Method for controlling the operation of a sieving device, sieving device, powder conveying system, and apparatus for manufacturing a three-dimensional workpiece.

Abstract

A method for controlling the operation of a sieving apparatus includes the steps of (i) supplying the powder to be sieved (56) onto the sieve through a powder inlet (22) and (ii) driving the sieve with a first driving force over a first time interval, the first driving force being set such that when the sieve is driven continuously with the first driving force, the powder to be sieved (56) flows over the entire sieve surface and / or into the oversized particle outlet (32). After the first time interval has elapsed, in step (iii), the sieve is driven over a second time interval with a second driving force lower than the first driving force. After the second time interval has elapsed, steps (ii) and (iii) are repeated.

Description

Technical Field

[0001] The present invention relates to a sieving device suitable for use in a powder conveying system of an apparatus for manufacturing a three-dimensional workpiece using, for example, a generative layer construction process, and a method for controlling the operation of the sieving device. The present invention also relates to an apparatus for manufacturing a three-dimensional workpiece using such a generative layer construction process and including such a sieving device.

Background Art

[0002] In a generative layer construction process for manufacturing a three-dimensional workpiece, particularly in so-called powder bed melting, raw material powder or granules are applied in layers on a carrier, and electromagnetic radiation such as laser light or particle radiation is selectively irradiated according to the desired shape of the workpiece to be manufactured. The radiation penetrating into the powder layer heats the raw material powder particles and melts or sinters them. Next, until the workpiece reaches the desired shape and size, raw material powder layers are sequentially applied to the layer on the carrier that has already been treated with radiation and solidified. The raw material powder can be composed of a ceramic, metal, or plastic material, or may be composed of a mixture of these materials. The generative layer construction process, particularly the powder bed melting process, can be used, for example, in the manufacture of prototypes, tools, spare parts, or medical prostheses such as dental restorations or orthopedic prostheses, and in the repair of parts based on CAD data.

[0003] An apparatus for manufacturing a three-dimensional workpiece by selectively irradiating raw material powder, which is well-known from, for example, EP2335848B1, includes a process chamber sealed against the surrounding atmosphere and a carrier disposed in the process chamber for accommodating the raw material powder to be irradiated. This apparatus includes an irradiation device having a radiation source, particularly a laser source, and an optical unit. The optical unit serves to selectively irradiate the irradiation beam generated by the radiation source onto the raw material powder layer applied to the carrier according to the shape of the workpiece to be manufactured. When manufacturing a three-dimensional workpiece by selectively irradiating the powder layer applied to the carrier, the powder particles are melted and / or sintered by the radiation energy introduced into the raw material powder.

[0004] In additive manufacturing of 3D parts on a powder bed (particularly selective laser melting and / or selective laser sintering), excess powder is generated when individual powder layers are applied, and this excess powder can be collected in one or more collection containers. Furthermore, excess solidified powder can be recovered when the workpiece is unpacked. The excess powder can be reused in the additive manufacturing process after appropriate reprocessing. For example, the reprocessed powder can be reused as raw material powder in the selective laser melting or laser sintering process, or mixed with fresh raw material powder used in these processes. However, reusing excess powder in the additive manufacturing process may contaminate the powder bed with particulate impurities or attached or sintered powder aggregates, potentially degrading the quality of the workpiece.

[0005] Therefore, sieving is an essential step in the reprocessing of excess powder, playing a role in removing unwanted particulate impurities larger than the particle size of the powder. Furthermore, the excess powder can be subjected to further powder reprocessing steps such as drying, washing, and component separation before and / or after sieving.

[0006] DE202021102494 describes a powder sieving apparatus suitable for use in equipment that manufactures three-dimensional workpieces by selective electron beam melting, selective laser melting, laser deposition welding, laser metal deposition, or selective laser sintering. The apparatus comprises a base unit equipped with a vibration generator and a control unit that controls the vibration generator. The base unit is equipped with an interface for connecting interchangeable modules, which are equipped with sieves and housings that hold the sieves. The interchangeable modules can be connected to the base unit via the interface.

[0007] The present invention aims to provide a sieving device that enables efficient sieving of powders and is therefore particularly suitable for use in a powder conveying system of an apparatus for manufacturing three-dimensional workpieces using a generative layering process, and a method for controlling the operation of the sieving device. Furthermore, the present invention aims to provide an apparatus for manufacturing three-dimensional workpieces using a generative layering process that enables the efficient production of high-quality workpieces.

[0008] This objective is addressed by a method for controlling the operation of a sieving apparatus having the features of claim 1, a sieving apparatus having the features of claim 13, and an apparatus for manufacturing a three-dimensional workpiece using a generative layer construction process having the features of claim 21.

[0009] In a method for controlling the operation of a sieving device, in step (i), the powder to be sieved is supplied to the sieve from the powder inlet. The sieve may comprise a sieve frame stretched with a sieve mesh defining the sieve surface. The sieve frame may be connected to or positioned in a sieve container. The sieved powder, after passing through the sieve mesh, is collected in the sieve container. The sieve container has a cross-section that tapers downwards, and the powder collected and sieved in the sieve container can be discharged from the sieve container by gravity through a sieved powder outlet provided 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 sieve mesh toward the sieve container. The powder inlet and oversized particle outlet are preferably located in the region of the side end opposite the sieve surface.

[0010] The sieving device preferably includes a drive device for driving the sieve. The drive device preferably engages with the sieve frame, and during the operation of the sieving device, the drive device causes the sieve frame, and consequently the sieve mesh, to vibrate. The drive device may be a mechanical drive device that vibrates and excites the sieve. However, preferably, the drive device is configured in the form of an ultrasonic drive device and is configured to apply ultrasonic vibrations to the sieve. By using an ultrasonic drive device instead of a mechanical drive device, it is possible to improve the powder processing capacity of the sieve, i.e., the sieving performance, and consequently improve the efficiency of the sieving device. In particular, by providing an ultrasonic drive device in the sieving device, the powder processing capacity of the sieve can be increased by about four times compared to a mechanically driven sieving device.

[0011] In ultrasonic drive devices, the driving force is primarily determined by frequency. While amplitude also affects the power consumption of the drive motor, frequency is the most important parameter for driving force because it influences the vibration of the sieve mesh and, consequently, the separation effect of the sieve. Higher frequencies improve the separation effect, leading to an improvement in the powder processing capacity of the sieve, i.e., the sieving performance.

[0012] In a loose powder bulk on a plane, a bulk angle is formed. The bulk angle is the angle between the horizontal plane and the maximum inclination angle that the powder can take without being further affected; that is, the angle at which the powder begins to flow when poured onto an inclined surface. The bulk angle depends on various factors such as the size and shape of the powder particles. Furthermore, the bulk angle is affected by process parameters such as relative humidity. Powder bulk sieved by a sieving device may have a bulk angle of, for example, about 20° to about 40°, preferably about 25° to about 35°, and particularly preferably about 30°.

[0013] On the other hand, the wall friction angle is defined as the angle between the horizontal plane and the angle at which the powder adheres to the wall and stops flowing. The wall friction angle depends on the type and properties of the wall, as well as the surface characteristics of the powder particles. The powder bulk to be sieved by the sieving device may have a wall friction angle of, for example, about 10° to about 30°, preferably about 15° to about 25°, and particularly preferably about 20°.

[0014] When powder is supplied from the powder inlet of the sieving device, a bulk cone is formed on the sieve, or sieve mesh. The shape and bulk angle of the bulk cone are affected by vibrations acting on the bulk cone, and consequently by the driving force of the drive mechanism that drives the sieve. In particular, as the driving force of the drive mechanism increases, the bulk angle decreases. At the same time, vibrations induced by the drive mechanism reduce wall friction, making it easier for the powder bulk to slide on the sieve surface. When the sieve is driven with a low driving force, the bulk cone formed below the powder inlet resembles a bulk cone formed on a stationary plane with a base region that occupies only a small portion of the sieve surface. In such operating conditions of the sieving device, only a small portion of the sieve surface adjacent to the powder outlet actually contacts the powder, resulting in a low utilization rate of the sieve surface.

[0015] On the other hand, when the sieve is driven with high force, the powder spreads across the entire sieve surface. In other words, the bulk angle of the bulk cone formed by the powder supplied onto the sieve from the powder inlet decreases as the driving force of the drive device for the sieve increases, and the wall friction angle also decreases similarly. As a result, the bottom area of ​​the bulk cone increases, improving the utilization rate of the sieve surface, and the part of the sieve surface that is far from the powder inlet and close to the oversized particle outlet is also covered with powder. However, if the bottom area of ​​the bulk cone becomes too large and the powder flows across the entire sieve surface, exposing the entire sieve surface to powder, there is a risk that the powder will flow into the oversized particle outlet without being screened. As a result, fine powder that can pass through the sieve mesh is wasted, and the screening efficiency decreases.

[0016] Therefore, in the method for controlling the operation of the sieving device, in step (ii), the sieve is driven by a first driving force over a first time interval. This first driving force is set so that when the sieve is driven continuously by the first driving force, the powder to be sieved flows across the entire sieve surface and / or into the oversized particle outlet. Thus, because the driving force is very high during the first time interval, if the sieving device is driven continuously, on the one hand, maximum utilization of the sieve area is guaranteed, but on the other hand, there is a high risk that at least unsieved powder will be lost from the oversized particle outlet.

[0017] Therefore, after the first time interval has elapsed, in step (iii), the sieve is driven for a second time interval with a second driving force lower than the first driving force. After the second time interval has elapsed, steps (ii) and (iii) are repeated, that is, the sieve is periodically driven alternately with the first high driving force and the second low driving force.

[0018] The first driving force may have different values ​​depending on the type of powder and process parameters (temperature, particle size distribution of the powder, moisture content of the powder, etc.). Therefore, the first driving force may be determined empirically before the sieving process, or it may be obtained from a driving force value table created in advance for each type of powder and process parameter. Alternatively, the first driving force may be selected based on empirical values.

[0019] In the first time interval, the high driving force allows for high sieve area utilization and, consequently, high sieving performance. Furthermore, in the first time interval, oversized particles are transported particularly toward the oversized particle outlet. Specifically, as the bulk cone "spreads out" across the entire sieve surface during the periodically repeated first time interval, oversized particles that gather and "accumulate" in a columnar shape within the bulk cone during the second time interval can be removed from the sieve surface through the oversized particle outlet. This suppresses the formation of so-called clogged particles, which occur when powder particles are pushed into the sieve mesh by back pressure and sieve vibration, causing the sieve mesh to become clogged. On the other hand, the decrease in driving force during the second time interval minimizes the loss of unsieved powder passing through the oversized particle outlet.

[0020] Therefore, the method for controlling the operation of the sieving apparatus described herein is particularly suitable for use in powder conveying systems of three-dimensional workpiece manufacturing equipment using generative layering processes, as it enables highly efficient sieving of powders. This process may require sieving large quantities of relatively expensive (metallic) powders. Furthermore, because the driving force changes periodically, the total mass of powder on the sieving mesh is reduced, and consequently, the stress on the sieving mesh is reduced. As a result, wear is reduced and the lifespan of the sieving mesh is extended.

[0021] Preferably, the second driving force is set such that when the sieve is continuously driven by the second driving force, the powder to be sieved forms a bulk cone in the powder inlet region on the sieve surface. This bulk cone substantially corresponds to the bulk cone formed on the stationary surface. The bulk cone formed on the sieve surface when the sieve is driven by the second driving force has a bulk angle that is up to 30%, preferably up to 20%, and especially preferably up to 10%, larger than the bulk angle of the bulk cone formed on the stationary surface. The bottom area of ​​the bulk cone formed on the sieve surface when the sieve is continuously driven by the second driving force occupies only a small section of the sieve surface located in the powder inlet region. Therefore, during the second time interval, the sieving device can be driven with a very low driving force. If this driving force is maintained continuously, there will be no or very little powder flowing into the oversized particle outlet without being sieved. However, on the other hand, the utilization rate of the sieve area is low, which reduces the amount of material the sieve can process, and consequently reduces the sieving performance. Therefore, the second driving force can be lower than the first driving force, but greater than zero.

[0022] However, in one or more embodiments, the second driving force may be zero. In this case, the sieve is not driven during the second time interval.

[0023] The second driving force may take on different values ​​depending on the type of powder and process parameters such as temperature, particle size distribution, and moisture content. Therefore, the second driving force may be determined empirically before the sieving process, or it may be obtained from a driving force value table created in advance for different powder types and process parameters. Alternatively, the second driving force may be selected based on empirical values.

[0024] In principle, the sieve surface can be positioned coplanar with the horizontal plane. However, it is also possible that the sieve surface is inclined with respect to the horizontal plane. When the sieve is driven by a second driving force, the bulk angle of the bulk cone formed in the powder inlet region on the sieve surface is preferably adjusted to match the arrangement of the sieve surface. This means that when the sieve surface is positioned coplanar with the horizontal plane, the powder supplied onto the sieve from the powder inlet preferably forms a symmetrical bulk cone having a constant bulk angle along its circumference. On the other hand, when the sieve surface is inclined with respect to the horizontal plane, it is preferable that the powder supplied to the sieve from the powder inlet forms a bulk cone whose bulk angle changes along its circumference depending on the direction of inclination and the inclination angle of the sieve surface.

[0025] Preferably, the sieve surface of the sieve is inclined with respect to the horizontal plane so that the powder supplied from the powder inlet flows by gravity toward the oversized particle outlet. In other words, it is preferable that the sieve surface of the sieve is inclined from the region below the powder inlet toward the oversized particle outlet. This not only facilitates the diffusion of the powder on the sieve surface but also facilitates the removal of oversized particles from the sieve surface toward the oversized particle outlet. Therefore, it is preferable that the bulk angle of the bulk cone formed on the sieve surface when the sieve is driven by the second driving force is smaller in the circumferential portion of the bulk cone facing the oversized particle outlet than in the circumferential portion of the bulk cone opposite the oversized particle outlet.

[0026] However, it is preferable that the inclination angle of the sieve surface of the sieve with respect to the horizontal plane is smaller than the bulk angle of the bulk cone formed by the powder to be sieved on the horizontal plane. Thereby, at least when the sieve is driven by the second driving force, a stable bulk cone is formed in the powder inlet region, and it is ensured that the powder does not flow down uncontrollably on the sieve surface. For example, the inclination angle of the sieve surface of the sieve with respect to the horizontal plane can be about 10° to about 25°, preferably about 15° to about 20°, and particularly preferably about 17°.

[0027] Similar to the first driving force, the first time interval can also be set to different values according to process parameters such as the type of powder, temperature, particle size distribution of the powder, and moisture content of the powder. Therefore, it is preferable that the first time interval is a value determined empirically prior to the sieving process of the powder to be sieved. However, the first time interval can also be obtained from a pre-created value table including different values of the first time interval for each type of powder and process parameter, or can be selected based on empirical values.

[0028] When determining the first time interval, it is preferable that the first time interval ends when the powder to be sieved flows into the oversize particle outlet. The inflow of the powder to be sieved into the oversize particle outlet can be detected by an oversize particle sensor. The oversize particle sensor is preferably arranged in the region of the oversize particle outlet.

[0029] Preferably, the first time interval is set so that by the end of the first time interval, the sieve surface utilization rate does not exceed about 70% to about 90%, preferably about 75% to about 85%, and particularly preferably about 80% of the total sieve surface area of the sieve. In other words, the first time interval preferably provides a "time safety margin" so that the powder does not spread over the entire sieve surface during the first time interval. Thereby, it is surely prevented that the unsieved powder is lost from the oversize particle outlet.

[0030] The second time interval can also be set to a different value depending on the type of powder and various process parameters such as temperature, particle size distribution, and moisture content. Therefore, it is preferable that the second time interval is also a value that is empirically determined prior to the sieving process of the powder to be sieved. However, the second time interval can be obtained from a pre-created table of values ​​that includes different values ​​for the second time interval for each type of powder and process parameter, or it can be selected based on empirical values.

[0031] When determining the second time interval, it is preferable that the second time interval ends no later than when the powder to be sieved has formed a bulk cone of a specified size on the sieve surface in the powder inlet region. This prevents the bulk cone from becoming excessive and blocking the powder inlet. On the other hand, during the transition to the first time interval, the sieve is driven with increased driving force, and as a result the sieve's processing capacity increases, thus improving the efficiency of the sieving process. The formation of a bulk cone of a specified size can be detected, for example, by a weighing sensor. The weighing sensor is preferably located in the powder inlet region.

[0032] The following describes the control of powder supply through the powder inlet of the sieve, which can also be claimed independently of the drive control described above.

[0033] JPEG2026521379000002.jpg82169

[0034] JPEG2026521379000003.jpg41162

[0035] JPEG2026521379000004.jpg52164

[0036] JPEG2026521379000005.jpg17170

[0037] JPEG2026521379000006.jpg41162

[0038] JPEG2026521379000007.jpg32169

[0039] In addition to this, or instead, the sieves may be cleaned at the end of each sieving process. The sieving process may be terminated, for example, when the powder supply container for the powder to be sieved, which can be connected to the powder inlet of the sieving apparatus, is empty.

[0040] In addition to, or instead of, the sieve cleaning can also be started manually, i.e., by user input. In addition to, or instead of, the sieve cleaning can also be started based on time control, for example, after a predetermined time (i.e., absolute time) has elapsed since the last sieve cleaning, or after a predetermined operating time of the sieving device (i.e., the time the sieving device has been operating).

[0041] It is preferable to stop the supply of powder from the powder inlet when starting sieve cleaning. Furthermore, any powder remaining in the sieve can be sieved off before starting sieve cleaning. After starting sieve cleaning, the sieve can be driven with maximum driving force. In addition to or instead of this, after starting sieve cleaning, a vibrator that drives the sieve independently of the drive device of the sieving device can be operated. The contact angle of the vibrator with respect to the sieve, the driving amplitude of the vibrator, and / or the driving frequency of the vibrator are preferably variably adjustable.

[0042] In addition to, or instead of, the powder to be sieved can be supplied to the sieve discontinuously from the powder inlet, at least temporarily. In the case of discontinuous powder supply, the powder to be sieved can first be supplied to the sieve from the powder inlet, but the sieve will not be driven until the powder to be sieved forms a bulk cone of a specified size on the sieve surface in the powder inlet region. The formation of a bulk cone of a specified size can be detected by a weighing sensor provided in the powder inlet region. After the powder supply is completed, the sieve can be driven to sieve the powder supplied on the sieve surface.

[0043] JPEG2026521379000008.jpg72169

[0044] In a method for controlling the operation of a sieving device, powder can be supplied continuously or discontinuously. However, it is also possible that the powder supply may be temporarily continuous and temporarily discontinuous.

[0045] In addition to, or instead of, the continuous or discontinuous supply of powder described above, the powder to be sieved can be supplied at least temporarily through the powder inlet at a supply mass flow rate determined depending on the driving force used to drive the sieve. Preferably, the first supply mass flow rate through the powder inlet in a first time interval is greater than the second supply mass flow rate through the powder inlet in a second time interval. In other words, when the sieve is driven with a higher driving force in the first time interval, more powder is sent from the powder inlet to the sieve than in the second time interval when the sieve is driven with a lower driving force. This prevents powder stagnation and / or the accumulation of a large amount of powder on the sieve mesh, which reduces sieving performance and leads to an improvement in powder processing capacity.

[0046] Depending on the characteristics of the powder to be sieved, the first and / or second supply mass flow rates, the lengths of the first and second time intervals, and the first and second driving forces can be adjusted. The first and second supply mass flow rates may each be positive values ​​greater than 0. However, when the second supply mass flow rate is 0, i.e., during the second time interval in which the sieve is driven by a second low driving force, it is possible that no powder is supplied from the powder inlet to the sieve.

[0047] JPEG2026521379000009.jpg82169

[0048] Preferably, in a method for controlling the operation of a sieving device, a warning signal is output when the oversized particle rate exceeds a limit value. When processing raw material powder used in a 3D workpiece manufacturing device using a generative layering process with a sieving device, an excessively high oversized particle rate may indicate that the process parameters of the device are inappropriate. For example, an excessively high oversized particle rate may indicate that large welding spatter is generated during irradiation of the powder, which may remain in the powder layer and impair the quality of the manufactured workpiece. Therefore, by monitoring the oversized particle rate, the process parameters in a 3D workpiece manufacturing device using a generative layering process can be monitored.

[0049] In a preferred embodiment of a method for controlling the operation of a sieving apparatus, the sieving apparatus is sealed from the ambient atmosphere and filled with a protective gas during operation. This prevents undesirable oxidation of the powder being sieved by the sieving apparatus. Preferably, if the inert gas pressure inside the sieving apparatus falls below a threshold, additional protective gas can be supplied to the sieving apparatus. This allows for the detection and compensation of leaks in the sieving apparatus.

[0050] Furthermore, during the sieving process, the step response of the total mass flow rate of the sieved powder and the oversized particles to the supply mass flow rate can be monitored. The “step response” of the total mass flow rate of the sieved powder and the oversized particles to the supply mass flow rate is understood to be the time difference between the time a specified supply mass flow rate is supplied to the sieving device and the time when the corresponding sieved powder mass flow rate passes through the sieve mesh. Therefore, the step response is a time parameter that indicates the duration of the sieving process for a given powder mass flow rate. The supply mass flow rate can be measured, for example, using a first measuring device provided in a powder supply container connectable to the powder inlet of the sieving device. The total mass flow rate of the sieved powder and the oversized particles can be detected, for example, by second and third measuring devices provided in an oversized particle container connectable to the oversized particle outlet of the sieving device and a sieved powder container connectable to the sieved powder outlet of the sieving device. The supply mass flow rate and the sum of the mass flow rates of the sieved powder and oversized particles can be measured continuously. Therefore, the step response of the sum of the mass flow rates of the sieved powder and oversized particles to the supply mass flow rate can also be continuously monitored.

[0051] If the sieve mesh becomes clogged during the sieving process, the step response of the combined mass flow rate of the sieved powder and oversized particles to the supply mass flow rate becomes longer. On the other hand, if the step response of the combined mass flow rate of the sieved powder and oversized particles to the supply mass flow rate becomes shorter, especially if it falls below a certain limit value, it is an indication of a defect such as a torn sieve mesh. Therefore, it is preferable to output a warning signal when the step response of the combined mass flow rate of the sieved powder and oversized particles to the supply mass flow rate falls below a first limit value. In addition to this, or instead, when the step response of the combined mass flow rate of the sieved powder and oversized particles to the supply mass flow rate exceeds a second limit value, sieve cleaning can be initiated. This allows for monitoring of the sieving volume, in addition to monitoring the formation of bulk cones exceeding a certain size in the powder inlet region as described above, and enables the initiation of subsequent sieve cleaning as needed.

[0052] A method for controlling the operation of the sieving device may further include changing the inclination angle of the sieve surface with respect to the horizontal plane.

[0053] This embodiment, and all embodiments described later in relation to changes in the inclination angle, can be applied to one of the methods described above, and / or, independently thereof, to a method for controlling the operation of a sieving device.

[0054] Therefore, a method for controlling the operation of a sieving device for sieving powder in an additive manufacturing apparatus (for example, an apparatus for manufacturing a three-dimensional workpiece by selective electron beam melting, selective laser melting, laser deposition welding, laser metal deposition, or selective laser sintering) may include the steps of supplying the powder to be sieved onto the sieve through a powder inlet, driving the sieve, and changing the inclination angle of the sieve surface with respect to the horizontal plane.

[0055] Changing the inclination angle may include, for example, initially changing, and therefore setting, the inclination angle, which is performed in particular before the step of supplying the powder to be sieved. In addition to this, or instead, changing the inclination angle may be performed during the operation of the sieving device, for example at the start of the first and / or second time intervals.

[0056] The sieve is housed in an airtight, sealed housing, and its tilt angle can be changed by rotating the sieve relative to the housing. The airtight, sealed housing can be sealed airtight by a flap. The sieve can be inserted into the housing via the flap.

[0057] A first tilt angle can be set during the first time interval, and a second tilt angle can be set during the second time interval, either (a) the first tilt angle is smaller than the second tilt angle, or (b) the first tilt angle is larger than the second tilt angle.

[0058] The tilt angle can be changed during the first time interval and / or the second time interval.

[0059] The method may further include detecting the diffusion rate of the powder to be sieved on the sieve and / or the position of the leading edge of the powder on the sieve. The inclination angle of the sieve surface with respect to the horizontal plane can be changed according to the detected diffusion rate and / or the detected position.

[0060] Detection can be performed, for example, using sensors, which may include, in particular, cameras, induction sensors, and / or light barriers. Sensors can be mounted on the housing, in particular on the upper wall of the housing. Detection can also be performed using a control unit. The diffusion rate of the powder to be sieved can be the diffusion rate of the front part of the powder.

[0061] The tilt angle can be changed such that it decreases when the diffusion rate of the detected sieving powder and / or the position of the detected leading edge of the powder exceeds a predetermined threshold. Furthermore, the tilt angle can be changed such that it increases when the diffusion rate of the detected sieving powder and / or the position of the detected leading edge of the powder falls below a predetermined threshold. The adjustment of the tilt angle can also be performed continuously within a closed control loop, for example, where a constant diffusion rate of the sieving powder is set by adjusting the tilt angle.

[0062] The sieving device comprises a powder inlet and a drive device configured to drive a sieve. The sieving device further comprises a control unit, which controls the powder inlet and the drive device to supply the powder to be sieved from the powder inlet to the sieve in step (i), and to drive the sieve with a first driving force for a first time interval in step (ii). Here, the first driving force is set such that when the sieve is continuously driven with the first driving force, the powder to be sieved flows across the entire surface of the sieve and / or into the oversized particle outlet. Furthermore, the control unit is configured to control the powder inlet and the drive device to drive the sieve with a second driving power lower than the first driving power for a second time interval in step (iii) after the first time interval has elapsed, and to repeat steps (ii) and (iii) in step (iv) after the second time interval has elapsed.

[0063] The second driving force is preferably set such that when the sieve is continuously driven by the second driving force, the powder to be sieved forms a bulk cone in the powder inlet region on the sieve surface. This bulk cone essentially corresponds to a bulk cone formed on a stationary surface, where the bulk angle of the bulk cone is particularly adapted to the orientation of the sieve surface.

[0064] In addition to or instead of the above, the sieve surface of the sieve may be inclined with respect to the horizontal plane so that the powder supplied from the powder inlet towards the oversized particle outlet flows by gravity. In this case, it is preferable that the angle of inclination of the sieve surface with respect to the horizontal plane is smaller than the bulk angle of the bulk cone formed by the powder to be sieved on the horizontal plane.

[0065] The first time interval can be a value empirically determined for the powder to be sieved. In addition to this, or instead, the control unit can be configured to end the first time interval no later than when the powder to be sieved has flowed into the oversized particle outlet when determining the first time interval. The sieving device may be provided with an oversized particle sensor located in the area of ​​the oversized particle outlet to monitor the inflow of the powder to be sieved into the oversized particle outlet. The control unit can be configured to determine the size of the first time interval such that by the end of the first time interval, the sieving area utilization rate does not exceed about 70% to about 90%, preferably about 75% to about 85%, and particularly preferably about 80% of the total sieving area of ​​the sieve.

[0066] The second time interval can be a value empirically determined for the powder to be sieved. In addition to this, or instead, the control unit may be configured to end the second time interval at the latest when the powder to be sieved has formed a bulk cone of a specified size in the powder inlet region of the sieve surface. The sieving device may be equipped with a weighing sensor located in the powder inlet region to detect the formation of a bulk cone of a specified size.

[0067] The following describes an embodiment of a sieving apparatus that is claimable independently of the above-described sieving apparatus, which includes a control unit for controlling the supply of powder through the powder inlet of the sieve and a control unit for drive control.

[0068] JPEG2026521379000010.jpg82169

[0069] JPEG2026521379000011.jpg20157

[0070] JPEG2026521379000012.jpg57164

[0071] The control unit can be configured to control the powder inlet so that the supply of powder from the powder inlet stops when sieving starts, and / or to control the drive unit so that any powder still present in the sieve is sieved before sieving starts, and / or to control the drive unit so that the sieve is driven with maximum driving force after sieving starts, and / or to activate an oscillator configured to drive the sieve independently of the drive unit of the sieving device after sieving starts. Preferably, the contact angle of the oscillator with respect to the sieve, the drive amplitude of the oscillator, and / or the drive frequency of the oscillator are variably adjustable.

[0072] JPEG2026521379000013.jpg77169

[0073] The sieving device is provided with a powder supply container that can be connected to the powder inlet of the sieving device, m fed A first measuring device for measuring m, and an oversized particle container connected to the oversized particle outlet of the sieving device, oversize particles A second measuring device for measuring m, and a sieving powder container that can be connected to the sieving powder outlet of the sieving device, sieved It may also include a third measuring device for measuring [the value].

[0074] The control unit may further be configured to control the powder inlet so that the powder to be sieved is supplied to the sieve at least temporarily through the powder inlet at a supply mass flow rate determined according to the driving force used to drive the sieve. In particular, the first supply mass flow rate through which the powder to be sieved is supplied to the sieve through the powder inlet during a first time interval is greater than the second supply mass flow rate through which the powder to be sieved is supplied to the sieve through the powder inlet during a second time interval.

[0075] The control unit can be configured to output a warning signal, particularly when the continuously measured oversize particle rate exceeds a limit.

[0076] The sieving apparatus is preferably sealed from the ambient atmosphere and filled with protective gas during operation. In addition, or instead, the control unit can be configured to supply additional protective gas to the sieving apparatus when the inert gas pressure inside the sieving apparatus falls below a threshold. For this purpose, the control unit can, for example, actuate a valve that controls the supply of inert gas to the sieving apparatus.

[0077] The control unit is preferably further configured to monitor the step response of the combined mass flow rate of the sieved powder and the oversized particles to the supply mass flow rate during the sieving process. Furthermore, the control unit may be configured to output a warning signal when the step response of the combined mass flow rate of the sieved powder and the oversized particles to the supply mass flow rate falls below a first limit value. Finally, the control unit may be configured to initiate sieving when the step response of the combined mass flow rate of the sieved powder and the oversized particles to the supply mass flow rate exceeds a second limit value.

[0078] The sieving apparatus may further include a lid that is removable from the sieving container. The lid may be provided with a seal. For example, the seal is located on the side of the lid facing the sieving container and serves to seal the sieving container from the ambient atmosphere when the lid is closed. Furthermore, the sieving apparatus may include a clamping device configured to apply a clamping force to the seal and hold the seal in place within the lid. The clamping device may include, for example, a clamping piece that can be pressed against the seal by an adjustment screw. The clamping device advantageously prevents the seal from coming off the lid when the lid is removed from the sieving container.

[0079] The sieving device may include a tilting device for changing the inclination angle of the sieve surface relative to the horizontal plane.

[0080] This embodiment, and all embodiments described below in relation to changes in the inclination angle, are applicable to one of the above-described sieving devices and / or are applicable to sieving devices independently thereof.

[0081] Therefore, a sieving device for sieving powder in an additive manufacturing apparatus (for example, an apparatus for manufacturing a three-dimensional workpiece by selective electron beam melting, selective laser melting, laser deposition welding, laser metal deposition, or selective laser sintering) may comprise a powder inlet, a drive device configured to drive a sieve, and a tilting device for changing the inclination angle of the sieve surface with respect to the horizontal plane.

[0082] Changing the inclination angle may include, for example, initially changing and adjusting the inclination angle, which is performed particularly before the step of supplying the powder to be sieved. In addition to this, or instead, the inclination angle may be changed during the operation of the sieving device, for example at the start of the first and / or second time intervals.

[0083] The sieving device may include a housing that can be sealed in an airtight manner, the sieves being placed inside the housing, and the tilting device being configured to rotate the sieves relative to the housing, thereby changing the tilt angle.

[0084] The powder inlet and oversized particle outlet can be permanently mounted to the housing. The powder inlet can be mounted on the top of the housing, and the oversized particle outlet can be mounted on the bottom of the housing. Furthermore, the sieving container can be permanently mounted on the bottom of the housing.

[0085] The sieving device may include a sieve holder for holding, and especially for inserting, sieves. The tilting device can be attached to the sieve holder and configured to rotate the sieve holder.

[0086] The control unit may be configured to set a first tilt angle during a first time interval and a second tilt angle during a second time interval, either (a) the first tilt angle is smaller than the second tilt angle, or (b) the first tilt angle is larger than the second tilt angle. The first and second tilt angles may be kept constant during the first and second time intervals, respectively.

[0087] The control unit may be configured to change the tilt angle during a first time interval and / or a second time interval.

[0088] The sieving device may further include at least one sensor for detecting the diffusion rate of the powder to be sieved on the sieve and / or the position of the leading edge of the powder to be sieved. The control unit can be configured to change the inclination angle of the sieve surface relative to the horizontal plane in accordance with the detected diffusion rate and / or position.

[0089] The sensor may include, in particular, a camera, an induction sensor, and / or a light barrier. The sensor can be mounted on the housing, in particular on the upper wall of the housing. Detection may be further assisted by a control unit. The diffusion rate of the powder to be sieved may be the diffusion rate of the front part of the powder.

[0090] The control unit may be configured to change the tilt angle so as to decrease when the detected diffusion rate of the powder to be sieved and / or the position of the detected leading edge of the powder exceeds a predetermined threshold. Furthermore, the control unit may be configured to change the tilt angle so as to increase when the detected diffusion rate of the powder to be sieved and / or the position of the detected leading edge of the powder falls below a predetermined threshold. The control unit may also permanently adjust the tilt angle, for example, within the framework of a closed control loop in which a constant diffusion rate of the powder to be sieved is set by adjusting the tilt angle.

[0091] The powder processing system comprises the sieving apparatus described above. The powder processing system can be configured, for example, as a sealed system that is enclosed from the ambient atmosphere. Furthermore, the powder processing system in operation may be partially or entirely filled with a protective gas. The powder processing system may include a powder supply container connectable to the powder inlet of the sieving apparatus, a sieved powder container connectable to the sieved powder outlet of the sieving apparatus, and an oversized particle container connectable to the oversized particle outlet of the sieving apparatus. The powder processing system is particularly intended for use in apparatuses that manufacture three-dimensional workpieces by irradiating a layer of raw material powder with electromagnetic radiation or particle radiation.

[0092] An apparatus for manufacturing a three-dimensional workpiece by irradiating a layer of raw material powder with particle radiation from an electromagnetic radiation source comprises the above-described sieving apparatus and / or the above-described powder processing system.

[0093] Furthermore, the apparatus may include a process chamber that is sealed from the ambient atmosphere and a carrier that contains the raw material powder to be irradiated. Excess powder generated when individual powder layers are applied to the carrier can be collected in one or more collection containers. The process chamber may include a gas inlet for supplying gas, particularly an inert gas, into the process chamber and a gas outlet for removing gas that may contain particulate impurities from the process chamber. The carrier can be positioned within the process chamber. However, the process chamber may also be movable above the carrier. The carrier may be fixed. However, preferably, the carrier is movable vertically, and as the height of the workpieces stacked on the carrier increases, the carrier can be moved vertically in stages downward.

[0094] For example, the raw material powder applied to the carrier by a powder application device that is movable on the carrier is preferably a metal powder, particularly a metal alloy powder. However, the raw material powder may also be a ceramic powder or a powder containing various materials. The powder may have any suitable particle size or particle size distribution, but it is preferable to process powder with a particle size of less than 100 μm. The apparatus preferably also includes an irradiation device that selectively irradiates the powder bed applied to the carrier with electromagnetic radiation or particle radiation. Furthermore, the apparatus may include an unpacking station that can transport the workpiece contained in the build chamber after its completion. At the unpacking station, after a cooling period as necessary, the workpiece can be removed from the build chamber along with the unsolidified powder surrounding the workpiece in the build chamber.

[0095] Preferred embodiments of the present invention will be described in further detail with reference to the accompanying schematic diagrams. [Brief explanation of the drawing]

[0096] [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 includes a powder processing system that includes a sieving device. [Figure 2] Figure 1 is a detailed view of the sieving device used in the powder processing system. [Figure 3] This shows a loose powder bulk on a plane. [Figure 4] Figure 2 shows a sieving device in which the sieve is continuously driven with a low (second) driving force. [Figure 5] Figure 2 shows a sieving apparatus in which the sieve is continuously driven with a high (first) driving force. [Figure 6] Figure 2 shows the operation of the sieving device, which is periodically and alternately driven by a first driving force and a second driving force. [Figure 7] This shows the changes in driving force (top) and supply mass flow rate (bottom) over time when the supply mass flow rate (bottom) is controlled according to the driving force (top). [Figure 8]This demonstrates that when there are defects in the sieve mesh, the sum of the mass flow rate of the sieved powder and the mass flow rate of oversized particles exhibits a step response with respect to the supply mass flow rate. [Figure 9] An alternative embodiment of a sieving device is shown, comprising a housing and a sieve mounted to the housing so as to be tiltable, wherein the tilt angle with respect to the horizontal plane is adjustable.

[0097] The apparatus 100 shown in Figure 1 manufactures a three-dimensional workpiece by irradiating a layer of raw material powder with electromagnetic radiation or particle radiation, and includes a process chamber 102 that is sealed from the ambient atmosphere. A powder application device 104 located inside the process chamber 102 applies layers of raw material powder to a carrier 106. Excess powder accumulated when applying individual powder layers to the carrier 106 is collected in a collection container 107. The carrier 106 is movable vertically, and as the height of the workpiece 108 built on the carrier 106 increases, the carrier 106 can be moved vertically downward in stages into the build chamber 109.

[0098] The process chamber 102 is provided with a gas inlet 110 for supplying an inert gas (e.g., argon) into the process chamber 102. A gas outlet 112 is also provided to generate a continuous gas flow through the process chamber 102. This gas flow helps remove unwanted contaminants such as molten splatter and welding fumes from the process chamber 102.

[0099] The apparatus 100 also includes an irradiation device 112, which selectively irradiates a powder layer applied on the carrier 106 with electromagnetic radiation or particle radiation. The exemplary apparatus 100 shown in Figure 1 includes only one irradiation device 112. However, the apparatus 100 may include multiple irradiation devices 112.

[0100] The irradiation device 112 includes a radiation source 114, which is specifically formed as a laser light source. The radiation source 114 can be, for example, a diode-pumped ytterbium fiber laser that emits laser light with a wavelength of approximately 1070-1080 nm, and may be integrated with the irradiation device 112. However, in the device 100 shown in Figure 1, the radiation source 114 is located outside the irradiation device 112, and the laser beam 116 emitted from the radiation source 114 is directed towards the irradiation device 112 via an optical fiber 118.

[0101] The irradiation unit 112 further comprises two lenses 120 and 122. In the embodiment of the irradiation unit 112 shown in Figure 1, both lenses 120 and 122 have positive refractive power. Lens 120 collimates the laser light emitted from the optical fiber 118 to produce a collimated or substantially collimated laser beam 116. Lens 122, on the other hand, is configured to focus the collimated (or substantially collimated) laser beam 116 to a desired z position along the z axis.

[0102] Finally, the irradiation unit 112 has a scanner system equipped with a scanner mirror 124 that can rotate around a pivot axis S. During the operation of the device 100, the scanner system, and in particular the scanner mirror 124, plays a role in deflecting the laser beam 116 emitted from the radiation source 114 so that the beam 116 strikes a desired position in the raw material powder layer applied to the carrier 106.

[0103] The apparatus 100 also includes an unpacking station 126. The build chamber 109, in which the workpiece 108 is placed, is transported to the unpacking station 126 once the manufacturing of the workpiece 108 is complete. The irradiation device 112 and process chamber 102 can then be used without delay for the manufacturing of new workpieces. At the unpacking station 126, the workpiece 108 is cooled as needed and then unpacked, i.e., removed from the build chamber 109. This process generates a potentially large amount of unsolidified powder in which the workpiece 108 before unpacking is embedded.

[0104] Both the powder collected in the collection container 107 and the powder recovered at the unpacking station 126 may contain particulate impurities or solidified or sintered powder aggregates. These impurities can lead to contamination of the powder layer if the powder is reused in the additive manufacturing process in the apparatus 100, and consequently, a decrease in the quality of the workpiece 108. Therefore, the apparatus 100 is equipped with a powder processing system 128, which is connected to the collection container 107 and the unpacking station 126 via a powder line 130. Powder can be transported from the collection container 107 and the unpacking station 126 to the powder processing system 128 using a blower, conveyor screw, or other suitable conveyor device (not shown in Figure 1). The powder processing system is configured as a sealed system from the ambient atmosphere and is completely filled with a protective gas such as argon during operation.

[0105] The powder processing system 128 includes a powder supply container 132 connected to the powder line 130. The powder supply container 132 receives the powder to be processed from the collection container 107 and the unpacking station 126. Furthermore, the powder processing system 128 includes a sieving device 10 equipped with a sieve formed by a sieve frame 14 and a sieve mesh 16 stretched over the sieve frame. The sieved powder passes through the sieve mesh 16 and is then collected in a sieving container 18.

[0106] A lid 20 is attached to the sieve frame 14, thereby sealing the sieve container 18 from the ambient atmosphere, as well as the other components of the powder processing system 128, and filling it with an inert gas during the operation of the sieving device 10. For example, argon can be used as the inert protective gas to prevent undesirable oxidation of the powder 56 to be sieved in the sieving device 10. The inert gas pressure inside the sieving device 10 is continuously monitored by a pressure sensor (not shown). When the inert gas pressure inside the sieving device 10 falls below a threshold, an additional protective gas is supplied to the sieving device 10 under the control of the control unit 40.

[0107] A detailed view of the sieving device 10 is shown in Figure 2. The powder inlet 22 of the sieving device 10 is equipped with a supply device 24 and a valve 26, enabling controlled supply of powder from the powder supply container 132 to the sieve through the powder inlet 22. A weighing sensor 23 is provided in the area of ​​the powder inlet 22, and its function will be described in more detail below. The sieving container 18 has a cross-section that tapers downwards. The sieved powder contained in the sieving container 18 is discharged from the sieving container by gravity through the sieved powder outlet 28 located at the bottom of the sieving container 18. The sieved powder outlet 28 is connected to the sieved powder container 134 of the powder processing system 128 and is equipped with a valve 30. This allows the sieved powder outlet 28 to discharge the sieved powder from the sieving container 18 to the sieved powder container 134 of the powder processing system 128 in a controlled manner.

[0108] Furthermore, the sieving device 10 includes an oversized particle outlet 32 ​​equipped with a valve 34. An oversized particle sensor 33 is provided in the area of ​​the oversized particle outlet 32 ​​to detect powder particles flowing into the oversized particle outlet 32. Oversized particles that are too coarse to pass through the sieve mesh 16 toward the sieve container 18 via the oversized particle outlet 24 are discharged from the sieving device 10 and supplied to the oversized particle container 136 of the powder processing system 128. The powder inlet 22 and the oversized particle outlet 32 ​​are located in the areas of the sieve surface defined by the sieve mesh 16 that are opposite each other. Furthermore, the sieve mesh 16, and by extension the sieve surface defined by the sieve mesh 16, are inclined with respect to the horizontal plane E, so that the powder supplied from the powder inlet toward the oversized particle outlet 32 ​​flows by gravity. In other words, the sieve surface is inclined from the area below the powder inlet 22 toward the oversized particle outlet 32, which allows the powder supplied from the powder inlet 22 to spread across the sieve surface, facilitating the removal of oversized particles toward the oversized particle outlet 32. Similar to the removal of the sieved powder, the removal of oversized particles from the sieving device 10 is also performed by gravity.

[0109] The sieving device 10 also includes a drive device 36 for driving the sieve. The drive device 36 engages with the sieve frame and vibrates the sieve frame 14, and consequently the sieve mesh 16, during the operation of the sieving device 10. A preferred embodiment of the sieving device 10 shown here includes a drive device 36 in the form of an ultrasonic drive device, which is configured to impart ultrasonic vibrations to the sieve. Furthermore, a transducer 38 is provided, which also engages with the sieve frame 14 and vibrates the sieve frame 14, and consequently the sieve mesh 16, for cleaning the sieve.

[0110] The operation of the sieving device 10 is controlled by the control unit 40. The control unit 40 may be a control unit specifically assigned to the sieving device 10. However, it is also conceivable that the control unit 40 may be integrated into a higher-level control unit, for example, a control unit for controlling the powder processing system 128 and / or a control unit for controlling the 3D workpiece manufacturing device 100.

[0111] Finally, the sieving device 10 comprises a first measuring device 42, a second measuring device 40, and a third measuring device 46. The first measuring device 42, here comprising one or more weighing cells, is located in the powder supply container 132 of the powder processing system 28 and detects the mass of the powder supplied from the powder supply container 32 to the powder inlet 22 of the sieving device 10. The second measuring device 44, here comprising one or more weighing cells, is located in the oversized particle container 136 of the powder processing system 28 and measures the mass of the oversized particles that have flowed into the oversized particle container 136 through the oversized particle outlet 32 ​​of the sieving device 10. Finally, the third measuring device 46, here comprising one or more weighing cells, is located in the sieved powder container 134 of the powder processing system 28 and is used to measure the mass of the sieved powder flowing from the sieved powder outlet 28 of the sieving device 10 into the sieved powder container 134.

[0112] As shown in Figure 3, a bulk angle αa is formed in the dispersed powder bulk 56 on a plane. The bulk angle αa is influenced by various factors such as the shape, density, particle size distribution, and surface properties of the powder particles, as well as process parameters such as relative humidity and temperature, and vibrations and movements acting on the bulk cone.

[0113] When the powder 56 to be sieved is supplied from the powder inlet 22 onto the sieve of the sieving device 10, a bulk cone is formed on the sieve, i.e., on the sieve mesh 16. The shape and bulk angle of the bulk cone are affected by vibrations acting on the bulk cone, and consequently by the driving force of the drive device 36 that drives the sieve. Furthermore, the shape and bulk angle of the bulk cone are also affected by the inclination angle of the sieve surface.

[0114] As shown in Figure 4, when the drive output of the drive unit 36 ​​is low, the bulk cone formed on the sieve below the powder inlet 22 resembles a bulk cone formed on a stationary surface whose bottom occupies only a small portion a of the sieve surface. In this operating state of the sieving device 10, only the small section a of the sieve surface adjacent to the powder inlet 22 actually contacts the powder 56, and the utilization rate of the sieve surface is correspondingly low. In contrast, the section b of the sieve surface that does not contact the powder is relatively large and, as a result, defines a "safe distance" between the section a of the sieve surface that contacts the powder and the oversized particle outlet 32.

[0115] By tilting the sieve surface toward the oversized particle outlet 32, the bulk cone becomes non-symmetrical, as shown in Figure 3, and adapts to the orientation of the sieve surface, resulting in a variable bulk angle. The variable bulk angle is smaller in the circumferential portion of the bulk cone facing the oversized particle outlet 32 ​​than in the circumferential portion of the bulk cone away from the oversized particle outlet 32. However, since the inclination angle αa-w of the sieve surface relative to the horizontal plane E (see Figure 2) is smaller than the bulk angle αa of the bulk cone formed on the horizontal plane by the sieved powder 56, a stable bulk cone is formed in the region of the powder inlet 22 even when the sieve is driven with a low driving force, and the powder 56 does not flow uncontrollably across the sieve surface.

[0116] On the other hand, as shown in Figure 5, when the sieve is driven with a high driving force, the powder 56 spreads across the entire sieve surface, meaning that the bulk angle αar of the bulk cone formed by the powder 56 supplied onto the sieve surface from the powder inlet decreases as the driving force of the drive device 36 that drives the sieve increases. At the same time, the bottom area of ​​the bulk cone increases, so the area a of the sieve surface that comes into contact with the powder 56 increases, and as a result, the utilization rate of the sieve surface increases until the powder eventually flows across the entire sieve surface and the entire sieve surface comes into contact with the powder. There are no areas b of the sieve surface that do not come into contact with the powder, and the areas a of the sieve surface that come into contact with the powder lose their "safe distance" from the oversized particle outlet 32. As a result, as shown in Figure 5, during continuous operation of the sieve with a high driving force, the powder 56 flows into the oversized particle outlet 32 ​​without being sieved. Consequently, powder 56 that is actually fine enough to pass through the sieve mesh 16 is lost without being used.

[0117] In the method for controlling the operation of the sieving device 10, as detailed in Figure 6, first, in step (i), the powder 56 to be sieved is supplied to the sieve from the powder inlet 22. Next, in step (ii), the sieve is driven by a first driving force for a first time interval (see the upper and middle parts of Figure 6). The first driving force is set such that, as shown in Figure 5, when the sieve is continuously driven by the first driving force, the powder 56 to be sieved flows across the entire sieve surface and / or into the oversized particle outlet. Therefore, if the first driving force is very high and maintained continuously, the maximum utilization rate of the sieve area is ensured, but there is at least a high risk that the powder 56 will be lost without being sieved through the oversized particle outlet 32. Consequently, there is a time limit to driving the sieve with the first driving force.

[0118] Therefore, after the first time interval has elapsed, in step (iii), the sieve is driven for a second time interval with a second driving force lower than the first driving force (see the bottom of Figure 6). The second driving force is specifically set such that, as shown in Figure 4, when the sieve is continuously driven by the second driving force, the powder 56 to be sieved forms a bulk cone on the sieve surface in the region of the powder inlet 22. This bulk cone is substantially equivalent to a bulk cone formed on a stationary surface, and its bottom area occupies only a small section a of the sieve surface of the sieve located in the region of the powder inlet 22. When the sieve is continuously driven by the second driving force, it is guaranteed that little to no powder 56 flows into the oversized particle outlet without being sieved. However, because the utilization rate of the sieve area is low, the processing capacity of the sieve and, consequently, the sieving performance decreases. Therefore, the driving of the sieve by the second driving force is also limited in time.

[0119] In the above case, the second driving force is greater than zero and less than the first driving force. In special cases, the second driving force may be zero, in which case no active sieving occurs during the second time interval. However, even in the non-driven state, passive sieving occurs, and the powder passes through the sieve little by little due to gravity.

[0120] After the second time interval has elapsed, steps (ii) and (iii) are repeated. That is, the sieve is periodically driven alternately with a first high driving force and a second low driving force. In the first time interval, when the sieve is driven with the first (high) driving force, the powder particles of the powder 56 to be sieved (including the oversized particles 50 contained in the powder 56) are dispersed across the entire sieve surface (see top of Figure 6), so the sieving process is performed with a high sieve area utilization rate, and the oversized particles 50 are transported toward the oversized particle outlet 32 ​​by gravity (see middle of Figure 6). In contrast, in the second time interval, the sieve area utilization rate is low. Furthermore, the oversized particles 50 "accumulate" in a columnar manner within the bulk cone. As a result, the powder particles pushed into the sieve mesh 16 by dynamic pressure and sieve vibration can clog and block the sieve mesh.

[0121] The first and second time intervals alternate periodically, and therefore the sieve is driven periodically with high and low driving forces, thus combining the advantages of both driving forces. Due to the time limit of the first time interval, the powder particles are well dispersed across the entire sieve surface, and oversized particles 50 are efficiently removed toward the oversized particle outlet 32. However, a section b of the sieve surface that does not come into contact with the powder always remains, and as a result, a "safe distance" is ensured between the section a of the sieve surface that comes into contact with the powder and the oversized particle outlet 32. Furthermore, because the mass of powder in contact with the sieve mesh 16 is low, the load on the sieve mesh 16 is small.

[0122] The first and second driving forces can be set to different values ​​for various powder types and various process parameters such as temperature, particle size distribution, and moisture content. Therefore, the first and second driving forces are either empirically determined before the sieving process, obtained from a table of driving force values ​​for various powder types and process parameters, or selected based on empirical values. Similarly, the first and second time intervals can also be set to different values ​​for various powder types and various process parameters such as temperature, particle size distribution, and moisture content. Therefore, the first and second time intervals are either values ​​empirically determined before sieving for the powder to be sieved, values ​​obtained from a value table, or values ​​selected based on empirical values.

[0123] When setting the first time interval, the first time interval ends at the latest when the powder 56 to be sieved flows into the oversized particle outlet 32. In other words, the first time interval is selected so that no powder to be sieved is lost while the sieve is being driven by the first driving force within the first time interval. The flow of powder to be sieved flowing into the oversized particle outlet 32 ​​is detected by the oversized particle sensor 33. In particular, the first time interval is set so that by the end of the first time interval, the sieve area utilization rate does not exceed approximately 70% to approximately 90%, preferably approximately 75% to approximately 85%, and especially preferably approximately 80% of the total sieve area of ​​the sieve. Therefore, the first time interval provides a "temporal safety margin," and the powder does not spread across the entire sieve surface during the first time interval.

[0124] When setting the second time interval, the second time interval ends at the latest when the powder 56 to be sieved has formed a bulk cone of a specified size on the sieve surface in the region of the powder inlet 22. The formation of a bulk cone of a specified size is detected by the weighing sensor 23, which is activated when the tip of the bulk cone protrudes into the detection area of ​​the weighing sensor 23. By limiting the second time interval in this way, it is possible to prevent the bulk cone from becoming excessively large and clogging the powder inlet 22 during the second time interval.

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[0128] When the control unit 40 detects the start of sieve cleaning, the supply of powder from the powder inlet 22 is first stopped. Any powder 56 remaining in the sieve is sieved before the start of sieve cleaning. After the start of sieve cleaning, the sieve is driven with maximum driving force. In addition to this, or instead, the vibrator 38 can be activated after the start of sieve cleaning. In this case, the contact angle of the vibrator 38 with respect to the sieve, the driving amplitude of the vibrator 38, and the driving frequency of the vibrator 38 are variably adjustable. In addition to the start of sieve cleaning due to clogging of the sieve mesh 16, or instead, sieve cleaning can also be started when the powder supply container 132 becomes empty after the completion of each sieving process.

[0129] In addition to, or instead of, the powder 56 to be sieved can also be supplied to the sieve discontinuously, at least temporarily, through the powder inlet 22. In the case of discontinuous powder supply, first, with the sieve not driven, the powder 56 to be sieved is supplied to the sieve through the powder inlet 22 until it forms a bulk cone of a specified size on the sieve surface in the area of ​​the powder inlet 22 and the weighing sensor 23 is activated. After that, the powder supply is stopped and the sieve is driven, and the powder 56 supplied onto the sieve surface is sieved.

[0130] In addition to, or instead of, the continuous or discontinuous supply of powder described above, the powder 56 to be sieved may also be supplied to the sieve at least temporarily through the powder inlet 22 at a supply mass flow rate determined according to the driving force used to drive the sieve. In particular, the first supply mass flow rate through the powder inlet 22 to supply the powder to be sieved in a first time interval may be greater than the second supply mass flow rate through the powder inlet 22 to supply the powder to be sieved in a second time interval.

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[0140] Figure 9 shows a schematic side view of a sieving apparatus 10 that can be considered an alternative embodiment or further development of the sieving apparatus 10 of Figure 2. The sieving apparatus 10 can be used in combination with all embodiments of the sieving apparatus 10, powder processing system 128, and / or three-dimensional workpiece manufacturing apparatus 100 described above. Elements and / or functions of the sieving apparatus 10 that are not described below correspond to the elements and / or functions of the sieving apparatus 10 described above, particularly the sieving apparatus 10 of Figure 2. Accordingly, some elements of the sieving apparatus 10 of Figure 9 are not illustrated or are shown only schematically, as they correspond to the elements of the sieving apparatus 10 of Figure 2, which have already been described in detail.

[0141] The upper part (a) of Figure 9 shows the sieving device 10 before the sieves (consisting of sieve frames 14 and sieve meshes 16) are placed inside the housing 60 of the sieving device 10. The lower part (b) of Figure 9 shows the sieving device with the sieves 14 and 16 in place.

[0142] The sieving apparatus 10 in Figure 9 includes a housing 60 suitable for sealing the sieving apparatus 10, similar to the lid 20. This allows the sieving process to be carried out in a sealed, inert gas atmosphere. The powder inlet 22 is located at the top of the housing 60. The oversized particle outlet 32 ​​and the sieving container 18 (not shown) are located at the bottom of the housing 60. The elements 22, 32 and 18 are attached to the housing 60 and are therefore fixed independently of changes in the inclination angle αa-w (see below).

[0143] The sieve consists of a sieve frame 14 and a sieve mesh 16, and can be inserted into the housing from the side via a flap 62. The flap 62 can be closed, and when closed, it airtightly seals the housing 60. Furthermore, a sieve holder 66 is provided to secure the sieves 14 and 16 after they are inserted, if necessary. This allows the sieves 14 and 16 to be easily removed, reinserted, or replaced as needed.

[0144] The inclination angles αa-w of the sieves 14 and 16 (more precisely, the sieve mesh 16) with respect to the horizontal plane E are adjustable. For this purpose, a tilting device 64 is provided, configured to change the inclination angles αa-w. The tilting device may include a motor, particularly a servo motor. In the example shown in Figure 9, the tilting device 64 is attached to the sieve holder 66 and configured to tilt the sieve holder 66 relative to the housing 60. More specifically, in the illustrated example, the tilting device is positioned in the center of the sieves 14 and 16 and configured to rotate the sieves 14 and 16 along a rotation axis extending horizontally.

[0145] In particular, the tilting device 64 is controllable by the control unit 40 so that any tilt angle αa-w can be set within a predetermined angular range (e.g., 0° to 45°). 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 change in angle is made at an interval shorter than the shorter of the first and second time intervals, specifically by a length of up to half, up to 1 / 4, up to 1 / 8, up to 1 / 10, up to 1 / 50, or up to 1 / 100.

[0146] However, the inclination angle αa-w can also be continuously varied during the first and / or second time intervals.

[0147] Thus, the control of sieving performance (i.e., different sieving performance in the first and second time intervals) can be supported by setting different inclination angles αa-w in each time interval. In particular, a larger inclination angle can be set in the first time interval than in the second time interval. Conversely, a smaller inclination angle can also be set in the first time interval than in the second time interval. Depending on the situation and purpose, either option may be advantageous. The smaller the inclination angle αa-w, the fewer oversized particles will be discharged, and the less likely powder will accumulate on the sieve mesh 16. The larger the inclination angle αa-w, the greater the effect of removing oversized particles, but there is also a possibility that "good quality" powder that can pass through the sieve mesh 16 will flow into the oversized particle outlet 32.

[0148] In some embodiments, the inclination angle can be adjusted depending on the powder used. This adjustment can be made initially before the start of the sieving process, for example, so that the inclination angle remains constant throughout the sieving process. For example, a higher inclination angle can be set for heavier materials than for lighter materials. Similarly, for powder materials containing non-circular and / or scattered powder particles with low fluidity, a higher inclination angle can be set than for powder materials containing circular powder particles with high fluidity. In this way, the inclination angle can be optimized considering the flow characteristics of the material being used.

[0149] Furthermore, a sensor (not shown) can be provided, configured to detect the diffusion rate of the powder to be sieved on the sieve and / or the position of the leading edge of the powder to be sieved. For this purpose, the sensor may include, for example, a camera, an induction sensor, and / or a light barrier. The sensor can be mounted, for example, inside the housing 60, particularly on the upper wall of the housing 60.

[0150] The control unit can be configured to change the inclination angle αa-w of the sieve surface with respect to the horizontal plane in accordance with the detected diffusion rate and / or detected position. In particular, the inclination angle αa-w can be changed so that it decreases when the detected diffusion rate of the powder to be sieved and / or the detected position of the leading edge of the powder exceeds a predetermined threshold. Similarly, the inclination angle αa-w can be changed so that it increases when the detected diffusion rate of the powder to be sieved and / or the detected position of the leading edge of the powder falls below a predetermined threshold.

[0151] This allows for automatic control of the tilt angle, thus avoiding time-consuming tests to determine the optimal tilt angle for each type of powder.

Claims

1. A method for controlling the operation of a sieving device (10), (i) A step of supplying the powder to be sieved (56) onto the sieve through the powder inlet (22), (ii) A step of driving the sieve with a first driving force over a first time interval, wherein the first driving force is set such that when the sieve is continuously driven with the first driving force, the powder to be sieved (56) flows over the entire sieve surface of the sieve and / or into the oversized particle outlet (32), (iii) After the first time interval has elapsed, the sieve is driven for a second time interval with a second driving force lower than the first driving force, (iv) After the second time interval has elapsed, the step of repeating steps (ii) and (iii), Methods that include...

2. A method for controlling a sieving apparatus (10) according to claim 1, wherein the second driving force is set such that when the sieve is continuously driven by the second driving force, the powder to be sieved (56) forms a bulk cone on the sieving surface of the sieve in the region of the powder inlet (22), the bulk cone substantially corresponds to a bulk cone formed on a stationary surface, and the bulk angle (αa) of the bulk cone is particularly adapted to the orientation of the sieving surface.

3. A method for controlling the operation of a sieving device (10) according to claim 1 or 2, wherein the sieving surface of the sieve is inclined with respect to a horizontal plane (E) so that the powder supplied through the powder inlet (22) toward the oversized particle outlet (32) flows by gravity, and the inclination angle (αa-w) of the sieving surface of the sieve with respect to the horizontal plane (E) is preferably smaller than the bulk angle (αa) of the bulk cone formed on the horizontal plane (E) by the powder to be sieved (56).

4. The first time interval is a value empirically determined for the powder (56) to be sieved, and / or When determining the first time interval, the first time interval ends at the latest when the powder to be sieved (56) flows into the oversized particle outlet (32), and the flow of the powder to be sieved (56) flowing into the oversized particle outlet (32) is detected in particular by an oversized particle sensor (33) provided in the region of the oversized particle outlet, and / or The first time interval is set so that by the end of the first time interval, the sieve area utilization rate does not exceed approximately 70% to approximately 90%, preferably approximately 75% to approximately 85%, and particularly preferably approximately 80% of the total sieve area of ​​the sieve, and / or The second time interval is a value empirically determined for the powder (56) to be sieved, and / or A method for controlling the operation of a sieving device (10) according to any one of claims 1 to 3, wherein when determining the second time interval, the second time interval ends at the latest when the powder to be sieved (56) forms a bulk cone of a specified size on the sieving surface of the sieve in the region of the powder inlet (22), and the formation of the bulk cone of a specified size is detected in particular by a weighing sensor (23) provided in the region of the powder inlet (22).

5.

6.

7.

8. When starting the sieve washing process, The supply of powder through the powder inlet (22) is stopped and / or, Before the start of the sieve cleaning, any powder remaining in the sieve is sieved off and / or After the start of the sieve cleaning, the sieve is driven with maximum driving force and / or, A method for controlling the operation of a sieving device (10) according to claim 7, wherein, after the start of the sieving cleaning, a vibrator (38) that drives the sieve is operated independently of the drive device (36) of the sieving device (10), and preferably the contact angle of the vibrator (38) with respect to the sieve, the driving amplitude of the vibrator (38), and / or the driving frequency of the vibrator (38) are variably adjustable.

9.

10. A method for controlling the operation of a sieving device (10) according to any one of claims 1 to 9, wherein the powder to be sieved (56) is supplied to the sieve at least temporarily through the powder inlet (22) at a supply mass flow rate determined according to the driving force used to drive the sieve, and in particular, the first supply mass flow rate at which the powder to be sieved (56) is supplied to the sieve through the powder inlet (22) during the first time interval is greater than the second supply mass flow rate at which the powder to be sieved (56) is supplied to the sieve through the powder inlet (22) during the second time interval.

11. A method for controlling the operation of a sieving device (10) according to any one of claims 1 to 10, wherein a warning signal is output when the oversized particle rate exceeds a threshold, and the oversized particle rate is continuously measured.

12. The sieving device (10) is sealed from the ambient atmosphere, filled with protective gas during operation, and / or A method for controlling the operation of a sieving device (10) according to any one of claims 1 to 11, wherein when the inert gas pressure in the sieving device (10) falls below a threshold, an additional protective gas is supplied to the sieving device (10).

13.

14. A method for controlling the operation of a sieving device (10) according to any one of claims 1 to 13, further comprising changing the inclination angle (αa-w) of the sieve surface of the sieve with respect to a horizontal plane (E).

15. A method for controlling the operation of a sieving device (10) according to claim 14, wherein the sieve is placed in an airtightly sealed housing (60), and the inclination angle (αa-w) changes as the sieve rotates relative to the housing (60).

16. A method for controlling the operation of a sieving device (10) according to claim 14 or 15, wherein a first inclination angle (αa-w) is set during the first time interval, and a second inclination angle (αa-w) is set during the second time interval, and (a) the first inclination angle is smaller than the second inclination angle, or (b) the first inclination angle is larger than the second inclination angle.

17. A method for controlling the operation of a sieving device (10) according to claim 14 or 15, wherein the inclination angle is changed during the first time interval and / or the second time interval.

18. The method further includes detecting the diffusion rate of the powder to be sieved (56) on the sieve, and / or the position of the leading part of the powder to be sieved (56) on the sieve. A method for controlling the operation of a sieving apparatus (10) according to any one of claims 14 to 17, wherein the change in the inclination angle (αa-w) of the sieving surface of the sieve with respect to the horizontal plane (E) is performed in accordance with the detected diffusion rate and / or the detected position of the front part of the powder.

19. A method for controlling the operation of a sieving device (10) according to claim 18, wherein the change in the inclination angle (αa-w) is performed such that the inclination angle (αa-w) decreases when the detected diffusion velocity and / or the detected position of the front part of the powder to be sieved (56) exceeds a predetermined threshold.

20. Powder inlet (22) and A drive device (36) configured to drive the sieve, A sieving device (10) comprising a control unit (40), The control unit is (i) The powder to be sieved (56) is supplied onto the sieve through the powder inlet (22), (ii) The sieve is driven by a first driving force over a first time interval, and the first driving force is set such that when the sieve is driven continuously by the first driving force, the powder to be sieved (56) flows over the entire sieve surface of the sieve and / or into the oversized particle outlet (32), (iii) After the first time interval has elapsed, the sieve is driven for a second time interval with a second driving force lower than the first driving force, (iv) A sieving device (10) configured to control the powder inlet (22) and the drive device (36) so that steps (ii) and (iii) are repeated after the second time interval has elapsed.

21. The second driving force is set such that when the sieve is continuously driven by the second driving force, the powder to be sieved (56) forms a bulk cone on the sieve surface of the sieve in the region of the powder inlet (22), the bulk cone substantially corresponds to a bulk cone formed on a stationary surface, and the bulk angle (αa) of the bulk cone is particularly adapted to the orientation of the sieve surface and / or The sieve surface of the sieve is inclined with respect to the horizontal plane (E) so that the powder supplied through the powder inlet (22) toward the oversized particle outlet (32) flows by gravity, and the inclination angle (αa-w) of the sieve surface of the sieve with respect to the horizontal plane (E) is preferably smaller than the bulk angle (αa) of the bulk cone formed on the horizontal plane (E) by the powder to be sieved (56), and / or The first time interval is a value empirically determined for the powder (56) to be sieved, and / or The control unit (40) is configured such that, when determining the first time interval, it terminates when the powder to be sieved (56) flows into the oversized particle outlet (32), even if the first time interval is delayed, and the sieving device (10) is provided in the region of the oversized particle outlet with an oversized particle sensor for detecting the flow of the powder to be sieved (56) flowing into the oversized particle outlet (32), and / or The control unit (40) is configured to set the first time interval so that by the end of the first time interval, the sieve area utilization rate does not exceed approximately 70% to approximately 90%, preferably approximately 75% to approximately 85%, and particularly preferably approximately 80% of the total sieve area of ​​the sieve, and / or The second time interval is a value empirically determined for the powder (56) to be sieved, and / or The control unit (40) is configured such that, when determining the second time interval, the process ends at the latest when the second time interval is late, when the powder to be sieved (56) forms a bulk cone of a specified size on the sieve surface of the sieve in the region of the powder inlet (22), and the sieving device (10) in particular has a weighing sensor (23) provided in the region of the powder inlet (22) for detecting the formation of a bulk cone of a specified size, as described in claim 20.

22.

23. The control unit (40) will, when the sieve cleaning starts, The powder inlet (22) is controlled so as to stop the supply of powder through the powder inlet (22), and / or Before the start of the sieve cleaning, the drive device (36) is controlled so that any powder remaining in the sieve is sieved off, and / or After the start of the sieve cleaning, the drive device (36) is controlled so that the sieve is driven with maximum driving force, and / or The sieving device (10) according to claim 22, wherein, after the start of the sieving cleaning, a vibrator (38) configured to drive the sieve independently of the drive device (38) of the sieving device (10) is operated, and preferably the contact angle of the vibrator (38) with respect to the sieve, the driving amplitude of the vibrator (38), and / or the driving frequency of the vibrator (38) are variably adjustable.

24.

25. The sieving apparatus (10) according to any one of claims 20 to 24, wherein the control unit (40) is configured to control the powder inlet (22) such that the powder to be sieved (56) is supplied to the sieve at least temporarily through the powder inlet (22) at a supply mass flow rate determined according to the driving force used to drive the sieve, in particular, a first supply mass flow rate through the powder inlet (22) to supply the powder to be sieved (56) to the sieve during a first time interval is greater than a second supply mass flow rate through the powder inlet (22) to supply the powder to be sieved (56) to the sieve during a second time interval.

26. The sieving apparatus (10) according to any one of claims 20 to 25, wherein the control unit (40) is configured to output a warning signal when the continuously measured oversized particle rate exceeds a threshold.

27. The sieving device (10) is sealed from the ambient atmosphere, filled with protective gas during operation, and / or The sieving apparatus (10) according to any one of claims 20 to 26, wherein the control unit (40) is configured to supply additional protective gas to the sieving apparatus (10) when the inert gas pressure in the sieving apparatus (10) falls below a threshold.

28.

29. A lid (20) that can be removed from the sieving container (18), The seal (48) is placed inside the lid (20), A sieving device (10) according to any one of claims 20 to 28, comprising a clamping device (50) configured to apply a clamping force to the seal (48), wherein the clamping device holds the seal (48) in a position within the lid (20).

30. A sieving device (10) according to any one of claims 20 to 29, comprising a tilting device (64) for changing the inclination angle (αa-w) of the sieve surface of the sieve with respect to a horizontal plane (E).

31. The sieving device (10) according to claim 30, further comprising a housing (60) that can be closed in an airtight manner, wherein the sieve is disposed within the housing (60), and the tilting device (64) is configured to rotate the sieve relative to the housing (60), thereby changing the tilting angle (αa-w).

32. The sieving apparatus (10) according to claim 30 or 31, wherein the powder inlet (22) and the oversized particle outlet (32) are fixedly attached to the housing (60).

33. A sieving device (10) according to any one of claims 30 to 32, wherein the device has a sieve holder (66) for holding a sieve for insertion, and the tilting device (64) is attached to the sieve holder (66) and configured to rotate the sieve holder (66).

34. The control unit (40) is configured to set a first inclination angle (αa-w) during the first time interval and a second inclination angle (αa-w) during the second time interval, wherein (a) the first inclination angle is smaller than the second inclination angle, or (b) the first inclination angle is larger than the second inclination angle, according to any one of claims 30 to 33, the sieving device (10).

35. The sieving device (10) according to any one of claims 30 to 33, wherein the control unit (40) is configured to change the inclination angle during the first time interval and / or the second time interval.

36. The system has at least one sensor that detects the diffusion rate of the powder to be sieved (56) on the sieve, and / or the position of the front part of the powder to be sieved (56) on the sieve. The sieving apparatus (10) according to any one of claims 30 to 35, wherein the control unit (40) is configured to change the inclination angle (αa-w) of the sieve surface of the sieve with respect to the horizontal plane (E) in accordance with the detected diffusion velocity and / or the detected position of the front part of the powder.

37. The sieving apparatus (10) according to claim 36, wherein the control unit (40) is configured to change the inclination angle (αa-w) such that the inclination angle (αa-w) decreases when the detected diffusion velocity of the powder to be sieved (56) and / or the detected position of the front part of the powder exceeds a predetermined threshold.

38. A powder processing system (128) comprising a sieving device (10) according to any one of claims 30 to 37.

39. An apparatus (100) for manufacturing a three-dimensional workpiece by irradiating a layer of raw material powder with electromagnetic radiation or particle radiation, comprising a sieving device (10) according to any one of claims 30 to 37, and / or a powder processing system (128) according to claim 38.

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