Method for preheating of a substrate body, method for additive manufacturing of a workpiece, machine tool and control device

Abstract

The invention relates to a method for preheating of a substrate body (200) in preparation for an additive manufacturing method, in particular of a metallic substrate body, by irradiation using a laser beam (L), comprising detecting an actual temperature of the substrate body (200), in particular by means of a thermal imaging camera (50), determining a movement parameter describing a relative movement between laser beam (L) and substrate body (200), at least on the basis of the detected actual temperature, and relatively moving laser beam (L) and substrate body (200) at least as a function of the determined movement parameter, wherein an incidence point (A) of the laser beam (L) is moved along a surface (201) to be irradiated at the substrate body (200).

Description

Method for preheating a substrate body, method for additive manufacturing of a workpiece, machine tool and control device DESCRIPTION Technical area

[0001] The present invention relates to a method for preheating a substrate body, a method for additively manufacturing a workpiece, a machine tool and a control device for use on a machine tool. Background of the invention

[0002] Additive manufacturing processes have recently gained importance for the industrial production of workpieces, as they offer a particularly flexible and fast way of primary forming said workpieces.

[0003] Said additive manufacturing processes include, in particular, processes for deposition welding, also known as DED processes (Directed Energy Deposition), in which a build-up material is applied to a surface of a workpiece blank (generally a substrate body) using an energy beam (laser, electron beam or plasma arc) in order to form a workpiece section.

[0004] To ensure the highest possible workpiece quality, the workpiece blanks are optionally preheated prior to build-up welding. This reduces, among other things, the risk of material defects at the interface between the workpiece blank and the applied build-up material. Preheating is carried out using non-melting heating, so that the workpiece blank retains its solid state and microstructure.

[0005] For preheating, the use of heating furnaces is known from the state of the art, among other things, in which the workpiece blanks are preheated before they are subjected to the build-up welding process. This requires several, particularly time-consuming, work steps, during which the workpiece blank must be transported from the heating furnace to the machine tool used for additive manufacturing and clamped there, followed by a measurement of the workpiece blank before the actual production begins.

[0006] Furthermore, WO 2021 099 459 A1 discloses a method for the additive manufacturing of a workpiece by means of build-up welding, in which the workpiece is pre-formed in advance by thermal energy input by means of stationary irradiation with a laser beam in order to compensate for deformation during the subsequent build-up welding.

[0007] Heating by means of the laser beam represents an alternative to the heating furnace with fewer work steps, but thermally induced stresses due to the uneven heating of the workpiece blank are accepted, which in the case of WO 2021 099459 A1 are deliberately intended to be used for deformation. Summary

[0008] An object of the present invention is to provide a more efficient method for additive manufacturing by deposition welding [DED process], which is characterized in particular by fewer work steps and high manufacturing quality.

[0009] To achieve this object, a method for preheating according to claim 1, a method for additive manufacturing according to claim 14, a machine tool according to claim 16 and a control device according to claim 22 are proposed.

[0010] The remaining dependent claims relate to preferred embodiments of the methods or the machine tool, which can be provided individually or in combination.

[0011] According to a first aspect of the invention, a method is provided for preheating a substrate body in preparation for an additive manufacturing process, in particular a metallic substrate body, by irradiation with a laser beam, comprising detecting an actual temperature of the substrate body, in particular by means of a thermal imaging camera, determining a movement parameter that describes a relative movement between the laser beam and the substrate body, at least on the basis of the detected actual temperature, and moving the laser beam and the substrate body relative to each other at least as a function of the determined movement parameter, wherein a point of impact of the laser beam on the substrate body is moved along a surface of the substrate body to be irradiated.

[0012] In other words, the laser beam is moved relative to the substrate body during irradiation based on the detected 1st temperature, so that the point of impact moves over the surface of the substrate body to be irradiated when the laser beam is switched on, in order to implement a locally distributed energy input into the substrate body and to control this specifically through the relative kinematics.

[0013] In this way, despite the use of a point energy source, the entire substrate body can be preheated evenly and particularly quickly, since the energy input by the laser beam is distributed over a large part of the substrate body by its movement. The consideration of the recorded 1st temperature ensures that, for example, no local overheating occurs, which in extreme cases leads to unwanted melting of the substrate body material.

[0014] Essentially, the energy input is controlled via the relative kinematics [and thus via the motion parameter]. For example, the motion parameter is determined such that when the actual temperature approaches the melting temperature of the substrate body, the relative speed is increased to reduce the energy input per area and thus avoid the aforementioned local overheating.

[0015] The method thus allows a high energy input into the substrate body for uniform heating thereof without the risk of local overheating, so that the substrate body can be preheated quickly and evenly without melting, which could not be achieved, for example, by merely point-based and stationary irradiation, as in the case of WO 2021 099 459 A1.

[0016] The uniform and rapid preheating of the substrate body implemented in this way provides an optimal starting point for subsequent additive manufacturing with the cohesive application of a build material. This reduces the risk of material defects or weak points that can arise from uneven or insufficient preheating prior to additive manufacturing, including internal stresses or cracks resulting from uneven cooling of the unevenly heated substrate body, as well as pores or gas inclusions.

[0017] Such material defects can be reliably avoided by the process according to the first aspect, without increasing the process times [compared to the use of a heating furnace]. Furthermore, the energy input with lasers is more targeted. than, for example, in a heater, which in turn has a positive effect on energy costs.

[0018] The laser beam is preferably operated at constant power, in particular in the nominal power range or at maximum power, so that the energy input per unit time into the substrate body can be maximized, thereby shortening the preheating time.

[0019] The substrate body is to be understood as a solid and integral body (i.e., not a powder), and preheating is to be understood as non-melting heating, during which the melting temperature of the substrate body material should not be exceeded. In other words, the substrate body to be preheated remains in its solid state.

[0020] The point of impact of the laser beam is not a point in the mathematical sense, but rather the area on the surface of the substrate body that receives energy input from the laser beam.

[0021] The surface to be irradiated is usually a continuous and in particular continuously differentiable surface, which can be limited by edges of the substrate body, and whose surface is in particular at least 5 times, preferably at least 10 times and particularly preferably at least 50 times the surface of a focal point of the laser beam used.

[0022] The temperature of the substrate body is typically inhomogeneous, so the recorded actual temperature is preferably the maximum of several recorded actual temperatures at different locations on the substrate body. These are usually derived from measurements taken with a thermal imaging or infrared camera.

[0023] The motion parameter in the sense of the method is to be understood as any motion parameter that is suitable for describing a relative movement between the substrate body and the laser beam, in which an impact point of the laser beam moves across a surface of the substrate body. For example, this can be a relative displacement, velocity, or acceleration, in particular of the impact point on the surface to be irradiated, or also a control parameter for a drive that implements the relative movement, for example, of NC axes of a machine tool. The relative displacement, velocity, or acceleration can also be, for example, averaged Values ​​of the relative movement, so that the relative movement should only satisfy the given movement parameter on average.

[0024] Preferably, at least the detection of the actual temperature, the determination of the movement parameter and the relative movement of the laser beam and the substrate body are carried out repeatedly, wherein a sequence of these steps can be understood as a heating cycle.

[0025] In other words, the laser beam is usually moved several times over the surface to be irradiated during the process, whereby the current actual temperature is recorded beforehand and on the basis of this the respective movement parameter is determined.

[0026] Preferably, the relative movement is carried out in such a way that the point of impact of the laser beam covers at least 60%, preferably at least 80% or 90% and particularly preferably at least 95% of the surface to be irradiated, in particular in the course of a single heating cycle.

[0027] This allows the energy input into the surface to be irradiated to be increased, for example during a single heating cycle, and to be distributed as evenly as possible over the substrate body.

[0028] The relative movement of the laser beam during irradiation can be a continuous movement with a relative speed other than zero or a piecemeal movement in which the point of impact moves or is moved between predetermined points and stops at each of these points for a predetermined duration.

[0029] The method is designed in particular for use on a machine tool, with the substrate body being irradiated using a laser device on the machine tool that provides the laser beam. The machine tool comprises at least one drive via which a relative movement between the laser beam and the substrate body can be implemented.

[0030] The step of relatively moving the laser beam and the substrate body comprises controlling the at least one drive as a function of the determined movement parameter, which in this case is in particular a feed parameter.

[0031] Preferably, preheating takes place with the substrate body already clamped, which can also be regarded as a workpiece blank, so that additive manufacturing can begin directly after preheating without having to re-clamp the substrate body.

[0032] In an alternative embodiment of the method according to the first aspect, which can be used particularly for particularly small workpieces, the method comprises detecting an actual temperature of the substrate body, in particular using a thermal imaging camera, stationary irradiation of the substrate body using a laser beam, and controlling the laser beam as a function of the detected actual temperature, in particular comprising terminating the irradiation if the detected actual temperature reaches a predefined limit temperature. This procedure is particularly suitable if the workpiece is so small that no traversing movements of the laser are feasible on the surface to be irradiated.Furthermore, this procedure can also be implemented in the method according to the first aspect in such a way that it comprises detecting a surface size of the surface to be irradiated and the movement parameter is set to a relative speed of laser and substrate body of zero if the detected surface size is smaller than a predefined minimum size.

[0033] In a preferred embodiment, the method further comprises providing a limit temperature for preheating, which depends in particular on one or more material parameters of the substrate body, wherein the movement parameter is determined at least based on the detected actual temperature and the provided limit temperature. The limit temperature preferably depends on a melting temperature of the substrate body and should not be exceeded during preheating.

[0034] In this way, when controlling the relative movement of the laser beam, both the current and a maximum permissible temperature of the substrate body are taken into account, so that the desired energy input into the substrate body during relative movement, especially during a heating cycle, can be determined, for example, based on the difference between the two values. Thus, the determination of the movement parameter can be carried out under the condition that, with constant laser beam power, a relative speed decreases with the difference between the two values. between the laser beam and the substrate body is increased in order to reduce the energy input during relative movement.

[0035] In a preferred embodiment, the movement parameter is additionally determined on the basis of a power parameter of the laser beam and / or an area of ​​the point of impact of the laser beam and / or an absorption coefficient of the substrate body.

[0036] In this way, the energy input into the substrate body can be estimated even better, so that the movement parameter can be set in such a way that a maximum energy input can be achieved without local overheating.

[0037] In a preferred embodiment, the movement parameter is a speed parameter that describes a relative speed of the laser beam to the substrate body, in particular a relative speed of the impact point.

[0038] In this way, the energy input into the substrate body is essentially determined by the relative velocity. Said velocity parameter can be a constant or averaged relative velocity, in particular a feed rate of a laser device providing the laser beam.

[0039] In a preferred embodiment, the method further comprises providing a preheating path running on the surface of the substrate body to be irradiated, wherein the relative movement of laser beam and substrate body additionally takes place as a function of the provided preheating path, such that the point of impact is moved along the provided preheating path over the surface of the substrate body to be irradiated.

[0040] The preheating path describes a path on the surface to be irradiated, which can be described, for example and not limited to, as a set of points or as a line.

[0041] The movement parameter can be understood as being designed for the preheating path, so that as a speed parameter it specifies, for example, the speed when traveling along the preheating path.

[0042] In a preferred embodiment, the preheating path extends spirally from an outer region of the surface to be irradiated to a central region of the surface to be irradiated.

[0043] The inventors discovered that this results in a particularly even heat distribution, as the energy input is concentrated toward the center as the movement progresses, from where it is conducted through the substrate body itself to its outer region. Furthermore, the spiral shape offers the possibility of minimizing the time between heating cycles during which the substrate body is unirradiated, especially when multiple heating cycles are used.

[0044] In a preferred embodiment, the provision of the preheating path comprises the sub-step of determining a preheating path running on the surface of the substrate body to be irradiated, at least as a function of a shape and / or dimensions of the surface to be irradiated and / or a diameter of the point of impact of the laser beam.

[0045] This allows an optimal preheating path to be determined for an individual substrate body, during which every possible surface point is hit by the laser beam.

[0046] Preferably, distances between adjacent sub-segments of the preheating path are selected such that they correspond to the diameter of the point of impact, so that when the preheating path is traversed, the entire surface to be irradiated is covered by the laser beam.

[0047] In a preferred embodiment, the method comprises several of the heating cycles mentioned above. The individual steps of a heating cycle can be designed in accordance with any of the preferred embodiments described above.

[0048] In a preferred embodiment, the determination of the movement parameter in the n-th heating cycle is additionally carried out on the basis of the determined movement parameter from the [nl)-th heating cycle.

[0049] In this way, a recursive determination of the movement parameter is implemented, in which the movement parameter from the previous heating cycle can be adjusted by a correction factor.

[0050] In a preferred embodiment, the determination of the movement parameter in the n-th heating cycle is carried out on the basis of the determined movement parameter from the [nl)-th heating cycle and a difference from the provided limit temperature and the recorded 1st temperature from the nth heating cycle.

[0051] This special form of recursive adaptation allows a simple and reliable implementation of the inventive strategy of maximum energy input without local overheating.

[0052] If the motion parameter is the velocity parameter that describes the relative velocity, such a recursive assignment can, for example and not restrictively, be as follows: [Equation v n , v ni describe the relative velocities in the n-th and in the [nl]-th heating cycle, a is an arbitrary adjustment factor, T G corresponds to the provided limit temperature and T Ist corresponds to the recorded actual temperature at the beginning of the nth heating cycle.

[0053] In order to take into account the technical limitations, for example the maximum speeds of drives for implementing the relative movement, especially in the case that T G T Ist n , it is advisable to integrate equation 1 into a recursive assignment rule with case differentiation according to the following equation 2: if and T G > T Ist n [Equation 2] v n = v max > otherwise

[0054] v max describes the maximum achievable or realizable relative speed. If the recursively determined relative speed v n the value v max , it will be set at this level and not higher.

[0055] In a preferred embodiment, the method further comprises providing a target temperature and terminating the preheating if an actual temperature greater than the provided target temperature is detected.

[0056] In this way, a target criterion is defined at which preheating is completed.

[0057] The actual temperature in question refers to the respective actual temperatures of several heating cycles.

[0058] If a recursive assignment is used, a Movement parameters are estimated or specified by an operator.

[0059] In an exemplary embodiment, during the relative movement of the laser beam and the substrate body, the point of incidence of the laser beam coincides with a focus point of the laser beam, in particular if a reciprocal expander (= “down further”, which reduces the raw beam in front of the focusing lens) is used on the laser device used for this purpose.

[0060] In a preferred embodiment, the method is carried out on a machine tool for additive manufacturing, in which the laser beam is provided by a laser device of the machine tool, in particular a DED laser device.

[0061] This allows additive manufacturing to be carried out directly after preheating without having to clamp a substrate body that serves as a material blank.

[0062] In a preferred embodiment, the method comprises fastening the substrate body in a receiving device of the machine tool or clamping the substrate body onto a workpiece carrier and fastening the workpiece carrier in a receiving device of the machine tool.

[0063] Preferably, the method further comprises the steps of setting a power parameter of the laser beam at least as a function of the detected actual temperature and / or setting a distance between the point of impact and a focal point of the laser beam.

[0064] In this way, the process control during preheating is expanded to include additional adjustment screws that can be used to avoid overheating, especially with comparatively small workpieces where maximum laser beam power might lead to direct melting of the substrate body.

[0065] According to a second aspect, a method for additively manufacturing a workpiece is provided, which comprises preheating a workpiece blank using a method according to the first aspect or one of its preferred embodiments and building up at least a portion of the workpiece to be manufactured by additively applying a build-up material to the preheated workpiece blank.

[0066] This provides an additive manufacturing process in which the workpiece blank is preheated evenly, quickly and reliably for additive construction.

[0067] In a preferred embodiment, the cohesive deposition is carried out by a DED laser process and the laser beam for preheating and a laser beam for the DED laser process are provided by the same laser device.

[0068] This means that additional laser devices are not required in additive manufacturing and the entire process can be carried out, for example, on a machine tool with only one laser device, which reduces, among other things, production time and production costs.

[0069] According to a third aspect, a machine tool is provided, comprising a laser device, a work space, a receiving device arranged in the work space and configured for the secure reception of a workpiece blank or a workpiece carrier carrying the workpiece blank, one or more drives, in particular numerically controlled drives, via which the laser device and the receiving device can be moved relative to one another, a temperature measuring device configured for detecting a temperature of a workpiece blank located in the work space, in particular the temperature measuring device is a thermal imaging camera, and a control device for controlling the machine tool, wherein the machine tool is configured to receive a workpiece blank received in the receiving device and / or a workpiece blank carried by a workpiece carrier received in the receiving device,in particular metallic material blanks, by irradiation with a laser beam of the laser device, for which purpose the control device is configured to determine a movement parameter describing a relative movement between the laser beam and the workpiece blank, at least on the basis of an actual temperature of the workpiece blank detected by the temperature measuring device, and to control the one or more drives of the machine tool depending on the determined movement parameter during irradiation of the workpiece blank with the laser beam, wherein an impact point of the laser beam is moved along a surface of the workpiece blank to be irradiated.

[0070] The machine tool according to the invention is thus designed to implement the preheating method described above, so that a repeated presentation of the associated advantages is omitted here.

[0071] In a preferred embodiment, the control device is provided with a path data set which describes a preheating path running on the surface of the workpiece blank to be irradiated, wherein the control device is configured to control the one or more drives in such a way that the point of impact moves along the preheating path described by the path data set when irradiating the workpiece blank.

[0072] In a preferred embodiment, the control device is configured to determine the path data set in advance at least as a function of data provided to the control device relating to the shape and / or dimensions of the surface to be irradiated and / or the diameter of the point of impact of the laser beam, in particular such that the preheating path described by the path data set extends in a spiral shape from an outer region of the surface to be irradiated to a central region of the surface to be irradiated.

[0073] In a preferred embodiment, the control device is configured to determine the movement parameter on the basis of the detected actual temperature and a limit temperature of the workpiece blank provided to the control device.

[0074] In a preferred embodiment, the movement parameter is a speed parameter that describes a relative speed of the laser beam to the substrate body, in particular a relative speed of the point of impact of the laser beam.

[0075] In a preferred embodiment, the machine tool is further configured for the additive manufacturing of a workpiece, for which purpose the laser device is configured for the additive cohesive application of a build-up material, in particular the laser device is a DED laser device.

[0076] In a preferred embodiment, the control device is configured to determine the movement parameter at least on the basis of the detected actual temperature and a provided limit temperature, which depends in particular on one or more material parameters of the workpiece blank.

[0077] In a preferred embodiment, the control device is configured to additionally determine movement parameters based on a power parameter of the laser device and / or an area of ​​the point of impact of the laser beam and / or an absorption coefficient of the workpiece blank.

[0078] In a preferred embodiment, the control device is configured to carry out the preheating in the form of several heating cycles.

[0079] In a preferred embodiment, the control device is configured to determine the movement parameter in the n-th heating cycle on the basis of the actual temperature detected for the n-th heating cycle and additionally on the basis of the previously determined movement parameter from the [nl]-th heating cycle.

[0080] According to a fourth aspect, the control device of a machine tool according to the third aspect or a preferred embodiment in this regard is provided, which is configured at least to control the machine tool and to preheat a workpiece blank received in the receiving device of the machine tool and / or a workpiece blank carried by a workpiece carrier received in the receiving device, in particular metallic material blanks, by irradiation by a laser beam of the laser device of the machine tool, for which purpose the control device is configured to determine a movement parameter describing a relative movement between the laser beam and the substrate body, at least on the basis of an actual temperature detected by the temperature measuring device,and during irradiation of the workpiece blank with the laser beam, to control the one or more drives of the machine tool depending on the determined movement parameter, wherein an impact point of the laser beam is moved along a surface of the workpiece blank to be irradiated.

[0081] In this way, an existing machine tool, which apart from the control device already comprises all the components according to the third aspect of the invention, can be further developed into such a machine tool.

[0082] Further aspects and their advantages as well as more specific embodiments of the aforementioned aspects and embodiments are described below with the aid of the drawings shown in the attached figures.

[0083] Fig. 1 shows a schematic flow diagram of an embodiment of the preheating method according to the invention.

[0084] Fig. 2 shows a schematic flow diagram of an embodiment of the method according to the invention for additive manufacturing.

[0085] Fig. 3 shows an exemplary movement pattern of an impact point according to an embodiment of the preheating method according to the invention.

[0086] Fig. 4 shows an exemplary distribution of several process parameters of an embodiment of the method according to the invention for preheating.

[0087] Fig. 5 shows a schematic representation of an embodiment of the machine tool according to the invention.

[0088] It is emphasized that the present invention is in no way limited to the exemplary embodiments described below and their implementation features. The invention further encompasses modifications of the aforementioned exemplary embodiments, in particular those resulting from modifications and / or combinations of individual or multiple features of the described exemplary embodiments within the scope of the independent claims. Detailed character description

[0089] Fig. 1 shows a schematic flow diagram of an embodiment of the method according to the invention for preheating a substrate body by irradiation with a laser beam.

[0090] In step S1, a limit temperature and a target temperature are provided for the method, wherein the target temperature describes the temperature to be reached during the preheating and the limit temperature describes a temperature of the substrate body that is not to be exceeded and at which the material of the substrate body begins to melt, for example.

[0091] In step S2, a preheating path is provided on which an impact point of the laser beam is to move on a surface of the substrate body to be irradiated.

[0092] The steps S3 to S6 are carried out repeatedly, whereby a sequence of the steps can be combined in a heating cycle Hi, which is carried out several times.

[0093] In step S3, an actual temperature of the substrate body to be preheated is recorded, in particular by means of a thermal imaging camera.

[0094] In step S4, the measured actual temperature is compared with the target temperature provided in step S1. Once the substrate body has reached this temperature, step S7 follows directly and preheating is terminated.

[0095] Otherwise, step S5 follows, in which a movement parameter is determined that describes a relative movement between the laser beam and the substrate body based on the detected actual temperature from step S3 and the provided limit temperature from step S1. In particular, this is a speed parameter that describes a relative speed of the laser beam and the substrate body.

[0096] In step S6, a relative movement of the laser beam and the substrate body takes place depending on the preheating path provided from step S2 and depending on the determined movement parameter from step S5, wherein an impact point of the laser beam is moved along the preheating path on the surface of the substrate body to be irradiated, in particular at the relative speed specified by the speed parameter.

[0097] Once the provided preheating path has been completed, step S6 ends and a new heating cycle begins with a new step S3.

[0098] Using the procedure described above, the energy input into the substrate body is controlled in each heating cycle at least as a function of the recorded actual temperature, which affects the relative kinematic movement of the laser beam and the substrate body based on the determined movement parameters.

[0099] In this way, the substrate body can be preheated quickly and evenly to the desired target temperature without risking local overheating, with the energy input being particularly advantageously controlled via relative kinematics. Furthermore, energy costs are significantly lower compared to preheating with a heating furnace, as the energy input can be applied more precisely using lasers.

[0100] Particularly advantageously, the above method is carried out on a machine tool, wherein step S6 preferably comprises the sub-step of controlling at least one drive of the machine tool, via which a relative movement between the laser beam and the substrate body can be implemented, depending on the determined movement parameter from step S3.

[0101] Fig. 2 shows a schematic flow diagram of an embodiment of the method according to the invention for the additive manufacturing of a workpiece.

[0102] The method comprises steps S1 to S7 for preheating a substrate body according to Fig. 1, which in this case corresponds to a workpiece blank. A repeated description of steps S1 to S7 is omitted here.

[0103] After completion of the preheating in step S7, at least a section of the workpiece to be manufactured is built up in step S8 by additively applying a build-up material to the preheated workpiece blank.

[0104] This provides an additive manufacturing process in which the workpiece blank is preheated evenly, quickly and reliably for additive construction, thereby reducing in particular the risk of internal stresses or cracks, but also of pores or gas inclusions in the workpiece.

[0105] Fig. 3 shows an exemplary movement path of an impact point A according to an embodiment of the inventive method for preheating a substrate body 200.

[0106] During the process, the laser beam is moved relative to the substrate body 200, so that the point of incidence A of the laser beam moves relative to the substrate body 200 along the surface 201 to be irradiated.

[0107] The energy input thus occurs via the said surface 201, which is limited by an outer edge 202.

[0108] The impact point A has a diameter dA and is moved along a preheating path P running on the surface 201 to be irradiated, starting from a starting point Po to an end point Pend. The positions Ao and Ai of the impact point A at the starting time and at a later time during the relative movement are shown as examples.

[0109] According to the invention, the relative movement of the point of impact A over the surface 201 to be irradiated takes place depending on the previously determined A movement parameter, which in turn depends on the measured actual temperature. For example, this could be a speed parameter that specifies the relative speed of the impact point A when moving along the preheating path P.

[0110] The preheating path P runs spirally from an outer region 201a of the surface 201 to be irradiated to a central region 201b of the surface 201 to be irradiated, whereby a particularly good energy input is implemented.

[0111] Preferably, the preheating path P is traversed several times with the laser beam as part of respective heating cycles during the process, wherein the relative kinematics during a heating cycle depends, via the movement parameter, on an actual temperature of the substrate body 200 detected at the beginning of the heating cycle.

[0112] The preheating path P is selected such that distances between adjacent sub-segments of the preheating path essentially correspond to the diameter dA of the impact point A, so that when the preheating path P is traversed, the entire surface 201 to be irradiated is also covered by the laser beam.

[0113] Fig. 4 shows an exemplary distribution of several process parameters of an embodiment of the method according to the invention for preheating.

[0114] A substrate body is to be heated, whereby a provided limit temperature TG is not to be exceeded.

[0115] As stated in the general part of the description, the relative movement of the laser beam and the substrate body is controlled as a function of a movement parameter based on a detected actual temperature Tact, which in the present case corresponds to a speed parameter that specifies a relative speed between the laser beam or its point of impact and the substrate body, in particular it is a feed parameter.

[0116] The diagram shows several heating cycles (one bar corresponds to one heating cycle) with the corresponding relative or feed speeds between the laser beam and the substrate body in bar graphs over time t.

[0117] The maximum relative speed is limited by the respective drives used to implement the relative movement.

[0118] As can be seen from the diagram, the relative velocities are comparatively low at the beginning, so that a high energy input is converted into the substrate body.

[0119] With increasing 1st temperature Tist, the relative velocities also increase, since the actual temperature Tist of the substrate body approaches the limit temperature TG and the energy input per heating cycle is reduced in order to avoid unwanted overheating and still implement uniform heating.

[0120] Fig. 5 shows a schematic representation of an embodiment of the machine tool 100 according to the invention.

[0121] The machine tool 100 comprises a laser device 10, a work space 20, a receiving device 30 which is arranged in the work space 20 and is designed for the fastening reception of a workpiece blank 200 or a workpiece carrier carrying the workpiece blank [not shown here], a plurality of numerically controlled drives 41, 42 via which the laser device 10 can be moved relative to the receiving device 30, in this case in a horizontal plane in the X and Y directions.

[0122] Furthermore, the machine tool 100 comprises a thermal imaging camera 50 as a temperature measuring device, which is configured to detect a temperature of a workpiece blank 200 located in the work space 20, and a control device 60 for controlling the machine tool 100.

[0123] The machine tool 100 is configured at least to carry out a method for preheating the workpiece blank according to the first aspect, in which a workpiece blank 200 held in the holding device 30 is preheated by irradiation with a laser beam L of the laser device 10, for which purpose the control device 60 is configured to determine a movement parameter that describes a relative movement between the laser beam and the workpiece blank 200, at least on the basis of an actual temperature of the workpiece blank 200 detected by the thermal imaging camera 50, and to control the drives 41, 42 of the machine tool 200 as a function of the determined movement parameter during irradiation of the workpiece blank 200 with the laser beam, wherein an impact point of the laser beam is moved along a surface of the workpiece blank 200 to be irradiated [see also Fig. 3].

[0124] The machine tool 100 is thus configured to implement the preheating method described above, which enables rapid and uniform preheating of the workpiece blank 200 without the risk of local overheating.

[0125] Preferably, the laser device 10 is a DED laser device, so that an additive material-to-material application of a build-up material to the workpiece blank can take place directly after the preheating, without having to first release the workpiece blank from the clamping of the holding device 30.

[0126] Embodiments of the present invention and their advantages have been described in detail above with reference to the accompanying figures.

[0127] It is emphasized again that the present invention is in no way limited to the above-described embodiments and their implementation features. The invention further encompasses modifications of the aforementioned embodiments, in particular those resulting from modifications and / or combinations of individual or multiple features of the described embodiments within the scope of the independent claims. List of reference symbols 10 Laser device 20 workspace 30 Recording device 41 numerically controlled drive X-direction 42 numerically controlled drive Y-direction 50 thermal imaging camera 60 Control device 100 machine tools 200 workpiece blanks 201 surface to be irradiated 201a outer area of ​​the surface to be irradiated 201b central area of ​​the surface to be irradiated 202 Edge of the surface to be irradiated A Point of impact of the laser beam L laser beam P Preheating path

Claims

CLAIMS 1. A method for preheating a substrate body (200) in preparation for an additive manufacturing process, in particular a metallic substrate body (200), by irradiating it with a laser beam (L), comprising the steps: a) detecting an actual temperature of the substrate body (200), in particular by means of a thermal imaging camera (50); b) determining a movement parameter that describes a relative movement between the laser beam (L) and the substrate body (200), at least based on the detected actual temperature; wherein the movement parameter is preferably a speed parameter that describes a relative speed of the laser beam (L) to the substrate body (200), in particular a relative speed of an impact point (A) of the laser beam (L).and c) relative movement of the laser beam (L) and the substrate body (200) at least as a function of the determined movement parameter, wherein the point of incidence (A) of the laser beam (L) is moved along a surface (201) of the substrate body (200) to be irradiated.

2. The method of claim 1, wherein the method further comprises: Providing a limit temperature for preheating, which depends in particular on one or more material parameters of the substrate body (200); wherein the movement parameter is determined at least on the basis of the detected actual temperature and the provided limit temperature.

3. Method according to one of claims 1 or 2, wherein the determination of the movement parameter is additionally carried out on the basis of a power parameter of the laser beam (L) and / or an area of ​​the point of impact (A) of the laser beam (L) and / or an absorption coefficient of the substrate body (200).

4. The method according to at least one of claims 1 to 3, wherein the method further comprises: Providing a preheating path (P) extending on the surface (201) of the substrate body (200) to be irradiated, which preheating path extends in particular in a spiral shape from an outer region (201a) of the surface (201) to be irradiated to a central region (201b) of the surface (201) to be irradiated; wherein the relative movement of the laser beam (L) and the substrate body (200) additionally takes place as a function of the provided preheating path (P) such that the point of impact (A) is moved along the provided preheating path (P) over the surface (201) of the substrate body (200) to be irradiated, and wherein the provision of the preheating path (P) preferably comprises the substep: Determining a preheating path (P) running on the surface (201) of the substrate body (200) to be irradiated at least as a function of a shape and / or dimensions of the surface (201) to be irradiated and / or a diameter of the point of impact (A) of the laser beam (L).

5. The method according to at least one of claims 1 to 4, wherein the method comprises a plurality of heating cycles, each heating cycle comprising at least steps a), b) and c).

6. The method according to claim 5, wherein the determination of the movement parameter in the n-th heating cycle is additionally carried out on the basis of the determined movement parameter from the (nl)-th heating cycle.

7. Method at least according to claim 2 and claim 5, wherein the determination of the movement parameter in the n-th heating cycle is carried out on the basis of the determined movement parameter from the (nl)-th heating cycle and a difference between the provided limit temperature and the detected 1st temperature from the n-th heating cycle.

8. The method according to at least one of claims 1 to 7, wherein the method further comprises: Providing a target temperature; Stop preheating if an actual temperature greater than the provided target temperature is detected.

9. Method according to at least one of claims 1 to 8, wherein the method is carried out on a machine tool (100) for additive manufacturing, in which the laser beam (L) is provided by a laser device (10) of the machine tool (100), in particular a DED laser device, and wherein the step of relatively moving the laser beam (L) and substrate body (200) further comprises controlling at least one drive of the machine tool (100) depending on the determined movement parameter, and wherein the method further preferably comprises: Fixing the substrate body (200) in a receiving device (30) (of the machine tool (100); or Clamping the substrate body (200) onto a workpiece carrier and fastening the workpiece carrier in a holding device (30) of the machine tool (100).

10. A method for additively manufacturing a workpiece, comprising: Preheating a workpiece blank (200) using a method according to one of claims 1 to 9; and Building up at least one section of the workpiece to be manufactured by additively applying a build-up material to the preheated workpiece blank, preferably by a DED laser process, wherein the laser beam (L) for the preheating and a laser beam (L) for the DED laser process are preferably provided by the same laser device (10).

11. A machine tool (100), comprising: a laser device (10); a work space (20); a receiving device (30) arranged in the work space (20) and configured to securely receive a workpiece blank (200) or a workpiece carrier carrying the workpiece blank; one or more drives (41, 42), in particular numerically controlled drives (41, 42), via which the laser device (10) and the receiving device (30) are movable relative to one another; a temperature measuring device (50) configured to detect a temperature of a workpiece blank (200) located in the work space (20), in particular the temperature measuring device is a thermal imaging camera (50); and a control device (60) for controlling the machine tool (100); wherein the machine tool (100) is configured to receive a workpiece blank received in the receiving device (30) and / or a workpiece blank,which is carried by a workpiece carrier received in the receiving device (30), in particular metallic material blanks, by irradiation by a laser beam (L) of the laser device (10), for which purpose the control device (60) is configured to determine a movement parameter describing a relative movement between the laser beam (L) and the workpiece blank (200), at least on the basis of an actual temperature of the workpiece blank (200) detected by the temperature measuring device (50), and to control the one or more drives (41, 42) of the machine tool (100) as a function of the determined movement parameter during irradiation of the workpiece blank (200) with the laser beam (L), wherein an impact point (A) of the laser beam (L) is moved along a surface (201) of the workpiece blank (200) to be irradiated, wherein the movement parameter is preferably a speed parameter,which describes a relative speed of the laser beam (L) to the substrate body (200), in particular a relative speed of the impact point (A)., 12. Machine tool (100) according to claim 11, wherein the control device (60) is provided with a path data set which describes a preheating path (P) running on the surface (201) of the workpiece blank (200) to be irradiated;and wherein the control device (60) is configured to control the one or more drives in such a way that the point of impact (A) moves along the preheating path (P) described by the path data set during the irradiation of the workpiece blank (200), wherein the control device (60) is preferably configured to determine the path data set in advance at least as a function of data provided to the control device (60) relating to the shape and / or dimensions of the surface (201) to be irradiated and / or the diameter of the point of impact (A) of the laser beam (L), in particular in such a way that the preheating path (P) described by the path data set runs spirally from an outer region (201a) of the surface (201) to be irradiated to a central region (201b) of the surface (201) to be irradiated.

13. Machine tool (100) according to at least one of claims 11 or 12, wherein the control device (60) is configured to determine the movement parameter on the basis of the detected actual temperature and a limit temperature of the workpiece blank (200) provided to the control device (60).

14. Machine tool (100) according to at least one of claims 11 to 13, wherein the machine tool (100) is further configured for additive manufacturing of a workpiece, for which purpose the laser device (10) is configured for additively cohesive application of a build-up material, in particular the laser device (10) is a DED laser device.

15. Control device (60) of the machine tool (100) according to one of claims 11 to 14.

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