WO2020127074A1

WO2020127074A1 - Method for treating a surface with energetic radiation

Info

Publication number: WO2020127074A1
Application number: PCT/EP2019/085382
Authority: WO
Inventors: Tobias Pichler; Christian Tenbrock; Wilhelm Meiners; Florian EIBL
Original assignee: Fraunhofer-Gesellschaft zur Förderung der angewandten Forschung e. V.
Priority date: 2018-12-17
Filing date: 2019-12-16
Publication date: 2020-06-25
Also published as: DE102018132441A1

Abstract

The invention relates to a method for treating a surface with energetic radiation, particularly for selective laser melting, in which at least one energetic beam is guided along a plurality of scan vectors (3) running spaced apart next to each other over one or more regions (2) of the surface. With varying length of the scan vectors (3) in one or more of the regions (2), the distance between adjacent scan vectors (3) is, in each case, selected as a function of the length of at least one of the adjacent scan vectors (3). The method allows the melting rate of powder bed-based radiation melting processes to be increased and hence reduces the construction time for the components to be fabricated.

Description

Process for processing a surface with energetic radiation

Technical application area

The present invention relates to a method for processing a surface with energetic radiation, in particular for selective laser melting, in which at least one energetic beam along a plurality of scan vectors running at a distance from one another over one or more regions of the

Surface is guided.

With such processing methods can

Surface layers melted or else

be removed. In additive manufacturing processes, especially powder bed-based beam melting processes such as Selective laser melting (SLM) is used to generate components directly from 3D CAD models

manufactured. Through a repetitive process of layer-by-layer application of a thin layer of powder with a thickness of, for example, less than IOOmpi and

then selective melting of certain

Areas of this powder layer through laser radiation, according to the geometry information of the 3D CAD model, create three-dimensional components of almost unlimited complexity. A substrate plate on which the powder layers are applied one after the other serves as the basis for powder bed-based beam melting processes. The laser radiation is then guided, for example with the aid of galvanometer scanners, over the substrate plate or the construction field. During the construction process, certain areas of the powder bed are covered in each layer using the

Laser beam remelted. The ones to be remelted

Areas are, depending on the process control strategy used, again divided into subordinate areas. With these subordinate

Areas can be strips or fields, for example. FIG. 1 shows an example of an exemplary component cross section of any layer of such a manufacturing process with a corresponding division into strips 2. The

Solid line represents the component contour 1 of the component to be manufactured. The width of the individual strips 2 is firmly defined. Each of these

Strip 2 is filled with individual scan vectors 3 running parallel to one another. These scan vectors 3 represent the path on which the laser beam is guided along for melting or exposing the layer. FIG. 2 shows an example of a strip 2 of the component cross section from FIG. 1 with the associated scan vectors 3. During the exposure process, the scan vectors 3 of a strip 2 are moved one after the other. The laser beam then jumps to

Start the next stripe and scan the vectors of that streak until all of the stripes of that particular one

Layer have been scanned. In alternative process management strategies, the area of each layer to be exposed can also be in instead of stripes

for example square fields, similar to one

Chessboards. The individual fields are then filled with scan vectors that are parallel to one another and identical to the strip exposure. Other patterns for dividing the exposing areas of a layer are possible. Below is an example of the stripe

Exposure considered. An essential property of conventional

Process control strategies for beam melting processes consist in defining a constant distance between the scan vectors lying within the strip. This distance is also called the track distance or hatch distance. The amount of

Track spacing is typically constant for all vectors within the stripes of a component. The process parameters in general or the track spacing in particular are in such a process

typically before performing the process on cube-shaped specimens with a constant

The scan vector length is determined, the scan vector length corresponding to the stripe width.

State of the art

A method for producing a three-dimensional object is known from DE 196 06 128 A1, in which the object is produced by successive

Solidification of individual layers of a solidifiable material at the points corresponding to the object cross section by the action of a beam electro

magnetic radiation is generated. With this

The scanning speed at which the beam is guided over the respective layer is moved into

Adjusted depending on the scan vector length. A short scan vector is assigned a higher speed than a long scan vector. By doing this, a Alignment of the temperature distribution within the component can be achieved, resulting in a homogeneous

Density distribution within the solidified layer leads. This strategy is particularly relevant for plastic components, for example to prevent overheating effects.

A fundamental problem with such

Additive manufacturing processes consist of the construction time required to manufacture a component. A

Shortening the construction time by choosing larger layer thicknesses or beam diameters leads to an undesirable loss of accuracy or resolution, as is required in particular with more complex components. A similar problem exists with other methods of surface treatment with energetic radiation, in which the energetic beam is guided along corresponding scan vectors over one or more areas of the surface.

The object of the present invention is to provide a generic method for processing a surface with energetic radiation, which increases the processing or construction speed without loss of processing accuracy

enables. The method is intended in particular to

Increasing the construction speed with a powder bed-based jet melting process for production

enable three-dimensional components.

Presentation of the invention

The task is performed according to the procedure

Claim 1 solved. Advantageous configurations the procedure are the subject of the dependent

Claims or can be found in the following description and the embodiment. In the proposed method for processing a surface with energetic radiation,

In particular for selective laser melting, at least one energetic beam is passed in a known manner along one or more scan vectors running alongside one another at a distance from one another at a distance

Areas of the surface led. Each of the scan vectors preferably extends over the entire area. The method is characterized in that, with a varying length of the scan vectors in one or more of the areas, the distance between adjacent scan vectors is selected depending on the length of at least one of the respectively adjacent scan vectors. Preferably the

The distance between adjacent scan vectors is selected depending on the length of the scan vector along which the energetic beam is first guided.

This variable adaptation of the distance between the scan vectors or the track distance as a function of the scan vector length increases the number of required components or components

Reduced scan vectors and thus the remelting rate increased. In addition, this results in a reduced number of non-productive times within the

Beam guidance system, so-called scanner delays. The

The process thus enables the construction speed to be increased in the area of additive manufacturing, for example in selective laser melting. The The process can be done without any modification of the

technical design of the construction or processing system can be used. Adjustments are primarily necessary in the software for data preparation and possibly in the software for controlling the system.

According to tests carried out to date, the method enables one, depending on the component geometry

Increase in construction speed with selective

Laser melting from 10% to 30% while maintaining the desired material density, for example in the range of 99.5% relative density. This density results from the proportion of the pores remaining in the material after the surface layer has been melted and solidified. Especially in the case of the filigree filaments that are preferably manufactured using the SLM process

Component structures with correspondingly short scan vectors can in particular benefit from the proposed method. The shorter the average vector length for the respective component, the greater the advantages of the method compared to conventional exposure strategies with a constant distance between the scan vectors.

In addition to the advantage described above

increased building speed with generative

Manufacturing processes can also be one

Homogenization of the temperature field during the

Remelting process can be achieved. This can have advantages in terms of process stability, for example reducing welding spatter, and

Component quality, for example through reduced

Internal stresses within the component. The proposed method takes advantage of the fact that the length of the individual scan vectors for most components is within one of those for the

Processing selected strips or fields varies according to the component contour. The shorter the length of one

If the scan vector fails, the shorter the cooling time of the associated melting trace until the laser beam for the exposure of the neighboring trace again heats up. This local preheating effect widens the weld pool. Accordingly, a larger one can be used with shorter scan vectors and a correspondingly shorter cooling time or wider weld pool

Track spacing or distance of the scan vectors is set and a connection of the tracks to one another is ensured. This variation of the distance between the scan vectors or track spacing as a function of the length of at least one of the adjacent scan vectors is carried out in the present method. The result is an increase in the remelting rate, a reduction in the number of vectors and one

Homogenization of the temperature distribution within the strip or field to be exposed.

The proposed method can be used for all beam-melting additive manufacturing processes in which the component areas are scanned vector by vector by means of electromagnetic radiation. The procedure can be under

Using appropriately adapted software both on existing and in the future

available facilities. In addition to the

additive manufacturing, the method can also be used for other areas in which the surface with at least one energy beam along several in one Distance of running scan vectors processed,

in particular is melted, and the length of the scan vectors varies over the respective area.

Brief description of the drawings

The proposed method is explained in more detail below using an exemplary embodiment in conjunction with the drawings. Here show:

1 shows a representation of a division of an exemplary component cross section of any layer in additive manufacturing into a plurality of strips to be exposed;

Fig. 2 shows an example of an arrangement of the

Scan vectors within a stripe;

Fig. 3 shows a comparison between the length of the

Scan vectors for a cube-shaped specimen and an application

specific component geometry;

Fig. 4 shows a comparison of the conventional

Exposure strategy with constant track spacing (partial illustration A) and the exposure strategy with variable

Track spacing in the proposed

Process (Part B); and

Fig. 5 is a diagram showing an exemplary

Relationship between scan vector length and track spacing in the proposed method.

Ways of Carrying Out the Invention

The conventional exposure strategy in powder bed-based beam melting processes has already been explained in the introduction to the description in conjunction with FIGS. 1 and 2. FIG. 3 shows a comparison between the scan vector length for one for the

Parameter determination of the selected cube-shaped test specimen (right part of the figure) and the scan vector length for an application-specific component (left part of the figure). Such cube-shaped test specimens are used to determine the process parameters, in particular the distance between the scan vectors or track spacing, in advance when manufacturing a component. The

Test specimens consist of the same material as the component to be manufactured. It can be seen from FIG. 3 that within the individual strips 2, into which the area to be melted is divided for processing, a constant scan vector length occurs in the cube-shaped test specimen, while it may vary within the strips 2 in the application-specific component geometry due to the component contour 1 . This variation results in cooling times of different lengths, before the laser beam on the adjacent track heats up again, and thus melting baths of different widths. This is exploited in the present method by using shorter scan vectors and correspondingly fewer

Cooling time or wider weld pool a longer one

Distance of the scan vectors (track spacing) is set, with which a connection of the material continues adjacent tracks to each other is ensured. The adjustment of the distance between the scan vectors and the

Track spacing is done by adjusting the distance between two tracks depending on the length of the track first exposed by these two tracks. Figure 4 shows this procedure schematically for a triangular component contour.

FIG. 4A shows the one typical of the SLM up to now

Strategy of exposure presented. The distance Dl between the individual is characteristic

Scan vectors 3, which is constant for all vectors, regardless of their length. FIG. 4B, on the other hand, shows schematically those in the proposed

Process used novel exposure strategy with variable track spacing. The distance between the scan vectors or the track spacing is adjusted as a function of the scan vector length. In the present case, D2> Dl applies since 3 is for shorter scan vectors

Track spacing is increased.

The enlargement or variation of the track spacing is carried out such that a predetermined relative minimum density, for example> 99.5%, of the components produced therewith is achieved even with a correspondingly enlarged track spacing.

Determining the relationship between

Scan vector length and distance of the scan vectors or

Track spacing can be done experimentally, for example, by producing test specimens of different sizes and thus vector lengths. In this way, a table of values with assignments between

Scan vector length and track spacing for the respective Material and the respective system can be created.

Alternatively, the relationship between scan vector length and track spacing can also be determined by means of simulation.

Below is an exemplary table of values with five discrete data points at five below

different scan vector lengths are shown.

FIG. 5 shows the graphic relationship between the scan vector length and the distance of the

Scan vectors or the track spacing. For each scan vector or its specific length, the associated distance is taken into account in the data preparation for production in accordance with the value table. You can interpolate between the individual discrete values. By increasing the track spacing, the

Remelting rate increased and the number of vectors required reduced. The preparation of the corresponding component data with variable track spacing is preferably carried out during path planning with the aid of special software that can process the experimentally determined value tables accordingly. In the present description and the

The exemplary embodiment was primarily referred to methods for selective laser melting of metallic materials, in which galvanoscanners are generally used as steel deflection units. However, it is also a transfer to other beam sources, for example electron beam sources, others

Beam deflection units such as XY plotter systems or other materials such as

Plastics easily possible. The present

The process is not based on selective laser melting, powder bed-based beam melting or

generative manufacturing processes in general

limited.

Reference list

1 component contour

2 strips

3 scan vectors

D1 / D2 distance of the scan vectors

Claims

1. Procedure for processing a surface with

energetic radiation, especially for

selective laser melting,

in which at least one energetic beam is guided along one or more regions (2) of the surface along a plurality of scan vectors (3) running at a distance from one another, characterized in that

that with a varying length of the scan vectors (3) in one or more of the areas (2)

Distance between adjacent scan vectors (3) is selected depending on the length of at least one of the adjacent scan vectors (3).

2. The method according to claim 1,

characterized,

that the distance between adjacent scan vectors (3) is chosen depending on the length of the scan vector (3) along which the energetic beam is first guided during processing.

3. The method according to claim 1 or 2,

characterized,

that the distance between adjacent scan vectors (3) is selected so that it is at

decreasing length of the scan vectors (3) increases and decreases with increasing length of the scan vectors (3).

4. The method according to any one of claims 1 to 3, characterized in

that the distance between neighboring ones

Scan vectors (3) are taken from a table in which different distances were previously assigned to different scan vector lengths.

5. The method according to any one of claims 1 to 4,

characterized,

that the dependence of the distance between adjacent scan vectors (3) on the length of at least one of the adjacent ones

Scan vectors (3) are determined beforehand experimentally or by simulation.

6. The method according to any one of claims 1 to 5,

characterized,

that the distance between neighboring ones

Scan vectors (3) in the production of

three-dimensional components is maximized by melting a powdery material in layers, in each case observing the condition that a predetermined density of the manufactured components is achieved at the respectively selected distance.

7. The method according to any one of claims 1 to 6,

characterized,

that the respective distance between the

neighboring scan vectors (3) before processing as part of a path planning using a

Software is determined.