EP3582914A1 - Method for powder-bed-based additive manufacture of a workpiece, method for producing correction parameters for said first method and computer program product for said second method - Google Patents

Abstract

The invention relates to a method for manufacturing a workpiece (19) in an additive manufacturing plant (11) in a powder bed (13). In this context, critical overheating of the generated molten bath can occur in component areas where there is little component volume of the already manufactured component available underneath a beam of energy (17). In order to prevent this, the invention proposes that a contour function (gcf) takes into account the component (19) located underneath the position (25) to be manufactured. Correction parameters (vf) which reduce the quantity of introduced energy of the beam of energy (17) in order to prevent overheating of the molten bath can be derived therefrom. The invention also relates to a method for determining a contour function (gcf) or for producing correction parameters of a correction function (vf) and computer program products (26, 27) with which the above-mentioned methods can be carried out.

Description

description

A method for powder bed-based additive manufacturing of a workpiece, method for establishing correction parameters for the former method and computer program product for the second-mentioned method

The invention relates to a method for powder bed-based additive manufacturing of a workpiece, wherein the workpiece is produced layer by layer in a powder bed, wherein the respective uppermost layer of the powder bed is solidified for producing the workpiece by an energy beam. Moreover, the invention relates to a method for creating a contour function for use in the aforementioned method. Furthermore, the invention relates to a method for generating correction parameters for a correction function relating to process parameters of the additive manufacturing method for use in the first-mentioned method. Furthermore, the invention relates to a computer program product for creating a contour function and a computer program product for Erstel ^¬ len of correction parameters for a correction function.

A method for the additive production of a workpiece in a powder bed is described in DE 10 2015 205 316. Thereafter, a workpiece in a powder bed is prepared by melting the powder by a laser beam. This can be problematic for certain materials, such as nickel-base superalloys, because the high cooling rates in the molten bath of the laser can lead to stresses in the component and to formation of an undesirable metallic structure. As a countermeasure, it is proposed that the powder bed be preheated by means of a heater, so that the temperature difference of the powder and the already produced component is lower compared to the molten bath and so the cooling rate can be reduced. According to US 2016/0332379 Al it is proposed that at ^¬ play, the introduced by the amount of laser energy can be adapted to a laser sintering, by the duration of a preceding solidification step of the preceding position is taken into account, at least in a partial region of the produced layer to the energy input in to determine the current situation. Here, a correction factor is determined, which takes into account how high the energy input in pre ^¬ forth positions of the component already produced. This is intended to counteract unwanted component distortion who ^¬ .

A further possibility according to WO 2016/049621 A1 is that a preheating of the currently to be solidified La ge can be accomplished by an external energy source. Here, a required heat profile of the ver ^¬ consolidating layer is calculated, in which case subsequent layers still to be produced can be taken into account. Procedures are to be understood as powder bed additive manufacturing method based in the sense of this application, in which the material from which a workpiece is to be prepared, is the workpiece during the formation of layer-wise added ^¬. In this case, the workpiece is already in its final shape or at least approximately in this Ge ^¬ stalt by solidification of the workpiece defining contours in the powder bed.

In order to be able to produce the workpiece, the workpiece becomes descriptive data (CAD model) for the selected additive

Production process processed. The data is converted to data of the workpiece adapted to the manufacturing process to produce instructions for the manufacturing plant so that the appropriate process steps for the successive production of the workpiece can take place in the production plant.

The data are processed in such a way that the geometric data for the contour of the layers to be produced in each case (FIG. ces) of the workpiece are available, which is also referred to as slicing.

As examples of additive manufacturing, selective laser melting (also known as SLM for selective laser melting) and electron beam melting (also known as EBM for electron beam

Melting). These processes are particularly suitable for processing metallic materials in the form of powders, with which structural components can be produced.

The starting point for carrying out an additive Ferti ^¬ off procedure is a description of the workpiece in a geometry data set, for example as STL file (STL stands for Standard Tessellation Language). The STL file contains the three-dimensional data for preparation by the additive manufacturing process. The STL file is used to generate a production data record, for example a CLI file (CLI stands for Common Layer Interface), which contains a preparation of the geometry of the workpiece in the contour describing disks (so-called slices) which is suitable for additive production. The transformation of the data is called slicing. The result of the slicing is that the layers of the workpiece to be produced with a certain z-height, z. B. 50 ym, ^{¬ are} permitted. This means that when a workpiece, wel ^¬ ches, for example, 100 mm high, 2,000 workpiece layers de ^¬ must be finiert. Each of these workpiece layers includes not only their height in the z-direction but also contour information in an xy plane, which consists of one or more closed polygons, in the interior of which the material of the workpiece position is located, while outside no Werkstückmate ^¬ rial is provided, ie the The position of the powder bed remains untreated.

Moreover, the machine requires further example, preferences for herstel ^¬ len, the amount of the produced documents, the orientation of the writing vectors, ie the direction and length of the path which the energy beam on the surface of the powder bed describes, and the division of the workpiece position to be generated in sectors in which certain process parameters apply. Furthermore, focus diameter and power of the energy beam used are to be determined. The CLI file and the production data together define a flow chart according to which the workpiece is described in the STL file can be made in the manufacturing plant location ^¬ additive for location.

Based on the creation of the flowchart, the individual workpiece layers with their stored contour information from which a Belichtungsstra ^¬ strategy will be determined on the work preparation. This consists essentially of steps of a contour exposure and tension relief. As part of the contour exposure, the energy beam travels one or more times the contour line of the workpiece position. In the ^{context of} the hatching direction (hatch), the area of the workpiece position is typically filled with exposure vectors carried in groups in parallel, the groups typically forming a rectangular pattern of individual segments.

In the execution of the flowcharts described above in an additive manufacturing process manufacturing problems are observed again and again, in the worst case too

Can lead to process interruptions. Particularly in the case of components in which filigree structures are produced with a low component volume, overheating repeatedly occurs - combined with an enlargement of the molten bath, so that too many powder particles are melted. In the procedure, then the formation of a

Watch the melt bead, which protrudes from the powder bed after solidification and hampers or even prevents the generation of subsequent powder layers, since the powder slider used to produce the powder layer sticks to the solidified bead, which leads to a process interruption. The object of the invention is to specify a method for powder-bed-based additive production of a workpiece, with which the probability of overheating of the molten bath is comparatively low. In addition, it is an object of the invention to provide a method for creating a contour function, which can be used in the aforementioned method. It is another object of the invention to provide a method for creating correction parameters that can be used in the above-mentioned method for producing a component. To the

 It is the object of the invention to specify computer program products which enable the creation of a contour function or the creation of correction parameters in accordance with the respective methods specified above.

This object is achieved with the method for powder bed-based additive manufacturing according to the invention by the fact that in the solidification of the uppermost layer of the powder bed, the underlying geometry of the already produced workpiece is taken into account. This consideration according to the invention causes the time-averaged power introduced by the energy beam per unit area of the powder bed to be reduced by using correction parameters if the heat flow into the workpiece already produced is reduced depending on the workpiece depth available below the energy beam. The available ^¬ de workpiece depth represents the available at this point workpiece ^¬ volume from which the heat dissipation from the molten bath is directly dependent. The larger the workpiece volume, the more heat can be absorbed from the molten bath and the derived ^¬. With a smaller workpiece volume, the heat dissipation is hindered because the powder bed, which surrounds this workpiece ^volume , has a significantly lower thermal conductivity and also a lower heat capacity.

The correction parameters advantageously cause the energy input by the energy beam in critical zones of the To be produced workpiece position is reduced. The energy ^¬ entry can be described by the per unit area of the powder bed ^¬ introduced time-averaged power. This results in the possibilities for defining correction parameters. These can be selected individually or in combination to influence the energy input.

A first option is to lower the power of the energy beam. Regardless of the exposure Strate ^¬ energy thereby the introduced into the component energy ^¬ density is proportionately reduced. Another possibility is ^¬ to increase the feed rate of the energy beam on the powder bed. This reduces the per unit area of the powder bed introduced power, since the energy beam sweeps over a given unit area of the powder ^¬ bed in a shorter time. Another possibility is that an irradiation break is maintained between the scanning of the exposure vector and the departure of an adjacent exposure vector. The Belichtungsvek ^¬ gates define respective portions of the path, which leaves the Ener ^¬ giestrahl for solidification of the powder bed, so that the pause between the retraction of adjacent exposure vectors to leads that power is Ringert published in the time average.

According to one embodiment of the invention provides that the fall below the energy beam available to work piece ^¬ depth is calculated from a geometry of the workpiece descriptive record. These data are available anyway because of the required work preparation for the additive manufacturing of the workpiece. It is possible, as the geometry of the descriptive data set to the workpiece Geomet ^¬ riedatensatz (for example as STL file executed) or the manufacturing data set (for example, as CLI-File out ^¬ leads) to be used. According to another embodiment of the invention, below the energy beam available to workpiece ^¬ depth can be only up to a specified maximum depth considered. It has been shown that see critical states of overheating of the melt and there ^¬ only occur with associated beading when the heat dissipation flux is significantly hampered the already manufactured component. From a certain workpiece depth however, it is un ^¬ much how much component volume below this particular workpiece depth is additionally available, as the

Workpiece to volume sufficient to this depth, to ensure reaching from ^¬ heat dissipation. Therefore, the workpiece areas that are not significantly involved in heat dissipation below this maximum depth are not taken into account in the calculation.

Advantageously, the maximum depth to be considered can be set to at least 0.5 mm and at most 2 mm, preferably to 1 mm. Alternatively, it is possible to specify the maximum depth to be taken into account in already produced workpiece ^layers , since these have a defined thickness due to the creation of the schedule. Thereafter, the maxi ^¬ can times Hoechsmann ^¬ least 40 layers are to be considered depth to at least 10, and preferably set to 20 layers.

The maximum depth to be considered depends in detail on the boundary conditions of the selected additive manufacturing process and the material to be processed. In the material to be processed, for example, the heat capacity and the thermal conductivity form an essential role. Wei ^¬ terhin are the process parameters, particularly the default provided energy input, so the introduced time-averaged power by the energy beam per unit area of the powder bed, tor an essential Einflussfak-.

According to a particular embodiment of the invention, it is possible to proceed in such a way that each of them is located below the energy source. Gies beam available workpiece depth for each ^¬ Weils uppermost layer (ie for each layer, since each layer in the process once represents the top layer while it is being produced) is described as a contour function location-dependent for the surface area of the top layer to be solidified , The proportion to be solidified surface of the uppermost layer of the powder bed is thus the area ratio, which defines the work ^¬ exposure and lies within the contour which is described by the contour function. The area fraction can thus be described in an xy coordinate system in a location-dependent manner. The contour function can advantageously be stored in tabular form from a grid of interpolation points (x, y). This can be used, for example, to create a modified CLI file.

It is advantageous if the contour function is normalized to 1, where the value 1 is reached where the maximum depth to be considered is reached. As a result, a correction value of the contour function can be easily taken into account, for example, depending on the support location, by using the value of the contour function as a correction factor. If the uncritical maximum depth to be taken into account in the workpiece already produced is reached, then this factor is 1, ie no correction of the introduced energy of the energy beam is necessary. Reaches the correction value is 0, it means that the workpiece was in the as ^¬ lying down position is not made at this point. ^¬ all recently allowed here introduced by the energy beam energy can not be set to 0, but malwert a mini, which is necessary for forming an unsupported by former erzeug ^¬ te workpiece layers new workpiece position.

Alternatively, according to a particular embodiment of the invention, provision may also be made for the contour function to be assigned a correction function in which the correction parameters for the temporally averaged value introduced by the energy beam per unit area of the powder bed are location-dependent Performance be filed. The correction function can also be stored in tabular form for a grid of interpolation points (x; y). This makes it possible to take account of empirical values as to how the energy introduced by the energy beam must be reduced as a function of the already produced workpiece volume. If there is sufficient knowledge of experience, the correction function can advantageously be fed from a library which makes available possible correction parameters. This correction parameter kön- nen compiled example for certain materials to be processed, for certain characteristic component geometries or for specific additive manufacturing process ^¬ to.

Another embodiment of the invention provides that the correction parameters of the correction function to be assigned are determined as a function of the averaged value of the correction function or of the minimum value of the correction function along an exposure vector, wherein the exposure vector is a rectilinear element of the advance of the energy beam. In this embodiment of the method, therefore, the exposure vector is treated as the smallest unit to be corrected. This can be corrected with the correction factor of the correction function individually or in groups with other, in particular, parallel exposure vectors of a segment within the contour to be exposed.

If the averaged value of the correction function is used, a correction is smaller than if the minimum value is used to determine the correction parameters. When using the minimum value, so to speak, the worst-case scenario for the exposure vector concerned is taken into account and the correction is correspondingly stronger. Egg ^¬ ne decision, which value should be taken into account, for example, can be made depending on the environment of the component. In particular, in addition in a peripheral area of the contour in accordance with another Substituted ^¬ staltung of the invention in the determination of the correction parameters a Distance to the edge of the contour to be considered. In the edge zone of the contour of a reduction in the molten bath lying below the workpiece volume kriti ^¬ shear normally precipitates out because the edge is in any case in a direction transverse to the Z-direction component less volume. Here, the minimum value of the correction function along an exposure vector may be used, for example, while au ^¬ ßerhalb the edge zone, the mean value is used. Furthermore, the above-mentioned object is achieved by a Ver ^¬ drive to create a contour function is achieved in that each is below a available for the preparation to USAGE ^¬ Denden energy beam workpiece depth for the processed layers of the powder bed as a contour function depending on the location for the to be solidified surface portion of the layer is calculated. The respective position to be produced, for which the contour function is calculated, is the uppermost layer during production in the production method already described above. However, the contour functions of all the layers to be produced can also be calculated in advance, since the information required for this purpose is already available in the data sets describing the workpiece. With the method, the advantages already explained above can be achieved in the process control, according to which an overheating of the molten bath can be prevented.

Furthermore, the object specified above is achieved according to the invention by a method for generating correction parameters for a correction function, which can be used in the above-described method for additive manufacturing. It is according to the invention provided that the measure for the Ver ^¬ ringerung the introduced through the beam of energy per unit area of the powder bed time-averaged power is determined by preparing a specimen. The correction parameters can be derived from the determined measure and stored with boundary conditions valid for the correction for the production. An iterative procedure for checking the correction parameters is possible. The Correction parameters can then be stored in a library, for example. The values can then be retrieved as needed if comparable structures result in the component to be produced as in the sample or 5 previously produced workpieces.

Alternatively, the object can also be achieved by calculating the measure for the reduction of the time-related power introduced by the energy beam per unit area of the powder bed with a simulation program in order to derive the correction partners from the measure. These can also be stored with marginal conditions for the production that are valid for the correction. Here, too, is an iterative procedure for checking the determined correction parameters

15 possible by the simulation program is repeated several times. The simulation program can be applied to the production of specimens or to the manufacture of structural components. It is also possible, the method described above, comprising the preparation of a pro ^¬

20 bodies with the method comprising a simulation to combine.

The object stated at the outset is finally also solved by a computer program product for creating a contour function 25 which is suitable for use in the additive manufacturing method described above. In this case, is vorgese ^¬ hen that a Erstellungspro ^¬ program module is provided in the computer program product with which the respectively below ei ^¬ nes to be used for producing the energy beam for Verfü- 30 supply standing workpiece depth depending on the location for a to be processed location as a contour function for the to be solidified surface portion This position of the powder bed is calculable. The build program module has a first interface for inputting a data set describing the geometry of a workpiece to be produced. It also shows that

Creation program module on a second interface for Ausga ^¬ be said contour function. Thus, the creation program module with the required data for the creation ^¬ be supplied to the contour function and then output the calculated contour function.

Finally, the object stated at the outset is also achieved by a computer program product for creating correction parameters for a correction function, wherein the contour function can be used in the additive manufacturing method described above. The object specified in the introduction is achieved by providing a simulation program module with which the measure for the reduction of the time-averaged power introduced per unit area by the energy beam can be calculated. This simulation program module comprises a third interface for entranc ^¬ be one of the geometry of a simulated workpiece to be produced descriptive record because this record is required for the simulation calculation. In addition, the simulation program module has a fourth interface for outputting said measure. Then be in consideration of the extent of the boundary conditions used in the simulation for production simulation as Korrekturpa ^¬ parameters store.

Further details of the invention are described below with reference to the drawing. Identical or corresponding drawing elements are each provided with the same Bezugszei ^¬ chen and are only explained several times as far as differences arise between the individual figures. 1 shows an arrangement for carrying out an exemplary embodiment of the method according to the invention with a sectional schematic representation of a laser melting system and exemplary embodiments of the computer program products according to the invention as a block circuit diagram, Figure 2 shows an embodiment of the method according to the invention for determining correction parameters by a test method three-dimensional, Figure 3 is a schematic representation of the inventive

 Contour function as a supervision,

FIG. 4 shows an exemplary embodiment for the determination of correction factors as a function of exposure vectors according to an exemplary embodiment of the invention

Method schematically three-dimensional and

Figure 5 shows an embodiment of the method according to the invention as a flowchart.

FIG. 1 schematically shows a system 11 for laser melting. This has a process chamber 12, in which a powder bed 13 can be produced. For the preparation per ^¬ weils a layer of the powder bed 13, a distribution device in the form of a doctor blade 14 via a powder supply 15, and then moves across the powder bed 13, whereby a thin layer is formed of powder in the powder bed 13, a top layer 25 of the powder bed forms. A laser 16 then generates a laser beam 17, which is moved by means of an optical deflecting device with mirror 18 over the surface of the powder ^¬ bed 13. In this case, the powder is melted at the point of incidence ^¬ the laser beam 17, whereby a workpiece 19 is formed. The powder bed 13 is formed on a building platform 20, which can be gradually lowered by an actuator 21 in a pot-shaped housing 22 by one powder layer thickness. In the housing 22 and the building platform 20 are heaters 23 in the form of electrical resistance heaters (al- ternatively also induction coils are possible) are provided, which can preheat the work in progress 19 and the Par ^¬ particles of the powder bed 13. To the Energiebe ^¬ must be limited to preheat, located on the Gehäu- se 22 outside an insulation 24 with low thermal conductivity.

The system 11 for laser melting is controlled by a control inputs CRL direction, which must be previously provided with appropriate Pro ^¬ process data. To prepare the production of the workpiece 19, it is first necessary to generate the three-dimensional geometric data of the workpiece in a design program CAD. The geometry data set STL thus generated is input via a fifth interface S5

System for manufacturing preparation CAM given. In the system for manufacturing CAM preparation a computer program product 26 is installed on the one hand, which has a Erstellungspro ^¬ program module CON, and a transformation program module SLC up. In the transformation of the program module Konstrukti ^¬ onsdatensatz STL is (received via the first interface Sl) into a manufacturing data set CLI. In addition, are established by the program module transformation process parameters PRT who possible to pass to the manufacturing data set CLI via the ERS te interface Sl to the creation program module CON wei ^¬. These are standardized production parameters.

The builder module CON is used to determine correction factors vf which are to be taken into account in the manufacturing parameters PRT, so it does not come to an over ^¬ overheating of the melt. These are passed to the He ^¬ position via an interface S2 to the control device CRL to the system 11, possibly supplemented by the control device CRL advantageously with specific data of the plant. 11 For this purpose, the control device CRL also requires the manufacturing data set CLI, which contains the geometry of the machines divided into workpiece layers. The control device communicates with the system via a ninth interface S9.

In order that correction parameters vf can be generated, the creation program module CON is initially calculated according to the invention Depth information supplemented contour functions gcf a workpiece to be produced, which in addition to the information of the extent of the workpiece layer to be consolidated also contains a location-dependent information about how large the workpiece depth z available under the energy beam (see Figure 2). This information depends on the variables x and y, which can be expressed by the expression gcf (x, y). From the contour function, the correction parameters vf, which are likewise dependent on the variables x and y, can then be determined spatially resolved, for which reason vf can also be written as a function vf (x, y).

To compute the correction function vf, the build program module CON requires data that can come from a library LIB. This is shown according to Figure 1 as an external Biblio ^¬ theque LIB and is connected via a sixth interface with the creation program module CON (communication in both directions). In order to obtain data for the generation of correction parameters vf, it is also possible to use a simulation program module SIM, which is implemented in a second computer program product 27. This receives, via a third ^interface S3, the production data set CLI and the production parameter PRT, with which data an additive production of the

Workpiece can be simulated. Alternatively, typical partial structures of workpieces or specimens can be calculated with the simulation program. The result of these simulation calculations can be stored in the library LIB via a sieve interface S7.

An alternative approach is to use test equipment TST with equipment 11 or other equipment to determine if overheating of the molten bath occurs. In this way also correction parameters can be tried out. These results can be stored in the S8 Bib ^¬ liothek LIB taking advantage of an eighth interface. Alternatively, the test results of the Tests TST or the simulation calculations in the simulation program module SIM are also passed through a fourth interface S4 to the creation program module CON, so that from this the correction parameters vf can be determined.

FIG. 2 shows a possible structure of a test specimen 28, which is shown with a part of the powder bed 13 surrounding the specimen 28. This one has a wedge-shaped

Structure, thereby resulting in an edge 29 in the uppermost layer, under which no material of the specimen 28 in the powder bed 13 is present. This results in a molten bath overheating (not shown), which leads to more material is solidified than provided due to the procedure. Therefore, the actual component geometry of the test specimen 28 produced so far deviates from the desired geometry, which is indicated by the dashed edge. Thus, more material is solidified, so that the edge 29 protrudes from the surface of the powder bed 13 forth ^¬ . The wedge-shaped region indicated by dashed lines is due to a limited depth z of the component to evaluate until the transition to the powder bed 13 as critical with respect to a possible overheating of the molten bath.

In order to overcome this problem, the following contour function gcf (x, y) is calculated from the test piece 28 (as well as from a workpiece 19, which is to be produced according to FIG. 1): gcf (x, y) = -2- f px, y , z) dz;

(l, (χ, γ, ζ) in the workpiece

p {x, y, z) ' ^y '

 {0, otherwise with z = actual depth of the specimen 28 below a surface 30 of the powder bed

z _m = the maximum depth of the specimen 28 to be considered. The arithmetic determination can be made on the basis of

Design data set STL or based on the produc ^¬ tion data set CLI done. Typically, the values for the available component depth z become tabular for a given number of in-frame

Support points (x; y) are stored and can according to the above calculation method between 0 and 1 are. By the calculation rule, there is thus a normalization of the contour function gcf, wherein the maximum depth of the specimen 28 to be considered is equated with 1.

According to FIG. 3, a certain contour described by the contour function gcf (x, y) is shown, which may also consist of several subregions. The areas in which are z <z _m are shown shaded in Figure 3 and ^¬ the delimited by a dash-dot line. These can lie on an outer contour 31 of the workpiece layer 32 to be produced or else the interior thereof. In addition, JE in Figure 3 weils an edge zone 33 of the manufactured workpiece position indicated by a dash-double dot line, can be taken into account in the determination of correction factors in the ^¬ to additionally applicable to the edge zone boundary conditions.

According to Figure 4, a section 34 of the exposed surface of a workpiece is shown. In this section is a segment 35, which is to be exposed with a number of Belich ^¬ tion vectors 36. These each have a certain length and run in the segment 35 with a certain distance (hatch) h parallel to each other. For determining the depth z of the workpiece under an exposure vector 36, either the average value zi or the minimum value Z2 can be determined. This is stored for the relevant exposure vector 36 as a base value in the contour function gcf under the relevant coordinates (x; y). It is clear from FIG. 4 that these values z change for each of the exposure vectors 36, since the Under the segment 35 located component volume is indicated by a wireframe model 37.

According to FIG. 5, the method according to the invention for additively producing a workpiece is shown as a flowchart. As described for Figure 1, the method of creating a geometry data set for a near, STL ^¬ alternate workpiece begins. This is transformed in a manner known per se in a subsequent step into a production data set CLI which describes the workpiece to be produced in slices. This manufacturing data set CLI can be used to produce the workpiece with standardized production parameters, whereby a test TST can be performed in which the workpiece is manufactured in an additive manufacturing plant. Alternatively, the production can also be checked by a simulation calculation CAL. In both cases, it is then determined whether DEV form deviations are due to overheating of the molten bath.

It should be noted that deviations in shape may have other reasons, so that in particular in critical zones after deviations in form must be searched, which suggest a molten bath overheating. These critical zones are, as already explained, to be found where only a small workpiece volume below the energy beam is available during the production of the relevant layer.

If the shape deviations DEV are smaller than the maximum permissible tolerances t _max , a production PRD of the workpiece can be started. The data that are necessary for the manufacturing development of this component can be saved as Korrekturda ^¬ th and used to create subsequent production records CLI.

If the shape deviations DEV is greater than the permissible tolerances t _max be, a modified contour function must gcf (x, y) are created workpiece been made of the function of the depths ^¬ information z of the correction parameter of the correction function vf (x, y) is determined can be NEN. These are then taken into account in another test TST or in another simulation calculation CAL, again determining the shape deviations DEV. These iterations are repeated until the form deviations DEV are smaller than the maximum permissible tolerances tmax ·

Claims

claims 1. A method for powder bed-based additive manufacturing of a workpiece (19), wherein the workpiece (19) layer by layer in a powder bed (13) is produced, wherein the respective uppermost layer (25) of the powder bed (13) for the preparation of the workpiece an energy steel is solidified, characterized, that, in the solidification of the uppermost layer (25) of the powder bed (13) under the top layer (25) lying Geomet ^¬ rie of the workpiece already manufactured is taken into account, wherein the by the energy beam (17) introduced per unit area of the powder bed temporally average Leis ^¬ processing is reduced by using correction parameters, if the heat flow into the already prepared workpiece (19) is reduced depending on the property below the energy beam to supply Availability checked ^¬ workpiece depth (z). 2. The method according to claim 1, characterized, that the time-averaged power introduced per unit area of the powder bed is reduced by applying the following correction parameters:  • the power of the energy steel (17) is lowered  and or  • A feed rate of the energy beam (17) on the powder bed (13) is increased and / or • between the retraction of an exposure vector (36) and the retraction of an adjacent exposure vector (36) is adhered to an exposure interval, wherein the Be ^¬ clearing vectors respectively sections of the path beschrei ^¬ ben that the energy beam (17) to solidify the powder bed (13) departs , 3. Method according to one of the preceding claims, characterized, the workpiece depth (z) available below the energy beam is calculated from a data record describing the geometry of the workpiece (19). 4. The method according to any one of the preceding claims, characterized that the workpiece depth (z) available below the energy beam is taken into account only up to a specified maximum depth (z _m ). 5. The method according to claim 4, characterized, that the maximum to consider depth (z _m) to Minim ^¬ 0.5 mm and at most 2 mm, is preferably set to 1 mm tens. 6. The method according to claim 4, characterized, that the maximum to consider depth (z _m) Any artwork least 10 and at most 40 layers, it is preferred to set firmly ^¬ 20 layers. 7. Method according to one of the preceding claims, characterized in that that the respective workpiece depth (z) available for the uppermost layer (25) below the energy beam is described as a contour function (gcf) in a location-dependent manner for the surface portion of the uppermost layer (25) to be consolidated. 8. A method according to claim 7, when dependent on one of claims 4, 5 or 6 characterized, that the contour function (gcf) is normalized to 1, where the value 1 is reached where the maximum depth (z _m ) to be taken into account is reached. 9. The method according to any one of claims 7 or 8, characterized, that the contour function (GCF) in the location-dependent correction parameters for by the energy beam (17) per unit area of Pul ^¬ verbettes introduced time-averaged power is stored, a correction function (vf) is assigned. 10. The method according to claim 9, characterized, in that the correction parameters of the correction function (vf) to be assigned are determined as a function of the averaged value of the correction function (vf) or the minimum value of the correction function (vf) along an exposure vector, the exposure vector being a rectilinear element of the advance of the energy beam. 11. The method according to one of the preceding claims, d a d u c h e c e n e c e n e, that, in the determination of the correction parameters within a boundary zone (33) of the contour, a distance to the edge of the contour is additionally taken into account. 12. A method for creating a contour function (gcf) for use in a method according to one of claims 7 to 11, characterized, that in each case below a for the preparation to USAGE ^¬ Denden energy beam (17) available to the workpiece depth (z) is calculated for the processed sheets (25) of the powder bed as a contour function (gcf) a function of location for the to be solidified surface portion of the layer (25). 13. A method for generating correction parameters for a correction function (vf) for use in a method according to one of claims 9 to 11, characterized, that The measure of the reduction in the energy beam (17) applied per unit area of the powder bed time-average power is determined by producing a test specimen (28),  • from which the correction parameters are derived and • the correction parameters are stored with marginal conditions for the production valid for the correction. 14. A method for generating correction parameters of a correction function (vf) for use in a method according to one of claims 9 to 11, characterized, that • the measure of the reduction of by the energy beam (17) per unit area of the powder bed time-averaged power introduced with a Simulationspro ^¬ program is calculated,  • from which the correction parameters are derived and • the correction parameters are stored with marginal conditions for the production valid for the correction. 15. A computer program product for creating a Konturfunkti ^¬ one (GCF) for use in a method according to any one of claims 7 to 11, characterized, that • a creation program module (CON) is provided with which each below a for the preparation to ver ^¬-inverting energy beam (17) available to the workpiece depth (z) for a produced sheet (25) contour function (GCF) a function of location for the to be solidified surface portion a layer (25) of the powder bed is calculable, • the creation program module (CON) has a first section ^¬ put (Sl) for the input of a geometry of a workpiece to be produced (19) descriptive data set and • the creation program module (CON) is a second sectional ^¬ point (S4) for outputting said contour function (GCF) has. 16. A computer program product for creating correction Para ^¬ meters for a correction function (VF) for use in a method according to any one of claims 9 to 11, characterized, that  A simulation program module (SIM) is provided, with which the measure for the reduction of the time-averaged power introduced per unit area by the energy beam (17) can be calculated, • the simulation program module (SIM) has a third ^interface (S3) for inputting a data record describing the geometry of a workpiece (19) to be simulated, and the simulation program module (SIM) has a fourth interface (S4) for outputting the said measure.