Method for additive manufacturing and process unit for controlling an additive manufacturing system

Abstract

Method for additive manufacturing in which a continuously supplied powder is melted using a laser beam (80) to build up a component (3), wherein the material of the already built section of the component (3) is preheated via at least one further energy source and / or the material just built up is reheated via the at least one further energy source, wherein at least two laser beams (130, 250) of different wavelengths are used as a further energy source, and wherein a material-specific temperature-time profile is used for each component (3), which is retrieved as a predefined temperature-time profile from a storage unit (22), characterized in that For each of the material-specific temperature-time profiles, it is stored which laser source (13, 25), with which wavelength and how strong, should be involved.

Description

[0001] The invention relates to a method for additive manufacturing in which a continuously supplied powder is melted by means of a laser beam, according to the type defined in more detail in the preamble of claim 1. Furthermore, the invention relates to a process unit for controlling an additive manufacturing system for carrying out this method.

[0002] The additive manufacturing process according to the preamble of claim 1 is fundamentally known from the prior art. This process is a so-called DED process, where DED stands for Direct Energy Deposition. If the supplied material is melted using a laser beam, the process is also referred to as L-DED (Laser-Direct Energy Deposition). Typically, a carrier gas continuously supplies powder, which is melted using the laser beam under a protective gas atmosphere in order to successively build the component on a build platform. In practice, a critical aspect of such processes is that cracks can repeatedly form in the material and / or the connection zone to the build platform of the additively manufactured component. The causes of this crack formation are known and essentially lie in thermally induced tensile-compressive residual stresses resulting from the material alloy.

[0003] It is known to preheat components during additive manufacturing to ensure good bonding of the molten powder to the substrate and / or the build platform. In this context, reference can be made to US Pat. No. 10,933,493 B2. A laser used as an energy source for this purpose can be designed, for example, according to DE 10 2010 048 645 A1.

[0004] In addition to preheating, the state of the art also includes postheating of the material. In this context, reference can be made to US Pat. No. 10,710,307 B2. Here, the material is preheated using an array of infrared LEDs, the additive manufacturing step is carried out, and the material is then postheated to slow cooling, thus reducing residual stresses and thus the risk of cracking. The document describes in general terms that lasers can be used instead of IR diodes, and that a desired temperature profile can be set on the surface of the material using control and temperature measurement.

[0005] DE 10 2020106 823 A1 relates to a device and a method for laser deposition welding, comprising a laser deposition welding unit with at least one laser deposition welding head arranged thereon, material sources for supplying the laser deposition welding head and a laser beam source for carrying out the laser deposition welding, wherein the device is designed to apply material layers from adjacent deposition welding tracks to a surface of a component in the form of at least a first layer made of a material which comprises structures with a first hardness protruding from the surface of the first layer and a second layer applied thereon made of a material with a second hardness less than the first hardness.

[0006] US 11 611 097 B2 describes a manufacturing method comprising applying a composition in slices to a substrate to form an object and heating the object in place using electromagnetic radiation; wherein the composition comprises a first material and a second material, the second material having a higher absorption of the radiation than the first material. In one embodiment, the radiation comprises light, near ultraviolet light, near infrared light, infrared light, visible light, lasers, or electron beams.

[0007] In practice, different materials react differently to preheating, and especially to postheating to slow cooling. This can result in different material properties and / or residual stresses within the material. This directly influences crack formation or the risk of crack formation.

[0008] The object of the present invention is therefore to provide an improved method for additive manufacturing according to the preamble of claim 1, which avoids these disadvantages.

[0009] According to the invention, this object is achieved by a method having the features in claim 1, and in particular by the features in the characterizing part of claim 1. Advantageous embodiments and further developments of the method according to the invention emerge from the subclaims dependent on the main claim. Furthermore, claim 7 specifies a process unit for controlling an additive manufacturing system for carrying out this method.

[0010] In the method according to the invention, a material-specific temperature-time profile is used for each component, which is retrieved as a predetermined temperature-time profile from a storage device.

[0011] In practice, it has been shown that different materials and material compositions require different post-treatments or different temperature profiles during cooling to reduce unwanted cracking. If separate temperature-time profiles are created for each individual component or the material used to manufacture this component and stored in a memory unit, these can be easily retrieved using the manufacturing process according to the invention, so that each individual component with its specific material composition can be manufactured simply, efficiently, and reliably using the temperature-time profile appropriate for that material. This significantly reduces the risk of cracking, and production remains very fast and efficient thanks to the retrieval of the pre-stored temperature-time profiles.

[0012] According to an advantageous development of the method according to the invention, the surface temperature can be recorded during preheating and / or postheating, with the measured temperature being controlled based on the temperature-time profile. This ensures that, based on the reported measured temperature, which according to an advantageous development can be measured in particular using a pyrometer, the specified temperature-time profile is maintained as precisely as possible in order to achieve the same properties of the additively manufactured component in a process-reliable and reproducible manner.

[0013] A particularly advantageous embodiment can also provide for several material-specific temperature-time profiles to be stored for post-heating for each material, in order to achieve a different, targeted structural change with each of the temperature-time profiles. In this particularly advantageous embodiment of the structure according to the invention, several temperature profiles are stored for the corresponding materials. This allows a targeted structural change to be achieved in desired areas of the component. In this way, component properties can be adjusted locally to suit the load and function. For example, in a punch used as a stamping tool, the cutting edge can be made correspondingly harder than the core of the component in order to achieve a targeted, function-specific influence on the properties.

[0014] Another very advantageous embodiment can also provide that the at least one further energy source for the post-heating is controlled, if necessary, in such a way that errors that occurred during melting of the supplied powder with the laser beam are corrected. If, for example, excessive material accumulation due to uneven powder conveyance or the like leads to errors in the area of ​​the material applied via additive manufacturing, then the at least one further energy source, particularly if it is also in the form of a laser beam, which is to be provided according to an advantageous development, can be used to specifically melt or remelt the material in order to correct the error that occurred.

[0015] According to the invention, the at least one further energy source is designed as a laser beam, which is provided in addition to the laser beam for melting the powder for additive manufacturing. It is provided that at least two laser beams of different wavelengths are used as a further energy source. In principle, any number of laser beams of the same wavelength could of course be used to achieve the desired preheating and / or postheating. If more than two laser beams are provided as a further energy source, then, according to this particularly advantageous embodiment of the method according to the invention, a different wavelength should be used for the laser beams. In this way, the laser beams can be ideally adapted as further energy sources for processing multi-material, for example made of copper and nickel-based alloys.By adapting the wavelength to the respective material, further specifications regarding the materials used are possible. For example, for various lasers, the predefined and stored profile also specifies which wavelength of laser radiation or which combination of wavelengths should be used to implement the corresponding temperature-time profile.

[0016] According to a very advantageous development of the method according to the invention, the material-specific temperature-time profiles can be created and stored on a model-based basis and / or based on test data. It is particularly advantageous if test data serves as the original starting point, via which corresponding material-specific temperature profiles, specific to the desired microstructure properties, can then be adjusted and calculated using mathematical models. This allows a large number of suitable temperature profiles to be provided computationally with minimal effort in order to obtain the specified temperature-time profiles as efficiently as possible. Furthermore, it is of course possible to use machine learning or similar methods toartificial intelligence, such as neural networks, to systematize test values ​​accordingly in order to derive material- and / or structure-specific temperature-time profiles and to make them available for the method according to the invention.

[0017] A process unit for controlling an additive manufacturing system, in particular an L-DED system, for carrying out the method according to the invention provides, in addition to its usual control modules, its sensors and actuators, at least one storage unit in which the individual material-specific temperature-time profiles are stored in a retrievable manner.

[0018] Further advantageous embodiments of the method according to the invention and the process unit also emerge from the exemplary embodiment, which is described in more detail below with reference to the figures.

[0019] Showing: Fig. 1 an additive manufacturing system in an embodiment according to the prior art; Fig. 2 an additive manufacturing system in a first possible embodiment according to the invention; Fig. 3 a schematic representation of two via the production plant according to Fig. 2 manufactured punching dies; Fig. 4 a schematic representation of a section of the manufactured component to explain a method aspect of the method according to the invention; and Fig. 5 an additive manufacturing system in a second first possible embodiment according to the invention.

[0020] In the presentation of the Fig. Figure 1 shows a simplified schematic representation of a production system 1 for a laser direct energy deposition (L-DED) process. A component, designated here by 3, is to be manufactured on a build platform designated by 2. To symbolize the additive manufacturing process, the component 3 is shown in several individual layers, starting from the build platform 2. In order to build this component 3 using the L-DED process, a material powder is conveyed from a powder depot 4 via a carrier gas originating from a carrier gas source 5. The powder supplied by the carrier gas is guided via a nozzle 6, indicated schematically here, into the area of ​​the component 3 in which it is to be added. In addition, protective gas is supplied from a protective gas source 7 to protect the powder, which is melted by means of a laser source 8, from oxidation by atmospheric oxygen.The laser source 8 sends its laser beam 80 to a beam guidance system 9, indicated here as a prism, and from there, via a focusing device such as a lens 10, the laser beam 80 reaches the area of ​​the surface of the component 3 to melt the powder. The problem with this design, which, as indicated by the coordinate system, allows movement in all spatial directions and is thus suitable for producing complex components 3, is that the comparatively rapid cooling of the molten powder material often leads to cracking. In the illustration of the . Fig. 1, several such cracks 12 are indicated in the component 3.

[0021] In order to remedy this situation efficiently, it is necessary to set up the production plant for additive manufacturing 1 in the representation of the Fig. 2, it is provided that the material of component 3 is reheated after the melting of the newly added powder. Alternatively or additionally, volume areas adjacent to the added and remelted powder can also be preheated. In the illustration of the Fig. 2 is the Fig. 1 is taken up again. As far as it corresponds to the illustration there, the components have the same reference numerals and have the same function. For reheating, the Fig. 2, a laser source 13, which, via a focusing system 14 and a mirror 15 adjustable in the plane, directs a laser beam designated 130 onto the component 3 in order to reheat the material just applied. Furthermore, it is also intended to use additional laser sources 13 for reheating. Alternatively or additionally, it is also possible to use at least one laser source 13 or several laser sources 13 for preheating. Alternatively or additionally to a laser source 13, another heat source, for example, a diode heat source, can also be used.

[0022] Overall, the purpose of preheating and / or postheating is to control the cooling of this material over time, in particular to slow it down, in order to reduce the residual stresses in the material, which demonstrably lead to the formation of cracks 12, which is often problematic in the prior art.

[0023] This reheating is shown in the enlarged section in the Fig. 2 is schematically indicated on the left. Laser beam 80 is visible on the far left, and laser beam 130 is visible to the right. After repeated remelting with laser beam 80 from right to left and the simultaneous melting of the applied powder, the material cools down accordingly. This cooling is delayed by reheating using laser beam 130. The cooling can be controlled via a predetermined temperature-time curve or a predetermined temperature-time profile. The reheating time can also be achieved by deliberately defocusing the laser with simultaneous adjustment of the laser power. In the illustration of the Fig. 2 shows a pyrometer 16 for measuring the surface temperature in the area of ​​the additional laser beam 130 impinging on the component 3 for post-heating. Furthermore, additional pyrometers 16 can also be used, for example, to measure the surface temperature in the area of ​​the component before the respective powder application and remelting.

[0024] This pyrometer, designated here with 16, records the current temperature and supplies it to a control 17 shown with a dotted border. This control 17 is thus supplied with the actual value of the temperature T in the box designated with 18. ist At the same time, it receives the current set temperature T soll according to a temperature-time profile according to which the material of component 3 is to cool. This target temperature T soll is in box 20 with the actual temperature T istIf a deviation occurs, the power P of the additional laser source 13 is adjusted accordingly via the box labeled 21 in order to determine the actual temperature T ist to correct up or down.

[0025] The special feature of the production plant described here is that various temperature-time profiles are stored in a memory unit designated 22. From this, the desired temperature-time profile can be retrieved. Based on the time t available to the control system 17, the current target temperature T can be determined. soll be determined in order to control production plant 1 and thus regulate the actual temperature at the respective time.

[0026] These temperature-time profiles stored in the storage unit 22 are material-specific. This means that the temperature-time profiles stored there represent a cooling curve for the respective material and its respective desired material properties, which leads to ideal cooling of the material and thus to a minimization or prevention of the formation of cracks 12. Since this is material-specific, separate temperature-time profiles are stored in the storage unit 22 for different materials used, so that, for example, the appropriate temperature-time profile for precisely this material can be selected through manual input or automatic recognition of the material used in the powder source 4.

[0027] Different temperature-time profiles can also be maintained for a material, which can also be specifically designed for different target microstructures, thus ensuring different microstructures during cooling of the material and thus, for example, different hardnesses in iron-carbon alloys or steel materials. Such different temperature-time profiles for the same material applied during additive manufacturing then allow the material properties to be adjusted within one and the same component by changing the temperature-time profile.

[0028] In the presentation of the Fig. 3 shows two components 3 purely as examples, which are intended to be used, for example, as punches for stamping. The component 3 shown on the right has offset areas 23 on its right and left edges, which are intended to represent a different material property of one and the same material. On the component 3 in the illustration of Fig. Four such areas 23 can be seen on the left side of Figure 3, each at the corner. These offset areas 23 are intended to be designed as cutting edges and accordingly have a higher hardness than the remaining material of the respective component 3. For identical materials, this can be achieved by varying the temperature-time profile accordingly.

[0029] Another possibility to go beyond the pure material-specific adaptation of the temperature-time profile is to represent the Fig. 4. In the representation of the Fig. 4 on the left shows the laser beam 80 used for additive manufacturing and, following this in the feed direction or scanning direction, which is indicated here by the arrow, the laser beam 130 used for post-heating. An error is said to have occurred during the production of the component. On component 3, in the illustration of the Fig. 4 on the left shows an undesirable accumulation of material, designated 24, for example, because the powder material was not melted properly, too much powder material was fed to this point, or the like. The laser beam 130, typically used for reheating, now offers the possibility of remelting the material in the area of ​​this defect 24, so that after repeated scanning or remelting of the material with the laser beam 130, this defect 24 has been corrected accordingly, as shown in the illustration of Fig. 4 can be seen on the right.

[0030] In the presentation of the Fig. 5 the previously entered Fig. 1 and Fig. 2 shown and described structure is taken up again. The structure corresponds exactly to that of the Fig. 2, with the exception that, in addition to the laser source 13, a second laser source, designated here by 25, is provided as an additional energy source. This also includes a focusing device 26 and a mirror 27 adjustable in a plane. Analogous to the previous numbering, its laser beam is designated 250.

[0031] This can now be directed onto the surface of component 3 alternatively or in addition to the laser beam 130. This increases the variability of the post-heating process.

[0032] In particular, and this is the decisive advantage of two or more dedicated laser sources 13, 25, it can also be provided that the two laser sources 13, 25 have different wavelengths, thus matching the different materials being processed. This allows multi-materials, such as copper and ion, to be easily processed and efficiently reheated using the corresponding wavelengths of the laser sources 13, 25, in order to efficiently set the appropriate predefined temperature-time profile and adjust it via the control unit 17. In addition to the temperature profiles, the memory unit 22 can also store corresponding information on the required wavelength and thus ultimately on the laser source 13, 25 used. The box designated 21 then controls not only the power P, but simultaneously also whether one laser source 13, the other laser source 25, or both laser sources 13, 25 are used.The power can be adjusted accordingly, so that, for example, one laser source 13 operates at a fraction of its power while the other laser source 25 operates at full power. All possible combinations are conceivable.

Claims

[1] Method for additive manufacturing, in which a continuously supplied powder is melted by means of a laser beam (80) in order to build up a component (3), wherein the material of the already built-up section of the component (3) is preheated via at least one further energy source and / or the material just built up is reheated via the at least one further energy source, wherein at least two laser beams (130, 250) of different wavelengths are used as a further energy source, and wherein for each component (3) a material-specific temperature-time profile is used, which is retrieved as a predetermined temperature-time profile from a storage unit (22), characterized by , that for each of the material-specific temperature-time profiles, it is stored which laser source (13, 25), with which wavelength and how strong, should be involved. [2] Method according to claim 1, characterized bythat the surface temperature (T soll ) in the pre- and / or post-heating area, whereby the required temperature (T soll ) is controlled according to the temperature-time profile. [3] Method according to claim 2, characterized by that the surface temperature is measured by means of a pyrometer (16). [4] Method according to one of claims 1 to 3, characterized by that for each material composition, several material-specific temperature-time profiles are maintained for pre- and / or post-heating in order to achieve a different targeted structural change with each of these temperature-time profiles. [5] Method according to one of claims 1 to 4, characterized by that the energy source for the post-heating is controlled, if necessary, in such a way that errors (24) that occurred when the supplied powder is melted by means of the laser beam (80) are corrected. [6] Method according to one of claims 1 to 5, characterized by that the material-specific temperature-time profiles are created and stored based on models and / or test data. [7] Process unit for controlling an additive manufacturing system (1) for carrying out the method according to one of claims 1 to 7, with a storage unit (22) in which various predetermined tool-specific temperature-time profiles are stored in a retrievable manner.

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