DE102021209506A1 - Multi-spot laser device and method for producing a workpiece - Google Patents

Abstract

The invention relates to a method for producing a workpiece by selective laser melting using a multi-spot laser device. A beam shaping device can split a laser beam into a large number of beams in order to direct a large number of laser spots onto the material at the same time. Information on technical features of the multi-spot laser device is given. Furthermore, information regarding surfaces of the material to be exposed in layers to produce the workpiece is specified. At least one surface subdivision is also created. For each area to be exposed and each area subdivision, the cells of the area subdivision are classified, the area subdivision being superimposed over the area to be exposed, and the cells being classified as a function of a degree of overlap of the area to be exposed with the respective cell. An exposure sequence for exposing the material to be processed using the multi-spot laser device is determined, depending on the information regarding the technical characteristics of the multi-spot laser device and on the classification of the cells of the at least one surface subdivision for each surface to be exposed. The workpiece is created by exposing the material to be processed using the multi-spot laser device based on the exposure sequence determined.

Description

The present invention relates to methods for producing a workpiece by selective laser melting using a multi-spot laser device. The invention further relates to a corresponding multi-spot laser device.

State of the art

Additive manufacturing processes for processing metallic materials are becoming increasingly important in industry. A promising representative of this manufacturing technology is selective laser melting (Powder Bed Fusion with Laser Beam, PBF-LB), which enables new ways of manufacturing highly complex metal components.

From the DE 10 2017 200 119 A1 a method for beam shape and beam orientation adjustment in a laser machining process is known, in which in a laser machining system a laser beam is focused onto the surface of a component using deflection mirrors and lens systems and the laser beam can be adjusted to the surface of the component to be machined in terms of its intensity distribution using at least one beam shaping module .

Next is from the DE 10 2016 213 420 A1 a method for the additive manufacturing of a component is known, a beam being guided through a beam-shaping element arranged in the beam path of the beam for power density distribution of the beam.

Disclosure of Invention

The invention provides a method for producing a workpiece by selective laser melting using a multi-spot laser device and a multi-spot laser device having the features of the independent patent claims.

In selective laser melting (Powder Bed Fusion with Laser Beam, PBF-LB), metallic powder is used as the starting material for the production of highly complex metal components and a laser is used to melt the powder. Melting takes place selectively in the powder bed. By repeating the process sequence, a complex component can be built up layer by layer. The process preferably takes place in a protective gas atmosphere.

The path planning for the laser systems plays a significant part in the productivity of the systems and thus of the selective laser melting. The method according to the invention advantageously contributes to high productivity.

Preferred embodiments are the subject of the respective dependent claims.

According to a first aspect, the invention relates to a method for producing a workpiece by selective laser melting using a multi-spot laser device, the multi-spot laser device having at least one laser for generating a laser beam, and the multi-spot laser device having a Has beam shaping device to direct the laser beam to a material to be processed. The beam shaping device can split the laser beam into a large number of beams in order to direct a large number of laser spots onto the material at the same time. Information on technical features of the multi-spot laser device is given. Furthermore, information regarding surfaces of the material to be exposed in layers to produce the workpiece is specified. At least one surface subdivision with a large number of cells is also created. For each area to be exposed and each area subdivision, the cells of the area subdivision are classified, the area subdivision being superimposed over the area to be exposed, and the classification of the cells depending on a

degree of overlapping of the area to be exposed with the respective cell. An exposure sequence for exposing the material to be processed using the multi-spot laser device is determined, depending on the information regarding the technical characteristics of the multi-spot laser device and on the classification of the cells of the at least one surface subdivision for each surface to be exposed. The workpiece is created by exposing the material to be processed using the multi-spot laser device based on the exposure sequence determined.

According to a second aspect, the invention relates to a multi-spot laser device for producing a workpiece by selective laser melting, with at least one laser, which is designed to generate a laser beam, and with a beam shaping device, which is designed to direct the laser beam onto a to direct the material to be processed, wherein the beam shaping device is further designed to split the laser beam into a plurality of beams in order to direct a plurality of laser spots onto the material at the same time. The multi-spot laser device also includes a control device which is designed to generate at least one area subdivision with a multiplicity of cells. The controller is further designed for classifying each area to be exposed of a plurality of areas to be exposed in layers and for each area division the cells of the area division, the area division being superimposed on the area to be exposed, and the classification of the cells depending on a degree of overlap of the area to be exposed with the respective cell takes place. The control device is also designed to determine an exposure sequence for exposing the material to be processed, depending on information regarding technical features of the multi-spot laser device and on the classification of the cells of the at least one area subdivision for each area to be exposed. The control device is also designed to control the at least one laser and the beam shaping device in order to produce the tool by exposing the material to be processed using the exposure sequence determined.

Advantages of the Invention

The invention provides a multi-spot laser device which, in contrast to multi-scanner systems, achieves a multiplication of the laser beams by beam splitting or beam shaping. The advantage here is that only one optical system is required. With multi-scanner systems, the maximum number of scanners is limited and thus also the maximum number of available laser spots that can be used for melting. The number of spots can be increased with a multi-spot laser device, since the available laser power can be distributed over any number of spots.

In contrast to multi-scanner systems with different lasers (shell-core), a multi-spot laser device, which has the option of beam shaping, allows an almost unlimited number of possible spot arrangements and thus optimizes path planning arbitrarily complex. The invention provides a method for optimal path planning, i. H. to determine the exposure sequence. Optimization determines which spot arrangement is best suited to providing a given application as quickly and precisely as possible. The spot arrangement can range from individual laser spots to broader multi-spots.

In general, the geometries and the spot arrangements can be arbitrary. The invention provides a method for making maximum use of the multi-spot laser device.

The subdivision of the area can be a grid that is made up of cells that are regularly distributed over an area. In particular, the grid can be made up of squares or rectangles. However, the surface subdivision can also be formed from irregular cells, the shape or orientation of which can differ for different spatial areas, for example.

According to a further embodiment of the method for producing a workpiece by selective laser melting using a multi-spot laser device, the multi-spot laser device further comprises at least one single-spot laser.

According to a further embodiment of the method for producing a workpiece by selective laser melting using a multi-spot laser device, the information regarding technical features of the multi-spot laser device includes at least one of technical features of the beam shaping device, a laser power of the at least one laser, an exposure type of the at least one laser, at least one quality parameter of the at least one laser, a focus position, a distance between the laser spots and an extent of the laser spots. This information serves as boundary conditions for optimizing the exposure process.

According to a further embodiment of the method for producing a workpiece by selective laser melting using a multi-spot laser device, a multiplicity of surface subdivisions are produced, with a surface subdivision being selected to determine the exposure process using an optimization criterion and the exposure process being determined based on the surface subdivision determined. The surface subdivisions can differ from one another in terms of their orientation, number of cells and/or cell shape.

According to a further embodiment of the method for producing a workpiece by selective laser melting using a multi-spot laser device, process parameters of the multi-spot laser device for exposing the cell are determined for determining the exposure sequence for each area to be exposed for each cell. The process parameters include an exposure time, number of spots, position of the spots or the like.

According to a further embodiment of the method for producing a workpiece by selective laser melting using a multi-spot laser device, the process parameters are determined using an optimization criterion.

According to a further embodiment of the method for producing a workpiece by selective laser melting using a multi-spot laser device comprises the optimization criterion at least one of criteria relating to a precision of structures of the workpiece to be produced, criteria relating to minimum distortion of the workpiece, criteria relating to an exposure time required to produce the workpiece and criteria relating to a density of the workpiece to be produced. Several criteria can also be optimized at the same time.

According to a further embodiment of the method for producing a workpiece by selective laser melting using a multi-spot laser device, the optimization criterion includes an approximation of the effective build-up rate to the theoretically maximum build-up rate.

According to a further embodiment of the method for producing a workpiece by selective laser melting using a multi-spot laser device, for each area to be exposed and each area subdivision, the cells of the area subdivision are further classified as a function of an overhang of the area to be exposed with at least one further surface to be exposed in a layer above the surface to be exposed and/or depending on an underhang of the surface to be exposed with at least one further surface to be exposed in a layer below the surface to be exposed. Surfaces with an underhang or overhang can be specially processed, for example with predetermined process parameters or settings of the at least one laser.

According to a further embodiment of the method for producing a workpiece by selective laser melting using a multi-spot laser device, in order to classify the cells of the surface subdivision, the surface subdivision can be subdivided into finer cells if the surface to be exposed overlaps only partially with the respective cell. The cells can be roughly halved, quartered, etc.

According to a further embodiment of the method for producing a workpiece by selective laser melting using a multi-spot laser device, the at least one surface subdivision is produced as a function of the information regarding technical features of the multi-spot laser device.

According to a further embodiment of the method for producing a workpiece by selective laser melting using a multi-spot laser device, the classification of the cells of the area subdivision includes the classification into full areas or partial areas, depending on whether the workpiece to be produced completely or only partially fills the cell.

According to a further embodiment of the method for producing a workpiece by selective laser melting using a multi-spot laser device, the number of process parameters is reduced in order to reduce the computing effort. For example, only essential spots can be considered, for example with a cell size of 1 x n with n = 2, 4, 6, 8, 10.

According to a further embodiment of the method for producing a workpiece by selective laser melting, the method is carried out in parallel, i. H. in a multi-core process. For this purpose, for example, each surface subdivision (e.g. with different angles) is calculated by a processor core and a build rate (or another selected quality criterion) is calculated for this angle. These build rates are then compared and the subdivision with the optimal value is selected.

character list

• 1 ein schematisches Blockdiagramm einer Multi-Spot-Laservorrichtung gemäß einer Ausführungsform der Erfindung;
• 2 eine schematische Darstellung unterschiedlich dimensionierter zu belichtender Flächen;
• 3 eine schematische Darstellung der effektiven Aufbaurate für verschiedene Nutzungsgrade;
• 4 eine schematische Illustration der Erzeugung und Klassifizierung von Flächenunterteilungen;
• 5 eine schematische Illustration der feineren Unterteilung von Zellen; und
• 6 ein Flussdiagramm zum Erzeugen eines Werkstücks durch selektives Laserschmelzen mittels einer Multi-Spot-Laservorrichtung gemäß einer Ausführungsform der Erfindung.

Show it:

• 1 12 is a schematic block diagram of a multi-spot laser device according to an embodiment of the invention;
• 2 a schematic representation of differently dimensioned areas to be exposed;
• 3 a schematic representation of the effective build-up rate for different degrees of utilization;
• 4 a schematic illustration of the generation and classification of surface subdivisions;
• 5 a schematic illustration of the finer subdivision of cells; and
• 6 a flowchart for producing a workpiece by selective laser melting using a multi-spot laser device according to an embodiment of the invention.

Elements and devices that are the same or have the same function are provided with the same reference symbols in all figures. The numbering of method steps is for the sake of clarity and should not generally imply a specific chronological order. In particular, several method steps can also be carried out simultaneously.

Description of the exemplary embodiments

1 shows a schematic block diagram of a multi-spot laser device 1 for producing a workpiece by selective laser melting of a material 5. The multi-spot laser device 1 comprises a laser 2, with several lasers 2 also being able to be present according to further embodiments.

The laser 2 generates a laser beam, which is directed onto a material to be processed by means of a beam shaping device 3 . For this purpose, the beam shaping device 3 can divide the laser beam into a large number of beams (multi-spot) in order to direct a large number of laser spots onto the material at the same time. In addition, single-spot lasers can also be provided.

The multi-spot laser device also includes a control device 4, which can include a microprocessor, microcontroller, integrated circuit or the like. The control device 4 calculates at least one area subdivision with a large number of cells. The control device 4 also receives information about the workpiece to be produced as input. In particular, the information includes a number of layers or areas to be exposed, as well as information about which sections of the respective areas to be exposed are to be exposed.

For each area to be exposed of the areas to be exposed in layers and for each area subdivision, the control device 4 classifies the cells of the area subdivision. For this purpose, the control device 4 places the area subdivision over the area to be exposed. Depending on whether the cell is fully or only partially exposed, the cell can be classified as full area or partial area. The classification thus depends on a degree of overlap of the area to be exposed with the respective cell.

The control device 4 now carries out path planning, thus determining an exposure sequence for exposing the material to be processed. An optimization algorithm is used in the planning, with information regarding technical features of the multi-spot laser device 1 being used as boundary conditions. Properties of the material 5, which is exposed to produce the workpiece, can also be specified as boundary conditions. For example, the material group can be specified.

The properties relating to the technical features of the multi-spot laser device 1 include, for example, the phase mask in the case of dynamic beam splitting, the diffractive optical element used in the case of static beam splitting, the total laser power used, the laser travel speed, the type of exposure (whether an alternating exposure is possible, for example), Quality parameters such as an achievable density, a theoretical build-up rate, a final distortion or a focus position.

Furthermore, passive properties can be specified as boundary conditions, such as a multi-spot distance, which results from the selected phase mask in combination with the power used and the traversing speed of the laser. Another passive property is the laser power per spot, which depends on the total laser power used, the phase mask and the diffractive optical elements.

Furthermore, the thermophysical properties of the material can be taken into account, which can influence the effectiveness of the process parameters. The theoretical build-up rates can be determined quantitatively, for example, from the process parameters used (e.g. laser travel speed and multi-spot distance) and the capabilities of the optical system (e.g. jump times).

Another input to the optimization is the classification of the cells of the at least one surface subdivision for each surface to be exposed, indicating which cells need to be fully or partially exposed.

After the control device 4 has carried out the path planning, the control device 4 sends a control signal to the laser 2 and the beam shaping device 3 in order to control them in such a way that the tool is produced by exposing the material 5 to be processed using the exposure sequence determined.

In 2 two differently dimensioned areas A1 and A2 to be exposed are shown as an example, with the first area A1 having a multi-spot utilization rate of 90 percent and the second area A1 having a multi-spot utilization rate of 50 percent.

In 3 the effective build-up rate A_eff (in cm ³ /h) for different degrees of utilization (multispot area MS_area in percent of the total area) is illustrated, each for three different theoretical build-up rates (R1: 30 cm ³ /h, R2: 40 cm ³ / h and R3: 50 cm ³ /h). The multi-spot system used has an exemplary 1×7 spot arrangement. A wide welding seam is connected with spot multiplications (in the near area), which prevents the exposure of fine structures or edge contours. The lower the degree of utilization, the lower the effective build-up rate A_eff. At a certain point, the use of beamforming, which adds complexity and therefore cost to the overall system, can no longer be justified.

4 Fig. 12 shows a schematic illustration of the generation and classification of surface subdivisions, where the surface subdivisions are grids with regular cells. For this purpose, a first grid with a first cell alignment 202, a second grid with a second cell alignment 203 and a third grid with a third cell alignment 204 are specified for an area 201 to be exposed. The overlap of the first to third grids 205, 206, 207 with the area 201 to be exposed is calculated. The cells are classified as full areas 210 if they overlap completely and as partial areas 211 if they only partially overlap. The optimal process parameters are then selected, 208, and the exposure sequence is determined, 209.

5 shows a schematic illustration of the finer subdivision of cells. In this case, a finer subdivision of cells 303 is undertaken for a grid 301, which cells only partially overlap with the area to be exposed. This results in new cells 304, 305 for the grid 301. Solid areas 302 are not further subdivided. The new cells 305, which only partially overlap with the area to be exposed, can optionally be further subdivided iteratively.

6 shows a flowchart for producing a workpiece by selective laser melting using a multi-spot laser device 1 as described above.

For this purpose, information regarding technical features of the multi-spot laser device 1 and the materials 5 used are specified in a step S1. Information regarding the component to be created is also generated or received, S2. Pre-processing takes place in that the areas (layers) to be exposed are determined, S3. The layer images or areas to be exposed depend essentially on the component geometry and the layer thickness used, but can have almost any appearance.

At least one quality criterion that is to be optimized is specified, S4. Quality criteria include, for example, an effective build-up rate, a density of the workpiece to be produced, a distortion of the workpiece or other properties of the workpiece.

The architecture of the multi-spot laser device 1 is also specified, S5, for example the number of available multi-spot lasers 2, the number of single-spot lasers that may be present, information on how quickly optical elements can be switched, or information whether a steerable prism is present.

Based on the information regarding the technical features of the multi-spot laser device 1 and the quality criteria, suitable tools can be preselected, S7. Suitable periodic grids are generated on the basis of this preselection, S8. This can be a rectangular raster or another strictly periodic raster, such as a hexagonal raster or the like. However, non-periodic area subdivisions can also be chosen instead of the grid. The size of the cells of the grid can be chosen based on the passive properties, so that the total number of cells is kept small. When assessing the use of the different lasers 2 for processing a component or a construction job, the selection of the grid, for example in terms of size or type, can be initially limited to one or more values or recalculated for each layer.

Provision can also be made for the scanning direction to be rotated across the layers at an angle (for example 67°) in order to statistically distribute any defects that may occur in the components.

The areas to be exposed are compared with the periodic grid, S9. The cells of the grid are then classified, S11. For example, it can be determined that a cell of the grid is to be exposed with a multi-spot laser. A further distinction can be made as to whether it is a full surface, a partial surface, a surface with an overhang or underhang or a small periodic structure. In the case of an overhang or underhang, additional information from the layer or layers above or below is taken into account.

It can also be determined that a cell of the grid is to be exposed with a single-spot laser of the multi-spot laser device 1 . A further distinction can be made here as to whether it is a contour or a small, non-periodic structure. Furthermore, it can also be classified that the cell is a transition area, such as an intermediate contour.

A finer subdivision can be made for partial areas, for example by halving the cells. If, for example, a 1x4 spot arrangement with a correspondingly wide melting path is used for the first grid, the division of the areas for a 1x2 spot arrangement can be taken into account. When working with a higher number of spots in the main grid, a further division may be possible (e.g. first a 1x8 spot, then a 1x4 spot, then a 1x2 spot). This allows the best possible exposure strategy to be achieved, similar to a fractal approximation.

Taking into account the architecture of the multi-spot laser device 1, the optimal combination of lasers to be used with appropriate settings is calculated, S10, in order to optimize the at least one desired quality criterion. Optionally, the method is carried out recursively, ie after step S10, suitable tools are again pre-selected, S7.

Full areas or periodic small structures (approximately in the millimeter range or centimeter range) and frequently recurring non-periodic structures can be exposed with at least one multi-spot laser 2 of the multi-spot laser device 1, S6.

Sub-surfaces can be measured using an adjustable prism (such as from the DE 10 2017 200 119 A1 known) or a single spot are exposed, S12.

For smaller periodic structures, the distances between the individual spots are adjusted to the distances between the periodic structures. In this case, the movement of the scanner builds up several identical structures next to each other. As an additional possibility for a simpler calculation for frequently recurring periodic structures (e.g. support structures), there is a simplification: The support structure usually extends over a larger area (in the maximum case the entire projection area of the component on the substrate). This can be viewed as a volume and exposed with appropriate spot spacing, reducing computational effort.

Small, non-periodic contours can be processed with a single spot, S13. The same can apply to transition areas that cannot be processed in any other way. Examples can be small circular geometry elements or thin walls. Appropriate process parameters can be defined and stored in a database for these structures, which are often recurring in components.

In overhang areas, the thermal energy can be more difficult to dissipate due to the geometric conditions that differ from the volume. The process parameters can thus be adjusted accordingly in order to prevent thermal distortion. To compensate for this effect, the area to be exposed of the underlying layer or of several underlying layers can optionally be taken into account.

Overhanging contours, for example the opposite overhangs of a lying hole, can be processed in a single exposure with a beam profile optimized for this application in order to optimize the quality of the overhang.

Overall, an exposure sequence for exposing the material 5 is thus determined, S14.

The workpiece is produced by exposing the material 5 using the multi-spot laser device 1 based on the exposure sequence determined, S15.

QUOTES INCLUDED IN DESCRIPTION

This list of documents cited by the applicant was generated automatically and is included solely for the better information of the reader. The list is not part of the German patent or utility model application. The DPMA assumes no liability for any errors or omissions.

Patent Literature Cited

• DE 102017200119 A1 [0003, 0056]
• DE 102016213420 A1 [0004]

Claims (10)

Method for producing a workpiece by selective laser melting using a multi-spot laser device (1), the multi-spot laser device (1) having at least one laser (2) for generating a laser beam, and the multi-spot laser device ( 1) has a beam shaping device (3) in order to direct the laser beam onto a material (5) to be processed, wherein the beam shaping device (3) can split the laser beam into a large number of beams in order to simultaneously cast a large number of laser spots on the material (5 ), the procedure comprising the following steps: Specification (S1, S5) of information regarding technical features of the multi-spot laser device (1); Specification (S3) of information relating to surfaces (201) of the material (5) to be exposed layer by layer in order to produce the workpiece; generating (S8) at least one surface subdivision (205-207, 301) having a plurality of cells (202-204, 302-305); Classifying (S11), for each area (201) to be exposed and each area subdivision (205-207, 301), of the cells (202-204, 302-305) of the area subdivision (205-207, 301), the area subdivision (205 -207, 301) is placed over the area (201) to be exposed, and wherein the classification of the cells (202-204, 302-305) takes place depending on a degree of overlap of the area (201) to be exposed with the respective cell; Determination (S14) of an exposure sequence for exposing the material (5) to be processed by means of the multi-spot laser device (1), depending on the information regarding the technical features of the multi-spot laser device (1) and on the classification of the cells (202-204, 302-305) of the at least one area subdivision (205-207, 301) for each area (201) to be exposed; and Generating (S15) the workpiece by exposing the material (5) to be processed using the multi-spot laser device (1) based on the determined exposure sequence. procedure after claim 1 , wherein the information regarding technical features of the multi-spot laser device (1) includes at least one of technical features of the beam shaping device (3), a laser power of the at least one laser (2), an exposure type of the at least one laser (2), at least one Quality parameter of the at least one laser (2), a focal position, a distance between the laser spots and an extent of the laser spots. procedure after claim 1 or 2 , wherein a multiplicity of surface subdivisions (205-207, 301) is generated, and wherein a surface subdivision (205-207, 301) is selected (S10) to determine the exposure sequence based on an optimization criterion and the exposure sequence based on the determined surface subdivision (205-207 , 301) is determined. Method according to one of the preceding claims, wherein process parameters of the multi-spot laser device (1) for exposing the cell are determined for each cell to determine the exposure sequence for each area (201) to be exposed. procedure after claim 4 , whereby the process parameters are determined using an optimization criterion. procedure after claim 3 or 5 , wherein the optimization criterion comprises at least one of criteria relating to a precision of structures of the workpiece to be produced, criteria relating to an exposure time required to produce the workpiece and criteria relating to a density of the workpiece to be produced. Method according to one of the preceding claims, wherein the classification, for each area (201) to be exposed and each area subdivision (205-207, 301), the cells (202-204, 302-305) of the area subdivision (205-207, 301) further depending on an overhang of the area (201) to be exposed with at least one further area (201) to be exposed in a layer above the area (201) to be exposed and/or depending on an underhang of the area (201) to be exposed with at least one further surface (201) to be exposed located in a layer below the surface (201) to be exposed. Method according to one of the preceding claims, in which, in order to classify the cells (202-204, 302-305) of the area subdivision (205-207, 301), the area subdivision (205-207, 301) is used if the area to be exposed (201 ) can be divided into finer cells (202-204, 302-305) with the respective cell. Method according to one of the preceding claims, in which the at least one surface subdivision (205-207, 301) is generated as a function of the information relating to technical characteristics of the multi-spot laser device (1). Multi-spot laser device (1) for producing a workpiece by selective laser melting, having: at least one laser (2) which is designed to generate a laser beam; a beam shaping device (3) which is designed to direct the laser beam onto a material (5) to be processed, the beam shaping device (3) being further designed to split the laser beam into a large number of beams in order to simultaneously produce a large number of laser spots to direct to the material (5); and a control device (4) which is designed to: generate at least one surface subdivision (205-207, 301) with a plurality of cells (202-204, 302-305); for each area to be exposed (201) of a plurality of areas (201) to be exposed in layers and for each area subdivision (205-207, 301) the cells (202-204, 302-305) of the area subdivision (205-207, 301). classify, wherein the area subdivision (205-207, 301) is placed over the area (201) to be exposed, and wherein the classification of the cells (202-204, 302-305) depending on a degree of overlap of the area (201) to be exposed done with the respective cell; to determine an exposure sequence for exposing the material (5) to be processed, depending on information regarding technical features of the multi-spot laser device (1) and on the classification of the cells (202-204, 302-305) of the at least one surface subdivision ( 205-207, 301) for each area (201) to be exposed; and to control the at least one laser (2) and the beam shaping device (3) in order to produce the tool by exposing the material (5) to be processed using the exposure sequence determined.

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