Technology for calibrating the irradiation device of equipment used to manufacture 3D workpieces.

Abstract

A method for calibrating an irradiation device of an apparatus for manufacturing a three-dimensional workpiece is provided. The method includes applying a first powder layer on a carrier or on a pre-applied powder layer, irradiating the first powder layer with an irradiation beam along at least one first irradiation unit, defining a first correction direction having an angle in the range of 70° to 110° with respect to at least one first irradiation unit, acquiring a first image of process irradiation light at a position where the irradiation beam impinges on the first powder layer during irradiation along at least one first irradiation unit, and determining a correction value along the first correction direction for calibration of the irradiation device based on the first image. Also provided are an apparatus for manufacturing a three-dimensional workpiece and a computer program product.

Description

Technical Field

[0001] The present invention generally relates to the calibration of irradiation devices, and particularly to a technique for calibrating an irradiation device of an apparatus for manufacturing a three-dimensional workpiece. The apparatus for manufacturing a three-dimensional workpiece may be, but is not limited to, an apparatus for additive manufacturing, more precisely, an apparatus for powder bed fusion such as selective laser sintering and / or selective laser melting.

Background Art

[0002] Powder bed fusion is an additional layer formation process capable of processing powdery raw materials, particularly metallic and / or ceramic raw materials, into three-dimensional workpieces of complex shapes. For this purpose, a raw material powder layer is applied onto a carrier, and the powder layer is irradiated with irradiation light (e.g., laser or particle light) in a manner of selecting sites according to the desired shape of the workpiece to be manufactured. The irradiation light penetrating the powder layer heats the raw material powder particles, resulting in melting or sintering of the raw material powder particles. Subsequently, additional raw material powder layers are continuously applied onto the layer on the carrier that has already undergone the irradiation process until the workpiece reaches the desired shape and size. Powder bed fusion can be used for the manufacture or repair of prototypes, tools, replacement parts, high-value parts, or medical prostheses such as dental or orthopedic prostheses based on CAD data. Examples of powder bed fusion techniques include selective laser melting and selective laser sintering.

[0003] Devices for manufacturing one or more workpieces according to the above techniques are known. For example, EP2961549A1 and EP2878402A1 describe devices for manufacturing three-dimensional workpieces related to the technique of selective laser melting. The general principles described in these documents are also applicable to the techniques of the present disclosure.

[0004] Apparatus for manufacturing three-dimensional workpieces typically includes an illumination device to direct and focus an illumination beam onto a predetermined specific spot within the uppermost powder layer. For this purpose, the illumination device may include an illumination source (such as a laser source or particle source), a focusing optical system (for focusing along the beam direction, which is substantially in the z direction), and / or a scanning optical system for moving the illumination beam in the xy plane (corresponding to the plane of the powder layer).

[0005] When two or more irradiation spots are to be irradiated (especially simultaneously), two or more irradiation devices may be provided. [Overview of the Initiative] [Problems that the invention aims to solve]

[0006] Current illumination devices (also called scanner heads) contain high-precision optical components and are therefore very expensive. Less expensive illumination devices may not be able to achieve the required accuracy (for example, with respect to long-term drift and / or thermal drift in the xy plane and / or z direction).

[0007] Furthermore, it is known that the irradiation device is calibrated to eliminate, or at least mitigate, the effects of inaccurate positioning and, in particular, drift. For example, a reference plate with reference marks can be placed in the processing chamber, the position of the laser beam relative to the reference marks can be determined, and calibration can be performed based on this determination. This calibration can be performed, for example, at the start of each construction process. In addition, it is known that a calibration pattern can be imprinted on a calibration film and the resulting pattern can be observed, for example, with a camera.

[0008] However, known calibration techniques are not sufficiently precise, are excessively complex, and / or do not allow for calibration that can address strong drift phenomena in low-cost irradiation devices. Furthermore, known calibration techniques often have the drawback of requiring time during which the melting process cannot occur. This can reduce the productivity of the device.

[0009] Therefore, the present invention relates to the above-mentioned section The title This addresses the objective of providing solutions. In particular, but not limited to, improved calibration techniques for irradiation devices in equipment for manufacturing 3D workpieces are desired.

[0010] This objective is addressed by the subject matter of the independent claim. Advantageous embodiments are shown in the dependent claims. [Means for solving the problem]

[0011] According to a first aspect, a method is provided for calibrating an irradiation device of an apparatus for manufacturing a three-dimensional workpiece. The method includes: applying a first powder layer on a carrier or a pre-applied powder layer; irradiating the first powder layer with an irradiation beam along at least one first irradiation term; defining a first correction direction having an angle in the range of 70° to 110° with respect to at least one first irradiation term; acquiring a first image of process irradiation light at the position where the irradiation beam collides with the first powder layer during irradiation along at least one first irradiation term; and determining a correction value along the first correction direction for calibration of the irradiation device based on the first image.

[0012] One or more of the following features of the method embodiment may also be applied to the apparatus of the apparatus embodiment described below.

[0013] This method can be carried out by an apparatus (hereinafter referred to as "apparatus") for manufacturing a three-dimensional workpiece. The apparatus may be an additive manufacturing apparatus, for example, an apparatus for powder bed fusion bonding such as selective laser melting or selective laser sintering. In this regard, the apparatus may exhibit the features described in the introduction above. The techniques of selective laser melting and selective laser sintering are well known to those skilled in the art and will only be described very briefly in this disclosure.

[0014] In particular, the build process performed by the apparatus may include depositing a first layer of raw material powder onto the apparatus's carrier. The first layer (and subsequent layers) may have a predetermined thickness, which may be adjusted for each layer or be a fixed value. The powder layers can be deposited by any suitable technique, and several methods and apparatuses for generating raw material powder layers are well known in the art. After depositing the first raw material powder layer, a predetermined area of ​​the powder is irradiated with an irradiation beam (e.g., a laser or electron beam) according to, for example, a CAD file. In this way, the first layer of the workpiece to be produced is irradiated and solidified. In the next step, a second layer of raw material powder is deposited, and a predetermined area of ​​the second layer is irradiated and solidified. In this way, the workpiece is produced layer by layer.

[0015] The method of the first embodiment may be performed on one or more layers of the workpiece to be manufactured. For example, this method can be performed on the bottom layer of the workpiece to be produced, or on every M layers of the workpiece, where M is 1 or more.

[0016] When expressions such as "first" and "second" are used in this disclosure, they are simply used to linguistically distinguish between the respective features. For example, the "first" powder layer does not have to be the first powder layer applied to the carrier (because other preceding powder layers may have been applied previously).

[0017] The carrier may be the carrier of the apparatus and may be movable in the z direction (perpendicular to the surface of the carrier in the xy plane) or static. If the first powder layer is applied on a previously applied powder layer, this previously applied powder layer may be part of the stack of powder layers applied on the carrier. However, hybrid manufacturing is also included, in which the part to be repaired or finished by powder bed fusion bonding is embedded in the powder bed beneath the pre-applied powder layer. The pre-applied powder layer may include solidified portions.

[0018] Irradiating the first powder layer along at least one first irradiation section may include irradiating it with an irradiation beam (e.g., a laser beam or a particle beam such as an electron beam). In particular, a beam source for generating the irradiation beam, such as a laser source or a particle source (electron source, etc.), may be provided. When discussing the following irradiation with a laser beam, it should be kept in mind that irradiation with a different irradiation beam (electron beam, etc.) is also possible and is included in this disclosure.

[0019] Irradiating a first powder layer along at least one first irradiation area may include sintering or melting the powder at a location corresponding to the first irradiation area. That is, the energy of the irradiation beam used in the irradiation step is suitable for solidifying the irradiated powder at a location corresponding to the first irradiation area. The irradiation area may be, in particular, the irradiation vector of the workpiece layer. The irradiation step may be part of the manufacturing process of a three-dimensional workpiece. The irradiation vector may be, for example, part of the hatch pattern of the inner portion (core) of the resulting workpiece. However, the irradiation area may also be the contour of the resulting workpiece.

[0020] If the irradiation unit is an irradiation vector, the irradiation vector is a linear vector along a predetermined direction (i.e., along a straight line in the xy plane). The irradiation vector has a start point and an end point, and the irradiation beam is scanned from the start point to the end point during the irradiation step. The first correction direction may be perpendicular to at least one first irradiation unit. The first correction direction lies in the xy plane (i.e., in the plane of the first powder layer). The fact that the first correction direction has an angle in the range of 70° to 110° with respect to at least one first irradiation unit may mean that the first correction direction is approximately perpendicular or perpendicular to the first irradiation unit. For example, the angle between the first correction direction and the first irradiation unit may be in the range of 80° to 100° or in the range of 85° to 95°. This angle may be 90° such that the first correction direction is perpendicular to the first irradiation unit.

[0021] In this disclosure, when the correction direction is described as “perpendicular” to the irradiation area, the irradiation vector, or the tangential direction of the irradiation area, this means that the angle between the two elements may actually be 90° or at least in the range of 70° to 110°. Thus, even if not explicitly stated below, the angle between the two “perpendicular” elements may be 90° or at least in the range of 70° to 110°.

[0022] The first image may be a digital image and therefore can be represented by digital image data. In particular, the first image can be acquired by a digital camera. The exposure time for the first image may be such that the direction of the first irradiation area can be derived from the first image. In other words, the first image may include not only the irradiation spot but also the irradiation line portion of the first irradiation area. In particular, the first image may include the entire first irradiation area, for example, the entire first irradiation vector (i.e., from its starting point to its ending point). In other words, the exposure time for the first image may be at least the time required to scan the first irradiation vector from its starting point to its ending point. However, since the first image particularly shows only the irradiation spot, it may include portions of the first irradiation area from which the direction of the first irradiation area cannot be derived. This may be because the exposure time is very short and / or the scanning speed of the laser along the first irradiation area is very slow. In this case, the direction of the first irradiation area can be determined by the device's control unit, for example, based on control data provided to the device's scanning unit. In other words, the direction of the first irradiation unit may be derived by the device's control unit for the purpose of determining a correction value along the correction direction, based on the irradiation pattern and / or scanning strategy stored in the control unit and / or provided to the scanning unit.

[0023] (Captured in the first image) The process irradiation light can correspond to scattered laser irradiation light (i.e., light of the wavelength of the laser beam used for irradiation) or melt pool irradiation light (e.g., thermal radiation in the visible wavelength region or infrared wavelength region), or a combination of both. In particular, a filter may be provided to block the laser irradiation light and allow the melt pool irradiation light to pass through, whereby the image contains only the melt pool irradiation light.

[0024] To determine the correction value, the position of the first irradiation part in the acquired image can be determined, particularly with respect to the first correction direction. The acquired position of the first irradiation part can be compared with the desired position of the first irradiation part, particularly with respect to the first correction direction. The desired position may be an expected position, for example, an expected position based on the previous calibration.

[0025] The correction value along the first correction direction may be a value applicable to the input data of the irradiation device to correct the irradiation position along the first correction direction. More precisely, the correction value is applicable to the scanner data for controlling the scanning unit of the irradiation device. The correction value may include a lateral shift value representing a length (e.g., in mm), or may include a linear correction coefficient or a non-linear correction value.

[0026] The method may further include performing calibration of the irradiation device along the first correction direction based on the first correction value. Calibration techniques are generally known and thus will not be described in detail in the present disclosure. Calibration can configure the irradiation device such that the actual irradiation position corresponds to the desired irradiation position. The correction value may represent the deviation between the actual irradiation position and the desired irradiation position. After the calibration process, the deviation should be zero or at least minimized.

[0027] The calibration may be absolute or relative to another irradiation device. Absolute calibration means a calibration regarding the position of the powder layer. In particular, it is with respect to the position of at least one reference mark provided on the carrier or within the processing chamber (e.g., on the floor of the processing chamber). Thus, absolute calibration may mean that a specific desired position of the powder bed can be accurately irradiated. Relative calibration (to another irradiation device) means that the position of the irradiation beam of the irradiation device is known relative to the position of the irradiation beam of the other irradiation device. In this way, for example, both irradiation devices can accurately irradiate the same irradiation spot.

[0028] To achieve absolute calibration, image field correction may be performed by a camera (optical detection device) used to obtain an image. For this purpose, a correction plate having reference marks can be used, which is arranged, for example, within the field of view of the camera before the build process is started.

[0029] The method may further include applying a second powder layer on the first powder layer or on a powder layer applied after the first powder layer, irradiating an irradiation beam along at least one second irradiation part to the second powder layer which is not parallel to the first irradiation part, defining a second correction direction having an angle in the range of 70° to 110° with respect to at least one second irradiation part, acquiring a second image of the process irradiation light at the position where the irradiation beam impinges on the second powder layer during irradiation along at least one second irradiation part, and determining a correction value along the second correction direction for calibration of the irradiation device based on the second image.

[0030] With respect to the irradiation of the second powder layer along at least one second irradiation area, the same details and / or features described above apply to the irradiation of the first powder layer along at least one first irradiation area. In particular, during irradiation along the second irradiation area, the irradiation area of ​​the second powder layer may melt or sinter and therefore solidify. The second irradiation area may also be an irradiation vector or a part of an irradiation vector for manufacturing a three-dimensional workpiece, for example, a part of the hatch pattern of the internal region (core) of the workpiece. However, the second irradiation area may also be a part of the contour of the workpiece.

[0031] Furthermore, the same or corresponding details and / or features described above for acquiring the first image are applicable to acquiring the second image. The first and second images can be acquired by the same optical detection device (particularly a camera).

[0032] With respect to the second correction value along the second correction direction, the same details and / or features described above apply to the first correction value along the first correction direction.

[0033] The method may further include performing calibration of the irradiation device along a second correction direction based on a second correction value.

[0034] In this context, it should be noted that calibration in the first correction direction may be performed before any further powder layers are irradiated after the first powder layer. More precisely, calibration in the first correction direction can be performed before the second powder layer is applied. Thus, calibration in the second correction direction may be performed after calibration in the first correction direction has been performed. Alternatively, however, a combined calibration may be performed based on the first and second correction values. In this way, calibration is performed not only along one direction (i.e., the first correction direction) but also along the xy plane.

[0035] Therefore, the method may further include performing a (combined) calibration of the irradiation device along both the first and second correction directions based on both the first and second correction values.

[0036] The second correction direction may be perpendicular to the first correction direction. Even if the second correction direction is not perpendicular to the first correction direction, it is sufficient to make the angle between these two directions greater than zero (in particular, greater than 10°, greater than 20°, or greater than 45°) so that the x and y components for calibration can be derived, for example.

[0037] The first irradiation unit may have a linear irradiation vector. The second irradiation unit may also have a linear irradiation vector.

[0038] However, the first and / or second irradiation section may be a curved section, i.e., a curve. In this case, the direction of the first and / or second correction direction is determined with respect to the tangential direction of the first and / or second irradiation section. The tangential direction may be determined at a specific point on the irradiation section, in particular a point considered for calibration.

[0039] The first irradiation term can be a first irradiation vector which is part of the first hatch pattern of the first layer of the three-dimensional workpiece to be manufactured. The second irradiation term can be a second irradiation vector which is part of the second hatch pattern of the second layer of the three-dimensional workpiece to be manufactured.

[0040] Each of the first and second hatch patterns may include multiple parallel illumination vectors.

[0041] The first hatch pattern and / or the second hatch pattern can be used as a filling structure for the internal region (core) of the workpiece being manufactured. The direction of the illumination vector of the first hatch pattern and the direction of the illumination vector of the subsequent hatch pattern can be rotated by a predetermined angle (e.g., 45° or 90°) for each layer or N layers (N is 2 or more).

[0042] As already mentioned above, since the first and / or second irradiation vectors can be part of the respective hatch patterns, irradiation by each (first and / or second) irradiation vector can cause melting (or sintering) and solidification of the irradiated portion of the respective powder layer. In other words, this calibration method can be performed in situ, i.e., during the build process of the 3D workpiece.

[0043] In this way, the calibration of the device's irradiation device (or multiple irradiation devices) can be maintained throughout the build process. Furthermore, since the calibration process does not need to be performed before the build process begins, time and effort can be saved. In this way, inexpensive irradiation devices that exhibit significant drift during the build process can be used.

[0044] At least one first irradiation vector and at least one second irradiation vector may form an angle greater than 10°, greater than 15°, or greater than 20°.

[0045] For example, that angle could be 45° or 90°.

[0046] The first image may include the start and end points of the first irradiation vector.

[0047] This can apply particularly to both temporal and spatial aspects. More precisely, the field of view of the camera acquiring the first image may be large enough to encompass the entire first illumination vector. Furthermore, the camera's exposure time may be long enough so that the entire first illumination vector is illuminated during the exposure time. The first image may further include one or more additional illumination vectors, or one or more parts thereof.

[0048] The first irradiation area may be a contour area, which is part of the contour of the three-dimensional workpiece being manufactured.

[0049] For example, calibration can be performed in both the x and y directions based on a single powder layer. For this purpose, different parts of the workpiece contour can be considered, and these different parts extend in different directions in the xy plane. Alternatively, an irradiation area, which is the irradiation vector of the hatch pattern, and a further irradiation area, which is the contour of the workpiece, can be considered, and the irradiation area and the further irradiation area are not parallel to each other. Furthermore, a second correction value obtained for a second powder layer can also be considered.

[0050] Using two or more correction values ​​may improve calibration accuracy. The contour is the contour of the workpiece being produced. Therefore, the powder melts (or sintersects) during irradiation of the contour.

[0051] The contour may be a straight contour. In other words, the contour may be the contour of the workpiece, which is a straight line. In this case, the first correction direction is defined perpendicular to the straight contour. However, the contour may also be a curved contour. In this case, the first correction direction is defined perpendicular to the tangent direction of the contour at a specific point that is part of the first image. Since the contour of the workpiece is usually a closed line, its direction changes during contour illumination. Therefore, complete calibration is possible in the xy plane, i.e., along several non-parallel first directions as well as one first direction.

[0052] The optical detection device of the apparatus, configured for acquiring images, can be controlled so that the contour of the workpiece is imaged without gaps or with very few gaps. In other words, the optical detection device can be controlled to acquire images continuously. This is also applicable to the illumination of hatch vectors and the determination of correction values ​​for hatch vectors. Therefore, the optical detection device can be controlled to acquire images continuously while illuminating a hatch pattern containing a first illumination vector and / or while illuminating the contour of a three-dimensional workpiece.

[0053] The apparatus may comprise an irradiation device for irradiating an irradiation beam and a further irradiation device for irradiating a further irradiation beam. The method may include selectively irradiating the first powder layer with a further irradiation beam. The irradiation device can be configured to scan the irradiation beam across a first scanning field, and the further irradiation device can be configured to scan the further irradiation beam across a second scanning field, the second scanning field at least partially overlapping with the first scanning field in the overlapping region. An optical detection device for acquiring the first image is orientable such that the field of view of the optical detection device includes at least a portion of the overlapping region.

[0054] By providing at least two scanning fields that overlap at least partially, at least two irradiation beams can be simultaneously irradiated in their corresponding scanning fields, thereby enabling the rapid generation of three-dimensional workpieces with large footprints. The optical detection device may be a camera. If the field of view of the optical detection device includes at least a portion of the overlapping area, the optical detection device can be used, for example, a) absolute calibration of both the irradiation device and any further irradiation devices (i.e., calibration with respect to the powder bed), and / or b) relative calibration of the irradiation device and any further irradiation devices with respect to each other. In the case of absolute calibration, the camera must be calibrated with respect to the powder bed, i.e., it must be known which position in the image obtained by the camera corresponds to which position on the powder bed. This can be done, for example, by using reference marks on a calibration plate.

[0055] The irradiation device and further irradiation devices may irradiate the overlapping region simultaneously and simultaneously image the region using an optical detection device. Alternatively, the irradiation device and further irradiation devices may irradiate the overlapping region sequentially and sequentially image the region using an optical detection device.

[0056] The direction of the irradiation area generated by the irradiation device and the direction of the irradiation area generated by the further irradiation device may be different. In this case, the correction directions of the irradiation device and the further irradiation device may be different. Therefore, the irradiation device may be calibrated along a different direction than the further irradiation device. In general, the calibration of the further irradiation device can be performed in the same manner as the calibration of the irradiation device.

[0057] According to a second embodiment, an apparatus for manufacturing a three-dimensional workpiece is provided. The apparatus comprises a powder dispensing device configured to dispense at least one powder layer onto a carrier or a pre-dispensed powder layer, an irradiation device for selectively irradiating an irradiation beam onto an irradiation surface corresponding to the dispensed powder layer, an optical detection device for optically detecting at least a portion of the irradiation surface, and a control unit. The control unit is configured to instruct the powder dispensing device to dispense a first powder layer onto the carrier or a pre-dispensed powder layer, to instruct the irradiation device to irradiate the first powder layer along at least one first irradiation section, to define a first correction direction having an angle in the range of 70° to 110° with respect to at least one first irradiation section, to instruct the optical detection device to acquire a first image of process irradiation light at the position where the irradiation beam collides with the first powder layer during irradiation along at least one first irradiation section, and to determine a correction value along the first correction direction for calibration of the irradiation device based on the first image.

[0058] In the context of the method of the first embodiment, all the details described above are applicable to the apparatus of the second embodiment. In other words, the apparatus of the second embodiment can be configured to perform each of the methods of the first embodiment described above.

[0059] The control unit can be configured to instruct the powder application device to apply a second powder layer on top of the first powder layer or on top of a powder layer applied after the first powder layer, to instruct the irradiation device to irradiate the second powder layer along at least one second irradiation unit that is not parallel to the first irradiation unit, to define a second correction direction having an angle in the range of 70° to 110° with respect to at least one second irradiation unit, to instruct the optical detection device to acquire a second image of the process irradiation light at the position where the irradiation beam collides with the second powder layer during irradiation along at least one second irradiation unit, and to determine a correction value along the second correction direction for calibration of the irradiation device based on the second image.

[0060] The first irradiation unit may have a linear irradiation vector.

[0061] The first irradiation area can be a first irradiation vector which is part of the first hatch pattern of the first layer of the three-dimensional workpiece to be manufactured. The second irradiation area can be a second irradiation vector which is part of the second hatch pattern of the second layer of the three-dimensional workpiece to be manufactured. Each of the first and second hatch patterns may include a plurality of parallel irradiation vectors.

[0062] According to a third aspect, a computer program product is provided. When executed by an apparatus for manufacturing a three-dimensional workpiece, the computer program product instructs the apparatus to perform the method of the first aspect.

[0063] The apparatus for manufacturing a three-dimensional workpiece may be the apparatus of the second embodiment described above. In particular, the computer program product can be executed by the apparatus's control device or control unit.

[0064] Preferred embodiments of the present invention will be described in further detail with reference to the accompanying schematic diagrams. [Brief explanation of the drawing]

[0065] [Figure 1]This is a schematic diagram of an apparatus for manufacturing a three-dimensional workpiece through additive manufacturing, as disclosed herein. [Figure 2] This is a schematic diagram of an apparatus for manufacturing a three-dimensional workpiece via additive manufacturing, including two irradiation devices, as disclosed herein. [Figure 3] This is a flowchart of a method for calibrating the irradiation device of an apparatus for manufacturing three-dimensional workpieces, as disclosed herein. [Figure 4] This is a schematic diagram of a control unit for an apparatus for manufacturing a three-dimensional workpiece via additive manufacturing, as disclosed herein. [Figure 5] (a) A top view of the first layer of a workpiece irradiated by two beams, where the workpiece layer is filled with a hatch pattern in the first direction. (b) A top view of the second layer of the workpiece in Figure 5(a), where the workpiece layer is filled with a hatch pattern in the second direction, which is different from the first direction. [Modes for carrying out the invention]

[0066] Figure 1 shows a schematic diagram of an apparatus 10 for manufacturing a three-dimensional workpiece 12. The apparatus 10 is generally well known to those skilled in the art, except for a calibration method programmed into the control unit 40 of the apparatus 10. The apparatus 10 may be, for example, a typical additive manufacturing apparatus, and a method for calibrating the irradiation apparatus 24 according to this disclosure is programmed into the control unit 40 of the apparatus 10.

[0067] The principle of the apparatus 10 is well known to those skilled in the art of additive manufacturing and will be described only briefly. For example, such apparatus 10 may be an apparatus for selective laser melting or an apparatus for selective laser sintering, in which one or more laser beams 14 can be used to selectively irradiate and solidify a subsequent layer of raw material powder.

[0068] An example of a device 10 for performing a selective laser melting process, as described below, is provided. A typical feature of powder bed fusion is that raw material powder is applied in layers, and each layer is selectively irradiated and solidified to produce one layer of the workpiece 12 to be manufactured. After removing excess powder and any post-processing steps (e.g., removal of one or more support structures), the final workpiece 12 is obtained.

[0069] Figure 1 shows an apparatus 10 for manufacturing a three-dimensional workpiece 12 by selective laser melting. The apparatus 10 includes a processing chamber 16. The processing chamber 16 can be sealed from the ambient atmosphere, i.e., from the environment surrounding the processing chamber 16. A powder dispensing device 18 located inside the processing chamber 16 has the function of dispensing raw material powder onto a carrier 20. A vertical movement unit 22 is provided, which can displace the carrier 20 in the vertical direction. Therefore, as the construction height of the workpiece 12, which is stacked in layers from the raw material powder on the carrier 20, increases, the carrier 20 can be moved vertically downward.

[0070] The fact that the carrier 20 is movable by the vertical movement unit 22 is well known in the field of selective laser melting and will not be described in detail here. Instead of a movable carrier 20, the carrier 20 may be provided as a static (or fixed) carrier (particularly with respect to the vertical z direction), in which case the irradiation device 24 (see below) and the processing chamber 16 are configured to move upward during the build process (i.e., as the construction height of the workpiece 12 increases). Furthermore, both the carrier 20 and the irradiation device 24 may be independently movable along the z direction.

[0071] The carrier surface of the carrier 20 defines a horizontal plane (xy plane), and the direction perpendicular to this plane is defined as the vertical direction or the construction direction (z direction). Therefore, each uppermost layer of the raw material powder and each layer of the workpiece 12 extend in a plane parallel to the horizontal plane (xy plane) defined above.

[0072] The apparatus 10 further includes a gas inlet 26 for supplying an inert gas (e.g., argon) into the processing chamber 16. By providing a gas outlet (not shown) and implementing a gas circuit, a continuous gas flow can be generated through the processing chamber 16. In a preferred embodiment, a unidirectional laminar flow is generated over the top layer of raw material powder.

[0073] Furthermore, a camera 28 is positioned inside the processing chamber 16 to observe the laser beam 14 directed toward the powder bed by the irradiation device 24 during operation, and / or to observe the irradiated area during and / or after irradiation by the laser beam 14. In addition, by blocking the wavelength of the laser beam 14 with an optical filter, only the heat dissipation of the generated melt pool (also referred to here as melt pool radiation) can be observed. The camera 28 may be part of a melt pool observation device. The field of view of the camera 28 includes either the entire top powder layer or a portion thereof.

[0074] The apparatus 10 further includes an irradiation device 24 (also referred to as an irradiation unit or optical unit) for selectively irradiating the uppermost layer of raw material powder applied to the carrier 20 with a laser beam 14. The irradiation device 24 allows the raw material powder applied to the carrier 20 to be selectively irradiated with a laser according to the desired shape of the workpiece 12 to be manufactured.

[0075] The irradiation device 24 includes a scanning unit 30 configured to selectively irradiate raw material powder applied on the carrier 20 with laser light 14. The scanning unit 30 is controlled by the control unit 40 of the device 10. The scanning unit 30 may include one mirror that is tiltable with respect to two vertical axes. Alternatively, the scanning unit 30 may include two tiltable mirrors, each configured to tilt with respect to a corresponding axis. The tiltable mirrors may be, for example, galvanometer mirrors.

[0076] The irradiation device 24 is supplied with laser light from the laser light source 32. The laser light source 32 may be located inside the irradiation device 24, or it may be located outside the irradiation device 24, as shown in Figure 1. In the former case, the laser light source 32 can be considered as part of the irradiation device 24. In the latter case, the laser beam is generated by the laser light source 32 and guided into the irradiation device 24 via the optical fiber 34. Alternatively, the laser beam may be guided into the irradiation device 24 via air or vacuum, for example, by using one or more mirrors.

[0077] The laser beam from the laser light source 32 is directed towards the scanning unit 30. The laser light source 32 may include, for example, a diode-pumped ytterbium fiber laser that emits a laser beam with a wavelength of approximately 1070-1080 nm (i.e., in the infrared wavelength range).

[0078] The irradiation device 24 further comprises two lenses 36 and 38, which are configured to focus the laser beam 14 to a desired focal position along the z-axis. In the embodiment shown in Figure 1, both lenses 36 and 38 have positive refractive power. The lens 38 upstream of the beam path is configured to collimate the laser light emitted by the fiber 34, thereby generating a collimated or substantially collimated laser beam. The lens 36 downstream of the beam path is configured to focus the collimated (or substantially collimated) laser beam to a desired z-position.

[0079] Furthermore, Figure 1 shows a reference mark. The reference mark 42 is located in the bottom region of the processing chamber 16, next to the top layer of raw material powder. At least one of the reference marks 42 is within the field of view of the camera 28. As will be described later, the reference mark 42 can be used for absolute calibration of the irradiation device 24. However, if, for example, the irradiation device 24 is calibrated only in relation to other irradiation devices (relative calibration), the reference mark 42 is not necessary. Therefore, they are optional.

[0080] The control unit 40 includes a processor and memory, which stores instructions for controlling the individual components of the apparatus 10. For example, the control unit 40 can be configured to control one or more of the following: the camera 28, the vertical movement unit 22, the powder dispensing device 18, the gas flow rate supplied by the gas inlet 26, and the irradiation device 24. A user input / output interface is available and connected to or connectable to the control unit 40. The control unit 40 also has an interface for receiving work data representing the three-dimensional shape of the workpiece 12 to be manufactured.

[0081] Figure 2 shows a different embodiment of apparatus 10, similar to apparatus 10 in the embodiment of Figure 1. The difference between the two apparatuses 10 is that apparatus 10 in Figure 2 has two irradiation devices 24a and 24b instead of one irradiation device 24 in apparatus 10 of Figure 1. However, the remaining parts of apparatus 10 in Figure 2 have the same components and functions as described above with respect to Figure 1, and therefore this description is omitted. Also, the components of irradiation devices 24a and 24b are given the same reference numerals as in Figure 2. However, the suffixes "a" and "b" are used to distinguish the components of irradiation device 24a (suffix a) from the components of the further irradiation device 24b (suffix b). The functions of the individual components in irradiation devices 24a and 24b are the same as described above with respect to irradiation device 24.

[0082] Hereafter, the use of reference numerals without a suffix (a or b) also refers to the respective elements that have suffixes a and b, unless otherwise specified. For example, when referred to as "scanning unit 30," it also refers to scanning units 30a and 30b.

[0083] The apparatus 10 in Figure 2 is configured such that the irradiation device 24a scans a first predetermined area (i.e., a first scanning field) of the uppermost powder layer. Similarly, a further irradiation device 24b is configured to scan a second predetermined area (i.e., a second scanning field) of the uppermost powder layer. The first and second scanning fields overlap in overlapping areas. In other words, there exists an area (i.e., an overlapping area) of the uppermost powder layer that can be reached and selectively irradiated by both laser beams 14a and 14b. The first and second scanning fields may each be rectangular or circular, and the size and / or shape of each scanning field may be predetermined by the range of motion of the scanning unit 30a of irradiation device 24a and the scanning unit 30b of irradiation device 24b.

[0084] To manufacture the three-dimensional workpiece 12, both laser beams 14a and 14b can simultaneously irradiate different parts of the same powder layer, in which case each of the laser beams 14a and 14b irradiates a part of the workpiece 12 in its corresponding scanning field. In this way, the workpiece 12 can be constructed faster than when only one laser beam 14 is used (see, for example, Figure 1).

[0085] However, in order to achieve high quality of the resulting workpiece 12, it is important that the two lasers 14a and 14b are calibrated relative to each other. In other words, it is important that the relative position of the first laser beam 14a with respect to the second laser beam 14b is known. For example, if both laser beams 14a and 14b illuminate the same spot (or if one laser beam continues to illuminate a line initiated by the other laser beam), then appropriate relative calibration is required.

[0086] Furthermore, in the case of only one irradiation device 24 (see Figure 1), and in the case of two or more irradiation devices 24a and 24b (see Figure 2), it may be important to perform absolute calibration, i.e., calibration with respect to the position of the uppermost powder layer. For example, in hybrid manufacturing where the object to be repaired is embedded in the powder bed below the uppermost powder layer, it may be important to hit a specific predetermined position within the uppermost powder layer in order to continue the construction of the object to be repaired.

[0087] The technology of this disclosure provides absolute and / or relative calibration of one or more irradiation devices, as described above. Providing calibration (in particular continuous calibration or calibration at short time intervals) is especially important when an irradiation device 24 is used that does not exhibit the same stability as a high-cost, high-precision irradiation device. An inexpensive irradiation device 24 may include less expensive components that exhibit significant drift (e.g., long-term drift or short-term drift), such as thermal drift during heating of individual components of the irradiation device 24 (e.g., lenses) during the build process. The drift may include, in particular, drift of the position of the laser beam 14 in the xy plane with respect to a fixed position of the top layer of powder. In other words, the irradiation device 24 is instructed (e.g., by each command) to irradiate a specific position of the top layer of powder, but the position actually irradiated changes over time and thus "drifts".

[0088] Furthermore, since these (expensive) irradiation devices can also struggle with drift in the xy plane, the method described herein may be very useful for high-cost and / or high-precision irradiation devices. In this case, the proposed method may help to further improve the accuracy of multi-laser alignment and the accuracy of the generated workpiece.

[0089] The drift phenomenon described above can be avoided by performing the calibration described in this disclosure.

[0090] Figure 3 shows a flowchart of a method for calibrating the irradiation device 24 of the apparatus 10 for manufacturing a three-dimensional workpiece 12 according to this disclosure.

[0091] This method is performed, for example, during the build process of a 3D workpiece 12 using one of the devices 10 shown in Figure 1 or Figure 2 described above.

[0092] This method begins with step 50, in which a first powder layer is applied to a carrier or to a previously applied powder layer. This application is performed using a powder application device 18 under the control of a control unit 40. The first powder layer extends in the xy plane and has a predetermined thickness. The first powder layer may be the actual first (i.e., initial) powder layer of the build process, or it may be a powder layer applied during the build process after previous powder layers have already been applied.

[0093] In step 52, the first powder layer is irradiated along at least one first irradiation section. This irradiation is performed by the irradiation device 24 or 24a. The irradiation is performed by an irradiation beam, particularly the laser beam 14 of the device 10 in Figure 1, or the laser beam 14a of the device 10 in Figure 2. The first irradiation section may be a straight section and may have a start point and an end point, in which case the irradiation beam is scanned from the start point to the end point. During irradiation, the powder melts or sintersects in the area irradiated by the irradiation beam. More precisely, a melt pool is formed from the molten liquid powder material, which is then cooled and solidifies. This leaves a solidification line of powder material along the irradiated section after irradiation.

[0094] In step 54, a first correction direction is defined having an angle in the range of 70° to 110° with respect to at least one first irradiation vector. This angle may be 90°. The first correction direction is defined by the control unit 40 of the apparatus 10. More precisely, the control unit 40 has relevant information on the scanning direction of the first irradiation unit, and therefore can define the first correction direction based on this information. For example, if the first irradiation unit is scanned along the x direction (1,0), the first correction direction may be defined along the y direction (0,1). The first irradiation unit and the first correction direction are in the plane of the uppermost powder layer (i.e., in the xy plane).

[0095] In step 56, a first image of process radiation is acquired at the location where the irradiation beam collides with the first powder layer during irradiation along at least one first irradiation section. This acquisition is performed by camera 28 under the control of control unit 40. The corresponding image data can be stored and / or processed by control unit 40.

[0096] In step 58, a correction value along the first correction direction is determined based on the first image for the calibration of the irradiation device. This step is performed by the control unit 40. This correction value is suitable for use in calculating the actual irradiation position along the correction direction, for example, based on position data input to the scanning unit 30 of the irradiation device 24. The correction value may represent an offset along the first correction direction, or it may represent a linear correction coefficient along the first correction direction. Furthermore, one or more nonlinear correction coefficients may be considered.

[0097] Based on the correction value along the first correction direction, the irradiation device 24 may be calibrated along the first correction direction. This calibration may be performed immediately after steps 50-58, or for a different (second) correction direction obtained after steps 50-58 have been repeated for a different (second) powder layer. In the former case, the calibration is performed only along the first correction direction. In the latter case, since the first and second correction directions are not parallel to each other, a complete xy calibration can be performed.

[0098] Figure 4 shows a schematic diagram of one of the control units 40 of the apparatus 10 in Figure 1 or Figure 2. The control unit 40 comprises several modules 60-68, each of which may be represented in hardware and / or software form. In one example, the control unit 40 comprises a processor and memory. Instructions stored in memory cause the processor to execute the method shown in Figure 3. For this purpose, the software stored in memory is thought to include modules 60-68 shown in Figure 4.

[0099] The following modules are included in detail. A first instruction module 60 instructs the powder application device to apply a first powder layer onto a carrier or onto a pre-applied powder layer. A second instruction module 62 that instructs the irradiation device to irradiate the first powder layer with an irradiation beam along at least one first irradiation section. A defining module 64 that defines a first correction direction having an angle in the range of 70° to 110° with respect to at least one first irradiation area. A third instruction module 66 instructs an optical detection device to acquire a first image of process radiation at a position where the irradiation beam strikes the first powder layer during irradiation along at least one first irradiation section. A determination module that determines correction values ​​along a first correction direction for calibrating the irradiation device based on a first image.

[0100] The details described herein with respect to individual method steps are also applicable to the corresponding modules 60-68 of the control unit 40. In other words, the control unit 40 is configured to perform the method shown in Figure 3 above, and the details of the method discussed herein are applicable to the software of the control unit 40, and / or the corresponding modules shown in Figure 4, and / or additional modules.

[0101] Figure 5 shows the build process for one or more three-dimensional workpieces 12 having two laser beams 14a and 14b. For the purposes of this explanation of Figure 5, it is irrelevant whether the two irradiated portions 70a / 70b and 72a / 72b of the first layer (Figure 5(a)) and the second layer (Figure 5(b)) are part of one identical workpiece 12 or part of two different workpieces 12. In either case, they are included in the following explanation and are broadly referred to as “workpiece 12” (singular).

[0102] In the build process shown in Figure 5, the apparatus 10 (having two irradiation devices 24a and 24b) shown in Figure 2 can be used. Furthermore, any other suitable additive manufacturing apparatus capable of emitting at least two irradiation beams can be used for the build process in Figure 5.

[0103] Figure 5(a) shows the irradiation of a first layer of workpiece 12, which may be an initial layer during the build process of workpiece 12 (i.e., the actual first layer on the carrier 20) or any other arbitrary layer. Figure 5(b) shows the irradiation of a second layer of workpiece 12, which may be immediately following the first layer or any other layer of the same workpiece 12 that is irradiated at some point after the irradiation of the first layer.

[0104] Similar to the discussion in Figure 2, the area of ​​the carrier 20 that defines the total footprint of the generated workpiece 12 is separated into two scanning fields 74a and 74b. The first scanning field 74a defines the area of ​​the uppermost powder layer that can be irradiated by the first laser beam 14a, while the second scanning field 74b defines the area of ​​the uppermost powder layer that can be irradiated by the second laser beam 14b. In other words, the laser beams 14a and 14b can scan any position within the scanning fields 74a and 74b by the scanning unit 30a of the irradiation device 24a and the scanning unit 30b of the irradiation device 24b, respectively.

[0105] The two scanning fields 74a and 74b define an overlapping region 76 where the two scanning fields 74a and 74b overlap. Both laser beams 14a and 14b can reach the overlapping region 76. Irradiation within the scanning fields 74a and 74b (within the overlapping region 76) can be performed simultaneously or sequentially.

[0106] Figure 5 also shows the field of view 78 of camera 28. The field of view 78 is defined as the region of the uppermost powder layer imaged by camera 28 when camera 28 acquires an image. As shown in Figure 5, the field of view 78 is an overlapping region. 76 It covers at least a portion of it. In the embodiment of Figure 5, the field of view 78 also covers portions of the first scanning field 74a and the second scanning field 74b that are not part of the overlapping region 76.

[0107] The first layer of the workpiece 12 includes a first portion 70a and a second portion 70b. According to an irradiation strategy stored and / or defined in the control unit 40, the first portion 70a is irradiated with a first laser beam 14a and the second portion 70b is irradiated with a second laser beam 14b. The same applies to portions 72a and 72b of the second layer, whose shapes may or may not be identical with respect to portions 70a and 70b.

[0108] In the first layer, the scanning strategy includes a hatch pattern that defines multiple parallel irradiation vectors 80. Note that in both the first portion 70a and the second portion 70b, only one irradiation vector 80 is assigned a reference number, but multiple irradiation vectors are defined in each of the first portion 70a and the second portion 70b. The hatch pattern defines multiple parallel irradiation vectors 80 that are used as filler in the inner portion (also referred to as the core) of the workpiece 12. In addition to the hatched inner portion, a contour 82 is provided, along which the outer shape of the workpiece 12 is solidified. The contour 82 may be irradiated with the same laser beams 14a, 14b as the corresponding hatch pattern (vectors 80), or with different laser beams (or the same laser beam but with different irradiation parameters, e.g., irradiation power).

[0109] The arrows in Figure 5(a) indicate directions perpendicular to the direction of each irradiation vector 80. As will be described later, this direction (following the arrows) corresponds to the first correction direction.

[0110] In the second layer shown in Figure 5(b), the scanning strategy also includes a hatch pattern that defines multiple parallel irradiation vectors 84. Note that in both the first portion 72a and the second portion 72b, only one irradiation vector 84 is assigned a reference numeral, but multiple irradiation vectors 84 are defined in each of the first portion 72a and the second portion 72b. The hatch pattern defines multiple parallel irradiation vectors 84 that are used as filler in the inner portion (also called the core) of the workpiece 12. In addition to the hatched inner portion, a contour 86 is provided, along which the outer shape of the workpiece 12 is solidified. The contour 86 may be irradiated with the same laser beams 14a, 14b as the corresponding hatch pattern (vectors 84), or with different laser beams (or the same laser beam but with different irradiation parameters, e.g., irradiation power).

[0111] The arrows in Figure 5(b) indicate directions perpendicular to the direction of each irradiation vector 84. As will be described later, this direction (following the arrow) corresponds to the second correction direction.

[0112] As shown in Figure 5, the directions of the irradiation vectors 80 and 84 are different. In other words, the direction in which the irradiation vectors 80 and 84 extend rotates between the first and second layers. For example, the scanning strategy may include a rotation of the irradiation vector by, for example, about 45° or 90° for each layer. The rotation of the direction of the irradiation vector in the xy plane may be performed, for example, for all layers or for all N layers, where N is 2 or greater. The important point for describing this embodiment is simply that the (first) irradiation vector 80 of the first layer and the (second) irradiation vector 84 of the second layer are not parallel to each other.

[0113] The following describes how the irradiation of irradiation vectors 80 and 84, performed to manufacture the 3D workpiece 12, can be used for the calibration of the corresponding irradiation devices 24a and 24b. The calibration of the first irradiation device 24a is described below, but the calibration of the second irradiation device 24b is performed in a similar manner.

[0114] The irradiation vector 80 is performed based on a scanning strategy stored in the control unit 40. Therefore, the direction of the irradiation vector 80 is predetermined by the scanning data stored in the control unit 40.

[0115] The control unit 40 defines a first correction direction perpendicular to the first irradiation vector 80 based on the scanning strategy and / or scanning data.

[0116] Camera 28 acquires a first image (covering the field of view 78) of at least a portion of one of the illumination vectors 80. In other words, camera 28 is operated with a predetermined exposure time that covers the illumination of at least a portion of one of the illumination vectors 80. According to one embodiment, the direction of the illumination vector 80 can be derived from the acquired image. Thus, the image does not merely show a single one-dimensional illumination spot. In one example considered in this embodiment, the exposure time of camera 28 is selected such that one complete illumination vector 80 is part of the image. Each of the illumination vectors 80 has a start point and an end point, and laser beams 14a and 14b are used to scan each illumination vector 80 from its start point to its end point. In the example described, the exposure time is selected to cover at least the scan from the start point to the end point. Thus, the direction of the illumination vector 80 can be obtained from the image.

[0117] However, according to another embodiment, the exposure time is very short, and the image shows only one single one-dimensional illumination spot. In this case, the direction of the first illumination vector 80 is known, as it can be derived from the scanning strategy and / or scanning data.

[0118] In this embodiment, two laser beams 14a and 14b are used, and the image includes one irradiation vector irradiated by the first laser beam 14a and one irradiation vector irradiated by the second laser beam 14b. Of course, the image may also include further irradiation vectors (or portions of irradiation vectors) irradiated, for example, before or after the irradiation vector 80 under consideration.

[0119] The control unit 40 analyzes the first image and, in particular, determines the position of the first irradiation vector 80 with respect to the first correction direction. The control unit 40 stores the desired position of the first irradiation vector 80 so that it can calculate the deviation of the acquired position from a desired position. For example, an offset value (e.g., in mm) that defines the offset of the desired position from the actual position in the image can be calculated. The offset value is also referred to as the first correction value. Other possible first correction values ​​are correction coefficients (for linear multiplication) or parameters applied to nonlinear correction functions.

[0120] In the subsequent calibration process, the control unit 40 calibrates the irradiation device 24a based on the first correction value. This calibration is performed along the first correction direction using the first correction value. For example, the calibration can be performed so that the control unit 40 applies the first correction value to the position data transferred to the irradiation device 24a, or more precisely, to the scanning unit 30a. As described above, the calibration of the second irradiation device 24b is performed in the same manner as described above for the first irradiation device 24a.

[0121] Furthermore, the calibration of the irradiation devices 24a and 24b may be absolute or relative to each other.

[0122] Absolute calibration refers to calibration with respect to the fixed position of the carrier 20, i.e., the powder bed. For this purpose, the camera 28 must be pre-calibrated, for example, by using a reference mark 42 located in a side region adjacent to the uppermost powder layer, as shown in Figures 1 and 2. More precisely, image field correction can be performed by using multiple reference marks 42. Instead of using reference marks 42 in a side region adjacent to the powder bed, a calibration carrier placed in the processing chamber 16 at a fixed position relative to the carrier 20 can be used. In each case, the camera 28 records an image of the calibration marks, and the control unit 40 is used to map the positions in the recorded image to the actual positions on the carrier 20.

[0123] Relative calibration means that the first laser beam 14a is calibrated with respect to the second laser beam 14b, thereby making the relative positions of the laser beams 14a and 14b known and controllable. For example, if two scanning units 30a and 30b are instructed to illuminate the same spot within the overlapping region 76, the two laser beams can be directed to the same spot. However, if absolute calibration is not performed, the position of the spot within the top powder layer may not be precisely known.

[0124] With respect to the second layer shown in Figure 5(b), calibration is performed as described above with respect to the first layer in Figure 5(a). However, the direction of the second irradiation vector 84 is different from the direction of the first irradiation vector 80, and thereafter, the combination of calibration after the first layer and calibration after the second layer results in a complete calibration with respect to both the x and y directions (i.e., in the xy plane).

[0125] In an alternative approach, a first correction value is obtained after irradiation of the first layer, and a second correction value is obtained after irradiation of the second layer. In the subsequent calibration step, calibration is performed based on the first and second correction values. As a result, calibration is performed in both the x and y directions.

[0126] Calibration relating to this technology can also be described as follows: The control unit 40 stores evaluation software. The evaluation software includes an interface to a scanner control device used to control the position and / or deviation of the scanning unit 30. This interface is used to acquire the current position of the scanning unit 30 (in particular, the scanner mirror of the scanning unit 30) in a time-series synchronous manner. The software automatically evaluates the image to obtain the actual position of the laser beam 14a. Optionally, interpolation between pixels may be performed to obtain a higher resolution. Furthermore, the detected deviation between the actual position of the laser spot and the desired position is corrected, in particular, for the list of scan vectors transmitted to the scanner control device, or even for each coordinate transmitted to the scanning unit 30.

[0127] The following discusses alternative or modified approaches to the embodiment of Figure 5 described above. Where applicable, the following alternatives may be implemented in conjunction with the techniques discussed above.

[0128] According to the first alternative example, either the apparatus 10 having only one irradiation device 24 (such as the apparatus 10 in Figure 1) is calibrated, or only one irradiation device 24a or 24b of the apparatus 10 having two or more irradiation devices is calibrated. For this purpose, the method is the same as the method described above, but only the first parts 70a and 70b are considered.

[0129] According to the second alternative, the direction of the first irradiation vector 80 of the first portion 70a is different from the direction of the first irradiation vector 80 of the second portion 70b. In general, the direction of the irradiation vector of the first irradiation device 24a may be different from the direction of the irradiation vector of the second irradiation device 24b. However, the calibration method is the same as described above. In this case, the first correction direction of the first irradiation device 24a is different from the correction direction of the second irradiation device 24. The same applies to the second layer.

[0130] The above technique can be performed in a step that determines the correction value along the first correction direction in such a way that correction values ​​are not obtained along different vertical correction directions. Therefore, in the first correction step performed after irradiation of the first layer, calibration is performed only with respect to the first correction direction (and not with respect to further correction directions). In other words, calibration performed after irradiation of the first layer can be one-dimensional. Similarly, calibration after irradiation of the second layer can also be one-dimensional.

[0131] However, according to the third alternative example, the start and / or end points of the first irradiation vector may be considered and used to perform calibration with respect to a direction perpendicular to the first correction direction. Similarly, the start and / or end points of the second irradiation vector may be considered and used to perform calibration with respect to a direction perpendicular to the second correction direction. However, these “perpendicular” calibrations may not be as accurate as the corresponding calibrations with respect to the first and second correction directions.

[0132] According to the fourth alternative example, two or more cameras 28 are available, and the combined field of view of the cameras can be considered for calibration.

[0133] Furthermore, according to the fifth alternative example, a movable camera 28 can be used to move its field of view on the carrier 20 in order to provide a larger field of view. Alternatively, the camera 28 may be a camera from a process observation system of a laser optical system.

[0134] According to the sixth alternative example, the contour portion of the contour 82 of the first layer and / or the contour portion of the contour 86 of the second layer are considered in order to determine the correction value. The contour portion may be a straight line (shown in Figure 5 with respect to the sides of the substantially rectangular shape of the irradiation pattern) or a curve (shown in Figure 5 with respect to the corners of the substantially rectangular shape of the irradiation pattern).

[0135] In addition to the irradiation vectors 80 and 84 for the calibration of the irradiation device 24, the contour portions of the contours 82 and 86 may also be considered. The contour portions are processed in the same way as the irradiation vectors 80 and 84 described above. Thus, a correction direction is defined perpendicular to the contour cross-section, and a corresponding correction value is calculated.

[0136] If the contour is a straight line (for example, one of the straight lines of the contour shown in Figure 5), the correction direction is defined perpendicular to the straight contour. However, the contour considered may also be a curved contour (for example, one of the corners of the contour shown in Figure 5). In this case, the correction direction is defined perpendicular to the tangential direction of the contour at the point considered.

[0137] One or more embodiments of this technology may have at least one of the following advantages: Calibration can be performed during the actual build process, eliminating the need for time-consuming pre-calibration. More precisely, embodiments described herein may have the advantage that calibration information can be obtained without disrupting the normal ongoing build process by simply observing the build process. Furthermore, since calibration is performed layer by layer or every N layers during the build process, it is ensured that the irradiation device is always calibrated and that drift is always compensated for during the build process. In this way, accuracy of the irradiation position can be ensured while using inexpensive irradiation devices with large drift.

Claims

1. A method for calibrating the irradiation devices (24; 24a, 24b) of an apparatus (10) for manufacturing a three-dimensional workpiece (12), The first powder layer (50) is applied to the carrier (20) or to a previously applied powder layer, Irradiating the first powder layer with an irradiation beam (14; 14a, 14b) along at least one first irradiation vector (80) (52), To define a first correction direction (54) that exists within the plane of the first powder layer and has an angle in the range of 70° to 110° with respect to the at least one first irradiation vector (80), (56) A first image of process radiation at the position where the irradiation beam (14; 14a, 14b) collides with the first powder layer during irradiation along the at least one first irradiation vector (80), Based on the first image, a correction value representing the deviation between the actual irradiation position and the desired irradiation position along the first correction direction is determined for the calibration of the irradiation device (24; 24a, 24b) (58). The second powder layer is applied on the first powder layer or on a powder layer applied after the first powder layer, The second powder layer is irradiated with the irradiation beam (14; 14a, 14b) along at least one second irradiation vector (84) that is not parallel to the first irradiation vector (80), A second correction direction is defined that exists within the plane of the second powder layer and has an angle in the range of 70° to 110° with respect to the at least one second irradiation vector (84), To acquire a second image of process radiation at the position where the irradiation beam (14; 14a, 14b) collides with the second powder layer during irradiation along the at least one second irradiation vector (84), Based on the second image, a correction value representing the deviation between the actual irradiation position and the desired irradiation position along the second correction direction is determined for the calibration of the irradiation device (24; 24a, 24b). Methods that further include the above.

2. The first irradiation vector (80) is part of a first hatch pattern comprising a plurality of parallel first irradiation vectors (80) of the first layer of the three-dimensional workpiece (12) to be manufactured. The method according to claim 1, wherein the second irradiation vector (84) is part of a second hatch pattern comprising a plurality of parallel second irradiation vectors (84) of a second layer of the three-dimensional workpiece (12) to be manufactured.

3. The method according to claim 2, wherein at least one of the first irradiation vectors (80) and at least one of the second irradiation vectors (84) form an angle greater than 10°.

4. The method according to claim 1, wherein the first irradiation vector is a contour portion which is part of the contour (82, 86) of the three-dimensional workpiece (12) to be manufactured.

5. The apparatus (10) comprises an irradiation device (24a) that irradiates with the irradiation beam (14a) and a further irradiation device (24b) that irradiates with a further irradiation beam (14b), The method includes selectively irradiating the first powder layer with the further irradiation beam (14b), The irradiation device (24a) is configured to scan a first scanning field (74a) with the irradiation beam (14a), and the further irradiation device (24b) is configured to scan a second scanning field (74b) with the further irradiation beam (14b) that at least partially overlaps with the first scanning field (74a) in an overlapping region (76). The method according to claim 1, wherein the optical detection device (28) that acquires the first image is configured to be oriented such that the field of view (78) of the optical detection device (28) includes at least a portion of the overlapping region (76).

6. The irradiation device (24a) and the further irradiation device (24b) irradiate the overlapping region (76) simultaneously and are simultaneously imaged by the optical detection device (28), or, The method according to claim 5, wherein the irradiation device (24a) and the further irradiation device (24b) sequentially irradiate the overlapping region (76) and the optical detection device (28) sequentially capture images.

7. Apparatus (10) for manufacturing a three-dimensional workpiece (12), A powder dispensing device (18) configured to apply at least one powder layer onto a carrier (20) or onto a pre-applied powder layer, An irradiation device (24; 24a, 24b) selectively irradiates the irradiation surface corresponding to the applied powder layer with an irradiation beam (14; 14a, 14b), An optical detection device (28) that optically detects at least a portion of the irradiation surface, It has a control unit (40) and The control unit (40) is The powder dispensing device (18) is instructed to apply the first powder layer onto the carrier (20) or onto the previously applied powder layer. The irradiation device (24; 24a, 24b) is instructed to irradiate the first powder layer along at least one first irradiation vector (80), A first correction direction is defined that exists within the plane of the first powder layer and has an angle in the range of 70° to 110° with respect to the at least one first irradiation vector (80), The optical detection device (28) is instructed to acquire a first image of the process irradiation light at the position where the irradiation beam (14; 14a, 14b) collides with the first powder layer during irradiation along the at least one first irradiation vector (80), Based on the first image, a correction value representing the deviation between the actual irradiation position and the desired irradiation position along the first correction direction is determined for the calibration of the irradiation device (24; 24a, 24b). The powder dispensing device (18) is instructed to apply the second powder layer on top of the first powder layer or on top of the powder layer applied after the first powder layer. The irradiation device (24; 24a, 24b) is instructed to irradiate the second powder layer along at least one second irradiation vector (84) that is not parallel to the first irradiation vector (80), A second correction direction is defined that exists within the plane of the second powder layer and has an angle in the range of 70° to 110° with respect to the at least one second irradiation vector (84), The optical detection device (28) is instructed to acquire a second image of the process irradiation light at the position where the irradiation beam (14; 14a, 14b) collides with the second powder layer during irradiation along the at least one second irradiation vector (84), A device (10) configured to determine a correction value representing the deviation between the actual irradiation position and a desired irradiation position along the second correction direction for calibration of the irradiation device (24; 24a, 24b) based on the second image.

8. The first irradiation vector (80) is part of a first hatch pattern comprising a plurality of parallel first irradiation vectors (80) of the first layer of the three-dimensional workpiece (12) to be manufactured. The second irradiation vector (84) is part of a second hatch pattern comprising a plurality of parallel second irradiation vectors (84) of the second layer of the three-dimensional workpiece (12) to be manufactured. The apparatus (10) according to claim 7.

9. A computer program product that, when executed by an apparatus (10) for manufacturing a three-dimensional workpiece (12), instructs the apparatus (10) to perform the method described in claim 1.

Images