Method and device for laser clad welding with varying layer thickness

Abstract

The invention relates to a method for performing laser build-up welding in a laser system (1), comprising the following steps: actuating a machining unit (2) having a multifunctional beam nozzle (3) in order to provide a laser beam (4) and a powder beam (5) such that the powder beam (5) interacts with the laser beam (3) for cladding a powder layer track (6) on a workpiece (7), in particular rotationally symmetrical; actuating a workpiece receiving unit (8) on which the workpiece (7) is arranged such that the rotational movement moves the workpiece (7) about the axis of rotation (9); and actuating the translating unit (10) such that the translating movement moves the beam nozzle (3) and / or the workpiece receiving unit (8) in an offset direction (11) substantially orthogonal to the axis of rotation (9); wherein the rotational movement and the translational movement occur simultaneously with the feed movement such that the powder layer track (6) is clad onto the workpiece (7) along a helical trajectory (12), and wherein the powder layer thickness (13) varies in the radial direction of the workpiece (7) as the feed movement of the machining proceeds. The invention also relates to a control unit for carrying out the method.

Description

Technical Field

[0001] The present invention relates to a method for performing laser cladding welding in a laser system and a control unit for use in a laser system. Background Technology

[0002] Laser cladding welding is used, for example, in repair, coating, and bonding technologies. A distinction can be made between conventional laser cladding welding techniques (laser metal deposition (LMD), direct metal deposition (DMD), or direct energy deposition (DED)) and so-called "high-speed laser cladding welding" (HS-LMD or ultra-high-speed laser cladding welding (EHLA)). The HS-LMD method is described, for example, in DE10 2011 100 456 B4 or DE 10 2018 130 798 A1. An unavoidable side effect of laser cladding welding is deformation of the workpiece due to heat input. This heat input induces internal stresses in the workpiece during laser cladding welding, which cause deformation during the cooling phase after laser cladding welding. Deformation results in concave or convex bending of the component. To ensure that the functional surfaces applied to the workpiece by means of laser cladding welding remain flat and unbent despite deformation for their intended use, the functional surfaces need to be ground after the cooling phase. Summary of the Invention

[0003] Based on known prior art, the object of the present invention is to provide an improved method and corresponding apparatus for laser cladding welding. In particular, the object of the present invention is to effectively compensate for the side effects of thermal deformation. To this end, it is particularly desirable to ensure low material loss during laser cladding welding.

[0004] This objective is achieved by the method for laser cladding welding in a laser system and the control unit for use in a laser system, according to the independent claims. Advantageous further improvements can be derived from the dependent claims, the specification, and the drawings.

[0005] Accordingly, a method for laser cladding welding in a laser system is proposed. The laser system can have a laser source for generating a laser beam with a wavelength in the range of 0.4 µm to 1.5 µm. The laser source can be a disk laser, a fiber laser, or a diode laser. In this way, for example, laser beams with wavelengths of about 450 nm, about 515 nm, between about 800 nm and about 1000 nm, or about 1030 nm, 1060 nm, or 1070 nm can be generated. The laser beam can be directed to the processing head by means of an optical fiber. The laser source can have a laser power between 2 kW and 24 kW. If the workpiece processed using this method is a brake disc, the laser power can be particularly between 8 kW and 24 kW, while if the workpiece is a sliding bearing, the laser power can particularly be 2 kW. The laser power can be constant during processing or vary depending on the stage of the method.

[0006] The method includes the following steps: driving a processing unit having a multifunctional beam nozzle for providing a laser beam and a powder beam, such that the powder beam, in interaction with the laser beam, applies a powder layer onto a workpiece, particularly a rotationally symmetric workpiece, such as a brake disc, hydraulic cylinder, pressure roller, or sliding bearing. Driving can be performed between a central control unit of the laser system and a local control unit of the processing unit. The beam nozzle is configured to direct the laser beam and the powder beam onto the workpiece. The powder beam may contain a powdery material, including hard material particles, particularly carbides, which do not dissolve after interacting with the laser beam in the interaction zone. The laser beam can be directed substantially orthogonally onto the surface of the workpiece to be processed. The powder beam can be tilted relative to the laser beam to form an interaction zone between the powder beam and the laser beam above the material surface. Such an interaction zone allows for more efficient application of the powdery material onto the workpiece. The laser beam emitted from the beam nozzle may have a reduced central intensity in the central region compared to the edge region. For example, the central intensity may be less than 90% of the edge intensity. Therefore, at least within the interaction region, the intensity of the laser beam in the edge region is higher than that in the center region, causing the powder material to be loaded with a higher intensity in the edge region when it enters the interaction region.

[0007] The method further includes the following steps: driving a workpiece receiving unit (on which a workpiece is arranged) such that rotational motion causes the workpiece to move about a rotational axis. Driving can be performed between the central control unit of the laser system and the local control unit of the workpiece receiving unit. The workpiece receiving unit can clamp the workpiece, ensuring it is securely supported within the unit, provided the unit itself is rotatable. The rotational axis can correspond to the rotational symmetry axis of a rotationally symmetric workpiece. The beam nozzle can be pointed at a position on the workpiece that is radially outside the workpiece's rotational symmetry axis. Therefore, rotation about the rotational axis causes the powder layer tracks to follow a path on the workpiece. The rotational motion of the workpiece receiving unit can be initiated by an independent drive device.

[0008] The method further includes the step of driving a translation unit such that the translational motion causes the beam nozzle and / or workpiece receiving unit to move in an offset direction substantially orthogonal to the axis of rotation. Driving can be performed between the central control unit of the laser system and the local control unit of the translation unit. The translational motion can be initiated by a drive mechanism separate from the workpiece receiving unit. Alternatively, the translational motion can be initiated by the same drive mechanism as the rotational motion. The orthogonal offset direction of the translational motion causes a translation orthogonal to the axis of rotation, which accordingly affects the trajectory of the powder layer tracks. The rotational motion can be significantly more pronounced than the translational motion.

[0009] Rotational and translational motions superimpose to form a feed motion, causing the powder layer to be applied to the workpiece along a helical trajectory. This results in a planar powder layer in the radial direction of the workpiece. The geometry of the helical trajectory is determined by the feed motion. The feed motion can influence process parameters, such as the duration of interaction between the powder beam, laser beam, and workpiece, to achieve robust bonding of the powder particles to the workpiece. The helical trajectory extends along a curve about the axis of rotation, where the distance from the axis of rotation increases if the application proceeds from the radially inward to the radially outward, and decreases if the application proceeds from the radially outward to the radially inward. The rotational motion has a rotational speed, while the translational motion has a translational speed. If the processing parameter is a feed motion, the variation is caused by changes in the rotational speed and / or translational speed.

[0010] As workpiece processing progresses, processing parameters change, causing the powder layer thickness to vary along the radial direction of the workpiece. Therefore, optimized processing can be ensured due to the correlation between powder layer thickness and processing parameters such as feed motion, powder mass flow rate of the powder beam, and / or laser power. To adjust the powder layer thickness, the processing parameters are changed accordingly. For each part, the processing parameters can be varied identically. Alternatively, the variation of processing parameters depends on the workpiece's behavior during laser cladding welding. For this purpose, the measurement system can send control signals to the translation unit and / or the workpiece receiving unit. This method enables variable adjustment of the powder layer thickness. Here, the target geometry of the workpiece and / or the powder layer thickness can be considered, just as process parameters and their results, such as workpiece deformation. The heat input during laser cladding welding causes internal stress and deformation in the workpiece, which can be compensated for or mitigated by changing the processing parameters in such a way that the cladding layer is substantially flat, i.e., not curved, or at least less curved than if the processing parameters were kept constant as processing progresses. This minimizes or reduces material removal caused by grinding of the applied layer, thereby enabling more efficient processing and lower material consumption.

[0011] In one implementation, the processing parameters are the feed motion, the powder mass flow rate of the powder beam, and / or the laser power of the laser beam. The thickness of the applied powder layer can be reliably varied by changing one or a combination of these parameters. This helps to efficiently compensate for thermal deformation.

[0012] In one embodiment, the powder layer tracks have a radial track width, wherein the offset between two adjacent helical flanks of the helical trajectory is less than the track width, causing the powder layer tracks to radially overlap along the helical trajectory. Therefore, when applying a coating from radially inward to radially outward, one radially inward powder layer track is positioned below the next radially outward powder layer track. Correspondingly, when applying a coating from radially outward to radially inward, one radially outward powder layer track is positioned below the next radially inward powder layer track. This radial overlap increases the powder layer thickness because these powder layer tracks that at least partially overlap, i.e., the overlapping powder layer tracks, have a greater powder layer thickness compared to two powder layer tracks whose offset is greater than their radial track width.

[0013] In one implementation, the radial overlap varies proportionally to the feed motion. This means that the radial track width remains unaffected by the feed motion, resulting in an efficient way to control the radial overlap. The greater the feed motion, the greater the radial overlap. For example, if the workpiece deformation due to heat input is known in advance, the powder layer thickness can be precisely and process-compliantly adjusted accordingly by controlling the feed motion, allowing the varying powder layer thickness to compensate for the deformation.

[0014] In one embodiment, during machining of the first workpiece side from the radially inner workpiece section to the radially outer workpiece section, as machining progresses, the feed rate increases, particularly linearly or gradually, such that the radial overlap of the helical trajectory in the radially outer section is less than that in the radially inner section. Alternatively, during machining of the first workpiece side from the radially outer workpiece section to the radially inner workpiece section, as machining progresses, the feed rate decreases, particularly linearly or decreasingly, such that the radial overlap of the helical trajectory in the radially outer section is less than that in the radially inner section. This ensures that the powder layer thickness is less in the radially outer section than in the radially inner section. This can counteract the convex deformation of the workpiece. Therefore, if the deformation causes the radially outer section to protrude further in the direction of the powder layer thickness, the above-described adjustment of the feed motion can at least partially compensate for the deformation.

[0015] In one embodiment, during machining of a second workpiece side, particularly different from the first workpiece side, from the radially inner workpiece section to the radially outer workpiece section, the feed rate decreases as machining progresses, particularly linearly or gradually, such that the radial overlap of the helical trajectory in the radially outer section is greater than that in the radially inner section. Alternatively, during machining of the second workpiece side from the radially outer workpiece section to the radially inner workpiece section, the feed rate increases as machining progresses, particularly linearly or gradually, such that the radial overlap of the helical trajectory in the radially outer section is greater than that in the radially inner section. This can counteract concave deformation of the workpiece. Therefore, if deformation causes the radially outer section to bend in the direction opposite to the powder layer thickness, adjusting the feed motion can at least partially compensate for the deformation. These two embodiments, where convex and concave deformations are inversely related, can be combined in a single workpiece, where the top side is the first workpiece side and the bottom side is the second workpiece side. If the radially outer section of the first workpiece side deforms upwards, this causes the radially outer section of the second workpiece side to bend. To compensate for deformation, while a radially decreasing powder layer thickness can be applied to the first workpiece side, a complementary radially increasing powder layer thickness can be applied to the second workpiece side. This extends the advantages of the method to workpieces processed on both sides.

[0016] In one implementation, the process determines whether a workpiece side is processed as a first workpiece side or a second workpiece side based on the deformation that occurs in the workpiece during laser cladding welding. Therefore, based on individualized deformation, the corresponding powder layer thickness can be adjusted for the corresponding workpiece side, which further contributes to reducing material consumption.

[0017] In one embodiment, the radial overlap of the powder layer tracks in the first radial end section, such as the radially inner workpiece section or the radially outer workpiece section, is greater than 50%, particularly 70% to 80%, of the track width, and the radial overlap of the powder layer tracks in the second radial end section, such as the radially outer workpiece section or the radially inner workpiece section, is less than 50%, particularly 20% to 40%, of the track width. If the radial overlap of the powder layer tracks is, for example, 70% to 80%, this means that 70% to 80% of one powder layer track lies on top of an adjacent, previously applied powder layer track. Correspondingly, if the radial overlap of the powder layer tracks is between 20% and 40%, this means that only 20% to 40% of one powder layer track lies on top of an adjacent, previously applied powder layer track. Whether the one powder layer track and the other powder layer track are radially inner or radially outer powder layer tracks depends on whether the application is performed from radially inner to radially outer or from radially outer to radially inner. The smaller the radial overlap, the smaller the powder layer thickness.

[0018] In one embodiment, the radial overlap of the powder layer tracks at a first radial end section, such as a radially inner workpiece section or a radially outer workpiece section, creates a first layer thickness, and the radial overlap of the powder layer tracks at a second radial end section, such as a radially outer workpiece section or a radially inner workpiece section, creates a second layer thickness, wherein the first layer thickness is more than 1.5 times or more, particularly 2 times or 2.5 times, the second layer thickness. Therefore, the powder layer thickness can vary radially in such a way that, for example, the powder layer thickness at one end section is more than twice the powder layer thickness at the other end section. This allows for large variations in the powder layer thickness and thus enables compensation for significant workpiece deformation.

[0019] In one implementation, varying processing parameters, particularly varying feed motion, are preset in response to the previously processed workpiece. That is, deformation resulting from laser cladding welding can be determined and evaluated from the processed workpiece, and this deformation can be used as an input parameter for the feed motion. When evaluating the previously processed workpiece, for example, a statistical evaluation module or a neural network can be used. This allows for precise matching of the powder layer thickness to the expected deformation of the workpiece.

[0020] In one embodiment, the rotational motion is constant, such that the varying feed motion is caused solely by the varying translational motion. The rotational motion of the workpiece receiving unit can have a greater impact on process parameters than the translational motion. In this respect, the translational motion can be used as the sole influencing factor for the variation in feed motion. This further promotes efficient workpiece machining. Within the scope of this disclosure, constant motion can be, in particular, motion with a constant speed. Correspondingly, varying motion can be, in particular, motion with a varying speed.

[0021] In one embodiment, the workpiece is positioned fixed along the offset direction, such that translational motion is caused by the movement of the beam nozzle. The workpiece is arranged to be rotatable along the rotational direction. This results in an effective separation of functions, where rotational motion is considered for variations in process-critical parameters, and translational motion is considered for variations in powder layer thickness. The translational motion of the beam nozzle can be achieved by driving the laser system along the feed direction. By separating these functions, the highest quality standards can be combined with the minimum processing time.

[0022] In one embodiment, the powder layer grooves form an adhesive layer, upon which a wear-resistant layer is applied in a next step. That is, the method produces a part coated with two layers. The adhesive layer is specifically used to improve the adhesion of the applied grooves. The wear-resistant layer improves the load-bearing capacity of the workpiece. Regarding the wear-resistant layer, machining parameters, especially the feed motion, can vary as machining progresses or alternatively remain constant. Alternatively, if the part involves only a component with a single coating, the powder layer grooves are the wear-resistant layer.

[0023] This disclosure also relates to a control unit for use in a laser system for laser cladding welding, wherein the control unit is configured to perform the methods as disclosed. The control unit may be part of a central control unit of the laser system or a separate local control unit. The effects and advantages disclosed in this method are correspondingly extended to the control unit.

[0024] This disclosure also relates to a laser system for laser cladding welding. The laser system has a processing unit with a multi-functional beam nozzle for providing a laser beam and a powder beam. The beam nozzle is configured to direct the laser beam and powder beam onto a workpiece. The powder beam may contain a powdered material comprising hard material particles, particularly carbides, which do not dissolve after interacting with the laser beam in an interaction zone. The laser beam may be directed substantially orthogonally onto the surface of the workpiece to be processed. The powder beam may be tilted relative to the laser beam to form an interaction zone between the powder beam and the laser beam above the material surface. Such an interaction zone allows for more efficient application of the powdered material onto the workpiece. The laser beam emitted from the beam nozzle may have a reduced central intensity in the central region compared to the edge regions. For example, the central intensity may be less than 90% of the edge intensity. Therefore, at least within the interaction zone, the intensity of the laser beam in the edge regions is higher than the central intensity, causing the powdered material to be loaded with the higher intensity of the edge regions upon entering the interaction zone.

[0025] The laser system also includes a workpiece receiving unit on which the workpiece is arranged. The workpiece receiving unit can clamp the workpiece, ensuring it is securely mounted within it, provided the unit itself is rotatable. The axis of rotation can correspond to the axis of rotational symmetry of a rotationally symmetric workpiece. The rotational movement of the workpiece receiving unit can be initiated by an independent drive device. The workpiece can be rotationally symmetric, particularly a brake disc, hydraulic cylinder, pressure roller, or sliding bearing.

[0026] The laser system also includes a translation unit configured to move the beam nozzle and / or workpiece receiving unit along an offset direction substantially orthogonal to the axis of rotation. The translational motion can be initiated by a drive mechanism separate from the workpiece receiving unit. Alternatively, the translational motion can be initiated by the same drive mechanism as the rotational motion. The orthogonal offset direction of the translational motion causes a translation orthogonal to the axis of rotation, which may correspondingly affect the path of the powder layer tracks. Rotational motion can be significantly more pronounced than translational motion.

[0027] The laser system also has a control unit as disclosed above. This control unit is configured and set to perform the method for laser cladding welding. Attached Figure Description

[0028] Preferred further embodiments of the invention will be described in more detail below with reference to the accompanying drawings, in which: Figure 1 This is a schematic diagram of a laser system; Figures 2a to 2d An exemplary intensity distribution of the laser beam is shown; Figure 3 A spiral trajectory is shown, along which a powder layer is applied to the workpiece; Figure 4 A schematic diagram of adjacent powder layer tracks is shown; and Figure 5 A schematic diagram of a workpiece machined on both sides is shown. Detailed Implementation

[0029] Preferred embodiments will now be described with reference to the accompanying drawings. Here, in different drawings, identical, similar, or having the same effect elements are given the same reference numerals, and repeated descriptions of these elements are partially omitted to avoid redundancy.

[0030] Figure 1A laser system 1 for laser cladding welding is shown. In laser cladding welding, a powder layer is applied to the workpiece by melting the powdered material with a laser and bonding it to the workpiece material. The laser system 1 has a control unit 100 that drives the various components of the laser system 1. A processing unit 2 is connected to a laser source (not shown). The laser source can be a disk laser, a fiber laser, or a diode laser. For example, laser beams with wavelengths of about 450 nm, about 515 nm, between about 800 nm and about 1000 nm, or about 1030 nm, 1060 nm, or 1070 nm can be generated. The laser generated by the laser source can be disposed in such a way that it can be guided, in particular by means of an optical fiber, to the processing head of the processing unit 2. The laser source can have a laser power between 2 kW and 24 kW. The processing head has a multi-functional beam nozzle 3 that directs a laser beam 4 and a powder beam 5, on the one hand, onto the powder layer channel 6 of the rotationally symmetrical workpiece 7 in a manner that meets process requirements. Laser beam 4 can have a ring-shaped portion and a central portion, such as in particular a combination of... Figures 2a to 2d As described, the laser beam can be guided to processing unit 2 via multi-clad optical fiber.

[0031] Workpiece 7 is arranged in receiving unit 8 and rotates about rotation axis 9. Translational motion initiated by translation unit 10 along offset direction 11 is superimposed with rotational motion, thereby generating a helical trajectory 12 on workpiece 7. The superposition of rotational and translational motion produces feed motion, with which laser beam 4 and powder beam 5 move relative to workpiece 7. Feed motion varies as processing progresses. For example, feed motion reaches 20 m / s at the start of processing and then increases during processing. Alternatively, feed motion may decrease during processing. Whether feed motion increases or decreases during processing depends on the deformation of the workpiece. For example, an increased feed motion can be used to process the top side, and a decreased feed motion can be used to process the bottom side (see further details below). Figure 5 (Related content).

[0032] The laser beam 4 may have a reduced intensity in the central region compared to the annular or edge regions. For example, the central intensity may be less than 90% of the edge intensity. Therefore, at least within the interaction zone between the laser beam 4 and the powder beam 5, the laser beam 4 has a higher intensity in the edge region than in the central region, causing the powder material in the powder beam 5 to be loaded with a higher intensity in the edge region upon entering the interaction zone. Due to the tilted orientation of at least one powder beam 5 relative to the laser beam 4, the interaction path with the laser beam 4 varies across the cross-section of the powder beam 5. Due to the reduced intensity in the central region, substantially uniform energy is supplied to each powder particle along the varying interaction path. In other words, the maximum intensity of the laser beam in the edge region results in a more uniform distribution of energy density per powder particle, and thus an expansion of the process window (Prozessfenster) while maintaining stable weld quality.

[0033] Workpiece 7 can be a metal workpiece. The powdered material can particularly contain metallic materials. The powdered material can be sprayed onto the workpiece surface by means of a carrier gas, particularly argon or helium, and / or by means of an inert gas mixture as a process protective gas. The process protective gas can additionally protect the processing position from the influence of the surrounding atmosphere. The focal point of the laser beam 4 can be located on the workpiece surface or directly above the workpiece surface. The beam nozzle 3 can have an annular opening for the laser beam 4 and one or more additional openings for the powder beam 5. The annular opening can be in the form of an annular gap nozzle, or configured as a multi-beam nozzle by means of multiple nozzles arranged annularly around a central opening. The workpiece can be, for example, a brake disc, a hydraulic cylinder, a pressure roller, a sliding bearing, or other rotationally symmetric workpiece.

[0034] Figures 2a to 2d Different intensity distributions of the laser beam 4 are shown. They schematically illustrate a front sectional view of a workpiece 7, which is locally melted by means of the laser beam 4 for laser cladding welding, resulting in a molten pool 14 on the workpiece surface. As the laser beam 4 moves perpendicular to the plane of the drawing over the workpiece 7, feed material in the form of a powder beam 5 is directed to the processing point by means of a preferably inert carrier gas. For simplicity, Figures 2a to 2dEach describes the application of powder from only one side. However, it goes without saying that in the case of laser cladding welding, the feedstock can be directed to the processing point as multiple individual beams arranged in a ring around the laser beam, or in the form of a ring beam, and, in the case of a linear beam profile of the laser beam, as a linear powder beam directed from the front and / or from the rear. Depending on the position of the powder particles within the powder beam 5, the interaction path within the interaction zone 15 varies in length, along which the powder particles in the powder beam 5 interact with the laser radiation and are thus loaded with its energy. Accordingly, depending on the trajectory of the powder particles, the powder particles are heated to different degrees by the laser beam 4. For example, the powder particles in the center of the powder beam 5 melt within the interaction zone 15, while the powder particles in the edge regions of the powder beam 5 evaporate due to longer or shorter interaction times with the laser beam 4 (see...). Figures 2a to 2d The powder particles (either on the right or at the top) or those impacting the workpiece surface in solid form (see...) Figures 2a to 2d (The powder particles are located on the left or at the bottom). If the laser beam 4 has a Gaussian intensity distribution I1 within the interaction region 15, the temperature gradient of the powder particles is particularly large during laser cladding welding. Figure 2a This situation is illustrated in the diagram. The powder particles at the outer (or lower) edge of the powder beam 5 are heated particularly weakly. The non-uniform interaction time between the powder particles and the laser beam 4 can negatively affect the welding result. High-quality welds can be ensured within a narrow process window with precisely matched process parameters, especially with precisely predetermined rotational motion. Variations in laser power or rotational motion can already cause sensitive quality fluctuations in the welding result. If the laser beam 4 used has a flat-topped or cap-shaped intensity distribution I2 (like... Figure 2b As shown in the diagram, this can improve the temperature gradient of the powder particles, or in other words, narrower temperature bandwidth.

[0035] If the laser beam 4 used has a certain condition within the interaction region 15, according to Figure 2c or Figure 2d The intensity distributions I3 and I4 can further heat the powder more uniformly. Figure 2c A laser beam 4 with a concave intensity distribution I3 in the interaction region 12 is depicted, where the intensity decreases from the annular maximum towards the central region of the laser beam 4. Due to the high intensity of the laser beam 4 in the edge region, even powder particles with short interaction times are still heated relatively strongly. The particularly uniform temperature distribution of the powder particles is achieved for coaxial powder supply with the following annular intensity profile of the laser beam 4, in which most of the laser energy is located in the edge region of the laser beam 4. The flat-topped or cap-shaped intensity distribution I4 of the laser beam 4 in the outer annular region (see...) Figure 2dThis can be particularly advantageous. Using a laser beam with such an intensity distribution makes it possible to advantageously influence process stability, especially in the case of high-speed laser cladding welding. Figure 2c and Figure 2d Each involves a variant of laser beam 4 with a substantially rotationally symmetric cross-section. It goes without saying that... Figure 2c and Figure 2d The description in the text can be similarly applied to a laser beam 4 with a linear beam profile, wherein the corresponding intensity distributions I3 and I4 exist transversely to the length of the linear beam profile.

[0036] Figure 3 A top view of workpiece 7 is shown. The superposition of rotational motion about axis 9 and translational motion along offset direction 11 produces helical trajectory 12. In this example, the beam nozzle 3 begins to apply powder layer channels 6 to workpiece 7 at the radially inner section. Translational motion from the radially inner section to the radially outer section causes the powder layer channels 6 to deviate along the trajectory of helical trajectory 12. In this example, the feed motion is increased. Accordingly, the offset 16 between two adjacent helical flanks of helical trajectory 12 increases radially outward. It should be noted that the powder layer channels 6 applied to workpiece 7 along helical trajectory 12 have channel width 17, such that the offset 16 does not refer to the distance between two adjacent helical flanks. Rather, adjacent helical flanks may overlap, as shown in the figure. Figure 4 As can be clearly seen from the schematic cross-sectional view along line IV-IV shown.

[0037] Figure 4 It shows that it can be along Figure 3A schematic cross-section generated by line IV-IV is shown to illustrate the effect of the increasing translational motion as processing progresses. A first powder layer groove 18a is applied to the radially inner section of the workpiece. As the workpiece 7 continues to rotate, the translational motion along the offset direction 11 causes a second powder layer groove 18b to be offset by an amount 16 relative to the first powder layer groove 18a. For example, the offset 16 is approximately 20% of the groove width 17, such that 80% of the second powder layer groove 18b overlaps with the first powder layer groove 18a to form a radial overlap 23. The translational motion increases as processing progresses. Accordingly, the offset 16 between the third powder layer groove 18c and the second powder layer groove 18b is greater than the offset between the second powder layer groove 18b and the first powder layer groove 18a. For example, the offset 16 between the second powder layer track 18b and the third powder layer track 18c is approximately 30% of the track width 17, such that 70% of the third powder layer track 18c overlaps with the second powder layer track 18b. The radial overlap of the individual tracks of the powder layer tracks 6 along the helical trajectory 12 decreases as processing proceeds (i.e., from the radially inner section of the workpiece to the radially outer section of the workpiece). As the overlap decreases, the layer thickness 13 decreases. This ensures that the layer thickness 13 decreases radially outward. For example, the offset 16 between the radially second outer powder layer track 18d and the radially outermost powder layer track 18e is approximately 80% of the track width 17, such that 20% of the radially outermost powder layer track 18e overlaps with the radially second outer powder layer track 18d. This has the effect that laser cladding welding introduces a large amount of energy, especially heat, into the workpiece 7. During the cooling phase after laser cladding welding, this leads to deformation of the workpiece 7. This deformation affects the applied layer, which must then be ground to give the finished part a flat and therefore non-curved surface. Since the outermost layer thickness 13, where the maximum deformation currently occurs, is smaller than the innermost layer thickness 13, material loss during grinding is reduced.

[0038] Figure 5 A workpiece 7 with a powder layer is schematically shown, wherein the radially outer powder layer thickness 13 on the first workpiece side 19 (in this case, the top side) is less than the radially inner powder layer thickness 13. Currently, workpiece 7 is a brake disc. For example, the radially outer powder layer thickness is 50 µm, and the radially inner powder layer thickness is 100 µm. It is also conceivable that the layer thickness is between 50 µm and 500 µm. Due to the heat input from the molten pool 14 during laser cladding welding, internal stress is generated in workpiece 7, particularly the brake disc, which causes deformation of workpiece 7 upon cooling. Because workpiece 7 exhibits a warped shape due to this deformation, it is also referred to as warping. This deformation can, in principle, be compensated for by an increased layer thickness 13 on the functional surface (i.e., the surface processed by laser cladding welding), thereby allowing the functional surface of the component to be ground to a planar parallel. Figure 5On workpiece 7, a first powder layer 20 has been applied to a first workpiece side 19, and a second powder layer 22 has been applied to a second workpiece side 21. During laser cladding welding, workpiece 7 has deformed, causing the first workpiece side 19 to become concave and the second workpiece side 21 to become convex. Corresponding to this deformation, the first powder layer 20 has been applied in such a way that the radially inner section has a higher layer thickness 13 than the radially outer section. During the application of the first powder layer 20 from the radially inner section to the radially outer section of workpiece 7, the translational movement increases as processing progresses. Alternatively, during the application from the radially outer section to the radially inner section of workpiece 7, the translational movement decreases. In a manner complementary to the behavior of the first powder layer 20 on the first workpiece side 19, the second powder layer 22 is applied to the second workpiece side 21. The radially inner section of the second powder layer 22 has a smaller layer thickness 13 than the radially outer section. During the application of the second powder layer 22 from the radially inner section to the radially outer section of the workpiece 7, the translational movement decreases as processing continues. Alternatively, during the application from the radially outer section to the radially inner section of the workpiece 7, the translational movement increases. For example, the first powder layer 20 and the second powder layer 22 can be applied simultaneously. The first powder layer 20 is complementary to the second powder layer 22 in terms of its powder layer thickness 13.

[0039] Within the scope of application, all individual features presented in the embodiments may be combined and / or interchanged with each other without departing from the scope of the invention.

[0040] List of reference numerals 1. Laser System 2 Processing Units 3. Beam nozzle 4. Laser beam 5 Powder Beam 6 Powder Layer Track 7. Workpiece 8. Workpiece receiving unit 9. Rotation axis 10 translation units 11 Offset Direction 12 Spiral Trajectory 13 Powder layer thickness 14 Molten Pool 15 Interaction Region 16 Offset 17. Track width Various powder layer tracks from 18a to 18d 19 First workpiece side 20 First powder layer 21 Second workpiece side 22 Second powder layer 23 Radial overlap 100 Control Unit I1 Gaussian intensity distribution I2 Flat-top intensity distribution I3 Reduced center intensity distribution I4 Intensity distribution without a central point of influence

Claims

1. Method for laser cladding welding in a laser system (1), the method comprising the following steps: - driving a machining unit (2) having a multifunctional beam nozzle (3) for providing a laser beam (4) and a powder beam (5) such that the powder beam (5) applies a powder layer track (6) on a workpiece (7), in particular rotationally symmetrical, under interaction with the laser beam (3); - driving a workpiece receiving unit (8) arranged with the workpiece (7) such that a rotational movement moves the workpiece (7) about a rotational axis (9); and - driving a translation unit (10) such that a translational movement moves the beam nozzle (3) and / or the workpiece receiving unit (8) in a deflection direction (11) essentially orthogonal to the rotational axis (9); wherein the rotational movement and the translational movement superimpose a feed movement such that the powder layer track (6) is applied onto the workpiece (7) along a helical trajectory (12), wherein a machining parameter is varied along the progress of machining of the workpiece (7) such that a powder layer thickness (13) varies along a radial direction of the workpiece (7).

2. Method according to claim 1, wherein the machining parameter is the feed movement, a powder mass flow of the powder beam (5) and / or a laser power of the laser beam (4).

3. Method according to any one of claims 1 or 2, wherein the powder layer track (6) has a radial track width (17), wherein a deflection (16) of two adjacent helical flanks of the helical trajectory (12) is smaller than the track width (17) such that the powder layer track (6) forms a radial overlap (23) along the helical trajectory (12).

4. Method according to claim 3, wherein the radial overlap (23) varies in proportion to a varying feed movement.

5. Method according to any one of claims 3 or 4, wherein in machining of a first workpiece side (19) from a radially inner workpiece section to a radially outer workpiece section, a rate of the feed movement increases, in particular linearly or progressively, along the progress of machining such that the radial overlap (23) of the helical trajectory (12) at the radially outer section is smaller than at the radially inner section, or wherein in machining of the first workpiece side (19) from a radially outer workpiece section to a radially inner workpiece section, a rate of the feed movement decreases, in particular linearly or progressively, along the progress of machining such that the radial overlap (23) of the helical trajectory (12) at the radially outer section is smaller than at the radially inner section.

6. Method according to any one of claims 3 to 5, wherein in the machining of the second workpiece side (21) from the radially outer workpiece section to the radially inner workpiece section, the rate of the feed motion increases, in particular linearly or progressively, as the machining progresses, so that the radial overlap (23) of the helical track (12) at the radially outer section is greater than at the radially inner section. in the machining of the second workpiece side (21) from the radially outer workpiece section to the radially inner workpiece section, the rate of the feed motion increases, in particular linearly or progressively, as the machining progresses, so that the radial overlap (23) of the helical track (12) at the radially outer section is greater than at the radially inner section.

7. The method according to any one of claims 5 or 6, wherein determined depending on a deformation occurring in the workpiece (7) during the laser cladding welding.

8. The method according to any one of claims 3 to 7, wherein the radial overlap (23) of the powder layer track (6) at a first radial end section, e.g. a radially inner workpiece section or a radially outer workpiece section, is greater than 50%, in particular 70% to 80%, of the track width (17), and the radial overlap of the powder layer track at a second radial end section, e.g. a radially outer workpiece section or a radially inner workpiece section, is less than 50%, in particular 20% to 40%, of the track width (17).

9. The method according to any one of claims 3 to 8, wherein the radial overlap (23) of the powder layer track (6) at a first radial end section, e.g. a radially inner workpiece section or a radially outer workpiece section, results in a first layer thickness, and the radial overlap of the powder layer track at a second radial end section, e.g. a radially outer workpiece section or a radially inner workpiece section, results in a second layer thickness, wherein the first layer thickness exceeds the second layer thickness by a factor of 1.5 or more, in particular by a factor of 2 or 2.

5.

10. The method according to any one of the preceding claims, wherein the machining parameters, in particular the varying feed motion, are preset in response to a previously machined workpiece (7).

11. The method according to any one of claims 3 to 10, wherein the rotational motion is constant, so that the varying feed motion is caused only by the varying translational motion.

12. The method according to any one of the preceding claims, wherein the workpiece (7) is positionally fixed arranged in the offset direction (11), so that the translational motion is caused by a motion of the beam nozzle (3).

13. The method according to any one of the preceding claims, wherein the powder layer track (6) forms a bond layer on which a wear-resistant layer is applied in a next step.

14. A control unit (100) for use in a laser system (1) for laser cladding welding, wherein the control unit (100) is set up and configured to perform the method according to the preceding claims.

15. A laser system (1) for laser cladding welding, the laser system comprising: the control unit (100) is set up and configured to perform the method according to the preceding claims. - Processing unit (2), which has a multi-functional beam nozzle (3) for providing a laser beam (4) and a powder beam (5); - Workpiece receiving unit (8), on which workpiece (7) is arranged; - A translation unit configured to move the beam nozzle (3) and / or the workpiece receiving unit (8) in an offset direction (11) substantially orthogonal to the axis of rotation (9); and - The control unit (100) according to the preceding claim.

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