CALIBRATION OF A SYSTEM FOR SELECTIVE POWDER MELTING

Abstract

A method for calibrating a system that includes a build chamber to accommodate powder to be melted and an object to be produced and a height-adjustable build plate support in the build chamber to support a build plate. The system also includes a controllable optical unit comprising (1) a laser source, (2) a plurality of lenses, and (3) a mirror arrangement having a plurality of adjustably arranged mirrors. The controllable optical unit is configured to selectively direct a laser beam to a point in the build chamber at which to melt the powder. The method includes placing a scanning field plate on the build plate support, creating a plurality of optical reference points on the scanning field plate, generating a measuring grid on the scanning field plate by adjusting the mirrors using a calibration data set, and determining a relative positioning between the optical reference points and the measuring grid.

Claims

1. A method for calibrating a system for producing objects made of a material powder by selective powder melting, the method comprising: placing a scanning field plate on a build plate support in a build chamber, wherein the build chamber is configured to accommodate a material powder to be melted and an object to be produced; creating a plurality of optical reference points on the scanning field plate at predefined positions using a controllable optical unit, wherein the controllable optical unit comprises a laser source, a plurality of lenses, and a mirror arrangement having a plurality of adjustably arranged mirrors, and wherein the controllable optical unit is configured to selectively direct a laser beam emitted by a laser source to a point in the build chamber at which the material powder is to be melted; generating a measuring grid on the scanning field plate using the controllable optical unit by adjusting the mirrors of the mirror arrangement using a calibration data set; and determining relative positionings between the optical reference points and the measuring grid.

2. The method of claim 1, further comprising adjusting the calibration data set based on the determination of the relative positionings between the reference points and the measuring grid.

3. The method of claim 2, wherein the placing, creating, generating, and determining steps are performed iteratively until the determined relative positionings meet one or more predetermined conditions.

4. The method of claim 1, wherein at least one of the optical reference points corresponds to an extreme position or another distinct position of at least one of the mirrors.

5. The method of claim 1, wherein the plurality of optical reference points comprise three or more optical reference points.

6. The method of claim 1, wherein the measuring grid comprises a plurality of crosses formed by intersecting line portions.

7. The method of claim 1, wherein the determination of the relative positionings is carried out in an automated manner using a readout device which is configured to determine the relative positionings using pattern recognition.

8. A method for calibrating a system for producing objects made of a material powder by selective powder melting, the method comprising: placing a scanning field plate on a height-adjustable build plate support in a build chamber, wherein the build chamber is configured to accommodate a material powder to be melted and an object to be produced; creating a plurality of optical reference points on the scanning field plate at predefined positions using the controllable optical unit, wherein the controllable optical unit comprises a laser source, a plurality of lenses, and a mirror arrangement having a plurality of adjustably arranged mirrors, and wherein the controllable optical unit is configured to selectively direct a laser beam emitted by a laser source to a point in the build chamber at which the material powder is to be melted; creating a measuring grid on the scanning field plate using the controllable optical unit by adjusting the mirrors of the mirror arrangement using a calibration data set; determining the relative positionings between the optical reference points and the measuring grid; and creating a unique identification element (ID) on the scanning field plate.

9. The method of claim 8, wherein the unique identification element (ID) comprises one or more of a QR code, a bar code, or an alphanumeric code; and wherein the unique ID encodes one or more of a serial number of the system, a current iteration number, a calibration data set used, or a key value for database access.

10. The method of claim 8, further comprising storing, in a database, (i) data relating to the method for calibration and (ii) the identification element.

11. A system for producing objects made of a material powder by selective powder melting, comprising: a build chamber to accommodate the material powder to be melted and an object to be produced; a height-adjustable build plate support provided in the build chamber to support a build plate on which the object to be produced will be built; a controllable optical unit comprising a laser source, a plurality of lenses, and a mirror arrangement having a plurality of adjustably arranged mirrors, wherein the controllable optical unit is configured to selectively direct a laser beam emitted by the laser source to a point in the build chamber at which the material powder is to be melted; and a control unit to control the controllable optical unit to create a plurality of optical reference points on the scanning field plate at predefined positions and generate a measuring grid on the scanning field plate by adjusting the mirrors of the mirror arrangement using a calibration data set; and a readout device to determine relative positionings between the optical reference points and the measuring grid.

12. The system of claim 11, wherein the controllable optical unit comprises a hermetically sealed housing in which at least some of the plurality of adjustably arranged mirrors and at least some of the plurality of lenses are arranged, wherein the controllable optical unit comprises a transparent pane which allows the laser beam to enter the build chamber from the housing.

13. The system of claim 11, wherein the readout device is configured to read out a unique on the scanning field plate.

14. The system of claim 11, wherein the readout device is further configured to automatically adjust the calibration data set based on the determination of the relative positionings.

15. The system of claim 11, wherein the readout device is further configured to read the calibration data out from a database.

16. The method of claim 1, wherein the plurality of optical reference points do not lie on a straight line.

17. The method of claim 1, wherein at least one of the optical reference points corresponds to a beam path of the laser beam that is incident perpendicularly to the scanning field plate.

18. The method of claim 6, wherein the intersecting line portions intersect at a right angle.

19. The method of claim 7, wherein the adjustment of the calibration data set is carried out in an automated manner using a readout device.

20. The system of claim 13, wherein the readout device is further configured to store data relating to the unique ID in a database.

Description

[0026] Further features and advantages of the present invention will become even clearer from the following description of an embodiment, when said embodiment is considered together with the accompanying drawings. In detail, in the drawings:

[0027] FIG. 1 is a schematic view of an inventive system; and

[0028] FIG. 2 is a schematic view of a scanning field plate used in a method according to the invention in the system from FIG. 1.

[0029] In FIG. 1, first a system for producing objects made of a material powder according to the method of selective powder melting is shown in a purely schematic cross-sectional view and is denoted by reference numeral 10.

[0030] The system 10 comprises optical and mechanical components which form an optical apparatus and a mechanical apparatus in the usual nomenclature in this field. In this case, the essential optical components are received in a so-called optics box 12 which accommodates, among other things, a plurality of adjustably arranged mirrors 14 and a lens system 16. Here, only one mirror 14 is shown for reasons of clarity, and the lens system 16 is also only indicated schematically. Overall, the mirrors 14 together with the lens system 16 and an externally arranged laser source 18, from which a laser beam is radiated into the optics box 12, form a controllable optical unit 20. Because the components of the optical unit 20 are suitably controlled by a control unit (not shown), the laser beam L, after passing through the lens system 16 and being reflected on the mirrors 14, can be directed at an angle out of the optics box 12 through a transparent pane 12a into a build chamber 22 such that the laser beam is to impinge on an irradiation plane at a target position S, on which plane a material powder is to be selectively melted during regular operation of the system 10.

[0031] For the present calibration process, however, there is no build plate and also no material powder in the build chamber 22 on the height-adjustable build plate support 24, but instead there is a scanning field plate 26. This scanning field plate 26 is made of a material in which markings can be written by irradiating the laser beam L. To this end, for example, anodised aluminium plates are used, but other suitable materials which can be written on with a laser beam typically used for melting material powder in such systems can also be considered.

[0032] In the illustration from FIG. 1, however, due to various possible interference effects, the laser beam L does not impinge on the scanning field plate 26 at the target position S, but instead at an actual position P. The deviation between the target position S and the actual position P when the laser beam L arrives at the scanning field plate 26 can be reduced by correspondingly calibrating the control of the controllable optical unit 20, wherein initially interferences in the coordinate system K1 of the controllable optical unit 20 can cause the deviation between the target position S and the actual position P. If, as has been customary in the prior art, an absolute position of the marking produced at the actual position P by irradiating the laser beam L onto the scanning field plate 26 is now taken as a measure for the deviation between the two positions, then additional interferences in the coordinate system K2 of the mechanical apparatus would have to be taken into account, since the positioning and also the rotational position of the scanning field plate 26 on the build plate support 24 and other degrees of freedom, such as the relative positioning of the optics box 12 to the build chamber 22, represent further sources of interference or errors. Since these mechanical sources of interference can deviate from measurement to measurement, this is a dynamic system error, which can lead to the iterative methods provided not converging quickly in a meaningful way or at all.

[0033] In contrast to this method known from the prior art, according to the present invention the irradiation of the scanning field plate 26 is carried out such that the pattern shown in FIG. 2 is generated on the scanning field plate 26. First, an optical coordinate system is generated on the scanning field plate 26 from three optical reference points O1 to O3, wherein the three points O1 to O3 are always generated at well-defined points that are not subject to calibration and that are preferably marked such that at least one of the mirrors 14 of the optical unit 20 is in an end position or in some other distinct position and/or the beam path of the laser beam L through the pane 12a, and thus the impingement on the scanning field plate 26, are perpendicular in order to exclude imaging errors.

[0034] Relative to the optical coordinate system formed from the points O1 to O3, a plurality of cross-shaped markings M1 to M4 are now inscribed on the scanning field plate 26 with the laser beam L using the calibration data set. By using the calibration data set from the control unit of the system 10 to generate these markings M1 to M4 forming a measuring grid M, which calibration data set would also be used in particular during regular operation of the system 10, the deviation between the expected target positions of the markings M1 to M4 and their true actual positions can now be determined independently of the mechanical apparatus in a subsequent step of determining these relative positionings.

[0035] On the basis of this determination, a corrected calibration data set can then be created, so that the actual positions can iteratively approach the target positions in several steps, wherein the reading out of the markings M1 to M4 on the scanning field plate 26 and also the subsequent creation of a new calibration data set can be carried out in a dedicated external readout device.

[0036] It should also be noted that identification elements ID have also been inscribed on the scanning field plate 26 using the laser beam L, wherein in the embodiment shown in FIG. 2 both a bar code and a QR code, as well as an alphanumeric code, are shown by way of example, while in practice usually only one of the codes will be used.

[0037] This identification element can be used, for example, to encode the current iteration, a serial number of the system 10, and other relevant data, which can then also be read out in an automated manner and operator errors when marking and handling the scanning field plates 26 from subsequent iterations or different systems can be prevented.