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EP-3323533-B2 - SELECTIVE SOLIDIFICATION APPARATUS AND METHODS

EP3323533B2EP 3323533 B2EP3323533 B2EP 3323533B2EP-3323533-B2

Inventors

  • BROWN, Ceri
  • MCFARLAND, GEOFFREY

Dates

Publication Date
20260506
Application Date
20150318

Claims (15)

  1. A selective solidification apparatus comprising a build chamber(101), a build platform (102) lowerable in the build chamber (101), a wiper (109) for spreading powder material across the build platform (102) to form successive powder layers of a powder bed (104), an energy beam unit (105) for generating an energy beam (118) for consolidating the powder material, a scanner (106) for directing and focussing the energy beam (118) onto each powder layer and a processor (131) for controlling the scanner (106), wherein the processor (131) is arranged to control the scanner (106) to scan the energy beam (118) across the powder bed (104) to consolidate powder material each side of the wiper (109) when the wiper (109) is moving across the powder bed (104), characterised in that the processor (131) is arranged to receive geometric data describing scan paths to take in solidifying areas of powder in each powder layer, to analyse the scan paths defined in the geometric data to determine which scan paths or which parts of the scan paths should be scanned one side of the wiper (109) and which scan paths or which parts of the scan paths should be scanned the other side of the wiper (109) and then to control the scanner (106) to scan each powder layer in accordance with the scan paths and scanning schedule; and the processor (131) is further arranged to control movement of the wiper (109) to vary a time the wiper (109) is stationary between strokes or a speed of the wiper (109) based upon a size of an area to be solidified in a layer and/or scan paths for the energy beam (118) to take in solidifying the powder material.
  2. A selective solidification apparatus according to claim 1, wherein the processor (131) is arranged to control the scanner (106) such that the energy beam is scanned (118) across the powder bed (104) when the wiper (109) is paused at a side of the powder bed (104).
  3. A selective solidification apparatus according to claim 2, comprising a dosing unit (108) for dispensing powder, wherein the processor (131) is arranged to control the scanner (106) such that the energy beam is scanned (118) across the powder bed (104) when powder is being dispensed by the dosing unit (108).
  4. A selective solidification apparatus according to any one of the preceding claims, wherein the processor (131) is arranged to control the scanner (106) to scan the energy beam (118) across the powder bed (104) during movement of the build platform (102).
  5. A selective laser solidification apparatus according to any one of the preceding claims, wherein the processor (131) is arranged to control the scanner (106) to change a focus of the energy beam (118) to adjust for a change in a level of a surface of the powder bed (104) such that an energy spot having a preset profile is maintained on the surface of the powder bed (104).
  6. A selective laser solidification apparatus according to claim 5, wherein, the processor (131) is arranged to control the scanner (106) to change the focus of the energy beam (118) to compensate for a change in level of the powder bed (104) as the energy spot is moved from one side of the wiper (109) to the other as the wiper (109) moves across the powder bed (104).
  7. A selective laser solidification apparatus according to claim 5 to claim 6, wherein the processor (131) is arranged to control the scanner (106) to change the focus of the energy beam (118) to compensate for a change in level of the upper surface of the powder bed (104) between an out stroke and a return stroke of the wiper (109).
  8. A selective laser solidification apparatus according to any one of claims 5 to 7, wherein the energy beam comprises a laser beam (118) and the scanner (106) comprises movable optics for changing the focus of the energy beam.
  9. A selective laser solidification apparatus according to claim 8, wherein the scanner (106) comprises titling optics (106a, 106b) for scanning the laser spot across the powder bed (104), wherein the processor (131) is arranged to control the tilting optics (106a, 106b) to automatically compensate for the fact that a single position of the titling optics (106a, 106b) will scan different spots on the surface of the powder bed (104) dependent on the level of the surface.
  10. A selective laser solidification apparatus according to any one of the preceding claims further comprising a position measuring device for measuring a position of the wiper (109) as the wiper (109) moves across the powder bed (104) and the processor (131) is arranged to receive signals from the position measuring device and control the scanner (106) based upon the signals from the position measuring device.
  11. A method for forming an object by selective solidification, in which powder layers are solidified using an energy beam (118) in a layer-by-layer manner to form an object, the method comprising, repeatedly, spreading powder material across a build platform (102) with a wiper (109) to form a powder layer of a powder bed (104), and, during movement of the wiper (109) across the powder bed (104), scanning the energy beam (118) across the powder bed (104) to consolidate the powder material each side of the wiper (109), characterised by receiving geometric data describing scan paths to take in solidifying areas of powder in each powder layer, analysing the scan paths defined in the geometric data to determine which scan paths or which parts of the scan paths should be scanned one side of the wiper (109) and which scan paths or which parts of the scan paths should be scanned the other side of the wiper (109) and then controlling the scanner (106) to scan each powder layer in accordance with the scan paths and scanning schedule; and controlling movement of the wiper (109) to vary a time the wiper (109) is stationary between strokes or a speed of the wiper (109) based upon a size of an area to be solidified in a layer and/or scan paths for the energy beam (118) to take in solidifying the powder material.
  12. A method according to claim 11, comprising controlling the scanner (106) such that the energy beam is scanned (118) across the powder bed (104) when the wiper (109) is paused at a side of the powder bed (104).
  13. A method according to claim 12, comprising controlling the scanner (106) such that the energy beam is scanned (118) across the powder bed (104) when powder is being dispensed by a dosing unit (108).
  14. A method according to any one of claims 11 to 13, comprising controlling the scanner (106) to scan the energy beam (118) across the powder bed (104) during movement the build platform (102).
  15. A data carrier having instructions stored thereon, the instructions for execution by a processor for controlling a selective solidification apparatus comprising a build chamber (101), a build platform (102) lowerable in the build chamber (101), a wiper (109) for spreading powder material across the build platform (101) to form successive powder layers of a powder bed (104), an energy beam unit (105) for generating an energy beam (118) for consolidating the powder material, and a scanner (106) for directing and focussing the energy beam (118) onto each powder layer, wherein, the instructions, when executed by the processor, cause the processor to carry out the method of any one of claims 11 to 14.

Description

Field of Invention This invention concerns selective solidification apparatus and methods in which powder layers are solidified in a layer-by-layer manner to form an object. The invention has particular, but not exclusive application, to selective laser solidification apparatus, such as selective laser melting (SLM) and selective laser sintering (SLS) apparatus. Background Selective laser melting (SLM) and selective laser sintering (SLS) apparatus produce objects through layer-by-layer solidification of a material, such as a metal powder material, using a high energy beam, such as a laser beam. A powder layer is formed across a powder bed in a build chamber by depositing a heap of powder adjacent to the powder bed and spreading the heap of powder with a wiper across (from one side to another side of) the powder bed to form the layer. A laser beam is then scanned across portions of the powder layer that correspond to a cross-section of the object being constructed. The laser beam melts or sinters the powder to form a solidified layer. After selective solidification of a layer, the powder bed is lowered by a thickness of the newly solidified layer and a further layer of powder is spread over the surface and solidified, as required. An example of such a device is disclosed in US6042774. A problem with such apparatus is that it can take a long time to build an object, often days and, for very large objects, over a week. Wipers are also used in stereolithography to accelerate the formation of a plane surface of the photocurable liquid resin suitable for subsequent curing with a laser beam. Displacement of the wiper and control of the laser beam can be carried out simultaneously in such a manner that the beam follows the wiper and strikes the resin layer within the region immediately behind the wiper. Examples of such arrangements are disclosed in US5582876, US5780070 and US5204823. 3D Systems' SmartSweep™ method provides a further enhancement wherein the recoater blade does not travel the entire length of the resin vat but only sweeps across the part of the vat where the part is being built. US8172563 discloses a device for manufacturing a three-dimensional object in which a material application device extends in a radial direction across a maximum radial extension of a circular build platform and the build platform is rotated (either in a continuous or stepwise manner) and lowered to move the wiper around the build platform to form a material layer. In one embodiment, four material application devices are provided and material is solidified in four solidification regions located between the material application devices. DE102007040755 discloses a laser sintering device for producing three-dimensional objects comprising ten coating devices for applying layers or powder. Each coating device may be associated with a laser. Summary of Invention According to a first aspect of the invention there is provided a selective solidification apparatus according to claim 1. The processor may be arranged to control the scanner to scan the energy beam across at least one of the powder layers during two or more strokes of the wiper across the powder bed. The two or more strokes may comprise a stroke in which the wiper forms the powder layer and one or more subsequent strokes. The one or more subsequent strokes may comprise a stroke in which the wiper forms a subsequent powder layer. Additionally or alternatively, the one or more subsequent strokes may comprise a return stroke in which the wiper does not form a powder layer. A first region on the powder layer may be consolidated by the energy beam when the wiper is moving away from the first region during formation of the powder layer with the wiper and a second region on the powder layer may be consolidated by the energy beam when the wiper is moving towards the second region during the subsequent stroke. It in this way, an object can be formed more quickly because powder is consolidated during the time that the wiper is moving across the powder bed. Accordingly, it may be possible to shorten build times compared to consolidating powder with the energy beam after the wiper has finished forming a layer. Furthermore, the area(s) of the powder bed being consolidated is not limited by the location of the wiper because powder located either side of the wiper can be consolidated during a wiper stroke. In particular, scanning the energy beam across at least one powder layer during two or more strokes may reduce a build time compared to completing the entire scanning of the powder layer during an initial stroke of the wiper and before a further stroke. This may allow optimization of the scanning strategy beyond simply scanning the energy beam behind the wiper. In particular, a cross-section of the object(s) being formed tends to cover a small area relative to the total cross-section of the powder bed and therefore, the energy beam spot will spend the majority of the time localised in s