Calibration method for a system for powder bed-based generating of three-dimensional components by means of electromagnetic radiation

Abstract

A calibration method for a system for powder bed-based generating of three-dimensional components by means of electromagnetic radiation, in particular such as a PBLS system, having a radiation source deflection unit and a raisable and lowerable carrier plate, above which a component is built, where, in order to calibrate the radiation source deflection unit, at least one virtual reference mark is used and, by means of a detector, a target-actual deviation between the virtual reference mark and a beam of the radiation source deflection unit is determined. An improved calibration method is achieved in that the at least one virtual reference mark is projected on a reference surface, which can travel vertically by means of the raisable and lowerable carrier plate, and independently of the vertical position thereof.

Claims

1. A calibration method for a powder-bed-based laser melting (PBLM) system for powder-bed-based production of three-dimensional components via electromagnetic radiation where the system comprises a working plane, a plurality of beam source deflection units each comprising at least one deflecting mirror and each configured to provide a laser beam, and a support plate that can be raised and lowered and above which a component is built up, wherein the laser beam provided by each beam source deflection unit is produced by an individual laser beam source, the method comprising: projecting at least one virtual reference mark onto a reference surface that can be moved vertically via the support plate; and determining with a detector a target-actual deviation between the at least one virtual reference mark and a laser beam of one of the beam source deflection units for calibration of that said one of the beam source deflection units; wherein each of the beam source deflection units with its respective at least one deflecting mirror is moveable in the vertical direction and the projecting the at least one virtual reference mark is projected onto the reference surface independently of whether the vertical position of the reference surface is below, above or in the working plane of the system; and wherein the at least one virtual reference mark comprises a relative reference mark provided by the laser beam of another one of the beam source deflection units.

2. The calibration method as claimed in claim 1, wherein the at least one virtual reference mark further comprises an absolute reference mark produced by a projection device that is different from the beam source deflection units.

3. The calibration method as claimed in claim 2, further comprising carrying out a focus calibration of a selected beam source deflection unit using the at least one absolute reference mark, and for this purpose determining the target-actual deviation between the absolute reference mark and the laser beam of the selected beam source deflection unit using the detector, and correcting a setting of the selected beam source deflection unit and/or of the laser beam of the selected beam source deflection unit in order to minimize or eliminate the determined target-actual deviation or to adjust it to a desired value.

4. The calibration method as claimed in claim 2, further comprising carrying out a position calibration of a selected beam source deflection unit using the at least one absolute reference mark, and for this purpose determining the target-actual deviation between the absolute reference mark and the laser beam of the selected beam source deflection unit using the detector and correcting a setting of the selected beam source deflection unit and/or of the laser beam of the selected beam source deflection unit in order to minimize or eliminate the determined target-actual deviation or to adjust it to a desired value.

5. The calibration method as claimed in claim 3, wherein said method further comprises carrying out a focus calibration of additional beam source deflection units of the plurality of beam source deflection units using the at least one absolute reference mark.

6. The calibration method as claimed in claim 4, wherein said method further comprises carrying out a position calibration of additional beam source deflection units of the plurality of beam source deflection units using the at least one absolute reference mark.

7. The calibration method as claimed in claim 1, wherein the at least one virtual reference mark is produced by a laser beam which has an intensity which does not cause any melting of powder for the PBLM system.

8. The calibration method of claim 3, wherein the selected beam source deflection unit comprises the said another one of the beam source deflection units and defines a first beam source deflection unit that provides the at least one virtual reference mark that comprises the relative reference mark, said method further comprising, after the focus calibration of the first beam source deflection unit using the at least one absolute reference mark, carrying out a focus calibration of one or more additional beam source deflection units of the plurality of beam source deflection units using the first beam source deflection unit, and for this purpose determining a target-actual deviation between the laser beam of the first beam source deflection unit that produces the relative reference mark and the laser beam of the one or more additional beam source deflection units, and correcting a setting of the one or more additional beam source deflection units and/or correcting the laser beams of the one or more additional beam source deflection units in order to minimize or eliminate the determined target-actual deviation or to adjust it to a desired value.

9. The calibration method as claimed in claim 7, said method further comprising carrying out a position calibration of one or more additional beam source deflection units of the plurality of beam source deflection units in relation to the relative reference mark, and for this purpose determining a target-actual deviation between the relative reference mark and a beam of the one or more additional beam source deflection units using the detector and correcting a setting of the one or more additional beam source deflection units and/or of the laser beam of the one or more additional beam source deflection units in order to minimize or eliminate the determined target-actual deviation or to adjust it to a desired value.

10. The calibration method as claimed in claim 1, wherein the detector comprises a general detector and is used for position calibration and/or focus calibration and is disposed above the reference surface and comprises a camera and is used for determination of a target-actual deviation between each reference mark and the beam of said plurality of beam source deflection units.

11. The calibration method as claimed in claim 1, wherein the detector comprises a local detector and is used for position calibration and/or focus calibration and is allocated to a particular beam source deflection unit and comprises a camera and is used for determination of a target-actual deviation between each reference mark and the laser beam of the particular beam source deflection unit allocated to said detector.

12. The calibration method as claimed in claim 1, further comprising carrying out a focus calibration of a selected beam source deflection unit using the detector and for this purpose determining a target-actual deviation between a lateral target expansion and/or target intensity, preset for the laser beam generated by the selected beam source deflection unit, and a lateral actual expansion and/or actual intensity of the laser beam generated by the selected beam source deflection unit, and correcting a setting of the selected beam source deflection unit and/or of the laser beam of the selected beam source deflection unit in order to minimize or eliminate the determined target-actual deviation or to adjust it to a desired value.

13. The calibration method as claimed in claim 4, wherein the position calibration and/or the focus calibration is carried out prior to and/or during a build job.

14. The calibration method as claimed in claim 1, wherein the system further includes a control unit configured to control the system for projecting the at least one virtual reference mark and determining the target-actual deviation.

15. The calibration method as claimed in claim 2, further comprising carrying out a focus calibration of the said another one of the beam source deflection units using the at least one absolute reference mark and further comprising carrying out a position calibration of the said another one of the beam source deflection units using the at least one absolute reference mark, and for this purpose determining the target-actual deviation between the absolute reference mark and the laser beam of the said another one of the beam source deflection units using the detector and correcting a setting of the said another one of the beam source deflection units and/or of the laser beam of the said another one of the beam source deflection units in order to minimize or eliminate the determined target-actual deviation or to adjust it to a desired value.

16. The calibration method as claimed in claim 15, wherein said method further comprises carrying out a focus calibration of one or more additional beam deflection units of the plurality of beam source deflection units using the at least one absolute reference mark.

17. The calibration method as claimed in claim 16, wherein said method further comprises carrying out a position calibration of one or more additional beam deflection units of the plurality of beam source deflection units using the at least one absolute reference mark.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

(1) FIG. 1 shows a view of an PBLM system with a laser scanner unit and an opened process chamber,

(2) FIG. 2 shows a view of a multi-scanner PBLM system with two laser scanner units and an opened process chamber,

(3) FIG. 3 shows a view of a component reservoir,

(4) FIG. 4 shows a schematic cross-sectional view of the component reservoir of FIG. 3,

(5) FIG. 5 shows a schematic illustration of a position calibration of the laser scanner unit of the PBLM system by means of an absolute reference mark and of a general detector,

(6) FIG. 5a shows a schematic illustration after the position calibration described in relation to FIG. 5,

(7) FIG. 6 shows a schematic illustration of a position calibration of the laser scanner unit of the PBLM system by means of an absolute reference mark and of a local detector,

(8) FIG. 6a shows a schematic illustration after the position calibration depicted in FIG. 6,

(9) FIG. 7 shows a schematic illustration of a focus calibration of the laser scanner unit of the PBLM system by means of an absolute reference mark and of a general detector,

(10) FIG. 7a shows a schematic illustration after the focus calibration described in relation to FIG. 7,

(11) FIG. 8 shows a schematic illustration of a focus calibration of the laser scanner unit of the PBLM system by means of an absolute reference mark and of a local detector,

(12) FIG. 8a shows a schematic illustration after the focus calibration depicted in FIG. 8,

(13) FIG. 9 shows a schematic illustration of a position calibration of one of two laser scanners units of the multi-scanner PBLM system by means of a relative reference mark and of a general detector,

(14) FIG. 9a shows a schematic illustration after the position calibration described in relation to FIG. 9,

(15) FIG. 10 shows a schematic illustration of a position calibration of one of two laser scanner units of the multi-scanner PBLM system by means of a relative reference mark and of a local detector,

(16) FIG. 10a shows a schematic illustration after the position calibration described in relation to FIG. 10,

(17) FIG. 11 shows a schematic illustration of a focus calibration of the laser scanner unit of the PBLM system by means of a local detector, and

(18) FIG. 11a shows a schematic illustration after the focus calibration described in relation to FIG. 11.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

(19) FIG. 1 shows a view of a PBLM system 1 with a beam source deflection unit formed as a laser scanner unit 2. The PBLM system 1 comprises a process chamber which comprises a process chamber upper part 3 and a process chamber lower part 4. Via at least one opening which is provided in the upper part 3 and which is closed in a gas-tight manner e.g. by means of glass, beams from the scanner unit 2 disposed outside the process chamber can be coupled into the process chamber. The lower part 4 is closed at the bottom by means of a chamber floor 5 of the process chamber. In the illustrated view, the process chamber is opened, for which purpose the upper part 3 has been pivoted upwards and laterally away from the stationary lower part 4 and the chamber floor 5, thus forming a hinged opening. A pusher 8 is mounted so as to move in a translational movement parallel to a chamber floor 5 of the process chamber on an inner side of the process chamber upper part 3. An application medium 7, which can be formed e.g. as a brush, blade or rubber lip, is fastened to the pusher 8 so that, when the process chamber is closed, a movement of the pusher 8 can move the application medium 7 in a translational movement and parallel to the chamber floor 5 of the process chamber. The application medium 7 is used to distribute or discharge powder on a build platform 6 which can be raised and lowered vertically with respect to the chamber floor 5. For this purpose the application medium 7 spans the build platform 6 transversely to its movement direction when the process chamber is closed. The powder is conveyed out of a powder reservoir 10 next to the build platform 6 via a so-called bottom-up powder conveying mechanism from below the chamber floor 5 in the direction of the chamber floor 5 and at that location is provided for the application medium 7 via an opening 10a in the powder reservoir 10. The powder reservoir 10 or the bottom-up powder conveying mechanism thereof can be supplied with powder, in particular during on-going operation of the PBLM system 1, via a storage reservoir 9 connected to the powder reservoir 10. The component is produced on the build platform 6 by means of the above-described PBLM method. A powder overflow 10b is disposed at a side of the build platform 6as seen in the movement direction of the pusher 8 or of the application medium 7opposite the powder reservoir 10a, said powder overflow receiving excess powder which, during the passage over the build platform 6 was not discharged thereto by the application medium 7. The build platform 6 is accordingly disposed between the powder reservoir 10 and the powder overflow 10b.

(20) FIG. 2 shows a view of a multi-scanner PBLM system 11 with two laser scanner units 2 which are both allocated to the build platform 6. Alternatively, the multi-scanner PBLM system 11 can also have more than two laser scanner units. Otherwise, the statements relating to FIG. 1 also apply to the PBLM system 1 illustrated in FIG. 2.

(21) FIG. 3 shows a view of a component reservoir 12. This is defined laterally by the component reservoir side wall 13. The build platform 6 is fitted corresponding to the base surface of the component reservoir 12 within its component reservoir side wall 13. The build platform 6 can be formed e.g. from a substrate plate, from which the finished component must be separated, or a preform which becomes part of the component. The build platform 6 is supported by a support plate 16, not illustrated in FIG. 3 (see FIG. 4), which in turn can be vertically raised and lowered jointly with the build platform 6 within the component reservoir 12 via a lifting drive. The lifting drive can comprise e.g. an electromechanical lifting cylinder, ball screw, belt drive, pneumatic or hydraulic drive. In the present example, the lifting drive comprises one or a plurality of drive blocks 15 (see FIG. 4) connected to the support plate 16, which can then be moved vertically along one or a plurality of drive rails 14.

(22) FIG. 4 shows a schematic cross-sectional view of the component reservoir 12 described in relation to FIG. 3. The support plate 16 forms the movable floor of the component reservoir 12 which, together with an upper opening opposite the floor, adjoins the working plane 17 below the working plane 17. In this case, the support plate 16 is fitted in the manner of a piston inside the component reservoir side wall 13 of the component reservoir 12, extending at a right angle to the floor, and is movable in order to be able to be lowered or raised incrementally by the lifting drive in relation to the working plane 17. The build platform 6 is supported by the support plate 16 and is disposed thereon, e.g. laid or releasably fastened, in particular screwed or clamped, thereon. A reference surface 30 is formed by the build platform 6 disposed on the support plate 16. Otherwise, the statements relating to FIG. 3 also apply to the component reservoir 12 illustrated in FIG. 4.

(23) FIG. 5 shows a schematic illustration of a position calibration of the laser scanner unit 2 of the PBLM system 1 by means of a virtual absolute reference mark and of a general detector 26. The construction required for this position calibration comprisesin addition to the laser scanner unit 2, the general detector 26 and a unit 24 producing the virtual absolute reference marka control unit 28 and a reference surface 30, onto which the absolute reference mark and the laser beam 20 of the laser scanner unit 2 are projected. The laser scanner unit 2 comprises a laser beam source 18 and a deflection unit 19. The deflection unit 19 comprises a deflecting mirror 21, two focussing lenses 22, of which at least one is movable, and two deflecting mirrors 23. The laser scanner unit 2 can move in the horizontal and/or vertical direction. The unit 24 and the reference surface 30 can be moved vertically by raising/lowering the support plate 16. This therefore makes it possible to adjust the relative position and in particular the distance between the reference surface 30 and the laser scanner unit 2 and the unit 24.

(24) The general detector 26 has a detection range 34 which is larger than the reference surface 30. For the purposes of the position calibration, the laser scanner unit 2 is actuated by the control unit 28 via the signal connection 29 so that this control unit generates a laser beam 20 which is projected onto the reference surface 30 with a corresponding cross-sectional surface (not illustrated). In addition, the unit 24 is actuated by the control unit 28 via the signal connection 29 so that it generates an electromagnetic beam 25 which projects onto the reference surface 30 the absolute reference mark with a corresponding cross-sectional surface (not illustrated). After detection of the cross-sectional surfaces of the beams 20, 25 projected onto the reference surface 30 by the general detector 26, a corresponding signal is transmitted via the signal connection 29 between general detector 26 and the control unit 28 for evaluation at the control unit 28. The control unit 28 evaluates the signal from the detector 26 in that the reference point 38 of the laser beam 20, in particular the cross-sectional surface thereby produced, and the reference point 31 of the absolute reference mark, in particular the cross-sectional surface thereby produced, is calculated and/or defined by the control unit 28. The reference points 31, 38 are each illustrated by means of a cruciform marking on the reference surface 30. The control unit 28 then evaluates a target-actual deviation 33 between the reference points 31, 38 in that it determines a distance between the reference points 31, 38 and transmits, for correction of the corresponding setting of the laser scanner unit 2, a signal via the signal connection 29 between the control unit 28 and the laser scanner unit 2. If necessary, the procedure is repeated until the reference point 38 of the laser beam 20 of the laser scanner unit 2 lies over the reference point 31 of the electromagnetic beam 25 of the device 24. According to this manner of proceeding, a position calibration is thus carried out by means of an absolute reference mark and a general detector 26. In the case of a multi-scanner PBLM system 11, this position calibration can be carried out analogously at each further one of the laser scanner units 2.

(25) FIG. 5a shows a schematic illustration after the position calibration described in relation to FIG. 5. The reference points 31 and 38 in this case lie one above the other owing to the position calibration carried out.

(26) FIG. 6 shows a schematic illustration of a position calibration of the beam source deflection unit 2 of the PBLM system 1 by means of an absolute reference mark and of a local detector 27. In contrast to the position calibration according to FIG. 5, a local detector instead of a general one is used. The local detector 27 has a detection range 35 which is smaller than the reference surface 30 and is allocated to the laser scanner unit 2. In order that the local detector 27 can detect the cross-sectional surface of the absolute reference mark and the cross-sectional surface of the laser beam 20, which is generated by the laser scanner unit 2 allocated to said detector, the deflecting mirror 21 is designed and arranged to be partially permeable in such a way that appropriate electromagnetic beams can penetrate through it, which beams are reflected by the reference surface 30. Otherwise, the statements relating to FIG. 5 also apply to the embodiment illustrated in FIG. 6.

(27) FIG. 6a shows a schematic illustration after the position calibration described in relation to FIG. 6. The reference points 31 and 38 in this case lie one above the other owing to the position calibration carried out.

(28) FIG. 7 shows a schematic illustration of a focus calibration of the laser scanner unit 2 of the PBLM system 1 by means of an absolute reference mark, projected by the device 24 onto the reference surface 30, and of a general detector 26. During the focus calibration, instead of the target-actual deviation 33 between the reference points of the laser beam 20 and of the electromagnetic beam 25, the target-actual deviation 33 between the lateral actual expansion 37 of the laser beam 20 and the lateral actual expansion 36 of the electromagnetic beam 25 is determined. The lateral actual expansion 37 of the laser beam 20 and the lateral actual expansion 36 of the electromagnetic beam 25 are illustrated by means of a round marking on the reference surface 30. The lateral actual expansion 37 of the laser beam 20 in this example is larger than the lateral actual expansion 36 of the electromagnetic beam 25. After appropriate evaluation by the control unit 28, the laser scanner unit 2 is actuated by the control unit 28 via the signal connection 29 between the control unit 28 and the laser scanner unit 2. The setting of the laser scanner unit 2 and in particular of the movable focussing lens(es) 22 is changed in such a way that the lateral actual expansion 37 of the laser beam 20 matches the lateral actual expansion 36 of the electromagnetic beam 25. Otherwise, the statements relating to FIG. 5 also apply to the embodiment illustrated in FIG. 7.

(29) FIG. 7a shows a schematic illustration after the focus calibration described in relation to FIG. 7. The lateral actual expansions 37 and 36 in this case lie congruently one above the other owing to the focus calibration carried out.

(30) FIG. 8 shows a schematic illustration of a focus calibration of the laser scanner unit 2 of the PBLM system 1 by means of an absolute reference mark, projected by the device 24 onto the reference surface 30, and of a local detector 27. In contrast to the focus calibration by means of a general detector 26, in this embodiment a local detector 27 is used. Otherwise, the statements relating to FIGS. 5, 6 and 7 also apply to the embodiment illustrated in FIG. 8.

(31) FIG. 8a shows a schematic illustration after the focus calibration described in relation to FIG. 8. The lateral actual expansions 37 and 36 in this case lie congruently one above the other owing to the focus calibration carried out.

(32) FIG. 9 shows a schematic illustration of a position calibration of one of two laser scanner units 2 of the multi-scanner PBLM system 11 by means of a virtual relative reference mark and of a general detector 26. The multi-scanner PBLM system 11 comprises two laser scanner units 2. One laser scanner unit 2 is calibrated by means of the other laser scanner unit 2. For this purpose, the laser scanner unit 2 generates a laser beam 20 which is projected onto the reference surface 30 and serves as a virtual relative reference mark. The reference point 32 of this relative reference mark is calculated and/or defined by the control unit 28 and is illustrated on the reference surface 30 by means of a cruciform marking. Subsequently or at the same time, the other laser scanner unit 2 generates a laser beam 20 and projects it onto the reference surface 30. The reference point 38 of the laser beam 20 is calculated and/or defined by the control unit 28 and is also illustrated on the reference surface 30 by means of a cruciform marking. Otherwise, the statements relating to FIG. 5 also apply to the embodiment illustrated in FIG. 9, wherein instead of the absolute reference mark the relative reference mark of one laser scanner unit 2 is used.

(33) FIG. 9a shows a schematic illustration after the position calibration described in relation to FIG. 9. The reference points 32 and 38 in this case lie one above the other as a result of the position calibration.

(34) FIG. 10 shows a schematic illustration of a position calibration of one of two laser scanner units 2 of the multi-scanner PBLM system 11 by means of a relative reference mark and of a local detector 27. In contrast to the embodiment illustrated in FIG. 9, instead of the general detector 26, two local detectors 27, allocated to the laser scanner units 2 respectively, are used in order to determine the target-actual deviation 33. However, it will suffice for only one of the two laser scanner units 2 to be allocated a corresponding local detector 27. Otherwise, the statements relating to FIGS. 6 and 9 also apply to the embodiment illustrated in FIG. 10.

(35) FIG. 10a shows a schematic illustration after the position calibration described in relation to FIG. 10. The reference points 32 and 38 in this case lie one above the other as a result of the position calibration.

(36) FIG. 11 shows a schematic illustration of a focus calibration of the laser scanner unit 2 of the PBLM system 1 by means of a local detector 27. In contrast to the focus calibration by means of an absolute reference mark, projected by the device 24 onto the reference surface 30, and of a local detector 27, no absolute reference mark is used in this embodiment. The lateral target expansion 39 is preset and is used by the control unit 28 to evaluate the target-actual deviation 33. The presetting can arise e.g. from an arithmetical or iterative determination of the target expansion, which is carried out during the evaluation of the target-actual deviation 33. Otherwise, the statements relating to FIGS. 5, 6 and 7 also apply to the embodiment illustrated in FIG. 11.

(37) FIG. 11a shows a schematic illustration of the laser scanner unit 2 of the PBLM system 1 after the focus calibration described in relation to FIG. 11. The lateral actual expansion 37 and the lateral target expansion 39 of the laser beam 20 in this case lie congruently one above the other owing to the focus calibration carried out.