Calibration board and calibration technique

Abstract

A calibration plate is described for calibrating an apparatus for producing a three-dimensional workpiece by irradiating a layer of a raw material powder with electromagnetic radiation or particle radiation, the calibration plate comprising surface features representing defects of the layer to be irradiated. Further described is a method of calibrating a device, the method comprising: obtaining at least one image of a calibration plate disposed within a build cavity of the device, detecting one or more of at least one surface feature of the calibration plate based on the obtained at least one image; and calibrating the device based on the detected one or more surface features. Further described is a system comprising the calibration board and an apparatus configured to perform the method.

Description

Field of the Invention

[0001] The present invention generally relates to calibration plates and calibration techniques using such calibration plates. In particular, a calibration plate for a device for producing three-dimensional workpieces by irradiating a layer of raw material powder with electromagnetic radiation or particle radiation, and a system including the calibration plate are provided. The present invention also relates to the device and a method for calibrating such a device. Background Art

[0002] In layer-by-layer additive methods, a workpiece is produced layer by layer by generating a series of cured and interconnected workpiece layers. These processes can be distinguished by the type of raw material and / or the manner in which the raw material is cured to produce the workpiece.

[0003] For example, powder bed fusion is a layer-by-layer additive process by which a powdered, especially metallic raw material powder and / or ceramic raw material powder can be processed into a three-dimensional workpiece with a complex shape. For this purpose, a layer of raw material powder is applied (e.g., deposited) onto a carrier (e.g., a build platform), and it is irradiated, for example, with electromagnetic radiation (e.g., a laser) or particles (e.g., an electron beam) in a position-selective manner according to the desired geometry of the workpiece to be produced. The radiation penetrating into the powder layer causes heating and thus causes selective curing of the powder layer (e.g., by melting or sintering of the raw material powder particles). Further, a layer of raw material powder is sequentially applied and processed onto the layer that has already been subjected to radiation treatment on the carrier until the workpiece has the desired shape and dimensions. Selective melting or sintering can be particularly used for the production of prototypes, tools, replacement parts, or medical prostheses, such as dental or orthopedic prostheses, based on computer-aided design (CAD) data.

[0004] In some cases, the deposited powder layer to be irradiated may include one or more defects, which can have a negative impact on subsequent processing steps, especially the selective curing of the defective powder layer and / or the subsequent deposition of a powder layer onto the defective powder layer. Defects in the powder layer to be irradiated may also have a negative impact on the physical properties (e.g., rigidity and / or surface smoothness) of the produced workpiece.

[0005] At least one defect in the deposited powder layer to be irradiated can be detected and / or classified, for example, using a detection system. The detection system can be part of a device for producing three-dimensional workpieces by irradiating a layer of raw material powder with electromagnetic radiation or particle radiation. The detection system can be implemented by the control unit of the device.

[0006] At least one defect in a powder layer to be irradiated can be detected and / or classified based on an image (e.g., two-dimensional or three-dimensional) of at least a portion of the powder layer to be irradiated (e.g., in the image). The image can include spatial information and / or depth information. The image can be acquired by an image acquisition unit (e.g., of a device and / or a detection system), e.g., by a camera (e.g., a stereo camera) included in the device.

[0007] The image acquisition unit can be configured to acquire a single image including the entire powder layer or the entire build area of the powder layer, where the build area is the portion of the powder layer that can be irradiated by electromagnetic radiation or particle radiation. Alternatively or additionally, the image acquisition unit can be configured to acquire a plurality of images, each image being a different portion of the powder layer and / or the build area. Defects in the powder layer can be detected and / or classified (e.g., by a detection system and / or a control unit) based on one or more (e.g., all) of the single image or the plurality of images. The single image and / or the plurality of images can be acquired via an optical scanning system of the device, the optical scanning system being configured to direct electromagnetic radiation towards the powder layer to be irradiated.

[0008] Detecting at least one defect can include: identifying one or more portions in at least one image that match at least one predefined criterion. Classifying at least one defect can include: classifying the detected defect based on at least one predefined criterion or based on another predefined criterion. The corresponding at least one predefined criterion can include one or more predefined geometric properties and / or one or more predefined optical properties. Geometric properties can include one or more of shape, contour, roughness, height, depth, width, length, and radius of curvature. Optical properties can include one or more of texture, color, brightness, and reflectivity. Detection and / or classification of at least one defect can be performed by or based on at least one of the following: (i) a pattern recognition algorithm, (ii) a blob detection algorithm, (iii) an edge detection algorithm, (iv) a shape detection algorithm, and (v) a trained machine learning model. Detecting and / or classifying at least one defect can include: adjusting (e.g., filtering, color correction, color space conversion, cropping, rotation, shifting, distortion, and / or scaling) at least one image of the powder layer to be irradiated (e.g., a portion of the powder layer) obtained, and detecting one or more surface features based on the adjusted image (e.g., in the adjusted image). Before acquiring at least one image for detecting and / or classifying at least one defect, at least one image can be adjusted (e.g., by the image acquisition unit).

[0009] Based on at least one detected and / or classified defect, a warning can be output (e.g., to a user or to a software component). Alternatively or additionally, one or more process parameters used by a device for producing a three-dimensional workpiece (e.g., for irradiating a layer to be irradiated, for depositing one or more subsequent powder layers, and / or for irradiating one or more subsequent powder layers) can be set or adjusted. The at least one detected and / or classified defect can be associated with predefined process parameters to be set (e.g., a set and / or values of process parameters to be set). Such process parameters can include one or more of the following: the gas composition in the build chamber of the device, the gas flow rate in the build chamber of the device, the temperature of the powder material to be deposited, the temperature of the deposited powder material (e.g., the deposited powder material to be irradiated), the control parameters of a powder deposition unit configured to deposit a powder layer and included in the device (e.g., attitude, speed, path, powder deposition rate, and / or powder deposition area), the attitude or movement of the build platform of the device, and irradiation control parameters (e.g., irradiation position, irradiation beam scan speed, irradiation power, irradiation beam shape, and irradiation beam focus). It will be apparent to those skilled in the art that other process parameters can be set or adjusted based on at least one detected and / or classified defect of the powder layer to be irradiated. Summary of the Invention

[0010] The present application provides a method for calibrating a device for producing a three-dimensional workpiece by irradiating a raw material powder layer with electromagnetic radiation or particle radiation.

[0011] The method can include or can not include the above steps. In any case, the method includes: obtaining at least one image of at least a portion of a calibration plate disposed in the build chamber of the device (e.g., the above build chamber), e.g., disposed in the build area (e.g., the above build area). The at least one image can be acquired by and / or obtained from an image acquisition unit (e.g., when the calibration plate is disposed in the build chamber in a predefined pose or in response to the calibration plate being disposed in the build chamber in a predefined pose). As explained above with reference to an image of a powder layer (e.g., a portion of a powder layer), the at least one image of the calibration plate (e.g., a portion of the calibration plate) can be a single image of the calibration plate (e.g., a portion of the calibration plate), or the at least one image can include multiple images, each image being a different sub-portion of the calibration plate (e.g., a portion of the calibration plate).

[0012] According to the present disclosure, and as described in detail below, the calibration plate includes at least one surface feature, and the at least one surface feature represents (e.g., mimics, simulates, replicates, and / or reproduces) a defect of the layer to be irradiated.

[0013] The method further includes: detecting one or more surface features of the calibration plate based on at least one obtained image (e.g., at least one image of at least a portion of a calibration plate disposed in a construction chamber of the device) (e.g., in the at least one image), (e.g., by a detection system and / or a control unit).

[0014] Detecting one or more surface features may include: identifying one or more portions in the at least one image that match at least one predefined criterion (e.g., the above-mentioned predefined criterion). The at least one predefined criterion may include: one or more predefined geometric properties (e.g., the above-mentioned one or more predefined geometric properties) and / or one or more predefined optical properties (e.g., the above-mentioned one or more predefined optical properties). As in the detection and / or classification of defects, these geometric properties may include one or more of shape, contour, roughness, height, depth, width, length, and radius of curvature, while the optical properties may include one or more of texture, color, brightness, and reflectivity. Detection of one or more surface features may be performed by or based on at least one of the following: (i) a pattern recognition algorithm (e.g., the above-mentioned pattern recognition algorithm), (ii) a blob detection algorithm (e.g., the above-mentioned blob detection algorithm), (iii) an edge detection algorithm (e.g., the above-mentioned edge detection algorithm), (iv) a shape detection algorithm (e.g., the above-mentioned shape detection algorithm), and (v) a trained machine learning model (e.g., the above-mentioned trained machine learning model). Detecting one or more surface features may include: adjusting the at least one obtained image of the calibration plate (e.g., a portion of the calibration plate) (e.g., filtering, color correction, color space conversion, cropping, rotation, shifting, distortion, and / or scaling), and detecting one or more surface features based on the adjusted image (e.g., in the adjusted image). Before obtaining the at least one image for the detection of one or more surface features, the at least one image may be adjusted. The same algorithm or multiple identical algorithms used for the detection and / or classification of at least one defect may be used for the detection of one or more surface features, and vice versa.

[0015] The method further includes: calibrating the device based on the detected one or more surface features (e.g., one or more surface features of the calibration plate).

[0016] The device can be calibrated by setting or adjusting one or more parameters based on one or more detected surface features. At least one of the one or more parameters can be used (e.g., by the device and / or by the detection system and / or by the control unit) (e.g., at a later time) (e.g., based on an image of the powder layer to be irradiated (e.g., a part of the powder layer to be irradiated)) to detect and / or classify defects in the layer to be irradiated. Such parameters can include: upper thresholds, lower thresholds, and / or ranges associated with one or more geometric properties and / or one or more optical properties of features to be detected and / or classified as defects (e.g., acceptable defects, unacceptable defects, or critical defects). Calibrating the device (e.g., setting or adjusting one or more parameters) can include: associating one or more detected surface features (e.g., one or more geometric properties and / or one or more optical properties of one or more detected surface features) with the associated defects represented by the corresponding one or more detected surface features (e.g., the type, size, acceptability, or criticality of the defects) (e.g., one or more geometric properties and / or one or more optical properties of the associated defects).

[0017] For example, at least one parameter set for calibrating the device can define the minimum height as a geometric property of a feature to be detected and / or classified as a defect (e.g., an acceptable defect, an unacceptable defect, or a critical defect). As another example, at least one parameter set for calibrating the device can define the maximum radius of curvature as a geometric property of a feature to be detected and / or classified as a defect (e.g., an acceptable defect, an unacceptable defect, or a critical defect). As yet another example, at least one parameter set for calibrating the device can define the maximum reflectivity or maximum luminance as an optical property of a feature to be detected and / or classified as a defect (e.g., an acceptable defect, an unacceptable defect, or a critical defect).

[0018] After calibrating the device, the method further includes: producing a three-dimensional workpiece by irradiating a raw material powder layer with electromagnetic radiation or particle radiation by the device. Before producing the three-dimensional workpiece, the calibration plate (e.g., and the holder of the calibration plate) can be removed from the build chamber. This removal can be performed automatically or manually.

[0019] The method can include: triggering or indicating the deposition of the powder layer to be irradiated (e.g., on the build platform). The method can include: depositing the powder layer to be irradiated (e.g., on the build platform and / or at least within the build area).

[0020] As described above, the method may include: obtaining at least one image of at least a portion of a powder layer to be irradiated (e.g., a deposited powder layer). The at least one image may be acquired during the production of a three-dimensional workpiece, e.g., after (e.g., at least partially) depositing the powder layer or after (e.g., at least partially) irradiating the powder layer.

[0021] As described above, the method may further include: detecting and / or classifying at least one defect in the powder layer to be irradiated based on the at least one image of the powder layer to be irradiated (e.g., a portion of the powder layer to be irradiated) obtained. This step may be performed based on at least one parameter set or adjusted when calibrating the device (e.g., the at least one parameter described above).

[0022] The method may include: outputting a warning based on the detected and / or classified at least one defect. Alternatively or additionally, the method may include: setting or adjusting one or more process parameters based on the detected and / or classified at least one defect, the process parameters being, for example, for subsequent process steps in manufacturing a three-dimensional workpiece.

[0023] As described above, the present disclosure provides a calibration plate for calibrating a device, i.e., a device for producing a three-dimensional workpiece by irradiating a raw material powder layer with electromagnetic radiation or particle radiation (e.g., the device for producing a three-dimensional workpiece by irradiating a raw material powder layer with electromagnetic radiation or particle radiation described above), the calibration plate including at least one surface feature, the at least one surface feature representing (e.g., mimicking, simulating, replicating, and / or reproducing) a defect of the layer to be irradiated (e.g., a typical defect, a regularly observed defect, an expected defect, and / or a possible defect).

[0024] A defect of the layer to be irradiated may be a local deviation of the surface of the layer (e.g., the upper surface and / or the surface to be irradiated) from a planar powder layer surface (e.g., an optimal planar powder layer surface and / or a predefined planar powder layer surface). In this regard, the roughness of the powder layer surface caused only by the particle size of the powder may be ignored. A defect of the layer to be irradiated may be caused by: incorrect deposition of the raw material powder of the layer to be irradiated, deposition of spatter or debris generated by irradiating a previous layer of raw material powder or by irradiating a portion of the layer to be irradiated, and / or damage to a previously irradiated portion of the raw material powder (e.g., damage to a previously irradiated portion of the raw material powder of the previous layer).

[0025] The at least one surface feature may be a permanent surface feature of the calibration plate. For example, the at least one surface feature may be a rigid (e.g., manually non-deformable), immovable, solid (e.g., single-piece), and / or non-temporary surface feature of the calibration plate. The at least one surface feature may not be composed of uncured powder material.

[0026] The calibration plate can be configured such that the pose (e.g., at least one of position and orientation) of one or more of at least one surface feature on the calibration plate can be adjusted (e.g., manually and / or automatically). Also in this case, the corresponding surface feature can be a rigid, solid, and / or non-temporary surface feature of the calibration plate, and the surface feature can optionally not be composed of uncured powder material.

[0027] The calibration plate can be configured such that one or more of at least one surface feature can be replaced (e.g., manually and / or automatically) with another surface feature representing a defect of the layer to be irradiated (e.g., the layer to be irradiated described above). Also in this case, the corresponding surface feature can be a rigid and / or solid surface feature of the calibration plate, and the surface feature can optionally not be composed of uncured powder material.

[0028] In an exemplary embodiment, at least one surface feature has fixed geometric properties (e.g., predetermined, permanent, and / or non-temporary geometric properties). These geometric properties can include one or more of shape, profile, roughness, height, depth, width, length, and radius of curvature. Alternatively or additionally, at least one surface feature can have fixed optical properties (e.g., predetermined, permanent, and / or non-temporary optical properties). These optical properties can include one or more of texture, color, brightness, and reflectivity.

[0029] At least one surface feature can represent a defect of the layer to be irradiated by mimicking or reproducing the geometric and / or optical properties of the defect. The geometric properties of at least one surface feature can be similar to the geometric properties of the defect of the layer to be irradiated (e.g., the defect represented by the surface feature). Alternatively or additionally, the optical properties of at least one surface feature can be similar to the optical properties of the defect of the layer to be irradiated (e.g., the defect represented by the surface feature).

[0030] In a variant, the calibration plate includes a coating that defines the optical properties of at least one surface feature. The coating can be configured to mimic the optical properties of the powder material (e.g., metal powder material) of the layer to be irradiated. The coating can include silver paint.

[0031] In a variant, at least one surface feature includes selectively cured (e.g., sintered or at least partially melted) powder material (e.g., metal powder material). At least one surface feature can be made of the same material as the raw material powder of the layer to be irradiated.

[0032] At least one surface feature and / or a calibration plate including surface features can be made of a selectively solidified powder material, e.g., a selectively solidified powder material of the same type, composition, material, and / or particle size as the powder material of the layer to be irradiated. At least one surface feature and / or a calibration plate including surface features can be made of a selectively solidified powder material, e.g., a selectively solidified powder material of the same type, composition, material, and / or particle size as the powder material used by the device for producing a workpiece.

[0033] The at least one surface feature can represent a defect caused by at least one of the following events:

[0034] (i) Mis-deposition of the raw material powder of the layer to be irradiated;

[0035] (ii) Deposition of spatter or debris generated by irradiating the raw material powder of the previous layer or by irradiating a portion of the layer to be irradiated; and

[0036] (iii) Damage to a previously irradiated portion of the raw material powder.

[0037] The calibration plate can be configured to be removably (e.g., in one or more predefined poses, e.g., relative to the build area and / or the image acquisition unit) arranged in the build chamber of the device. The calibration plate can be configured to be arranged in the build chamber such that the surface including the surface features is arranged in an attitude (e.g., height) similar to the surface of the raw material powder layer to be irradiated.

[0038] The calibration plate can be configured to be arranged in the build chamber such that at least one surface feature, all surface features, or the entire calibration plate of the calibration plate is located within the build area. The calibration plate can be configured to be arranged in the build chamber such that the image acquired by the image acquisition unit depicts at least one surface feature, e.g., all such surface features of the calibration plate or the complete surface of the calibration plate including the surface features.

[0039] In an exemplary embodiment, the calibration plate is configured to be removably arranged in a holder. The holder is removably arranged in the build chamber (e.g., in one or more predefined poses, e.g., relative to the build area and / or the image acquisition unit) and is configured to arrange (e.g., position) the calibration plate (e.g., in one or more predefined poses) in the build chamber (e.g., when the holder holds the calibration plate). The holder can be configured to be mounted on a build plate (e.g., the above-mentioned build plate) in the build chamber and / or be embedded in a recess of the build chamber, the recess being configured to hold a layer of powder material (e.g., a deposited layer and / or a selectively irradiated layer of powder material).

[0040] The present disclosure also provides an apparatus for producing a three-dimensional workpiece by irradiating a layer of raw material powder with electromagnetic radiation or particle radiation, the apparatus including a control unit (e.g., a processor) configured to perform the method described herein.

[0041] The present disclosure also provides a system. The system includes at least one calibration plate as disclosed herein. The system also includes at least one of the following entities: (i) the apparatus, and (ii) the holder.

[0042] The system may include two or more calibration plates configured to be replaceably arranged in the same holder and different from each other at least in at least one surface feature (e.g., the type, size, orientation, number, and / or alignment of the surface feature). BRIEF DESCRIPTION OF THE DRAWINGS

[0043] These aspects of the invention, as well as other aspects, will now be further illustrated, by way of example only, with reference to the accompanying drawings, in which:

[0044] Figure 1 a schematic layout of an apparatus according to the present disclosure is shown;

[0045] Figure 2 a schematic layout of a calibration plate according to the present disclosure is shown;

[0046] Figures 3a to 3i a schematic diagram of different types of defects according to the present disclosure is shown;

[0047] Figures 4a to 4f a schematic diagram of different types of defects according to the present disclosure is shown;

[0048] Figure 5 a schematic layout of a system according to the present disclosure is shown;

[0049] Figure 6 a flowchart of a method according to the present disclosure is shown. DETAILED DESCRIPTION

[0050] Figure 1Shows a schematic layout of a device 100 according to the present disclosure. The device 100 includes a build chamber 2 in which a three-dimensional workpiece can be produced by selectively irradiating a layer of powder material. A recess 4 in the build chamber 2 is configured to receive a respective layer of the powder material to be irradiated. At the bottom of the recess 4, a build plate 6 is arranged movably. The build plate 6 can be controllably moved downward to provide space for an additional powder layer within the recess 4. Such a powder layer can be deposited by a powder deposition unit 8 slidably arranged on two rails 10. In the illustrated variant, the powder deposition unit 8 includes: a body 12 and a doctor blade 14. The body 12 is configured to hold the powder material to be deposited, and the doctor blade 14 is configured to smooth the powder material deposited in front of the doctor blade 14 when the powder deposition unit 8 moves along the rails 10. It should be noted that other variants of depositing the powder layer are possible and should not be excluded.

[0051] The device 100 includes an energy source 16 configured to emit electromagnetic radiation or particle radiation 18. A beam steering system 20 is configured to controllably direct the radiation 18 to the build plate 6. In the case where a powder layer is deposited on the build plate 6, the powder layer (e.g., within the build area) can be irradiated with the radiation 18 to selectively cure it.

[0052] An image acquisition unit 20 (e.g., a camera such as a stereo camera) is configured to acquire an image of a predefined region 22 (e.g., an adjustable region) in the build chamber 2. The predefined region 22 may include a build area in which the powder material can be cured by the radiation 18. When viewed along the z-direction, the build area may be defined by the contour of the recess 4 and / or the build area may be located within the recess 4.

[0053] In the example shown, the image acquisition unit 20 acquires an image via the same beam steering system 23 that is used to direct the radiation 18 to the build plate 6. In this variant, the radiation 18 is electromagnetic radiation, and the beam steering system 23 may include an optical scanning mirror 24 and / or a beam splitter 26.

[0054] It should be noted that, compared with Figure 1Other arrangements that are different from the arrangement of the image acquisition unit 20 are possible and should not be excluded. For example, an image acquisition unit 20 can be provided that is configured to acquire an image of a predefined area 22 (e.g., a predefined area) without using the beam steering system 23. That is, the optical path of the image acquisition unit 20 and the path of the radiation 18 can (e.g., at least partially) coincide or not coincide. For example, in the case where the radiation 18 is particle radiation, the beam steering system 23 can include an electromagnetic beam conditioning assembly (e.g., an electromagnetic lens and / or an electromagnetic deflector) that can be not used to define the optical path of the image acquisition unit 20. Additionally, instead of acquiring a single image of the predefined area 22, multiple images can also be acquired with the image acquisition unit 20, each image covering a different part of the predefined area 22.

[0055] The device 100 also includes a control unit 28 (e.g., a processor). The control unit 28 is configured to control the operation of the device 100, e.g., the operation of the build plate 6, the powder deposition unit 8, the energy source 16, the beam steering system 23, the image acquisition unit 20, and other components of the device 100 (e.g., a gas supply system, a heating system, and / or a powder supply system). The control unit 28 is configured to perform the methods described herein. To this end, the control unit 28 can be communicatively coupled to a memory 30 that stores instructions that, when executed by the control unit 28, cause the control unit 28 to perform the methods described herein.

[0056] Figure 2 A schematic layout of an exemplary calibration plate 200 according to the present disclosure is shown. The calibration plate 200 includes a body 31 having an upper surface 32. The calibration plate 200 includes at least one surface feature 34 on the upper surface 32. Each surface feature 34 of the at least one surface feature 34 represents a defect of the powder layer to be irradiated by the radiation 18. In other words, each surface feature 34 mimics a surface defect that may exist when a powder layer has been deposited (e.g., and has been at least partially irradiated) on the build plate 6.

[0057] Any deviation (e.g., bulge, depression, incomplete, and / or incorrect curing) of the powder layer surface from a planar powder layer surface (e.g., an optimal, preferred, and / or expected powder layer surface) can be considered a surface defect. Since a completely smooth surface cannot be formed using a powder material, the roughness of the powder layer surface caused only by the particle size of the powder can be ignored.

[0058] In the example shown, multiple surface features 34a represent powder ridges as defects of the layer to be irradiated. The ridges have different predetermined sizes and extend across the entire width of the calibration plate 200 in the x-direction. Multiple surface features 34b represent powder grooves as defects of the layer to be irradiated. The grooves have different predetermined sizes and extend across the entire width of the calibration plate 200 in the x-direction. Multiple surface features 34c represent raised overhangs as defects of the layer to be irradiated. The raised overhangs have different sizes and are located at different parts of the calibration plate 200. Multiple surface features 34d represent splashes as defects of the layer to be irradiated. The splash simulation features have different sizes and are located at different parts of the calibration plate 200. It should be understood that Figure 2 the calibration plate 200 shown in

[0059] is an example, and the calibration plate 200 according to the present disclosure may include different numbers, sizes, arrangements, and / or types of surface features 34.

[0060] In the example, each surface feature 34 is a solid and permanent surface feature of the calibration plate 200 and has fixed, predefined geometric and optical properties. The optical and geometric properties of each surface feature 34 are similar to the optical and geometric properties of the defect represented by the corresponding surface feature 34. Figure 2 In the example of

[0061] a part of the calibration plate 200 includes such a coating 33 that covers the surface features 34c and 34d and thus defines the optical properties of the surface features 34c and 34d.

[0062] Figures 3a to 4g A schematic diagram showing different types of defects 35 according to the present disclosure is shown. One or more of these defects 35 may be represented by the corresponding surface features 34 of the calibration plate 200. When referring to the x-direction, y-direction, or z-direction, it means Figure 2The directions indicated. When the calibration plate 200 is arranged in the construction chamber in its predefined pose, these directions coincide with or are parallel to the x-direction, y-direction, and z-direction shown in Figure 1 In Figures 3a to 4g , the build plate 6 of the device 100 is shaded with parallel lines, the uncured powder material of the layer to be irradiated is indicated by dots, and the cured powder material is highlighted with white filling.

[0063] Figures 3a to 3i Shows different defects 35, each defect 35 being caused by incorrect deposition of the raw material powder of the layer to be irradiated.

[0064] Figure 3a Shows a powder agglomerate as a defect 35a of the layer to be irradiated. The typical size of a single agglomerate is in the range of 200 - 1000 μm in the x and y directions and in the range of 30 - 5000 μm in the z direction.

[0065] Figure 3b Shows an uneven powder delivery as a defect 35b of the layer to be irradiated. Depending on the selected layer thickness, the typical size of this defect is in the range of 200 - 2000 μm in the x and y directions and between 30 - 120 μm in the z direction.

[0066] Figure 3c Shows an incomplete distribution of the powder layer as a defect 35c of the layer to be irradiated. This defect is also known under the term "short feed". Depending on the selected layer thickness, the lack of powder in the layer typically extends 1000 μm in the x direction to the full width of the powder bed, 1000 μm in the y direction to the full length of the powder bed, and 30 - 120 μm in the z direction.

[0067] Figure 3d Shows a powder trough as a defect 35b of the layer to be irradiated. The typical size of this defect is in the range of 500 - 5000 μm in the x direction and 10000 μm to the full length of the powder layer in the y direction. The powder trough can extend more than 1000 μm in the z direction.

[0068] Figure 3e Shows ejected powder as a defect 35e of the layer to be irradiated, which may occur when the doctor blade 14 bends when passing over a previously cured part and then immediately returns to its unbent shape. The typical size of such defects is in the range of 500 - 5000 μm in the x and y directions and between 100 - 500 μm in the z direction.

[0069] Figure 3fShows a powder ridge that is a defect 35f of the layer to be irradiated. The typical size of this defect is in the range of 500 - 5000 μm in the x-direction and 10000 μm in the y-direction up to the length of the complete powder layer. The powder trough can extend more than 1000 μm in the z-direction.

[0070] Figure 3g Shows a powder heap that is a defect 35g of the layer to be irradiated, which may occur due to the bending of the doctor blade 14 when passing over a previously cured part. The typical size of this defect is in the range of 500 - 50000 μm in both the x-direction and the y-direction and in the range of 30 - 2000 μm in the z-direction.

[0071] Figure 3h Shows parallel waves that are a defect 35h of the layer to be irradiated. Such waves typically extend between 10000 μm and the complete width of the powder layer in the x-direction, between 2000 - 5000 μm in the y-direction, and between 100 - 2000 μm in the z-direction.

[0072] Figure 3i Shows parallel stripes that are a defect 35i of the layer to be irradiated. Such stripes typically extend between 10000 μm and the complete width of the powder layer in the x-direction, between 200 - 1000 μm in the y-direction, and between 100 - 2000 μm in the z-direction.

[0073] Figure 4a Shows deposited spatter that is a defect 35i of the layer to be irradiated. Such spatter can be produced and deposited by irradiating the previous layer of the raw material powder or by irradiating a part of the layer to be irradiated. In the x-direction, y-direction, and z-direction, the typical size of the spatter is between 200 - 500 μm.

[0074] Figure 4b Shows a defect 35k caused by the deposition of debris. Such debris may be produced and deposited by irradiating the previous layer of the raw material powder or by irradiating a part of the layer to be irradiated. In the x-direction, y-direction, and z-direction, the typical size of the debris is between 200 - 2000 μm.

[0075] Figures 4c to 4f Shows different defects 35 caused by the damage of the previously irradiated part of the raw material powder.

[0076] Figure 4c Shows a raised overhang that is a defect 35l of the layer to be irradiated. The typical size of such a defect is in the range of 500 - 5000 μm in both the x- and y-directions and between 100 - 5000 μm in the z-direction.

[0077] Figure 4dShows an elevated build sample of a defect 35m in the layer to be irradiated. The typical dimensions of such a defect are in the range of 500 - 5000 μm in the x and y directions and between 100 - 5000 μm in the z direction.

[0078] Figure 4e Shows a fractured support structure of a defect 35n in the layer to be irradiated. The typical dimensions of such a defect are in the range of 200 - 5000 μm in the x and y directions and in the range of 100 - 5000 μm in the z direction.

[0079] Figure 4f Shows a broken cured material of a defect 35o in the layer to be irradiated. The typical dimensions of such a defect are in the range of 200 - 5000 μm in the x and y directions and in the range of 100 - 5000 μm in the z direction.

[0080] Figure 4g Shows an elevated edge of a defect 35p in the layer to be irradiated. Due to the elevated edge of the previously cured part, the doctor blade 14 may be deformed, resulting in an uneven distribution of the deposited powder layer to be irradiated. The typical dimensions of such a defect are in the range of 200 - 5000 μm in the x and y directions and in the range of 30 - 200 μm in the z direction.

[0081] The calibration plate 200 can be configured to be removably arranged in the build chamber 2 of the device 100. The calibration plate 200 can be arranged in the build chamber (e.g., arranged in the recess 4), and / or arranged on the build plate 6 in order to calibrate the device 100 using the methods described herein. Before the device 100 produces a three-dimensional workpiece by selective layer radiation of a powder material, the calibration plate 200 can be removed from the build chamber. The calibration plate 200 can be (e.g., configured to be) arranged in the build chamber 200 in a predefined position and orientation such that Figure 1 and Figure 2 the x-direction, y-direction, and z-direction in

[0082] Figure 5 Shows a schematic layout of a system 1000 according to the present disclosure. The system 1000 includes a plurality of calibration plates 200a, 200b and a holder 300, which are removably arranged in the build chamber 2 of the device 2. The calibration plates 200a, 200b each correspond to the calibration plate 200 as described herein, but are different from each other in one or more surface features 34. For example, the surface features 34 of the calibration plates 200a, 200b can be different from each other in the defects they represent, dimensions, and / or positions on the respective calibration plates.

[0083] The retainer 300 is configured to arrange one of the calibration plates 200a, 200b in the construction chamber 2 at a predefined position and orientation at a time. The retainer 300 can be adapted to fit tightly into the recess 4 and / or be mounted on the construction plate 6. In an exemplary variant, fixings (e.g., screws or bolts) can be used to temporarily fix the calibration plates 200, 200a, 200b and / or the retainer 300 to the device, e.g., to temporarily fix to the device at a predefined position and orientation relative to the construction area.

[0084] Figure 6 A flowchart of a method according to the present disclosure is shown. Optional steps of the method are indicated by dashed lines. The method can be performed by the control unit 28.

[0085] In step 602, at least one image I1 (e.g., a first image) of at least a portion of the calibration plate 200 arranged in the construction chamber 2 is obtained. The at least one image I1 can be obtained by the image acquisition unit 20 (e.g., once the calibration plate 200 is arranged in the construction chamber 2 at its predefined position and orientation).

[0086] In step 604, based on the obtained at least one image I1, one or more surface features 34 of the calibration plate 200 are detected. The detection can be based on an algorithm (e.g., a pattern recognition algorithm) configured to identify the portion of the obtained image I1 corresponding to the surface feature 34.

[0087] In step 606, the device 100 is calibrated based on the detected surface features 34. Calibrating the device 100 can include: setting or adjusting one or more parameters based on the detected surface features 34, the one or more parameters (e.g., subsequently) being used for detecting and / or classifying defects in the layer to be irradiated, e.g., predefined geometric criteria and / or optical criteria used by the same algorithm (e.g., a pattern recognition algorithm) to identify the portions of the image representing defects (e.g., unacceptable defects). The algorithm can be tuned by setting or adjusting one or more parameters such that the algorithm only detects and / or classifies defects in the powder layer that are unacceptable by exhibiting predefined geometric properties and / or optical properties (e.g., a height above 250 μm) that are unacceptable. These unacceptable predefined geometric properties and / or optical properties can be derived from the detected surface features 34 known to represent unacceptable defects.

[0088] For example, in step 606, each identified part of image I1 can be associated with predefined geometric and / or optical characteristics associated with the corresponding surface feature 34. This allows mapping the true, predefined geometric and / or optical characteristics of surface feature 34 to their depiction in at least one image I1. It can be said that calibrating the device includes teaching the device which depictions of surface feature 34 and / or defect 35 in the acquired image represent acceptable surface feature 34 and / or defect 35, and which depictions represent unacceptable surface feature 34 and / or defect 35.

[0089] In optional step 608, calibration plate 200 can be removed from build chamber 2 (e.g., automatically). In the case of manually removing calibration plate 200, this step may not be part of the method performed by control unit 28.

[0090] In optional step 610, a powder layer to be irradiated can be deposited, for example, by instructing deposition unit 8 via control unit 28 to deposit a powder layer.

[0091] In optional step 612, at least one image I2 (e.g., a second image) of at least a portion of the powder layer to be irradiated is obtained. The at least one image I2 can be acquired by image acquisition unit 20.

[0092] In optional step 614, at least one defect 35 in the deposited powder layer is detected and / or classified based on the at least one image I2. Due to the calibration in step 606, the at least one defect 35 can be detected and / or classified taking into account the geometric and / or optical characteristics of the surface feature 34 of the calibration plate. For example, based on the calibration in step 606, in step 614, only the portions of image I2 that depict unacceptable defects are identified. This can ensure reliable detection and / or classification of unacceptable defects in the powder layer.

[0093] In optional step 616, a warning is output based on the detected and / or classified at least one defect 35. Alternatively or additionally, one or more process parameters can be adjusted and / or set based on the detected and / or classified at least one defect 35.

[0094] It should be understood that steps 602 - step 608 can be repeated during the manufacturing process of a three-dimensional workpiece. That is, the manufacturing process including layer-by-layer deposition and selective curing can be interrupted to calibrate the device using calibration plate 200, and then the manufacturing process can be continued after device calibration, for example, by performing steps 612 - step 616.

[0095] In an exemplary configuration, one or more of steps 602 - 606 and / or one or more of steps 612 - 616 may be performed by a detection system or processor separate from (e.g., remote from) device 100. The detection system or processor may include image acquisition unit 20 and / or control unit 28, or be communicatively coupled to image acquisition unit 20 and / or control unit 28. Other distributed processing arrangements are possible. In these variations, calibration may be performed in step 606 on at least the entity performing steps 612 - 616 (e.g., instead of calibrating device 100, the detection system and / or processor may be calibrated).

[0096] Without doubt, many other effective alternatives will occur to those skilled in the art. It should be understood that the present invention is not limited to the described embodiments and example implementations, and includes modifications that are obvious to those skilled in the art and fall within the scope of the appended claims.

Claims

1. A calibration plate (200, 200a, 200b) for calibrating an apparatus (100) for producing a three-dimensional workpiece by irradiating a layer of raw material powder with electromagnetic radiation or particle radiation (18), the calibration plate (200) comprising at least one surface feature (34), the at least one surface feature representing defects (35a - 35p) of the layer to be irradiated.

2. The calibration plate (200, 200a, 200b) according to claim 1, wherein, The at least one surface feature (34) is a permanent surface feature of the calibration plate.

3. The calibration plate (200, 200a, 200b) according to claim 1 or 2, wherein, The at least one surface feature (34) has fixed geometric properties and / or optical properties.

4. The calibration plate (200, 200a, 200b) according to any one of claims 1 to 3, wherein the optical properties of the at least one surface feature (34) are similar to the optical properties of the defects (35a - 35p) of the layer to be irradiated.

5. The calibration plate (200, 200a, 200b) according to claim 3 or 4, wherein the calibration plate (200, 200a, 200b) comprises: A coating (33) defining the optical properties of the at least one surface feature (34).

6. The calibration plate (200, 200a, 200b) according to any one of claims 1 to 5, wherein, The geometric properties of the at least one surface feature (34) are similar to the geometric properties of the defects (35a - 35p) of the layer to be irradiated.

7. The calibration plate (200, 200a, 200b) according to any one of claims 1 to 6, wherein, The at least one surface feature comprises selectively cured powder material.

8. The calibration plate (200, 200a, 200b) according to any one of claims 1 to 7, wherein, The at least one surface feature (34) is made of the same material as the raw material powder of the layer to be irradiated.

9. The calibration plate (200, 200a, 200b) according to any one of claims 1 to 8, wherein, The at least one surface feature (34) represents defects (35a - 35p) caused by at least one of the following events: (i) Incorrect deposition of the raw material powder of the layer to be irradiated; (ii) Deposition of spatter and debris produced by irradiating a previous layer of the raw material powder or by irradiating a part of the layer to be irradiated; and (iii) Damage to a previously irradiated part of the raw material powder.

10. The calibration plate (200, 200a, 200b) according to any one of claims 1 to 9, wherein the calibration plate (200, 200a, 200b) is configured to be removably arranged within a build chamber (2) of the apparatus (100).

11. The calibration plate (200, 200a, 200b) according to claim 10, wherein the calibration plate (200, 200a, 200b) is configured to be removably arranged in a holder (300), the holder (300) being removably arranged within the build chamber (2) and being configured to arrange the calibration plate (200) within the build chamber (2).

12. A method for calibrating an apparatus (100) for producing a three-dimensional workpiece by irradiating a layer of raw material powder with electromagnetic radiation or particle radiation (18), the method comprising: Obtaining at least one image (I1) of the calibration plate (200, 200a, 200b) according to any one of claims 1 to 11, the calibration plate (200, 200a, 200b) being arranged within a build chamber (2) of the apparatus (100); Detecting one or more of the at least one surface feature (34) of the calibration plate (200) based on the obtained at least one image (I1); And Calibrating the apparatus (100) based on the detected one or more surface features (34).

13. The method according to claim 12, wherein, Based on one or more detected surface features, the device (100) is calibrated by setting one or more parameters, which are used by the device (100) to detect and / or classify defects (35a - 35p) in the layer to be irradiated.

14. A device (100) for producing a three - dimensional workpiece by irradiating a layer of raw material powder with electromagnetic radiation or particle radiation (18), the device comprising a control unit (28) configured to perform the method according to claim 12 or 13.

15. A system (1000), the system comprising: at least one calibration plate (200, 200a, 200b) according to any one of claims 1 to 11; and at least one of the following entities: (i) a device (100) as defined, for example, in claim 14; and (ii) a holder (300).

16. The system (1000) according to claim 15, the system comprising two or more calibration plates (200a, 200b) according to claim 11, the two or more calibration plates (200a, 200b) being configured to be replaceably arranged in the same holder (300) and being at least different from each other in at least one surface feature (34).

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