Method and device for laser build-up welding with variable layer thickness

Abstract

The present invention relates to a method for laser build-up welding in a laser system (1), comprising the following steps: actuating a processing unit (2) having a multifunctional jet nozzle (3) for providing a laser beam (4) and a powder jet (5), such that the powder jet (5) in interaction with the laser beam (3) deposits a powder-layer trace (6) onto an in particular rotationally symmetrical workpiece (7); actuating a workpiece receiving unit (8), on which the workpiece (7) is arranged, with the result that a rotational movement moves the workpiece (7) about an axis of rotation (9); and actuating a translation unit (10), with the result that a translational movement moves the jet 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 concurrently with an advancing movement such that the powder-layer trace (6) is deposited onto the workpiece (7) along a spiral path (12), with the advancing movement varying as the processing progresses, with the result that a powder layer thickness (13) varies along a radial direction of the workpiece (7). The invention also relates to a control unit for carrying out the method.

Description

[0001] Method and device for laser cladding with varying layer thickness

[0002] Technical area

[0003] The present invention relates to a method for laser cladding in a laser system and a control unit for use in a laser system.

[0004] State of the art

[0005] Laser cladding is used in repair, coating, and joining technology, for example. A distinction can be made between conventional laser cladding (laser metal deposition (LMD), direct metal deposition (DMD), or direct energy deposition (DED)) and so-called high-speed laser cladding (HS-LMD or extremely high-speed laser cladding (EHLA)). HS-LMD processes are described, for example, in DE 10 201 1 100 456 B4 or DE 10 2018 130 798 A1. An unavoidable side effect of laser cladding is distortion of the machined workpiece due to the thermal input. This causes residual stresses in the machined workpiece during laser cladding, which cause distortion in the cooling phase following laser cladding. This distortion results in a concave or convex component curvature.In order to ensure that functional surfaces applied to the workpiece by laser deposition welding have a flat, non-curved surface for their intended use despite the distortion, grinding of the functional surfaces following the cooling phase is necessary.

[0006] Description of the invention

[0007] Based on the known prior art, it is an object of the present invention to provide an improved method for laser cladding and a corresponding device. In particular, the invention aims to efficiently compensate for side effects of thermal distortion. To this end, it is particularly desirable to ensure low material wear during laser cladding. This object is achieved by a method for laser cladding and a control unit for use in a laser system according to the independent claims. Advantageous further developments emerge from the subclaims, the description, and the figures.

[0008] Accordingly, a method for laser material deposition 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 between 0.4 pm and 1.5 pm. 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 approximately 450 nm, approximately 515 nm, between approximately 800 nm and approximately 1000 nm, or approximately 1030 nm, 1060 nm, or 1070 nm can be generated. The laser beam can be designed such that it can be guided to a processing head by means of an optical fiber. The laser source can have a laser power of between 2 kW and 24 kW. If a workpiece being treated by means of the method is a brake disk, the laser power can in particular be between 8 kW and 24 kW; if it is a plain bearing, the laser power can in particular be 2 kW.The laser power can be constant during processing or vary depending on the process stage.

[0009] The method comprises the step of controlling a processing unit with a multifunctional jet nozzle for providing a laser beam and a powder jet, such that the powder jet, in interaction with the laser beam, applies a powder layer trace to a particularly rotationally symmetrical workpiece, such as a brake disc, a hydraulic cylinder, a printing roller, or a plain bearing. The control can take place between a central control unit of the laser system and a local control unit of the processing unit. The jet nozzle is provided to align the laser beam and the powder jet onto the workpiece. The powder jet can contain a powdery material comprising hard material particles, in particular carbides, which do not dissolve in an interaction zone after interaction with the laser beam. The laser beam can be directed essentially orthogonally onto a surface of the workpiece to be machined.The powder jet can be inclined relative to the laser beam in order to form an interaction zone between the powder jet and the laser beam above the material surface. Such an interaction zone enables more efficient application of the powdered material to the workpiece. The laser beam emerging from the jet nozzle can have a reduced core intensity in a core region compared to an edge region. The core intensity can, for example, be less than 90% of the edge intensity. Thus, at least within the interaction zone, the laser beam has an intensity in an edge region that is higher than a core intensity of the laser beam, so that the powdered material is exposed to the higher intensity of the edge region upon entering the interaction zone.

[0010] The method further comprises the step of controlling a workpiece holding unit on which the workpiece is arranged, such that a rotational movement moves the workpiece about a rotational axis. The control can take place between the central control unit of the laser system and a local control unit of the workpiece holding unit. The workpiece holding unit can clamp the workpiece so that it is fixedly mounted therein, provided the workpiece holding unit itself is rotationally movable. The rotational axis can correspond to a rotational symmetry axis of the rotationally symmetrical workpiece. The jet nozzle can be directed at a location on the workpiece that lies radially outside its rotational symmetry axis. Thus, rotation about the rotational axis causes the powder layer track to follow a trajectory on the workpiece. The rotational movement of the workpiece holding unit can be initiated by an independent drive.

[0011] The method further comprises the step of controlling a translation unit such that a translational movement moves the jet nozzle and / or the workpiece holding unit in an offset direction substantially orthogonal to the rotation axis. The control can take place between the central control unit of the laser system and a local control unit of the translation unit. The translational movement can be initiated by a drive independent of the workpiece holding unit. Alternatively, the translational movement can be initiated by the same drive as the rotational movement. The orthogonal offset direction of the translational movement causes a translation orthogonal to the rotation axis, which can accordingly affect a trajectory of the powder layer track. The rotational movement can be very high compared to the translational movement.

[0012] The rotational movement and the translational movement overlap to form a feed movement such that the powder layer track is applied to the workpiece along a spiral trajectory. This enables powder coating over the entire surface in a radial direction of the workpiece. The geometric shape of the spiral trajectory is predetermined by the feed movement. The feed movement can influence process parameters, such as the duration of action between the powder jet, laser beam and workpiece, in order to enable robust bonding of the powder particles with the workpiece. The spiral trajectory extends along a curve around the rotational axis, with the distance from the rotational axis increasing if the application occurs from radially inward to radially outward, or decreasing if the application occurs from radially outward to radially inward. The rotational movement comprises a rotational speed, the translational movement comprises a translational speed.If the machining parameter is the feed movement, the variation results from a variation in the rotational speed and / or the translational speed.

[0013] A processing parameter varies as the workpiece is processed, causing the powder layer thickness to vary along a radial direction of the workpiece. Optimized processing can be ensured based on the correlation between powder layer thickness and processing parameters such as feed motion, powder mass flow of the powder jet, and / or laser power. To adjust the powder layer thickness, the processing parameter is varied accordingly. The processing parameter can be varied in the same way for each component. Alternatively, the variation in the processing parameter depends on how the workpiece behaves during laser deposition. For this purpose, a measuring system can send a control signal to the translation unit and / or the workpiece holding unit. This process enables the powder layer thickness to be variably adjusted.The target geometry of the workpiece and / or the powder layer thickness can be taken into account, as can process parameters and their consequences, such as workpiece distortion. The thermal input during laser material deposition leads to residual stresses and distortion of the workpiece, which can be compensated or mitigated by varying the processing parameters so that the applied layer is essentially flat, i.e., non-curved, or at least less curved than with constant processing parameters as processing progresses. This minimizes or reduces material removal by grinding the applied layer, thus enabling more efficient processing and lower material consumption.

[0014] In one embodiment, the processing parameter is the feed motion, a powder mass flow of the powder jet, and / or a laser power used to provide the laser beam. By varying one of these parameters or a combination thereof, the applied powder layer thickness can be reliably varied. This efficiently contributes to compensating for thermal distortion.

[0015] In one embodiment, the powder layer track has a radial track width, wherein an offset between two adjacent spiral flanks of the spiral trajectory is less than the track width, such that the powder layer track forms a radial overlap along the spiral trajectory. Thus, when applied from radially inside to radially outside, a radially inner powder layer track is arranged below the nearest radially outer powder layer track. Correspondingly, when applied from radially outside to radially inside, a radially outer powder layer track is arranged below the nearest radially inner powder layer track. This radial overlap increases the powder layer thickness because powder layer tracks that are at least partially superimposed, and therefore overlapping powder layer tracks, have a greater powder layer thickness than two powder layer tracks whose offset is greater than their radial track width.

[0016] In one embodiment, the radial overlap varies proportionally with the varying feed motion. This means that the radial track width remains unaffected by the feed motion, providing an efficient way to control the radial overlap. The greater the feed motion, the greater the radial overlap. For example, if a workpiece distortion due to thermal input is known in advance, a precise and process-compliant adjustment of the powder layer thickness can be achieved by controlling the feed motion, so that the varying powder layer thickness compensates for the distortion.

[0017] In one embodiment, a speed of the feed movement - i.e. the feed rate - increases during machining of a first workpiece side from a radially inner workpiece section to a radially outer workpiece section as machining progresses, in particular linearly or progressively, so that the radial overlap of the spiral trajectory is less at the radially outer section than at the radially inner section. Alternatively, the feed rate decreases during machining of the first workpiece side from a radially outer workpiece section to a radially inner workpiece section as machining progresses, in particular linearly or degressively, so that the radial overlap of the spiral trajectory is less at the radially outer section than at the radially inner section. This ensures that the powder layer thickness is less at the radially outer section than at the radially inner section.This can counteract convex distortion of the workpiece. If the distortion is such that the radially outer section protrudes further in the direction of the powder layer thickness, adjusting the feed movement can at least partially compensate for the distortion.

[0018] In one embodiment, the feed rate during machining of a second workpiece side, which differs in particular from the first workpiece side, decreases from a radially inner workpiece section to a radially outer workpiece section as machining progresses, in particular linearly or degressively, so that the radial overlap of the spiral trajectory is higher at the radially outer section than at the radially inner section. Alternatively, the feed rate during machining of the second workpiece side increases from a radially outer workpiece section to a radially inner workpiece section as machining progresses, in particular linearly or progressively, so that the radial overlap of the spiral trajectory is higher at the radially outer section than at the radially inner section. This can counteract concave distortion of the workpiece.If the distortion is such that the radially outer section is curved opposite to the direction of the powder layer thickness, adjusting the feed movement can at least partially compensate for the distortion. The two embodiments in which the convex distortion and the concave distortion are counteracted can be combined, in particular in the case of a workpiece in which the top side is the first workpiece side and the underside is the second workpiece side. If the radially outer section of the first workpiece side distorts upwards, this causes the radially outer section of the second workpiece side to curve. While a powder layer thickness that decreases radially outwards can be applied to the first workpiece side in order to compensate for the distortion, a powder layer thickness that increases radially can be applied to the second workpiece side in a complementary manner. This extends the advantages of the method to workpieces machined on both sides.

[0019] In one embodiment, depending on the distortion that occurs in the workpiece during laser deposition welding, it is determined whether a workpiece side is machined as the first or second workpiece side. Thus, depending on the individual distortion, the corresponding powder layer thickness can be adjusted to the corresponding workpiece side, further contributing to a reduction in material consumption.

[0020] In one embodiment, the radial overlap of the powder layer track at a first radial end section, for example a radially inner workpiece section or a radially outer workpiece section, is above 50%, in particular 70% to 80%, of the track width, and at a second radial end section, for example the radially outer workpiece section or the radially inner workpiece section, is below 50%, in particular 20% to 40%, of the track width. If the radial overlap of the powder layer track is, for example, 70% to 80%, this means that 70% to 80% of one powder layer track lies above the adjacent, previously applied other powder layer track. If the radial overlap of the powder layer track is, for example, 20% to 40%, this means that only 20% to 40% of one powder layer track lies above the adjacent, previously applied other powder layer track.Whether one or the other powder layer track is the radially inner or radially outer powder layer track depends on whether the coating is applied from radially inside to radially outside or from radially outside to radially inside. The smaller the radial overlap, the thinner the powder layer thickness.

[0021] In one embodiment, the radial overlap of the powder layer track results in a first layer thickness at a first radial end section, for example a radially inner workpiece section or a radially outer workpiece section, and a second layer thickness at a second radial end section, for example the radially outer workpiece section or the radially inner workpiece section, wherein the first layer thickness exceeds the second layer thickness by a factor of 1.5 or more, in particular 2 or 2.5. The powder layer thickness can thus vary along the radial direction such that it is, for example, more than twice as large at one end section than at the other end section. This enables a strong variance in the powder layer thickness and accordingly the compensation of considerable workpiece distortions.

[0022] In one embodiment, the varying processing parameter, in particular the varying feed movement, is preset in response to previously machined workpieces. This allows the distortion caused by laser cladding on previously machined workpieces to be determined and evaluated, serving as an input variable for the feed movement. Statistical evaluation modules or neural networks, for example, can be used to evaluate previously machined workpieces. This enables precise adjustment of the powder layer thickness to the expected distortion of the workpiece.

[0023] In one embodiment, the rotational movement is constant, so that the varying feed movement results exclusively from the varying translational movement. The rotational movement of the workpiece holding unit can have a greater influence on the process parameters than the translational movement. In this respect, the translational movement can be used as the sole influencing factor for the variation in the feed movement. This further contributes to efficient workpiece processing. A constant movement within the scope of this disclosure can, in particular, be a movement with a constant speed. Accordingly, a varying movement can, in particular, be a movement with a varying speed.

[0024] In one embodiment, the workpiece is stationary in the offset direction, so that the translational movement results from the movement of the blasting nozzle. In the rotational direction, the workpiece is arranged so that it can rotate. This results in an efficient separation of functions, with the rotational movement being used to vary process-relevant parameters and the translational movement being used to vary the powder layer thickness. The translational movement of the blasting nozzle can be realized by a drive of the laser system in the feed direction. By separating the functions, the highest quality standards can be combined with minimal processing times.

[0025] In one embodiment, the powder coating trace forms an adhesion layer, onto which a wear-resistant coating is applied in a subsequent step. Thus, using the process, a component is coated in two layers. The adhesion layer serves in particular to improve the adhesion properties of the applied trace. The wear-resistant layer increases the load-bearing capacity of the workpiece. With the wear-resistant layer, the machining parameters, in particular the feed motion, can vary as machining progresses or, alternatively, remain constant. Alternatively, if the component is coated with a single layer, the powder coating trace is a wear-resistant layer.

[0026] The disclosure further relates to a control unit for use in a laser system for laser deposition welding, wherein the control unit is provided and configured to carry out the disclosed method. The control unit can be a component of a central control unit of the laser system or a standalone, local control unit. The effects and advantages disclosed in connection with the method extend accordingly to the control unit.

[0027] The disclosure further relates to a laser system for laser material deposition. The laser system has a processing unit with a multifunctional jet nozzle for providing a laser beam and a powder jet. The jet nozzle is intended to direct the laser beam and the powder jet onto a workpiece. The powder jet can contain a powdered material comprising hard material particles, in particular carbides, which do not dissolve in an interaction zone after interaction with the laser beam. The laser beam can be directed substantially orthogonally onto a surface of the workpiece to be machined. The powder jet can be inclined relative to the laser beam in order to form an interaction zone between the powder jet and the laser beam above the material surface. Such an interaction zone enables more efficient application of the powdered material to the workpiece.The laser beam emerging from the jet nozzle can have a reduced core intensity in a core region compared to an edge region. The core intensity can, for example, be less than 90% of the edge intensity. Thus, at least within the interaction zone, the laser beam has an intensity in an edge region that is higher than a core intensity of the laser beam, so that the powdery material is exposed to the higher intensity of the edge region upon entering the interaction zone. The laser system further comprises a workpiece holder unit on which a workpiece is arranged. The workpiece holder unit can clamp the workpiece so that it is firmly mounted therein, provided the workpiece holder unit itself is rotationally movable. The axis of rotation can correspond to a rotational symmetry axis of the rotationally symmetrical workpiece. The rotational movement of the workpiece holder unit can be initiated by an independent drive.

[0028] The workpiece can be rotationally symmetrical, in particular it is a brake disc, a hydraulic cylinder, a pressure roller or a plain bearing.

[0029] The laser system further comprises a translation unit configured to move the jet nozzle and / or the workpiece holder in an offset direction substantially orthogonal to the rotation axis. The translational movement can be initiated by a drive independent of the workpiece holder. Alternatively, the translational movement can be initiated by the same drive as the rotational movement. The orthogonal offset direction of the translational movement causes a translation orthogonal to the rotation axis, which can accordingly affect the trajectory of the powder layer track. The rotational movement can be very high compared to the translational movement.

[0030] The laser system further comprises a control unit according to the above disclosure. This control unit is configured to carry out the laser deposition welding method.

[0031] Short description of the characters

[0032] Preferred further embodiments of the invention are explained in more detail in the following description of the figures. In the figures:

[0033] Figure 1 is a schematic view of a laser system;

[0034] Figure 2a-d exemplary intensity distributions of a laser beam;

[0035] Figure 3 shows a spiral trajectory along which a powder layer track is applied to a workpiece;

[0036] Figure 4 is a schematic view of adjacent powder layer tracks; and

[0037] Figure 5 is a schematic view of a workpiece machined on both sides.

[0038] Detailed Description of Preferred Embodiments Preferred embodiments are described below with reference to the figures. Identical, similar, or equivalent elements in the different figures are provided with identical reference numerals, and a repeated description of these elements is partially omitted to avoid redundancies.

[0039] Figure 1 shows a laser system 1 for laser material deposition. During laser material deposition, a powder layer is applied to a workpiece by melting a powdered material with a laser and bonding it to the workpiece. The laser system 1 has a control unit 100 that controls the individual 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 approximately 450 nm, approximately 515 nm, between approximately 800 nm and approximately 1000 nm, or approximately 1030 nm, 1060 nm, or 1070 nm can be generated. The laser generated by the laser source can be designed such that it can be guided, among other things, to a processing head of the processing unit 2 by means of an optical fiber. The laser source can have a laser power of 2 kW to 24 kW.The processing head has a multifunctional jet nozzle 3, which directs a laser beam 4 and a powder jet 5 onto a powder layer track 6 of a rotationally symmetrical workpiece 7 in a process-oriented manner. The laser beam 4 can have a ring and a core component, as described in particular in connection with Figures 2a to 2d. It can be guided to the processing unit 2 via a multi-clad fiber.

[0040] The workpiece 7 is arranged in a holding unit 8 and rotates about a rotation axis 9. The rotational movement is superimposed by a translational movement, which is initiated by a translation unit 10, along the offset direction 11 to result in a spiral trajectory 12 on the workpiece 7. The superposition of rotational movement and translational movement results in the feed movement with which the laser beam 4 and the powder jet 5 move relative to the workpiece 7. The feed movement varies as processing progresses. For example, it is 20 m / s at the beginning of processing and then increases over the course of the process. Alternatively, it can decrease over the course of the process. Whether the feed movement increases or decreases over the course of the process depends on how the workpiece distorts.For example, a top side can be machined with increasing feed movement and a bottom side with decreasing feed movement (see particularly below in connection with Figure 5). The laser beam 4 can have a reduced intensity in a core region compared to a ring or edge region. The core intensity can, for example, be less than 90% of the edge intensity. Thus, at least within an interaction zone between the laser beam 4 and the powder jet 5, the laser beam 4 has an intensity in an edge region that is higher than an intensity in the core region of the laser beam 4, so that the powdery material in the powder jet 5 is exposed to the higher intensity of the edge region upon entering the interaction zone. Due to the inclined alignment of the at least one powder jet 5 to the laser beam 4, the interaction distance with the laser beam 4 varies across the cross-section of the powder jet 5.Due to the reduced intensity in the core region, a substantially homogeneous energy is supplied to the individual powder particles over varying interaction distances. In other words, an intensity maximum in the edge region of the laser beam leads to a more uniform distribution of fluence per powder particle, thus expanding the process window while maintaining stable weld quality.

[0041] The workpiece 7 can be a metallic workpiece. The powdered material can in particular comprise a metallic material. The powdered material can be blasted onto the workpiece surface by means of a conveying gas, in particular argon or helium, and / or by means of an inert gas mixture as a process shielding gas. The process shielding gas can additionally shield the processing location from the surrounding atmosphere. The focus of the laser beam 4 can be on the workpiece surface or directly above the workpiece surface. The jet nozzle 3 can have an annular opening for the laser beam 4 and one or more further openings for the powder jet 5. The annular opening can be designed in the manner of an annular gap nozzle or by means of several nozzles arranged in a ring around the core opening in the manner of a multi-jet nozzle.The workpiece can be, for example, a brake disc, a hydraulic cylinder, a pressure roller, a plain bearing or another rotationally symmetrical workpiece.

[0042] Figures 2a to 2d show various intensity distributions of the laser beam 4. They schematically show a sectional front view of the workpiece 7, which is locally melted by means of the laser beam 4 for laser cladding, so that a molten pool 14 is created on the workpiece surface. While the laser beam 4 is moved perpendicular to the plane of representation over the workpiece 7, a filler material is blasted as a powder jet 5 onto the processing point by means of a preferably inert conveying gas. For the sake of simplicity, Figures 2a-d only show the powder application from one side. It is understood, however, that during laser cladding the filler material can be directed onto the processing point in several individual beams arranged in a ring around the laser beam or as a ring beam, and in the case of a linear beam profile of the laser beam, for example, from the front and / or from the rear as a linear powder jet.Depending on the position of a powder particle within the powder jet 5, the interaction distance within an interaction zone 15, along which a powder particle of the powder jet 5 interacts with the laser radiation and is thus exposed to its energy, varies in length. Accordingly, the powder particles are heated to varying degrees by the laser beam 4 depending on their trajectory. While powder particles in the center of the powder jet 5 within the interaction zone 15, for example, are melted, powder particles in the edge region of the powder jet 5 can simultaneously evaporate due to their longer or shorter interaction time with the laser beam 4 (cf. right-hand or upper powder particle in Figures 2a-d) or impact the workpiece surface in a solid state (cf. left-hand or lower powder particle in Figures 2a-d).The temperature gradient of the powder particles during laser cladding is particularly large when the laser beam 4 has a Gaussian-shaped intensity profile 11 within the interaction zone 15. This case is shown in Figure 2a. Powder particles at the outer (or lower) edge of the powder jet 5 are heated particularly weakly. The uneven interaction time of the powder particles with the laser beam 4 can have a negative influence on the welding result. A high-quality weld bead can be guaranteed in a narrow process window with precisely coordinated process parameters, in particular a precisely predetermined rotational movement. Changes in the laser power or the rotational movement can already lead to sensitive fluctuations in the quality of the welding result. An improvement in the temperature gradient or a narrower temperature bandwidth of the powder particles can be achieved if the laser beam 4 has a plateau orTop-hat shaped intensity profile I2 is used, as shown in Figure 2b.

[0043] Furthermore, the homogeneity of the powder heating can be improved if the laser beam 4 is used which has an intensity distribution I3, I4 within the interaction zone 15 as shown in Figures 2c or 2d. In Figure 2c, the laser beam 4 is shown with a concave intensity profile I3 in the interaction zone 12, in which the intensity decreases from an annular maximum to the core region of the laser beam 4. Due to the high intensity in the edge region of the laser beam 4, even powder particles with a short interaction time are still heated comparatively strongly. A particularly uniform temperature distribution of the powder particles can be achieved for coaxial powder feed with an annular intensity profile of the laser beam 4, in which the majority of the laser energy is present in the edge region of the laser beam 4. A plateau-like or top-hat-shaped intensity distribution I4 in the annular outer region of the laser beam 4 (cf.Figure 2d) can be advantageous. Using laser beam 4 with such an intensity distribution can advantageously influence process stability, particularly during high-speed laser cladding. Figures 2c and 2d each refer to variants in which laser beam 4 has a substantially rotationally symmetrical cross-section. It is understood that the representations in Figures 2c and 2d are analogously applicable to a laser beam 4 with a linear beam profile, with the respective intensity distribution I3, I4 then being transverse to the length of the linear beam profile.

[0044] Figure 3 shows a plan view of the workpiece 7. The superposition of the rotational movement about the rotation axis 9 and the translational movement along the offset direction 11 results in the spiral trajectory 12. In the present example, the jet nozzle 3 has begun to apply the powder layer track 6 to the workpiece 7 at the radially inner section. The translational movement from the radially inner section to a radially outer section causes a track offset of the powder layer track 6 along the spiral trajectory 12. The feed movement increases in the present example. Accordingly, an offset 16 between two adjacent spiral flanks of the spiral trajectory 12 increases radially outwards. It should be noted that the powder layer track 6, which is applied to the workpiece 7 along the spiral trajectory 12, has a track width 17, so that the offset 16 does not represent a distance between two adjacent spiral flanks.Rather, adjacent spiral flanks may overlap, as can be seen from the schematic sectional view along the line IV-IV shown in Figure 4.

[0045] Figure 4 shows a schematic cross-section, as it could result along the line IV-IV in Figure 3, in order to illustrate the effect of an increasing translational movement as machining progresses. A first powder layer track 18a is applied to a radially inner workpiece section. While the workpiece 7 continues to rotate, the translational movement along the offset direction 11 causes an offset 16 of a second powder layer track 18b relative to the first powder layer track 18a. The offset 16 is, for example, around 20% of the track width 17, so that 80% of the second powder layer track 18b overlaps with the first powder layer track 18a to form a radial overlap 23. The translational movement increases as machining progresses. Accordingly, the offset 16 between a third powder layer track 18c and the second powder layer track 18b is higher than between the second powder layer track 18b and the first powder layer track 18a.The offset 16 between the second powder layer track 18 b and the third powder layer track 18 c is, for example, around 30% of the track width 17, so that 70% of the third powder layer track 18 c overlaps with the second powder layer track 18 b. The radial overlap of the individual tracks of the powder layer track 6 along the spiral trajectory 12 decreases as machining progresses, i.e. from the radially inner workpiece section to the radially outer workpiece section. As the overlap decreases, the layer thickness 13 decreases. This ensures that the layer thickness 13 decreases radially outwards. The offset 16 between the radially second outermost powder layer track 18 d and the radially outermost powder layer track 18 e is, for example, around 80% of the track width 17, so that 20% of the radially outermost powder layer track 18 e overlaps with the radially second outermost powder layer track 18 d.This has the following effect: laser cladding introduces a high amount of energy, particularly thermal energy, into the workpiece 7. In a cooling phase following laser cladding, this leads to distortion of the workpiece 7. This distortion affects the applied layer, which must then be ground off again so that the finished component has a flat, i.e., non-curved surface. The material wear occurring during grinding is reduced by the fact that the radially outer layer thickness 13, where the maximum distortion occurs in this case, is smaller than the radially inner layer thickness 13.

[0046] Figure 5 schematically shows a workpiece 7 with a powder layer whose radially outer powder layer thickness 13 on a first workpiece side 19, in this case the top side, is less than the radially inner powder layer thickness 13. In this case, the workpiece 7 is a brake disc. For example, the radially outer powder layer thickness is 50 pm and the radially inner powder layer thickness is 100 pm. Layer thicknesses between 50 pm and 500 pm are also conceivable. Due to the heat input by the melt pool 14 during laser deposition welding, residual stresses arise in the workpiece 7, in particular the brake disc, which lead to distortion of the workpiece 7 when the workpiece 7 cools. Since the workpiece 7 takes on a shield shape due to this distortion, this is also referred to as shielding.In principle, the distortion can be compensated for by means of an increased layer thickness 13 on functional surfaces, i.e., the surfaces that are machined by laser deposition welding, so that the functional surfaces of the component can be ground plane-parallel. A first powder layer 20 was applied to the first workpiece side 19 of the workpiece 7 from Figure 5, and a second powder layer 22 was applied to a second workpiece side 21. During laser deposition welding, the workpiece 7 distorted, so that the first workpiece side 19 became concave and the second workpiece side 21 became convex. Corresponding to this distortion, the first powder layer 20 was applied such that a radially inner section had a greater layer thickness 13 than a radially outer section.When the first powder layer 20 was applied from the radially inner section of the workpiece 7 to the radially outer section of the workpiece 7, the translational movement was increased as the machining progressed. Alternatively, the translational movement was reduced when applied from the radially outer section of the workpiece to the radially inner section of the workpiece. Complementary to this behavior of the first powder layer 20 on the first workpiece side 19, the second powder layer 22 was applied to the second workpiece side 21. A radially inner section of the second powder layer 22 has a smaller layer thickness 13 than a radially outer section. When the second powder layer 22 was applied from the radially inner section of the workpiece 7 to the radially outer section of the workpiece 7, the translational movement was reduced as the machining progressed.Alternatively, the translational movement was increased during application from the radially outer section of the workpiece 7 to the radially inner section of the workpiece 7. The first powder layer 20 and the second powder layer 22 can, for example, be applied simultaneously. The first powder layer 20 is complementary to the second powder layer 22 in its powder layer thickness 13.

[0047] Where applicable, all individual features presented in the embodiments may be combined and / or exchanged without departing from the scope of the invention.

[0048] List of reference symbols

[0049] 1 laser system 16 offset

[0050] 2 processing units 17 track width

[0051] 3 Blasting nozzle 18a-d various powder layer traces 4 Laser beam 20 19 First workpiece side

[0052] 5 Powder jet 20 First powder layer

[0053] 6 Powder layer track 21 Second workpiece side

[0054] 7 Workpiece 22 Second powder layer

[0055] 8 Workpiece holder unit 23 Radial overlap 9 Rotation axis 25 100 Control unit

[0056] 10 translation units

[0057] 11 Offset direction 11 Gaussian intensity profile

[0058] 12 Spiral trajectory 12 Plateau-shaped intensity profile

[0059] 13 Powder layer thickness 13 Reduced core intensity profile 14 Melt pool 30 14 Core intensity-free intensity profile

[0060] 15 Interaction zone

Claims

Claims 1 . Method for laser cladding in a laser system (1), comprising the following steps: Controlling a processing unit (2) with a multifunctional jet nozzle (3) for providing a laser beam (4) and a powder jet (5), so that the powder jet (5) in interaction with the laser beam (3) applies a powder layer track (6) to a particularly rotationally symmetrical workpiece (7); Controlling a workpiece holding unit (8) on which the workpiece (7) is arranged, so that a rotational movement moves the workpiece (7) about a rotation axis (9); and Controlling a translation unit (10) such that a translation movement moves the jet nozzle (3) and / or the workpiece holding unit (8) in an offset direction (11) that is substantially orthogonal to the rotation axis (9); wherein the rotation movement and the translation movement overlap to form a feed movement such that the powder layer track (6) is applied to the workpiece (7) along a spiral trajectory (12), wherein a processing parameter varies as processing of the workpiece (7) progresses, such that a powder layer thickness (13) varies along a radial direction of the workpiece (7).

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

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

4. The method according to claim 3, wherein the radial overlap (23) varies proportionally with the varying feed movement.

5. The method according to any one of claims 3 or 4, wherein a speed of the feed movement during the machining of a first workpiece side (19) from a radially inner workpiece section to a radially outer workpiece section increases as machining progresses, in particular increases linearly or progressively, so that the radial overlap (23) of the spiral trajectory (12) is less at the radially outer section than at the radially inner section, or wherein a speed of the feed movement during the machining of the first workpiece side (19) from a radially outer workpiece section to a radially inner workpiece section decreases as machining progresses, in particular decreases linearly or degressively, so that the radial overlap (23) of the spiral trajectory (12) is less at the radially outer section than at the radially inner section.

6. The method according to one of claims 3 to 5, wherein a speed of the feed movement during the machining of a second workpiece side (21) from a radially inner workpiece section to a radially outer workpiece section decreases as the machining progresses, in particular decreases linearly or degressively, so that the radial overlap (23) of the spiral trajectory (12) is higher at the radially outer section than at the radially inner section, or wherein a speed of the feed movement during the machining of the second workpiece side (21) from a radially outer workpiece section to a radially inner workpiece section increases as the machining progresses, in particular increases linearly or progressively, so that the radial overlap (23) of the spiral trajectory (12) is higher at the radially outer section than at the radially inner section.

7. Method according to one of claims 5 or 6, wherein, depending on a distortion occurring in the workpiece (7) during laser deposition welding, it is determined whether a workpiece side is machined as a first workpiece side (19) or as a second workpiece side (21).

8. Method according to one of claims 3-7, wherein the radial overlap (23) of the powder layer track (6) at a first radial end section, for example a radially inner workpiece section or a radially outer workpiece section, is above 50%, in particular 70% to 80%, of the track width (17) and at a second radial end section, for example the radially outer workpiece section or the radially inner workpiece section, is below 50%, in particular 20% to 40%, of the track width (17).

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

5.

10. Method according to one of the preceding claims, wherein the varying machining parameter, in particular the varying feed movement, is preset in response to previously machined workpieces (7).

11. Method according to one of claims 3-10, wherein the rotational movement is constant, so that the varying feed movement results exclusively from the varying translational movement.

12. Method according to one of the preceding claims, wherein the workpiece (7) is arranged stationary in the offset direction (11) so that the translational movement results from the movement of the jet nozzle (3).

13. Method according to one of the preceding claims, wherein the powder layer track (6) forms an adhesive layer to which a wear-resistant layer is applied in a next step.

14. Control unit (100) for use in a laser system (1) for laser deposition welding, wherein the control unit (100) is provided and configured to carry out the method according to the preceding claims.

15. Laser system (1) for laser material deposition, comprising a processing unit (2) with a multifunctional jet nozzle (3) for providing a laser beam (4) and a powder jet (5); a workpiece holding unit (8) on which a workpiece (7) is arranged; a translation unit configured to move the jet nozzle (3) and / or the workpiece holding unit (8) in an offset direction (11) substantially orthogonal to the rotation axis (9); and a control unit (100) according to the preceding claim.

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