DE102011105045B3 - Producing a component by a layered structure using selective laser melting, comprises for each layer fusing a powdery component material corresponding to a desired geometry of the component, using a laser beam and solidifying by cooling - Google Patents

Abstract

Producing a component by a layered structure using selective laser melting, comprises for each layer fusing a powdery component material corresponding to a desired geometry of the component, using at least a laser beam and then solidifying by cooling. More layers of a shell region of the component are successively constructed with a first beam diameter of the laser beam up to a first thickness and then a layer of the first thickness of a core region remaining within the shell region, is constructed with a second beam diameter of the laser beam, which is greater than the first beam diameter. Producing a component by a layered structure using selective laser melting, comprises for each layer fusing a powdery component material corresponding to a desired geometry of the component, using at least a laser beam and then solidifying by cooling. More layers of a shell region of the component are successively constructed with a first beam diameter of the laser beam up to a first thickness and then a layer of the first thickness of a core region remaining within the shell region, is constructed with a second beam diameter of the laser beam, which is greater than the first beam diameter. The laser beam for melting the powdery component material is conducted to a given path over the shell region and the core region. The paths, on which the laser beam for melting the powdery component material is conducted over the core region, is selected in such a manner that it always reaches at least approximately perpendicular to the envelope region, during contact with the shell region.

Description

Technical application

The present invention relates to a method for producing a component by layered structure by means of selective laser melting, wherein for each layer a powdered component material is melted according to a desired geometry of the component with at least one laser beam and then solidified by cooling, the structure with different laser beam diameters for envelope region and core region of the component.

The generative production process of selective laser melting (SLM: selective laser melting) can be used for the direct production of metallic functional components. The range of application depends not only on the quality of the components that can be produced, but above all on their cost-efficient production. For a broad industrial applicability of the process, the build-up rate of the component must be significantly increased. Decisive for the build-up rate are the process parameters of the layer thickness of the molten layers, the scanning speed of the laser beam and the track pitch of the laser beam. Layer thickness and scan speed are u. a. limited by the available laser power and the maximum intensity, the quotient of laser power and beam diameter. An increase in the scanning speed and / or the layer thickness is only possible by increasing the laser power. With a constant beam diameter, the intensity at the processing location also increases. As a result, a part of the powder grain fraction reaches the evaporation temperature and there is an increase in spatter formation, which impairs robust process control. If, in addition to the laser power, the beam diameter is also increased, this problem can be avoided. However, the achievable detail resolution of the outer contours of generatively manufactured components deteriorates with increasing beam diameter. This in turn results in an increase in the post-processing effort, so that economic benefits are at least partially revised by the increased build-up rate.

State of the art

To circumvent this problem, a technique is known in which the processing is carried out with different laser powers and beam or focus diameters depending on the required component characteristics. With this known technique, also known as the shell-core principle, the envelope region of the component which defines the fine outer contours is generated with a smaller beam diameter than the core region lying within the envelope region. Thus, in analogy to conventional roughing-finishing processes, component cores with high build-up rates (large beam diameter or focus) can be constructed, while in the envelope region (small beam diameter or focus) the required detail resolution and surface quality can be ensured. In the construction of the component, a plurality of superimposed layers having the smaller laser beam diameter are respectively initially formed in the cladding region, and then the powdered component material is melted in the core region over a correspondingly thick layer with the larger laser beam diameter and higher laser power. The thickness of the layer in the core region corresponds to the sum of the layer thicknesses of the layers previously produced in the cladding region. The DE 2007 061 549 A1 describes a corresponding method and an arrangement with which this construction technique can be performed.

In the DE 198 18 469 A1 Also, a method for producing a laminated article is described, in which the envelope region of the component is produced with a smaller laser steel diameter than the core region.

Also the DE 102 45 617 A1 describes such a method for producing three-dimensional objects in layers by means of selective solidification by laser radiation, in which the laser radiation is focused more strongly in an envelope region of the component than in the core region.

1 shows a partial sectional view of a generatively manufactured cubic component 1 with core area and envelope area, in which the ratio of the layer thicknesses of the layers 2 of the envelope area to the layers 3 of the core area is visible. In the figure, the tracks of the laser beam can be seen on which this was performed to melt the powdered component material over the respective area. 2 shows a section parallel to a layer plane of such a component 1 , wherein in the left partial image of the already exposed envelope region 4 and the still unexposed powdery core area 5 can be seen.

An essential prerequisite for the usability of the components produced by the shell-core principle is the fusion metallurgical connection of shell and core. It is thus ensured by the fact that a dependent of the layer thickness overlap 6 between shell and core is realized in the process, as shown in the right part of the picture 2 is indicated schematically. 3 shows an example of the scan vectors or webs 7 on which the laser beam passes over the core area 5 is guided to the overlap 6 in the Transition area to the envelope area 4 to achieve. With such a choice of parallel paths of the laser beam in the core area 5 However, only layer thickness ratios between the cladding region and the core region of 1: 2 can be realized with a good fusion metallurgical connection between cladding region and core region. This means that in each case after two layers produced one above the other in the envelope region, a layer twice as thick is produced in the core region. However, for an economical production of a component on an industrial scale, the achieved speed gain is not enough.

The object of the present invention is to provide a method for producing a component by layered structure by means of selective laser melting, which enables a higher layer thickness ratio between the cladding region and core region of the component with good fusion metallurgical connection between cladding region and core region.

Presentation of the invention

The object is achieved by the method according to claim 1. Advantageous embodiments of the method are the subject of the dependent claims or can be found in the following description and the embodiment.

In the proposed method for producing a component by layered structure by means of selective laser melting, a powdered component material is melted in a known manner for each layer according to a desired geometry of the component with at least one laser beam and then solidifies by cooling. Here, according to the sheath-core principle, an envelope region of the component is constructed with a smaller laser beam or focus diameter at the point of impact and lower laser power than the core region. Thus, in each case several successive layers of the envelope region of the component with a first laser beam or focus diameter are first built one above the other up to a first thickness. Subsequently, a layer of the first thickness of a core region remaining within the envelope region is then constructed with a second laser beam or focus diameter, which is greater than the first laser beam or focus diameter at the point of incidence of the laser beam. In this case, the envelope region is to be understood as meaning an area of the component which comprises its outer contour and extends inwardly up to a certain distance from the outer contour. The remaining inner area of the component is the core area. In addition to the outer contour, the component can also have an inner contour. If this inner contour also has to be manufactured with high level of detail or accuracy, a second envelope region is defined, which comprises the inner contour and extends up to a certain distance in the direction of the outer contour. In such a case, the core region represents the region between the two cladding regions. Furthermore, it is possible for only a region of the outer contour of the component to be manufactured with high accuracy. In this case, the envelope region then does not include the complete outer contour, but only the part of the outer contour that is to be produced with high accuracy. Again, if necessary, it is possible to specify several separate envelope areas. Of course, can be used for the construction of the envelope region and the core area and different laser or from the DE 10 2007 061 549 A1 use known arrangement.

The proposed method is characterized in that the tracks on which the laser beam is guided for melting the powdery component material in the core region, are selected so that they meet at least approximately perpendicular to the envelope region in contact with the envelope region in the entire core region, d. H. at an angle of 90 ° ± 20 °, preferably 90 ° ± 10 °. In this case, the contact of a web with the enveloping region means that the laser beam guided over the core region partially overlaps on this web with the enveloping region. Thus, in the case of the proposed method, this overlap always occurs only at a guidance of the laser beam approximately perpendicular to the boundary of the envelope region at the respective point and never parallel to the boundary of the envelope region when the laser beam is guided. By this choice of the paths of the laser beam in the core region, a good fusion metallurgical connection between the cladding region and the core region is achieved even with layer thickness ratios of less than 1: 2. For example, with the method, layer thickness ratios of 1: 6 with good fusion metallurgical connection, i. H. largely defect-free, realize. This means that in each case six layers of the envelope region can be produced with a smaller laser beam diameter and then a layer thickness corresponding to the six layers in the core region with a significantly larger one. Laser beam diameter. This shortens the time required to build a component so that the process can also be used economically on an industrial scale.

In the proposed method has been recognized that the problems in the construction of a component using the shell-core principle can be avoided by a suitable choice of the tracks for guiding the laser beam in the core area. 3 shows the scan vectors or webs 7 on which on which the laser beam according to the state technology about the core area 5 to be led. The laser beam is hereby alternately in y- or x-scan direction from layer to layer on an inner side of the envelope region 4 until it is finally reached at an angle of 90 °. In the envelope area 4 is the inflection point of the scan vector. The outer edge of the laser beam corresponds in this area to the overlap between the core and the cladding region. After the change of direction, the laser beam moves with an offset of typically Δy _s = (0.7 x beam diameter) parallel to the first melt track in the opposite direction up to the opposite side of the envelope region 4 where the new direction change takes place. In this way, the core scan vector approximates Δy _{s of} the side of the envelope region lying parallel to the scan direction per direction change. On the last track, the outer edge of the laser beam is already within the envelope area 4 at the height of the set overlap. In terms of hot melt metallurgy, there are two different mechanisms in the overlap or transition region, depending on whether the bond between the shell and the core with scan vectors or webs 7 below 90 ° to the envelope area 4 in many small steps or in continuous parallel paths 7 will be produced. It has been found that the fusion metallurgical compound in the transition region in which the scan vectors or webs 7 below 90 ° on the inside of the envelope area 4 is significantly better than in the transition region in which the scan vectors or paths 7 upon contact with the envelope area 4 parallel to the inside of the envelope area. The melt traces produced by the laser melt the powder material lying laterally next to the actual track by heat conduction and draw it into the melt track, so that powder depletion occurs in the immediate vicinity of the melt tracks. This powder depletion proves to be problematic especially for the core scan vectors parallel to the envelope area. The last core scan vectors are close to the transition area but do not yet touch the shell. In this case, the powder, which is to ensure the connection between the shell and core, mainly melted. Thus, only after little metal powder in the transition region shell core is present when the scan vectors parallel to the envelope region reach the inner edge of the envelope region. In contrast, the core scan vectors orthogonal to the envelope end at each inflection point at the set overlap, so that the melt trace extends continuously into the envelope region and the powder depletion has no appreciable influence on the bond here.

In the proposed method, this problem is avoided in that the core scan vectors or laser tracks in the core region are each selected such that they always meet approximately perpendicular to the envelope region and thus never run parallel to the inside of the envelope region in the transition region or overlap region with the envelope region ,

Due to this scanning strategy, layer thickness ratios <1: 2 (shell: core) can be realized in the generative component production. Thus, the build-up rate in the core can be significantly increased without compromising the required accuracy, the detail resolution and surface finish (shell). There are thus considerable economic savings.

The method can be used, for example, in tool and mold making. Due to the freedom of geometry of the generative production, great potentials arise here, for example through the use of close-to-contour cooling. By applying the proposed method, it is possible to produce the tools much cheaper with consistent quality, as has been possible. Further fields of application lie in particular in areas characterized by a large variety of complex metal components. Since the manufacturing costs in the generative component manufacturing depend only on the volume to be built, but not on the complexity of the components, the use of the proposed method considerable rationalization potentials are available. The areas mentioned include, for example, aerospace and automotive engineering.

Brief description of the drawings

The proposed method will be briefly explained again with reference to an embodiment in conjunction with the drawings. Hereby show:

1 a partial sectional view of a manufactured according to the prior art component;

2 a section parallel to a layer plane in the manufacture of a component;

3 an example of the Kernscanvektoren in the construction of a component according to 1 ; and

4 an example of the core scan vectors in the proposed method.

Ways to carry out the invention

The procedure in the generative production of a component by means of selective laser melting according to the prior art has already been described in the introductory part with respect to 1 to 3 which is therefore no longer discussed.

In the method of the present patent application, the core region is exposed or scanned with the laser beam in such a way that the core scan vectors or paths run orthogonally to the enveloping structure, ie to the boundary between enveloping region and core region. This is in the left picture of the 4 indicated in a section parallel to a layer plane. This figure shows the already exposed envelope area 4 and the tracks 7 on which the laser beam passes over the core area 5 to be led. From the figure can be clearly seen that the tracks 7 or Kernscanvektoren the laser beam in each case perpendicular to the inner boundary of the envelope region 4 to meet. For this purpose, in this example, a scanning strategy is used with sections of straight-line tracks, each having a deflection within the core area, ie spaced from the envelope area. In the case of the present rectangular core region, this can take place with a 90 ° deflection on the diagonals of the rectangular core region, so that then the laser beam must continue to be moved only in the x or y direction.

An example of a component with a circular core region is shown in the right figure of FIG 4 represented in a section parallel to a layer plane. This component has the same scanning strategy as the example of the left figure 4 used, wherein the Kernscanvektoren of the laser beam then also approximately perpendicular to the inner boundary of the envelope region 4 to meet.

With such a scanning strategy it is achieved that the laser beam strikes the enveloping region approximately perpendicularly in the entire exposed core region and thus a constant good fusion metallurgical connection between the core region and the enveloping region is achieved. This allows a significantly smaller layer thickness ratio between the layers in the cladding region and in the core region, so that larger laser beam diameters or layer thicknesses can be generated in the core region and thus the build-up speed of the component can be significantly increased.

LIST OF REFERENCE NUMBERS

1

component

2

Layers in the envelope area

3

Layers in the core area

4

exposed envelope area

5

powdery core area

6

overlap

7

Webs or core scan vectors

Claims (5)

Method for producing a component ( 1 ) by layered structure by means of selective laser melting, wherein for each layer a powdered component material corresponding to a desired geometry of the component ( 1 ) is melted with at least one laser beam and then solidified by cooling, each first successively several layers ( 2 ) of an envelope region ( 4 ) of the component ( 1 ) are constructed with a first beam diameter of the laser beam to a first thickness one above the other and then a layer ( 3 ) of the first thickness of one within the envelope region ( 4 ) remaining core area ( 5 ) is constructed with a second beam diameter of the laser beam, which is greater than the first beam diameter, and wherein the laser beam for melting the powdery component material on predetermined paths ( 7 ) over the envelope area ( 4 ) and the core area ( 5 ), characterized in that the tracks ( 7 ), on which the laser beam for melting the powdery component material over the core area ( 5 ) are chosen so that they are in contact with the envelope region ( 4 ) always at least approximately perpendicular to the envelope region ( 4 ) to meet. Method according to Claim 1, characterized in that in each case at least three layers of the envelope region ( 4 ) of the component ( 1 ) are constructed with the first laser beam diameter. Method according to claim 1 or 2, characterized in that the webs ( 7 ), on which the laser beam for melting the powdery component material over the core area ( 5 ) are selected so that they each extend in sections in a straight line and on diagonals one into the core area ( 5 ) fitted rectangular shape have a 90 ° deflection. Method according to claim 1 or 2, characterized in that the core area ( 5 ) regardless of a geometric shape of the component ( 1 ) is selected such that in each layer plane it has a shape composed of one or more contiguous rectangles. Method according to claim 4, characterized in that the tracks ( 7 ), on which the laser beam for melting the powdery component material over the core area ( 5 ), are selected so that they each extend in sections in a straight line and diagonals of the individual adjacent rectangles have a 90 ° deflection.

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