Technique for calibrating an irradiation device of an apparatus for manufacturing a three-dimensional workpiece

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 in particular, 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, 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 way 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, and as a result, melting or sintering of the raw material powder particles occurs. Then, until the workpiece reaches the desired shape and size, additional raw material powder layers are continuously applied onto the layer on the carrier that has already been irradiated. 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 apparatuses 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] To focus an irradiation beam onto a predefined specific spot within the uppermost powder layer, an apparatus for manufacturing a three-dimensional workpiece usually includes an irradiation device. For this purpose, the irradiation device may include an irradiation source (such as a laser source or a particle source), a focusing optical system (for performing focusing along the beam direction which is substantially in the z direction), and / or a scanning optical system for moving the irradiation beam within the x-y plane (corresponding to the plane of the powder layer).

[0005] When two or more irradiation spots are irradiated (especially simultaneously), two or more irradiation devices may be provided.

SUMMARY OF THE INVENTION

PROBLEMS TO BE SOLVED BY THE INVENTION

[0006] Current irradiation devices (also referred to as scanner heads) include high-precision optical components and are thus very expensive. A less expensive irradiation device may not be able to achieve the required accuracy (e.g., with respect to each long-term drift and / or thermal drift within the x-y plane and / or the z direction).

[0007] Furthermore, it is known to calibrate the irradiation device in order to eliminate or at least mitigate the effects of inaccurate positioning and especially drift. For example, a reference plate having reference marks can be placed within the processing chamber, the position of the laser beam with respect 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. Furthermore, it is known to burn a calibration pattern onto a calibration film and observe the generated pattern with a camera, for example.

[0008] However, the known calibration techniques are not precise enough, are overly complex, and / or do not enable calibration that can cope with strong drift phenomena for low-cost irradiation devices. Furthermore, the known calibration techniques often have the drawback of requiring a time when the melting process cannot occur. For this reason, the productivity of the device may decrease.

[0009] Accordingly, the present invention addresses the objective of providing a technology that solves at least one of the above-described problems and / or other related problems. In particular, although not limited thereto, an improved calibration technique for the irradiation device of an apparatus for manufacturing a three-dimensional workpiece is desired.

[0010] This objective is addressed by the subject matter of the independent claims. Advantageous embodiments are set out in the dependent claims.

Means for Solving the Problems

[0011] According to a first aspect, 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 onto a carrier or a pre-applied powder layer, irradiating the first powder layer with an irradiation beam along at least one first irradiation item, defining a first correction direction having an angle in the range of 70° to 110° with respect to at least one first irradiation item, acquiring a first image of process irradiation light at a position where the irradiation beam collides with the first powder layer during irradiation along at least one first irradiation item, 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 aspect may also be applicable to the apparatus of the apparatus aspect described below.

[0013] This method can be performed by an apparatus for manufacturing a three-dimensional workpiece (hereinafter referred to as the apparatus). 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 can exhibit the features described in the above introduction section. The techniques of selective laser melting and selective laser sintering are well-known to those skilled in the art and are only briefly described in the present disclosure.

[0014] In particular, the build process performed by the apparatus may include depositing a first layer of raw material powder onto a carrier of the apparatus. The first layer (and subsequent layers) may have a predetermined thickness, which may be adjusted for each layer or may be a fixed value. The powder layer can be deposited by any suitable technique, and several methods and apparatuses for generating a layer of raw material powder are well known in the art. After depositing the first layer of raw material powder, a predetermined area of the powder is irradiated with an irradiation beam (e.g., a laser or electron beam), for example, according to a CAD file. In this way, the first layer of the workpiece to be produced can be irradiated and thereby 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 aspect may be performed on one or more layers of the workpiece to be manufactured. For example, this method can be performed on the bottommost layer of the workpiece to be produced, or it can be carried out 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 merely used to linguistically distinguish the respective features. For example, the "first" powder layer does not necessarily have to be the first powder layer applied onto the carrier (since other preceding powder layers may have been applied previously).

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

[0018] Irradiating the first powder layer along at least one first irradiation part may include irradiating an irradiation beam (for example, a particle beam such as a laser beam or an electron beam). In particular, a beam source for generating the irradiation beam, such as a laser source or a particle source (such as an electron source), can be provided. When discussing the following irradiation by a laser beam, irradiation by different irradiation beams (such as an electron beam) is also possible and should be borne in mind as being included in the present disclosure.

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

[0020] When the irradiation part is an irradiation vector, the irradiation vector is a linear vector along a predetermined direction (that is, along a straight line in the x-y plane). The irradiation vector has a starting point and an ending point, and the irradiation beam is scanned from the starting point to the ending point during the irradiation step. The first correction direction can be perpendicular to at least one first irradiation part. The first correction direction exists in the x-y plane (that is, 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 part may mean that the first correction direction is substantially perpendicular or perpendicular to the first irradiation part. For example, the angle between the first correction direction and the first irradiation part may be in the range of 80° to 100°, or may be in the range of 85° to 95°. This angle may be 90° so that the first correction direction is perpendicular to the first irradiation part.

[0021] In the present disclosure, when it is stated that the correction direction is "perpendicular" to the irradiation unit, the irradiation vector, or the tangent direction of the irradiation unit, this means that the angle between the two elements may actually be 90°, or may be in the range of at least 70° to 110°. Therefore, even if not explicitly stated below, the angle indicated by two "perpendicular" elements may be 90°, or may be in the range of at least 70° to 110°.

[0022] The first image may be a digital image and can thus 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 can be such that the direction of the first irradiation unit can be derived from the first image. In other words, the first image may include not only the irradiation spot but also the portion that is the irradiation line in the first irradiation unit. In particular, the first image can include the entire first irradiation unit, for example, the entire first irradiation vector (i.e., from its starting point to its ending point). In other words, the exposure time of the first image can 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 a portion of the first irradiation unit from which the direction of the first irradiation unit cannot be derived. This reason may be that the exposure time is very short and / or the scanning speed of the laser along the first irradiation unit is very slow. In this case, the direction of the first irradiation unit can be determined by the control unit of the device based on, for example, the control data provided to the scanning unit of the device. In other words, the direction of the first irradiation unit can be derived by the control unit of the device for the purpose of determining a correction value along the correction direction based on the irradiation pattern and / or the 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 this 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 in 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 irradiated accurately. Relative calibration (with respect 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 a 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 a second powder layer that 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 a position where the irradiation beam collides with 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] Regarding the irradiation of the second powder layer along at least one second irradiation unit, the same details and / or features as described above regarding the irradiation of the first powder layer along at least one first irradiation unit are applicable. In particular, during the irradiation along the second irradiation unit, the irradiated portion of the second powder layer may melt or sinter and thus solidify. Also, the second irradiation unit may 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 unit may also be a part of the contour of the workpiece.

[0031] Furthermore, regarding obtaining the second image, the same or corresponding details and / or features as described above regarding obtaining the first image are applicable. The first image and the second image can be obtained by the same optical detection device (in particular, a camera).

[0032] Regarding the second correction value along the second correction direction, the same details and / or features as described above regarding the first correction value along the first correction direction are applicable.

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

[0034] It should be noted that in this context, the calibration regarding the first correction direction may be performed before a further powder layer is irradiated after the first powder layer. More precisely, the calibration regarding the first correction direction can be performed before the second powder layer is applied. Therefore, the calibration regarding the second correction direction may be performed after the calibration regarding the first correction direction has been performed. However, alternatively, a combined calibration may be performed based on the first correction value and the second correction value. In this way, not only the calibration along one direction (i.e., the first correction direction) but also the calibration regarding the x - y plane is performed.

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

[0036] The second correction direction may be perpendicular to the first correction direction. Even when the second correction direction is not perpendicular to the first correction direction, for example, in order to derive the x-component and y-component for calibration, the angle between these two directions should be greater than zero (in particular, greater than 10°, or greater than 20°, or greater than 45°) to be sufficient.

[0037] The first irradiation part may be a linear irradiation vector. The second irradiation part may be a linear irradiation vector.

[0038] However, the first and / or second irradiation part may be a curved part, that is, a curve. In this case, the direction of the first and / or second correction direction is determined with respect to the tangent direction of the first and / or second irradiation part. The tangent direction may be determined at a specific point of the irradiation part, particularly at the point considered for calibration.

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

[0040] Each of the first hatch pattern and the second hatch pattern may include a plurality of parallel irradiation vectors.

[0041] The first hatch pattern and / or the second hatch pattern can be used as the filling structure of the internal region (core) of the work to be manufactured. The direction of the irradiation vector of the first hatch pattern and the direction of the irradiation vector of the next hatch pattern can be rotated at a predetermined angle (for example, 45° or 90°) for each layer or every N layers (N is 2 or more).

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

[0043] In this way, the calibration of the irradiation device (or irradiation devices) of the apparatus can always be maintained during the build process. Furthermore, since there is no need to perform a calibration process before the build process is started, time and labor can be saved. In this way, an inexpensive irradiation device that exhibits significant drift during the build process can be used.

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

[0045] For example, the angle can be 45° or 90°.

[0046] The first image can include the starting and ending points of the first irradiation vector.

[0047] This can apply particularly to both the temporal aspect and the spatial aspect. More precisely, the field of view of the camera that acquires the first image can be large enough for the entire first irradiation vector to fit within the field of view. Furthermore, the exposure time of the camera can be long enough so that the entire irradiation of the first irradiation vector is performed during the exposure time. The first image can further include one or more additional irradiation vectors, or one or more portions thereof.

[0048] The first irradiation portion can be a contour portion that is part of the contour of the three-dimensional workpiece to be manufactured.

[0049] For example, it is possible to perform calibration with respect to both the x-direction and the y-direction based on one powder layer. For this purpose, any different parts of the contour of the workpiece can be considered, and the different parts extend in different directions within the x-y plane. Further, an irradiation part that is an irradiation vector of the hatch pattern and a further irradiation part that is a contour part of the workpiece may be considered, and the irradiation part and the further irradiation part are not parallel to each other. Furthermore, the second correction value obtained for the second powder layer can also be considered.

[0050] When using two or more correction values, the accuracy of calibration may be improved. The contour part is the contour part of the generated workpiece. Therefore, during the irradiation of the contour part, the powder melts (or sinters).

[0051] The contour part may be a linear contour part. In other words, the contour part may be the contour part of the workpiece, and this is a straight line. In this case, the first correction direction is defined perpendicular to the linear contour part. However, the contour part may also be a curved contour part. In this case, the first correction direction is defined perpendicular to the tangent direction of the contour part 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 the irradiation of the contour. Therefore, complete calibration is feasible within the x-y plane, that is, it can be performed not only along one first direction but also along several non-parallel first directions.

[0052] The optical detection device of the apparatus, which is configured to acquire an image, can be controlled such that the contour of the workpiece is imaged without a gap or with almost no gap. In other words, the optical detection device can be controlled to continuously obtain images. This also applies to the irradiation of the hatch vector and the determination of the correction value regarding the hatch vector. Therefore, the optical detection device can be controlled to continuously acquire images during the irradiation of the hatch pattern including the first irradiation vector and / or during the irradiation of the contour of the three-dimensional workpiece.

[0053] The device 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 a further irradiation beam onto a first powder layer. 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, and the second scanning field at least partially overlaps with the first scanning field in an overlapping region. The optical detection device for acquiring the first image is oriented or can be oriented 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 at least partially overlap, at least two irradiation beams can be irradiated simultaneously in their corresponding scanning fields, so that a three-dimensional workpiece having a large footprint can be generated in a short time. The optical detection device can be a camera. When the field of view of the optical detection device includes at least a part of the overlapping region, the optical detection device can be used, for example, for a) absolute calibration of both the irradiation device and the further irradiation device (i.e., calibration with respect to the powder bed), and / or b) relative calibration of the irradiation device and the further irradiation device with respect to each other. In the case of a) absolute calibration, the camera must be calibrated with respect to the powder bed, that is, 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 the further irradiation device may perform irradiation simultaneously in the overlapping region and may be imaged simultaneously by the optical detection device. Alternatively, the irradiation device and the further irradiation device may perform sequential irradiation in the overlapping region and may be imaged sequentially by the optical detection device.

[0056] The direction of the irradiation part generated by the irradiation device and the direction of the irradiation part generated by a further irradiation device may be different. In this case, the correction directions of each of the irradiation device and the further irradiation device may be different. Accordingly, the irradiation device may be calibrated along a direction different from that of the further irradiation device. Generally, 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 aspect, there is provided an apparatus for manufacturing a three-dimensional workpiece. The apparatus includes a powder application device configured to apply at least one powder layer onto a carrier or onto a powder layer previously applied, an irradiation device configured to selectively irradiate an irradiation surface corresponding to the applied powder layer with an irradiation beam, an optical detection device configured to optically detect at least a part of the irradiation surface, and a control unit. The control unit instructs the powder application device to apply a first powder layer onto the carrier or onto the powder layer of powder previously applied, instructs the irradiation device to irradiate the first powder layer along at least one first irradiation part, defines a first correction direction having an angle in a range of 70° to 110° with respect to at least one first irradiation part, instructs the optical detection device to acquire 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 part, and is configured to determine a correction value along the first correction direction for calibration of the irradiation device based on the first image.

[0058] All the details described above in the context of the method of the first aspect are applicable to the apparatus of the second aspect. In other words, the apparatus of the second aspect can be configured to execute each of the methods of the first aspect described above.

[0059] The control unit instructs the powder application device to apply a second powder layer onto the first powder layer or onto a powder layer applied after the first powder layer, instructs the irradiation device to irradiate the second powder layer along at least one second irradiation part that is not parallel to the first irradiation part, defines a second correction direction having an angle in the range of 70° to 110° with respect to at least one second irradiation part, instructs 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 part, and is configured 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 part may be a linear irradiation vector.

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

[0062] According to a third aspect, a computer program product is provided. The computer program product, when executed by a device for manufacturing a three-dimensional workpiece, instructs the device to execute the method of the first aspect.

[0063] The device for manufacturing a three-dimensional workpiece may be the device of the second aspect. In particular, the computer program product is executable by a control device or a control unit of the device.

[0064] Preferred embodiments of the present invention will be described in more detail with reference to the accompanying schematic drawings.

Brief Description of the Drawings

[0065]

Figure 1

Figure 2

Figure 3

Figure 4

Figure 5

Embodiments for Carrying Out the Invention

[0066] FIG. 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 the 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 the method for calibrating the irradiation device 24 according to the present 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 field of additive manufacturing and will only be briefly described. For example, such an apparatus 10 may be an apparatus for selective laser melting or an apparatus for selective laser sintering, and one or more laser beams 14 can be used to selectively irradiate and solidify subsequent layers of raw material powder.

[0068] An apparatus 10 for performing a selective laser melting process as described below is given as an example. A typical feature of powder bed fusion is to apply raw material powder in layers and selectively irradiate each layer to solidify it to form one layer of the workpiece 12 to be manufactured. After removing the excess powder and after any optional steps of post-processing (e.g., removal of one or more support structures), the final workpiece 12 is obtained.

[0069] FIG. 1 shows an apparatus 10 for manufacturing a three-dimensional workpiece 12 by selective laser melting. The apparatus 10 includes a processing chamber (process chamber) 16. The processing chamber 16 can be sealed against the ambient atmosphere, i.e., against the environment surrounding the processing chamber 16. A powder application device 18 disposed within the processing chamber 16 has a function of applying raw material powder onto a carrier 20. A vertical movement unit 22 is provided and can displace the carrier 20 in the vertical direction. Thus, when the build height of the workpiece 12 stacked layer by layer from the raw material powder on the carrier 20 increases, the carrier 20 can be moved vertically downward.

[0070] The movability of the carrier 20 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 the movable carrier 20, the carrier 20 may be provided as a static (or fixed) carrier (especially with respect to the vertical z direction). In that case, the irradiation device 24 (see below) and the processing chamber 16 are configured to be moved upward during the build process (i.e., as the build height of the workpiece 12 increases). Further, both the carrier 20 and the irradiation device 24 may be individually movable along the z direction.

[0071] The carrier surface of the carrier 20 defines a horizontal plane (x - y plane), and the direction perpendicular to this plane is defined as the vertical direction or the build direction (z direction). Accordingly, each topmost layer of the raw material powder and each layer of the workpiece 12 extend in a plane parallel to the horizontal plane (x - y plane) defined above.

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

[0073] Furthermore, in the processing chamber 16, a camera 28 is arranged for observing the laser beam 14 directed towards the powder bed by the irradiation device 24 during operation and / or for observing the irradiation area during and / or after irradiation by the laser beam 14. Also, 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 herein 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 uppermost powder layer or a part thereof.

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

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

[0076] The irradiation device 24 is supplied with laser light from a laser light source 32. The laser light source 32 may be provided inside the irradiation device 24 or may be provided outside the irradiation device 24 as shown in FIG. 1. In the former case, the laser light source 32 can be regarded as a 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 through air or through a vacuum, for example, by using one or more mirrors.

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

[0078] The irradiation device 24 further includes two lenses 36 and 38, which are configured to focus the laser beam 14 at a desired focal position along the z-axis. In the embodiment shown in FIG. 1, both lenses 36 and 38 have a positive refractive power. The lens 38 on the upstream side 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 on the downstream side of the beam path is configured to focus the collimated (or substantially collimated) laser beam at a desired z position.

[0079] Also, reference marks are shown in FIG. 1. The reference mark 42 is provided in the bottom region of the processing chamber 16 adjacent to the uppermost layer of the 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, for example, when the irradiation device 24 is calibrated only with respect to another irradiation device (relative calibration), the reference mark 42 is not necessary. Therefore, these are optional.

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

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

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

[0083] In the apparatus 10 of FIG. 2, the irradiation device 24a is configured to scan a first predetermined region (i.e., the first scanning field) of the uppermost powder layer. Similarly, a further irradiation device 24b is configured to scan a second predetermined region (i.e., the second scanning field) of the uppermost powder layer. The first scanning field and the second scanning field overlap each other in the overlapping region. In other words, there is a region of the uppermost powder layer (i.e., the overlapping region) where both of the laser beams 14a and 14b can reach and selectively irradiate. The first scanning field and the second scanning field may each be rectangular or circular, and the size and / or shape of each scanning field may be predetermined by the movement ranges of the scanning unit 30a of the irradiation device 24a and the scanning unit 30b of the irradiation device 24b.

[0084] To manufacture the three-dimensional workpiece 12, both of the laser beams 14a and 14b can simultaneously irradiate different portions of the same powder layer, in which case each of the laser beams 14a and 14b irradiates a portion of the workpiece 12 in the 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, FIG. 1).

[0085] However, in order to achieve the high quality of the generated 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 of the laser beams 14a and 14b irradiate the same spot (or one laser beam continues to irradiate a line started by the other laser beam), appropriate relative calibration is required.

[0086] Furthermore, in the case of only one irradiation device 24 (see FIG. 1), as well as in the case of two or more irradiation devices 24a and 24b (see FIG. 2), it may be important to perform absolute calibration, i.e., calibration regarding the position of the uppermost powder layer. For example, in the case of 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 building the object to be repaired.

[0087] As described above, the techniques of the present disclosure provide absolute and / or relative calibration of one or more irradiation devices. Providing calibration (especially continuous calibration or calibration at short time intervals) is particularly important when irradiation devices 24 are used that do not exhibit the same stability as high-cost and high-precision irradiation devices. Inexpensive irradiation devices 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 (e.g., lenses) of the irradiation device 24 during the build process. The drift may include, in particular, drift of the position of the laser beam 14 in the x-y plane with respect to the fixed position of the uppermost powder layer. In other words, the irradiation device 24 is instructed (e.g., by each command) to irradiate a specific position of the uppermost powder layer, but the actual position irradiated changes over time and thus "drifts".

[0088] Also, since these (expensive) irradiation devices may also struggle with drift in the x-y plane, the methods described herein may be very useful for high-cost and / or high-precision irradiation devices as well. In this case, the proposed methods may help to further improve the accuracy of multi-laser alignment and the accuracy of the produced workpieces.

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

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

[0091] This method is executed during the build process of the three-dimensional workpiece 12, for example, using one of the apparatuses 10 shown in FIG. 1 or FIG. 2 described above.

[0092] This method starts with step 50 of applying a first powder layer onto a carrier or onto a previously applied powder layer. This application is executed under the control of the control unit 40 using the powder application device 18. The first powder layer extends in the x-y 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 alternatively, a powder layer applied during the build process after a previous powder layer has already been applied.

[0093] In step 52, the first powder layer is irradiated along at least one first irradiation portion. This irradiation is performed by the irradiation device 24 or 24a. The irradiation is performed with an irradiation beam, particularly the laser beam 14 of the apparatus 10 in FIG. 1, or the laser beam 14a of the apparatus 10 in FIG. 2. The first irradiation portion may be a straight portion and may have a starting point and an end point, in which case the irradiation beam is scanned from the starting point to the end point. During irradiation, the powder melts or sinters in the region irradiated by the irradiation beam. More precisely, a melt pool is formed from the molten liquid powder material and then cooled, thereby solidifying. As a result, a solidification line of the powder material remains along the irradiated portion after irradiation.

[0094] In step 54, a first correction direction having an angle in the range of 70° to 110° with respect to at least one first irradiation vector is defined. 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 information related to the scanning direction of the first irradiation portion, and thus can define the first correction direction based on this information. For example, when the first irradiation portion is scanned along the x direction (1,0), the first correction direction can be defined along the y direction (0,1). The first irradiation portion and the first correction direction are in the plane of the uppermost powder layer (i.e., in the x-y plane).

[0095] In step 56, a first image of process radiation at a position where the irradiation beam impinges on the first powder layer during irradiation along at least one first irradiation unit is acquired. 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, based on the first image, a correction value along a first correction direction is determined for calibration of the irradiation device. This step is executed by control unit 40. This correction value is suitable for use, for example, in calculating the actual irradiation position along the correction direction based on the 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 a linear correction coefficient along the first correction direction. Furthermore, one or more non-linear 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 to 58, or may be performed for a different (second) correction direction obtained after steps 50 to 58 are 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 correction direction and the second correction direction are not parallel to each other, a complete x-y calibration can be performed.

[0098] FIG. 4 shows a schematic diagram of a control unit 40 of one of the devices 10 of FIG. 1 or FIG. 2. The control unit 40 comprises a plurality of modules 60 to 68, each of these modules being representable in the form of hardware and / or software. In one example, the control unit 40 comprises a processor and a memory. Instructions stored in the memory cause the processor to execute the method shown in FIG. 3. For this purpose, the software stored in the memory is considered to include the modules 60 to 68 shown in FIG. 4.

[0099] Specifically, there are the following modules. A first instruction module 60 that instructs a powder applying device to apply a first powder layer onto a carrier or onto a powder layer previously applied. A second instruction module 62 that instructs an irradiation device to irradiate a first powder layer with an irradiation beam along at least one first irradiation part. 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 part. A third instruction module 66 that instructs an optical detection device to acquire a first image of process radiation at a position where the irradiation beam hits the first powder layer during irradiation along at least one first irradiation part. A determination module that determines a correction value along the first correction direction for calibration of the irradiation device based on the first image.

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

[0101] FIG. 5 shows a build process of one or more three-dimensional workpieces 12 having two laser beams 14a and 14b. Regarding the description of FIG. 5, whether the two irradiation parts 70a / 70b and 72a / 72b of the first layer (FIG. 5(a)) and the second layer (FIG. 5(b)) are part of one and the same workpiece 12 or part of two different workpieces 12 is irrelevant. In either case, it is included in the following description and is broadly referred to as the "workpiece 12" (singular).

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

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

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

[0105] The two scan fields 74a and 74b define an overlapping region 76 where the two scan fields 74a and 74b overlap. In the overlapping region 76, both the laser beams 14a and 14b can reach. The irradiation within the scan 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 the camera 28. The field of view 78 is defined when the camera 28 acquires an image as the region of the uppermost powder layer imaged by the camera 28. As shown in Figure 5, the field of view 78 covers at least a portion of the overlapping region 78. Also in the embodiment of Figure 5, the portions of the first scan field 74a and the second scan field 74b that are not part of the overlapping region 76 are also covered by the field of view 78.

[0107] The first layer of the workpiece 12 includes a first portion 70a and a second portion 70b. According to the 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 the portions 72a and 72b of the second layer, and the shape may or may not be the same as that of the portions 70a and 70b.

[0108] In the first layer, the scanning strategy includes a hatch pattern that defines a plurality of parallel irradiation vectors 80. In both the first portion 70a and the second portion 70b, only one irradiation vector 80 is labeled with a reference sign, but it should be noted that a plurality of irradiation vectors are defined in each of the first portion 70a and the second portion 70b. The hatch pattern defines a plurality of parallel irradiation vectors 80 used as a filling 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 with the same laser beam but with different irradiation parameters, such as irradiation power).

[0109] The arrow in Fig. 5(a) indicates a direction perpendicular to the direction of each irradiation vector 80. As will be described later, this (arrow-following) direction corresponds to the first correction direction.

[0110] In the second layer shown in FIG. 5(b), the scanning strategy also includes a hatch pattern that defines a plurality of parallel irradiation vectors 84. In both the first portion 72a and the second portion 72b, only one irradiation vector 84 is labeled with a reference sign, but it should be noted that a plurality of irradiation vectors 84 are defined in each of the first portion 72a and the second portion 72b. The hatch pattern defines a plurality of parallel irradiation vectors 84 that are used as fillings in the inner portion (also referred to as 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 solidifies. The contour 86 may be irradiated with the same laser beams 14a, 14b as the corresponding hatch pattern (vector 84), or may be irradiated with different laser beams (or with the same laser beam but with different irradiation parameters, such as irradiation power).

[0111] The arrow in FIG. 5(b) indicates a direction perpendicular to the direction of each individual irradiation vector 84. As will be described later, this (arrow-following) direction corresponds to the second correction direction.

[0112] As shown in FIG. 5, the directions of the irradiation vectors 80 and 84 are different. In other words, the directions in which the irradiation vectors 80 and 84 extend rotate between the first layer and the second layer. For example, the scanning strategy may include a rotation of the irradiation vectors of, for example, about 45° or 90° for each layer. The rotation of the direction of the irradiation vectors in the x-y plane may be performed, for example, for all layers or for all N layers, where N is 2 or more. What is important for the description of 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] Hereinafter, it will be described how the irradiation of the irradiation vectors 80 and 84 performed to manufacture the three-dimensional workpiece 12 can be used for the calibration of the corresponding irradiation devices 24a and 24b. Hereinafter, the calibration of the first irradiation device 24a will be described, but the calibration of the second irradiation device 24b is also performed in the same manner.

[0114] The irradiation of the irradiation vector 80 is performed based on the 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 the scanning data.

[0116] The camera 28 acquires a first image (covering the field of view 78) of at least a part of one of the irradiation vectors 80. In other words, the camera 28 is operated with a predetermined exposure time that covers the irradiation of at least a part of one of the irradiation vectors 80. According to one embodiment, the direction of the irradiation vector 80 can be derived from the acquired image. Therefore, the image does not only show a single one-dimensional irradiation spot. In an example considered in this embodiment, the exposure time of the camera 28 is selected such that one complete irradiation vector 80 is part of the image. Each of the irradiation vectors 80 has a starting point and an ending point, and the laser beams 14a and 14b are used to scan each respective irradiation vector 80 from its starting point to its ending point. In the example described, the exposure time is selected to cover at least the scan from the starting point to the ending point. Therefore, the direction of the irradiation 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 a single one-dimensional irradiation spot. In this case, the direction of the first irradiation vector 80 is known because it can be derived from the scanning strategy and / or the 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 include additional 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 desired position of the first irradiation vector 80 is stored in the control unit 40 so that the deviation of the acquired position from the desired position can be calculated. For example, an offset value (e.g., in mm) that defines the offset of the desired position from the actual position within the image can be calculated. The offset value is also referred to as the first correction value. Other possible first correction values are correction factors (for linear multiplication) or parameters applied to non-linear correction functions.

[0120] In a 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, calibration can be executed such that the first correction value is applied by the control unit 40 to the position data transferred to the irradiation device 24a, more precisely the scanning unit 30a. As described above, the calibration of the second irradiation device 24b is executed in the same manner as described above with respect to the first irradiation device 24a.

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

[0122] Absolute calibration means calibration with respect to a 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 provided in a side region next to the uppermost powder layer, as shown in FIGS. 1 and 2. More precisely, the image field correction can be performed by using a plurality of reference marks 42. Instead of using the reference marks 42 in the side region next to the powder bed, a calibration carrier arranged in the processing chamber 16 at a position fixed with respect to the carrier 20 can be used. In each case, the camera 28 records an image of the calibration mark, and the control unit 40 is used to map the position in the recorded image to the actual position on the carrier 20.

[0123] Relative calibration means that the first laser beam 14a is calibrated with respect to the second laser beam 14b, whereby the relative positions of the laser beams 14a and 14b become known and controllable. For example, if the two scanning units 30a and 30b are instructed to irradiate the same spot within the overlapping region 76, the two laser beams can be directed to the same spot. However, if no absolute calibration has been performed, the position of the spot within the uppermost powder layer may not be precisely known.

[0124] For the second layer shown in FIG. 5(b), the calibration is performed as described above for the first layer in FIG. 5(a). However, the direction of the second irradiation vector 84 is different from the direction of the first irradiation vector 80, whereby the combination of the calibration after the first layer and the calibration after the second layer results in a complete calibration in both the x-direction and the y-direction (i.e., within the x-y plane).

[0125] In another 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 a subsequent calibration step, the calibration is performed based on the first correction value and the second correction value. As a result, calibration is performed in both the x-direction and the y-direction.

[0126] The calibration according 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 that is used to control the position and / or deviation of the scanning unit 30. This interface is used to synchronously acquire the current position of the scanning unit 30 (in particular, the scanner mirror of the scanning unit 30) over time. The software automatically evaluates the image in order to obtain the actual position of the laser beam 14a. Optionally, interpolation may be performed between pixels to obtain a higher resolution. Further, the detected deviation between the actual position and the desired position of the laser spot is corrected, in particular, for the list of scanning vectors transmitted to the scanner control device or even for each coordinate transmitted to the scanning unit 30.

[0127] An alternative or modified approach regarding the above-described embodiment of FIG. 5 is discussed below. Where applicable, the following alternatives may be implemented in conjunction with the techniques discussed above.

[0128] According to the first alternative, a device 10 having only one irradiation device 24 (such as the device 10 in FIG. 1) is calibrated, or only one of the irradiation devices 24a or 24b of a device 10 having two or more irradiation devices is calibrated. For this purpose, the method is the same as the above-described method in which 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 part 70a is different from the direction of the first irradiation vector 80 of the second part 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 that 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 such that correction values along different vertical correction directions cannot be obtained in the step of determining the correction value along the first correction direction. Therefore, in the first correction step performed after the irradiation of the first layer, the calibration is performed only with respect to the first correction direction (not with respect to further correction directions). In other words, the calibration performed after the irradiation of the first layer can be one-dimensional. Similarly, the calibration after the irradiation of the second layer can also be one-dimensional.

[0131] However, according to a third alternative, the start point and / or end point of the first irradiation vector can be considered and used to perform calibration with respect to a direction perpendicular to the first correction direction. Similarly, the start point and / or end point of the second irradiation vector can 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 a fourth alternative, two or more cameras 28 can be used and the combined field of view of the cameras can be considered for calibration.

[0133] Furthermore, according to a fifth alternative, a movable camera 28 whose field of view can be moved on the carrier 20 to provide a larger field of view can be used. Also, as the camera 28, a camera of a process observation system of a laser optical system may be used.

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

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

[0136] When the contour portion is a straight line (for example, one of the straight lines of the contour shown in FIG. 5), the correction direction is, in this case, defined perpendicular to the linear contour portion. However, the contour portion to be considered may also be a curved contour portion (for example, one of the corners of the contour shown in FIG. 5). In this case, the correction direction is defined perpendicular to the tangent direction of the contour portion at the point under consideration.

[0137] One or more embodiments of the present technology can have at least one of the following advantages. Since calibration can be performed during the actual build process, there is no need to perform time-consuming calibration in advance. More precisely, the embodiments described herein can have the advantage that calibration information can be obtained without disturbing the normal ongoing build process by simply observing the build process. Further, since calibration is performed for each layer or every N layers during the build process, it is ensured that the irradiation device is always calibrated and the drift is always compensated during the build process. In this way, it is possible to ensure the accuracy of the irradiation position while using an inexpensive irradiation device with a large drift.

Claims

1. A method for calibrating an irradiation device (24; 24a, 24b) of an apparatus (10) for manufacturing a three-dimensional workpiece (12), comprising: applying a first powder layer (50) onto a carrier (20) or onto a pre-applied powder layer; irradiating the first powder layer with an irradiation beam (14; 14a, 14b) along at least one first irradiation section (80) (52); defining a first correction direction having an angle in the range of 70° to 110° with respect to the at least one first irradiation section (80) (54); acquiring a first image of process radiation at a position where the irradiation beam (14; 14a, 14b) impinges on the first powder layer during irradiation along the at least one first irradiation section (80) (56); determining, based on the first image, a correction value along the first correction direction for calibrating the irradiation device (24; 24a, 24b) (58). A method comprising the above steps.

2. applying a second powder layer onto the first powder layer or onto a powder layer applied after the first powder layer; irradiating the second powder layer with the irradiation beam (14; 14a, 14b) along at least one second irradiation section (84) that is not parallel to the first irradiation section (80); defining a second correction direction having an angle in the range of 70° to 110° with respect to the at least one second irradiation section (84); acquiring a second image of process radiation at a position where the irradiation beam (14; 14a, 14b) impinges on the second powder layer during irradiation along the at least one second irradiation section (84); determining, based on the second image, a correction value along the second correction direction for calibrating the irradiation device (24; 24a, 24b). The method according to claim 1, further comprising the above steps.

3. The method according to claim 1 or 2, wherein the first irradiation section (80) is a linear irradiation vector (80).

4. The first irradiation section (80) is a first irradiation vector that is part of a first hatch pattern of a first layer of the three-dimensional workpiece (12) to be manufactured, and the second irradiation section (84) is a second irradiation vector that is part of a second hatch pattern of a second layer of the three-dimensional workpiece (12) to be manufactured. The method according to claim 3.

5. The method according to claim 4, wherein each of the first hatch pattern and the second hatch pattern includes a plurality of parallel irradiation vectors (80, 84).

6. The method according to claim 4, 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°, greater than 15°, or greater than 20°.

7. The method according to any one of claims 3 to 6, wherein the first image includes the starting point and the ending point of the first irradiation vector (80).

8. The method according to claim 1 or 2, wherein the first irradiation unit is a contour portion that is a part of the contour (82, 86) of the three-dimensional workpiece (12) to be manufactured.

9. The apparatus (10) has an irradiation device (24a) for irradiating the irradiation beam (14a) and a further irradiation device (24b) for irradiating a further irradiation beam (14b), The method includes selectively irradiating the further irradiation beam (14b) onto the first powder layer, 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) that at least partially overlaps in an overlapping region (76) with the first scanning field (74a) with the further irradiation beam (14b), The method according to any one of claims 1 to 8, wherein the optical detection device (28) for acquiring the first image is oriented or can be oriented such that the field of view (78) of the optical detection device (28) includes at least a part of the overlapping region (76).

10. The irradiation device (24a) and the further irradiation device (24b) perform irradiation simultaneously in the overlapping region (76) and are simultaneously imaged by the optical detection device (28), or The irradiation device (24a) and the further irradiation device (24b) perform sequential irradiation in the overlapping region (76) and are sequentially imaged by the optical detection device (28). The method according to claim 9.

11. An apparatus (10) for manufacturing a three-dimensional workpiece (12), A powder applying device (18) configured to apply at least one powder layer onto a carrier (20) or onto a powder layer pre-applied, An irradiation device (24; 24a, 24b) that selectively irradiates an 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 part of the irradiation surface, and a control unit (40), wherein the control unit (40) instructs the powder application device (18) to apply a first powder layer onto the carrier (20) or onto the previously applied powder layer, instructs the irradiation device (24; 24a, 24b) to irradiate the first powder layer along at least one first irradiation part (80), defines a first correction direction having an angle in the range of 70° to 110° with respect to the at least one first irradiation part (80), instructs the optical detection device (28) to acquire a first image of the process irradiation light at a position where the irradiation beam (14; 14a, 14b) impinges on the first powder layer during irradiation along the at least one first irradiation part (80), and is configured to determine a correction value along the first correction direction for calibration of the irradiation device (24; 24a, 24b) based on the first image. **Claim 12** The control unit (40) instructs the powder application device (18) to apply a second powder layer onto the first powder layer or onto a powder layer applied after the first powder layer, instructs the irradiation device (24; 24a, 24b) to irradiate the second powder layer along at least one second irradiation part (84) that is not parallel to the first irradiation part (80), defines a second correction direction having an angle in the range of 70° to 110° with respect to the at least one second irradiation part (84), instructs the optical detection device (28) to acquire a second image of the process irradiation light at a position where the irradiation beam (14; 14a, 14b) impinges on the second powder layer during irradiation along the at least one second irradiation part (84), and is configured to determine a correction value along the second correction direction for calibration of the irradiation device (24; 24a, 24b) based on the second image, according to the device (10) of claim 11. **Claim 13** The first irradiation part (80) is a linear irradiation vector (80), according to the device (10) of claim 11 or 12. **Claim 14** The first irradiation unit (80) is a first irradiation vector that is part of a first hatch pattern of a first layer of the three-dimensional workpiece (12) to be manufactured, The second irradiation unit (84) is a second irradiation vector that is part of a second hatch pattern of a second layer of the three-dimensional workpiece (12) to be manufactured, The apparatus (10) according to claim 13, wherein each of the first hatch pattern and the second hatch pattern includes a plurality of parallel irradiation vectors (80, 84).

15. A computer program product that, when executed by an apparatus (10) for manufacturing a three-dimensional workpiece (12), instructs the apparatus (10) to execute the method according to any one of claims 1 to 10.

Images