METHOD FOR PROCESSING MATERIALS

Abstract

A method for material processing is disclosed, the method comprising applying a laser beam, directing the laser beam to a processing location to melt material at the processing location, and providing a shielding gas flow. The shielding gas flow is controlled dependent on at least one of a processing location position, a processing advance vector, and a processing trajectory.

Claims

1. A method for material processing, the method comprising applying a laser beam, directing the laser beam to a processing location to melt material at the processing location, and providing a shielding gas flow, further comprising controlling the shielding gas flow dependent on at least one of a processing location position, a processing advance vector, and a processing trajectory.

2. The method according to claim 1, comprising advancing the processing location position along a processing trajectory, an advance vector being related to each position along said trajectory, providing a shielding gas flow having a shielding gas flow vector, the advance vector and the shielding gas flow vector forming an angle, further comprising controlling the shielding gas flow vector such that the angle is larger than or equal to 45 degrees.

3. The method according to claim 1, further comprising advancing the processing location position along a processing trajectory, an advance vector being related to each position along said trajectory, choosing the trajectory such that all advance vectors are located in a first and a second quadrant (I, II), and controlling the shielding gas flow vector such that an angle formed between an advance vector and the shielding gas flow vector is larger than or equal to 45 degrees.

4. The method of claim 3, further comprising controlling the shielding gas flow vector such that an angle formed between each advance vector along a trajectory and the shielding gas flow vector is larger than or equal to 45 degrees, and wherein the shielding gas flow vector is located in one of a third and a fourth quadrant (III, IV).

5. The method according to claim 2, further comprising controlling the shielding gas flow vector such that the angle is larger than or equal to 60 degrees, in particular is larger than or equal to 90 degrees, and more particular is larger than or equal to 135 degrees.

6. The method according to claim 1, wherein controlling the shielding gas flow comprises determining all advance vectors applied during a processing cycle, adjusting the shielding gas flow vector, and maintaining the shielding gas flow vector constant during the processing cycle.

7. The method according to claim 1, further comprising determining a projection of the laser beam on a plane and a laser beam direction projection in said plane, said laser beam direction projection pointing from a projection of a laser beam source on said plane towards a projection of the processing location on said plane, providing a shielding gas flow having a shielding gas flow vector, the laser beam direction projection and the shielding gas flow vector forming an angle, and controlling the shielding gas flow vector such that the angle is smaller than or equal to 135 degrees.

8. The method according to claim 7, further comprising controlling the shielding gas flow vector such that the angle is smaller than or equal to 120 degrees, in particular is smaller than or equal to 90 degrees, and more particular is smaller than or equal to 45 degrees.

9. The method according to claim 7, further comprising advancing the processing location along a trajectory during a processing cycle, determining all laser beam directions during said processing cycle, controlling the shielding gas flow vector and adjusting the shielding gas flow vector before the processing cycle is carried out, and choosing the shielding gas flow vector such that the angle is smaller than or equal to 135 degrees, in particular is smaller than or equal to 120 degrees, more particular is smaller than or equal to 90 degrees, and even more particular is smaller than or equal to 45 degrees.

10. The method according to claim 7, further comprising advancing the processing location along a trajectory during a processing cycle, determining all laser beam directions during said processing cycle, choosing the trajectory such that all laser beam direction projections are located in a first and a second quadrant (I, II), and in particular controlling the shielding gas flow vector such that the shielding gas flow vector is located in one of the first and the second quadrant (I, II).

11. The method according to claim 1, further comprising providing at least one movable shielding gas inflow nozzle and/or outlet nozzle, and controlling the shielding gas flow in moving at least one of the shielding gas inflow nozzle and/or the shielding gas outlet nozzle, in particular in moving said at least one nozzle on an arcuate trajectory and more in particular moving said nozzle on a part-circular or circular trajectory.

12. The method according to claim 1, further comprising providing at least one of a multitude of shielding gas inflow nozzles being oriented in various directions and/or a multitude of shielding gas outlet nozzles being oriented in various directions and controlling the shielding gas flow in selectively controlling a gas flow through nozzles being oriented in at least one selected direction.

13. The method of claim 1, further comprising providing a movable shielding gas outlet, wherein controlling the shielding gas flow comprises adjusting a position and/or direction of the shielding gas outlet.

14. A machine for performing a laser based method for processing a material, the machine comprising means for generating a shielding gas flow over a processing location, wherein that the machine comprises means for varying at least one of a shielding gas flow intensity and/or a shielding gas flow direction.

15. The machine according to claim 14, further comprising a shielding gas inlet device for providing a shielding gas flow over a processing location, and a shielding gas outlet device, wherein that at least one of the shielding gas inlet device and/or the shielding gas outlet device is movable, and is in particular movable on an arcuate trajectory and more in particular on a part-circular or circular trajectory, in order to adjust a shielding gas flow vector and thus the shielding gas flow direction, and/or in that at least one of the shielding gas inlet device and/or the shielding gas outlet device comprises a multitude of nozzles pointing in different directions, wherein the flow through selected nozzles and/or groups of nozzles is selectively controllable and/or switchable in order to adjust a shielding gas flow vector and thus the shielding gas flow direction.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

[0045] The subject matter of the present disclosure is now to be explained more closely by means of exemplary embodiments and with reference to the attached drawings. The figures of the drawings show

[0046] FIG. 1 shows a schematic depiction of a selective laser melting process;

[0047] FIG. 2 shows a schematic top view of a selective laser melting process with a processing trajectory;

[0048] FIG. 3 is an illustration of exemplary processing trajectories and shielding gas flows in two consecutive layers;

[0049] FIGS. 4a-4d show schematic illustrations of further modes of carrying out a method according to the present disclosure;

[0050] FIG. 5 is an illustration of the directional relationships underlying the disclosed method; and

[0051] FIG. 6 shows an exemplary embodiment of a processing trajectory and angular ranges in which the shielding gas flow vector may be located.

[0052] The illustrations are schematic, and elements not required for understanding have been omitted for the ease of understanding and depiction.

DETAILED DESCRIPTION

[0053] The method according to the present disclosure shall now be lined out in more detail by means of exemplary embodiments in the context of a selective laser melting process. It is understood that the choice of this exemplary process is not intended to be limiting, and that any features shown or described in the exemplary embodiments are intended for illustrative purposes.

[0054] FIG. 1 shows a schematic view of a selective laser melting process and apparatus. A building platform 1 is arranged in a casing 2. The building platform is adjustable in a vertical direction. A metal powder 3 is brought onto the building platform layer by layer, forming a metal powder bed. A laser system 4, for instance comprising a laser of sufficient power and an optical system for deviating and guiding the beam, is used to direct a laser beam 5 onto a top layer of the metal powder. The laser power is chosen sufficiently high to melt the metal powder. Preferably the laser power is sufficient to melt the metal powder at the processing location 6, located at the point of incidence of the laser beam on the top surface of the bed of metal powder, within fractions of seconds. The laser beam 5, and consequently the processing location 6, is advanced along the top surface of the bed of metal powder along a predefined trajectory. The metal powder is molten, and subsequently solidified, along said trajectory, forming a solid element. After said processing cycle has finished, a new layer of metal powder is disposed on top of the bed of metal powder, and a new processing cycle is initiated. Thus, layer by layer, a solid component 7 is formed. A shielding gas flow 8 is provided in introducing a shielding gas, such as for instance argon or nitrogen, through at least one shielding gas inflow nozzle 9, and extracting said shielding gas at the shielding gas outlet 10. Due to the high laser power, a plume 11 of fume and/or vapor emanates from the processing location 6 and is purged by the shielding gas flow 8. It will be appreciated that, if said plume interacts with the laser beam, the laser beam will be attenuated, and less laser power will reach the processing location 6. As has been described above, this may lead to an inhomogeneous and consequently poor material quality of solid component 7.

[0055] Multiple solid components may be manufactured in parallel in one bed of metal powder. The process may then comprise a multitude of independent trajectories, that is, for instance, the laser beam target point is subsequently moved to a multitude of processing cycle start points, and is moved along a trajectory from said start point. Each start point and each trajectory may be related to one component to be manufactured. However, it may be the case that manufacturing a component may at certain positions also require processing along multiple processing trajectories. It is understood, that preferably the laser beam will be switched off, will be attenuated, or will be deviated, such that no material melting is effected, while the laser beam target point is advanced from one trajectory endpoint to a consecutive trajectory starting point.

[0056] It is moreover understood that the laser beam needs not to be incident or incident at full power while the processing location is advances along a trajectory, but may be temporarily switched off, deviated, or be attenuated.

[0057] FIG. 2 schematically depicts the process in a top view of metal powder bed 3. The processing location is advanced along processing trajectory 12 from a starting point 13 to an end point 14. At each location of trajectory 12 a related advance vector 15 exists, defining the direction into which the incident point of the laser beam performs a movement from one point of the trajectory to a consecutive point of the trajectory.

[0058] With reference to FIG. 3, an exemplary mode of carrying out processing cycles in consecutive layers of the metal powder bed 3 is illustrated. In FIG. 3a), the incident point of a laser beam is placed onto a layer of metal powder and advanced over the top surface of said layer from a start point 13 to an end point 14 along a processing trajectory. The processing trajectory is made up of scanning lines 121 and transition trajectories 122. The processing location advances from the trajectory start point 13 to the trajectory end point 14 as indicated by arrows on the trajectory. During the processing cycle, the laser beam is controlled such that melting only occurs while advancing the processing location along the multitude of parallel or at least approximately parallel scanning lines 121. The scanning lines may be equidistant. While transferring the processing location from one scanning line to a subsequent scanning line, the laser beam is switched off, attenuated, deviated or otherwise controlled such that no melting of material occurs. In fact, the movement of the laser beam which might be implied by the movement of optical components of the machine, might follow arbitrary implied beam movement lines 123. However, as no melting occurs during this implied movement, this is not relevant to the subject matter of the present disclosure. The processing trajectory is understood as a connection between two subsequent points where melting takes place. Thus, the processing trajectory in the sense of the present disclosure is defined by scanning lines 121 and the transition trajectories 122. For the processing cycle depicted in FIG. 3a) a mean advance vector 151 may be defined which is essentially the vector along which the scanning lines 121 are staggered. After said processing cycle, a new layer of metal powder is disposed. As depicted in FIG. 3b), the trajectory for the processing cycle in said consecutive layer is chosen such that the processing trajectories of two consecutive processing cycles cross each other. In particular, the scanning lines 121 in the consecutive layer processing cycle are chosen such as to cross the scanning lines of the previous processing cycle, which is depicted in FIG. 3a). In particular, they are chosen such as to cross each other at least approximately at a right angle. Thus, also the mean advance vectors 151 in consecutive layers cross each other, and in particular cross each other at least approximately at a right angle. Thus, the emergence of lamellar structures in the solid component is avoided. Furthermore shown is the shielding gas flow 8 with a shielding gas flow vector 81. As is seen, the direction of the shielding gas flow is varied from one layer to a consecutive layer. Generally spoken, the shielding gas flow vector is oriented to comprise a vector component from the trajectory end point 14 towards the trajectory start point 13, and is chosen such that a counterflow or at least a flow perpendicular to all advance vectors along the trajectory is maintained. In particular, in the example provided, the shielding gas flow vector 81 is directed against the mean advance vector for each layer. As a result, the plume is always blown away from a consecutive processing location on the trajectory.

[0059] It is noted, that in this example the shielding gas vector is maintained constant during a processing cycle. It is appreciated, that ideally the shielding gas flow vector would follow the local advance vector on the trajectory to always provide a counterflow. However, due to the high advance speed along the trajectory, this may be hard to achieve, if technically feasible at all. Thus, in this method, a layer of metal powder is disposed, the trajectory for the processing cycle is determined, and the shielding gas flow direction is adjusted such as to always form an appropriate angle with each advance direction along said trajectory, and is only adjusted while depositing a consecutive layer of metal powder into an appropriate direction for a consecutive processing cycle. However, controlling and varying the shielding gas flow vector during a processing cycle, or while the processing location is advanced along a processing trajectory, is well within the scope of the present disclosure.

[0060] FIGS. 4a-4d depict further modes of carrying out methods according to the present disclosure. The metal powder bed 3 is shown in a top view in FIGS. 4a-4d. The processing location 6, or the solid component 7 to be built, are located in different locations of the building platform. Accordingly, the laser beam, or its projection 51 on the metal powder bed 3, respectively, have different orientations. A shielding gas flow is provided by shielding gas inflow nozzles 9. The position and orientation of the shielding gas inflow nozzles 9 is adapted to the laser beam direction. In certain embodiments, the shielding gas flow 8 would be directed along the laser beam projection 51 and towards the processing location 6. However, it might be desirable to place the processing location not too far from the shielding gas inflow nozzles 9. Thus, a trade-off is chosen, and the shielding gas inflow nozzles 9 are placed and oriented such that the shielding gas flow 8 is approximately perpendicular, i.e. includes a 90 degrees angle, with the laser beam projection 51. As is seen, this blows the plume 11 away from the laser beam, such that the laser beam will not or only negligibly be affected by the plume. It is appreciated that a processing trajectory will be primarily directed against the shielding gas flow direction.

[0061] With reference to FIG. 5, a processing advance vector 15 or a laser beam projection 51, and a shielding gas flow vector 81 are shown, forming an angle 16 with each other. Angle 16 may be chosen to be as close as possible to 180 degrees, but also angles of 45 degrees or larger may be acceptable. For a processing cycle as depicted in FIG. 3 it might be beneficial to choose all advance vectors which appear during a processing cycle, or along a processing trajectory, to be located in a first quadrant I and a second quadrant II. The shielding gas flow vector 81 may be located in one of the third quadrant III and fourth quadrant IV, and in particular on the borderline between the third and the fourth quadrant.

[0062] FIG. 6 finally depicts an exemplary processing trajectory 12 along which a processing location is advanced from a start point 13 to an end point 14, and angular ranges in which the shielding gas vector may be located while processing along said trajectory. Plainly spoken, all advance vectors are oriented from the top to the bottom and vice versa, and to the right. In such scanning processes the laser beam may be switched off, be attenuated, or be deviated or covered while moving from one perpendicular scanning line to a consecutive scanning line. On the right-hand side of FIG. 6, a circle is shown in which the shielding gas flow vector 81 is located. Area A depicts an angular range in which the shielding gas flow vector 81 is considered inadequate. Area B represents an angular range in which shielding gas flow vector 81 is found acceptable. Area C represents a preferred angular range for the orientation of the shielding gas flow vector 81 for all processing locations and advance vectors on processing trajectory 12. Dependent on the laser beam orientation and the achievable position of the shielding gas inflow nozzles, a trade-off may need to be chosen to select the specific orientation of the shielding gas flow vector 81. It is understood that the delimitations between areas A, B, and C are merely exemplary and may vary for specific cases, and will in fact rather be smooth transitions than hard boundaries.

[0063] While the method according to the present disclosure has been described by virtue of exemplary embodiments, it is apparent that the methods and devices characterized in the claims are not restricted to these embodiments. In particular, while the details of the disclosure have been described in the context of a selective laser melting method, it is apparent for the person skilled in the art that the teaching of the present disclosure may be readily applied to other laser-based material processing methods, such as, but not limited to, laser welding. The exemplary embodiments are shown for the sake of a better understanding of the invention only and are in no way intended to limit the invention as claimed. Deviations and variations from the exemplary embodiments shown within the teaching of the present disclosure will be obvious to the skilled person.