DEVICE AND METHOD FOR CALIBRATING AN IRRADIATION SYSTEM USED TO PRODUCE A THREE-DIMENSIONAL WORKPIECE

Abstract

The invention relates to a device (10) for the layered production of a three-dimensional workpiece, comprising: a build space (30) in which the workpiece is manufacturable by selectively solidification of raw material powder layers; an irradiating system (20) which is adapted to selectively solidify the raw material powder layers in the build space (30) by emitting a processing beam; at least one calibrating structure (36); a sensor arrangement (25) which is adapted to detect an irradiation of the calibrating structure (36) by the irradiating system (20); and a control unit (26) which is adapted to calibrate the irradiating system (20) on the basis of detection information of the sensor arrangement, wherein the calibrating structure (36) is arranged outside the build space (30). The invention also relates to a method for calibrating an irradiating system of a device for the layer-by-layer manufacture of a three-dimensional workpiece.

Claims

1-14. (canceled)

15. A device for the layer-by-layer manufacture of a three-dimensional workpiece, comprising: a build space in which the workpiece is manufacturable by selective solidification of raw material powder layers; an irradiation system which is adapted to selectively solidify the raw material powder layers in the build space by emitting at least one processing beam; at least one calibrating structure; a sensor arrangement which is adapted to detect a back reflection of irradiation emitted by the irradiation system at the calibrating structure; and a control unit (26) which is adapted to calibrate the irradiation system on the basis of detection information of the sensor arrangement, wherein the calibrating structure is arranged outside the build space, and wherein the calibrating structure comprises at least one depression and/or elevation, and wherein the irradiation system is adapted to carry out irradiation of the calibrating structure in the region of the depression and/or elevation within the context of a calibration operation.

16. The device as claimed in claim 15, wherein the calibrating structure is arranged within a process chamber of the device, in particular in such a manner that it extends at least in part between an inner wall region of the process chamber and the build space.

17. The device as claimed in claim 15, wherein the build space comprises a build area, wherein the calibrating structure extends along at least one side of the build area.

18. The device as claimed in claim 17, wherein the calibrating structure comprises at least two calibrating portions which extend along different sides of the build area, in particular wherein the different sides of the build area run at an angle to one another.

19. The device as claimed in claim 17, wherein the device further comprises a base region which surrounds the build area (28) at least in part, and wherein the calibrating structure is arranged in or parallel to the base region.

20. The device as claimed in claim 16, wherein the calibrating structure is arranged at least in part in or parallel to a side wall region of the process chamber.

21. The device as claimed in claim 15, wherein the calibrating structure comprises at least in part a material whose absorption behavior, based on the irradiation of the irradiation system, differs from the absorption behavior in the surroundings of the calibrating structure.

22. The device as claimed in claim 21, wherein the material for influencing the absorption behavior is arranged close to or in a transition region between the depression and/or elevation and the surroundings of the calibrating structure.

23. The device as claimed in claim 15, wherein the depression comprises at least one edge, preferably at an upper edge and/or in a transition region to the surroundings of the calibrating structure.

24. The device as claimed in claim 17, wherein the depression and/or elevation comprises a main portion which extends substantially along the build area, and wherein the depression and/or elevation comprises at least one secondary portion which extends at an angle to the main portion.

25. The device as claimed in claim 24, wherein there are provided a plurality of secondary portions which are arranged preferably at regular intervals along the main portion.

26. The device as claimed in claim 15, wherein the sensor arrangement is configured to detect the entry and/or exit of the processing beam into or out of the depression, and/or wherein the sensor arrangement is configured to detect the reaching and/or leaving of the elevation.

27. The device as claimed in claim 15, wherein the control system is configured to control the irradiation system in such a manner that, at least during a calibration operation, the irradiation system emits a processing beam with a power that does not have solidifying action.

28. A method for calibrating an irradiation system of a device for the layer-by-layer manufacture of a three-dimensional workpiece, wherein the device is configured in particular as claimed in claim 15, wherein the method comprises the following steps: irradiating a calibrating structure outside a build space, wherein the irradiation takes place by means of an irradiation system and the workpiece is manufacturable in the build space by selective solidification of raw material powder layers; detecting a back reflection of an irradiation emitted by the irradiation system at the calibrating structure; calibrating the irradiation system on the basis of the detected back reflection of the irradiation emitted by the irradiation system at the calibrating structure, wherein the calibrating structure comprises at least one depression and/or elevation, and wherein the irradiation system is adapted to carry out irradiation of the calibrating structure in the region of the depression and/or elevation within the context of a calibration operation.

Description

[0054] The invention will be explained hereinbelow with reference to the accompanying figures, in which:

[0055] FIG. 1: is a view of a device according to the invention which performs a method according to the invention;

[0056] FIG. 2: is a perspective view of a process chamber of the device of FIG. 1; and

[0057] FIGS. 3a, 3b: are schematic representations of the detection operation and of the profile over time of the detection signals in the device of FIG. 1.

[0058] FIG. 1 shows a device 10 which is configured to carry out a method according to the invention for the additive manufacture of three-dimensional workpieces from a metallic powder bed. More precisely, the method relates to a manufacturing process in the manner of so-called selective laser melting (SLM). The device 10 comprises a process chamber 12. The process chamber 12 can be sealed with respect to the atmosphere so that an inert gas atmosphere can be established therein. A powder application device 14, which is arranged in the process chamber 12, applies raw material powder layers to a carrier 16. As shown in FIG. 1 by an arrow A, the carrier 16 is adapted to be displaced in a vertical direction. The carrier 16 can thus be lowered in the vertical direction as the build height of the workpiece increases, when the workpiece is built up layer by layer from the selectively solidified raw material powder layers.

[0059] The device 10 further comprises an irradiation system 20 for selectively and location-specifically directing a plurality of laser beams 24a,b onto the raw material powder layers on the carrier 16. More precisely, the raw material powder material can be exposed to radiation by means of the irradiation system 20 in accordance with a geometry of a workpiece layer that is to be produced, and thus locally melted and solidified. The irradiation of the raw material powder layers by the irradiation system 20 is thereby controlled by a control unit 26.

[0060] In the exemplary embodiment shown, the irradiation system comprises two irradiation units 22a,b, which together can irradiate the raw material powder material. It is, however, also conceivable to provide only one such irradiation unit 22a,b or a plurality of irradiation units 22a,b arranged, for example, in a matrix.

[0061] Each of the irradiation units 22a,b shown is coupled to a common laser beam source. The laser beam emitted by the laser beam source can be split and/or deflected by suitable means, such as, for example, beam splitters and/or mirrors, in order to guide the laser beam to the individual irradiation units 22a,b. Alternatively, it would be conceivable to allocate each of the irradiation units 22a,b its own laser beam source. A suitable laser beam source can be provided, for example, in the form of a diode-pumped ytterbium fiber laser having a wavelength of approximately from 1070 to 1080 nm.

[0062] Each of the irradiation units 22a,b further comprises a processing beam optics, in order to interact with the laser beam provided. The processing optics each comprise a deflection device in the form of a scanner unit, which is able flexibly to position the focus point of the laser beam 24a,b emitted in the direction of the carrier 16 within an irradiation plane extending parallel to the carrier 16.

[0063] The surface of the carrier 16 facing the irradiation system 20 forms a build area 28, which defines a maximum possible base area or, in other words, a maximum cross-sectional area of the workpiece which can be produced. The build area 28 is of generally rectangular shape. A position of the build area 28 within the process chamber 12 can further be varied according to a lowering of the carrier 16. The build area 28 further forms the base area of a three-dimensional virtual build space 30 of the device 10, in which the workpiece can be manufactured. Owing to the described movement of the build area 28, the build space 30 is generally cylindrical with a correspondingly rectangular base area. An extent of the build space 30 is further shown in FIGS. 1 and 2 by a broken line.

[0064] Finally, a sensor arrangement 25 is shown schematically in FIG. 1, which sensor arrangement is able to detect back reflections of the laser beams 24a,b from the build area 28 and the surroundings. The sensor arrangement 25 is likewise connected to the control device 26 of the device 10. It is to be noted that the positioning of the sensor arrangement 25 shown is merely by way of example. In particular when the sensor arrangement 25 is in the form of a constituent of an existing melt pool monitoring system, it can instead be integrated in the beam path of the irradiation system 20 or interact at least indirectly therewith. A so-called in-line measurement of the back-reflected radiation can thus be carried out.

[0065] In FIG. 2, the process chamber 12 is shown in perspective, wherein the powder application device 14 has been omitted, however. There will again be seen the carrier 16, which forms the build area 28. The build space 30 is again defined as a cylinder with a rectangular base. The irradiation system 20 is indicated in FIG. 2 as a merely schematic rectangle and is generally configured selectively to irradiate the raw material powder layer within the build area 28. In FIG. 2 there is additionally shown gas outlet 32, which forms a known component of a process gas loop (not shown) of the device 10, in order to establish a protecting gas atmosphere within the process chamber 12.

[0066] It will be seen that the process chamber 12 comprises a base region 34. The base region is generally planar and extends parallel to the build area 28. The base region 34 is formed by a conventional base plate of the device 10, which is connected to a machine frame (not shown) and which is located generally opposite the irradiation system 20. In the starting state shown, in which the carrier 16 and thus the build area 28 have not yet been lowered, a surface of the base region 34 is further flush with the build area 28. The base region 34 overall forms a frame structure around the build area 28.

[0067] Within the base region 34 there is provided a calibrating structure 36, comprising two calibrating portions 37. The calibrating portions are in the form of depressions within the base region 34 and, more precisely, in the form of elongate recesses formed by cutting. This is clear from the enlarged partial view B in FIG. 2, which shows an end portion of one of the calibrating portions 37. It is also conceivable to provide a calibrating structure 36 having only one such calibrating portion 37.

[0068] The calibrating portions 37 each comprise a main portion 38 which extends along a longitudinal axis L1, L2. The calibrating portions 37 or, in other words, the main portions 38 thereof are further arranged substantially orthogonally to one another. Concretely, it will be seen in FIG. 2 that the main portions 38 extend along and parallel to different side regions of the rectangular build area 28. This relates to a first side 40 and a second side 42 of the rectangular build area 28, which run orthogonally to one another. Figuratively speaking, the calibrating portions 37 accordingly extend across a corner, based on the build area 28. With regard to the position of the calibrating portions 37, FIG. 2 also shows that these are arranged between an inner side wall region of the process chamber 12 facing the build area 28 and the build area 28. They are at only a small distance of a few centimeters from the build area 28.

[0069] It will further be seen in FIG. 2 that each of the calibrating portions 37 comprises a plurality of secondary portions 44, which are distributed at regular intervals along the main portions 38. In the example of FIG. 2, each of the calibrating portions 37 comprises more than six such secondary portions 44. For reasons of representation, not all the secondary portions 44 are provided with a corresponding reference numeral. As further becomes clear from the detail view in FIG. 2, the secondary portions 44 are likewise in the form of depressions and extend orthogonally to the main portion 38, wherein the secondary portions 44 are divided in the middle by the longitudinal axes L1, L2 of the main portions.

[0070] The secondary portions 44 thus form depression portions running transversely to the main portions 38, so that the calibrating portions 37 are each composed of individual cross-shaped depression regions along their respective longitudinal axes L1, L2.

[0071] In order to carry out a calibration operation, the control unit 26 causes the irradiation system 20 to direct a processing beam in the form of one of the laser beams 24a,b from FIG. 1 according to a predetermined movement path onto at least one of the calibrating portions 37. In particular, the processing beam, which is provided during the calibration with a deliberately reduced power which does not have solidifying action, can first be directed onto a surface of the base region 34, which surrounds the calibrating structure 36, and then be moved in the direction of one of the calibrating portions 37. The sensor arrangement 25 can, parallel thereto, detect the back reflections of the radiation from the base region 34 and/or the calibrating structure 36.

[0072] When the processing beam passes from the surface of the base region 34 for the first time into one of the calibrating portions 37 and into the depression formed thereby, the intensity of the back reflections detected by the sensor arrangement changes. This is further assisted in the present case in that the side and bottom walls of the calibrating portions 37 are each coated with a material which absorbs at least some of the laser radiation. The absorption of the laser radiation by that material is further greater than the absorption that occurs at the surface of the base region 34 surrounding the calibrating portions 37.

[0073] A profile over time of the signals detected by the sensor arrangement 25 is shown in FIGS. 3a,b. FIG. 3a shows a situation in which a laser beam 24a,b emitted by the irradiation system 20 passes for the first time into one of the secondary portions 44 of one of the calibrating portions 37. A movement path P on which this occurs is likewise indicated in FIG. 2. It will further be seen in FIG. 3a that the calibrating portions 37 form step-like depressions within the base region 34 and thus comprise sharp-edged transitions in the form of edges 45. Similarly to the absorbing material described hereinbefore, these lead to a particularly marked change in the reflection behavior on entry into the calibrating portions 37, which can be detected particularly reliably by the sensor arrangement 25.

[0074] FIG. 3b shows a profile over time of a sensor signal of the sensor arrangement 25 during this operation, wherein the sensor signal is shown by way of example as a sensor voltage V. Up to time t1, the laser beam 24a,b is moved along the planar surface of the base region 34, so that its back reflection does not change. The sensor signal of the sensor arrangement 25 is therefore substantially constant in the time period t0 to t1. At time t1, the laser beam 24a,b enters the secondary portion 44 forming a depression, so that its back reflection behavior changes suddenly and in the example shown falls suddenly. This also manifests itself in a change in the sensor signal at that time. Likewise, a reverse change of the sensor signal occurs when the laser beam 24a,b leaves the secondary portion 44 again at time t2. Between times t1 and t2 and also from time t2, the sensor signal is substantially constant, although at different voltage levels.

[0075] In summary, it will thus be seen that the control unit 26 is able to determine from the sensor signal of the sensor arrangement 25 the entry time t1 and also the exit time t2 from a region having an overbar (here: secondary portion 44) of the calibrating structure 36. Likewise, the parameters of the irradiation system 20 can be determined at that point in time, for example a current deflection position of the processing beam at the particular points in time in question. Since the position and extent of the calibrating structure 36 and in particular of the individual calibrating portions 37 thereof within the device 10 are known and generally unchangeable, it can thus be checked whether the determined times t1, t2 correspond to expected desired time points for particular specified irradiation parameters.

[0076] If that is not the case, this is an indication that the irradiation system 20 is not irradiating the calibrating structure 36 as expected, that is to say, for example because of too small a deflection, the calibrating portions 37 are not being reached at the expected times. The control unit 26 can then carry out a desired-actual comparison between the specified and the actually determined irradiation behavior and, on the basis thereof, calibrate the irradiation system 20 in order to compensate for a desired-actual deviation which may be determined.

[0077] Such a deviation, which suggests, for example, too early or too late entry into or exit from the calibrating portions 37, can lead to the conclusion that a deflection of the processing beam is not taking place in the desired manner and/or that there is a relative offset between the irradiation system 20 and the calibrating structure 36 which has not been taken into account. Such a relative offset also relates to a relative offset between the irradiation system 20 and the build area 28, since it can be assumed with sufficient accuracy that the relative position of the build area 28 and the calibrating structure 36 is known and constant. This offset can be compensated for by calibrating the irradiation system 20, for example by a suitable readjustment of the deflection of the processing beam and/or by calculating beforehand correspondingly adapted control signals for the irradiation system 20.

[0078] By arranging the calibrating portions 37 along two orthogonal sides of the build area 28 (or along the X-Y-axes of the build area 28 according to a conventional axis definition), the irradiation system 20 can thus reliably be calibrated relative to the build area 28. The plurality of secondary portions 44 thereby permits calibration in a plurality of predetermined positions along the corresponding sides of the build area 28.