argon gas. The density of air, the density of the protective gas used, and the oxygen content of the air can be found in the corresponding tables in the technical literature. The oxygen content of the air can also be the measured oxygen content of the ambient air.

[0024] The oxygen content can be measured by a suitable sensor placed in the gas flow. The necessary sensor can be placed upstream of the conveying device, between the target tank to which the bulk material is being transported and the conveying device. In particular, the sensor can be placed directly upstream of the conveying device.

[0025] The control value applied to the supply device can be the motor speed of the supply device's motor, particularly the motor that drives the conveyor screw of the supply device.

[0026] However, the control value may be a current or voltage applied to the motor. Generally speaking, the control value may represent any signal (e.g., an electrical signal) suitable for changing the amount of material dispensed by the feeder (more precisely, the amount dispensed per hour), and especially suitable for setting it to a predetermined value. As described above, the feeder may include a conveyor screw configured to transport bulk material from a source tank. Furthermore, the feeder may include at least one of the following elements: a rotary valve, a metering slide, and a valve (in particular, a valve with a variable opening diameter).

[0027] gas flow set speed v set Determining the set velocity v may include calculating the jump velocity based on the determined gas density and the determined mass flow rate of the bulk material. set This can be calculated using the following formula. JPEG2026522228000004.jpg7169 Here v saltation v is the calculated jump velocity of the bulk material being transported. safety This is a predetermined safe speed.

[0028] The jump velocity is the speed below which the particles of the bulk material being conveyed (e.g., powder) will begin to fall and accumulate at the bottom of the conveyor line. To prevent this from happening, a predetermined safety velocity can be added to the calculated jump velocity. This creates a kind of safety margin for the jump velocity, ensuring that the bulk material does not accumulate on the conveyor line. Instead of adding a safety velocity, the jump velocity can also be multiplied by a safety factor.

[0029] Jump velocity can be calculated using the following formula. JPEG2026522228000005.jpg19169 Here M s is the mass flow rate (kg / s) of the required bulk material, and g is the predetermined gravitational acceleration (m / s²). 2 ) where D is the diameter of the transport line (m) and ρ is the calculated gas density of the gas flow (kg / m³). 3 ) and a and b are parameters that depend on the particle size d of the bulk material.

[0030] The given gravitational acceleration is 9.81 m / s², which is the gravitational acceleration at the Earth's surface. 2 This corresponds to the following. Parameters a and b can each be a predetermined constant and / or a pre-stored constant for each bulk material. Furthermore, parameters a and / or b can be determined depending on the particle size d of the bulk material used. In other words, the formulas for calculating parameter a and / or parameter b may depend on the particle size d. The particle size d can be obtained from the specifications of the bulk material used. The particle size d can be stored, for example, in the memory of the control device. In particular, the memory of the control device can store a table in which the particle size d values ​​for each different powder material are stored. In this way, each particle size d can be used when calculating the set speed.

[0031] The control of a conveying device for transporting a gas flow at a predetermined set speed can be performed using a speed sensor to measure the gas flow velocity and, in particular, a control loop including a PID control device.

[0032] A PID control device is a "proportional-integral-differential controller," and PID control is well known in control engineering as a method for setting and maintaining a predetermined value (in this case, gas flow rate).

[0033] The control device can also be configured to determine whether at least one measurement parameter of the bulk material transport system exceeds a predetermined maximum value for each parameter, and if at least one measurement parameter exceeds a predetermined maximum value, to reduce the control value of the supply device by a predetermined value.

[0034] Multiple parameters can be determined (especially measured), and if at least one of the determined parameters exceeds a predetermined maximum value, the control value is reduced by a predetermined amount.

[0035] A bulk material conveying system may be equipped with one or more sensors for measuring each parameter. Determining whether at least one measurement parameter exceeds a predetermined maximum value and adjusting the control value accordingly can be performed after the steps of determining the gas density, determining the mass flow rate of the bulk material, determining the set speed, and controlling the conveying device. These steps can be performed again with the new control value after the adjustment of the control value. Thus, the determination (and adjustment as necessary) of the set speed and the adjustment of the control value as necessary can be performed alternately. Reducing the control value means that the amount of bulk material discharged by the feeder per cycle decreases.

[0036] The control device can also be configured to increase the control value of the supply device by a predetermined value when at least one measurement parameter falls below a predetermined maximum value.

[0037] Multiple parameters can be determined (especially measured), and if all of the determined parameters fall below a predetermined maximum value for each parameter, the control value is increased by a predetermined value. Therefore, the control value can only be increased if all of the determined parameters do not exceed their respective maximum values. Increasing the control value means increasing the amount of bulk material dispensed per unit time by the feeder.

[0038] At least one parameter may include at least one of the following: conveying speed, pump outlet pressure, pump capacity, and bulk material supply rate per hour.

[0039] Each parameter can be measured, for example, using a sensor provided for this purpose, or determined by other means. For example, the parameters can be calculated based on at least one input value (e.g., applied voltage) applied to an element of the powder conveying system (e.g., a conveying device).

[0040] The control device can be configured to terminate transport by stopping the transport device if at least one of the following events is detected: the source tank from which the bulk material is discharged by the supply device is empty; the target tank to which the bulk material is transported is full; a predetermined maximum transport time has been exceeded; or the total pressure loss of the transported gas has exceeded a predetermined limit.

[0041] Each event can be detected, for example, by a corresponding sensor. In detail, these events can be detected as follows: The source tank from which bulk material is discharged by the supply device can be determined to be empty by a corresponding level sensor (e.g., a capacitive sensor, radar sensor, ultrasonic sensor, or optical sensor). The target tank from which bulk material is transported can be determined to be full by a corresponding level sensor (e.g., a capacitive sensor, radar sensor, ultrasonic sensor, or optical sensor). Whether or not the predetermined maximum transport time has been exceeded can be determined by a corresponding timer that is activated at the start of transport. Whether or not the total pressure loss of the transported gas has exceeded a predetermined limit can be determined by one or more pressure sensors in the transport line.

[0042] The bulk material conveying system may further include a pressure regulating tank connected to the conveying line downstream of the conveying device and upstream of the supply device.

[0043] A pressure regulating tank may be configured to reduce the positive pressure at the outlet of a conveying device (e.g., a pump). Therefore, a positive pressure tank may be provided at the outlet of the conveying device.

[0044] The bulk material transport system may include at least one first transport circuit for transporting raw material powder from a main storage unit into a first tank of a apparatus for manufacturing a three-dimensional workpiece by irradiating a layer of raw material powder with electromagnetic radiation or particle radiation. The lower outlet of the first tank can be connected to the upper inlet of an intermediate tank of the apparatus, and powder is supplied from the intermediate tank to the manufacturing process in the process chamber of the apparatus. The upper inlet of the main storage unit may be connected to the outlet of a sieve for screening the raw material powder.

[0045] The main storage unit may be, for example, a storage unit or tank permanently installed in the bulk material conveying system. The main storage unit may be installed at a lower height than the first tank. The first conveying circuit is operated by a control device opening at least one valve, and the conveying device can convey gas through this first conveying circuit. The bulk material conveying system may be configured to supply powder to the sieve from a buffer container located above the sieve. The powder can be conveyed to the buffer container by a second conveying circuit, for example, from the device's overflow tank and / or an external tank.

[0046] In this specification, the terms “tank,” “storage section,” and “container” are used synonymously. However, different containers will be referred to by specific terms such as “tank,” “buffer container,” “main storage section,” and “external tank.” However, these terms are not restrictive and are used solely to distinguish different containers from one another. For example, a “buffer container” may also be referred to as a “second tank.”

[0047] The bulk material transport system may include at least one second transport circuit for transporting raw material powder from an overflow tank to a buffer container. The overflow tank can be configured to receive excess powder from the process chamber of an apparatus that manufactures three-dimensional workpieces by irradiating a layer of raw material powder with electromagnetic 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.

[0048] The second transport circuit is activated by opening at least one valve by the control device, and the transport device can transport gas through this second transport circuit. An overflow tank can be located, for example, in a lateral area adjacent to the build cylinder of the device, and the top of the overflow tank is open, so that excess powder can be pushed into the overflow tank, for example, by a powder dispenser.

[0049] The bulk material transport system may include at least one third transport circuit for transporting raw material powder from an external tank into a buffer container. The external tank may be detachable from or detachably connected to the bulk material transport system. The lower outlet of the buffer container may be connected to the inlet of a sieve for sieving the raw material powder.

[0050] The third transport circuit is activated by the control device opening at least one valve, thereby allowing the transport device to transport gas through the third transport circuit. The third transport circuit operates simultaneously with the second transport circuit, and the powder from the external tank and the powder from the overflow tank are mixed in an adjustable mixing ratio. The mixing ratio can be adjusted, for example, by the respective supply devices of each container (external tank, overflow tank).

[0051] The supply device can be positioned at the outlet of each source tank, and a cyclone can be positioned at the inlet of each target tank to separate the raw material powder from the gas flow and supply the raw material powder to the target tank.

[0052] The supply device allows the bulk material flow to be introduced into the gas flow, and the cyclone allows the bulk material to be removed from the gas flow again.

[0053] According to a second aspect, the present invention relates to a method for conveying bulk material, and more particularly to a method for conveying raw material powder in an apparatus for manufacturing a three-dimensional workpiece by irradiating a layer of raw material powder with electromagnetic radiation or particle radiation. The method includes conveying a gas flow and a bulk material flow moved by the gas flow through a conveying line, and supplying a predetermined amount of bulk material at time through a supply device. The supply amount can be determined by a control value applied to the supply device. The method further includes conveying the gas flow through a conveying line using a conveying device, and measuring at least one parameter of the gas flow using a measuring device. The method further includes determining the gas density of the gas flow based on the measured at least one parameter of the gas flow, and determining the bulk material mass flow rate of the bulk material flow based on a control value applied to the supply device. The method further includes determining a set velocity of the gas flow based on the gas density and the bulk material mass flow rate, and controlling the conveying device to convey the gas flow at the determined set velocity.

[0054] All the details and features of the first embodiment (bulk material transport system) described above are also applicable (individually or in any combination) to the bulk material transport method according to the second embodiment. The bulk material transport system according to the first embodiment can be configured to carry out the bulk material transport method according to the second embodiment.

[0055] The gas density can be determined based on at least one of the following parameters of the gas flow: oxygen content, pressure, temperature, dew point, and humidity.

[0056] Gas density can be calculated using the following formula. JPEG2026522228000006.jpg10150 Here p meas This is the measured pressure of the gas flow, and T meas is the measurement temperature of the gas flow, and p n It is a predetermined normal pressure, T n ρ is at a predetermined room temperature, mixture It is given by the following equation. JPEG2026522228000007.jpg10155 Here ρ air ρ is the known density of air, which is a component of the gas flow. protective gas This is the known density of the protective gas, which is a component of the gas flow, and the oxygen content. air This is the known oxygen content of air. measured This represents the measured oxygen content of the gas flow.

[0057] The control value applied to the supply device can be the motor speed of the supply device's motor, particularly the motor that drives the conveyor screw of the supply device.

[0058] gas flow set speed v set Determining the set velocity v may include calculating the jump velocity based on the determined gas density and the determined mass flow rate of the bulk material. set This can be calculated using the following formula. JPEG2026522228000008.jpg7169 Here v saltation v is the calculated jump velocity of the bulk material being transported. safety This is a predetermined safe speed.

[0059] Jump velocity can be calculated using the following formula. JPEG2026522228000009.jpg19169 Here M s is the mass flow rate (kg / s) of the required bulk material, and g is the predetermined gravitational acceleration (m / s²). 2 ) where D is the diameter of the transport line (m) and ρ is the calculated gas density of the gas flow (kg / m³). 3 ) and a and b are parameters that depend on the particle size d of the bulk material.

[0060] The control of the conveying device for transporting the gas flow at the desired set speed is performed using a speed sensor to measure the gas flow velocity and a control loop that includes a PID control device in particular.

[0061] The method may include determining whether at least one measurement parameter of the bulk material transport system exceeds a predetermined maximum value for each parameter, and if at least one measurement parameter exceeds a predetermined maximum value, reducing the control value of the supply device by a predetermined value.

[0062] The method may further include increasing the control value of the supply device by a predetermined value when at least one measurement parameter is below a predetermined maximum value.

[0063] At least one parameter may include at least one of the following: conveying speed, pump outlet pressure, pump capacity, and bulk material supply rate per hour.

[0064] The method may further include terminating transport by stopping the transport device if at least one of the following events is detected: namely, the source tank from which the bulk material is discharged by the supply device is empty; the target tank to which the bulk material is transported is full; a predetermined maximum transport time has been exceeded; or the total pressure loss of the transport gas has exceeded a predetermined limit.

[0065] The method may include transporting raw material powder from a main storage unit to a first tank of an apparatus for manufacturing a three-dimensional workpiece by irradiating a layer of raw material powder with electromagnetic radiation or particle radiation, via at least one first transport circuit. The lower outlet of the first tank can be connected to the upper inlet of an intermediate tank of the apparatus, and powder is supplied from the intermediate tank to the manufacturing process in the process chamber of the apparatus. The upper inlet of the main storage unit may be connected to the outlet of a sieve for sieving the raw material powder.

[0066] The method may include transporting the raw material powder from an overflow tank to a buffer container via at least one second transport circuit. The overflow tank may be configured to receive excess powder from the process chamber of an apparatus that manufactures a three-dimensional workpiece 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.

[0067] The method may include transporting raw material powder from an external tank to a buffer container via at least one third transport circuit. The external tank may be detachable from or detachably connected to the bulk material transport system. The lower outlet of the buffer container may be connected to the inlet of a sieve for sieving the raw material powder.

[0068] The supply device can be positioned at the outlet of each source tank. A cyclone can be positioned at the inlet of each target tank to separate the raw material powder from the gas flow and supply it to the target tank.

[0069] An apparatus for manufacturing a three-dimensional workpiece by irradiating a layer of raw material powder with electromagnetic or particle radiation, as described herein, may include, for example, a carrier apparatus for applying powder in multiple layers to form a powder bed. Furthermore, it may include one or more powder application devices for applying powder, and optionally for applying powder of different materials. Separate powder application devices may be provided for each material. The carrier apparatus can be moved vertically downward by a lifting device so that the uppermost powder layer is always kept at the same height relative to the build chamber of the apparatus. Furthermore, 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 with one or more optical components (e.g., a beam expander, a focusing unit, a scanner device, an F-theta lens) for shaping and deflecting the beam. Alternatively, the beam source may be located outside each irradiation unit, in which case the beam is directed to the irradiation unit via an optical guide (e.g., a glass fiber).

[0070] The present invention will be described below with reference to the accompanying drawings. [Brief explanation of the drawing]

[0071] [Figure 1] The diagram shows an apparatus for manufacturing a three-dimensional workpiece by irradiating a layer of raw material powder with electromagnetic radiation or particle radiation, and the apparatus is equipped with a bulk material transport system. [Figure 2] This is a schematic diagram of a conveyor screw type supply device, where the parameters of the conveyor screw are specified to calculate the mass flow rate conveyed by the conveyor screw. [Figure 3] This is a flowchart of the limit value control process. [Figure 4] This is a schematic diagram of a bulk material handling system for a selective laser melting apparatus capable of performing at least three handling processes a, b, and c. [Figure 5] This is a schematic diagram highlighting the transport process a of the system in Figure 4. [Figure 6] This is a schematic diagram highlighting the transport process b of the system in Figure 4. [Figure 7] This is a schematic diagram highlighting the transport process c of the system in Figure 4.

[0072] Figure 1 shows an apparatus 1100 for manufacturing 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 manufacturing a three-dimensional workpiece by an additive manufacturing process using raw material powder, such as selective laser melting or selective laser sintering.

[0073] The bulk material transport system of this disclosure will be described below in relation to the apparatus described above, but the bulk material transport system or bulk material transport method is not limited to use in relation to an additive manufacturing apparatus. The advantages derived from the bulk material transport system and related methods presented herein are generally applicable to situations in which bulk material is transported by pneumatic transport.

[0074] The apparatus 1100 comprises a carrier 1002 and a powder dispensing device 1003 for dispensing raw material powder 1004 onto the carrier 1002. The carrier 1002 and the powder dispensing device 1003 are located within a process chamber 1011, which can be sealed from the ambient atmosphere, i.e., the environment surrounding the process chamber 1011. The apparatus 1100 further comprises an irradiation device 1005 for selectively irradiating the raw material powder 1004 dispensed onto the carrier 1002 with electromagnetic radiation or particle radiation.

[0075] The process chamber 1011, or powder dispensing device 1003, is supplied with raw material powder 1004 via a bulk material conveying system 1001, which will be described later. In this powder conveying case, the bulk material conveying system 1001 is a powder conveying system. The bulk material conveying system 1001 includes a powder storage section 1006 for storing the raw material powder 1004 supplied to the process chamber 1011. The powder storage section 1006 is connected to the conveying line 1007 via a supply device 1008. The gas flow 1009 is conveyed by a conveying device 1019 through the conveying line 1007 in the direction indicated by the arrow in Figure 1. In the exemplary powder conveying system 1001 shown in Figure 1, the conveying device 1009 is configured as a vacuum pump.

[0076] The supply device 1008 is configured to supply a desired amount of raw material powder 1004 to the gas flow 1009 flowing through the conveyor line 1007. In particular, the supply device 1008 is equipped with a first powder valve 1021 having a continuously variable flow path cross-sectional area, thereby continuously changing the amount of powder 1004 introduced into the gas flow 1009 per unit time through the metering opening 1023 of the supply device 1008. In other words, a control value can be applied to the supply device 1008 by the control device 1040 described later, and the supply amount per unit time is determined by this control value. In the case of the valve 1021 having the variable flow path cross-sectional area described above, the flow path cross-sectional area is determined by the control value, and therefore the supply amount is determined. Alternatively, the valve 1021 can be replaced with a conveyor screw and a motor to drive it. In this case, the motor speed is determined by the control value, and therefore the discharge amount is determined. Thus, by applying a predetermined control value, a desired supply amount of powder discharged per unit time can be specified.

[0077] The mixture of raw material powder and gas flowing through the conveyor line 1007 downstream of the supply device 1008 is transported to a cyclone 1010 that functions as a separation device. The cyclone 1010 has an inlet 1020 that tangentially flows the mixture of raw material powder and gas into a conical separation chamber 1022. Powder particles 1004 that fall from the swirling flow of the mixture of raw material powder and gas formed in the conical separation chamber 1022 are discharged from the cyclone 1010 by a powder outlet 1024 located in the lower region of the cyclone 1010. These powder particles 1004 are supplied to the process chamber 1011, i.e., the powder dispensing device 1003, via a connecting line 1026 that connects the powder outlet 1024 of the cyclone 1010 to the powder inlet 1028 of the process chamber 1011.

[0078] A second powder valve 1030 is provided in the connection line 1026. Similar to the first powder valve 1021 of the supply device 1008, the second powder valve 1030 also has a continuously variable flow path cross-sectional area, allowing for a continuous variation in the amount of powder 1004 supplied from the powder outlet 1024 of the cyclone 1010 to the process chamber 1011. The second powder valve 1030 (similar to the first powder valve) can also be replaced by a conveyor screw with an associated motor.

[0079] In the case shown in Figure 1, the powder is transported from a supply tank formed by the powder storage unit 1006 to a target tank, which can be considered, for example, as the volume below the powder valve 1030 in the connection line 1026. In the schematic diagram of Figure 1, this volume represents a powder container for the powder dispensing device 1003, from which powder is supplied to the powder dispensing device 1003 to apply individual layers. Alternatively, this powder storage unit (and target tank) can be integrated into the powder dispensing device 1003.

[0080] The gas separated from the powder particles 1004 in the cyclone 1010 is returned to the transport line 1007 through the gas outlet 1032 of the cyclone 1010. The gas outlet 1032 is located at the top of the cyclone 1010.

[0081] Since the gas stream 1009 discharged from the gas outlet 1032 of the cyclone 1010 may contain residual raw material powder particles 1004, a filter unit 1014 is placed in the transport line 1007 downstream of the cyclone 1010. The filter unit 1014 includes a replaceable filter 1013 configured to filter out residual raw material powder particles 1004 present in the gas stream 1009 discharged from the gas outlet 1032.

[0082] The bulk material transport system 1001 further includes a measuring device 1050 for measuring parameters of the gas flow being transported within the transport line 1007. In the embodiment shown in Figure 1, the measuring device 1050 is a pressure sensor located directly downstream of the transport device 1019 and for measuring the pressure (gas pressure) within the transport line 1007. In addition to the measuring device 1050, further measuring devices 1015, 1016, 1017, and 1018 are provided along the transport 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 in the gas flow. Measuring devices 1016 and 1017 may each be further sensors for measuring any of the aforementioned characteristics (pressure, temperature, oxygen content). Furthermore, measuring devices 1016 and 1017 may each be independently sensors for measuring flow velocity, sensors for detecting the presence or absence of bulk material (e.g., capacitive sensors or ultrasonic sensors), sensors for measuring dew point, etc. In addition to measuring devices 1050 and 1015-1018, a smaller or larger number of sensors may also be provided. Furthermore, the measuring devices may be installed in a different location on the conveyor line.

[0083] The pressure sensor 1050, temperature sensor 1018, and oxygen sensor 1015 are particularly relevant to the functions of the control device 1040 (see below) described herein.

[0084] Finally, the bulk material transport system 1001 has a control device 1040. The control device 1040 controls the operation of each element of the bulk material transport system, in particular all controllable elements. For example, the control device 1040 can control the transport device 1019 so that a predetermined flow rate of the transported gas is set, for example, by applying a voltage of a 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 supply device 1008. In particular, the control device 1040 applies a predetermined control value to the supply device 1008 so that the supply device supplies a predetermined amount of raw material powder to the gas flow per unit time. Furthermore, the control device 1040 can increase or decrease the currently supplied amount by a predetermined value. The control device 1040 also receives measurement data from all measuring devices. Furthermore, the control device 1040 controls the valve 1030.

[0085] The control device 1040 can also be configured to control all operations of the device 1010, namely irradiation by the irradiation device 1005, powder dispensing by the powder dispensing device 1003, and the descent of the carrier 1002.

[0086] To determine an appropriate set value for the gas velocity in the conveyor line 1007 and to set the velocity corresponding to that set value, 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 of the bulk material flow based on the control values ​​applied to the supply device. C. Determine the set gas flow rate based on the gas density and bulk material mass flow rate. D. Control the conveying device to transport the gas flow at the determined set speed.

[0087] About each step Step A The control device 1040 calculates the gas density of the gas flow based on the measured parameters of the gas flow. There are several ways to determine (e.g., calculate or estimate) the gas density of the gas flow based on one or more measured parameters. One example is shown below. Here, the control device 1040 uses the measured pressure (measured by the pressure sensor 1050), the measured temperature (measured by the temperature sensor 1018), and the measured oxygen content (measured by the oxygen sensor 1015).

[0088] Gas density can be calculated using the following formula. JPEG2026522228000010.jpg10150 Here p meas This is the measured pressure of the gas flow, and T meas is the measurement temperature of the gas flow, and p n It is a predetermined atmospheric pressure (for example, atmospheric pressure p n =1013.25mbar), T n ρ is a predetermined room temperature (for example, room temperature of 293.15K), mixture It is given by the following equation. JPEG2026522228000011.jpg10155 Here ρ air ρ is the known density of air, which is a component of the gas flow. protective gas This is the known density of the protective gas, which is a component of the gas flow, and the oxygen content. air This is the known oxygen content of air. measured This is the oxygen content of the gas stream measured by the oxygen sensor 1015. For example, ρ is the density of air. air = 1.225 kg / m 3 When argon is used as the protective gas, the density of the protective gas is ρ protective gas = 1.784 kg / m 3 It can be used. The oxygen content in the air is air It can be set to 20.94%. Alternatively, the oxygen content of the ambient air can be measured and used.

[0089] Step B The control device 1040 determines the bulk material mass flow rate of the bulk material flow based on the control value applied to the supply device 1008. In the case of powder conveying described above, the bulk material mass flow rate is the powder mass flow rate. The mass flow rate is specified, for example, in kg / s.

[0090] The determination of the mass flow rate of the bulk material depends on the feeder 1009 used, particularly its shape. If the feeder 1009 has already been calibrated, the relevant volumetric flow rate of the bulk material being conveyed can be calculated or read from a table, for example, depending on the applied control value (e.g., the rotational speed of the conveyor screw). In particular, there may be a linear relationship between the control value and the volumetric flow rate, in which case the coefficients characterizing the linear relationship can be determined in advance by calibration. The desired mass flow rate (kg / s) is calculated based on the known density (kg / m³) of the bulk material being conveyed. 3 Using ), the determined volumetric flow rate (m 3 It can be calculated from ( / s). A calibration table or method for calculating the volumetric flow rate based on a given control value is described, for example, in the manual or specifications of the supply device 1009.

[0091] If corresponding calibration data is not available, the supply device 1009 can be calibrated to determine the relationship between the control value and the volumetric flow rate.

[0092] Furthermore, it is also possible to calculate the mass flow rate of bulk materials. Using a conveyor screw as an example, the corresponding calculation formula is shown below.

[0093] The mass flow rate of bulk material is calculated using the following formula. JPEG2026522228000012.jpg8169 Here, M s D is the mass flow rate of the bulk material, z This is the outer diameter of the conveyor screw, G w H is the height of the screw wall. w,1 is the first screw pitch, e is the thickness of the screw wall, and n m ρ is the rotational speed of the conveyor screw, i is the transmission ratio, and ρ s This is bulk density.

[0094] Details of the above parameters related to the conveyor screw can also be seen in Figure 2, which shows the conveyor screw and related parameters.

[0095] Step C The control device 1040 determines the set gas flow rate based on the gas density obtained in step A and the mass flow rate of the bulk material obtained in step B.

[0096] gas flow set speed v set Determining the set velocity v may include calculating the jump velocity based on the determined gas density and the determined mass flow rate of the bulk material. set According to the embodiment, this can be calculated using the following formula. JPEG2026522228000013.jpg7169 Here v saltation v is the calculated jump velocity of the bulk material being transported. safety This is a predetermined safe speed.

[0097] The jump velocity is the speed below which, if any, the particles of the bulk material being conveyed (e.g., powder) will fall and begin to accumulate at the bottom of the conveyor line 1007. To prevent this from happening, a predetermined safety velocity can be added to the calculated jump velocity. This creates a kind of safety margin for the jump velocity, ensuring that the bulk material does not accumulate on the conveyor line 1007. Instead of adding a safety velocity, the jump velocity can also be multiplied by a predetermined safety factor (e.g., 1.1 or 1.2).

[0098] Jump velocity can be calculated using the following formula. JPEG2026522228000014.jpg19169 Here M s is the mass flow rate (kg / s) of the required bulk material, and g is the predetermined gravitational acceleration (m / s²). 2 ) where D is the diameter of the transport line (m) and ρ is the calculated gas density of the gas flow (kg / m³). 3) where a and b are parameters that depend on the particle size d of the bulk material. Parameters a and b can be stored, for example, in the memory of the control device as constants of the bulk material used. Furthermore, at least one of the two parameters a and b is calculable, and each calculation depends on the particle size d of the bulk material used.

[0099] The particle size d is obtained from the specifications of the bulk material used, for example, from the data sheet of the powder used. The particle size d can also be stored in the memory of the control device 1040, for example. In particular, the memory of the control device 1040 can store a table containing the particle size d values ​​for each different powder material. In this way, when calculating the set speed, the respective particle size d can be used by inputting or selecting the powder to be used via the user interface of the control device 1040.

[0100] Step D The control device 1040 controls the conveying device 1019 to convey the gas flow at the set speed determined in step C. Here, for example, it is known that a signal having a predetermined voltage value or a predetermined frequency is applied to the conveying device 1019, and that voltage value or frequency results in a desired conveying speed for the conveying device 1019.

[0101] If the conveying device 1019 is not properly calibrated, 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 may be a corresponding velocity sensor. For example, a desired set velocity can be adjusted using PID control.

[0102] The above technology allows for the rapid, easy, and uncomplicated setting of the operating points for bulk material transport (i.e., the transport speed of the transport gas, and therefore the transport speed of the transported bulk material). On the other hand, data on various types of powders (e.g., bulk density and particle size) stored in the memory of the control device 1040 is used. Furthermore, it is possible to accommodate changes in operating parameters, particularly changes in measured values ​​such as oxygen content, pressure, and / or temperature within the transport line 1007. It is also possible to accommodate changes in the mass flow rate of the transported bulk material by adjusting the gas flow rate.

[0103] According to one embodiment, so-called limit value control may be performed after the above step AD performed by the control device 1040. However, this is optional, and only the determination of the set speed may be performed according to step AD.

[0104] Details of the limit control are shown in Figure 3. In this regard, the control device 1040 is configured to determine whether at least one measurement parameter of the bulk material transport system 1001 exceeds a predetermined maximum value for each parameter. If the measurement parameter exceeds the predetermined maximum value, the control device 1040 reduces the control value of the supply device 1008 by a predetermined value, thereby reducing the amount of bulk material supplied to the gas flow per unit time.

[0105] Figure 3 shows an example of limit control using specific parameters. Figure 3 shows a flowchart of the process executed by the control device 1040 after determining the set speed and controlling the transport device.

[0106] 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, such as sensor 1016 or 1017 in Figure 1, is used, which is placed in the gas flow or gas-powder mixture flow.

[0107] If the answer is "yes," the process proceeds to step 1204, which asks whether the measured pump outlet pressure is below a predetermined maximum value. A pressure sensor (e.g., sensor 1050 in Figure 1) installed in the gas flow downstream of pump 1019 is used to measure the pump outlet pressure.

[0108] If the answer is "yes," the process proceeds to step 1206, which inquires whether the pump power consumed by pump 1019 is below a predetermined maximum value.

[0109] If the answer is "yes," the process proceeds to step 1208, which asks whether the amount of bulk material supplied per unit time by the supply device 1008 is within a predetermined maximum range.

[0110] If the answer is "yes," the process is complete. Next, you can be asked whether to stop the transport. If you do not want to stop, the aforementioned step AD is executed again, and the transport speed is readjusted as needed.

[0111] If, in step 1208, it is determined that the supply amount of bulk material discharged per unit time is not within a predetermined maximum range ("No" after step 1208), then in step 1210, the system queries whether the supply amount is below the predetermined maximum range. If so ("Yes"), in step 1212, the supply amount is increased by a predetermined value. Otherwise ("No" after step 1210), in step 1214, the supply amount is decreased by a predetermined value.

[0112] Following step 1214, step 1216 asks whether the supply quantity is less than a predetermined minimum value. If not ("No"), the process terminates. However, if it is ("Yes" after step 1216), filter cleaning is performed in step 1218.

[0113] If at least one result of queries 1202, 1204, and 1206 is "no," meaning that the corresponding maximum value has been reached or exceeded, the process proceeds to step 1214 to reduce the supply amount from the supply device 1008.

[0114] After the process shown in Figure 3, it is checked whether the transport process has finished, and in particular whether the transport device 1019 has stopped.

[0115] This occurs when at least one of the following events is detected: the source tank 1006 from which the bulk material is discharged by the supply device 1008 is empty; the target tank (or corresponding cyclone 1010) to which the bulk material is transported is full; the predetermined maximum transport time has been exceeded; or the total pressure loss of the transported gas exceeds a predetermined limit.

[0116] If the transport process is not yet complete, the method executed by the control device 1040 returns to step A (see above).

[0117] Figure 4 is a schematic diagram of a bulk material transport system used to transport raw material powder in an apparatus 1100 that manufactures a three-dimensional workpiece by irradiating a layer of raw material powder with electromagnetic radiation or particle radiation.

[0118] The bulk material handling system in Figure 4 represents a more detailed diagram of the bulk material handling system compared to Figure 1, showing specific components with reference numbers. These components may also be present in the system in Figure 1, but are not explicitly described.

[0119] However, the system in Figure 4 also represents a more complex configuration of the bulk material conveying system described herein, particularly because it can perform multiple conveying processes within the system, namely conveying processes from different raw material tanks to different target tanks. The exact configuration and operating modes of the bulk material conveying system will be described later.

[0120] In particular, a method including step AD for adjusting the transport speed can also be implemented in combination with the system in Figure 4. The same applies to the limit control in Figure 3. For this purpose, the bulk material transport system in Figure 4 also includes a control device (not shown) for controlling the individual components of the system in Figure 4.

[0121] Apparatus 1100 corresponds to, for example, the apparatus 1100 in Figure 1, and generally corresponds to a commonly known apparatus for additive manufacturing by selective laser melting or selective laser sintering. Figure 4 shows only the process chamber of apparatus 1100. The raw material powder is supplied from the intermediate tank 2102 (also called a hopper) of apparatus 1100 to the process chamber (more precisely, the powder dispenser or coater in the process chamber 1011) via the loader 2104.

[0122] Excess powder generated from the additive manufacturing process can be collected in the front overflow tank 2 or the rear overflow tank 3. This is mainly powder that is not needed when coating a new powder layer, and is therefore pushed into either the overflow tank 2 or 3 by the powder dispensing device. An inlet valve 19 or 17 is provided at the inlet of each powder tank 2 or 3.

[0123] Each of the overflow tanks 2 and 3 has an outlet valve 34 or 25. Furthermore, powder sensors 35 or 26 are provided in the outlet areas of each of the overflow tanks 2 and 3. These monitor the inlet of the associated supply device in the form of a metering screw (also referred to as a conveyor screw) 36 or 27. Additionally, powder sensors 37 or 28 are provided at the outlet of each metering screw 36 or 27.

[0124] Overflow tanks 2 and 3 each have upper powder sensors 31 and 22 and lower powder sensors 32 and 23 for monitoring the filling level of overflow tanks 2 and 3. Furthermore, overflow tanks 2 and 3 are provided with metering cells 33 and 24, respectively. To adjust (equalize) the pressure, valves 30 and 21 are provided at the top of each of the overflow tanks 2 and 3, respectively. Overflow tanks 2 and 3 are connected to the conveying line via valves 30 and 21, respectively. For this purpose, valves 38 and 29 are further provided at each access point to the conveying line.

[0125] The process chamber is connected to a line connecting valves 31 and 21 and valves 38 and 29 via corresponding valves 20 and 18 for pressure adjustment.

[0126] The powder is transported from overflow tanks 2 and 3 to buffer container 4 via a transport line. Above buffer container 4, a cyclone 42 is positioned to separate the powder.

[0127] After the powder is separated in the cyclone 42, the conveying gas flows through the conveying line to the filter 41, where any remaining powder particles are filtered out. To clean the filter, a compressed gas supply source 39 is in contact with the filter 41 and can be switched on or off by a control device. Downstream of the filter 41 is a valve 40. The conveying circuit returns to the conveying device 79, which is provided in the form of a pump 79. The path of the conveying gas starts from the valve 40 and passes through the pump protection filter 74, the dew point sensor 75, the oxygen sensor 76, the redundant oxygen sensor 77, the pressure sensor 78, and more precisely, the pressure sensor 78 on the suction side of the pump, in this order.

[0128] The transport gas flows from the pump 79, through the pressure sensor 80 on the pump pressure side (not individually shown on the pump pressure side in the schematic diagram of Figure 4). Downstream of the pressure sensor 80, a pressure compensation tank 84 is provided. This tank is equipped with an inert gas supply source 82 and a safety valve 83. The pressure compensation tank 84 plays a role in preventing excessive positive pressure on the pump pressure side, i.e., downstream of the pump 79.

[0129] An exhaust valve 81 is provided between the pressure sensor 80 and the pressure compensation tank 84, allowing gas to be discharged from the conveying line through the exhaust valve 81. Further downstream of the pressure compensation tank 84 is a speed / temperature sensor 86. After exhausting the ports via valves 88 and 87, the conveying gas can be directed by opening valve 72 to convey powder from the main storage unit 6, or by opening valve 73 to convey powder from the external tank 8, or by conveying powder from one or both of the overflow tanks 2 and 3.

[0130] When valve 72 is open, powder from the main storage tank 6 is introduced into the gas flow via valve 60, and then the transport gas flows to cyclone 9 located above the first tank 1. There the powder is separated and can be transported into the first tank 1. The transport gas flows through cyclone 42, through filter 41, and back to pump 79, following the aforementioned path (including multiple sensors).

[0131] When valve 73 is open, powder from external tank 8 can be added to the conveying gas flow by supply device 70 (conveyor screw 70). Furthermore, powder can be added from overflow tank 3 via conveyor screw 27 and / or from overflow tank 2 via conveyor screw 36. The mixture of conveying gas and powder can flow to cyclone 42 as described above, where it can be conveyed to buffer container 4.

[0132] The powder discharged from the conveyor screw 58 of the main storage unit 6 is supplied to the conveying gas of the conveying line associated with valve 72 via valve 60, or alternatively or additionally, supplied to the conveying gas of the conveying line associated with valve 73 via valve 61.

[0133] The powder separated by the cyclone 9 enters the first tank 1 via the inlet valve 12. From there, the powder is transported to the intermediate tank 2102 (also called a hopper) via the outlet valve 16, for example by gravity. The powder is then supplied from the intermediate tank 2102 to the process chamber 1011 of the apparatus 1100 via the loader 2104 and can be used in the additive manufacturing process.

[0134] The powder separated by the cyclone 42 enters the buffer container 4 via the inlet valve 44. The powder is then supplied from the buffer container 4 to the sieving device 5 via the outlet valve 48 (by gravity). The sieving device 5 plays a role in filtering out large particles and impurities from the powder, especially if the powder supplied to the sieving device 5 has already been used in the additive manufacturing process, for example, if it was supplied from one or both of the overflow tanks 2 and 3.

[0135] The sieving device 5 has a feeding device 49 in the form of a conveyor screw 49 for quantitatively supplying the powder to be sieved to the ultrasonic sieve 50 of the sieving device 5. The sieved powder or sieved particles are supplied via a line to the oversized particle container 7.

[0136] The sieved powder enters the main storage section 6 via the inlet valve 52. From the main storage section 6, the powder is supplied to the first tank 1 as described above via the outlet valve 56 and the conveyor screw 58 of the air transport line.

[0137] Furthermore, an external tank 8 can be connected to the conveying line, and the external tank 8 may be, for example, a mobile tank that can be connected to the conveying line via a suitable interface. Alternatively, for example, a mobile tank can be connected to the external tank 8 via the inlet valve 63 of the external tank 8 to supply fresh powder to the system.

[0138] The powder from the external tank 8 is sent to the conveyor screw 70 via the outlet valve 67 of the external tank 8 and the inlet valve 68 of the conveyor screw 70. The powder then enters the conveying line and is transported by the gas flow when the valve 73 is open.

[0139] 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 adjustment (equalization), powder containers 1, 2, 3, 4, 6, and 8 also have valves 10 or 11, 30, 21, 43, 51, and 62, respectively. Through these pressure adjustment valves, each powder container is connected to a conveying line through its respective pressure adjustment line, to which the supply gas flows. However, in the case of tank 1, the pressure equalization line is connected to an intermediate tank.

[0140] The pressure equalization lines for powder containers 2, 3, 4, 6, and 8 are connected to the conveying line via corresponding valves 38, 29, 8 (and similarly for containers 4 and 6) and 87.

[0141] To measure the filling level of powder containers 1, 2, 3, 4, 6, and 8, each powder container 1, 2, 3, 4, 6, and 8 has upper powder sensors 13, 31, 22, 45, 53, and 64 and lower powder sensors 14, 32, 23, 46, 54, and 65.

[0142] Furthermore, each powder container 1, 2, 3, 4, 6, and 8 is equipped with weighing cells 15, 33, 24, 47, 55, and 66. These are also useful for measuring the weight of each container and thus determining the filling level of each container.

[0143] In particular, to prevent and / or detect clogging, powder sensors 35, 26, 57, and 69 are provided at the inlets of conveyor screws 36, 27, 58, and 70, and powder sensors 37, 28, 59, and 71 are provided at the outlets of conveyor screws 36, 27, 58, and 70.

[0144] The individual elements of the bulk material transport system shown in Figure 4 are listed below again by reference number, but this list is not exhaustive.

[0145] 1 - Tank 1 2 - Front overflow tank 3 - Rear overflow tank 4 - Rock 5 - Sieve 6 - Main Storage Unit 7 - Oversized Particle Barrel (Oversized Particle Container) 8 - External Tank Module (External Tank) 9 - Cyclone 10 - Pressure regulating valve, first tank 11 - Pressure regulating valve, first tank, machine side 12 - Inlet valve, first tank 13 - Upper powder sensor, first tank 14 - Lower powder sensor, first tank 15 - Measuring cell, first tank 16 - Outlet valve, first tank 17 - Inlet valve, rear overflow tank 18 - Pressure regulating valve, rear overflow tank, machine side 19 - Inlet valve, front overflow tank 20 - Pressure regulating valve, front overflow tank, machine side 21 - Pressure regulating valve, rear overflow tank 22 - Upper powder sensor, rear overflow tank 23 - Lower powder sensor, rear overflow tank 24 - Measuring cell, rear overflow tank 25 - Outlet valve, rear overflow tank 26 - Inlet powder sensor, supply screw, rear overflow tank 27 - Supply screw, rear overflow tank 28 - Outlet powder sensor, feed screw, rear overflow tank 29 - Pressure regulating valve, conveyor line, rear overflow tank 30 - Pressure regulating valve, front overflow tank 31 - Upper powder sensor, front overflow tank 32 - Lower powder sensor, front overflow tank 33 - Measuring cell, front overflow tank 34 - Outlet valve, front overflow tank 35 - Inlet powder sensor, supply screw, front overflow tank 36 - Supply screw, front overflow tank 37 - Outlet powder sensor, feed screw, front overflow tank 38 - Pressure regulating valve, conveyor line, front overflow tank 39 - Compressed gas supply source, filter cleaning 40 - Suction valve, filter 41 - Filter 42 - Cyclone 43 - Pressure regulating valve, lock 44 - Inlet valve, lock 45 - Upper powder sensor, lock 46 - Lower powder sensor, lock 47 - Measuring cell, lock 48 - Outlet valve, lock 49 - Supply screw, sieve 50 - Ultrasonic sieve 51 - Pressure regulating valve, main storage unit 52 - Inlet valve, main storage unit 53 - Upper powder sensor, main storage unit 54 - Lower powder sensor, main storage unit 55 - Weighing cell, main storage unit 56 - Outlet valve, main storage unit 57 - Inlet powder sensor, supply screw, main storage unit 58 - Supply screw, main storage section 59 - Outlet powder sensor, supply screw, main storage unit 60 - Outlet powder valve "a" 61 - Outlet powder valve "b" 62 - Pressure regulating valve, external tank module 63 - Inlet valve, external tank module 64 - Upper powder sensor, external tank module 65 - Lower powder sensor, external tank module 66 - Measuring cell, external tank module 67 - Outlet valve, external tank module 68 - Inlet valve, supply screw, external tank module 69 - Inlet powder sensor, supply screw, external tank module 70 - Supply screw, external tank module 71 - Outlet powder sensor, feed screw, external tank module 72 - Gas supply valve "a" 73 - Gas supply valves "b" and "c" 74 - Pump protection filter 75 - Dew point sensor 76 - Oxygen sensor 77 - Redundant oxygen sensors 78 - Pump suction side pressure sensor 79 - Pump 80 - Pump pressure side pressure sensor 81 - Exhaust valve 82 - Inert gas supply source, pressure compensation tank 83 - Safety valves, pressure compensation tanks 84 - Pressure Compensation Tank 85 - Inert gas supply source, conveyor line 86 - Pressure and temperature sensors 87 - Pressure regulating valves, conveyor lines, external tank modules 88 - Pressure regulating valve, conveying line, main storage unit

[0146] In relation to the arrangement of the bulk material transport system shown in Figure 4 above, at least three transport processes ac can be implemented. In other words, the bulk material transport system comprises at least three transport circuits ac, where these transport circuits share, at least partially, a transport line through which the transport gas circulates. Furthermore, two transport processes, particularly transport processes b and c described later, can be operated in parallel. This allows the powders from the overflow tanks 2 and 3 and the external tank 8 to be mixed, and the powders to be mixed in the buffer container 4.

[0147] The individual transport processes and transport circuits are described below. These are shown in Figures 5-7. Figure 5 shows transport process a, Figure 6 shows transport process b, and Figure 7 shows transport process c. Active elements are shown in bold so that the flow of powder or gas can be tracked.

[0148] Conveying process a (Figure 5) In conveying process a, the powder is conveyed from the main storage unit 6 (source tank) to the first tank 1 (target tank). Conveying in conveying process a includes opening the first valves 56 and 60. The powder in the main storage unit 6 is powder that has been pre-sieved by the sieving device 5. The powder can be supplied from the first tank 1 to the additive manufacturing process in the process chamber. The powder is supplied to the conveying line via the conveyor screw 58 and separated by the cyclone 9. The conveying gas returns to the pump 79 via the filter 41.

[0149] Conveying process b (Figure 6) 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). Conveying in conveying process b first involves opening valves 25 and 34. The powder in the overflow tank may be contaminated powder that was not solidified in the additive manufacturing process. The contaminated powder is sent from buffer container 4 to sieving device 5. The powder is sent to the conveying line via conveyor screws 36 and 27 and separated by cyclone 42. The conveying gas returns to pump 79 via filter 41.

[0150] Conveying process c (Figure 7) In conveying process c, the powder is conveyed from the external tank 8 (source tank) to the buffer container 4 (target tank). Conveying in conveying process c first involves opening valves 67 and 68. The powder in the external tank 8 may be contaminated powder supplied to the process from the outside, but it may also be fresh, uncontaminated powder. The powder conveyed to the buffer container 4 is sent to the sieving device 5. The powder is sent to the conveying line via the conveyor screw 69 and separated by the cyclone 42. The conveying gas returns to the pump 79 via the filter 41.

[0151] During each operation of the transport process ac described above (i.e., transport operation), a method can be implemented to determine the gas velocity (set velocity) and adjust the pump 79 to transport the transport gas at the determined set velocity. For this purpose, step AD described above can be performed by the control device of the bulk material transport system.

[0152] In one embodiment, for example, the gas density of the gas flow is determined using sensor data from a pressure sensor 80, a temperature sensor 86, and an oxygen sensor 76. The shape of each conveyor screw located at the outlet of each raw material tank is taken into consideration in order to determine the mass flow rate of the bulk material. The velocity sensor 86 is used to adjust the velocity of the gas conveyed by the pump 79, for example by PID control.

[0153] Furthermore, limit control, as shown in Figure 3, can be implemented in relation to each of the transport processes ac (see the explanation above).

[0154] The closed powder circuit provided by the AC conveying process has several advantages, particularly in that it minimizes the need for manual intervention by the equipment operator and minimizes contact with the powder. Contact with powder can pose health risks, for example, and certain types of powders can pose explosion or fire hazards. Automatic adjustment of the conveying speed has the advantage of allowing for quick and easy setting of the optimal operating point (i.e., optimal conveying speed) for different powder types and different process conditions.

Claims

1. A bulk material transport system, particularly a system for transporting raw material powder in an apparatus for manufacturing a three-dimensional workpiece by irradiating a layer of raw material powder with electromagnetic radiation or particle radiation, A conveying line configured to convey a gas flow and, at least partially, a bulk material flow moved by the gas flow, A supply device configured to supply a predetermined amount of bulk material to the gas flow at regular intervals, wherein the amount is determined by a control value applied to the supply device, and A conveying device configured to convey the gas flow through the aforementioned conveying line, At least one measuring device for measuring at least one parameter of the gas flow, A control device is provided, The control device is Based on at least one parameter of the measured gas flow, the gas density of the gas flow is determined. Based on the control value applied to the supply device, the bulk material mass flow rate of the bulk material flow is determined. Based on the gas density and the bulk material mass flow rate, the set velocity of the gas flow is determined. The conveying device is configured to control the conveying device so as to convey the gas flow at the determined set speed. Bulk material handling system.

2. The bulk material transport system according to claim 1, wherein the gas density is determined based on at least one of the parameters of the gas flow, namely oxygen content, pressure, temperature, dew point, and humidity.

3. The aforementioned gas density is, It can be found using the following formula: p ｍｅａｓ is the measured pressure of the gas flow, and T ｍｅａｓ is the measurement temperature of the gas flow, and p ｎ It is a predetermined normal pressure, T ｎ ρ is at a predetermined room temperature, ｍｉｘｔｕｒｅ teeth, It is given by the following formula, ρ ａｉｒ is the known density of air, which is a component of the gas stream, ρ ｐｒｏｔｅｃｔｉｖｅ ｇａｓ is the known density of the protective gas, which is a component of the gas stream, oxygen content ａｉｒ is the known oxygen content of the air, oxygen content ｍｅａｓｕｒｅｄ is the measured oxygen content of the gas stream, the bulk material conveying system according to claim 2.

4. The bulk material conveying system according to any one of claims 1 to 3, wherein the control value applied to the supply device is the motor speed of the motor of the supply device, in particular the motor for driving the conveyor screw of the supply device.

5. The set speed v of the gas flow ｓｅｔ Determining the set velocity v includes calculating the jump velocity based on the determined gas density and the determined bulk material mass flow rate, and the set velocity v ｓｅｔ teeth, It can be found using the following formula: Check here ｓａｌｔａｔｉｏｎ v is the calculated jump velocity of the bulk material being transported. ｓａｆｅｔｙ The bulk material transport system according to any one of claims 1 to 4, wherein is a predetermined safe speed.

6. The aforementioned jumping speed is, It is calculated using the following formula: Here M ｓ is the calculated mass flow rate (kg / s) of the bulk material, and g is the predetermined gravitational acceleration (m / s²). ２ ) where D is the diameter of the conveyor line (m) and ρ is the calculated gas density of the gas flow (kg / m³). ３ The bulk material transport system according to claim 5, wherein a and b are parameters that depend on the particle size d of the bulk material.

7. The bulk material conveying system according to any one of claims 1 to 6, wherein the control of the conveying device for conveying the gas flow at the determined set speed is performed using a speed sensor for measuring the speed of the gas flow and a control loop including, in particular, a PID control device.

8. The control device further, It is determined whether at least one measurement parameter of the bulk material transport system exceeds a predetermined maximum value for each parameter. A bulk material transport system according to any one of claims 1 to 7, wherein when at least one of the measurement parameters exceeds the predetermined maximum value, the control value of the supply device is reduced by a predetermined value.

9. The control device further, The bulk material transport system according to claim 8, wherein when at least one of the measurement parameters is below the predetermined maximum value, the control value of the supply device is increased by a predetermined value.

10. The bulk material conveying system according to claim 8 or 9, wherein the at least one parameter includes at least one of the following parameters: conveying speed, pump outlet pressure, pump capacity, and supply rate of bulk material per hour.

11. The bulk material transport system according to any one of claims 1 to 10, wherein the control device is configured to terminate transport by stopping the transport device when at least one of the following events is detected: namely, the source tank from which the bulk material is discharged by the supply device is empty; the target tank to which the bulk material is transported is full; a predetermined maximum transport time has been exceeded; or the total pressure loss of the transport gas exceeds a predetermined limit value.

12. The bulk material conveying system according to any one of claims 1 to 11, further comprising a pressure adjustment tank connected to a conveying line downstream of the conveying device and upstream of the supply device.

13. The apparatus includes at least one first transport circuit for transporting raw material powder from a main storage unit to a first tank of an apparatus for manufacturing a three-dimensional workpiece by irradiating a layer of the raw material powder 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, and in the manufacturing process within the process chamber of the apparatus, powder is supplied from the intermediate tank. The bulk material conveying system according to any one of claims 1 to 12, wherein the upper inlet of the main storage section is connected to the outlet of a sieve for sieving the raw material powder.

14. The system includes at least one second transport circuit for transporting raw material powder from an overflow tank to a buffer container, The overflow tank is configured to receive excess powder from the process chamber of an apparatus that manufactures a three-dimensional workpiece by irradiating a layer of raw material powder with electromagnetic radiation or particle radiation. The bulk material conveying system according to any one of claims 1 to 13, wherein the lower outlet of the buffer container is connected to the inlet of a sieve for sieving the raw material powder.

15. The system includes at least one third transport circuit for transporting raw material powder from an external tank to a buffer container, The external tank is either detachably attached to or detachably connected to the bulk material transport system. The bulk material conveying system according to any one of claims 1 to 14, wherein the lower outlet of the buffer container is connected to the inlet of a sieve for sieving the raw material powder.

16. The bulk material transport system according to any one of claims 1 to 15, wherein the supply device is located at the outlet of each source tank, and a cyclone is located at the inlet of each target tank for separating the raw material powder from the gas flow and supplying the raw material powder into the target tank.

17. A method for transporting bulk materials, particularly a method for transporting raw material powder in an apparatus for manufacturing a three-dimensional workpiece by irradiating a layer of raw material powder with electromagnetic radiation or particle radiation, The gas flow and the bulk material flow moved by the gas flow are transported through a conveying line. A predetermined amount of bulk material, determined by a control value applied to the supply device, is supplied to the gas flow at regular intervals by the supply device. Using a conveying device, the gas flow is conveyed through the conveying line, Using a measuring device, 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 value applied to the supply device, the bulk material mass flow rate of the bulk material flow is determined, Based on the aforementioned gas density and the bulk material mass flow rate, the set velocity of the gas flow is determined. The gas flow is transported at the determined set speed, Methods that include...

18. The method according to claim 17, wherein the gas density is determined based on at least one of the parameters of the gas flow, namely oxygen content, pressure, temperature, dew point, and humidity.

19. The aforementioned gas density is, It can be found using the following formula: p ｍｅａｓ is the measured pressure of the gas flow, and T ｍｅａｓ is the measurement temperature of the gas flow, and p ｎ It is a predetermined normal pressure, T ｎ ρ is at a predetermined room temperature, ｍｉｘｔｕｒｅ teeth, It is given by the following formula, ρ ａｉｒ ρ is the known density of air, which is a component of the gas flow. ｐｒｏｔｅｃｔｉｖｅ ｇａｓ This is the known density of the protective gas, which is a component of the gas flow, and the oxygen content ａｉｒ This is the known oxygen content of the air. ｍｅａｓｕｒｅｄ The method according to claim 18, wherein is the measured oxygen content of the gas flow.

20. The method according to any one of claims 17 to 19, wherein the control value applied to the supply device is the motor speed of the motor of the supply device, in particular the motor for driving the conveyor screw of the supply device.

21. The set speed v of the gas flow ｓｅｔ Determining the set velocity v includes calculating the jump velocity based on the determined gas density and the determined bulk material mass flow rate, and the set velocity v ｓｅｔ teeth, It can be found using the following formula: Check here ｓａｌｔａｔｉｏｎ v is the calculated jump velocity of the bulk material being transported. ｓａｆｅｔｙ The method according to any one of claims 17 to 20, wherein is a predetermined safe speed.

22. The aforementioned jumping speed is, It is calculated using the following formula: Here M ｓ is the calculated mass flow rate (kg / s) of the bulk material, and g is the predetermined gravitational acceleration (m / s²). ２ ) where D is the diameter of the conveyor line (m) and ρ is the calculated gas density of the gas flow (kg / m³). ３ The method according to claim 21, wherein a and b are parameters that depend on the particle size d of the bulk material.

23. The method according to any one of claims 17 to 22, wherein the control of the conveying device for conveying the gas flow at the determined set speed is performed using a speed sensor for measuring the speed of the gas flow and a control loop including, in particular, a PID control device.

24. To determine whether at least one measurement parameter of the bulk material transport system exceeds a predetermined maximum value for each parameter, The method according to any one of claims 17 to 23, further comprising: when the at least one measurement parameter exceeds the predetermined maximum value, reducing the control value of the supply device by a predetermined value.

25. The method according to claim 24, further comprising increasing the control value of the supply device by a predetermined value when the at least one measurement parameter is below the predetermined maximum value.

26. The method according to claim 24 or 25, wherein the at least one parameter includes at least one of the following parameters: transport speed, pump outlet pressure, pump capacity, and bulk material supply rate per hour.

27. The method according to any one of claims 17 to 26, further comprising terminating transport by stopping the transport device when at least one of the following events is detected: namely, the source tank from which the bulk material is discharged by the supply device is empty; the target tank to which the bulk material is transported is full; a predetermined maximum transport time has been exceeded; or the total pressure loss of the transport gas exceeds a predetermined limit.

28. The process includes transporting raw material powder from a main storage unit to a first tank of an apparatus for manufacturing a three-dimensional workpiece by irradiating a layer of the raw material powder with electromagnetic radiation or particle radiation, via at least one first transport circuit. The lower outlet of the first tank is connected to the upper inlet of the intermediate tank of the apparatus, and in the manufacturing process within the process chamber of the apparatus, powder is supplied from the intermediate tank. The method according to any one of claims 17 to 27, wherein the upper inlet of the main storage section is connected to the outlet of a sieve for sieving the raw material powder.

29. The process includes transporting the raw material powder from an overflow tank to a buffer container via at least one second transport circuit. The overflow tank is configured to receive excess powder from the process chamber of an apparatus that manufactures a three-dimensional workpiece by irradiating a layer of raw material powder with electromagnetic radiation or particle radiation. The method according to any one of claims 17 to 28, wherein the lower outlet of the buffer container is connected to the inlet of a sieve for sieving the raw material powder.

30. The process includes transporting the raw material powder from an external tank to a buffer container via at least one third transport circuit. The external tank is either detachably attached to or detachably connected to the bulk material transport system. The method according to any one of claims 17 to 29, wherein the lower outlet of the buffer container is connected to the inlet of a sieve for sieving the raw material powder.

31. The method according to any one of claims 17 to 30, wherein the supply device is located at the outlet of each source tank, and a cyclone is located at the inlet of each target tank for separating the raw material powder from the gas flow and supplying the raw material powder into the target tank.

Images