CALCULATION OF EXPOSURE PATHS WITH LOW COMPONENT DISTORTION

Description

[0001] The present invention relates to a method for the computer-assisted provision of control data for an additive manufacturing device for producing a three-dimensional object by layer-by-layer application and selective solidification of a build-up material. Furthermore, the invention relates to a method and a device for the computer-assisted control of a number of energy input devices in an additive manufacturing device, as well as to an additive manufacturing device and an additive manufacturing method for producing a three-dimensional object.

[0002] Additive manufacturing devices and processes of this type are used, for example, in rapid prototyping, rapid tooling, or additive manufacturing. One example of such a process is known as "selective laser sintering or laser melting." In this process, a thin layer of a powdered build material is repeatedly applied, and the build material is selectively solidified in each layer by selectively irradiating areas corresponding to a cross-section of the object to be manufactured with a laser beam.

[0003] The energy input from the laser beam leads to a partial or complete melting of the build material. After cooling, the molten build material then exists as a solid. Due to the large temperature differences, intrinsic mechanical stresses (residual stresses) can develop in the object, particularly during cooling of the molten or partially molten build material, for example when different areas of the object cool at different rates and thus deform plastically and / or elastically. On the one hand, this leads to a deformation of the finished object and thus impairs the quality and dimensional accuracy of the object. On the other hand, deformations of already finished object areas during the manufacturing process can lead to collisions with a coater who is applying a new layer of build material and thus influence and / or hinder the layer application.

[0004] The deformation of the finished object due to thermally induced residual stresses is also referred to as (component) warpage. Particularly when the build material is solidified using an exposure pattern that repeats in each layer or at least in a plurality of consecutive layers, e.g., when the laser beam is guided over the build material layers within the object's cross-section on parallel solidification paths, this can lead to a temperature gradient. This results in significant warpage of the finished object or an object with significant residual stresses.

[0005] In order to reduce distortion of the object, it is known, for example from WO 2008 / 116518 A1, to expose layers of the build-up material in a pattern of parallel solidification lines, wherein solidification lines in successive build-up material layers are rotated by an angle relative to each other.

[0006] EP 3 170 648 A1 shows an exposure strategy in which the build-up material is scanned in mutually parallel scan vectors, wherein the area to be exposed is divided into segments and the scan vectors run perpendicular to a principal stress direction present in the respective segment after the application of a component layer.

[0007] The technical article by Thomas Töppel et al., "RESIDUAL STRESSES AND Distortion in Additive Manufacturing," in Welding and Cutting, Volume 68, Issue 4, January 1, 2016 (2016-01-01), pages 176-186, XP055641178, describes investigations into influencing factors and measures for reducing residual stresses and distortion in laser beam melting.

[0008] It is an object of the present invention to provide an alternative or improved method and an alternative or improved device for the additive production of a three-dimensional object by layer-by-layer application and selective solidification of a building material, by means of which in particular the mechanical properties of the object to be produced can be improved.

[0009] The object is achieved by a computer-aided method for providing control data according to claim 1, a method for computer-aided control of a number of energy input devices according to claim 2, a device for computer-aided control of a number of energy input devices according to claim 7, an additive manufacturing device according to claim 10, an additive manufacturing method according to claim 11, and a computer program according to claim 15. Further developments of the invention are specified in the dependent claims. The methods can also be further developed by the features of the devices listed below or in the subclaims, or vice versa. The features of the methods or devices can also be used for further development among each other.

[0010] A computer-aided method according to a first aspect of the invention serves to provide control data for an additive manufacturing device for producing a three-dimensional object by means of the device, wherein the object is produced by applying a build material, layer upon layer, and solidifying the build material by supplying radiant energy to locations, preferably all locations, in a layer that are associated with the cross-section of the object in this layer, by at least one energy input device for introducing energy into the build material scanning these locations with at least one energy beam according to a set of energy input parameters along a number of solidification paths in a build plane. The method for providing control data comprises: a first step of accessing computer-based model data of two sequentially generated components during production,preferably in immediate temporal succession, cross-sections of an object section to be solidified, a second step of generating a data model of each of the two cross-sections, wherein in the data model for each of the two cross-sections a scanning of the building material layer with at least one energy beam along at least one solidification path is specified, wherein it is specified that when scanning the locations of a building material layer that are assigned to the respective cross-section to be solidified, the impact area of at least one energy beam on the building material is moved along at least a section of a warpage field isoline, wherein a section of a warpage field isoline, along which the impact area is moved when scanning the cross-section to be solidified later, is selected such that it is opposite a section of a warpage field isoline,along which the impact area is moved when scanning the cross-section to be solidified first, has a different position and / or orientation in the construction plane, and a third step in which control data according to the data model generated in the second step are provided for the generation of a control data set for the additive manufacturing device.

[0011] The two cross-sections of an object section to be solidified sequentially, preferably immediately following one another, during production can in particular be located in superimposed, i.e., directly successive, layers of the build-up material. The object section can be a section defined by a number (in particular two) layers of the build-up material (i.e., delimited in a direction perpendicular to the build plane), and / or a section that, with respect to the extent of the object, forms part of the object in at least one direction parallel to the build plane. The term "number" in the present application is always to be understood as "one or more."

[0012] The energy input device is suitable for introducing energy in the form of one or more energy beams into the build material. For example, an energy input device can comprise one or more lasers for generating laser radiation (electromagnetic radiation) or one or more energy sources for generating particle radiation, e.g., an electron beam source for generating an electron beam. The energy introduced into a build material layer partially or completely melts the build material, so that it exists as a solid after cooling. The term "energy beam bundle" expresses that a single energy beam or a plurality of energy beams can be directed at a defined area in the build plane, which has a predefined size and / or geometric shape and is therefore referred to as the impact area (rather than the impact point).

[0013] To solidify the build material, the impact area of the energy beam is moved along a number of solidification paths in the build plane. Since the impact area, or its effective area, has a surface area in the build plane and is generally not point-shaped, a solidification path cannot be a line, but rather a dimension (width or track width) that is non-zero and transverse to its main direction of extension, i.e., transverse to its longest extension.

[0014] A control data set is a sequence of commands that specify the layer-by-layer application of the build material in the build plane and the selective solidification of the locations corresponding to the object cross-section in the respective layer by scanning with the energy beam. The control data of the control data set is based on a computer-based model of the three-dimensional object to be manufactured, for example, a CAD model, from which the locations corresponding to the respective object cross-section and to be scanned with the energy beam are determined for each layer. Thus, the control data includes position information of the locations of the respective cross-sections or build material layers to be selectively solidified. The control data also specifies how the solidification of the build material is to be carried out during the manufacture of the object. This includes, for example, a scanning sequence of the locations to be scanned with the energy beam, i.e.the solidification paths, as well as energy input parameters that specify, among other things, the energy density of the energy beam, the speed at which the impact area of the energy beam is moved across the build material layer, and the geometric shape and / or size of the impact area. The entirety of all control data required to carry out a manufacturing process is referred to as a control data set.

[0015] Within the scope of the invention, the impact area of the energy beam is moved at least in sections along warpage field isolines in at least two successive building material layers to be selectively solidified. An isoline is a line that connects points of the same value (isovalue). In three-dimensional space, points of the same value (isovalue) are accordingly referred to as isosurfaces. Isolines and isosurfaces are therefore, by definition, perpendicular to a gradient of the field strength. Isolines and isosurfaces are generally determined using a vector or scalar field, in the present case using a warpage field, which can be, for example, a residual stress field and / or a deformation field. The warpage field, on the basis of which the warpage field isolines (in the above-mentioned example, residual stress field isolines orDeformation field isolines) can relate to deformations of the object and / or to residual stresses in the object, such as would be achieved without the above-described inventive scanning of the building material along warpage field isolines. It is therefore a prerequisite that information about the warpage field in the object section, which allows a calculation of warpage field isolines, is already available before the production of the three-dimensional object or at least before the selective solidification of a building material layer in which the impact area is to be moved at least partially along a warpage field line according to the invention.

[0016] The inventor has recognized that residual stresses preferably develop parallel to the direction of movement of the impact region of the energy beam. By moving the impact region according to the invention along warpage field isolines, i.e. perpendicular to a gradient of the warpage field and thus perpendicular to the local warpage directions, this warpage is counteracted. As a result, for example, residual stresses and deformations in an object manufactured using control data provided according to the invention can be reduced, and thus its dimensional accuracy and quality can be improved. In particular, deformations of the object that already occur during production can also be at least reduced, whereby, for example, a collision between a coating element (e.g. a blade) of the coater and an already selectively solidified build-up material layer can be avoided.

[0017] Furthermore, according to the invention, the impact area is moved along warpage field isolines in successive cross-sections of the object section to be consolidated, which warpage field isolines have, at least in sections, a different position and / or orientation with respect to the build plane. "Different position and / or orientation" means that the warpage field isoline sections are offset from one another and / or enclose an angle with one another in the build plane. This therefore excludes identical line sections in the build plane. Accordingly, two cross-sections to be consolidated one after the other or two building material layers to be selectively consolidated are therefore not scanned along the same consolidation path, at least in sections, even if the same warpage field isolines are calculated for the layers. Due to the different position and / or orientation of the warpage field line sections in successive cross-sections orFor example, building material layers can avoid or at least reduce preferred directions of mechanical properties in the finished object, which can further improve the dimensional accuracy and quality of the three-dimensional object.

[0018] A method according to a further aspect of the invention serves for the computer-assisted control of a number of energy input devices of an additive manufacturing device for producing a three-dimensional object by means of the same, wherein the object is produced by applying a building material, layer upon layer, and solidifying the building material by supplying radiant energy to locations, preferably all locations, in a layer that are assigned to the cross-section of the object in this layer, by at least one energy input device for introducing energy into the building material scanning these locations with at least one energy beam according to a set of energy input parameters along a number of solidification paths in a building plane. In the method, the number of energy input devices is controlled such that for two consecutively during production,preferably in immediate temporal succession, cross-sections of an object section to be solidified, for each of the two cross-sections, a scanning of the building material layer with at least one energy beam along at least one solidification path is specified, wherein it is specified that when scanning the locations of a building material layer that are assigned to the respective cross-section to be solidified, the impact area of at least one energy beam on the building material is moved along at least a section of a distortion field isoline, wherein a section of a distortion field isoline along which the impact area is moved when scanning the cross-section to be solidified later in time is selected such that it is opposite a section of a distortion field isoline along which the impact area is moved when scanning the cross-section to be solidified first in time,has a different position and / or orientation in the construction plane. This makes it possible, for example, to achieve the effects described above with regard to a method for providing control data with a method for computer-assisted control of a number of energy input devices within the framework of an additive manufacturing process.

[0019] Preferably, in the methods described above or in at least one of the methods for the two cross sections, it is specified that the impact region is moved along a plurality of sections of distortion field isolines, which are selected such that their mutual spacing substantially corresponds to the width or track width of a solidification path on the build material transversely to the direction of movement of the impact region. The width, also referred to as track width, of a solidification path is a dimension of a solidification path perpendicular to the direction in which the impact region is or is to be guided along the solidification path. This width can correspond in particular to the size of an effective area of the energy beam in the build plane, in particular to the size of the melt pool created by the energy beam in the build plane.The width of a solidification path can vary locally, for example, depending on the angle of incidence of the energy beam on the build plane. Therefore, a local width of the solidification path is meant here, i.e., the distance between adjacent warpage field isoline sections can vary across the build plane. By selecting a distance between adjacent warpage field isoline sections according to the width of the solidification path(s), it can be ensured, for example, that the solidification paths have a predefined distance from one another or a distance that lies within a predefined interval. This allows, for example, the energy input to be homogenized, which also further improves the quality of the object to be manufactured.

[0020] Preferably, a section of a warpage isoline along which the impact region is moved when scanning the cross-section to be solidified later in time has an offset within the build plane compared to a section of a warpage isoline along which the impact region is moved when scanning the cross-section to be solidified first in time. It may thus be preferable to maintain an extension direction or orientation of the warpage isoline sections in the build plane in successive layers to be selectively solidified and to adapt their position in the build plane by a lateral offset of the warpage isoline section in the layer to be solidified later in time. Thus, it is possible, for example, to provide solidification paths with different positions in the build plane in building material layers to be solidified one after the other.This can, for example, further improve the quality of the object being manufactured.

[0021] Preferably, the sections of the distortion field isolines along which the impact area is moved in the two cross sections each extend over the entire length of a distortion field isoline. This allows, for example, the energy input into a build-up material layer to be selectively strengthened to be homogenized.

[0022] Preferably, the sections of the distortion field isolines along which the impact area is moved in the two cross-sections are selected such that the sections in different cross-sections belong to different distortion field iso-surfaces. As mentioned above, a distortion field iso-surface is understood to be an equipotential surface of the distortion field, i.e., in particular, a residual stress field iso-surface (surface with a constant residual stress value) or a deformation field iso-surface (surface with a constant deformation value). This makes it easy to determine distortion field iso-line sections for the cross-sections in successive layers that have a different position and / or orientation relative to one another.

[0023] A device according to the invention serves for the computer-assisted control of a number of energy input devices of an additive manufacturing device for producing a three-dimensional object by means of the same, wherein the object is produced by applying a building material, layer upon layer, and solidifying the building material by supplying radiant energy to locations, preferably all locations, in a layer that are assigned to the cross-section of the object in this layer, by at least one energy input device for introducing energy into the building material scanning these locations with at least one energy beam according to a set of energy input parameters along a number of solidification paths in a building plane. The device is designed such that the number of energy input devices is controlled such that for two consecutively during production,preferably in immediate temporal succession, cross-sections of an object section to be solidified, for each of the two cross-sections, a scanning of the building material layer with at least one energy beam along at least one solidification path is specified, wherein it is specified that when scanning the locations of a building material layer that are assigned to the respective cross-section to be solidified, the impact area of at least one energy beam on the building material is moved along at least a section of a distortion field isoline, wherein a section of a distortion field isoline along which the impact area is moved when scanning the cross-section to be solidified later in time is selected such that it is opposite a section of a distortion field isoline along which the impact area is moved when scanning the cross-section to be solidified first in time,has a different position and / or orientation in the construction plane. With such a device for computer-assisted control of a number of energy input devices, it is also possible, for example, to achieve the effects described above with regard to the method for computer-assisted control of a number of energy input devices.

[0024] The device for computer-assisted control of a number of energy input devices preferably comprises an isoline receiving unit for receiving data describing the position (in particular the position and course) of warpage field isolines in the at least one object, and / or an isoline storage unit for storing data describing the position (in particular the position and course) of warpage field isolines in the at least one object. This makes it possible, for example, to control the number of energy input devices based on pre-provided warpage field isolines.

[0025] An additive manufacturing device according to the invention serves to produce a three-dimensional object, wherein the object is produced by applying a building material, layer upon layer, and solidifying the building material by supplying radiant energy to locations, preferably all locations, in a layer that are assigned to the cross-section of the object in this layer, by at least one energy input device for introducing energy into the building material scanning these locations with at least one energy beam according to a set of energy input parameters along a number of solidification paths in a build plane, wherein the additive manufacturing device has a device as described above for the computer-assisted control of a number of energy input devices and / or is connected thereto by means of signal technology.This makes it possible, for example, to achieve the effects described above with regard to the processes also with an additive manufacturing device.

[0026] An additive manufacturing method according to the invention serves to produce a three-dimensional object, wherein the object is produced by applying a building material, layer upon layer, and solidifying the building material by supplying radiant energy to locations, preferably all locations, in a layer that are assigned to the cross-section of the object in this layer, by at least one energy input device for introducing energy into the building material scanning these locations with at least one energy beam according to a set of energy input parameters along a number of solidification paths in a build plane, wherein a computer-aided method described above for providing control data and / or a method described above for computer-aided control of the at least one energy input device is a component of the additive manufacturing method.This makes it possible, for example, to achieve the effects described in relation to the processes described above using an additive manufacturing process.

[0027] Preferably, in the additive manufacturing process and / or in one of the processes described above, the residual stress field and / or deformation field for the two cross-sections is determined by means of simulation, and the warpage field isolines are subsequently determined, preferably using a marching squares algorithm. Additionally or alternatively, the residual stress field and / or deformation field for the object section is preferably determined based on a measurement of a previously produced test specimen, and the warpage field isolines are subsequently determined for the two cross-sections, preferably using a marching squares algorithm. Additionally or alternatively, warpage field isolines of the two cross-sections are determined by determining the residual stress field and / or deformation field in the two cross-sections based on values of process monitor parameters measured during the manufacturing process of the object section.

[0028] A deformation field is a vector field that assigns a deformation vector to each point in the original CAD model of the three-dimensional object. This vector describes a (simulated or measured) displacement if the object were manufactured without the inventive method. The residual stress field describes a spatial distribution of the mechanical stresses occurring in the object (e.g., as a stress tensor) if the object were manufactured without the inventive method.

[0029] Within the scope of the invention, the deformation field or residual stress field of an object is used to calculate the warpage field isolines, assuming that the object is manufactured without the inventive scanning of the building material along warpage field isolines. This assumption can be realized by simulating the manufacturing process or the object to be manufactured, or by producing a corresponding test specimen. The test specimen is a three-dimensional object manufactured by an additive manufacturing process, which differs from the object to be manufactured in an additive manufacturing process according to the invention only in that the solidification paths along which the impact area of the energy beam(s) is moved for selectively solidifying the building material layers are not selected along warpage field isolines.For example, during the production of the test specimen, the impact area of the energy beam can be moved in stripes, i.e. in so-called hatch lines, over the areas of the build-up material to be solidified in each layer.

[0030] A simulation or measurement of a test specimen to determine a warpage field is generally carried out before the additive manufacturing of the object to be produced, so that the warpage field isolines are already available in advance and the control data for controlling the at least one energy input device can be determined in advance. This is preferably done using a marching squares algorithm, which calculates isolines (deformation field isolines or residual stress field isolines) from a two-dimensional scalar field (scalar deformation values or scalar residual stress values in the object plane corresponding to the respective cross-section). The algorithm is based on a decomposition of the scalar field into square grid cells, whereby for each grid cell its key values are compared with a predetermined isovalue, i.e. the isoline is calculated based on the key values.

[0031] Calculating the warpage field isolines based on process monitor parameters, however, takes place during the production of the three-dimensional object, but before the selective solidification of the respective cross-section for which the solidification paths are to be calculated based on warpage field isolines. Process monitor values are measured values determined from process radiation detected by a suitable sensor or detector during the production process. Process radiation can, for example, be electromagnetic and / or thermal radiation emanating from one or more applied and / or already selectively solidified layers and detected by the sensor / detector. A corresponding measured value can be a temperature value or a radiation value.In a laser sintering or laser melting process, such process monitoring can, for example, include melt pool monitoring, which detects thermal and / or electromagnetic radiation emitted when the energy beam hits the build material. The distortion field isolines can be calculated, for example, based on a temperature distribution or maximum temperature differences in one or more layers.

[0032] The recorded measured values (process monitor values) are usually scalar values, which are recorded with respect to their (two-dimensional) distribution in the build plane and are therefore usually already present as a scalar field. The distortion field isolines are then calculated based on the scalar field, for example, using a marching squares algorithm.

[0033] By calculating the warpage field isolines as described above based on a simulation, a test specimen or process monitor parameters, various procedures are provided by which it is possible, for example, to determine warpage field isolines in a simple manner.

[0034] A computer program according to the invention comprises program code means for carrying out all steps of one of the methods described above when the computer program is executed on a data processor, in particular a data processor cooperating with an additive manufacturing device.

[0035] Further features and advantages of the invention will become apparent from the description of embodiments with reference to the accompanying drawings. Fig. 1 is a schematic, partially sectioned view of an additive manufacturing apparatus for producing a three-dimensional object according to an embodiment of the present invention, Fig. 2 is a schematic block diagram schematically illustrating a method for providing control data for the Fig. 1 shown manufacturing device, and Fig. 3a shows schematically a plan view of a section of a construction field with consolidation tracks in a first layer of the building material and Fig. 3b shows a schematic plan view of the Fig. 3a shown section of the construction field with consolidation tracks in a second layer of the construction material.

[0036] In the following, with reference to Fig. 1 An example of an additive manufacturing device with which the present invention can be carried out is described. Fig. 1 The device shown is a laser sintering or laser melting device 1. For building an object 2, it contains a process chamber 3 with a chamber wall 4.

[0037] Arranged in the process chamber 3 is an upwardly open container 5 with a container wall 6. The upper opening of the container 5 defines a working plane 7, which is also referred to as the construction plane. The area of the working plane 7 located within the opening, which can be used to construct the object 2, is referred to as the construction field 8.

[0038] Arranged within the container 5 is a carrier 10 movable in a vertical direction V, to which a base plate 11 is attached, which closes off the container 5 at the bottom and thus forms its base. The base plate 11 can be a plate formed separately from the carrier 10 and fastened to the carrier 10, or it can be formed integrally with the carrier 10. Depending on the powder and process used, a construction platform 12 can also be attached to the base plate 11 as a construction base, on which the object 2 is built. However, the object 2 can also be built on the base plate 11 itself, which then serves as the construction base. Fig. 1 the object 2 to be formed in the container 5 on the construction platform 12 is shown below the working level 7 in an intermediate state with several solidified layers, surrounded by unsolidified building material 13.

[0039] The laser sintering device 1 further contains a storage container 14 for a powdered build material 15 that can be solidified by electromagnetic radiation, and a coater 16 movable in a horizontal direction H for applying the build material 15 within the build field 8. The coater 16 preferably extends transversely to its direction of movement over the entire area to be coated. Optionally, a radiant heater 17 is arranged in the process chamber 3, which serves to heat the applied build material 15. An infrared radiator, for example, can be provided as the radiant heater 17.

[0040] The laser sintering device 1 further contains an energy input device which is Fig. 1 is designed as an exposure device 20. The exposure device 20 comprises a laser 21 that generates a laser beam 22, which is deflected by a deflection device 23 and focused onto the working plane 7 by a focusing device 24 via a coupling window 25 that is mounted on the top side of the process chamber 3 in the chamber wall 4.

[0041] Optionally, the laser sintering device contains a sensor 30 which is suitable for detecting a process radiation 34 which is emitted when the laser beam 22 strikes the build-up material 15 in the working plane 7. The sensor 30 is connected to an (optional) process monitoring device 31. The sensor 30 can be arranged as in Fig. 1 shown in the process chamber 3. Alternatively, the sensor 30 can be arranged outside the process chamber 3 and the process radiation 34 can impinge on the sensor 30 through the coupling window 25 or another window (not shown).

[0042] The sensor 30 can be designed, for example, as an optical camera (e.g., CCD or image cell detector) or as a photodiode for detecting electromagnetic radiation emitted by the incident laser beam 22, or as a temperature sensor for detecting emitted thermal radiation. Furthermore, multiple sensors 30 can also be provided for detecting optical and / or thermal process radiation 34.

[0043] The process monitoring device 31 is preferably designed to evaluate a signal detected by the sensor 30 and to determine warpage field isolines.

[0044] The laser sintering device 1 further includes a control unit 29, via which the individual components of the device 1 are controlled in a coordinated manner to carry out the construction process. The control unit may include a CPU whose operation is controlled by a computer program (software). The computer program may be stored separately from the device on a storage medium, from which it can be loaded (e.g., via a network) into the device, in particular into the control unit.

[0045] The control unit 29 is connected via a data connection to a device 100 for providing control data, which optionally comprises at least one isoline receiving unit 101 and one isoline storage unit 102. The device for providing control data 100 transmits control data to the control unit 29, which data is used by the control unit 29 when carrying out the manufacturing process of a three-dimensional object. The device 100 for providing control data can be a component of the laser sintering device 1 or provided separately therefrom. The device 100 for providing control data can, for example, be an appropriately programmed computer or be implemented by means of software that runs, for example, on the control device 29.

[0046] The exposure device 20 is used in the Fig. 1 shown laser sintering or laser melting device is controlled by the control unit 29. Alternatively, a separate device for controlling the exposure device 20 can be provided, which controls the operation of the exposure device 20. Such a device for controlling the exposure device 20 can be connected via a data connection to the device 100 for providing control data in order to receive corresponding control data therefrom. Alternatively, the device for controlling the exposure device 20 itself can be designed to provide corresponding control data, for example by comprising corresponding software. In this case, the isoline receiving unit 101 and an isoline storage unit 102 are preferably not as in Fig.1 shown component of the device 100 for providing control data, but component of the device for controlling the exposure device 20.

[0047] During operation of the laser sintering or laser melting device 1, to apply a powder layer, the carrier 10 is first lowered by a height corresponding to the desired layer thickness. The coater 16 first moves to the storage container 14 and takes from it a quantity of build material 15 sufficient to apply one layer. It then moves over the build area 8, where it applies powdered build material 15 to the build substrate or a previously existing powder layer, and spreads it out into a powder layer. The application takes place at least over the entire cross-section of the object 2 to be produced, preferably over the entire build area 8, i.e., the area delimited by the container wall 6. Optionally, the powdered build material 15 is heated to a working temperature by means of a radiant heater 17.

[0048] Subsequently, the applied powder layer is scanned by the laser beam 22 at the locations corresponding to the cross-section of the object 2 to be produced, so that the powdered build-up material 15 is solidified at the locations corresponding to the cross-section of the object 2 to be produced. The applied powder layer is scanned along predetermined solidification paths, i.e., the impact point or impact area of the laser beam 22 in the working plane 7 is moved along the solidification paths. These steps are repeated until the object 2 is completed and can be removed from the process chamber 3.

[0049] During the manufacturing process, the sensor 30 optionally detects a process radiation 34 emanating from the impact area of the laser beam 22 and transmits a corresponding signal to the process monitoring device 31, which then evaluates the signal.

[0050] The individual components of the laser sintering or laser melting device 1, in particular the carrier 10, the coater 16, and the exposure device 20, are controlled by the control unit 29 according to a control data set provided by the device 100 for providing control data. Optionally, the exposure device 20 can be controlled by a separate device for controlling the exposure device 20, as mentioned above.

[0051] Such a control data set is based on a computer-aided model (usually a CAD model) of the object to be manufactured and specifies how the solidification is to be carried out for each point in a layer to be selectively solidified. In a laser sintering or laser melting process, for example, this includes information about the laser intensity or energy density of the laser radiation, the laser beam diameter, and the travel speed at which the impact point or impact area of the laser beam is moved across the applied powder layer, as well as the solidification paths along which the impact point or impact area of the laser beam is moved.

[0052] To provide control data, the device 100 comprises at least the isoline receiving unit 101 and the isoline storage unit 102 (see Fig. 1 ) for receiving or storing data that describe warpage field isolines in the at least one object. Furthermore, the device 100 can comprise, for example, a model data access unit (not shown) for accessing the computer-based model (CAD model) of the object 2 to be manufactured, as well as a data model generation unit (not shown) for generating a data model of the object cross-sections that specifies the scanning of the building material layers with the laser beam 22, in particular the solidification paths. Furthermore, the device 100 can comprise a control data generation unit (not shown) for generating control data for providing control commands.

[0053] The model data access unit and the contour line reception unit are, for example, a software or hardware interface that enables access to the model data stored in the memory of a CAD design computer or the calculated distortion field contour lines (possibly via a network). Alternatively, the access unit(s) can be a reader that reads the data stored on a mobile data storage device.

[0054] The generation of control data for the laser sintering or laser melting device 1 is described below with reference to Fig. 2 described. In a first step S1, the computer-based model data (CAD data) of the object to be manufactured is accessed, e.g., by the model data access unit. Preferably, the model data is already available as layer information, so that in step S1, access to the computer-based model data of the object cross-sections to be solidified takes place.

[0055] In a second step S2, a data model is generated for each object cross-section (i.e., for each build-up material layer to be selectively solidified), e.g., by the data model generation unit, wherein the scanning of the build-up material layer with the laser beam 22 along solidification paths is specified in the data model for each object cross-section. For this purpose, the data model generation unit accesses distortion field isoline data that was previously provided and received by the isoline receiving unit 101. The isoline receiving unit 101 feeds the data corresponding to the distortion field isolines to the isoline storage unit 102, where they are stored and are available for calculating the solidification paths as part of generating the data model.

[0056] In a third step S3, control data corresponding to the data model generated in the second step S2 is provided, e.g., by the control data generation unit, which serves to generate a control data set. The control data thus provided comprises at least the solidification paths along which the point of impact of the laser beam 22 is to be moved for the selective solidification of the respective build-up material layer, and can then be integrated into a control data set.

[0057] The provision of warpage isolines can occur even before the start of the manufacturing process, e.g., if the warpage isolines are determined as described below using a test specimen or by simulation. In this case, the warpage isolines are preferably received by the isoline receiving unit 101 in step S1 and stored in the isoline storage unit 102. This allows a complete control data set to be provided even before the three-dimensional object is manufactured.

[0058] If the warpage field isolines are determined during the manufacturing process, e.g., by means of a process monitoring method, the warpage field isolines are preferably received by the isoline receiving unit 101 in step S2 and stored in the isoline storage unit 102. The control data specifying the solidification paths are then integrated into the control data set during the manufacture of the object, but before the selective solidification of the respective layer, or the exposure device 20 is controlled via the control unit 29 using at least the control data specifying the solidification paths.

[0059] The provision of control data specifying the hardening paths before and during the manufacturing process can also be combined. For example, some control data can be provided before the start of the manufacturing process and another part of the control data only during the manufacturing process. Furthermore, distortion field contour line data provided before the start of the manufacturing process can also be modified during the manufacturing process, e.g., based on information obtained through process monitoring.

[0060] The following procedure can be used to determine warpage field isolines: In a first exemplary embodiment for determining warpage field isolines, a manufacturing process of a three-dimensional object 2 in the laser sintering or laser melting device 1 is simulated using a computer simulation, wherein the simulated solidification paths do not run along warpage field isolines, i.e., a different exposure pattern than the exposure pattern according to the invention is used. For example, the simulated layer-by-layer selective solidification can take place under the assumption that the laser beam is moved across the build field along mutually parallel lines. Based on this simulation, the resulting mechanical residual stresses in the object, in particular thermally induced, are calculated, and / or the resulting deformation of the object is calculated.Subsequently, using the layer data based on the CAD data set, residual stress values or deformation values are calculated for each object cross-section. These values are scalar values, meaning a scalar distortion field is calculated for each object cross-section. To calculate scalar residual stress values, for example, an equivalent stress can be calculated, which allows a simplified description of the actual multiaxial stress state. Then, distortion field isolines—i.e., lines with constant distortion field isovalues (residual stress field isovalues or deformation field isovalues)—are calculated for each object cross-section from the scalar distortion field calculated for the respective object cross-section, for example, using a marching squares algorithm.

[0061] In a second embodiment for determining warpage field isolines, a test specimen is produced in the laser sintering or laser melting device 1. The test specimen is produced using the same CAD data as the object to be produced, but using a different exposure strategy. In particular, the solidification paths selected for producing the test specimen do not run along warpage field isolines or sections thereof; e.g., the laser beam is moved across the build field along parallel lines. The test specimen is then measured, i.e., the mechanical residual stresses and / or deformations occurring in the test specimen are determined. Subsequently, as above with regard to the first embodiment, warpage field isolines are determined for each cross-section of the object using a scalar field in the respective cross-section.

[0062] A third exemplary embodiment for determining warpage field isolines is based on values of process monitoring parameters measured during the manufacturing process of the object 2. For example, process radiation 34 emanating from the point of impact of the laser beam 22, for example thermal radiation, can be detected by the sensor 30 and forwarded to the process monitoring device 31. The process monitoring device 31 evaluates this signal and thus determines, for example, a two-dimensional temperature distribution in the build field 8. Based on the temperature distribution thus detected, warpage field isolines are calculated, for example based on temperature gradients. The warpage field isolines calculated for a build material layer or for an object cross-section are thus based on a temperature distribution of at least one underlying (previously selectively solidified) build material layer orat least one underlying object cross-section.

[0063] In the first and second exemplary embodiments described above for determining warpage field isolines, the mechanical stress states (e.g. in the form of a stress tensor) or a warpage field (e.g. a vector field) are essentially first calculated. This is then converted layer by layer into a scalar, two-dimensional field, if necessary with the aid of suitable simplifications such as the assumption of an equivalent stress, from which the warpage field isolines are then calculated. Alternatively, warpage field iso-surfaces can also be calculated first based on the mechanical stress states or the warpage field for the entire object. The warpage field iso-surfaces in the respective cross-section are then determined from the intersection lines of the warpage field iso-surfaces with the respective object cross-sections.This calculation of the warpage field isolines from warpage field isosurfaces does not have to be carried out in advance, it can also be carried out when the data model is generated, ie in this case the isoline receiving device 101 does not receive the warpage field isolines, but the warpage field isosurfaces.

[0064] Preferably, the warpage field isovalues for which warpage field isolines or warpage field isosurfaces are calculated are selected such that a distance between adjacent warpage field isolines or warpage field isosurfaces is smaller than a width of a consolidation path.

[0065] In particular, it is also possible to combine the procedures of the first to third embodiments, i.e., for example, to modify warpage field isolines determined from simulations after test specimen measurements or to modify warpage field isolines obtained by simulation or test specimen measurement using process monitor data.

[0066] Determining the solidification paths as part of creating a data model (step S2 in Fig. 2 ) of a first cross-section (build-up material layer n) based on the distortion field isolines determined for this cross-section is described below with reference to Fig. 3a described. Fig. 3a shows a plan view of a section of the construction field 8, in which an n-th layer of building material is applied. Furthermore, Fig. 3a schematically solidification paths 30 are shown, along which the impact area of the laser beam is to be guided over the n-th build-up material layer in order to solidify the build-up material in the Fig. 3a To simplify the illustration, the consolidation paths 30, 31 are shown in Fig. 3a und 3b shown as solidification lines, ie without a dimension perpendicular to their main direction of extension, along which the impact area of the laser beam is or is to be guided to solidify the build-up material. The width (see below) of the solidification paths 30, 31 is shown in the Fig. 3a, 3b therefore not shown. The Fig. 3a, 3b The lines representing the solidification paths can, for example, be lines on which a defined point of the impact area of the laser beam, for example the center of the impact area, is or is to be guided to solidify the build-up material.

[0067] To determine the solidification paths 30, the distortion field isolines calculated for this cross-section are iteratively deleted section by section until only sections of distortion field isolines remain in which adjacent distortion field isolines or distortion field isoline sections are spaced apart by a distance d. The distance d is selected such that it corresponds to the width of the solidification path(s) 30 at the respective location in the build field 8. The width or track width (not shown in the figures) of a solidification path is to be understood as a dimension of the solidification path 30 perpendicular to the direction in which the impact area of the laser beam 22 is or is to be guided along the solidification path. For example, the width can correspond to the size of the melt pool created by the laser beam in the build plane.Since the width of a consolidation path can vary across the build area 8, the local width of the consolidation path in the working plane 7 is meant here. The distance d between adjacent warpage field isolines or warpage field isoline sections can thus vary across the build area 8. The warpage field isolines or sections determined in this way are then provided as consolidation paths 30 as a data model for this cross-section for specifying the scanning of the build material layer n.

[0068] Determining the solidification paths as part of creating a data model (step S2 in Fig. 2 ) of a second cross-section (build-up material layer n+1) based on the distortion field isolines determined for this cross-section is described below with reference to Fig. 3b described. Fig. 3b shows the same section of construction site 8 in a plan view as Fig. 3a with a build-up material layer n+1 and schematically illustrated strengthening tracks 31. The strengthening tracks 30 of the n-th layer lying directly below the (n+1)-th layer are in Fig. 3b shown schematically as dashed lines.

[0069] In principle, the consolidation paths 31 of the second cross-section, i.e., in the (n+1)th layer, are calculated as described above based on the distortion field isolines. However, the consolidation paths 31 of layer n are determined in such a way that they are not identical to the consolidation paths 30 in the underlying layer n. For this purpose, the consolidation paths 31 are determined in such a way that they have a different position and / or orientation in the plane of the construction area 8 (the construction plane or working plane 7) than the consolidation paths 30 in the underlying layer n.

[0070] For example, the warpage field isolines on the basis of which the solidification paths 31 of layer n+1 are determined can belong to different warpage field iso-surfaces than the warpage field iso-lines on the basis of which the solidification paths 30 of layer n are determined. As a result, the solidification paths 31 of layer n+1 have, at least in sections, at least one offset a compared to the solidification paths 30 of layer n, i.e., a section of a solidification path 31 has a different position, but essentially the same two-dimensional course in the build field 8, as a corresponding section of a solidification path 30 in layer n.

[0071] The Fig. 3a, 3b The solidification paths 30, 31 shown may be merely sections of the underlying distortion field isolines. However, the solidification paths 30, 31 preferably extend over the entire length of the underlying distortion field isolines.

[0072] The procedure described above for determining hardening paths based on warpage field isolines does not have to be carried out for the entire three-dimensional object to be manufactured. Rather, it is also possible to carry out the described method only in sections, i.e. for at least one area of the three-dimensional object. The other object areas can then be hardened using any other exposure pattern. For example, the hardening paths can be determined based on warpage field isolines only for areas of the three-dimensional object in which a previously defined warpage value (residual stress value or deformation value) is exceeded. If the previously defined warpage value is undershot, a different exposure pattern can be used in the respective areas. Areas with essentially constant warpage values (so-calledPlateaus) using a conventional exposure pattern, ie exempt from scanning along distortion field isolines or distortion field isoline sections.

[0073] The determination of hardening paths based on distortion field isolines is described above using a first layer n and a second layer n+1 applied directly to the first layer n, whereby the hardening paths of layer n+1 are selected such that they are not identical to the hardening paths of layer n. Alternatively or additionally, the hardening paths in layer n+1 (i.e., in a cross-section n+1) can also be selected taking into account the hardening paths of another, but not directly underlying, layer of the build-up material (i.e., a cross-section), i.e., a layer nx (or a cross-section nx) with x ≥ 1.

[0074] As an alternative to calculating the warpage field isolines based on a deformation field or a residual stress field, the stiffness of the three-dimensional object can also be used to calculate the warpage field isolines. Analogous to the deformation or residual stresses of the object, the stiffness refers to a simulation or measurement of a test specimen under the condition that the exposure pattern underlying the simulated object or the test specimen does not include scanning the build material along warpage field isolines or sections thereof.

[0075] The above in relation to Fig. 1The exposure device 20 described comprises a laser 20 for generating a laser beam 22, wherein the point of incidence of the laser beam is moved accordingly over the building material layer for selectively solidifying a building material layer. The exposure device of the laser sintering or laser melting device can also comprise several gas or solid-state lasers or any other type of laser, such as laser diodes, in particular VCSELs (Vertical Cavity Surface Emitting Lasers) or VECSELs (Vertical External Cavity Surface Emitting Lasers), or a row of these lasers. Therefore, particularly in the case where several lasers are directed simultaneously onto the building material in the working plane, the term "energy beam bundle" is used instead of "laser beam," or the term "impact area" is used instead of "impact point."

[0076] Furthermore, the present invention is not limited to laser sintering or laser melting; rather, it can be applied to any method for the additive manufacturing of a three-dimensional object by layer-by-layer application and selective solidification of a building material. In general, any device with which energy can be selectively applied to a layer of the building material as wave or particle radiation in the form of an energy beam or energy beam bundle can be used as the energy input device. Instead of a laser, for example, one or more other light sources, one or more electron beams, or any other energy or radiation source suitable for solidifying the building material can be used.

[0077] Various types of powder can be used as build-up material, including metal powder, plastic powder, ceramic powder, sand, filled powder, or mixed powder. Instead of powder, other suitable materials can also be used as build-up material.

Claims

1. Computer-aided method for providing control data for an additive manufacturing device (1) for manufacturing a three-dimensional object (2) by means thereof, wherein the object (2) is manufactured by applying a building material (15) layer upon layer and solidifying the building material (15) by supplying radiation energy to locations in a layer which are assigned to the cross-section of the object (2) (2) in this layer, by means of at least one energy input device (20) for inputting energy into the building material (15), which scans these locations with at least one energy beam (22) in accordance with a set of energy input parameters along a number of solidification paths (30, 31) in a building plane, wherein the method for providing control data comprises: a first step (S1) of accessing computer-based model data of two cross-sections of an object section to be solidified in temporal succession, preferably immediately in temporal succession, during manufacture, a second step (S2) of generating a data model of each of the two cross-sections, wherein in the data model for each of the two cross-sections, a scanning of the building material layer with at least one energy beam (22) along at least one solidification path (30, 31) is specified, wherein it is specified that, when scanning the locations of a building material layer which are assigned to the respective cross-section to be solidified, the impact area of at least one energy beam (22) on the building material is moved along at least a section of a distortion field isoline, wherein the residual stress field and / or deformation field or a stiffness of the three-dimensional object is determined for the two cross-sections by means of simulation and the distortion field isolines are subsequently determined, and / or wherein the residual stress field and / or deformation field or a stiffness of the three-dimensional object for the object section is determined by measuring a test specimen produced in advance and the distortion field isolines for the two cross-sections are then determined, and / or wherein distortion field isolines of the two cross-sections are determined by determining the residual stress field and / or deformation field in the two cross-sections on the basis of values of process monitoring parameters measured during the manufacture of the three-dimensional object and before the solidification of the object section, wherein a section of a distortion field isoline along which the impact area is moved during scanning of the cross-section to be solidified later in time is selected such that it has a different position and / or orientation in the building plane compared to a section of a distortion field isoline along which the impact area is moved during scanning of the cross-section to be solidified first, and a third step (S3) in which control data corresponding to the data model generated in the second step (S2) are provided for generating a control data set for the additive manufacturing device (1).

2. Method for computer-aided control of a number of energy input devices (20) of an additive manufacturing device (1) for manufacturing a three-dimensional object (2) by means thereof, wherein the object (2) is manufactured by applying a building material (15) layer upon layer and solidifying the building material (15) by supplying radiation energy to locations in a layer that are assigned to the cross-section of the object (2) in this layer, by means of at least one energy input device (20) for inputting energy into the building material (15), which scans these locations with at least one energy beam (22) according to a set of energy input parameters along a number of solidification paths (30, 31) in a building plane, wherein the number of energy input devices (20) is controlled using control data provided in a method according to claim 1.

3. Method according to claim 1 or 2, wherein it is specified for the two cross-sections that the impact area is moved along a plurality of sections of distortion field isolines which are selected such that their mutual distance (d) substantially corresponds to the width of a solidification path on the building material transverse to the direction of movement of the impact area.

4. Method according to one of claims 1 to 3, wherein a section of a distortion field isoline along which the impact area is moved when scanning the cross-section to be solidified later in time, has an offset (a) within the building plane relative to a section of a distortion field isoline along which the impact area is moved when scanning the cross-section to be solidified first.

5. Method according to one of claims 1 to 4, wherein the sections of distortion field isolines along which the impact area is moved in the two cross-sections extend over the entire length of a distortion field isoline.

6. Method according to one of claims 1 to 5, wherein the sections of distortion field isolines along which the impact area is moved in the two cross-sections are selected such that the sections in different cross-sections belong to different distortion field isosurfaces.

7. Device for computer-aided control of a number of energy input devices (20) of an additive manufacturing device (1) for manufacturing a three-dimensional object (2) by means thereof, wherein the object (2) is manufactured by applying a building material (15) layer upon layer and solidifying the building material (15) by supplying radiation energy to locations in a layer which are assigned to the cross-section of the object (2) in this layer, by means of at least one energy input device (20) for introducing energy into the building material (15), which scans these locations with at least one energy beam (22) in accordance with a set of energy input parameters along a number of solidification paths (30, 31) in a building plane, wherein the device is configured such that the number of energy input devices (20) is controlled in such a way that, for two cross-sections of an object section to be solidified in temporal succession, preferably immediately in temporal succession, during manufacture, it is specified that the building material layer is scanned with at least one energy beam bundle (22) along at least one solidification path (30, 31), wherein it is specified that, when scanning the locations of a building material layer which are assigned to the respective cross-section to be solidified, the impact area of at least one energy beam (22) on the building material (15) is moved along at least one section of a distortion field isoline, wherein the residual stress field and / or deformation field or a stiffness of the three-dimensional object is determined for the two cross-sections by means of simulation and the distortion field isolines are subsequently determined, and / or wherein the residual stress field and / or deformation field or a stiffness of the three-dimensional object is determined for the object section on the basis of a measurement of a test specimen produced in advance and the distortion field isolines for the two cross-sections are subsequently determined, and / or wherein distortion field isolines of the two cross-sections are determined by determining the residual stress field and / or deformation field in the two cross-sections on the basis of values of process monitoring parameters measured during the manufacture of the three-dimensional object and before the solidification of the object section, wherein a section of a distortion field isoline along which the impact area is moved during scanning of the cross-section to be solidified later in time is selected such that it has a different position and / or orientation in the building plane relative to a section of a distortion field isoline along which the impact area is moved during scanning of the cross-section to be solidified first.

8. Device according to claim 7, further having an isoline receiving unit (101) for receiving data describing the position of distortion field isolines in the at least one object (2).

9. Device according to claim 7 or 8, further having an isoline storage unit (102) for storing data describing the position of distortion field isolines in the at least one object (2).

10. Additive manufacturing device (1) for manufacturing a three-dimensional object (2), wherein the object (2) is manufactured by applying a building material (15) layer upon layer and solidifying the building material (15) by supplying radiation energy to locations in a layer which are assigned to the cross-section of the object (2) in this layer by means of at least one energy input device (20) for introducing energy into the building material (15), which scans these locations with at least one energy beam (22) in accordance with a set of energy input parameters along a number of solidification paths (30, 31) in a building plane, wherein the additive manufacturing device (1) comprises a device according to one of claims 7 to 9.

11. Additive manufacturing method for manufacturing a three-dimensional object (2), wherein the object (2) is manufactured by applying a building material (15) layer upon layer and solidifying the building material (15) by supplying radiation energy to locations in a layer which are assigned to the cross-section of the object (2) in this layer by means of at least one energy input device (20) for introducing energy into the building material (15), which scans these locations with at least one energy beam (22) in accordance with a set of energy input parameters along a number of solidification paths (30, 31) in a building plane, wherein a method according to one of claims 1 to 6 is part of the additive manufacturing method.

12. Additive manufacturing method according to claim 11, wherein the residual stress field and / or deformation field for the two cross-sections is determined by means of simulation and the distortion field isolines are subsequently determined by a marching squares algorithm.

13. Method according to claim 11 or 12, wherein the residual stress field and / or deformation field for the object section is determined on the basis of a measurement of a test specimen produced in advance and the distortion field isolines for the two cross-sections are subsequently determined by a marching squares algorithm.

14. Computer program having program code means for executing all steps of a method according to one of claims 1 to 6 when the computer program is executed on a data processor, in particular a data processor cooperating with an additive manufacturing device (1).