Method of operating an apparatus for producing a three-dimensional workpiece and apparatus for producing a three-dimensional workpiece

Abstract

Method of operating an apparatus for producing a three-dimensional workpiece and apparatus for producing a three-dimensional workpiece. A method of operating an apparatus (10) for producing a three-dimensional workpiece (1S) by irradiating layers of a feedstock powder with electromagnetic or particle radiation, the method comprising the steps of: a) applying a layer of feedstock powder onto a carrier (12); b) selectively irradiating the layer of feedstock powder with electromagnetic or particle radiation in accordance with the geometry of the corresponding layer of the workpiece (18) to be produced; and c) repeating steps a) and b) until the workpiece (18) reaches the desired shape and dimensions. For at least some of the layers, for at least a portion of the layers, the scan time (G) from the beginning of exposure to electromagnetic or particle radiation of the respective feedstock powder layer portion until the beginning of exposure to electromagnetic or particle radiation of a new feedstock powder layer applied on top of said layer portion is controlled so as to be not lower than a specific minimum value set individually for said layer portion in accordance with a layer portion specific quality parameter. Layer portion specific quality parameter.

Description

Technical Field

[0001] This invention relates to a method and an irradiation system for operating an apparatus for producing three-dimensional workpieces by irradiating layers of raw material powder with electromagnetic radiation or particle radiation. Furthermore, this invention relates to an apparatus for producing three-dimensional workpieces. Background Technology

[0002] Powder bed melting is a layer-by-layer additive manufacturing process that allows powdered raw materials, particularly metals and / or ceramics, to be shaped into complex three-dimensional workpieces. To do this, layers of raw powder are applied to a carrier and subjected to laser irradiation in a position-selective manner, depending on the desired geometry of the workpiece to be produced. The laser irradiation penetrating the powder layers causes heating, thus melting or sintering the raw powder particles. Further layers of raw powder are then continuously applied to the laser-treated layers on the carrier until the workpiece achieves the desired shape and dimensions. Based on CAD data, powder bed melting can be used for the production or restoration of prototypes, tools, replacement parts, high-value components, or medical prostheses (e.g., dental or orthopedic prostheses).

[0003] An exemplary apparatus for producing three-dimensional workpieces by powder bed melting, as described in EP 3 023 227 B1, includes a processing chamber housing a powder application device for continuously applying layers of raw material powder onto a carrier. An irradiation unit is configured to selectively irradiate the raw material powder layer with a laser beam.

[0004] When constructing three-dimensional workpieces on a carrier in a powder bed fusion apparatus, heat dissipation from the current irradiation layer can become more difficult as the workpiece's construction height increases. This can lead to thermal gradients within the workpiece and thus affect its quality. If the workpiece geometry requires abrupt changes in the irradiated area (so-called exposed area) between adjacent layers, undesirable effects may also occur, potentially degrading the overall quality of the workpiece. Summary of the Invention

[0005] The object of the present invention is to provide a method for operating an apparatus for producing three-dimensional workpieces by irradiating a layer of raw material powder with electromagnetic radiation or particle radiation, and an apparatus for producing three-dimensional workpieces by irradiating a layer of raw material powder with electromagnetic radiation or particle radiation, which enables the efficient production of high-quality workpieces.

[0006] In a method of operating an apparatus for producing three-dimensional workpieces by irradiating a layer of raw material powder with electromagnetic radiation or particle radiation, the layer of raw material powder is applied to a carrier. To apply the raw material powder to the surface of the carrier, a powder application device can be used, which moves across the carrier to distribute the raw material powder. The carrier and the powder application device can be housed within a processing chamber that is sealed from the ambient atmosphere. The raw material powder applied to the carrier within the processing chamber is preferably a metal powder, particularly a metal alloy powder, but it can also be a ceramic powder or a powder containing different materials. The powder can have any suitable particle size or particle size distribution. However, it is preferable to process powders with a particle size <100 μm.

[0007] Depending on the geometry of the corresponding layer of the workpiece to be produced, the layers of raw material powder are selectively irradiated with electromagnetic radiation or particle radiation. The irradiation apparatus for selectively irradiating the raw material powder onto a carrier with electromagnetic radiation or particle radiation may include a radiation beam source (particularly a laser beam source) and may additionally include an optical unit for guiding and / or processing the radiation beam emitted by the radiation beam source. The optical unit may include optical elements, such as objective lenses and a scanner unit, which preferably includes diffractive optical elements and deflecting mirrors.

[0008] The process involves repeatedly applying layers of raw material powder onto a carrier and selectively irradiating the powder layers with electromagnetic or particle radiation, according to the geometry of the corresponding layers of the workpiece to be produced, until the workpiece achieves the desired shape and size. The carrier can be rigidly fixed. However, preferably, the carrier is designed to be vertically movable, such that as the workpiece is constructed within the layers of raw material powder, the carrier can move downwards vertically as the workpiece's construction height increases.

[0009] For at least a portion of at least some layers, the scan time is controlled from the start of exposure to electromagnetic radiation or particle radiation of the corresponding raw material powder layer until a new raw material powder layer on top of the layer portion begins to be exposed to electromagnetic radiation or particle radiation, so that the scan time is not less than a specific minimum. Specifically, the exposure time, waiting time, and raw material powder application time are controlled such that the scan time is limited by the following formula:

[0010] Scan time (t) s ) = Exposure time (t) e ) + Waiting time (t) w ) + Raw material powder application time (t) p )

[0011] The scanning time is not less than a specific minimum. Exposure time is defined as the period during which the raw material powder layer is exposed to electromagnetic or particle radiation. Waiting time is defined as the period during which the raw material powder layer is not exposed to electromagnetic or particle radiation and a new raw material powder layer has not yet been applied on top of the layer. Raw material powder application time is defined as the period during which a new raw material powder layer is applied on top of the layer.

[0012] Therefore, in order to control the scanning time of the corresponding raw material powder layer portion, exposure time, waiting time, and raw material powder application time are considered. Typically, exposure time, waiting time, and raw material powder application time can take any desired value, including zero. Depending on the exposure time and raw material powder application time, a waiting time may be required to obtain or not obtain the desired scanning time. Therefore, providing a waiting time can be optional.

[0013] Specifically, to adapt to the scanning time of the corresponding raw material powder layer portion, the exposure time, waiting time, or raw material powder application time can be changed. Of course, one or more of the exposure time, waiting time, and raw material powder application time can be changed as needed to adapt to the scanning time, for example, to correspond to the minimum scanning time. For example, the exposure time can be extended by reducing the scanning speed of the radiation beam, increasing the number of vectors in the radiation pattern (in other words, increasing the length of the radiation path), or using only a few radiation beams when using multiple radiation beams. For example, the waiting time can be implemented or extended by delaying the start of applying a new raw material powder layer and / or delaying the start of exposure after applying a new raw material powder layer. For example, the raw material powder application time can be extended by slowing down the moving speed of the powder application device, adding a new powder layer in multiple sublayers, or creating additional channels in the powder bed without adding additional powder, for example, to compress the powder layer and make the powder layer uniform. In the sense of this invention, the time for the powder application device to create additional channels is understood as part of the raw material powder application time.

[0014] The exposure time can be a single period of time that begins when selective irradiation of a portion of the raw material powder layer begins and ends when the corresponding workpiece layer portion has been formed within the raw material powder layer. The waiting time can be a single period of time that begins immediately after the exposure time ends and continues until the application of a new raw material powder layer begins. However, it is also conceivable that the exposure time comprises multiple exposure intervals during which portions of the raw material powder layer are exposed to electromagnetic radiation or particle radiation. These exposure intervals can be interrupted and / or followed by corresponding waiting intervals.

[0015] A specific minimum scan time is set for each layer based on its specific quality parameters; this minimum scan time is defined individually. In other words, in a method of operating equipment for producing three-dimensional workpieces, a minimum scan time is set individually for each layer based on quality parameters that are layer-specific and therefore can vary from layer to layer. Consequently, the minimum scan time can also vary from layer to layer.

[0016] Of course, specific quality parameters for a layer can be equal across multiple layers, and in particular across all layers, and the quality parameters can be equal for all layer portions (i.e., all exposed areas). Due to various effects on the processing, the minimum scan time can vary from layer portion to layer portion to achieve equal specific quality parameters.

[0017] The corresponding layer portion can be a predetermined part of a layer with fixed coordinates (i.e., fixed dimensions and position) in the plane of the build field. Alternatively, the corresponding layer portion can be determined based on the shape of the workpiece to be produced, particularly based on the cross-section of the workpiece in the current layer; thus, the size and position of the corresponding layer portion can vary from layer portion to layer portion. The corresponding layer portion can also be defined as encompassing the entire layer. Of course, a layer can include more than one corresponding layer portion, for example, if more than one workpiece is nested in a build job. In this case, it should be understood that a minimum scan time can be set for each corresponding layer portion, a group of corresponding layer portions (e.g., in a specific locally related section), or all corresponding layer portions (i.e., the entire layer).

[0018] Layer-specific quality parameters are parameters that indicate the quality of a layer portion of a workpiece to be produced. For example, layer-specific quality parameters may be adapted to indicate that the workpiece layer portion is free of material defects, has the required dimensions and size, has the required microstructure, has the required crystal structure (e.g., austenitic, martensitic, or any other crystal structure or material phase depending on the type of raw material powder), etc. The minimum scan time is a sufficiently long scan time to ensure that the workpiece layer portion can be produced with the required quality.

[0019] By individually adjusting the minimum scan time for each layer, variations or uniformities in layer-specific quality parameters from layer to layer can be considered. Therefore, each layer can be produced in a manner that ensures the desired quality. Simultaneously, since a minimum scan time can be set for each layer to be sufficiently long to ensure that the workpiece layer can be produced with the desired quality rather than requiring a longer time, efficient workpiece production is achieved. For example, for each layer, the layer-specific quality parameters indicate that if the layer is scanned with the expected scan time determined by the geometry of the workpiece layer to be produced and the operating parameters of the irradiation apparatus (such as scan speed, spot size, and irradiation beam power), the desired quality can be achieved without extending the scan time. However, if, for each layer, the layer-specific quality parameters indicate that the desired quality cannot be achieved by scanning the layer with the expected scan time determined by the geometry of the workpiece layer to be produced and the operating parameters of the irradiation apparatus, the scan time can be extended to the minimum scan time.

[0020] For at least a portion of at least some layers of a workpiece to be produced, layer-specific quality parameters and / or minimum scan times can be determined before production of the three-dimensional workpiece begins. For example, for a layer of interest, layer-specific quality parameters and / or minimum scan times can be determined based on geometric data indicating the overall geometry of the workpiece to be produced and / or the geometry of the layer of interest. Furthermore, to determine the layer-specific quality parameters and / or minimum scan times, the position of the layer of interest within the workpiece in the vertical direction can be considered. Additionally, the expected scan times and / or exposure times for the layer of interest, resulting from the geometry of the layer of interest and the expected operating parameters of the radiating device, can be considered. For example, for each layer of interest, layer-specific quality parameters and / or minimum scan times can be determined by means of preferred computer-aided simulations before production of the three-dimensional workpiece begins.

[0021] Alternatively or additionally, for at least a portion of at least some layers of a workpiece to be produced, specific quality parameters of the layer portion can be determined on-site during the production of the three-dimensional workpiece. For example, these specific quality parameters can be monitored using suitable sensor equipment.

[0022] In a preferred embodiment, a layer-specific quality parameter indicates the temperature of the corresponding layer portion at a predetermined time, such that the scanning time is controlled based on the temperature of the corresponding layer portion at the predetermined time. In other words, the temperature of the corresponding layer portion at the predetermined time can be used as a control parameter, determined on-site before the start of production of the 3D workpiece or during production, and the scanning time is then controlled based on the determined temperature. In one embodiment, the layer-specific quality parameter indicates the temperature of the corresponding layer portion at the end of the scanning time.

[0023] As the height of the workpiece increases, it becomes increasingly difficult to dissipate heat from the workpiece layer sections after scanning. Therefore, during the production of workpieces with large vertical heights, a thermal gradient may be generated within the workpiece, meaning that the upper layer sections of the workpiece may not cool as required during the routine process of scanning the layer sections and applying a new layer of raw material powder to the top of the scanned layer sections.

[0024] In an alternative embodiment, the specific quality parameter of the layer portion indicates the temperature of the corresponding layer portion before a new layer of raw material powder is applied.

[0025] A specific minimum scanning time can be set such that the temperature of the corresponding layer portion does not exceed a predetermined maximum at the end of the scanning time. Extending the scanning time, and thus extending the time until the next layer of raw material powder is applied on top of the corresponding layer portion, allows the corresponding layer portion to cool as needed. Therefore, the generation of thermal gradients within the workpiece or the thermal gradients can be limited to a predetermined allowable range during workpiece production. To ensure that the temperature of the corresponding layer portion does not exceed the predetermined maximum at the end of the scanning time, it is particularly preferable to extend the scanning time up to the specific minimum by selecting an appropriate waiting time while keeping the exposure time constant. During the waiting time, no further heat is introduced into the workpiece, allowing the previously produced layer portion to cool to the required temperature. However, it is also conceivable to extend the exposure time or extend both the exposure time and the waiting time.

[0026] To adjust the scanning time and, in particular, to determine a suitable waiting time, other parameters of the process can be considered, such as the total or relative or average value of the radiation power received from the layer portion, the number of irradiation beams used simultaneously, the exposed area within the layer portion, the path length of the irradiation beam within the layer portion, the exposure duration of the layer portion, the temperature at one or more specific points in the processing chamber, the temperature of the carrier, the temperature at one or more specific points in the build area, the average temperature of the layer portion, the radiation value emitted from the build area, the radiation value emitted from the layer portion, the radiation value emitted from the region containing the focal point of the radiation beam, the thermal expansion value of the build area, the temperature of the processing gas supplied to the layer portion, the temperature or composition of the processing gas extracted from the layer portion, the temperature, quantity and rate of the processing gas, or the power of the heater or cooler (e.g., the power of the heater or cooler in or near the carrier or within the carrier), to name just a few examples.

[0027] Of course, in addition to adjusting the minimum scan time, the above parameters and other parameters can also be adjusted, and the adjustment of the scan time, especially the determination of a suitable waiting time, can be considered.

[0028] Another option affecting specific quality parameters of a layer is the choice of scanning strategy. Particularly when powder bed melting equipment includes more than one irradiation beam and / or layers include more than one corresponding layer portion, such as when multiple workpieces are nested in a build operation, there may be differences between irradiating more than one layer portion simultaneously, in groups simultaneously, or one after another. In a preferred embodiment, the maximum number of layer portions irradiated simultaneously is equal to the number of available irradiation beams; in other words, when an irradiation beam begins irradiating a first layer portion, it will not begin irradiating another layer portion until all areas to be exposed to irradiation have been irradiated. Therefore, in the case of multiple workpieces, a preferred embodiment first irradiates all areas belonging to one workpiece and then irradiates the second workpiece. The number, size, and location of the layer portions can also be considered when selecting a scanning strategy. In a preferred embodiment, the irradiation sequence of the layer portions can be determined to avoid or at least limit temperature gradients between and / or within the layer portions. In an alternative embodiment, the irradiation sequence of the layer portions can be determined by allowing the first irradiated layer portion to cool slightly before irradiating adjacent layer portions.

[0029] Powder bed melting equipment can be designed to simultaneously irradiate one portion of a powder bed and apply new feedstock powder to another portion of the powder bed. This method can be used because it only determines the minimum scan time for the layer portion.

[0030] A specific minimum scan time can be set such that the corresponding layer portion has the desired crystal structure at the end of the scan time. This can be achieved by appropriately controlling the cooling rate of the corresponding layer portion. For example, a minimum scan time can be set such that during the scan time, i.e., until a new layer of raw material powder is applied on top of the corresponding layer portion, the transformation from an austenitic crystal structure to a martensitic crystal structure is achieved in the layer portion. This can be achieved, for example, by ensuring that the temperature of the corresponding layer portion at the end of the scan time does not exceed a value associated with the structural transformation (e.g., 200°C for most martensitic aging steels). The most preferred, but not limiting, material used with the method is a steel with a martensitic structural transformation, such as 1.2709, 17-4PH, or M789, with a preferred temperature value at the end of the scan time below the transformation temperature.

[0031] Other alloys and materials also involve transformations in crystal structure, so the preferred temperature value at the end of the scan time can be within a predetermined range based on the material properties where no transformation occurs. Therefore, the temperature value can be limited not only to a maximum value but also to a minimum value. Thus, an additional maximum scan time can also be determined. Typical temperature limits are material-based and range from 100°C to 800°C. In a preferred embodiment, at a predetermined time during the scan time, such as at the end of the scan time, the measured temperature at a specific point on the layer portion or the average temperature on the layer portion is in the range of less than 60°C, for example, in the range between 150°C and 210°C, and particularly preferably in the range of less than 30°C, for example, in the range between 175°C and 205°C. It should be noted that, for example, when the powder bed melting apparatus includes a heater, a minimum scan time can also ensure heating of the layer portion.

[0032] Even when the material does not involve structural transformation, it has been found that controlling the minimum scan time to reach the predetermined temperature range in the layer portion improves the quality of the workpiece.

[0033] Layer-specific quality parameters can indicate abrupt changes in the exposed area between at least a portion of a corresponding layer and at least a portion of an adjacent layer. These layer-specific quality parameters can then be readily determined based on the geometry data of the workpiece to be produced. Sudden changes in the exposed area and exposure time within at least a portion of an adjacent layer can lead to undesirable effects in the workpiece to be produced, such as the formation of horizontal lines. Therefore, it is preferable to avoid abrupt changes in exposed area / exposure time from layer to layer.

[0034] Alternatively or additionally, when more than one material is used, specific quality parameters of the layer portion can indicate abrupt changes in the radiant power received from the layer portion, changes in the layer thickness, or changes in the proportion of the raw material powder. When there are more than one corresponding layer portion in a layer, changes in a particular portion can cancel each other out from the perspective of the complete layer or the group of layer portions. This must be taken into account when grouping layer portions for determination.

[0035] A specific minimum scan time can be set such that the difference in scan time between at least a portion of adjacent layers does not exceed a predetermined maximum value. To ensure that the difference in scan time does not exceed the predetermined maximum value, it is particularly preferable to extend the scan time until the specific minimum value by selecting an appropriate exposure time while keeping the waiting time constant. Continuous increases and decreases in exposure time, rather than sudden changes in exposure time, avoid undesirable effects, such as creating horizontal lines in the workpiece.

[0036] Essentially, the method described herein for operating an apparatus for producing three-dimensional workpieces requires only the use of a single layer-specific quality parameter. However, it is also conceivable to control the scan time based on more than one layer-specific quality parameter. For example, the scan time can be controlled such that the temperature of the corresponding layer portion at the end of the scan time does not exceed a predetermined maximum value, and the difference in scan time between at least a portion of adjacent layers does not exceed a predetermined maximum value.

[0037] An apparatus for producing three-dimensional workpieces by irradiating a layer of raw material powder with electromagnetic radiation or particle radiation includes a powder application device for applying the layer of raw material powder onto a carrier. The apparatus also includes an irradiation device for selectively irradiating the layer of raw material powder with electromagnetic radiation or particle radiation according to the geometry of the corresponding layer of the workpiece to be produced. Furthermore, the apparatus includes a control device adapted to control the powder application device and the irradiation device to apply the layer of raw material powder and irradiate the layer of raw material powder with electromagnetic radiation or particle radiation until the workpiece achieves the desired shape and size. For at least a portion of at least some layers, the control device is adapted to control the exposure time, the waiting time, and the raw material powder application time (the exposure time is defined as the time period during which the layer portion is exposed to electromagnetic radiation or particle radiation, the waiting time is defined as the time period during which the layer portion is not exposed to electromagnetic radiation or particle radiation and no new raw material powder layer is applied on top of the layer portion, and the raw material powder application time is defined as the time period during which a new raw material powder layer is applied on top of the layer portion), such that the scan time from the start of exposure to electromagnetic radiation or particle radiation of the corresponding raw material powder layer portion until the start of exposure to electromagnetic radiation or particle radiation of the new raw material powder layer applied on top of the layer portion is defined by the following formula:

[0038] Scan time (t) s ) = Exposure time (t) e ) + Waiting time (t) w ) + Raw material powder application time (t) p )

[0039] The scanning time is not less than a specific minimum value set individually for the layer based on specific quality parameters of the layer.

[0040] The control device can be adapted to control the scanning time based on layer-specific quality parameters and / or minimum scanning time, which are determined on-site before the start of production of the 3D workpiece and / or during the production of the 3D workpiece.

[0041] A specific quality parameter for a layer portion can indicate the temperature of the corresponding layer portion at the end of the scan time, allowing the control device to be adapted to control the scan time based on the temperature of the corresponding layer portion at a predetermined time. The control device can be adapted to set a specific minimum scan time such that the temperature of the corresponding layer portion at the end of the scan time does not exceed a predetermined maximum value. Alternatively or additionally, the control device can be adapted to set a specific minimum scan time such that the corresponding layer portion has the desired crystal structure at the end of the scan time.

[0042] A specific quality parameter for a layer can indicate abrupt changes in the exposed area between at least a portion of the corresponding layer and at least a portion of an adjacent layer. The control device can be adapted to set a specific minimum scan time such that the difference in scan time between adjacent layer portions does not exceed a predetermined maximum value. Attached Figure Description

[0043] Preferred embodiments of the present invention will be described in more detail with reference to the accompanying schematic diagrams, in which:

[0044] Figure 1 An apparatus for producing three-dimensional workpieces by irradiating a layer of raw material powder with electromagnetic radiation or particle radiation is shown.

[0045] Figure 2a and Figure 2b This illustrates how scanning time can be controlled based on specific quality parameters of the layer portion. Figure 1 The influence of the equipment on the microstructure of the workpiece produced;

[0046] Figure 3a and Figure 3b This illustrates how scanning time can be controlled based on specific quality parameters of the layer portion. Figure 1 The influence of the size of the workpiece produced by the equipment; and

[0047] Figure 4 The graph shows the evolution of exposure time with build height, both with and without considering specific quality parameters of the layer portion. Detailed Implementation

[0048] Figure 1An apparatus 10 for producing three-dimensional workpieces via a layer-by-layer additive manufacturing process is shown. The apparatus includes a carrier 12 and a powder application device 14 for applying raw material powder onto the carrier 12. The carrier 12 and the powder application device 14 are housed within a processing chamber 16, which is sealable from the ambient atmosphere. An internal atmosphere is established using a protective gas supplied from a processing gas inlet 15. The machine also includes a processing gas outlet (not shown). The processing gas can flow from the outlet to the inlet 15, thereby being cooled or heated. The carrier 12 can be vertically displaced within the constructed cylinder 13 such that the carrier 12 can move downwards as the workpiece 18 is constructed within layers of raw material powder on the carrier 12, with increasing workpiece construction height. The carrier may include a heater and / or a cooler.

[0049] The apparatus 10 also includes an irradiation device 20 for selectively irradiating the raw material powder applied to the carrier 12 with electromagnetic radiation or particle radiation. The irradiation device 20 includes a radiation beam source 22 (particularly a laser beam source) and an optical unit 24 for guiding and processing the radiation beam emitted by the radiation beam source 22. A control device 26 is configured to control the operation of the apparatus 10, particularly the operation of the powder application device 14 and the irradiation device 20.

[0050] Finally, the device 10 is equipped with multiple sensor devices. A first sensor device 27 is adapted to measure the temperature of the atmosphere inside the processing chamber 16. A second sensor device 28 is adapted to detect the temperature of the raw material powder / workpiece layer during and after irradiation with electromagnetic radiation or particle radiation. Sensor device 28 can, for example, be designed as a suitable camera adapted to detect infrared radiation distributed to multiple locations on the raw material layer. In another exemplary embodiment, sensor device 28 can be a pyrometer device capable of detecting the temperature at a specific point inside the processing chamber 16 (e.g., on the raw material layer), or the average temperature over a region inside the processing chamber 16 (e.g., on the raw material layer). A third sensor device 29 is adapted to detect radiation emitted from the raw material layer at the focal point and / or in the region surrounding the focal point of a radiation beam emitted by the radiation beam source 22. The sensed radiation is guided to the third sensor device 29 via an optical unit 24. In a preferred exemplary embodiment, the carrier 12 includes another fourth sensor device (not shown) for measuring the temperature of the carrier. Device 10 may include additional sensor devices, such as those for measuring the temperature of the processing gas at the processing gas inlet 15 or another location, or for measuring the composition of the processing gas inside the processing chamber 16. It should be understood that this example is not limiting, and devices according to the invention may include only a few named sensors or all named sensors, and may include additional sensors.

[0051] During operation of the equipment 10 for producing three-dimensional workpieces, a layer of raw material powder is applied to a carrier 12 by a powder application device 14. To apply the raw material powder layer, the powder application device 14 is moved across the carrier 12 under the control of a control unit 26. Then, again under the control of the control unit 26, the raw material powder layer is selectively irradiated with electromagnetic radiation or particle radiation by an irradiation device 20 according to the geometry of the corresponding layer of the workpiece 18 to be produced. The steps of applying the raw material powder layer to the carrier 12 and selectively irradiating the raw material powder layer with electromagnetic radiation or particle radiation according to the geometry of the corresponding layer of the workpiece 18 to be produced are repeated until the workpiece 18 reaches the desired shape and size.

[0052] The scanning time of the corresponding raw material powder (i.e., the time period from the start of exposure to electromagnetic radiation or particle radiation of at least a portion of the corresponding raw material powder layer until the start of exposure to electromagnetic radiation or particle radiation of a new raw material powder layer applied on top of said layer portion) is defined by the following formula:

[0053] Scan time (t) s ) = Exposure time (t) e ) + Waiting time (t) w ) + Raw material powder application time (t) p )

[0054] The exposure time is defined as the period during which the raw material powder layer is actually exposed to electromagnetic radiation or particle radiation. The waiting time is defined as the period during which the raw material powder layer is not exposed to electromagnetic radiation or particle radiation and no new raw material powder layer is applied on top of the layer. The raw material powder application time is defined as the period during which a new raw material powder layer is applied on top of the layer.

[0055] For at least a portion of at least some raw material powder / workpiece layers, the scanning time from the start of exposure to electromagnetic radiation or particle radiation of the corresponding raw material powder layer portion until the start of exposure to electromagnetic radiation or particle radiation of a new raw material powder layer applied on top of said layer portion is controlled by control device 26, so that the scanning time is not less than a specific minimum value. Specifically, the exposure time, waiting time, and raw material powder application time are controlled so that the scanning time is not less than a specific minimum value. A specific minimum value of the scanning time, i.e., the minimum scanning time, is set individually for said layer portion according to a specific quality parameter of the layer portion. The specific quality parameter of the layer portion can vary from layer portion to layer portion. Therefore, the minimum scanning time can also vary from layer portion to layer portion.

[0056] As the height of workpiece 18 increases, heat dissipation from the workpiece layer portion becomes increasingly difficult after scanning. Therefore, a thermal gradient may occur within workpiece 18 during its production; that is, the upper layer portion of workpiece 18 may not cool as required during the routine process of scanning the layer portion and applying a new layer of raw material powder to the top of the scanned layer portion. In the production of large-volume parts made of maraging steel 1.2709, this can lead to insufficient cooling of the upper layer portion of workpiece 18 to achieve the desired austenite / martensite transformation. Specifically, if the layer portion is not cooled below the austenite / martensite transformation temperature, i.e., not below 200°C, the austenite-to-martensite transformation will not occur.

[0057] Therefore, the portion of the workpiece layer that did not undergo the austenitic / martensitic transformation during the construction of workpiece 18 only undergoes the transformation after workpiece 18 has been completed. However, this can cause a size deviation in the height of workpiece 18. In particular, when the phase transformation occurs only after workpiece 18 is completed, the volume change associated with the austenitic / martensitic transformation may lead to an increase in the width of the upper part of workpiece 18 because the material cannot expand in the vertical direction.

[0058] To address this issue, in the apparatus 10 described herein, during the production of workpiece 18 from maraging steel 1.2709, a control unit 26 controls the temperature of the corresponding layer portion at the end of the scanning time using a specific quality parameter indicating the first layer portion's temperature. Specifically, a specific minimum value for the scanning time is set such that the corresponding layer portion has the desired crystal structure, i.e., a martensitic structure, at the end of the scanning time. In the exemplary embodiments described herein, this is achieved by ensuring that the temperature of the corresponding layer portion does not exceed 200°C at the end of the scanning time.

[0059] For at least a portion of at least some layers of a workpiece to be produced, specific quality parameters and / or minimum scan time for the first layer portion are determined before production of the 3D workpiece begins. Specifically, for each layer portion, before production of the 3D workpiece begins, by means of, Figure 2a and Figure 2b The computer-aided simulation shown determines the first-layer portion-specific quality parameters and minimum scan time. The first-layer portion-specific quality parameters indicate the temperature of the corresponding layer portion at the end of the scan time.

[0060] from Figure 2aIt is evident that the temperature of the raw material powder / workpiece layer portion at the end of the expected scanning time increases with the increase of the vertical height of workpiece 18. The expected scanning time is determined by the geometry of the workpiece layer portion to be produced and the expected operating parameters of the radiation device (such as scanning speed, spot size, and radiation beam power). In the upper part of workpiece 18, the temperature rises to 272°C, and therefore the aforementioned austenite / martensite transformation temperature is 200°C. Therefore, these workpiece layer portions only undergo the austenite / martensite transformation after workpiece 18 is completed. The volume change associated with the austenite / martensite transformation thus results in an increase in the width of workpiece 18 in the upper part of workpiece 18, such as... Figure 3a As shown.

[0061] Figure 2b The temperature of the raw material powder / workpiece layer portion at the end of the scan time is shown. This scan time is controlled to be no less than the minimum scan time specific to the layer portion, while taking into account the specific quality parameters of the first layer portion. If the scan time is controlled to be long enough, the layer portion in the upper part of workpiece 18 has sufficient time to cool to a temperature below 156°C. Therefore, during the production of workpiece 18, each layer portion has undergone an austenitic / martensite transformation, resulting in volume changes associated with the austenitic / martensite transformation occurring in all directions (i.e., also in the vertical direction). Thus, a continuous width of workpiece 18 can be achieved, such as... Figure 3b As shown.

[0062] In the exemplary embodiments described herein, where a minimum scan time is determined taking into account heat dissipation that varies with the vertical height of the workpiece 18, such that a specific quality parameter of the first layer portion (i.e., the temperature of the raw material powder / workpiece layer portion at the end of the scan time) does not exceed 200°C, the control device 26 adapts the scan time to the minimum scan time by simply extending the waiting time while maintaining a constant exposure time (for workpieces with a constant exposure area). However, it is also conceivable that the control device 26 adapts to both the exposure time and the waiting time to ensure that the scan time is not less than the minimum scan time.

[0063] Furthermore, although in the exemplary embodiments described herein, the specific quality parameters and minimum scan time of the layer portion are determined by means of computer-aided simulation before the production of workpiece 18 begins, it is also conceivable to determine the specific quality parameters and / or minimum scan time of the layer portion on-site during the production of the three-dimensional workpiece. For example, sensor device 28 can be used to measure the temperature of the raw material powder / workpiece layer portion during the production of workpiece 18, for example, the temperature of local decomposition or the temperature with an average value in that area. Then, control device 26 can determine a suitable minimum scan time to ensure that the temperature does not exceed 200°C and adjust the current scan time accordingly.

[0064] In another exemplary embodiment, during the production of the three-dimensional workpiece, the control device 26 determines specific quality parameters and / or minimum scan time of a layer portion on-site in a closed-loop control manner. This means that the control device 26 can extend the minimum scan time, for example, by extending the waiting time in intervals, determining the current temperature in each interval, and stopping the waiting time when the determined temperature drops below a predetermined threshold (e.g., 200°C) to extend the minimum scan time.

[0065] Quality issues in the workpiece 18 to be produced may also cause sudden changes in the exposed area, and thus cause sudden changes in the exposure time of portions of adjacent layers, such as... Figure 4 The lower discontinuity curve is shown. Therefore, in the apparatus 10 described herein, during the production of workpiece 18, the second layer portion-specific quality parameter, used by the control unit 26 to control the scanning time, indicates a sudden change in the exposed area between at least a portion of the corresponding layer and at least a portion of the adjacent layer. The second layer portion-specific quality parameter can be easily determined based on the geometric data of the workpiece to be produced before production of workpiece 18 begins. Therefore, “critical” layer regions with layer portions that exhibit a sudden change in exposed area relative to at least a portion of the adjacent layer, and thus a sudden change in exposure time, can be easily identified.

[0066] To avoid abrupt changes in exposure area / exposure time between adjacent layer sections, a specific minimum scan time is set such that the difference in scan time between adjacent layer sections does not exceed a predetermined maximum value. This is achieved, in particular, by selecting an appropriate exposure time while maintaining a constant waiting time. Therefore, control unit 26 controls the scan time so that, in the "critical" layer region, the exposure time increases and decreases continuously, rather than changing abruptly, as... Figure 4 The upper continuous curve is shown.

Claims

1. Method of operating an apparatus (10) for producing a three-dimensional workpiece (18) by irradiating layers of a feedstock powder with electromagnetic or particle radiation, the method comprising the steps of: a) applying a layer of a feedstock powder onto a carrier (12); b) selectively irradiating the layer of the feedstock powder with electromagnetic or particle radiation in accordance with the geometry of the corresponding layer of the three-dimensional workpiece (18) to be produced; and c) repeating steps a) and b) until the three-dimensional workpiece (18) reaches the desired shape and size, wherein, for at least some layers and at least one portion thereof, - exposure time t e is defined as the time period during which the layer portion is exposed to electromagnetic or particle radiation, - waiting time t w is defined as the time period during which the layer portion is not exposed to electromagnetic or particle radiation and no new layer of raw material powder is applied on top of the layer portion, and - raw material powder application time t p is defined as the time period during the application of a new raw material powder layer on top of the layer portion, the exposure time, the waiting time and the raw material powder application time are controlled such that the scan time t from the beginning of the exposure to electromagnetic or particle radiation of a respective raw material powder layer portion until the beginning of the exposure to electromagnetic or particle radiation of a new raw material powder layer applied on top of the layer portion s is defined by the equation Scan time t s = Exposure time t e + Wait time t w + Raw material powder application time t p the scan time is not lower than a specific minimum value individually set for the layer portion in accordance with a layer portion specific quality parameter, wherein the layer portion specific quality parameter is indicative of an abrupt change of an exposure area between at least one portion of a respective layer and at least one portion of an adjacent layer.

2. Method according to claim 1, wherein, the layer portion specific quality parameter and / or the corresponding minimum scan time is determined on site before starting the production of the three-dimensional workpiece and / or during the production of the three-dimensional workpiece.

3. Method according to claim 1, wherein, the scan time t s The specific minimum value of the scan time t s is set such that the difference in the scan time t between adjacent layer portions does not exceed a predetermined maximum value.

4. Apparatus (10) for producing a three-dimensional workpiece (18) by irradiating layers of a feedstock powder with electromagnetic or particle radiation, the apparatus (10) comprising: a powder application device (14) for applying a layer of a feedstock powder onto a carrier; an irradiation device (20) for selectively irradiating the layer of the feedstock powder with electromagnetic or particle radiation in accordance with the geometry of the corresponding layer of the three-dimensional workpiece (18) to be produced; and a control device (26) adapted to control the powder application device (14) and the irradiation device (20) for applying a layer of a feedstock powder and for irradiating the layer of the feedstock powder with electromagnetic or particle radiation until the three-dimensional workpiece reaches the desired shape and size, wherein, for at least some layers and at least one portion thereof, the control device (26) is adapted to control an exposure time, a waiting time and a feedstock powder application time, the scan time is not lower than a specific minimum value individually set for the layer portion in accordance with a layer portion specific quality parameter, - exposure time t e is defined as the time period during which the layer portion is exposed to electromagnetic or particle radiation, - waiting time t w is defined as the time period during which the layer portion is not exposed to electromagnetic or particle radiation and no new layer of raw material powder is applied on top of the layer portion, and - raw material powder application time t p is defined as the time period during the application of a new raw material powder layer on top of the layer portion, such that the scanning time t from the beginning of the exposure of the respective raw material powder layer portion to electromagnetic or particle radiation until the beginning of the exposure of the new raw material powder layer applied on top of the layer portion to electromagnetic or particle radiation s is defined by the following equation: Scan time t s = Exposure time t e + Wait time t w + Raw material powder application time t p wherein the layer portion specific quality parameter is indicative of an abrupt change of an exposure area between at least one portion of a respective layer and at least one portion of an adjacent layer.

5. Apparatus (10) according to claim 4, 6. Apparatus (10) according to claim 4, wherein The control device (26) is adapted to control the scanning time t depending on a layer portion specific quality parameter and / or a minimum scanning time s , which layer portion specific quality parameter and / or minimum scanning time is determined on site before starting the production of the three-dimensional workpiece and / or during the production of the three-dimensional workpiece. ​ wherein The control device (26) is adapted to set the scan time t s to the specific minimum value such that the difference of the scan time t s between adjacent layer portions does not exceed a predetermined maximum value.

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