Irradiation in generative fabrication

Abstract

The present invention relates to a method for the generative production of components, particularly of single-crystalline or directionally-solidified components, particularly for the production of components for turbomachines, in which the component is constructed in layers on a substrate or a previously produced part of the component (3), wherein a construction in layers takes place by melting of powder material in layers with a high-energy beam (14) and solidification of the powder melt (16) takes place, wherein the high-energy beam has a beam cross section (19) in the area of its impingement on the powder material that is altered in comparison to a circular or other symmetrical cross section and/or the beam energy is distributed non-uniformly, in particular asymmetrically or eccentrically, over the beam section.

Claims

1. A method for the generative production of components for turbomachines, in which the component is constructed in layers on a substrate or a previously produced part of the component (3), wherein a construction in layers results by melting of powder material in layers with a high-energy beam (13) and solidification of the powder melt (16), wherein the high-energy beam has a beam cross section (19) in the area of its impingement on the powder material that is altered in comparison to a circular or other symmetrical cross section and/or the beam energy is distributed, over the beam cross section, in a shape that is selected from the group consisting of non-uniform, asymmetrical and eccentric, and that the powder material, after melting has occurred, is irradiated a second time, at a time delay to the melting, by a high-energy beam with an energy input into the powder material that is altered in comparison to the melting, and wherein the solidification of the powder melt occurs epitaxially.

2. The method according to claim 1, wherein at least two high-energy beams (13) are irradiated on the powder material in temporal succession at spatially adjacent sites of the component or a part thereof.

3. The method according to claim 1, wherein the second irradiation or additional irradiations with a high-energy beam (13) occurs or occur at time points when the melted powder material has not yet fully solidified.

4. The method according to claim 1, further comprising the step of: preheating the powder material by radiant heating or induction heating, prior to the melting.

5. The method according to claim 1, wherein the high-energy beam (13) is a laser or electron beam.

6. The method according to claim 1, wherein at least one high-energy beam is directed along movement tracks (20, 20) over the powder material arranged in a powder bed.

7. The method according to claim 6, wherein the tracks of movement (20, 20) of the high-energy beams with beam cross section (19) that deviates from circular or otherwise symmetrical cross section and/or non-uniform and/or asymmetrical and/or eccentric energy distribution over the beam cross section, and/or the movement tracks for which the high-energy beam impinges for the first time on the powder material at least partially for melting of the powder material overlap one another.

8. The method according to claim 1, wherein a computer-assisted simulation of the energy input and the local and/or temporal temperature distribution in the powder material and/or the already produced component (3) takes place.

9. The method according to claim 1, wherein a computer-assisted simulation of the phase state of the powder material and/or the direction of solidification and/or the rate of solidification of the melted powder material takes place.

10. The method according to claim 8, wherein by a computer-assisted simulation, one or more parameters for the irradiation with high-energy beams is or are determined, wherein said parameters are chosen from the group that includes the power of the high-energy beam or beams, the number of high-energy beams, the shape of the beam cross section of the beam or beams, the non-uniform, asymmetric or eccentric energy distribution of the high-energy beam or beams over the beam cross section, the time interval of a second irradiation or of additional irradiations of the powder material, the geometry of the tracks of the high-energy beams, and the track separation of the movement tracks of the high-energy beams.

11. The method according to claim 10, wherein by a computer-assisted simulation, the parameters for irradiation with high-energy beams are determined so that a desired structure can be created.

12. The method according to claim 1, wherein the method is used for the production of single-crystalline or directionally solidified components.

13. The method according to claim 9, wherein by a computer-assisted simulation, one or more parameters for the irradiation with high-energy beams is or are determined, wherein said parameters are chosen from the group that includes the power of the high-energy beam or beams, the number of high-energy beams, the shape of the beam cross section of the beam or beams, the non-uniform, asymmetric or eccentric energy distribution of the high-energy beam or beams over the beam cross section, the time interval of a second irradiation or of additional irradiations of the powder material, the geometry of the tracks of the high-energy beams, and the track separation of the movement tracks of the high-energy beams.

Description

BRIEF DESCRIPTION OF THE FIGURES

(1) The appended drawings show in a purely schematic manner:

(2) FIG. 1 is a schematic illustration of a device for the generative production of components as exemplified by selective laser melting;

(3) FIG. 2 is a partial sectional view through an already produced component and the powder bed with the melted and solidified area; and

(4) FIG. 3 is an illustration of the tracks of movement and the beam cross section of laser beams during implementation of the method according to the invention.

DETAILED DESCRIPTION OF THE INVENTION

(5) Further advantages, characteristics, and features of the present invention will be elucidated in the following detailed description of an exemplary embodiment, with the invention not being limited to this exemplary embodiment.

(6) FIG. 1 shows a purely schematic illustration of an apparatus 1, such as may be used, for example, for selective laser melting for the generative production of a component. The apparatus 1 comprises a lift table 2, on the platform of which a semi-finished product 3 is arranged, on which a material is deposited in layers in order to produce a three-dimensional component. To this end, powder 10, which is situated above a lift table 9 in a powder hopper, is pushed layer by layer over the semi-finished product 3 by means of a slider 8 and subsequently bonded to the already present semi-finished product 3 by melting brought about by the laser beam 13 of a laser 4. The bonding of the powder material in a powder layer with the semi-finished product 3 is brought about by the laser 4 regardless of the desired contour of the component being fabricated, so that any desired three-dimensional shapes can be produced. Accordingly, the laser beam 13 is directed over the powder bed 12 in order to melt powder material, corresponding to the contour of the three-dimensional component in the sectional plane corresponding to the produced sectional plane, by way of different points of impingement on the powder bed and to bond them with the already produced part of a component or an initially already prepared substrate. In the process, the laser beam 13 can be directed by a suitable deflecting device over the surface of the powder bed 12 and/or the powder bed could be moved relative to the laser beam 13.

(7) In order to prevent undesired reactions with the surrounding atmosphere during melting or sintering, the process can take place in an enclosed space, which is provided by a housing 11 of the apparatus 1, and, in addition, an inert gas atmosphere can be provided in order to prevent, for example, oxidation of the powder material and the like during deposition. Nitrogen, which is supplied via a gas source that is not illustrated, may be used as inert gas, for example.

(8) In place of the inert gas, a different process gas could also be used, if, for example, a reactive deposition of the powder material is desired.

(9) Moreover, other types of beams are also conceivable, such as, for example, electron beams or other particle beams or light beams that are used in stereolithography.

(10) For adjustment of the desired temperatures in the produced component 3 and/or in the powder bed 12, an electric resistance heater with a resistance heating control 5 and an electric heating wire 6 is provided in the lift table, so that the powder bed 12 and the component 3 can be brought to a desired temperature by appropriate heating from below and/or a desired temperature gradient, in particular one in relation to the just processed layer at the surface of the powder bed, can be adjusted. In a similar manner, heating with a heating device from the top side of the powder bed 12 and the already produced component 3 is provided and, in the exemplary embodiment shown, said heating device is constituted by an induction heater with an induction coil 14 and an induction heating control 15. In this process, the induction coil 14 surrounds the laser beam 13 and, as needed, can be moved parallel to the surface of the powder bed 12 depending on the laser beam 13.

(11) In place of the illustrated induction heating, any other type of heating that enables a heating of the powder bed 12 and the already produced component 3 from the top side can be provided, such as, for example, radiant heating devices, such as infrared emitters and the like. In the same way, the resistance heater 5, 6 can also be replaced by other suitable types of heaters that enable a heating of the powder bed 12 and the already produced component 3 from below. Moreover, other heating devices can be provided surrounding the already produced component 3 and/or the powder bed 12 in order to make possible lateral heating of the powder bed 12 and/or the already produced component 3.

(12) Besides heating devices, cooling devices or combined heating/cooling devices can also be provided in order to be able to perform, in addition to a heating of the already produced component 3 and the powder bed 12, also a targeted cooling so as to be able to adjust and influence in a targeted manner the temperature balance in the powder bed 12 and/or the produced component 3, particularly with respect to the powder layer melted by the laser beam 13 and the solidification front at the melted powder material.

(13) FIG. 2 shows the situation in the area of an additional layer in the area of the solidification front that is to be applied directly to the already produced component 3.

(14) In FIG. 2, a part of the already produced component 3 can be seen as well as a part of the powder bed 12 with the powder particles prior to melting. Next to the powder particles of the powder bed 12 is the melt 16 of the already melted powder material after the laser beam 13 has impinged on the powder material of the powder bed 12. Because the laser beam 13 is directed further over the powder bed 12 to produce the contour in the corresponding layer of the component, the melt 16 cools again after irradiation by the laser beam 13, so that solidification of the melted powder material ensues. In the process, regardless of the temperature distribution in the melt 16 and the surrounding areas, a solidification front 17 is formed, which progresses in the direction of the melt 16 and in the direction of the adjusted and directional temperature gradient and at which the melted material is transformed into solidified material.

(15) In accordance with the invention, the energy is input through the laser beam or beams 13 and the heating devices 5, 6, 14, 15 so that the desired solidification structure and crystal orientation are achieved. By means of a slow rate of solidification, that is, slow progression of the solidification front 17 with a simultaneously high temperature gradient at the solidification front, a planar single-crystalline solidification of the melted powder material or an epitaxial growth of the latter occurs on the already produced component 3. This is schematically highlighted in FIG. 2 by illustration of a uniform lattice 18, which represents the uniform crystal structure of the already produced component 3 and the solidified melt 16 at the solidification front 17.

(16) FIG. 3 shows, in a schematic illustration, the movement of one or more laser beams 13 over the powder bed 12. As illustrated in FIG. 3, the laser beam moves, for example, in the form of a meandering movement track 20 over the powder material present in the powder bed 12. In the case of the movement track 20, the laser beam 13 moves in the direction of the arrow 21 along the movement track 20.

(17) The beam cross section 19 in the area of the impingement face of the laser beam on the powder material is not circular in the exemplary embodiments shown, but rather has a rounded wedge shape. At the same time, the beam energy distribution is non-uniform over the beam cross section and is indeed such that, in the area of the thicker end of the wedge-shaped beam cross section, there is a higher beam energy per unit area than in the pointed end of the wedge-shaped beam cross section. This means that the beam cross section 19 has a greater melting area 22 in terms of its diameter and a smaller post-heating area 23 in terms of its diameter. As a result, the beam energy is distributed non-uniformly over the beam cross section 19 and is indeed such that, in the melting area 22, there is a higher beam energy than in the post-heating area 23.

(18) The movement track 20 of the laser beam 13 is then shaped such that, in the case of the meandering track, the parallel track segments are separated by a distance D that is smaller than the longitudinal extension of the beam cross section 19, so that the beam cross section 19 at least partially overlaps the already irradiated area. In particular, the laser beam 13 is directed along the movement track 20 such that the post-heating area 23 of the beam cross section 19 overlaps during further movement of the laser beam 13 in the area in which the powder material had previously been melted by the melting area 22 of the beam cross section 19. In this way, it is possible to use a single laser beam 13 to bring about the melting and the requisite post-heating so as to achieve a low rate of solidification and/or a high temperature gradient in a simple manner.

(19) Alternatively or additionally, it is possible to direct a second laser beam in temporal succession on the same movement track 20 and/or simultaneously and/or at a time delay on a second movement track 20, which is spatially offset with respect the first movement track 20, in order to adjust, in conjunction with the heating devices 5, 6, 14, 15, the desired temperature distribution in the area of the powder bed 12, the melt 16, the solidification front 17, and the already produced component 3, so that an epitaxial growth of the solidifying powder material on the already produced component 3 or on a provided substrate occurs.

(20) The measures described make it possible to control the temperature conditions in the melt and surroundings and thus the magnitude and direction of the temperature gradient at the solidification front as well as its rate and direction during passage through the melt and hence the solidification direction and the orientation of the solidified crystallite or crystallites.

(21) In place of a completely epitaxial growth to obtain a single-crystalline component, it is possible, depending on the chosen method parameters, also to achieve a directionally solidified growth so as to create a component with a plurality of crystal grains, which are oriented along a preferred direction. In addition, globulitically solidified structures can be produced.

(22) Although the present invention has been described in detail on the basis of exemplary embodiments, it is understandable to the person skilled in the art that the invention is not limited to these exemplary embodiments, but rather alterations are possible in such a manner that individual features can be omitted or other types of combinations of features can be implemented, as long as there is no departure from the protective scope of the appended claims. The present disclosure includes all combinations of the individual features presented.