ADDITIVE MANUFACTURING APPARATUS AND METHOD

• US 20160236279A1
• Filed: 09/23/2014
• Published: 08/18/2016
• Est. Priority Date: 09/23/2013
• Status: Active Grant

• Current Assignee: Renishaw PLC
• Original Assignee: Renishaw PLC
• Inventors: ASHTON, Ian Robert Thomas, KLOSS, Stephan, SUTCLIFFE, Christopher, FERRAR, Ben Ian
• Granted Patent: US 10,850,326 B2
• Time in Patent Office: Days
• US Class Current: 1/1
• CPC Class Codes: B22F 10/00 Additive manufacturing of workpieces or articles from metallic powder apparatus or devices therefor B22F12/00
• CPC Class Codes: B22F 10/28 Powder bed fusion, e.g. selective laser melting [SLM] or electron beam melting [EBM]
• CPC Class Codes: B22F 10/31 Calibration of process steps or apparatus settings, e.g. before or during manufacturing
• CPC Class Codes: B22F 10/36 of energy beam parameters
• CPC Class Codes: B22F 10/366 Scanning parameters, e.g. hatch distance or scanning strategy
• CPC Class Codes: B22F 10/368 Temperature or temperature gradient, e.g. temperature of the melt pool
• CPC Class Codes: B22F 12/41 characterised by the type, e.g. laser or electron beam
• CPC Class Codes: B22F 12/44 characterised by the configuration of the radiation means
• CPC Class Codes: B22F 12/49 Scanners
• CPC Class Codes: B22F 12/90 Means for process control, e.g. cameras or sensors
• CPC Class Codes: B29C 64/153 using layers of powder being selectively joined, e.g. by selective laser sintering or melting
• CPC Class Codes: B29C 64/268 using laser beams; using electron beams [EB]
• CPC Class Codes: B29C 64/393 for controlling or regulating additive manufacturing processes
• CPC Class Codes: B33Y 10/00 Processes of additive manufacturing
• CPC Class Codes: B33Y 30/00 Apparatus for additive manufacturing; Details thereof or accessories therefor
• CPC Class Codes: B33Y 50/02 for controlling or regulating additive manufacturing processes
• CPC Class Codes: G01J 3/28 Investigating the spectrum using colour filters G01J3/51
• CPC Class Codes: G01N 21/274 Calibration, base line adjustment, drift correction
• CPC Class Codes: G01N 21/718 Laser microanalysis, i.e. with formation of sample plasma
• CPC Class Codes: G01N 2201/06113 Coherent sources; lasers
• CPC Class Codes: Y02P 10/25 : Process efficiency

Abstract

This invention concerns a laser solidification apparatus for building objects by layerwise solidification of powder material. The apparatus including a build chamber containing a build platform, a device for depositing layers of powder material on to the build platform, an optical unit for directing a laser beam to selectively solidify areas of each powder layer and a spectrometer for detecting characteristic radiation emitted by plasma formed during solidification of the powder by the laser beam. The invention also relates to a spectrometer for detecting characteristic radiation generated by interaction of the metal with the or a further laser beam. The spectra recorded using the spectrometer may be used for feedback control during the solidification process.

Claims

1. A laser solidification apparatus for building objects by layerwise solidification of powder material, the apparatus comprising a build chamber containing a build platform, a device for depositing layers of powder material on to the build platform, an optical unit for directing a laser beam to selectively solidify areas of each powder layer and a spectrometer for detecting characteristic radiation emitted by plasma formed during solidification of the powder by the laser beam.

4. A laser solidification apparatus according to claim 1, wherein the spectrometer is arranged to detect characteristic radiation generated by creating a melt pool with the laser.

5. A laser solidification apparatus according to claim 4, wherein the characteristic radiation comprises radiation emitted by laser ionised vapour emitted from the melt pool.

6. A laser solidification apparatus according to claim 1, comprising a control unit arranged to determine a characteristic of the material in the layer from a detected spectrum/detected spectra.

7. A laser solidification apparatus according to claim 6, wherein the characteristic is a temperature, diameter and/or depth of a melt pool generated by the laser beam and/or a temperature of plasma generated during the solidification process.

8. A laser solidification apparatus according to claim 6, wherein the characteristic is a location of a focal point of the laser beam.

9. A laser solidification apparatus according to claim 6, wherein the characteristic is a relative concentration of elements of the powder material in a melt pool and/or plasma generated by the laser beam.

10. A laser solidification apparatus according to claim 1, comprising a control unit for controlling the optical unit and/or a laser based upon a detected spectrum/detected spectra.

11. A laser solidification apparatus according to claim 10, wherein the control unit is arranged to alter point distance, exposure time, scan speed, hatch spacing, laser power and/or focussing of the laser based upon the detected spectrum/detected spectra.

12. A laser solidification apparatus according to claim 1, comprising a validation unit for storing a log of spectra detected for different locations on each layer.

13. A laser solidification apparatus according to claim 1, wherein the spectrometer is arranged for detecting characteristic radiation collected by the optical unit.

14. A laser solidification apparatus according to claim 13, wherein the optical unit comprises an optical scanner for steering the laser beam to the desired point on a powder layer, the spectrometer arranged to detect characteristic radiation that is collected through the optical scanner.

15. A laser solidification apparatus according to claim 14, wherein the optical scanner comprises movable focussing optics for focussing the laser beam on the powder layer, the spectrometer arranged to detect characteristic radiation that is collected through the focussing optics.

16. A laser solidification apparatus according to claim 13, wherein the optical scanner is arranged such that the characteristic radiation collected by the optical scanner travels along a transmission path shared with the laser beam and comprises a beam splitter for dividing the optical paths of the laser beam and the radiation to direct the radiation onto a detector of the spectrometer.

17. A laser solidification apparatus according to claim 16, wherein the beam splitter is located upstream, relative to a direction of travel of the laser beam, of steerable optics for steering the laser beam and movable focussing optics for focussing the laser beam.

18. A laser solidification apparatus according to claim 16, wherein the beam splitter is arranged to reflect the laser beam and transmit the characteristic radiation.

19. A laser solidification apparatus according to claim 16, wherein the beam splitter is a notch filter.

20. A laser solidification apparatus according to claim 19, wherein the filter is a dichroic filter.

21. A laser solidification apparatus according to claim 16, comprising a heat dump for capturing a proportion of the laser beam that is not transmitted along the transmission path shared with the characteristic radiation.

2. A laser solidification apparatus for building objects by layerwise solidification of metal powder, the apparatus comprising a build chamber containing a build platform, a device for depositing layers of metal powder on to the build platform, an optical unit for directing a laser beam to selectively solidify areas of each metal powder layer and a spectrometer for detecting characteristic radiation generated by interaction of the metal with the or a further laser beam.

3. A laser solidification apparatus according to claim 2, wherein the spectrometer is arranged for detecting a spectrum/spectra emitted by the material during solidification.

22. A laser solidification apparatus for building objects by layerwise solidification of powder material, the apparatus comprising a build chamber containing a build platform, a device for depositing layers of powder material on to the build platform, an optical unit for directing a laser beam to selectively solidify areas of each powder layer and a spectrometer arranged for detecting characteristic radiation, generated by interaction of the material in the layer with the or a further laser beam, that is collected by the optical unit.

23. An optical unit directing a laser beam to selectively solidify areas of powder layers in a selective laser solidification apparatus, the optical unit comprising a spectrometer arranged for detecting characteristic radiation, generated by interaction of the material in the layer with the or a further laser beam, that is collected by the optical unit.

24. A laser solidification apparatus for building objects by layerwise solidification of powder material, the apparatus comprising a build chamber containing a build platform, a device for depositing layers of powder material on to the build platform, an optical unit for directing a laser beam to selectively solidify areas of each powder layer, the optical unit comprising steerable optics for steering the laser beam onto the powder layer and movable focussing optics for focussing the laser beam, and a photodetector arranged for detecting characteristic radiation, generated by interaction of material in the layer with the or a further laser beam, that is collected by the steerable optics and movable focussing optics.

25. An optical unit directing a laser beam to selectively solidify areas of powder layers in a selective laser solidification apparatus, the optical unit comprising steerable optics for steering the laser beam onto the powder layer and movable focussing optics for focussing the laser beam, and a photodetector arranged for detecting characteristic radiation, generated by interaction of material in the layer with the or a further laser beam, that is collected by the steerable optics and movable focussing optics.

26. A process of selective laser solidification comprising depositing layers of powder material on to the build platform and directing a laser beam to selectively solidify areas of each powder layer to build an object, the method further comprising detecting a characteristic of the laser solidification process by spectroscopically analysing radiation emitted by plasma formed during solidification of the powder by the laser beam.

28. A process according to claim 26, wherein the characteristic of the laser solidification process is a temperature, diameter and/or depth of a melt pool generated by the laser and/or temperature of plasma generated during the solidification process.

44. A data carrier having instructions thereon, which, when executed by a processor of a selective laser solidification apparatus, causes the selective laser solidification apparatus to carry out the process of claim 26.

27. A process of selective laser solidification comprising depositing layers of metal powder on to the build platform and directing a laser beam to selectively solidify areas of each metal powder layer to build an object, the method further comprising detecting a characteristic of the laser solidification process by spectroscopically analysing radiation generated by interaction of the metal with the or a further laser beam.

29. A process according to claim 27, wherein the characteristic of the laser solidification process is an offset of a focus of the laser beam from a plane of the powder layer.

30. A process according to claim 27, wherein the spectroscopic analysis comprises identifying a portion of the spectrum that is a result of thermal emission from the melt pool.

31. A process according to claim 30, wherein the spectroscopic analysis comprises identifying a portion of the spectrum that at least approximates blackbody radiation.

32. A process according to claim 27, wherein the spectroscopic analysis comprises identifying a portion of the spectrum that is a result of spectral emission from a plasma plume generated when creating a melt pool.

33. A process according to claim 32, wherein a temperature of the melt pool and/or the plasma plume is determined from the portion of the spectrum that is identified as relating to spectral emission.

34. A process according to claim 32, wherein the spectroscopic analysis comprises determining an offset of the focus from a plane of the powder layer from an intensity of portions of the spectrum identified as spectral emission from the plasma plume.

35. A process according to claim 30, wherein the spectroscopic analysis comprises determining an offset of the focus from a plane of the powder layer from a portion of the spectrum identified as relating to thermal emissions/blackbody radiation.

36. A process according to claim 35, wherein an offset of the focus is determined by comparing an intensity of the spectral emissions to an intensity of the thermal emissions.

37. A process according to claim 27, comprising adjusting the laser solidification process based upon the spectroscopic analysis.

38. A process according to claim 37, comprising adjusting point distance, exposure time, scan speed, hatch spacing, laser power and/or focussing of the laser based upon the spectroscopic analysis.

39. A method of calibrating a selective laser solidification apparatus comprising a build chamber containing a build platform, a device for depositing layers of powder material on to the build platform, an optical unit for directing a laser beam to selectively solidify areas of each powder layer and a camera arranged for imaging the build platform through the optical unit along an optical path common with the laser beam such that the relative location of the image and focus of the laser beam are fixed, the method comprising locating in the build chamber a calibrated artefact, the calibrated artefact having a series of calibration marks thereon, operating the optical module to direct the laser beam to a location on the calibrated artefact, activating the laser to form a laser mark on the calibrated artefact, using the camera to capture an image of the calibrated artefact with the laser mark thereon and determining an offset of the focus of the laser beam from a desired position by comparing a location of the laser mark in the image to a location of at least one of the calibration marks in the image.

40. A method according to claim 39, wherein the optical module is operated to be in a configuration programmed for directing the laser beam onto a specified one of the calibration marks on the calibrated artefact, activating the laser to form a laser mark on the calibration artefact, using the camera to capture the image of the calibrated artefact with the laser mark thereon and determining the offset of the focus of the laser beam from the desired position by comparing a location of the laser mark in the image to a location of the specified calibration mark.

41. A method according to claim 40, wherein the optical module is updated to alter the programmed configuration(s) for directing the laser beam based on the determined offset.

42. A method according to claim 41, wherein updating of the configurations is based on multiple laser marks and comparisons of these laser marks to corresponding calibration marks.

43. A method according to claim 39, wherein the calibrated artefact is calibrated to the extent that the calibrated marks are located at known relative locations on the calibrated artefact.

45. A laser solidification apparatus for building objects by layerwise solidification of powder material, the apparatus comprising a build chamber containing a build platform, a device for depositing layers of powder material on to the build platform, an optical unit for directing a laser beam to selectively solidify areas of each powder layer, a device for projecting a light pattern onto each powder layer and a camera for capturing images of the light pattern on each powder layer.

46. A method of measuring an object built using a selective laser solidification process, wherein an object is built by depositing layers of powder material on to the build platform and directing a laser beam to selectively solidify areas of each powder layer to build an object, the method comprising after selectively solidifying areas of at least one of the powder layers, projecting a light pattern on to the powder layer and capturing an image of the projected light.

47. A method according to claim 46, wherein the light pattern is a fringe/diffraction pattern.

48. A data carrier having instructions stored thereon, wherein the instructions, when executed by a processor, cause the processor to receive at least one image of a powder layer having areas that have been solidified by a selective solidification process and onto which a pattern of light is projected, determining a geometry of solidified areas of each powder layer from the pattern of light on the powder layer, comparing the measured geometry to input geometric data, on which the build is based to identify differences between the actual object built and the object that was intended to be built.

49. A laser solidification apparatus for building objects by layerwise solidification of powder material, the apparatus comprising a build chamber containing a build platform, a device for depositing layers of powder material on to the build platform, an optical unit for directing a laser beam to selectively solidify areas of each powder layer, a camera for capturing images of each powder layer and an analysis unit for analysing the images to identify solidified areas of the powder layer.

50. A laser solidification apparatus for building objects by layerwise solidification of powder material, the apparatus comprising a build chamber containing a build platform, a device for depositing layers of powder material on to the build platform, an optical unit for directing a laser beam to selectively solidify areas of each powder layer and a photodetector for detecting characteristic radiation generated by stimulated emission of material in the layer, the photodetector arranged to detect wavelengths within a wavelength band including a wavelength of a characteristic spectral peak of the characteristic radiation.

51. A laser solidification apparatus according to claim 50, wherein the wavelength band consists of wavelengths less than 700 nm.

52. A laser solidification apparatus according to claim 51, wherein the wavelength band is between 300 and 600 nm.

53. A laser solidification apparatus according to claim 50, wherein the photodetector comprises a photodiode.

54. A laser solidification apparatus according to claim 50, wherein the photodetector comprises a bandpass (notch) filter.

55. A laser solidification apparatus according to claim 54, wherein the bandpass filter blocks wavelengths of light above 700 nm.

56. A laser solidification apparatus according to claim 54, wherein the bandpass filter has a bandwidth of or within 300 nm to 600 nm.

57. A laser solidification apparatus according to claim 50, comprising a control unit for controlling the laser unit based upon a light intensity detected by the photodetector.

58. A laser solidification apparatus according to claim 57, wherein the control unit is arranged to alter point distance, exposure time, scan speed, hatch spacing, laser power and focussing of the laser based upon the detected light intensity.