Calibration Plates and Calibration Techniques

Abstract

A calibration plate for calibrating an apparatus for manufacturing three-dimensional workpieces by irradiating a layer of raw material powder with electromagnetic or particle radiation is described, the calibration plate having surface features representative of defects in the layer being irradiated. Additionally, a method for calibrating the apparatus is described. The method includes acquiring at least one image of the calibration plate disposed in a build chamber of the apparatus, detecting one or more of the at least one surface features of the calibration plate based on the acquired at least one image, and calibrating the apparatus based on the detected one or more surface features. A system including the calibration plate and an apparatus configured to perform the method is also described.

Description

[Technical Field]

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

[0002] In additive manufacturing, a workpiece is produced layer by layer by solidifying to produce a series of interconnected workpiece layers. Such processes may be distinguished by the type of feedstock and / or the method by which the feedstock solidifies to produce the workpiece.

[0003] For example, powder bed fusion is a type of additive manufacturing method that can process powdered raw materials, particularly metal and / or ceramic raw material powders, into three-dimensional workpieces with complex shapes. To do this, a layer of raw material powder is applied (e.g., deposited) onto a carrier (e.g., a build platform) and selectively irradiated with, for example, electromagnetic radiation (e.g., laser) or particle radiation (e.g., electron beam) depending on the desired shape of the workpiece to be manufactured. The radiation that penetrates the powder layer causes heating, resulting in selective solidification of the powder layer (e.g., by melting or sintering the raw material powder particles). Next, additional layers of raw material powder are applied to the previously irradiated carrier layer, and the workpiece is processed sequentially until the desired shape and size are achieved. Selective melting or sintering can be particularly used to manufacture prototypes, tools, replacement parts, or medical prostheses (e.g., dental or orthopedic prostheses) based on computer-aided design (CAD) data.

[0004] In some cases, the irradiated deposited powder layer may contain one or more defects that can adversely affect subsequent processing steps, particularly the selective solidification of the defective powder layer and / or the deposition of subsequent powder layers onto the defective powder layer. Defects in the irradiated powder layer can also adversely affect the physical properties (e.g., stiffness and / or surface smoothness) of the produced workpiece.

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

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

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

[0008] Detecting the at least one defect may include identifying one or more portions of the at least one image that match at least one predetermined criterion. Classifying the at least one defect may include classifying the detected defect based on the at least one predetermined criterion or another predetermined criterion. Each of the at least one predetermined criterion may include one or more predetermined geometric characteristics and / or one or more predetermined optical characteristics. The geometric characteristics may include one or more of shape, contour, roughness, height, depth, width, length, and radius of curvature. The optical characteristics may include one or more of texture, color, brightness, and reflectance. The detection and / or classification of the at least one defect may be performed by or based on at least one of: (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 the at least one defect may include adjusting (e.g., filtering, color correcting, color space correcting, cropping, rotating, shifting, skew, and / or scaling) the acquired at least one image of the irradiated powder layer (e.g., a portion of the powder layer) and detecting one or more surface features based on (e.g., in) the adjusted image. The at least one image may be adjusted (e.g., by the image acquisition unit) before being acquired for detecting and / or classifying the at least one defect.

[0009] Based on the at least one detected defect and / or the at least one classified defect, a warning may be output (e.g., to a user or a software component). Alternatively, or additionally, one or more process parameters used by the apparatus to manufacture the three-dimensional workpiece (e.g., irradiate the layer to be irradiated, deposit one or more subsequent powder layers, and / or irradiate one or more subsequent powder layers) may be set or adjusted. The at least one detected and / or classified defect may be correlated with a predetermined process parameter (e.g., a set and / or value thereof) to be set. Such process parameters may include one or more of a gas composition in a build chamber of the apparatus, a gas flow rate in a build chamber of the apparatus, a temperature of the powder material to be deposited, a temperature of the deposited (e.g., irradiated) powder material, control parameters (e.g., attitude, speed, path, powder deposition rate, and / or powder deposition area) of a powder deposition unit configured to deposit the powder layer and included in the apparatus, an attitude or movement of a build platform of the apparatus, and irradiation control parameters (e.g., irradiation position, irradiation beam scanning speed, irradiation power, irradiation beam shape, and irradiation beam focus). Other process parameters that may be set or adapted based on at least one detected and / or classified defect in the irradiated powder layer will be apparent to those skilled in the art. Summary of the Invention

[0010] The present disclosure provides a method for calibrating an apparatus (such as those described above) for manufacturing three-dimensional workpieces by irradiating a layer of raw material powder with electromagnetic or particle radiation.

[0011] The above method may or may not include the steps described above. In either case, the method includes acquiring at least one image of at least a portion of a calibration plate positioned within a build chamber (e.g., described above), e.g., a build region (e.g., described above), of the apparatus. The at least one image may be collected by and / or obtained from an image collection unit (e.g., when or in response to the calibration plate being placed in a predetermined orientation within the build chamber). As described above with respect to the image of the powder layer (e.g., portion thereof), the at least one image of the calibration plate (e.g., portion thereof) may be a single image of the calibration plate (e.g., portion thereof), or the at least one image may include multiple images each including a different sub-portion of the calibration plate (e.g., portion thereof).

[0012] In accordance with this disclosure, as described in detail below, the calibration plate includes at least one surface feature that represents (eg, mimics, simulates, replicates, and / or reproduces) a defect in the layer to be irradiated.

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

[0014] Detecting the one or more surface features may include identifying one or more portions in at least one image that match at least one predetermined criterion (e.g., as described above). The at least one predetermined criterion may include one or more predetermined geometric properties (e.g., as described above) and / or one or more predetermined optical properties (e.g., as described above). As with defect detection and / or classification, such geometric properties may include one or more of shape, contour, roughness, height, depth, width, length, and radius of curvature, and optical properties may include one or more of texture, color, brightness, and reflectance. Detecting the one or more surface features may be performed by or based on at least one of: (i) a pattern recognition algorithm (e.g., as described above), (ii) a blob detection algorithm (e.g., as described above), (iii) an edge detection algorithm (e.g., as described above), (iv) a shape detection algorithm (e.g., as described above), and (v) a trained machine learning model (e.g., as described above). Detecting the one or more surface features may include adjusting (e.g., filtering, color correcting, color space correcting, cropping, rotating, shifting, skew, and / or scaling) at least one acquired image of the calibration plate (e.g., a portion thereof) and detecting the one or more surface features based on (e.g., in) the adjusted image. The at least one image may be adjusted before being acquired for detection of the one or more surface features. The same algorithm or multiple identical algorithms used for detection and / or classification of the at least one defect may be used for detection of the one or more surface features, or vice versa.

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

[0016] The apparatus may be calibrated by setting or adjusting one or more parameters based on the detected surface features. At least one of the one or more parameters may be used (e.g., by the apparatus and / or detection system and / or control unit) to (e.g., later) detect and / or classify defects in the irradiated layer (e.g., based on acquired images of the irradiated powder layer (e.g., portion thereof)). Such parameters may include upper and lower thresholds and / or ranges associated with one or more geometric and / or optical characteristics of features to be detected and / or classified as defects (e.g., acceptable defects, unacceptable defects, or severe defects). Calibrating the apparatus (e.g., setting or adjusting one or more parameters) may include correlating the one or more detected surface features (e.g., their one or more geometric and / or optical characteristics) with associated defects (e.g., their type, size, tolerance, or severity) represented by each of the one or more detected surface features (e.g., their one or more geometric and / or optical characteristics).

[0017] For example, at least one parameter configured for calibrating the apparatus may define a minimum height as a geometric characteristic of a feature that will 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 configured for calibrating the apparatus may define a maximum radius of curvature as a geometric characteristic of a feature that will 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 configured for calibrating the apparatus may define a maximum reflectance or a maximum brightness as an optical characteristic of a feature that will be detected and / or classified as a defect (e.g., an acceptable defect, an unacceptable defect, or a critical defect).

[0018] After calibrating the apparatus, the method may include fabricating a three-dimensional workpiece by irradiating a layer of raw material powder with electromagnetic or particle radiation using the apparatus. Prior to fabricating the three-dimensional workpiece, the calibration plate (e.g., its holder) may be removed from the build chamber. This removal may be performed automatically or manually.

[0019] The method may include initiating or directing deposition (e.g., on a build platform) of the irradiated powder layer. The method may include depositing (e.g., on a build platform and / or at least within a build region) the irradiated powder layer.

[0020] The method may include acquiring at least one image of at least a portion of an irradiated (e.g., deposited) powder layer, as described above. The at least one image may be collected during manufacturing of the three-dimensional workpiece, for example, after (e.g., at least partial) deposition of the powder layer or after (e.g., at least partial) irradiation of the powder layer.

[0021] The method may further include detecting and / or classifying at least one defect in the irradiated powder layer based on the acquired at least one image of the irradiated powder layer (e.g., a portion thereof), as described above. This step may be performed based on at least one parameter set or adjusted (e.g., as described above) during calibration of the apparatus.

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

[0023] As noted above, the present disclosure provides a calibration plate for calibrating an apparatus, i.e., an apparatus for manufacturing three-dimensional workpieces (e.g., as described above), by irradiating a layer of raw material powder with electromagnetic or particle radiation, the calibration plate including at least one surface feature representative of (e.g., mimicking, simulating, replicating, and / or reproducing) defects (e.g., typical defects, regularly observed defects, expected defects, and / or possible defects) in the layer being irradiated.

[0024] A defect in the irradiated layer may be a local deviation of the (e.g., top and / or irradiated) surface of this layer from a (e.g., optimal and / or predetermined) planar powder layer surface. In this regard, roughness of the powder layer surface due solely to the powder grain size may be ignored. A defect in the irradiated layer may be caused by incorrect deposition of raw material powder of the irradiated layer, deposition of spatter or debris caused by irradiation of raw material powder on a previous layer or part of the irradiated layer, and / or damage to previously irradiated parts of raw material powder (e.g., of a 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 hard surface feature (e.g., a surface feature that cannot be manually deformed), an immovable surface feature, a solid (e.g., one-piece) surface feature, and / or a non-temporary surface feature of the calibration plate. The at least one surface feature may not be composed of unsolidified powder material.

[0026] The calibration plate may be configured to allow adjustment (e.g., manually and / or automatically) of one or more attitudes (e.g., position and / or orientation) of at least one surface feature on the calibration plate. Again, each surface feature may be a hard, solid, and / or non-transient surface feature of the calibration plate, and the surface features may not necessarily be composed of unsolidified powder material.

[0027] The calibration plate may be configured to allow for replacement (e.g., manually and / or automatically) of one or more of the at least one surface feature with another surface feature that is indicative of a defect in the layer (e.g., described above) to be irradiated, where again, each surface feature may be a hard and / or solid surface feature of the calibration plate, and the surface features may not be composed of unsolidified powder material.

[0028] In one embodiment, at least one surface feature has fixed (e.g., predetermined, permanent, and / or non-transient) geometric properties. Such geometric properties may include one or more of shape, contour, roughness, height, depth, width, length, and radius of curvature. Alternatively, or in addition, at least one surface feature may have fixed (e.g., predetermined, permanent, and / or non-transient) optical properties. Such optical properties may include one or more of texture, color, brightness, and reflectance.

[0029] The at least one surface feature may represent a defect in the irradiated layer by mimicking or replicating geometric and / or optical properties of the defect. The at least one surface feature may have similar geometric properties as the defect in the irradiated layer (e.g., the defect represented by the surface feature). Alternatively, or in addition, the at least one surface feature may have optical properties similar to the defect in the irradiated layer (e.g., the defect represented by the surface feature).

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

[0031] In one variation, the at least one surface feature comprises a selectively solidified (e.g., sintered or at least partially melted) powder material (e.g., a metal powder material), which may be made from the same material as the raw powder of the layer being irradiated.

[0032] The at least one surface feature and / or calibration plate including the surface feature may be made from selectively solidified powder material, for example, selectively solidified powder material of the same type, composition, material and / or particle size as the powder material of the layer to be irradiated.The at least one surface feature and / or calibration plate including the surface feature may be made from selectively solidified powder material, for example, selectively solidified powder material of the same type, composition, material and / or particle size as the powder material used by the apparatus to manufacture the workpiece.

[0033] The at least one surface feature may represent a defect resulting from at least one of the following phenomena: (i) Incorrect deposition of raw powder in the layer to be irradiated. (ii) Spatter or debris deposits produced by irradiating a previous layer of raw powder or by irradiating a portion of the layer being irradiated. (iii) Damage to previously irradiated parts of the raw powder.

[0034] The calibration plate may be configured to be removably positioned within a build chamber of the apparatus (e.g., at one or more predetermined orientations relative to the build region and / or image collection unit). The calibration plate may be configured to be positioned within the build chamber such that a surface including the surface features is positioned at an orientation (e.g., height) similar to the surface of the layer of feedstock powder to be irradiated.

[0035] The calibration plate may be configured to be positioned within the build chamber such that at least one surface feature, all surface features of the calibration plate, or the entire calibration plate is located within the build region. The calibration plate may be configured to be positioned within the build chamber such that an image acquired by the image acquisition unit represents at least one surface feature, e.g., all surface features of the calibration plate, or a finished surface of the calibration plate including the surface feature.

[0036] In one embodiment, the calibration plate is configured to be removably positioned in a holder. The holder is removably positionable within the build chamber (e.g., at one or more predetermined orientations relative to the build region and / or image acquisition unit) and configured to position (e.g., position) the calibration plate (e.g., at one or more predetermined orientations) within the build chamber (e.g., while holding the calibration plate). The holder may be configured to be mounted on a build plate (e.g., as described above) within the build chamber and / or to be inserted into a recess in the build chamber configured to hold (e.g., a layer to be deposited and / or selectively irradiated) of powder material.

[0037] The present disclosure also provides an apparatus for manufacturing a three-dimensional workpiece by irradiating a layer of raw material powder with electromagnetic or particle radiation, the apparatus comprising a control unit (e.g., a processor) configured to perform the methods described herein.

[0038] The present disclosure also provides a system comprising at least one calibration plate as disclosed herein, the system further comprising at least one of (i) a device and (ii) a holder.

[0039] The system may include two or more calibration plates configured to be interchangeably positioned in the same holder and differing from each other in at least one surface feature (e.g., its type, size, orientation, number and / or location). [Brief explanation of the drawings]

[0040] These and other aspects of the present invention will now be further described, by way of example only, with reference to the accompanying drawings, in which: [Figure 1] FIG. 1 shows a schematic diagram of an apparatus according to the present disclosure. [Figure 2] FIG. 2 shows a schematic diagram of a calibration plate according to the present disclosure. [Figure 3a] FIG. 3a shows a schematic diagram of various types of defects according to the present disclosure. [Figure 3b] FIG. 3b shows a schematic diagram of various types of defects according to the present disclosure. [Figure 3c] FIG. 3c shows a schematic diagram of various types of defects according to the present disclosure. [Figure 3d] FIG. 3d shows a schematic diagram of various types of defects according to the present disclosure. [Figure 3e] FIG. 3e shows a schematic diagram of various types of defects according to the present disclosure. [Figure 3f] FIG. 3f shows a schematic diagram of various types of defects according to the present disclosure. [Figure 3g] FIG. 3g shows a schematic diagram of various types of defects according to the present disclosure. [Figure 3h] FIG. 3h shows a schematic diagram of various types of defects according to the present disclosure. [Figure 3i] FIG. 3i shows a schematic diagram of various types of defects according to the present disclosure. [Figure 4a] FIG. 4a shows a schematic diagram of various types of defects according to the present disclosure. [Figure 4b] FIG. 4b shows a schematic diagram of various types of defects according to the present disclosure. [Figure 4c] FIG. 4c shows a schematic diagram of various types of defects according to the present disclosure. [Figure 4d] FIG. 4d shows a schematic diagram of various types of defects according to the present disclosure. [Figure 4e] FIG. 4e shows a schematic diagram of various types of defects according to the present disclosure. [Figure 4f] FIG. 4f shows a schematic diagram of various types of defects according to the present disclosure. [Figure 5] FIG. 5 shows a schematic diagram of a system according to the present disclosure. [Figure 6] FIG. 6 shows a flow diagram of a method according to the present disclosure. DETAILED DESCRIPTION OF THE INVENTION

[0041] FIG. 1 shows a schematic diagram of an apparatus 100 according to the present disclosure. The apparatus 100 includes a build chamber 2 capable of producing three-dimensional workpieces by selectively irradiating layers of powder material. Recesses 4 in the build chamber 2 are configured to receive respective layers of powder material to be irradiated. A build plate 6 is movably disposed at the bottom of the recesses 4. The build plate 6 can be controllably moved downward to create space within the recesses 4 for forming additional powder layers. Such powder layers can be deposited using a powder deposition unit 8 slidably disposed on two tracks 10. In the illustrated variant, the powder deposition unit 8 includes a body 12 configured to hold the powder material to be deposited and a scraper 14 configured to smooth the deposited powder material ahead of the body 12 as the powder deposition unit 8 moves along the tracks 10. It should be noted that other variants for depositing powder layers are possible and are not intended to be exclusive.

[0042] Apparatus 100 includes an energy source 16 configured to emit electromagnetic or particle radiation 18. A beam steering system 20 is configured to controllably direct radiation 18 toward a build plate 6. When a powder layer is deposited on build plate 6, the powder layer (e.g., within the build region) may be irradiated with radiation 18 for selective solidification thereof.

[0043] The image collection unit 20 (e.g., a camera such as a stereo camera) is configured to collect images of a predetermined (e.g., adjustable) area 22 of the build chamber 2. The predetermined area 22 may include a build area where the powder material can be solidified by radiation 18. The build area may be defined by the outline of the recess 4 when viewed along the Z direction and / or may be located within the recess 4.

[0044] In the illustrated example, image collection unit 20 collects images via the same beam steering system 23 used to direct radiation 18 towards build plate 6. In this variation, radiation 18 is electromagnetic radiation, and beam steering system 23 may include an optical scanning mirror 24 and / or a beam splitter 26.

[0045] It should be noted that other configurations of the image collection unit 20 different from that shown in FIG. 1 are possible and should not be excluded. For example, the image collection unit 20 may be provided configured to collect an image of the predetermined (e.g., adjustable) area 22 without using the beam steering system 23. That is, the optical path of the image collection unit 20 and the path of the radiation 18 may or may not coincide (e.g., at least partially). For example, if the radiation 18 is particle radiation, the beam steering system 23 may include electromagnetic beam conditioning components (e.g., electromagnetic lenses and / or electromagnetic deflectors) that may not be used to define the optical path of the image collection unit 20. Furthermore, instead of collecting a single image of the predetermined area 22, the image collection unit 20 may be used to collect multiple images, each covering a different portion of the predetermined area 22.

[0046] Apparatus 100 further comprises a control unit 28 (e.g., a processor). Control unit 28 is configured to control the operation of apparatus 100, such as the operation of build plate 6, powder deposition unit 8, energy source 16, beam steering system 23, image collection unit 20, and other components (e.g., gas supply system, heating system, and / or powder supply system) of apparatus 100. Control unit 28 is configured to perform methods described herein. To this end, control unit 28 may be communicatively connected to memory 30 that stores instructions that, when executed by control unit 28, cause control unit 28 to perform methods described herein.

[0047] 2 shows a schematic diagram of an exemplary calibration plate 200 according to the present disclosure. Calibration plate 200 comprises a body 31 having a top surface 32. Calibration plate 200 comprises at least one surface feature 34 on top surface 32. Each of the at least one surface feature 34 represents a defect in the powder layer to be irradiated with radiation 18. In other words, each surface feature 34 mimics a surface defect that may be present when the powder layer is deposited (e.g., at least partially irradiated) on build plate 6.

[0048] Any deviations (e.g., bumps, depressions, imperfections, and / or erroneous solidification) from a flat (e.g., optimal, preferred, and / or intended) powder bed surface may be considered surface defects. Because a perfectly smooth surface cannot be formed with powder materials, powder bed surface roughness due solely to powder particle size can be ignored in this regard.

[0049] In the illustrated example, the plurality of surface features 34a represent powder bumps as defects in the layer to be irradiated. Each bump has a different predetermined size and extends across the entire width of the calibration plate 200 in the x-direction. The plurality of surface features 34b represent powder grooves as defects in the layer to be irradiated. Each groove has a different predetermined size and extends across the entire width of the calibration plate 200 in the x-direction. The plurality of surface features 34c represent raised overhangs as defects in the layer to be irradiated. Each raised overhang has a different size and is located in a different portion of the calibration plate 200. The plurality of surface features 34d represent sputter as defects in the layer to be irradiated. Each feature simulating sputter has a different size and is located in a different portion of the calibration plate 200. It should be understood that the calibration plate 200 shown in FIG. 2 is an example, and that a calibration plate 200 according to the present disclosure may include a different number, size, arrangement, and / or type of surface features 34.

[0050] In one example, each surface feature 34 is a solid, permanent surface feature of the calibration plate 200 and has fixed, predetermined geometric and optical properties. Each surface feature 34 may have optical and geometric properties similar to the defect represented by the respective surface feature 34.

[0051] Calibration plate 200 and / or surface features 34 may be made from a plastic material such as PA12 or PA-GF. To mimic the optical properties of imperfections in a metal powder layer, calibration plate 200 may include a coating of silver paint that defines the optical properties of the surface features. In the example of FIG. 2, a portion of calibration plate 200 includes coating 33 that covers surface features 34c and 34d and defines their respective optical properties.

[0052] In another variation, the calibration plate 200 and / or the surface features 34 may be made from a metallic material, such as a selectively solidified metallic powder material (e.g., the same material as the raw powder to be irradiated with radiation 18). Examples of such metallic materials include AlSi10Mg, Ti6Al4V, IN718, and 316L. The surface features 34 may be made by irradiating such metallic powder material at a relatively low irradiation intensity so as not to completely melt the powder material. Such partial melting or sintering results in a surface texture and roughness similar to that of the unirradiated powder material.

[0053] 3a-4g show schematic diagrams of different types of defects 35 according to the present disclosure. One or more of such defects 35 may be represented by respective surface features 34 of calibration plate 200. When referring to the x-, y-, or z-directions, the directions shown in FIG. 2 are meant. When calibration plate 200 is positioned in a predetermined orientation within the build chamber, such directions are coincident with or parallel to the x-, y-, and z-directions shown in FIG. 1. In FIGS. 3a-4g, build plate 6 of apparatus 100 is shaded with parallel lines, unsolidified powder material of the layer to be irradiated is shown as dots, and solidified powder material is highlighted with white.

[0054] 3a-3i show different defects 35, each resulting from an incorrect deposition of raw material powder in the layer being irradiated.

[0055] Figure 3a shows powder agglomerates as defects 35a in the irradiated layer, with typical dimensions of the individual agglomerates in the range of 200-1000 μm in the x and y directions and 30-5000 μm in the z direction.

[0056] Figure 3b shows the non-uniformity of the powder supply as a defect 35b in the irradiated layer, with typical dimensions of 200-2000 μm in the x and y directions and 30-120 μm in the z direction, depending on the selected layer thickness.

[0057] Figure 3c shows the incomplete spreading of the powder layer as a defect 35c in the irradiated layer, which is also called an "underfeed." This powder underfeed in the layer typically extends up to 1000 μm across the entire width of the powder bed in the x-direction, 1000 μm across the entire length of the powder bed in the y-direction, and 30-120 μm in the z-direction, depending on the selected layer thickness.

[0058] Figure 3d shows a powder groove as a defect 35d in the irradiated layer. Typical dimensions of this defect are in the range of 500-5000 μm in the x-direction and 10,000 μm in the y-direction, up to the length of the entire powder layer. The powder groove may extend more than 1000 μm in the z-direction.

[0059] Figure 3e shows the powder ejected as a defect 35e in the irradiated layer. This can occur when the scraper 14 bends as it passes over the already solidified part and then quickly returns to its original shape. Typical dimensions of such defects are 500-5000 μm in the x and y directions and 100-500 μm in the z direction.

[0060] Figure 3f shows powder protrusions as defects 35f in the irradiated layer. Typical dimensions of the defects are in the range of 500-5000 μm in the X direction and 10,000 μm in the Y direction up to the length of the entire powder layer. Powder grooves may extend more than 1000 μm in the Z direction.

[0061] Figure 3g shows a pile of powder as a defect 35g in the irradiated layer, which can be caused by the scraper 14 bending as it passes through an already solidified part. Typical dimensions of the defect are in the range of 500-50,000 μm in the x and y directions and 30-2,000 μm in the z direction.

[0062] Figure 3h shows a parallel wave as a defect 35h in the irradiated layer. Such waves typically extend from 10,000 μm in the x direction to the full width of the powder layer, 2,000–5,000 μm in the y direction, and 100–2,000 μm in the z direction.

[0063] Figure 3i shows parallel stripes as defects 35i in the irradiated layer. Such stripes typically extend from 10,000 μm to the full width of the powder layer in the X direction, 200-1000 μm in the Y direction, and 100-2000 μm in the Z direction.

[0064] Figure 4a shows spatter deposited as a defect 35j in the irradiated layer. Such spatter can be generated and deposited by irradiating a previous layer of raw powder or by irradiating part of the layer being irradiated. Typical dimensions of the spatter are 200-500 μm in the X, Y, and Z directions.

[0065] Figure 4b shows defect 35k caused by debris deposition. Such debris can be generated and deposited by irradiating a previous layer of raw powder or by irradiating part of the layer being irradiated. Typical dimensions of the debris are 200-2000 μm in the x, y, and z directions.

[0066] Figures 4c-4f show various defects 35 caused by damage to the irradiated part of the raw powder.

[0067] Figure 4c shows a raised overhang as a defect 35l in the irradiated layer. Typical dimensions of such defects are 500-5000 μm in the x and y directions and 100-5000 μm in the z direction.

[0068] Figure 4d shows a built-up sample with raised defects 35m in the irradiated layer. Typical dimensions of such defects are 500-5000 μm in the x and y directions and 100-5000 μm in the z direction.

[0069] Figure 4e shows the fracture of the support structure as a defect 35n in the irradiated layer. Typical dimensions of such defects are 200-5000 μm in the x and y directions and 100-5000 μm in the z direction.

[0070] Figure 4f shows the fracture of solidified material as a defect 35o in the irradiated layer, with typical dimensions of such defects being 200-5000 μm in the x and y directions and 100-5000 μm in the z direction.

[0071] Figure 4g shows a raised edge as a defect 35p in the irradiated layer. The raised edge of the already solidified part can deform the scraper 14 and cause uneven distribution of the irradiated deposited powder layer. Typical dimensions of such defects range from 200-5000 μm in the x and y directions and 30-200 μm in the z direction.

[0072] Calibration plate 200 may be configured to be removably positioned within build chamber 2 of apparatus 100. Calibration plate 200 may be positioned within the build chamber, e.g., within recess 4 and / or on build plate 6, to calibrate apparatus 100 using the methods described herein. Calibration plate 200 may be removed from the build chamber before apparatus 100 fabricates a three-dimensional workpiece by selectively irradiating powder material layer-wise. Calibration plate 200 may be positioned (e.g., configured to be positioned) within build chamber 200 at a predetermined position and orientation such that the x, y, and z directions of FIGS. 1 and 2 are aligned (e.g., extend parallel to or coincide with each other).

[0073] 5 shows a schematic diagram of a system 1000 according to the present disclosure. The system 1000 comprises a plurality of calibration plates 200a, 200b and a holder 300 removably positionable within a build chamber 2 of an apparatus 2. The calibration plates 200a, 200b each correspond to the calibration plate 200 described herein, but differ from each other in one or more surface features 34. For example, the surface features 34 of the calibration plates 200a, 200b may differ from each other in the defects they represent, their size, and / or their location on the respective calibration plates.

[0074] The holder 300 is configured to simultaneously position one of the calibration plates 200a, 200b at a predetermined position and orientation within the build chamber 2. The holder 300 may be configured to fit snugly into the recess 4 and / or to be attached to the build plate 6. In one exemplary variation, the calibration plate 200, 200a, 200b and / or the holder 300 may be temporarily secured to the apparatus using fasteners (e.g., screws or bolts), for example, at a predetermined position and orientation relative to the build area.

[0075] 6 shows a flow diagram of a method according to the present disclosure. Optional steps of the method are indicated by dashed lines. The method may be implemented by the control unit 28.

[0076] In step 602, at least one (e.g., a first) image I1 is acquired of at least a portion of the calibration plate 200 positioned within the build chamber 2. The at least one image I1 may be acquired by the image acquisition unit 20, for example, once the calibration plate 200 is positioned in a predetermined position and orientation within the build chamber 2.

[0077] In step 604, one or more surface features 34 of the calibration plate 200 are detected based on the at least one acquired image I1. The detection is based on a (e.g., pattern recognition) algorithm configured to identify portions of the acquired image I1 that correspond to the surface features 34.

[0078] In step 606, the apparatus 100 is calibrated based on the detected surface features 34. Calibrating the apparatus 100 may include setting or adjusting one or more parameters used (e.g., hereinafter) to detect and / or classify defects in the irradiated layer based on the detected surface features 34, such as predetermined geometric and / or optical criteria used by the same (e.g., pattern recognition) algorithm to identify portions of the image that represent (e.g., unacceptable) defects. The algorithm may be tuned by setting or adjusting one or more parameters such that the algorithm detects and / or classifies only powder layer defects that are unacceptable by exhibiting unacceptable predetermined geometric and / or optical characteristics (e.g., heights greater than 250 μm). Such unacceptable predetermined geometric and / or optical characteristics may be derived from detected surface features 34 known to represent unacceptable defects.

[0079] For example, in step 606, each identified portion of image I1 may be correlated with predetermined geometric and / or optical properties associated with each surface feature 34. This allows the actual predetermined geometric and / or optical properties of the surface features 34 to be mapped to their respective depictions in at least one image I1. Calibrating the device may also involve teaching the device which depictions of surface features 34 and / or defects 35 in the acquired images represent acceptable surface features 34 and / or defects 35 and which do not.

[0080] In optional step 608, the calibration plate 200 may be removed (e.g., automatically) from the build chamber 2. If the calibration plate 200 is removed manually, this step may not be part of the method performed by the control unit 28.

[0081] In optional step 610, a layer of irradiated powder may be deposited, for example, by instructing deposition unit 8 via control unit 28 to deposit a layer of powder.

[0082] In optional step 612, at least one (e.g., second) image 12 of at least a portion of the irradiated powder layer is acquired. The at least one image 12 may be collected by image collection unit 20.

[0083] 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 12. Due to the calibration in step 606, the detection and / or classification of the at least one defect 35 may be performed taking into account geometric and / or optical characteristics of the surface features 34 of the calibration plate. For example, in step 614, based on the calibration in step 606, only portions of image 12 that exhibit unacceptable defects are identified. This allows for reliable detection and / or classification of unacceptable defects in the powder layer.

[0084] In optional step 616, a warning is output based on the detected and / or classified at least one defect 35. Alternatively, or in addition, one or more process parameters may be adjusted and / or set based on the detected and / or classified at least one defect 35.

[0085] It should be understood that steps 602-608 may be repeated during the manufacturing process of a three-dimensional workpiece, i.e., the manufacturing process, including layer-wise deposition and selective solidification, may be interrupted for apparatus calibration using calibration plate 200, and then continued after apparatus calibration, including, for example, performing steps 612-616.

[0086] In one 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) apparatus 100. The detection system or processor may comprise image collection unit 20 and / or control unit 28 or may be communicatively coupled to these units. Other distributed processing configurations are possible. In such variations, the actors performing at least steps 612-616 may be calibrated in step 606 (e.g., the detection system and / or processor may be calibrated instead of apparatus 100).

[0087] No doubt many other effective alternatives will occur to those skilled in the art. It will be understood that the present invention is not limited to the described embodiments and examples, but encompasses modifications that are obvious to those skilled in the art and that fall within the scope of the claims appended hereto.

Claims

1. A calibration plate (200, 200a, 200b) for calibrating an apparatus (100) for manufacturing three-dimensional workpieces by irradiating a layer of raw material powder with electromagnetic or particle radiation (18), comprising: The calibration plate (200) comprises at least one surface feature (34) that represents a defect (35a-35p) in the layer to be irradiated.

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

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

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

5. 5. The calibration plate (200, 200a, 200b) according to claim 3 or 4, comprising a coating (33) that defines 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 at least one surface feature (34) has geometric characteristics similar to the defects (35a-35p) in the layer to be irradiated.

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

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

9. The at least one surface feature (34) is (i) erroneous deposition of the raw material powder in the layer to be irradiated; (ii) sputter or debris deposits generated by irradiating a previous layer of the raw material powder or by irradiating a portion of the layer being irradiated; (iii) Damage to previously irradiated portions of the raw material powder.

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

11. 11. The calibration plate (200, 200a, 200b) of claim 10, configured to be removably placed in a holder (300) that is removably placeable in the build chamber (2) and configured to place the calibration plate (200) in the build chamber (2).

12. 1. A method of calibrating an apparatus (100) for manufacturing three-dimensional workpieces by irradiating a layer of raw material powder with electromagnetic or particle radiation (18), comprising: acquiring at least one image (I1) of a calibration plate (200, 200a, 200b) according to any one of claims 1 to 11, placed in a build chamber (2) of the device (100); detecting one or more of the at least one surface features (34) of the calibration plate (200) based on the acquired at least one image (I1); and calibrating the device (100) based on the detected one or more surface features (34).

13. 13. The method of claim 12, wherein the device (100) is calibrated by setting one or more parameters used by the device (100) for detecting and / or classifying defects (35a-35p) in the layer to be irradiated based on the detected one or more surface features.

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

15. At least one calibration plate (200, 200a, 200b) according to any one of claims 1 to 11, The following actors: (i) the device (100), e.g., as claimed in claim 14, and (ii) a system (1000) comprising at least one of the holders (300).

16. 16. A system (1000) according to claim 15, comprising two or more calibration plates (200a, 200b) according to claim 11, The system (1000) is configured so that the two or more calibration plates (200a, 200b) are interchangeably placed in the same holder (300), and the at least one surface feature (34) differs from each other.

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