Method of providing control data for manufacturing a workpiece by a laser powder bed fusion device, method to operate a laser powder bed fusion device, control unit, computer program and storage medium

Abstract

The invention relates to method of providing control data (11) for manufacturing a workpiece (1) by a laser powder bed fusion device (2), comprising the following steps performed by a control unit (3): evaluating a function describing a local modified mass integral value within a respective of the layers (6), the local modified mass integral value describing a local portion of a predefined reference volume (7) in a local depth within a volume of the model (4); dividing the respective layers (6) into continuous regions (9) of predefined categories based on the local modified mass integral values, wherein the categories are defined by predefined local mass integral value ranges and wherein the categories are assigned respective manufacturing parameters and exposure vectors (10); and generating control data (11) to control the laser powder bed fusion device (2) to manufacture the workpiece.

Description

[0001] 202318346 1 Description Method of providing control data for manufacturing a workpiece by a laser powder bed fusion device, method to operate a laser powder bed fusion device, control unit, computer program and storage medium The present invention relates to a method of providing con- trol data for manufacturing a workpiece by a laser powder bed fusion device, and a method to operate a laser powder bed fu- sion device to manufacture a workpiece. Furthermore the pre- sent invention relates to a corresponding control unit and a corresponding laser powder bed fusion device. Additionally, the present invention relates to a respective computer pro- gram and a respective storage medium. Laser powder bed fusion (LPBF) technology is well suited for manufacturing of complex shape structures. With this technol- ogy, overhang regions of a workpiece of angles usually lower than 45° require support structures. Support structures are light-weighted parts that typically connect the overhang re- gions with a build plate. They provide additional stability during LPBF manufacturing process. Support structures are re- moved in a post-processing and surfaces where supports were attached require additional treatment. If supports can be omitted, then the process requires less manufacturing time, requires less material and post-pro- cessing effort is reduced. It is an object of the present invention to allow a manufac- turing of a workpiece comprising overhangs with lower angles than 45° and overhangs of a larger area in a laser powder bed fusion procedure without a need for support structures. 202318346 2 This objective is achieved by the respective subject matter of the independent claims. Further implementations and pre- ferred embodiments are subject matter of the dependent claims. A first aspect of the present invention is related to a method of providing control data for manufacturing of a work- piece by a laser powder bed fusion device. The method com- prises the following steps performed by a control unit. The control data may comprise instructions for a laser powder bed fusion device to manufacture the workpiece. A first step of the method comprises a reception of the vol- ume model of the workpiece by the control unit. The volume model describes a volume of material of the workpiece to be manufactured by the laser powder bed fusion device. The vol- ume model of the workpiece may comprise a 3-D model of the workpiece and material parameters of the workpiece. The vol- ume model may be a CAD file for example. The method comprises a step of evaluating a stack of consecu- tive layers for manufacturing the workpiece based on the vol- ume model. In other words, as the workpiece is to be produced in a layer-by-layer procedure by the laser powder bed fusion device, the control unit determines the respective layers for manufacturing the workpiece and aligns them in a stack. The method comprises a step of evaluating for each of the layers a local material depth function describing a local ma- terial depth of the volume module below the respective layer by the control unit. The local material depth is limited by a predefined maximal depth. In other words, the control unit evaluates for each of the layers the material of the volume model below the respective layer. The control unit determines the local material depth of the volume model below the layer. The local material depth is limited to the predefined maximal depth. In other words, the control unit determines the local 202318346 3 material depth under the respective layer up to the prede- fined maximal depth. Therefore, the control unit ignores a portion of the material depth larger than the predefined max- imal depth. As the material depth of the volume below the layer may depend on the lateral position within the layer, the control unit evaluates the local material depth function, wherein the local material depth function assigns the respec- tive local material depth to the respective position within the layer. The method comprises a step of evaluating a function describ- ing a local modified mass integral value within the respec- tive layer. The local modified mass integral value describes a local portion of the predefined reference volume within a local depth volume of the local material depth. In other words, a predefined reference volume is given. The predefined reference volume may describe a half cavity of a specific ra- dius. The modified mass integral value describes the portion of the predefined reference volume that is covered by the lo- cal depth volume at a specific position of the layer. The method comprises a step of dividing the respective layers into continuous regions of predefined categories based on the local modified mass integral values. In other words, the lo- cal modified mass integral value may change within the re- spective layers. The respective layers are divided into the continuous regions. The regions are attributed to predefined categories. The categories are defined by predefined local mass integral value ranges. The categories are associated with respective manufacturing parameters for manufacturing the respective regions. The method comprises a step of generating control data to control the laser powder bed fusion device to manufacture the workpiece by the control unit. 202318346 4 The invention has the advantage that the control data assign respective manufacturing parameters to regions of the respec- tive workpiece depending on an overlap of the workpiece in the regions, described by the local modified mass integral values. Therefore, the method allows overhanging regions to be taken into account in the manufacturing of the workpiece. According to a further embodiment of the invention, the method comprises the following steps performed by the control unit. The method comprises a step of evaluating for each re- gion of at least one first category of the predefined catego- ries a respective exposure vector orientation according to a predefined orientation evaluation method. In other words to manufacture the workpiece, an energy beam has to be guided along the respective exposure vectors within the respective layers. Each region of the at least one of the predefined categories may comprise respective exposure vectors oriented in the same exposure vector orientation within the respective region. The orientation of the exposure vectors within the respective region may influence a quality of the material of the workpiece within the respective region. Therefore, it is an object of the orientation evaluation method to improve the quality of the respective region by investigating the expo- sure vector orientation for the respective region. The orien- tation evaluation method may be performed for each region of the first category. The orientation evaluation method may also be performed for each region of one or more other of the categories. The orientation evaluation method comprises a calculation for each candidate exposure vector orientation of the respective region an average absolute difference value describing an av- erage of absolute difference values of the exposure vectors in the region, oriented in the respective candidate exposure vector orientation. In other words, there may be several can- didate exposure vector orientations for the respective re- gion. The candidate exposure vector orientations may be pre- defined or investigated. The control unit draws the exposure 202318346 5 vectors of the respective region for each of the candidate exposure vector orientation. The control unit evaluates for each of the exposure vectors the respective mass integral value at the start point of the respective exposure vector and a mass integral value at the end point of the respective exposure vector. In a next step, the control unit calculates the absolute dif- ference value describing the absolute difference between the mass integral value at the start point of the respective ex- posure vector and the endpoint of the respective exposure vector. In a next step, the control unit determines the aver- age absolute difference value describing the average of the absolute difference values of the exposure vectors in the re- gion of the respective candidate exposure vector orientation. In a next step, the control unit compares the average abso- lute difference values evaluated for the respective candidate exposure vector orientations of the region. A next step comprises a selecting of the respective exposure vector orientation for the respective region out of the can- didate exposure vector orientations depending on the average absolute difference values calculated for the respective can- didate exposure vector orientations. In other words, the ex- posure vector orientation for the respective region is se- lected as a function of the average absolute difference value. The selection may be performed by the control unit by choosing the candidate exposure vector orientation giving the highest absolute difference value. According to a further embodiment of the invention, the ori- entation evaluation method comprises a step of evaluating the respective exposure vector orientation of an underlying re- gion of an underlying layer of the region. In other words, the control unit may evaluate the respective exposure vector orientations of the regions layer by layer. Therefore, the region in a respective layer may be above an underlying re- gion in an underlying layer. A quality of the workpiece may 202318346 6 depend on a relation between the exposure vector orientation of the underlying layer and the layer above the underlying layer. In particular, a uniform orientation of the exposure vectors of superimposed regions may lead to a decrease in stability. It may be necessary to select the exposure vector orienta- tions of stacked regions so that they are different in order to improve the quality of the part. Therefore, the respective exposure vector orientation of the respective region above the underlying region is selected as a function of the expo- sure vector orientation of the underlying region. For that reason, the control unit limits the candidate expo- sure vector orientations of the respective region to those having an orientation difference above a predefined orienta- tion difference value with respect to the respective exposure vector orientation of the underlying region. In other words, only candidate exposure vector orientations are analysed dur- ing the orientation evaluation method that have the orienta- tion difference to the respective exposure vector orientation of the underlying region above the predefined orientation difference value. The predefined orientation difference value may be 45°. According to a further embodiment of the invention, the ori- entation evaluation method comprises a step of calculating for each region of at least a second category a maximum value of an onset exposure vector of an exposure sequence. The max- imum value gives a maximum of the mass integral value at the start point of the respective onset exposure vector and the mass integral value at the end point of the respective onset exposure vector. The exposure sequence sets the chronological order in which the exposure vectors are illuminated during manufacturing. The exposure sequence starts with the onset exposure vector. 202318346 7 The method comprises a step of performing for each region having the onset exposure vector with a maximum value below a threshold value a predefined reordering algorithm for evalu- ating a new exposure sequence. The reordering algorithm comprises a step of calculating the maximum values of the exposure vectors of the exposure se- quence. If at least one of the exposure vectors of the exposure se- quence has a maximum value above the threshold value, a first of the respective exposure vectors according to the exposure sequence is defined as a new onset exposure vector of the new exposure sequence. Otherwise the exposure vector of the highest maximum value is defined as the new onset exposure vector of the new exposure sequence. According to a further embodiment of the invention, the method comprises a step of evaluating for each of the expo- sure vectors of the region of at least a third category of the categories, the respective mass integral value along the respective exposure vector. The method comprises a step of evaluating manufacturing pa- rameters along the exposure vectors depending on the respec- tive mass integral value along the respective exposure vec- tor. The step of evaluating manufacturing parameters along the exposure vectors may also be performed on exposure vec- tors of the regions of the second category of the categories. According to a further embodiment of the invention, the method comprises a step of removing contours of the regions of at least a fourth category of the categories from the lay- ers. In other words, the contours of the regions of at least the fourth category are deleted. It may not be possible to produce the contours of the regions in a stable manner. For that reason, the control data for the laser powder bed fusion 202318346 8 device to manufacture the respective regions are generated for the respective region without a part of the region com- prising the contour. The contour may comprise grid points of the region of a local modified mass integral value below a predefined threshold. . According to a further embodiment of the invention, the func- tion describing a local modified mass integral value within the respective of the layers is a pattern comprising grid points. As second aspect of the present invention relates to a method to operate a laser powder bed fusion device to manufacture a workpiece. The method to operate a laser powder bed fusion device com- prises steps of a method of providing control data for manu- facturing a workpiece by a laser powder bed fusion device ac- cording to the first aspect of the present invention. The method to operate a laser powder bed fusion device com- prises a step of providing the control data to the laser pow- der bed fusion device by the control unit to control the la- ser powder bed fusion device to manufacture the workpiece. For use cases or use situations which may arise in the meth- ods and which are not explicitly described here, it may be provided that, in accordance with the methods, an error mes- sage and / or a prompt for user feedback is output and / or a de- fault setting and / or a predetermined initial state is set. A third aspect of the present invention relates to a control unit. The control unit is configured to perform a method of providing control data for manufacturing a workpiece by a la- ser powder bed fusion device according to the first aspect of the present invention and / or to perform a method for provid- ing the control data to the laser powder bed fusion device to control the laser powder bed fusion device to manufacture the 202318346 9 workpiece according to the second aspect of the present in- vention. A fourth aspect of the present invention relates to a laser powder bed fusion device, configured to manufacture a work- piece. The laser powder bed fusion device comprises a control unit according to the third aspect of the present invention. A fifth aspect of the invention is related to a computer pro- gram product comprising program code for performing a method according to the first aspect and / or the second aspect. The computer program product may also be regarded to a computer program. A sixth aspect of the invention is related to a computer- readable storage medium comprising at least the computer pro- gram product according to the fifth aspect. The control unit may comprise a computing unit. A computing unit may in particular be understood as a data processing de- vice, which comprises processing circuitry. The computing unit may therefore in particular process data to perform com- puting operations. This may also include operations to per- form indexed accesses to a data structure, for example a look-up table, LUT. In particular, the computing unit may include one or more computers, one or more microcontrollers, and / or one or more integrated circuits, for example, one or more application- specific integrated circuits, ASIC, one or more field-pro- grammable gate arrays, FPGA, and / or one or more systems on a chip, SoC. The computing unit may also include one or more processors, for example one or more microprocessors, one or more central processing units, CPU, one or more graphics pro- cessing units, GPU, and / or one or more signal processors, in particular one or more digital signal processors, DSP. The computing unit may also include a physical or a virtual clus- ter of computers or other of said units. 202318346 10 In various embodiments, the computing unit includes one or more hardware and / or software interfaces and / or one or more memory units. A memory unit may be implemented as a volatile data memory, for example a dynamic random access memory, DRAM, or a static random access memory, SRAM, or as a non-volatile data memory, for example a read-only memory, ROM, a programmable read-only memory, PROM, an erasable read-only memory, EPROM, an elec- trically erasable read-only memory, EEPROM, a flash memory or flash EEPROM, a ferroelectric random access memory, FRAM, a magnetoresistive random access memory, MRAM, or a phase- change random access memory, PCRAM. Further features of the invention are apparent from the claims, the figures and the figure description. The features and combinations of features mentioned above in the descrip- tion as well as the features and combinations of features mentioned below in the description of figures and / or shown in the figures may be comprised by the invention not only in the respective combination stated, but also in other combina- tions. In particular, embodiments and combinations of fea- tures, which do not have all the features of an originally formulated claim, are also comprised by the invention. Moreo- ver, embodiments and combinations of features which go beyond or deviate from the combinations of features set forth in the recitations of the claims are comprised by the invention. Independent of the grammatical term usage, individuals with male, female or other gender identities are included within the term. In the following, the invention will be explained in detail with reference to specific exemplary implementations and re- spective schematic drawings. In the drawings, identical or functionally identical elements may be denoted by the same reference signs. The description of identical or functionally 202318346 11 identical elements is not necessarily repeated with respect to different figures. In the figures FIG 1 shows a schematic illustration of a method to oper- ate a laser powder bed fusion device to manufacture a workpiece; FIG 2 shows a schematic illustration of a model of the workpiece separated into a stack of layers; FIG 3 shows a schematic illustration of reference vol- umes; FIG 4 shows a schematic illustration of regions within a layer; FIG 5 shows a schematic illustration of exposure vectors in a region; FIG 6 shows a schematic illustration of vector grid points along an exposure vector; and FIG 7 shows a schematic illustration of the vector of FIG 6 divided in three vectors. FIG 1 shows a schematic illustration of a method to operate a laser powder bed fusion device to manufacture a workpiece. The method to operate the laser powder bed fusion device 2 may comprise steps of a method of providing control data 11 for manufacturing a workpiece 1 by the laser powder bed fu- sion device 2. A first step S1 of the method may comprise a reception of a volume model 4 of the workpiece 1 by a control unit 3. The volume model 4 may describe a volume of a material of the 202318346 12 workpiece 1 to be manufactured by the laser powder bed fusion device 2. The volume model 4 may be a CAD file defining the workpiece 1. A second step S2 of the method may comprise an evaluation of a stack 5 of consecutive layers 6 for manufacturing the work- piece 1 based on the volume model 4 by the control unit 3. The layers 6 may define a deposition of material in a plane of the workpiece 1 in an additive manufacturing procedure for manufacturing the workpiece 1 by the laser powder bed fusion device 2. A stack 5 orientation of the stack 5 of layers 6 may depend on a geometry of the volume model 4. A third step S3, a fourth step S4 and a fifth step S5 may re- late to a separation of the layers 6 into regions 9 of dif- ferent modified mass integral values. The next steps may also refer to FIG 3. In the third step S3 of the method, the control unit 3 may evaluate for each of the layers 6 a local material depth function describing a local material depth of the volume model 4 below the respective layer 6. The local material depth may be limited to a predefined maximum depth. In other words, the control unit 3 determines the depth of the volume model 4 beneath the respective layers 6. It may be possible that the local material depth is only relevant up to the pre- defined maximum depth. Therefore the maximum possible local material depth of the volume model 4 may be the predefined maximum depth. The fourth step S4 of the method may comprise an evaluation of a function describing a local modified mass integral value within a respective one of the layers 6. The local modified mass integral value may describe a local proportion of a pre- defined reference volume 7 within a local depth volume of the local material depth. The local modified mass integral value may be calculated for grid points 12 of a regular grid within the respective layers 6. In other words, the control unit 3 202318346 13 may generate for each of the layers 6 the respective regular grid. The respective regular grid may comprise the grid points 12 of a regular grid distance of 0.1 mm. The control unit 3 may calculate the local modified mass integral value for each of the grid points 12 of the regular grid. In other words, for each layer 6 an interior of the workpiece 1 may be covered by the regular grid points 12. An example of one of the layers 6 for manufacturing the workpiece 1 part is shown in FIG 2. Typically, a regular distance of 0.1 mm is chosen for the grid of the grid points 12. For each of the grid points 12, the modified mass integral may be evaluated. The modified mass integral is shift into the local material depth ^^ௗ^^௧^. The local material depth ofgrid point ^^^,^^, ^^^ may be limited to the maximal depth ^^^^௫ andmay be defined by The local material depth value gives a distance of downwards material that contribute to the workpiece 1. The modifiedmass integral value for the grid point with coordinates^^^, ^^, ^^^ may be evaluated as The modified mass integral value may determine how much of the predefined reference volume 7 which may be a halfsphere of a predefined radius ^^^^௧is enclosed in the model 4 in lo- cal depth ^^ௗ^^௧^. The values of ^^^^௧and ^^^^௫may be chosen empirically. The values ^^^^௧= 0.7 mm and ^^^^௫= 2 mm may be possible selections. 202318346 14 Alternatively, other convolutional kernels in the local mate- rial depth ^^ௗ^^௧^may be used as the predefined reference vol- ume 7 besides the halfsphere described above. For example, cylindrical or half-ellipsoidal forms are also well suited. Other shapes such as ellipsoid and cylinder can be also ap- plied as the predefined reference volume 7. Possible formulas for the mass integral of the ellipsoidal predefined reference volume 7 and the cylindrical predefined reference volume 7 are stated below: The fifth step S5 of the method may comprise a division of the respective layers 6 into continuous regions 9 of prede- fined categories based on the local modified mass integral value within the respective layers 6. The categories are de- fined by predefined local modified mass integral value ranges. A stable manufacturing of the regions 9 may require manufacturing parameters adjusted to the local modified mass integral values. Therefore, the categories are assigned re- spective manufacturing parameters. In other words, for manu- facturing the respective layer 6, the respective layer 6 may be divided into lateral regions 9. Each of the regions 9 may be assigned to a respective of the categories. The categories define the manufacturing parameters to manufacture the re- spective regions 9 by the laser powder bed fusion device 2. The category of the respective region 9 is selected based on the local modified mass integral values of the grid points 12 of the region 9. In other words, after evaluation of the local modified massintegral values ^^^^^^^^ௗ^^௧^^^^,^^, ^^^ for each layer 6, one or multi-ple threshold values ^^^^௧of the modified mass integral values may be selected. The threshold values ^^^^௧may define the 202318346 15 ranges of the categories. The layers 6 of the workpiece 1 may then be separated into the regions 9 accordingly to the dif- ferent ^^^^௧values. FIG 4 shows an example of a separation of one of the layers 6 in two of the regions 9. One of the two regions 9 may comprise grid points 12 of local modified massintegral values above a threshold ^^^^^^^^ௗ^^௧^ > ^^^^௧ . The other ofthe two regions 9 may comprise grid points 12 of the localmodified mass integral values below or equal to the threshold^^^^^^^^ௗ^^௧^ ≤ ^^^^௧.A reasonable choice of threshold values from experiments may be between ^^^^௧=0.25 to ^^^^௧=0.1. The identified regions 9 may be assigned respective, different manufacturing parameters. The regions 9 with low ^^^^^^^^ௗ^^௧^values correspond to low- pitched overhangs of the model 4. These regions 9 are typi- cally assigned manufacturing parameters comprising a lower laser power in combination with a smaller hatch distance and / or shorter pauses between the exposition of the exposure vectors 10. A small overlap between the regions 9, for exam- ple 0.1 mm to 0.3 mm may be intended. Regions 9 of higher modified mass integral values may be exposed first, followed by the regions 9 with lower modified mass integral values. A sixth step S6 of the method may comprise a removing of con- tours of regions 9 of the at least a fourth category from the layers 6. In other words, the categories comprise a fourth category associated with grid points 12 having the local mod- ified mass integral values below a predefined fourth thresh- old. The modified local mass integral values below the prede- fined fourth threshold may be too low to allow a stable manu- facturing of the contours of the specific regions 9. There- fore, the respective regions 9 may be deleted. In other words, contours of the very low mass regions 9 below a prede- fined threshold may advised to be skipped in most cases. The steps S7 to S9 may be related to a choice of an optimal exposure vector 10 orientation for at least the regions 9 of a first category. 202318346 16 In the seventh step S7 of the method, the control unit 3 may evaluate for each region 9 of at least the first category the respective exposure vector 10 orientation according to a pre- defined orientation evaluation method. In other words, the regions 9 are manufactured by guiding an energy beam along the exposure vectors 10 within the regions 9. The exposure vectors 10 of the respective region 9 may be oriented in a respective exposure vector 10 orientation of the respective region 9. The exposure vector 10 orientation of the exposure vectors 10 of the respective region 9 may influence a quality of the respective region 9. Therefore, the exposure vector 10 orientations of the regions 9 of at least the first category may be evaluated using the predefined orientation evaluation method. In other words, for every isolated region 9 of at least the first category associated with a low modified mass integralvalue (^^^^^^^^ௗ^^௧^ ≤ ^^^^௧) below a first threshold value the opti-mal exposure vectors 10 orientation may be evaluated. Expo- sure vectors 10 orientations of regions 9 of other categories may be selected using standard layer 6 to layer 6 rotation methods. In order to find the optimal hatch vectors 10 orien- tation of the region 9, different angles may be compared. It may be possible to evaluate candidate exposure vector 10 ori- entations which may differ by 5° or 10°. As an example, forevery region 9 360° / 5° = 72 or 360° / 10° = 36 different candidateexposure vector 10 orientations may be compared. For the se- lected exposure vector 10 orientation, the region 9 may be hatched using a standard zig-zag exposure vector 10 technique according to the state of the art. An example of hatched re- gion 9 is shown in FIG 5. The standard mass integral valuewith ^^ௗ^^௧^ = 0 may be calculated for the start point and theend point of each exposure vector 10. For comparison, the av-erage of absolute values of the differences may be taken 202318346 17 The candidate exposure vector 10 orientation whose average value ^^^^^^^௧is maximal may be chosen as the exposure vector 10 orientation of the region 9. It means that with this expo- sure vector 10 orientation, a majority of the exposure vec- tors 10 start or end at points of a higher standard mass in- tegral value. Additionally, consecutive layer 6 regions 9 should have suf- ficiently different exposure vector 10 orientations to aver- age out orientation dependent effects as e.g., surface corru- gation. Therefore, if the optimal exposure vector 10 orienta- tion may differs by less than 45° from the previous layer 6 region 9, than the candidate exposure vector 10 orientation with a maximal ^^^^^^^௧value may be chosen only from candidate exposure vector 10 orientations that are different enough from the exposure vector 10 orientation of the region 9 of the previous layer 6. The eighth step S8 of the method may comprise a calculation for each candidate exposure vector 10 orientation of the re- spective region 9 an average absolute difference value de- scribing an average of an absolute difference value of the exposure vectors 10 in the region 9 oriented in the respec- tive candidate exposure vector 10 orientation. In other words, there may be multiple candidate exposure vector 10 orientations for the respective region 9. A group of candi- date exposure vector 10 orientations of the respective region 9 may depend on the exposure vector 10 orientation of one or more regions 9 below the respective region 9. In other words, only candidate exposure vector 10 orientations may be used, having an orientation difference above a predefined differ- ence value with respect to the exposure vector 10 orientation of the region 9 below the respective region 9. In order to select the exposure vector 10 orientation of the respective region 9 from the candidate exposure vector 10 orientations, the control unit 3 may calculate the respective average absolute difference value for each of the candidate 202318346 18 exposure vector 10 orientations. The control unit 3 may ar- range the exposure vectors 10 of the respective candidate ex- posure vector 10 orientation in the respective region 9. Each of the candidate exposure vectors 10 may have a start point and a respective end point. The control unit 3 may calculate the modified mass integral value for the start point of the respective exposure vector 10 and the end point of the re- spective exposure vector 10. In a next step, the control unit 3 may calculate the absolute difference value, defining the absolute difference between the modified mass integral value at the start point of the respective exposure vector 10 and the endpoint of the respective exposure vector 10. Each of the exposure vectors 10 may have a respective absolute dif- ference value. In a next step, the control unit 3 may calcu- late the average absolute difference value giving the average of the absolute difference values of the exposure vectors 10. The ninth step S9 of the method may comprise a selection of the respective exposure vector 10 orientation for the respec- tive region 9 out of the candidate exposure vector 10 orien- tations depending on the average absolute difference values calculated for the respective candidate exposure vector 10 orientations. As an example, the control unit 3 may select the exposure vector 10 orientation having a biggest average absolute difference value as the exposure vector 10 orienta- tion of the respective region 9. The steps S10 to S13 may relate to a resorting of the expo- sure vectors 10 in the regions 9 of at least a second cate- gory according to maximum mass integral values. A tenth step S10 of the method may comprise a calculation for each region 9 of at least a second category a maximum value of an onset exposure vector 10 of an exposure sequence. The maximum value gives a maximum of the mass integral value at the start point of the respective onset exposure vector 10 and the mass integral value at the end point of the respec- tive onset exposure vector 10. In other words, to manufacture 202318346 19 the respective region 9, the control unit 3 may generate an exposure sequence describing the sequence of the exposure vectors 10 during the manufacturing. The exposure sequence may be determined according to a standard method. However, the exposure sequence may be replaced by a new exposure se- quence. A need to replace the exposure sequence with a new exposure sequence may depend on the maximum value of the on- set exposure vector 10. An eleventh step S11 may comprise performing for each region 9 having an onset exposure vector 10 with the maximum value below a predefined threshold value, a predefined reordering algorithm for evaluating the new exposure sequence. In a twelfth step S12 the control unit 3 may calculate the maximum values of the other exposure vectors 10 of the expo- sure sequence. In a thirteenth step S13, if at least one of the exposure vectors 10 of the sequence has a maximum value above the threshold value, the control unit 3 may define a first of the respective exposure vectors 10 according to an order of the exposure sequence as a new onset exposure vector 10 of the new exposure sequence. Otherwise the control unit 3 may define the exposure vector 10 of the highest maximum value as the onset exposure vector 10 of the new exposure sequence. In other words, a reordering algorithm for exposure vectors 10 is introduced, since even with the optimal exposure vector 10 orientation and the exposure vectors 10 as described above, it may still happen that the exposure of a respective one of the exposure vectors 10 starts at an inappropriate point in the layer 6 with a very low modified mass integral value. Similar to step S8, the standard mass integral values(with ^^ௗ^^௧^ = 0) for the start point and the end point of the 202318346 20 respective exposure vector 10 may be used. The maximum of these two values may be evaluated as where ^^ is the serial number of the exposure vector 10 in the hatch. An exposure vector 10 enumeration of the region 9 maybegin with ^^ = 0. If the maximal valuemax^^ூ^௧ < ^^௩of the first exposure vector 10 is below a chosen threshold^^௩, then an attempt to find another exposure vector 10 forhatching start will be made. A value for the threshold ^^௩may be 0.25 or above. If the region 9 has been defined beforewith ^^^^௧ < 0.25, then the threshold value ^^௩ = ^^^^௧ may be taken.If the above condition is false, no reordering is required. Otherwise, the exposure vectors 10 from the region 9 may be proved consecutively until a false condition for the exposure vector 10 of some index ^^^^௪is found. If no exposure vector10 with max^^ூ^௧ ≥ ^^௩ is found, then ^^^^௪ may chosen as the ex-posure vector 10 with max (max^^ூ ). The new onset exposure ^^௧vector 10 ^^^^௪may start the new hatch exposure vectors 10 or- der, defined by the exposure sequence. The following exposurevectors 10 ^^^^௪ + 1, ^^^^௪ + 2, … may be exposed in succession. Andafterwards the exposure vectors 10 in reverse order ^^^^௪ −1, ^^^^௪ − 2,… may be exposed. Effectively, exposure vectors 10with critically low start / end-point masses may be exposed in a decreasing mass order. The next steps may relate to a tuning of exposure parameters and / or vector 10 splitting according to the mass integral value along the respective exposure vector 10. The steps may serve to refine the laser powder bed fusion process parameter selection. A regular vector 10 grid may be 202318346 21 applied to each of the exposure vectors 10, covering its be- ginning and end. Similar to the grid of grid points 12 a rea- sonable choice for the vector 10 grid step size may be 0.1 mm. An example is shown in FIG 6. The standard mass integral values may be evaluated for each vector 10 grid point. One possible tuning of the exposure pa- rameters is to assign a continuous function that reduces la- ser power according to the mass integral values. Another pos- sibility is to split the respective exposure vector 10 into several vectors 10 according to sections of different mass integral thresholds. A fourteenth step S14 of the method may comprises an evalua- tion for each of the exposure vectors 10 of the region 9 of a third category the respective mass integral value along the respective exposure vector 10. Therefore the control unit 3 may arrange a regular vector 10 grid of vector grid points 13 along each of the exposure vectors 10. A fifteenth step S15 of the method comprises an evaluation of manufacturing parameters along the exposure vectors 10 de- pending on the respective mass integral value along the re- spective exposure vector 10. In other words, the control unit 3 may change the manufacturing parameters along the exposure vectors 10. A sixteenth step S16 of the method may comprise a generation of control data 11 to control the laser powder bed fusion de- vice 2 to manufacture the workpiece 1. In other words the control unit 3 may generate the control data 11 necessary to manufacture the workpiece 1 by the manufacture device. A seventeenth step S17 of the method may comprise a provision of the control data 11 to the laser powder bed fusion device 2 by the control unit 3 to control the laser powder bed fu- sion device 2 to manufacture of the workpiece 1. 202318346 22 An eighteenth step S18 of the method may comprise a manufac- turing of the workpiece 1 by the laser powder bed fusion de- vice 2. Note that a respective one of the procedures may be used sep- arately or combined with at least another one of the proce- dures. The respective procedures alone may also improve laser powder bed fusion manufacturing process. With the method described above, overhang regions 9 of low angles may be manufactured without supports. Long overhangs of 17.5° can be built with Inconel 718 material. In compari- son, standard techniques led to crash in the manufacturing. FIG 2 shows a schematic illustration of a model 4 of the workpiece separated into a stack 5 of layers 6. The stack 5 of layers 6 may be a sequence of layers 6 aligned in parallel and separated by appropriate distances. The fig- ure shows one of the layers 6 which may be placed on top of other layers 6. A portion of the layer 6 within the model 4 may have a regular grid of grid points 12. The grid points 12 may be separated by a grid spacing. For each of the grid points 12, the control unit 3 may evaluate the respective modified mass integral value. The evaluation of the respec- tive modified mass integral values is shown in FIG 3. FIG 3 shows a schematic illustration of reference volume 7s. FIG 3 shows a cross section of the model 4. A depth of the model 4 below the layer 6 surface may increase in an x-direc- tion. Therefore the two grid points 12 may have different lo- cal depths ^^ௗ^^௧^giving the depth of the model 4 below the grid point. The local depth ^^ௗ^^௧^may be limited to the maxi- mum depth ^^^^௫, as volume below the maximum depth ^^^^௫may ne- glected. The reference volumes 7 may be half spheres, wherein each of the reference volumes 7 may have a centerpoint 8 be- low a respective one of the grid points 12 in the local depth 202318346 23 ^^ௗ^^௧^. The reference volumes 7 may have a radius ^^^^௧around the centerpoint 8. The modified mass integral value for therespective grid point with coordinate (^^, ^^, ^^) may be evaluatedas It gives how much of the reference volume 7 of radius ^^^^௧isenclosed in the model 4 of the workpiece 1 in local depth^^ௗ^^௧^. The values of ^^^^௧ and ^^^^௫ may be chosen empiri-cally. The values ^^^^௧= 0.7 mm and ^^^^௫= 2 mm have proven to be a good selection. FIG 4 shows a schematic illustration of regions 9 within a layer 6. The workpiece 1 may be separated into regions 9. The two re- gions 9 may correspond to different categories. The respec- tive grid points 12 may be assigned to one of the two regions9 depending on the respective modified mass integral values^^^^^^^^ௗ^^௧^. The workpiece 1 may be separated into two regions 9by a threshold value ^^^^௧ of the modified mass integral value^^^^^^^^ௗ^^௧^, seperating the ranges of the two categories. FIG 4shows an example of separation in the two regions 9 whereingrid points 12 of ^^^^^^^^ௗ^^௧^ > ^^^^௧ are assigned to one of the re-gions 9 and grid points 12 of ^^^^^^^^ௗ^^௧^ ≤ ^^^^௧ to the other ofthe two regions 9. The region 9 with grid points 12^^^^^^^^ௗ^^௧^ ≤ ^^^^௧ may be close to a border of the model 4. Thelower modified mass integral values ^^^^^^^^ௗ^^௧^of the region 9 may be associated with steep borders of the workpiece 1. Theregion 9 with the lower modified mass integral values^^^^^^^^ௗ^^௧^ correspond to low-pitched overhangs. These regions 9are typically assigned with lower laser power in combination with smaller hatch distance and / or pauses between exposure vectors 10. It may be intended to define a small overlap be- tween the two regions 9 of 0.1 mm to 0.3 mm. 202318346 24 FIG 5 shows a schematic illustration of exposure vectors 10 in a region FIG 5 shows the exposure vectors 10, also called hatch vec- tors 10, for the region 9 of FIG. 4 having the lower modified mass integral values ^^^^^^^^ௗ^^௧^. FIG 6 shows a schematic illustration of vector grid points 13 along an exposure vector 10. The control unit 3 may arrange vector grid points 13 along each of the exposure vectors 10. The Control unit 3 may cal- culate the modified mass integral values ^^^^^^^^ௗ^^௧^for each of the vector grid points 13. The control unit 3 may change man- ufacturing parameters along the exposure vector 10 as a func- tion of the modified mass integral values ^^^^^^^^ௗ^^௧^along the exposure vector 10. FIG 7 shows a schematic illustration of the vector 10 of FIG 6 divided in three vectors 10. The control unit 3 may divide the exposure vector 10 of FIG 6 into shorter exposure vectors 10, wherein each of the vectors 10 may comprise vector 10 grid points of a similar modified mass integral value ^^^^^^^^ௗ^^௧^.

[0002] 202318346 25 Reference signs 1 workpiece 2 laser powder bed fusion device 3 control unit 4 model 5 stack 6 layer 7 reference volume 8 centerpoint 9 region 10 exposure vector 11 control data 12 grid point 13 vector grid point

Claims

202318346 26 Claims 1. Method of providing control data (11) for manufacturing a workpiece (1) by a laser powder bed fusion device (2), com- prising the following steps performed by a control unit (3): - receiving a volume model (4) of the workpiece (1), the vol- ume model (4) describing a volume of material of the work- piece (1) to be manufactured by the laser powder bed fusion device (2); - evaluating a stack (5) of consecutive layers (6) for manu- facturing the workpiece (1) based on the volume model (4); - evaluating for each of the layers (6) a local material depth function describing a local material depth of the vol- ume model (4) below the respective layer (6), wherein the lo- cal material depth is limited to a predefined maximal depth; - evaluating a function describing a local modified mass in- tegral value within a respective of the layers (6), the local modified mass integral value describing a local portion of a predefined reference volume (7) in a local depth within a volume of the model (4); - dividing the respective layers (6) into continuous regions (9) of predefined categories based on the local modified mass integral values, wherein the categories are defined by prede- fined local mass integral value ranges and wherein the cate- gories are assigned respective manufacturing parameters and exposure vectors (10); and - generating control data (11) to control the laser powder bed fusion device (2) to manufacture the workpiece (1).

2. Method according to claim 1, comprising the following steps performed by the control unit (3): - evaluating for each region (9) of at least one first cate- gory a respective exposure vector (10) orientation according to a predefined orientation evaluation method, the orienta- tion evaluation method comprising the steps of:202318346 27 - calculating for each candidate exposure vector (10) orien- tation of the respective region (9) an average absolute dif- ference value describing an average of absolute difference values of the exposure vectors (10) in the region (9) ori- ented in the respective candidate exposure vector (10) orien- tation; wherein the absolute difference value of the exposure vector (10) describes an absolute difference between a mass integral value at a start point of the respective exposure vector (10) and a mass integral value at an end of the respective expo- sure vector (10); and - selecting the respective exposure vector (10) orientation for the respective region (9) out of the candidates depending on the average absolute difference values calculated for the respective candidate exposure vector (10) orientations.

3. Method according to claim 2, the orientation evaluation method comprising the following steps of: - evaluating the respective exposure vector (10) orientation of an underlying region (9) of an underlying layer (6) of the respective region (9); - limiting the candidate exposure vector (10) orientations of the respective region (9) to those having an orientation dif- ference above a predefined orientation difference value with respect to the respective exposure vector (10) orientation of the underlying region (9).

4. Method according to claim 1 to 3 the orientation evaluation method comprising the following steps of: - calculating for each region (9) of at least one second cat- egory a maximum value of an onset exposure vector (10) of an exposure sequence with a predefined threshold value, the max- imum value giving a maximum of the mass integral value at the start point of the respective exposure vector (10) and the mass integral value at the end point of the respective expo- sure vector (10);202318346 28 - performing for each region (9) of the at least one category having an onset exposure vector (10) with a maximum value be- low the threshold value a predefined reordering algorithm for evaluating a new exposure sequence, the reordering algorithm comprising the steps of: - calculating the maximum values of the exposure vectors (10) of the exposure sequence; - if at least one of the exposure vectors (10) of the se- quence has a maximum value above the threshold value, defin- ing a first of the respective exposure vectors (10) according to the sequence as an onset exposure vector (10) of the new exposure sequence; and otherwise - defining the exposure vectors (10) of the highest maximum value as the onset exposure vector (10) of the new exposure sequence.

5. Method according to any one of the preceding claims comprising the following steps performed by the control unit (3): - evaluating for each of the exposure vectors (10) of at least one third category, the respective mass integral value along the respective exposure vector (10); and - evaluating manufacturing parameters along the exposure vec- tors (10) depending on the respective mass integral value along the respective exposure vector (10).

6. Method according to any one of the preceding claims, comprising the following steps performed by the control unit (3): - removing contours of regions (9) of at least one fourth category of the categories from the layers (6).

7. Method according to any one of the preceding claims, wherein the function describing a local modified mass inte- gral value within the respective of the layers (6) is a pat- tern comprising grid points (12).202318346 29 8. Method to operate a laser powder bed fusion device (2) to manufacture a workpiece (1), comprising: - the steps of a method according to any one of the preceding claims; and - Provision of the control data (11) to the laser powder bed fusion device (2) by the control unit (3) to control the la- ser powder bed fusion device (2) to manufacture the workpiece (1).

9. Control unit (3), configured to perform a method according to any one of the claims 1 to 7 or according to a method ac- cording to claim 8.

10. Laser powder bed fusion device (2), configured to manu- facture a workpiece (1), comprising a control unit (3) ac- cording to claim 9.

11. Computer program which is directly loadable into a memory of a computing device, comprising program means for executing the steps of the method according to any one of the claims 1 to 7 and / or to perform a method according to claim 8 when the program is executed in the electronic computing device.

12. Storage medium having electronically readable control in- formation stored on it comprising at least one computer pro- gram according to claim 11 and configured to perform a method according to any one of the claims 1 to 7 and / or to perform a method according to claim 8 when the storage medium is used in a computing device.

Images