Abstract
A method of heating a portion of an object includes the steps of projecting an energy beam onto a surface of the object so as to produce a primary spot on the surface, and repetitively scanning the beam in two dimensions in accordance with a scanning pattern so as to establish an effective spot on the surface, and displacing the effective spot in relation to the surface of the object to progressively heat the at least one selected portion of the object. Displacing the effective spot in relation to the surface of the object includes displacing the effective spot following a track featuring at least one change of direction.
The effective spot is maintained aligned with the track by modifying operation of a scanner in correspondence with the at least one change of direction.
Claims
1. A method of heating at least one selected portion of an object, the method including the following steps: projecting, with a device comprising a scanner, an energy beam onto a surface of the object so as to produce a primary spot on the surface, and repetitively scanning the beam in two dimensions in accordance with a scanning pattern so as to establish an effective spot on the surface, the effective spot having a two-dimensional energy distribution, displacing the effective spot in relation to the surface of the object to progressively heat the at least one selected portion of the object, wherein displacing the effective spot in relation to the surface of the object comprises displacing the effective spot following a track featuring at least one change of direction; wherein the method includes maintaining the effective spot aligned with the track by modifying operation of the scanner in correspondence with the at least one change of direction.
2. The method according to claim 1, wherein the step of maintaining the effective spot aligned with the track is carried out without pivoting the device around any axis for the purpose of aligning the effective spot with the track.
3. The method according to claim 1, wherein the step of modifying operation of the scanner is carried out so as to turn the effective spot around an axis substantially aligned with the energy beam, without turning the device and without turning the object around any axis substantially aligned with the energy beam.
4. The method according to claim 1, wherein the track extends in a plane, and wherein the step of modifying operation of the scanner is carried out so as to turn the effective spot around an axis substantially perpendicular to the plane, without turning the device and without turning the object around any axis substantially perpendicular to the plane.
5. The method according to claim 1, including the step of maintaining the geometric shape of the effective spot and/or of the scanning pattern constant in correspondence with said at least one change of direction.
6. The method according to claim 1, including the step of modifying a geometric shape of the effective spot and/or of the scanning pattern in correspondence with said at least one change of direction.
7. A method of heating at least one selected portion of an object, the method including the following steps: projecting, with a device comprising a scanner, an energy beam onto a surface of the object so as to produce a primary spot on the surface, and repetitively scanning the beam in two dimensions in accordance with a scanning pattern so as to establish an effective spot on the surface, the effective spot having a two-dimensional energy distribution, displacing the effective spot in relation to the surface of the object to progressively heat the at least one selected portion of the object, wherein displacing the effective spot in relation to the surface of the object comprises displacing the effective spot following a track featuring at least one change of direction; wherein the method includes modifying a geometric shape of the effective spot and/or of the scanning pattern in correspondence with said at least one change of direction.
8. The method according to claim 7, wherein modifying the geometric shape of the effective spot and/or of the scanning pattern includes the following step: modifying the scanning pattern, wherein at least some portions of the scanning pattern are modified as a function of their distance to a center of the change of direction; and/or modifying the scanning pattern so that all parts of the scanning pattern are displaced at substantially the same angular velocity along a curved portion of the track in correspondence with the at least one change of direction; and/or displacing characteristic points of the scanning pattern at the same linear velocity along a straight portion of the track, and displacing the characteristic points of the scanning pattern at the same angular velocity throughout a curved portion of the track in correspondence with said change of direction, at least one of the characteristic points being displaced at a different linear velocity than at least another one of the characteristic points at said curved portion of the track.
9. The method according to claim 6, wherein the scanning pattern is substantially symmetric with respect to a centerline parallel with the track when the scanning pattern is at a straight portion of the track, and wherein the scanning pattern is not symmetric with respect to any centerline in correspondence with the change of direction.
10. The method according to claim 7, for additive manufacturing, for joining at least two workpieces by welding them together, for laser cladding or for laser hardening.
11. The method according to claim 7, wherein the effective spot is displaced along the track by relative movement of the device in relation to the object, and/or wherein the scanner is additionally operated to displace the effective spot along the track.
12. The method according to claim 7, wherein the two-dimensional energy distribution of the effective spot is dynamically adapted during displacement of the effective spot in relation to the at least one change of direction of the track so that it is different in a radially outer portion of the effective spot than in a radially inner portion of the effective spot.
13. The method according to claim 7, wherein the energy beam is a laser beam and wherein the device is a laser head for projecting the laser beam onto the object.
14. A system for heating at least one selected portion of an object, the system comprising: means for supporting an object; and a device for projecting an energy beam onto a surface of the object; wherein the device comprises a scanner for scanning the energy beam in at least two dimensions; and wherein the system is programmed for carrying out the method of claim 1.
15. The system according to claim 14, comprising means for relative movement between the object and the device by displacing the device according to at least two orthogonal axes, wherein the system does not allow for pivotation of the device with regard to any axis substantially parallel to the energy beam.
16. The system according to claim 15, wherein the device is not capable of pivotation with regard to any axis.
Description
BRIEF DESCRIPTION OF THE DRAWINGS
[0064] To complete the description and in order to provide for a better understanding of the disclosure, a set of drawings is provided. Said drawings form an integral part of the description and illustrate embodiments of the disclosure, which should not be interpreted as restricting the scope of the disclosure, but just as examples of how the disclosure can be carried out. The drawings comprise the following figures:
[0065] FIGS. 1A-1C are schematic perspective views of a prior art system for heat treatment of sheet metal.
[0066] FIGS. 1D and 1E are schematic top views of a prior art system for laser welding.
[0067] FIGS. 2A and 2B schematically illustrate a method in accordance with an embodiment of the disclosure, for heat treatment of a vehicle component.
[0068] FIGS. 3A and 3B schematically illustrate a method in accordance with an embodiment of the disclosure, for laser welding.
[0069] FIG. 4 illustrates an embodiment of the disclosure including means for displacing a laser head in relation to an object subjected to heat treatment.
[0070] FIG. 5 is a schematic perspective view of a system for powder bed fusion in accordance with an embodiment of the disclosure.
[0071] FIGS. 6 and 7 schematically illustrate how the shape of the scanning pattern is adapted in correspondence with a curve in a track followed by the effective spot, in accordance with two embodiments of the disclosure.
[0072] FIG. 8 schematically illustrates how control points of a scanning pattern advance along a curved portion of a track, in accordance with one possible embodiment of the disclosure.
[0073] FIG. 9 schematically illustrates how control points of a scanning pattern advance along a curved portion of a track, in accordance with another possible embodiment of the disclosure.
DETAILED DESCRIPTION OF THE DRAWINGS
[0074] FIG. 2A illustrates a system in accordance with one possible embodiment of the disclosure, in this case for heat treatment of a sheet metal object such as a pillar for a vehicle. The system comprises a laser head 10 for directing a laser beam 11 onto a workpiece 100, such as a workpiece for a vehicle body component, such as a vehicle pillar that is to be subjected to heat treatment. The laser beam can be originated by a laser source remote from the laser head 10 or within the laser head 10. Just as in the case of FIGS. 1B and 1C, FIGS. 2A and 2B illustrate how the laser spot is to be displaced along a track 104 including a curve, such as a curve in the X-Y plane.
[0075] However, in the system of the embodiment of the disclosure, the spot that is displaced along the track is an effective spot (also known as an equivalent or virtual spot) 12 created by repetitive scanning of the laser beam in two dimensions, according to a scanning pattern. For this purpose, the laser head includes a scanner 2, such as a galvanometric scanner with two scanning mirrors 21 and 22, as schematically illustrated in FIGS. 2A and 2B. The scanning pattern followed by the primary spot projected by the laser beam 11 on the surface of the workpiece 100 at each specific moment is schematically illustrated as a set of parallel lines in FIGS. 2A and 2B. However, any other suitable scanning pattern can be used, including scanning patterns as known from WO-2015/135715-A1 referred to above, scanning patterns with curved segments, etc.
[0076] Thus, as known from for example WO-2016/146646-A1, the two-dimensional energy distribution within the effective spot 12 can be tailored by the choice of scanning pattern, velocity of the primary spot along the scanning pattern, beam power at each specific portion of the scanning pattern, etc. This allows for dynamic adaptation of the two-dimensional energy distribution so as to optimize the heat treatment. Additionally, and differently from what is suggested in FIGS. 1B and 1C, the re-orientation of the effective spot 12 so as to align it with the track 104 while following the curved portion and transiting from the curved portion to the straight portion of the track can be implemented without turning the laser head around the Z axis: instead, the re-orientation is achieved by adapting the operation of the scanner 2, thereby maintaining the scanning pattern and the effective spot 12 produced thereby correctly aligned with the track. This is schematically illustrated in FIGS. 2A and 2B by the way in which the lines of the schematically illustrated scanning pattern have been reoriented between FIGS. 2A and 2B. Basically, the projection of the scanning pattern on the X-Y plane has turned approximately 45 degrees around the Z axis, whereas the laser head has not turned. Thus, compared to the operation in accordance with FIGS. 1B and 1C, a mechanical degree of freedom (rotation or turning of the physical laser head 1000 around the Z axis) has been replaced by what can be regarded as an electronic degree of freedom, namely, by a change in the instructions that control the scanner mirrors 21 and 22.
[0077] Movement of the effective spot 12 according the X and Y axes can be performed using the scanner mirrors and/or by relative displacement between laser head 10 and workpiece 100.
[0078] FIGS. 3A and 3B schematically illustrate these principles applied to laser welding. The layout is similar to the one shown in FIGS. 1D and 1E, but in the embodiment of FIGS. 3A and 3B the system creates an effective spot 12 by repetitive scanning of the laser beam in two dimensions, for example, using a galvanometric scanner with two mirrors (not shown in FIGS. 3A and 3B). In FIGS. 3A and 3B the scanning pattern is illustrated as a set of parallel lines, but any other suitable scanning pattern can be used. As explained, the use of this kind of effective spot allows for flexible adaptation of the two-dimensional energy distribution, for example, taking into account how the welding is progressing, how the weld seam is being formed, irregularities in the workpieces 101, 102 or in the spacing between them, etc. Additionally, and as schematically illustrated in FIGS. 3A and 3B, the system is configured for aligning the effective laser spot with the track 104 in the X-Y plane by modifying the operation of the scanner in correspondence with the curve in the X-Y plane. This is schematically illustrated by the way in which the parallel lines are oriented in FIG. 3B if compared to FIG. 3A. Thus, alignment of the effective spot 12 with the track 104 in correspondence with the curve is achieved by the way in which the scanner is operated (as schematically illustrated in FIGS. 3A and 3B), instead of by turning or pivoting the laser head around the Z axis (as schematically illustrated in FIGS. 1D and 1E). Thus, also here a degree of freedom based on mechanics (that is, based on physically turning the laser head 1000 around the Z axis as shown in FIGS. 1D and 1E) has been replaced by what can be regarded as an electronic degree of freedom, based on the way in which the scanner is operated, that is, based on the instructions sent to the scanner.
[0079] FIG. 4 schematically illustrates a system in accordance with an embodiment of the disclosure in which the laser head 10 (including a scanner, not shown) can be displaced in the X, Y and Z directions in relation to a workpiece 100. The laser head 10 is connected to actuators 10a through linkages 10b. The workpiece 100 is supported by schematically illustrated support means 10c. In this embodiment of the disclosure, the displacement is based on the parallel manipulator concept. However, any other suitable means of displacement of the laser head 10 can be used, such as a robot arm, etc. In some embodiments of the disclosure, it is the workpiece 100 that is displaced in relation to the laser head 10. Also, a combination of these two approaches can be used. Additionally or alternatively, displacement of the effective spot over a track on the workpiece can be carried out using the scanner (not shown) to progressively displace the effective spot created by the two-dimensional scanning discussed above, along its track. Now, differently from systems mechanically adapted to align a laser spot with a curved track as shown in FIGS. 1B-1E, the system of FIG. 4 does not have (or does not require) rotation of the laser head 10 according to the Z axis for adapting the orientation of the effective spot in the X-Y plane.
[0080] FIG. 5 shows how the disclosure can be applied in the context of additive manufacturing, for example, in the context of an SLS system for producing an object out of a building material that is supplied in powder form, such as metal powder. The system 200 comprises a laser equipment including a laser head 10 for producing a laser beam 11 as described above, including the scanner 2 including two mirrors 21, 22 or similar for two-dimensional scanning of a laser beam 11 in two dimensions X, Y. The system further comprises an arrangement for distribution of the building material, comprising a table-like arrangement with a top surface 201 with two openings 202 through which the building material is fed from two feed cartridges 203. In the center of the top surface 201 there is an additional opening, arranged in correspondence with a platform 204 which is displaceable in the vertical direction, that is, in parallel with a Z axis of the system. Powder is supplied from the cartridges 203 and deposited on top of the platform 204. A counter-rotating powder leveling roller 205 is used to distribute the powder in a layer 206 having a homogeneous thickness.
[0081] The laser beam is projected onto the layer 206 of the building material on top of the platform 204 to fuse the building material in a selected region or area 207, which corresponds to a cross section of the object that is being produced. Once the building material in this area 207 has been fused, the platform is lowered a distance corresponding to the thickness of each layer of building material, a new layer of building material is applied using the roller 205, 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.
[0082] In accordance with the present embodiment of the disclosure, the laser beam 11 (and the primary laser spot that the beam projects on the building material) is repetitively scanned at a relatively high speed following a scanning pattern (schematically illustrated as a set of parallel lines in the effective spot 12 of FIG. 5), thereby creating an effective laser spot 12, illustrated as a square in FIG. 5. This is achieved using the scanner 2. This effective spot 12 is displaced according to a defined track 104, schematically illustrated by the arrows within the region 207. The track includes bends and sections that extend at different angles to each other in the X-Y plane. In accordance with the disclosure, the effective spot 12 can be aligned with the path or track followed by the effective spot, for example, “turned” at the bends of the track, by modifying operation of the scanner rather than by turning the laser head 10 around the Z axis. These principles can be very useful in the context of additive manufacturing, for example, as they allow an effective spot with a carefully selected energy distribution to be correctly aligned in correspondence with bends or curves of a track, for example, when solidifying layers in correspondence with curved portions of an object being formed.
[0083] FIG. 6 schematically illustrates an effective spot 12 travelling along a track 104, schematically illustrated as an arrow. In correspondence with a straight portion of the track, the effective spot has a substantially rectangular shape, and is established by a scanning pattern 12a shaped as a “digital 8”, as known from for example WO-2015/135715-A1. When reaching the curved portion of the track, this scanning pattern is changed so that the effective spot 12 progressively acquires a non-rectangular shape (schematically illustrated as a six-sided polygon in FIG. 6). FIG. 6 schematically illustrates how, when the center portion of the effective spot 12 has reached the center portion of the curve)(α≈45°, the effective spot is determined by a scanning pattern 12b in which the segments as such correspond to those of the original scanning pattern 12a, but with their relative orientations and dimensions changed. The radially inner side of the scanning pattern 12b is now shorter than the radially outer side, thereby providing for a scanning pattern basically composed of two trapezoids, and a corresponding six-sided polygonal shape of the effective spot 12. As schematically illustrated in FIG. 6, in this embodiment the extensions of the segments in the direction aligned with the track are a function of the distance of the segments to the center C of the curve, in the radial direction.
[0084] The scanning patterns 12a and 12b are defined by characteristic points, in this case, control points that establish the start and the end of the segments making up the scanning pattern (schematically illustrated as control points a, b, c, d, e, fin FIG. 6), and the method can for example involve adapting the relative (and absolute) positions of these control points, as a function of the angle α and of the distance of the respective control point to the center C of the curve. The control points a-f can travel in a straight direction while the relevant part of the scanning pattern is travelling along the straight portion of the track 104, with a linear velocity corresponding to the velocity with which the effective spot 12 is to be displaced along the straight portion of the track. When reaching the curved portion of the track, the control points a-f will travel along a curve with a linear velocity (that is, the velocity in terms of mm/s) which will be determined by the angular velocity (doc/dt, the angular velocity with which the effective spot and the control points travel along the curve) and the distance between the respective control point and the center C of the curve. This means that whereas all control points and portions of the effective spot may travel at the same angular velocity, the radially outer control points a, c and e will travel at a higher linear velocity than the radially inner control points, which will give rise to the conversion of the originally rectangular shape or outline of the scanning pattern and of the effective spot, into a substantially six-sided polygonal shape or outline of the scanning pattern and of the effective spot (of course, in practice, the “real” outline of the effective spot will also depend on scanning speed and beam power throughout the scanning pattern; thus, there can be cases in which the shape of the scanning pattern may differ substantially from the shape of the effective spot).
[0085] Thus, an enhanced performance of the effective spot can be achieved, for example, to keep the width of a heated track and/or the temperature profile across the track substantially constant along the track, also in correspondence with a curve or bend in the track.
[0086] The specific scanning pattern shown in FIG. 6 is just an example, and the principles are obviously applicable to any other scanning pattern. In many embodiments, it is preferred that the scanning pattern be adapted so that if it is originally (that is, at the straight portion of the track) symmetric with respect to a centerline (schematically illustrated as “g” in FIG. 6) aligned with the track, at the curved portion it is no longer symmetric with regard to any such centerline.
[0087] An additional example is schematically illustrated in FIG. 7, which shows how a substantially circular or elliptical scanning pattern 12c at the straight portion of the track 104 can be modified at the curve of the track, so that it ceases to be symmetric in relation to any centerline aligned with the track.
[0088] FIG. 8 schematically illustrates how control points (for example, leading control points a and b of a scanning pattern as the one illustrated in FIG. 6) advance along a curved portion of the track. Trailing control points (such as for example control points e, f, c, d of a scanning pattern as the one illustrated in FIG. 6) advance accordingly. It can be readily understood from FIG. 8 how this implies that the curve will be heated substantially as if it were heated by a spot substantially shaped as the curve. Thus, and depending on the resolution of the scanning pattern in terms of the distance between the control points, a very good or quasi perfect alignment between the effective spot and the track can be achieved, also at the curve. The alignment is not only due to the orientation of the effective spot, but also due to its shape which has been adapted to the curvature of the curve.
[0089] FIG. 9 schematically illustrates another embodiment in which the scanning pattern is kept constant throughout straight and curved portions of a track 104. Here, a trapezoidal scanning pattern defined by four control points a, b, c and d pivots with regard to a reference point P of the scanning pattern while the scanning pattern follows the track 104. That is, the scanning pattern 12a at the end of a straight portion of the track has the same shape as the scanning patterns 12b and 12c at other positions along the track, but compared to scanning pattern 12a, scanning patterns 12b and 12c have pivoted around their reference point P. The orientation of the scanning patterns 12b (d.sub.αB) and 12c (d.sub.αC) in the X-Y plane onto which they are projected with regard to, for example, the X axis will correspond to the tangent to the track at the relevant position of the track, as schematically illustrated in FIG. 9.
[0090] 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.
[0091] On the other hand, the disclosure 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 disclosure as defined in the claims.
