Method and system for additive manufacturing using a light beam

Abstract

The method comprises the steps of: a) supplying building material; and b) fusing the building material using a light beam (2); wherein steps a) and b) are carried out so as to progressively produce the object out of the fused building material. In step b), the beam (2) is projected onto the building material so as to produce a primary spot on the building material, the beam being repetitively scanned in two dimensions in accordance with a first scanning pattern so as to establish an effective spot (21) on the building material, said effective spot having a two-dimensional energy distribution. The effective spot (21) is displaced in relation to the object being produced to progressively produce the object by fusing the building material.

Claims

1. A method for producing an object by successive fusing of a building material, the method comprising the steps of: a) supplying building material to a fusing site; b) generating a light beam and directing it at a selected spot on the building material, creating a primary spot; c) repetitively scanning the light beam primary spot in two dimensions in accordance with a first scanning pattern establishing an effective spot larger than the primary spot on the building material the two-dimensional scanning being at a mean velocity at least ten times higher than the mean velocity the effective spot is displaced on the building material, the effective spot having a two-dimensional energy distribution; and d) displacing the effective spot at a mean velocity on the building material in accordance with a second scanning pattern to progressively fuse the building material; whereby the object is produced.

2. The method according to claim 1, wherein the two-dimensional energy distribution of the effective spot is dynamically adapted during displacement of the effective spot on the building material, in accordance with the second scanning pattern.

3. The method of claim 2, wherein the two-dimensional energy distribution of the effective spot is dynamically adapted during displacement of the effective spot along a track, to change the width of the effective spot to correspond with a portion of the object being produced.

4. The method according to claim 2 wherein adaptation of the two-dimensional energy distribution of the effective spot is carried out by changing the power of the beam.

5. The method according to claim 2 wherein adaptation of the two-dimensional energy distribution of the effective spot is carried out by changing the first scanning pattern.

6. The method according to claim 2 wherein adaptation of the two-dimensional energy distribution of the effective spot is carried out by changing the velocity of the primary spot moving along the first scanning pattern.

7. The method according to claim 1 wherein the size of the primary spot is dynamically adapted during displacement of the primary spot along the first scanning pattern and/or during displacement of the effective spot on the object being produced.

8. The method according to claim 1 wherein the effective spot has a leading portion with a higher energy density than a trailing portion, or the effective spot has a leading portion with a lower energy density than a trailing portion, or the effective spot has an intermediate portion with a higher energy density than the leading portion and the trailing portion, or the effective spot has a substantially constant energy density throughout the effective spot.

9. The method according to claim 1 wherein the mean velocity of the primary spot along the first scanning pattern is higher than the mean velocity of the effective spot displaced on the building material.

10. The method according to claim 1 wherein the beam is scanned at a frequency of more than 10 Hz in the first scanning pattern.

11. The method according to claim 1 wherein the size of the effective spot is more than 4 times the size of the primary spot.

12. The method according to claim 1 wherein the steps of the method are carried out repeatedly in a plurality of cycles.

13. The method according to claim 1 wherein steps a) and b) are carried out in parallel.

14. The method according to claim 1 wherein the first scanning pattern comprises a plurality of lines.

15. The method according to claim 14, wherein the lines are substantially parallel lines.

16. The method according to claim 1 wherein the first scanning pattern is a polygon.

17. The method according to claim 1 wherein the first scanning pattern comprises at least three linear segments and scanning of the beam causes the beam to follow at least one of the segments more frequently than it follows another one of the segments.

18. The method according to claim 17, wherein the first scanning pattern comprises at least three substantially parallel lines distributed one after the other in a first direction, and extending in a second direction, and three lines comprising a first line, an intermediate line, and a last line arranged one after the other in the first direction, wherein scanning of the beam causes the beam to follow the intermediate line more frequently than the beam follows the first line or the last line.

19. The method according to claim 17, wherein the first scanning pattern comprises at least three substantially parallel lines distributed one after the other in a first direction, and extending in a second direction, the three lines comprising a first line, an intermediate line, and a last line arranged one after the other in the first direction, wherein scanning of the beam causes the beam to follow the first line, follow the intermediate line, follow the last line, follow the intermediate line, and follow the first line (a), in that order.

20. The method according to claim 18 wherein the first scanning pattern comprises a plurality of the intermediate lines (b), and/or the beam is displaced with a higher velocity along the intermediate line than along the first line and last line, and/or wherein the first scanning pattern further comprises lines extending in the first direction, between the ends of the first, last and intermediate lines, the beam (2) following the lines extending in the first direction when moving between the first line, the intermediate lines and the last line, and/or the beam is displaced with a higher velocity along the lines extending in the first direction, than along the first line and the last line.

21. The method according to claim 1 wherein the beam is displaced along the first scanning pattern with the power of the beam substantially constant.

22. The method according to claim 1 wherein the beam creates a melt pool corresponding to the effective spot, the melt pool being displaced in accordance with the displacement of the effective spot on the building material.

23. The method according to claim 1 wherein the light beam is a laser beam.

24. The method according to claim 23, wherein the power of the laser beam is higher than 1 kW.

25. The method according to claim 1, wherein the mean velocity of movement of the light beam primary spot along the first scanning pattern is at least 100 times higher than the mean velocity with which the effective spot is displaced on the building material in accordance with the second scanning pattern.

26. The method according to claim 1 wherein the effective spot has a width in a direction perpendicular to a direction in which the effective spot is displaced, the width of the effective spot being modified during displacement on the building material.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

(1) To complete the description and in order to provide for a better understanding of the invention, a set of drawings is provided. Said drawings form an integral part of the description and illustrate embodiments of the invention, which should not be interpreted as restricting the scope of the invention, but just as examples of how the invention can be carried out. The drawings comprise the following figures:

(2) FIG. 1 is a schematic perspective view of a system in accordance with one possible embodiment of the invention, adapted for powder bed fusion.

(3) FIG. 2 schematically illustrates an example of the two-dimensional energy distribution.

(4) FIG. 3A is a schematic perspective view of a part of a system in accordance with another possible embodiment of the invention.

(5) FIG. 3B is a top view of the powder spray head of the system in accordance with the embodiment of FIG. 3A.

(6) FIGS. 4A-4C schematically illustrate three different powder spray heads in accordance with three different embodiments of the invention.

(7) FIGS. 4D and 4E illustrate how the powder spray head can be associated to the scanner allowing the two parts to be displaced jointly in relation to an object being produced.

(8) FIG. 5 schematically illustrates an effective spot created by a scanning pattern comprising a plurality of parallel lines.

(9) FIGS. 6A and 6B illustrate one possible scanning pattern comprising a plurality of parallel lines.

(10) FIGS. 7A and 7B illustrate a scanning pattern for creating an effective spot in accordance with an embodiment of the invention.

(11) FIGS. 8A and 8B illustrate a scanning pattern for creating an effective spot in accordance with another embodiment of the invention.

(12) FIGS. 9A-9C illustrate scanning patterns according to other embodiments of the invention.

(13) FIG. 10 schematically illustrate an effective spot in accordance with one possible embodiment of the invention.

(14) FIGS. 11A-11D schematically illustrate different two-dimensional energy distributions of an effective spot in accordance with an embodiment of the invention.

(15) FIGS. 12A-12G schematically illustrate how the two-dimensional energy distribution of an effective spot is dynamically adapted during a sweep of the effective spot along a track, in accordance with an embodiment of the invention.

DESCRIPTION OF WAYS OF CARRYING OUT THE INVENTION

(16) FIG. 1 schematically illustrates an SLS system in accordance with one possible embodiment of the invention, for producing an object out of a building material that is supplied in powder form, such as metal powder. The system comprises a laser equipment 1 for producing a laser beam 2, and a scanner 3 including two mirrors or similar for two-dimensional scanning of the laser beam 2 in the horizontal (X-Y) plane. The equipment for producing a laser beam can, in some embodiments of the invention, be an equipment suitable for producing laser beams having a relatively high power content, such as 1 kW or more. One example of a suitable device is the Ytterbium Laser System Model YLS-6000-CT-Y13, by IPG Photonics, with a nominal power of 6 kW.

(17) The system further comprises an arrangement for distribution of the building material, comprising a table-like arrangement with a top surface 101 with two openings 102 through which the building material is fed from two feed cartridges 103. In the center of the top surface 101 there is an additional opening, arranged in correspondence with a platform 104 which is displaceable in the vertical direction, that is, in parallel with a Z axis of the system. Powder is supplied from the cartridges 103 and deposited on top of the platform 104. A counter-rotating powder leveling roller 105 is used to distribute the powder in a layer 106 having a homogeneous thickness.

(18) The laser beam is projected onto the layer 106 of the building material on top of the platform 104 to fuse the building material in a selected region or area 11, which corresponds to a cross section of the object that is being produced. Once the building material in this area 11 has been fused, the platform is lowered a distance corresponding to the thickness of each layer of building material, a new layer 106 of building material is applied using the roller 105, and the process is repeated, this time in accordance with the cross section of the object to be produced in correspondence with the new layer.

(19) Traditionally, fusing was carried out by scanning the laser beam over the area 11 to be fused, for example, by making the projected laser spot follow a plurality of parallel lines extending across the area to be fused, until the entire selected area had been fused. In accordance with the present embodiment of the invention, the laser beam (and the primary laser spot that the beam projects on the building material) is repetitively scanned at a relatively high speed following a first scanning pattern (illustrated as a set of lines extending in parallel with the Y axis in FIG. 1), thereby creating an effective laser spot 21, illustrated as a square in FIG. 1. This is achieved using the scanner 3. This effective laser spot 21 is displaced according to a second scanning pattern, for example, in parallel with a plurality of parallel lines. In FIG. 1, an arrow indicates how the effective laser spot 21 can, for example, be displaced in parallel with the X axis of the system. FIG. 1 illustrates how a portion 11A of the area 11 to be fused has been fused during a preceding sweep of the effective laser spot 21 in parallel with the X axis, whereas another portion 11B is still waiting to be fused. After it has been fused, the platform 104 will be lowered and a new layer of building material in powder form will be applied.

(20) The displacement of the effective laser spot 21 according to the second scanning pattern can likewise be achieved by the scanner 3, and/or due to displacement of the scanner or associated equipment, for example, along tracks (not shown in FIG. 1), such as tracks extending in parallel with the X axis and/or the Y axis.

(21) In many variants of this embodiment, pre-heating means such as IR light sources or other heating devices are provided for pre-heating the powder layer, for example, to a temperature close to the melting point and/or glass transition temperature of the building material, thereby reducing the power that has to be applied by the laser beam to achieve the fusion of the building material. In other variants of the embodiment, or in addition to the pre-heating means, preheating can be carried out by a leading portion of the effective laser spot 21.

(22) In some embodiments of the invention, the system can include means 5 for dynamically adapting the size of the primary spot (for example, so as to modify the two-dimensional energy distribution and/or the size of the effective laser spot 21) and/or the focus of the laser beam along the optical axis. This makes it possible to control (such as to vary or maintain) the size of the primary laser spot while it is being displaced along the first scanning pattern, and/or while the effective laser spot 21 is being displaced in relation to the object being produced. For example, the optical focus can be adapted to keep the size of the primary spot constant while the primary spot is moving over the surface of the object being produced (for example, to compensate for varying distances between the scanner and the position of the primary laser spot on the object being produced). For example, means for dynamically adapting the focus of the laser beam can in some embodiments of the invention comprise a varioSCAN® focusing unit, obtainable from SCANLAB AG (www.scanlab.de).

(23) FIG. 2 schematically illustrates how the effective laser spot 21 features a two-dimensional energy distribution where more energy is applied in some parts of the effective laser spot than in others during one sweep of the primary laser spot throughout the first scanning pattern. Here, the arrow indicates how the effective laser spot is travelling along a layer of metal powder, whereby the layer features a fused portion 11A and a portion 11B that has not yet been fused. Here, more energy is applied in correspondence with the leading portion than in correspondence with the trailing portion of the effective laser spot 21.

(24) FIGS. 3A and 3B illustrate part of the system in accordance with an alternative embodiment of the invention, in which the building material is fed in parallel with the heating thereof using the laser beam and the scanner 3. As illustrated in FIG. 3A, the system comprises an apparatus including a processing head 200 comprising a powder supply head 201 integrated with the scanner 3, the powder supply head 201 comprising a substantially rectangular frame 202 in which a plurality of nozzles 203 are arranged, the nozzles receiving the building material, typically in the form of powder, through channels 205 shown in FIG. 3B. Thus, the building material in powder form 204 is ejected through the nozzles 203, forming a relatively thin film or layer of powder, in correspondence with an opening defined by the frame 202. The scanner 3 projects the laser beam 2 through this opening, and scans the laser beam to produce the effective laser spot 21, as explained above and as schematically shown in FIGS. 3A and 3B. In some embodiments of the invention, the powder supply head 201 and the scanner 3 are arranged to move together, for example, forming part of one and the same device, which can be displaced in relation to the object that is being produced, so that material is thus selectively applied and fused onto this object, in correspondence with the areas in which the object is growing as it is being produced. In FIGS. 3A and 3B, the scanning pattern is schematically illustrated as a pattern in the shape of a “digital 8”, that is, with three parallel lines interconnected by two lines at the ends of the three parallel lines.

(25) FIGS. 4A, 4B and 4C illustrate some different design options for the powder supply head, corresponding to three different embodiments of the invention. FIG. 4A illustrates the powder supply head in accordance with the embodiments of FIGS. 3A and 3B. FIGS. 4B and 4C illustrate some alternative designs. In all of these cases, there is a frame 202 defining an opening or channel through which the laser beam can be projected onto the powder that is ejected through the nozzles 203. Basically, this approach is in line with some of the so-called coaxial laser and powder nozzles that are known in the art, but with the central opening being large enough so as to allow for the scanning of the laser beam 2 in two dimensions, along the first scanning pattern. In some embodiments of the invention, the processing head including the powder supply head 201 with frame 202 and nozzles 203, as well as the scanner 3, can be displaced so as to displace the effective laser spot in relation to the object being produced. That is, in these embodiments of the invention, the scanner can be used to create the effective laser spot with its two-dimensional energy distribution, whereas the displacement of the processing head 200 with the powder supply head 201 and scanner 3 provides for the displacement of the effective laser spot and the pool. In other embodiments of the invention, the processing head 200 can be fixed and the object being produced can be displaced in relation to the processing head.

(26) The powder supply heads 201 of FIGS. 4A, 4B and 4C all include a plurality of nozzles, arranged to provide a substantially two-dimensional stream of the building material, that is, a stream being relatively thin compared to its extension in the other two directions. Instead of a plurality of nozzles, one wider nozzle can be used. In some embodiments of the invention, the means for spraying the powder can be implemented based on the teachings of US-2011/0168090-A1 and US-2011/0168092-A1.

(27) The powder supply head can also incorporate suction means 206 for recovery of powder that has not been fused by the laser beam, as schematically illustrated in FIG. 4B.

(28) FIGS. 4D and 4E schematically illustrate how the processing head 200, in accordance with one possible embodiment of the invention, can include a scanner 3 placed adjacent to the powder supply head 201, in this case, above it so as to project the laser beam downwards, through the opening in the frame, onto the object 4 that is being produced. The building material is being selectively fused by the laser beam while it is being fed through the nozzles. The processing head 200 is connected to actuators 300 through linkages 301. In this embodiment of the invention, the displacement is based on the parallel manipulator concept. However, any other suitable means of displacement of the processing head can be used. In some embodiments of the invention, it is the object being produced that is displaced in relation to the processing head. Also, a combination of these two approaches can be used.

(29) It has been found that it can often be practical to provide a scanning pattern comprising more than two lines arranged after each other in the direction of travelling of the effective laser spot (that is, the direction of the relative movement between the effective laser spot and the object that is being built), such as schematically illustrated in FIG. 5, where the effective laser spot 21 is created by a plurality of parallel lines, extending in a direction perpendicular to the direction in which the effective laser spot is being displaced in relation to the object being built (this direction is indicated with an arrow in FIG. 5). The lines can have the same or different lengths, and the space between subsequent lines is one of the parameters that can be used to control the two-dimensional energy distribution.

(30) Such a scanning pattern can be created by repetitively scanning the primary laser spot in the direction perpendicular to the direction in which the effective laser spot is travelling, displacing the laser beam a small distance between each scanning step, so as to trace two, three or more parallel lines. Once the primary laser spot has completed the scanning pattern, it will return to its original position and carry out the scanning pattern once again. The frequency with which this occurs is preferably high, so as to avoid undesired temperature fluctuations within the effective laser spot 21.

(31) The laser beam can be switched off while it is being displaced towards a new line to be followed, and/or between finishing the last line of the scanning pattern and returning to the first line of the scanning pattern. However, switching laser beams on and off requires time, and can slow down the scanning frequency. Also, the time during which the laser beam is switched off is time that is lost in terms of efficient use of the laser for heating and fusing.

(32) FIGS. 6A and 6B illustrate one possible scanning pattern comprising three main lines a-c (illustrated as continuous lines) of the scanning pattern, and hatched lines illustrating the path which the laser spot follows between said lines. In FIG. 6B, the arrows schematically illustrate the way in which the primary laser spot travels over the surface.

(33) Now, this scanning pattern involves a problem in that the heat distribution will not be symmetric. The same applies if, at the end of the pattern, when finishing the last line c (that is, from the head of the arrow of line c in FIG. 6B), the laser beam returns vertically to line a.

(34) A more symmetrical energy distribution with regard to the axis parallel with the direction in which the effective laser spot is being displaced can be obtained with a scanning pattern as per FIGS. 7A and 7B, likewise comprising three parallel lines a-c interconnected by the lines d followed by the primary laser spot when moving between the three parallel lines. As illustrated in FIG. 7B, the laser beam, from the beginning of the first line a, travels as follows: a-d1-b-d2-c-d3-b-d4.

(35) That is, the primary laser spot travels along the intermediate line b twice as often as it travels through the first line and the last line: it travels along the intermediate line b twice for each time it travels along the first line a and the last line c. Thereby, a completely symmetrical scanning pattern can be obtained, in relation to the axis parallel with the direction in which the effective laser spot is travelling.

(36) The energy distribution along this axis can be set by adjusting, for example, the distance between the lines a-c and the speed with which the laser beam travels along the lines. By adjusting the speed and/or scanning pattern, the energy distribution can be dynamically adapted without turning the laser beam on and off or without substantially modifying the power of the laser beam. For example, if the energy is to be distributed substantially equally throughout the effective laser spot, the laser beam can travel with a higher speed along the intermediate line b than along the first line a and the last line c. For example, the velocity of the primary laser spot along line b can be twice the speed of the primary laser spot along lines a and c. In some embodiments of the invention, the velocity of the effective laser spot along lines d1-d4 can also be substantially higher than the velocity of the effective laser spot along lines a and c.

(37) Thus, tailoring of the energy distribution can be achieved by adapting the distribution of the lines, such as the first, last and intermediate lines a-c, and by adapting the velocity of the laser spot along the different segments a-d (including d1-d4) of the scanning pattern. The distribution of the segments and the velocity of the segments can be dynamically modified while the effective laser spot is being displaced in relation to the object that is being produced, so as to adapt the two-dimensional energy distribution. Also, the scanning pattern can be adapted by adding or deleting segments during the travelling of the effective laser spot.

(38) The same principle can be applied to other scanning patterns, such as the scanning pattern of FIGS. 8A and 8B, which includes an additional intermediate line b. Here, the path followed by the primary laser spot s: a-d1-b-d2-b-d3-c-d4-b-d5-b-d6.

(39) FIGS. 9A-9C illustrate some alternative scanning patterns. For example, the first scanning pattern can be a polygon such as the triangle of FIG. 9A, the rectangle of FIG. 9B, and the octagon of FIG. 9C.

(40) FIG. 10 schematically illustrates an effective spot 21 in accordance with one possible embodiment of the invention. The effective spot has a substantially rectangular configuration, with a height and a width. The arrow at the top of the figure illustrates the direction in which the effective spot 21 is being displaced.

(41) The effective spot 21 is obtained by scanning the primary spot 2A projected by the beam, following a scanning pattern comprising five parallel lines, indicated by the rows of arrows within the effective spot 21. In this embodiment, a leading portion 21A of the effective spot provides a certain pre-heating of the building material, and a trailing portion 21C is provided to slow down the cooling process. The actual fusion of the material takes place in the central portion 21B of the effective spot 21, that is, between the leading portion 21A and the trailing portion 21C. This central portion 21B corresponds to the pool. That is, as explained above, contrary to what was generally the case in prior art systems, in this embodiment the pool has a two-dimensional configuration with a size substantially larger than the one of the primary spot, and the pool does not travel with the primary spot 2A along the first scanning pattern, but rather with the effective spot 21. The size and/or the shape of the effective spot 21 and/or of the pool 21B can be dynamically adapted during the displacement of the effective spot along the track followed by the effective spot 21, for example, taking into account the configuration of the object to be produced in the region where heating is taking place.

(42) FIGS. 11A-11D schematically illustrate different two-dimensional energy distributions of an effective spot in accordance with an embodiment of the invention. For example, FIG. 11A illustrates an effective spot featuring three bands extending across the effective spot, in the direction perpendicular to the direction of travelling of the effective spot. These three bands represent areas with high energy density. The first band may be intended to provide for pre-heating of the material to be fused, the second band may be intended to provide for the actual fusion, and the third band may be intended for post-treatment of the fused material, for example, to relieve tensions. Other energy distributions are schematically shown in FIGS. 11B-11D. The two-dimensional energy distribution can be adapted dynamically, for example, adding or removing bands with high energy density, etc. For example, FIG. 11F illustrates a two-dimensional energy distribution with enhanced energy density towards the sides of the effective spot. This can often be preferred in order to provide for a substantially constant temperature along the track, in spite of the fact that, for example, heat dissipation away from the track may be higher at the edges of the track.

(43) Feedback, such as feed-back based on thermal imaging, can be used to trigger the dynamic adaptation of the two-dimensional energy distribution, for example, so as to achieve and maintain a desired temperature distribution in the area being treated.

(44) FIGS. 12A-12G illustrate an example of how the two-dimensional energy distribution of an effective spot 21 can be adapted while the effective spot is being displaced along a track (in a direction schematically illustrated with an arrow in FIG. 12A), over a layer 106 of building material. FIG. 12A illustrates how the effective spot 21 is first applied to the building material 106 and starts to heat the building material, and in FIG. 12B the two-dimensional energy distribution has been modified so that the effective spot has increased in length along the track (in the direction of the arrow in FIG. 12A), featuring a leading portion with high energy density so as to provide for a rapid increase of the temperature of the building material when the leading portion reaches the building material.

(45) In FIG. 12C, the effective spot 21 has moved along the track also with its trailing edge, and a fused portion 11A of the building material can be observed behind the effective spot 21.

(46) In FIG. 12D, the effective spot has reached a section of the object being produced in which the portion of the object begins to decrease in width, that is, a portion where the track to be fused progressively becomes narrower. Here, the two-dimensional energy distribution is dynamically adapted to adapt itself to the dimensions of the portion of the object being produced at each moment. As shown in FIGS. 12D and 12E, the two-dimensional energy distribution is adapted so that the effective spot progressively grows narrower, and in addition, also the edges of the effective spot feature an outline corresponding to the shape of the portion being fused. That is, here, the projection of the effective spot onto the building material is substantially wedge-shaped.

(47) In FIG. 12E, the effective spot 21 has reached a position where the object being built has a portion of constant width. Here, the two-dimensional energy distribution is adapted accordingly. Here, the projection of the effective spot onto the building material 106 becomes substantially rectangular. In FIG. 12G, the effective spot can be seen moving further along the track. Thus, it can be seen how the shape of the fused material 11A corresponds to the way in which the two-dimensional energy distribution of the effective spot has been dynamically adapted as the effective spot 21 has moved along the track. However, the present invention is obviously not limited to this kind of dynamical adaptations of the effective spot and its two-dimensional energy distribution.

(48) In this text, the term “comprises” and its derivations (such as “comprising”, etc.) should not be understood in an excluding sense, that is, these terms should not be interpreted as excluding the possibility that what is described and defined may include further elements, steps, etc.

(49) On the other hand, the invention is obviously not limited to the specific embodiment(s) described herein, but also encompasses any variations that may be considered by any person skilled in the art (for example, as regards the choice of materials, dimensions, components, configuration, etc.), within the general scope of the invention as defined in the claims.