Method and device for laser build-up welding by means of primary and secondary laser energy

Abstract

The invention relates to a method for laser build-up welding in a feed direction by means of a beam nozzle having a light channel for guiding at least one laser beam directed onto a workpiece, having a powder unit arranged outside the light channel for guiding at least one filler to be applied onto the workpiece, the method comprises the following steps: directing a first laser beam onto the workpiece for generating a first irradiation zone, directing a second laser beam onto the workpiece for generating a second irradiation zone, the second irradiation zone being located in front of the first irradiation zone in the feed direction; introducing a filling material into the first irradiation zone, the filling material entering at least partially into the first laser beam before impacting the workpiece and thereby being at least partially heated; the secondary laser energy of the second laser beam introduced into the second irradiation zone is greater than the primary laser energy of the first laser beam introduced into the first irradiation zone. The application also relates to a beam nozzle.

Description

Technical Field

[0001] The present application relates to a method for laser surfacing along a feed direction and a beam nozzle for laser surfacing. Background Art

[0002] Laser surfacing is usually applied in repair, coating and / or joining technologies. A distinction can be made between conventional laser surfacing (laser metal deposition (LMD), direct metal deposition (DMD) or direct energy deposition (DED)) and so-called high-speed laser surfacing (HS-LMD or extremely high-speed laser surfacing (EHLA)). The HS-LMD method is described, for example, in the published documents DE 10 2011 100456 A and DE 10 2018130 798A1. In addition, the published document DE 10 2022 100 173 A1 discloses an additive manufacturing method in which a first laser beam emanates from a nozzle unit and a second laser beam is directed from a separate head onto a workpiece in order to apply a powdery structural material in an additive manner.

[0003] By means of laser surfacing, a functional layer can be applied to a workpiece. This functional layer generally improves the load-bearing performance of the workpiece machined by means of laser surfacing relative to the unprocessed workpiece. The functional layer can be used, for example, as a wear protection layer. The application of the functional layer can be based on diffusion processes, welding and / or melting of the workpiece surface, application of a filler and subsequent cooling, such that a substrate structure with hard particles is locked to the workpiece surface material. Laser surfacing affects the internal material structure of the workpiece and the material to be applied and changes this internal material structure. In some cases, this can lead to deficiencies in the internal material structure, such as cracks and / or bonding defects. It is also possible that the hard particles form an alloy with the substrate material, which leads to embrittlement of the substrate structure and thus to embrittlement of the applied functional layer. Therefore, the deficiencies may impair the effort to achieve an improvement in the load-bearing performance. They are usually of a microscopic nature and can therefore only be identified and their root causes determined with great expense. Summary of the Invention

[0004] Due to known prior art, the task of the present application is to provide an improved method for laser surfacing along a feed direction and an improved beam nozzle. The aim of the present application is in particular to apply the filler to the workpiece in such a way that deficiencies in the internal material structure are reduced or even avoided and the welding quality of the applied functional layer and the workpiece is generally improved. The deficiencies can be bonding defects between the workpiece surface and the applied functional layer or between the individually applied functional layers. The deficiencies can also be pores, i.e. air inclusions, which occur inside the applied functional layer or between the applied functional layer and the workpiece surface. In particular, when the workpiece surface is a casting material, the pores may occur more frequently. The deficiencies can also be cracks, which extend in particular perpendicular to the workpiece surface inside the applied functional layer. The deficiencies can also arise from the dissolution of the powder particles of the powdered filler, in particular carbides, in the base material of the powdered filler, thereby forming an alloy, which leads to embrittlement of the base material. The aim of the present application is in particular also to provide a reliable beam nozzle which enables a process-compliant application of the functional layer. The present application can also achieve that the beam nozzle is configured in such a way that the beam nozzle ensures reliable and precise laser surfacing in a very high number of cycles.

[0005] The task is solved by a method and a beam nozzle having the features of the independent claims. Advantageous developments result from the dependent claims, the description and the drawings.

[0006] Accordingly, a method for laser surfacing along a feed direction by means of a beam nozzle is proposed. The laser surfacing can be a method for high-speed laser material deposition (HS-LMD). The feed direction is the direction along which the beam nozzle moves relative to the workpiece. The feed direction can be formed by the movement of the workpiece, in particular a rotational movement, by the movement of the beam nozzle, or by the superposition of these two movements. The workpiece can be a rotationally symmetric workpiece, such as a brake disc, a hydraulic cylinder, a pressure roller or a sliding bearing. The beam nozzle has an optical channel for guiding at least one laser beam, which is directed onto the workpiece. The optical channel can be a hollow channel that passes through the entire beam nozzle along the longitudinal direction. In addition to the laser beam, process gas can also be guided to the workpiece surface through the optical channel. The beam nozzle also has a powder unit, which is arranged in particular radially outside the optical channel, for guiding at least one filler, in particular powder or alternatively a wire, wherein the filler is to be applied to the workpiece. The powder unit can start from the longitudinal direction of the beam nozzle and be radially outside the optical channel and can be part of an outer structure that encloses the optical channel in a closed manner. The powder jet can guide the powdered filler, which consists of hard particles, in particular carbides and a base material. The powder unit can be a component of the beam nozzle that is provided for directly or indirectly guiding the powdered filler. The powder unit can have an injector guide into which a powder injector can be inserted. The powder unit can also have an annular gap inside which the powdered filler is guided.

[0007] The method includes the step of directing a first laser beam onto the workpiece to generate a first irradiation zone. The first laser beam can be used to heat and in particular at least partially melt the filler and the workpiece. Thus, the thermal energy delivered by the first laser beam, i.e., the primary laser energy, can be used to melt the filler and the workpiece in a manner desired for laser surfacing. Therefore, the first irradiation zone can be referred to as the process zone because the process of applying the functional layer to the workpiece takes place here.

[0008] The method further includes the step of directing a second laser beam onto the workpiece to generate a second irradiation zone. The second laser beam can be used to preheat the workpiece. Thus, the thermal energy delivered by the second laser beam, i.e., the secondary laser energy, can be used to preheat the workpiece or the base layer to be coated in time before melting. Therefore, the second irradiation zone can be referred to as the preheating zone because the preheating of the base layer to be coated takes place here. The second laser beam can be directed in such a way that the second laser beam does not interact or only interacts to a negligible extent with the filler before the filler impinges on the workpiece.

[0009] The second irradiation zone is located in front of the first irradiation zone in the feed direction such that the first irradiation zone follows the second irradiation zone. The second irradiation zone can be located directly in front of the first irradiation zone such that as little time as possible elapses between preheating and melting.

[0010] The method further includes the step of introducing a filler into the first irradiation zone, wherein the filler enters at least partially into the first laser beam before impinging on the workpiece and is thereby at least partially heated. Heating of the filler by the first laser beam can improve the melting behavior of the filler on the workpiece. The filler can be introduced circumferentially around the first laser beam, for example along a semi-circular shape or a partial slot shape.

[0011] According to the present application, the secondary laser energy introduced into the second irradiation zone by the second laser beam is greater than the primary laser energy introduced into the first irradiation zone by the first laser beam. The higher secondary laser energy can be caused by a higher irradiation intensity (W / cm2) of the laser beam. The higher secondary laser energy can also be caused by the wavelength of the laser, which has a higher absorption on the workpiece. This can occur in particular by means of diode laser radiation, which is approximately 800 nm in the case of aluminum and approximately 515 nm or 450 nm in the case of copper. Thus, the thermal energy introduced into the preheating zone exceeds the thermal energy introduced into the process zone. Thus, the present application deviates from the basic principle widely adopted in the current art: for the actual process, i.e., the applied energy for the process is greater than the energy for the accompanying phenomenon i.e., the energy applied for preheating. In this way, the heat input into the filler can be large enough to facilitate melting, but without the risk that hard particles alloy with the substrate, which has been proven to be the cause of embrittlement and cracking of the substrate.

[0012] Accordingly, the present application is based on thermal management, in which less energy is applied to heat and partially melt the filler before the filler impacts the workpiece than is applied to preheat the workpiece. The workpiece is preheated relatively strongly by means of a secondary laser energy that is higher than the primary laser energy, thereby reducing the heat transfer from the heated filler to the workpiece after the application of the filler. The reduced heat transfer from the filler, for example in the form of molten liquid powder, to the workpiece can cause that in neither the first irradiation zone nor the second irradiation zone is a melt pool, in particular a homogeneous melt pool, necessarily required to ensure a defect-free application of the functional layer to the workpiece. In the case of a correspondingly high secondary laser energy, it is also possible that a melt pool can already be generated on the workpiece surface in the second laser beam, i.e., before the powder beam impacts the workpiece. In addition, the reduced primary laser energy can cause that the filler only undergoes a part of the preheating in the process zone. Therefore, the direct energy input to the filler and the hard particles contained therein is relatively small compared to the indirect energy input from the preheated workpiece into the filler. The indirect energy input enables a smooth and uniform production of the connection of the filler with the workpiece and possibly previously applied layers, so that the production is provided with a smaller temperature gradient. This smooth and uniform production reduces the risk that the hard particles form an alloy with the base material and thus contribute to the production of a brittle and / or cracked functional layer.

[0013] As the laser source, a disk laser or a fiber laser can be used for the first laser beam and / or the second laser beam. A diode laser can also be used. In this way, for example, a laser beam with a wavelength 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 corresponding laser beam can be realized such that it can be guided to the processing head by means of an optical fiber. Due to the large available fiber diameter, the laser beam can be satisfactorily coupled, for example, in the case of a diode emitter or a bar emitter or a stack with a limited brightness, into the relatively large annular and core part of a multi-clad fiber, as described in detail below. The laser source can have a laser power between 2 kW and 100 kW. When the workpiece is a brake disc, the laser power can particularly be between 8 kW and 50 kW, and when the workpiece is a sliding bearing, the laser power can particularly be 2 kW. The laser beam can be directed substantially vertically onto the surface of the workpiece to be machined. The powder beam can be inclined relative to the laser beam in order to construct an interaction zone between the powder beam and the laser beam above the workpiece surface. Such an interaction zone enables a more effective application of the powdery material to the workpiece.

[0014] In an embodiment, the second laser beam has an increasing laser power and / or a higher power per unit of W / cm relative to the first laser beam 2The unit of increase in irradiation intensity and / or is cm 2 The cross-sectional area. The secondary laser energy increased relative to the primary laser energy can be achieved geometrically by splitting off a larger area for the second laser beam from the laser output beam. The secondary laser energy can also be achieved by the first laser beam and the second laser beam having different laser sources. The cross-sectional areas of the first laser beam and / or the second laser beam can be adapted by means of adapted focusing lenses. This helps to avoid crack formation and / or adhesion defects by means of optimized heat treatment.

[0015] In an embodiment, the ratio of the secondary laser energy to the primary laser energy is greater than 11:10, in particular greater than 5:4, and further in particular greater than 3:2. It has been shown that in the case of this ratio, there is an optimized characteristic between the sufficient heating of the filler by the first laser beam and subsequent melting and the sufficient thermal energy in the second irradiation zone. This can avoid the alloying of hard particles in the surrounding metallic material.

[0016] In an embodiment, the method further has the step of controlling a workpiece receiving unit on which a workpiece is arranged such that a rotational movement causes the workpiece to move around a rotational axis. The control can be carried out between a central control unit of the laser system and a local control unit of the processing unit. The workpiece receiving unit can clamp the workpiece such that if the workpiece receiving unit itself rotates, the workpiece is fixedly supported in the workpiece receiving unit. The rotational axis can correspond to the axis of rotational symmetry of a rotationally symmetric workpiece. The beam nozzle can be directed to a position on the workpiece that is radially outside the axis of rotational symmetry of the workpiece. Thus, the rotation around the rotational axis causes the powder layer trace to follow a trajectory on the workpiece. The rotational movement of the workpiece receiving unit can be driven by an independent drive.

[0017] The method further has the step of controlling a translation unit such that a translational movement causes the beam nozzle and / or the workpiece receiving unit to move in a direction of displacement that is substantially perpendicular to the rotational axis. The translational movement can be driven by a drive that is separate from the workpiece receiving unit. Alternatively, the translational movement can be driven by the same drive as the rotational movement. The direction of displacement of the translational movement can cause a translation perpendicular to the rotational axis, which can correspondingly affect the trajectory of the powder layer trace. The rotational movement can be very fast compared to the translational movement.

[0018] The rotational movement and the translational movement are superimposed on one another to form a feed movement, such that a powder layer trace having a radial trace width is applied to the workpiece along a helical trajectory. This enables a planar powder coating in the radial direction of the workpiece. The geometry of the helical trajectory is pre-given by the feed movement. The feed movement can influence process parameters, such as the interaction time between the powder beam, the laser beam and the workpiece, in order to enable a firm connection of the powdery particles and the workpiece. The helical trajectory extends along a curve around the axis of rotation, wherein the distance from the axis of rotation increases if applied from the radial inside to the radial outside, or the distance from the axis of rotation decreases if applied from the radial outside to the radial inside. The rotational movement is caused by the rotational speed and the translational movement is caused by the translational speed. When the processing parameter is the feed movement, the variable is caused by a variable of the rotational speed and / or the translational speed.

[0019] The offset of two adjacent helical surfaces of the helical trajectory is less than the trace width, such that the powder layer traces form a radial superposition along the helical trajectory. Thus, when applied from the radial inside to the radial outside, the powder layer trace in the radial inside is arranged below at least the immediately adjacent powder layer trace in the radial outside. In particular, the first single trace of the powder layer trace can be formed into a powder layer by superposition of a plurality of, for example three, four, five or six, further traces of the powder layer trace. Correspondingly, when applied from the radial outside to the radial inside, the powder layer trace in the radial outside is arranged below the immediately adjacent powder layer trace in the radial inside. This radial superposition increases the powder layer thickness, since the at least partially superposed powder layer traces, i.e. the superposed powder layer traces, have a greater powder layer thickness than two powder layer traces whose offset is greater than their radial trace width.

[0020] In an embodiment, the ratio of the trace width to the offset is greater than 2:1, in particular greater than 5:1, or even greater than 15:1. This ensures the corresponding layer thickness of the applied functional layer. By means of the ratio of the trace width to the offset, the process speed of the laser surfacing can also be adapted in addition to the induced layer thickness of the functional layer. The aforementioned ratio enables a reliable and sufficiently thick functional layer in the case of an effective processing time.

[0021] In an embodiment, the radial superposition and the feed movement are such that a second laser beam reheats the powder layer trace already applied before the second laser beam is applied along the helical trajectory, in order to improve its welding properties by means of reprocessing, in particular reheating. Thus, the second irradiation zone, i.e. the preheating zone, caused by the second laser beam can simultaneously implement a reheating zone for adjacent helical surfaces. Therefore, the second irradiation zone is not only beneficial for the application of the individual traces, but also beneficial for the gentle cooling phase of the adjacent helical surfaces, i.e. the cooling phase with a small temperature gradient.

[0022] In an embodiment, the first laser beam and / or the second laser beam has a reduced intensity in a core region of the respective laser beam compared to an edge region of the respective laser beam. The core intensity can be, for example, less than 90% of the edge intensity. Thus, the laser beam has, at least inside the interaction zone, an intensity in the edge region that is higher than the intensity in the core region of the laser beam, such that the powdery filler is loaded by the higher intensity in the edge region when entering the interaction zone. By the inclined orientation of the at least one powder beam relative to the laser beam, the interaction distance (Wechselwirkungsstrecke) with the laser beam changes across the cross-section of the powder beam. By the changed intensity in the core region, a substantially uniform energy supply is provided to the individual powder particles when the interaction distance changes. In other words, the intensity maximum in the edge region of the laser beam results in a more uniform distribution of the energy density of each powder particle and thus, while maintaining a stable welding quality, an expansion of the process window towards higher laser powers. Applicable to the intensity distribution of the laser beam in the focal plane is: I Rand ≥I Zentrum ≥0.

[0023] In an embodiment, the first laser beam and / or the second laser beam has a plateau-shaped intensity distribution. The plateau shape can also be referred to as a top-hat. The plateau-shaped or top-hat-shaped intensity distribution describes a stepwise increase in intensity from the edge of the laser beam to the intensity maximum, which remains substantially over the entire width of the edge region before stepping down again in the direction towards the core region of the laser beam. Compared to a Gaussian-shaped intensity distribution, the plateau-shaped or top-hat-shaped intensity distribution in the edge region of the laser beam is favorable for reducing the roughness of the applied material layer. At at least one location inside the interaction zone, the intensity in the core region of the laser beam can be at most 90%, preferably at most 50%, more preferably at most 10% of the intensity maximum in the edge region of the laser beam. By the following intensity distribution, which has a decreasing intensity in the core region of the laser beam, the process window can be increased with respect to the variability of the laser power used. In particular, by the described intensity distribution in the focal plane, a laser power greater than 4 kW can be used while maintaining the welding quality, since more laser power is used for preheating and / or melting the powder for coating the workpiece. The power in the core region of the laser beam can be, for example, between 7% and 9% of the laser power of the entire laser beam at least at one location inside the interaction zone. The power in the core region can also be between 5% and 7% of the total power of the laser beam, in particular about 6%. According to an alternative variant, the power in the core region can be reduced to a minimum, i.e., in particular 0% of the total laser power.

[0024] In an embodiment, the first laser beam and the second laser beam are generated in a common optical device by beam splitting from a common laser output beam. This simplifies the construction of the laser system and enables a space-saving arrangement. The beam splitting is produced in particular by means of a prism, a cylindrical lens and / or a diffractive optical element (DOE). A faceted optical device or a microlens array can also be used as a beam splitter element. By means of a prism and by means of a DOE and also by means of a faceted optical device or by means of a microlens array, independent partial beams can be generated respectively, and the workpiece surface in the corresponding irradiation area is irradiated by means of the partial beams. By means of a cylindrical lens, an elliptical beam profile of the laser beam can be generated, such that the laser beam irradiates the corresponding irradiation area on the workpiece surface with a continuous light spot. In addition, a displacement unit can be included, by means of which an optical element configured as a prism or a DOE for distributing the laser power to the generated laser beams can be displaced transversely in the beam path of the laser output beam.

[0025] In an embodiment, the first laser beam and the second laser beam can be provided by two separate laser beam sources, in particular by means of two separate laser optics, wherein the second laser beam is supplied to a second irradiation area outside the light channel. Thereby, the provision of the laser beams can take into account the predetermined irradiation energy of the corresponding irradiation areas.

[0026] In an embodiment, a protective gas is supplied in the light channel, by means of which the first irradiation area and / or the second irradiation area is protected from ambient oxygen. The protective gas can surround the first laser beam and / or the second laser beam annularly in order to prevent undesired oxidation in the first irradiation area and / or the second irradiation area.

[0027] In an embodiment, the introduction of a filler into the first irradiation area is achieved by means of a powder injector. The powder injector can enter into a corresponding injector guide in the powder unit of the beam nozzle. The powder injector can achieve high precision during the process-compliant supply of the filler. The separation achieved by the powder focusing and the preheating zone of the second laser beam can be realized particularly effectively by means of the powder injector.

[0028] The present application also relates to a beam nozzle for laser surfacing along a feed direction. The beam nozzle has an optical channel for guiding at least one laser beam that is directed onto a workpiece. The workpiece can be a rotationally symmetric workpiece, such as a brake disc, a hydraulic cylinder, a pressure roller, or a sliding bearing. The optical channel can be a hollow channel that passes through the entire beam nozzle along a longitudinal direction. Through the optical channel, in addition to the laser beam, process gas can also be guided to the workpiece surface. The beam nozzle also has a powder unit, which is particularly arranged radially outside the optical channel, for guiding at least one filler, in particular powder or wire, which is to be applied to the workpiece. The powder unit can start from the longitudinal direction of the beam nozzle and be radially outside the optical channel and can be part of an outer structure that encloses the optical channel in a closed manner. The powder beam can guide a powdery filler that consists of hard particles, in particular carbides, and a base material. The powder unit can be a component of the beam nozzle that is arranged to directly or indirectly guide the powdery filler. The powder unit can have an injector guide into which a powder injector can be inserted. The powder unit can also have an annular gap inside which the powdery filler is guided.

[0029] The beam nozzle is configured and arranged to implement the method according to the present disclosure. The beam nozzle is coupled by means of a control unit that predefines a primary laser energy and a secondary laser energy such that the application of the filler can be achieved by means of an optimized thermal management according to the present disclosure.

[0030] In an embodiment, the beam nozzle is manufactured by means of an additive manufacturing method, in particular by means of powder bed melting. For this purpose, the beam nozzle can consist of copper or a copper alloy, in particular a copper-chromium-zirconium alloy. This applies on the one hand to the additive manufacturing method and on the other hand ensures sufficient strength, thermal conductivity, and heat resistance to meet the process requirements. In powder bed melting, the material to be processed is present in powder form. The laser beam heats the powder along a predefined geometry, whereby the powder liquefies and the material is joined in a material-locking manner. Powder bed melting can be carried out, for example, in the form of selective laser melting ("SLM") or in the form of selective laser sintering ("SLS"). The beam nozzle can consist of a non-ferromagnetic and / or non-ferromagnetizable material.

[0031] The features according to the present disclosure are used individually or in partial combination to overcome the aforementioned deficiencies during laser surfacing. Description of the Drawings

[0032] Preferred embodiments of the present application are explained in detail by the following description of the drawings. Shown herein are:

[0033] Figure 1 A schematic view of the beam nozzle during laser surfacing, having a first irradiation zone and a second irradiation zone;

[0034] Figure 2 Schematic view of a laser optical device for generating a first irradiation area and a second irradiation area;

[0035] Figure 3 Microscopic view of a functional layer applied by a conventional method for laser surfacing and a functional layer applied by a method according to the present disclosure;

[0036] Figure 4 Schematic top view of a brake disc, with a powder layer trace applied thereto along a spiral trajectory;

[0037] Figure 5 Schematic cross-section of a brake disc, with a first powder layer trace (above) or an additional powder layer trace (below) applied thereto;

[0038] Schematic top view of a brake disc in FIG. 6, with a first powder layer trace (left) or an additional powder layer trace (right) applied thereto;

[0039] Figure 7 Stereoscopic view of a beam nozzle seen from above, with a powder injector loaded therein;

[0040] Figure 8 Stereoscopic view of a beam nozzle seen from below; and

[0041] Figure 9 Schematic view of the interaction between a filler and a first laser beam and the lack of interaction between the filler and a second laser beam. Detailed Description

[0042] Preferred embodiments are described below with reference to the accompanying drawings. Herein, the same, similar or functionally identical elements are provided with the same reference numerals in different drawings, and the repeated description of these elements is partially omitted to avoid redundancy.

[0043] Figure 1 A beam nozzle 1 for laser surfacing along a feed direction 2 is shown. The feed direction 2 is the direction along which the beam nozzle 1 moves relative to the workpiece 100. The feed direction can be generated by the movement of the workpiece 100, in particular a rotational movement, by the movement of the beam nozzle 1 or by a superposition of the movements of the workpiece 100 and the beam nozzle 1. The feed direction 2 and the associated feed movement can be constant during the process. Alternatively, the feed direction can change with the corresponding process stage. The workpiece 100 can be a rotationally symmetric workpiece, such as a brake disc, a hydraulic cylinder, a pressure roller or a sliding bearing.

[0044] The beam nozzle 1 has an optical channel 3 for guiding a laser output beam 50, which is composed of a first laser beam 51 and a second laser beam 52. The first laser beam 51 and the second laser beam 52 can be traced back to the same laser source or alternatively to two different laser sources. The optical channel 3 has a side surface 4 inside which the laser output beam 50 is guided. Outside the optical channel 3 radially is an outer structure 5. In the region of the end of the beam nozzle 1 facing the workpiece 100, a nozzle opening 6 forms a powder unit 7. Inside the powder unit 7, a plurality of injector guides 8 can be constructed, and each powder injector 9 can be inserted into the respective injector guide.

[0045] The first laser beam 51 is directed onto the workpiece 100 and forms a first irradiation zone 101. The second laser beam 52 is likewise directed onto the workpiece 100 and generates a second irradiation zone 102. The second irradiation zone 102 is located in front of the first irradiation zone 101 in the feed direction 2. The filler 60 is introduced into the first irradiation zone 101 through the powder unit 7, wherein the filler 60 at least partially enters the first laser beam 51 before impinging on the workpiece 100 and is thereby partially heated. The secondary laser energy introduced by the second laser beam 52 into the second irradiation zone 102 is greater than the primary laser energy introduced by the first laser beam 51 into the first irradiation zone 101.

[0046] Accordingly, a laser output beam 50 composed of a first laser beam 51 and a second laser beam 52 can be emitted from a beam nozzle 1. The first laser beam 51 generates a first irradiation zone 101 on the surface of a workpiece (not shown) when irradiating the workpiece surface, and the second laser beam 52 generates a second irradiation zone 102 in a similar manner. Through the relative movement of the workpiece 100 to be coated and the beam nozzle 1, the laser beams 51, 52 move along a pre-given machining trajectory in the feed direction 2 on the workpiece surface. In addition, a powdery filler 60 is injected into the first laser beam 51 through the beam nozzle 1, such that the powder particles are heated by the first laser beam 51 and impinge on the workpiece surface in the first irradiation zone 101 along the machining trajectory, and the first irradiation zone is also referred to as the process zone. Through the simultaneous heating of the powder particles and the workpiece surface in the process zone 101, a firm connection is generated very rapidly when the powder particles impinge on the workpiece surface. Here, a partial melt pool different from a complete melt pool can be constructed. The partially molten material in the process zone 101 accumulates and solidifies into a trace in the form of a weld bead 61 in subsequent processes. In order to accelerate the coating process and simultaneously minimize the occurrence of adhesion defects, the workpiece surface is preheated in the second irradiation zone 102 by the second laser beam 52 before reaching the process zone 101, and the second irradiation zone is also referred to as the preheating zone. In order to further improve the adhesion of the material accumulation of the filler 60 on the workpiece 100 or the adhesion of the superposed trajectories of the material accumulation to each other, the weld bead 61 can also be heated in a third irradiation zone after the process zone 101, and the third irradiation zone is generated by irradiation with a third laser beam (not shown). The first laser beam 51 and / or the second laser beam 52 can have a reduced core intensity.

[0047] In Figure 2Schematically shows the construction of a laser optical device 110, which can be used in a laser system having a beam nozzle 1. The laser optical device 110 can in particular be arranged in the processing head of the laser system. The laser output beam 50 is aligned to a collimation unit 112, in particular a collimation lens, by means of an optical fiber cable 111, for example having a two-in-one fiber. A beam splitter element 113, in particular in the form of an optical wedge, is arranged in the beam path of the collimated laser output beam 50. The beam splitter element 113 can be moved transversely to the propagation direction of the laser output beam 50 and thus divides the laser output beam 50 into a first laser (partial) beam 51 and a second laser (partial) beam 52 as required by the process. For example, by the transverse positioning of the beam splitter element 113 in the laser output beam 50, the total power of the laser output beam 50 can be targeted to be divided between the laser partial beams 51, 52. The first laser beam 51 can, for example, deliver 30% of the energy of the laser output beam 50, while the second laser beam 52 delivers 70% of the energy of the laser output beam 50. Subsequently, the laser beams 51, 52 are focused onto the surface of the workpiece 100 to be coated by a focusing unit 114, in particular in the form of a focusing lens, and corresponding irradiation areas 101, 102 are respectively generated on the workpiece surface.

[0048] In Figure 3 shows a cross-section of the coating of the workpiece 100 coated by laser surfacing. The workpiece 100 includes a substrate 80 and an intermediate layer 81 applied on the substrate 80. A functional layer 82 is applied on the intermediate layer 81, and the functional layer has powder particles embedded in the base material. The functional layer 82 includes a plurality of powder layer traces superimposed on each other, as further described below. According to Figure 3 the functional layer 82 in the above diagram in Figure 3 shows an adhesion defect 83 between the powder particles and the substrate. In the above diagram, the primary laser energy exceeds the secondary laser energy during laser surfacing. By the coating method proposed here, the formation of adhesion defects should be resisted, as shown in

[0049] Figure 4The workpiece 100 in the form of a brake disc with a hub shell is shown. The brake disc is arranged on a workpiece receiving unit which moves the workpiece 100 along a rotational movement 115. In addition, the workpiece receiving unit and / or the beam nozzle 1 is provided with a translation unit which causes a translational movement 116 of the beam nozzle and / or the workpiece receiving unit. The rotational movement 115 and the translational movement 116 are superimposed to form a feed movement along the feed direction 2. Here, the powder layer traces 62 are applied to the workpiece along a helical trajectory 63. There is an offset 64 between two adjacent helical surfaces of the helical trajectory 63 due to the feed movement. The dimension of the offset 64 is combined with Figure 5 further processing.

[0050] Figure 5 The workpiece 100 is shown. In the upper figure, the first powder layer trace 62 with a trace width 65 has been applied as a single trace. In a further process of laser surfacing, the powder layer traces 62 are applied to the workpiece 100 along the helical trajectory 63. Here, the offset 64 between two adjacent helical surfaces is selected such that the offset is less than the trace width 65, so that the powder layer traces 62 form a radial superposition 66 along the helical trajectory 63. The ratio of the trace width 65 to the offset 64 is 4 to 1 in the present example, so that four partial traces in the lower figure are applied to the single trace in the upper figure. The radial superposition 66 has the following advantages in connection with the division of the primary laser energy and the secondary laser energy according to the present disclosure: The powder layer trace 62 applied first, for example the single trace in the upper figure, is reheated when the superimposed traces are applied. This reheating is beneficial to the solidification behavior of the applied functional layer 82 and results in a higher welding quality. By means of the superposition 66, the previously welded trace is overwelded (überschweiβt) and remelting is facilitated.

[0051] Figure 6a and 6b The workpiece 100 in the form of a brake disc is shown in a top view. In Figure 6a the powder layer trace 62 is still a single trace. The powder layer trace 62 has a trace width 65. In Figure 6b the process of laser surfacing is continued. In addition to Figure 6aThree additional traces are marked outside the single trace in [reference], and the traces are applied to the workpiece 100 along a helical track 63. The offset 64 between two adjacent helical surfaces of the helical track 63 is less than the trace width 65. Accordingly, a radial overlap 66 is formed between adjacent helical surfaces, and the ratio of the trace width 65 to the offset 64 can be greater than 2 to 1, for example 3 to 1 or 4 to 1. Once the entire helical track 63 is applied, the functional layer 82 covers the substrate 80. In the case of a brake disc, the friction surface serves as the substrate 80 and is provided with an HS-LMD coating as the functional layer. This reduces the fine dust load (Feinstaubbelastung) associated with the braking process.

[0052] Figure 7 and 8 Shows an embodiment of a beam nozzle 1 for laser surfacing along the feed direction 2. The laser output beam 50 exits from an optical channel 3 having a side surface 4. In addition, the optical channel 3 can be adapted to guide a process protection gas in a radially outer section for protecting the process zone and for avoiding oxidation. The optical channel 3 is surrounded by an outer structure 5 which has a nozzle orifice 6 which in turn includes a powder unit 7. The powder unit 7 can have, for example, a plurality of injector guides 8, and each powder injector 9 can be inserted into the respective injector guide. Instead of the individual injector guides 8, the powder unit 7 can have a powder annulus channel (not shown). The filler 60 is aligned onto the workpiece 100 by the powder unit 7 and the powder injectors 9 arranged therein, for example. The laser output beam 50 heats the workpiece 100 such that a molten pool is at least partially formed on the workpiece surface. Here, the division between the primary laser energy and the secondary laser energy according to the present disclosure helps to avoid deficiencies in the functional layer 82. Here, the first laser beam 51 heats the filler 60. Once the molten pool cools, a welded functional layer 82, such as a welded wear protection layer, is formed from hard particles and a base material. The welded functional layer 82 makes the workpiece surface more resistant and increases its load-carrying capacity.

[0053] A flange section with a coupling ring 10 can be joined to the beam nozzle 1, and the coupling ring fixes the beam nozzle 1 to the joined unit, such as a laser optic 110 or a process adapter. The powder injector 9 is inserted into the injector guide 8 of the powder unit 7. The filler 60 is conveyed by means of the powder injector 9 and applied to the workpiece 100 through an especially adjustable focus. Each of the powder injectors 9 can apply different powder foci. Alternatively, the powder injectors 9 can be directed to the same focal point. The powder injectors 9 are arranged in the powder section 11 in the injector guides 8 provided therefor in the powder unit 7. The feed section 12 without a powder unit joins the powder section 11 in the circumferential direction, and there are no powder injectors 9 in the feed section. In addition, an inlet sleeve 13 is inserted into the coolant inlet and an outlet sleeve 14 is inserted into the coolant outlet. These sleeves connect the coolant inlet and the coolant outlet of the beam nozzle to the coolant circuit of the laser system. The nozzle opening 6 has an arched funnel shape. An injector guide 8 is formed inside each of the arches, and the powder injector 9 can be inserted into the injector guide. In the feed direction 2, the optical channel 3 extends non-circularly, so as to guide the first laser beam 51 and the second laser beam 52 according to the present disclosure and contribute to the advantages according to the present disclosure.

[0054] Figure 9 The beam nozzle 1 is shown from which the first laser beam 51 and the second laser beam 52 emerge. Each one powder beam emerges from the injector guide 8 respectively, and the powder beam interacts with the first laser beam 51. According to the present disclosure, the second laser beam 52 is used to preheat the workpiece surface. The second laser beam 52 is arranged in front of the first laser beam 51 in the feed direction 2. In order to avoid interaction between the powder beam and the second laser beam 52, a feed section 12 without a powder unit is provided in the region of the nozzle opening 6, and no filler 60 is conveyed to the workpiece surface in this feed section. The cross-section of the optical channel 3 extending orthogonally to the longitudinal direction of the beam nozzle 1 extends non-circularly in the feed direction 2. The extension is conducive to the first irradiation area 101 being configured as a process area and the second irradiation area 102 being configured as a preheating area. In other words, the following cross-section is orthogonal to the longitudinal direction of the beam nozzle 1, and a part of the cross-section is in the shape of the optical channel 3. The cross-section can extend in the feed direction 2 and can be axisymmetric along the feed direction 2 and symmetric about the center point of the cross-section of the optical channel 3. The minimum cross-section of the optical channel is predefined by the size of the laser beam, especially the diameter. Relative to the minimum size, the cross-section extends along the feed direction.

[0055] As long as applicable, all the individual features shown in the embodiments can be combined with each other and / or replaced without departing from the scope of this application.

[0056] List of reference numerals

[0057] 1 Beam nozzle

[0058] 2 Feed direction

[0059] 3 Light channel

[0060] 4 Side

[0061] 5 Outer structure

[0062] 6 Nozzle opening

[0063] 7 Powder unit

[0064] 8 Injector guide

[0065] 9 Powder injector

[0066] 10 Coupling ring

[0067] 11 Powder section

[0068] 12 Feed section

[0069] 13 Inlet sleeve

[0070] 14 Outlet sleeve

[0071] 50 Laser output beam

[0072] 51 First laser beam

[0073] 52 Second laser beam

[0074] 60 Filler

[0075] 61 Weld bead

[0076] 62 Powder layer trace

[0077] 63 Helical trajectory

[0078] 64 Offset

[0079] 65 Trace width

[0080] 66 Radial superposition part

[0081] 80 Substrate

[0082] 81 Intermediate layer

[0083] 82 Functional layer

[0084] 83 Adhesion defect

[0085] 100 Workpiece

[0086] 101 First irradiation area

[0087] 102 Second irradiation area

[0088] 110 Laser optical device

[0089] 111 Optical fiber cable

[0090] 112 Collimation unit

[0091] 113 Beam splitter element

[0092] 114 Focusing unit

[0093] 115 Rotational motion

[0094] 116 Translational motion

Claims

1. A method for laser deposition welding in a feed direction (2) by means of a jet nozzle (1), the jet nozzle having a light channel (3) for guiding at least one laser beam (51, 52) directed onto a workpiece (100), and the jet nozzle having a powder unit (7) arranged in particular outside the light channel (3) for guiding at least one filler material (60), in particular a powder, to be applied to the workpiece (100), the method comprising the following steps: - directing a first laser beam (51) onto the workpiece (100) for producing a first irradiation zone (101), and directing a second laser beam (52) onto the workpiece (100) for producing a second irradiation zone (102), wherein the second irradiation zone (102) is located in front of the first irradiation zone (101) in the feed direction (2); and - introducing the filler material (60) into the first irradiation zone (101), wherein the filler material (60) at least partially enters the first laser beam (51) before impinging on the workpiece (100) and is thereby at least partially heated; The secondary laser energy introduced into the second irradiation zone (102) by the second laser beam (52) is greater than the primary laser energy introduced into the first irradiation zone (101) by the first laser beam (51).

2. The method according to claim 1, wherein: The second laser beam (52) has an increased laser power and / or a higher irradiation intensity and / or an increased cross-sectional area relative to the first laser beam (51).

3. A method according to any one of the preceding claims, wherein: The ratio of the secondary laser energy to the primary laser energy is greater than 11:10, in particular greater than 5:4, and further in particular greater than 3:

2.

4. The method according to any one of the preceding claims, further comprising the following steps: - manipulating a workpiece receiving unit on which the workpiece (100) is arranged so that a rotational movement (115) moves the workpiece (100) about an axis of rotation; and - controlling the translation unit so that the translation movement (116) moves the jet nozzle (1) and / or the workpiece receiving unit in a deflection direction substantially perpendicular to the axis of rotation; in, The rotational motion (115) and the translational motion (116) are superimposed into a feeding motion, so that a powder layer trace (62) having a radial trace width (65) is applied to the workpiece (100) along a spiral trajectory (63); The offset (64) of two adjacent spiral surfaces of the spiral track (63) is smaller than the trace width (65), so that the powder layer trace (62) forms a radial overlapping portion (66) along the spiral track (63).

5. The method according to claim 4, wherein: The ratio of the track width (65) to the deflection (64) is greater than 2:1, in particular greater than 4:1 or 15:

1.

6. The method according to any one of claims 4 or 5, wherein: The radial overlap (66) and the feed movement are configured such that the second laser beam (52) reheats previously applied powder layer traces when applied along the spiral path (63) in order to improve the welding properties by means of post-processing.

7. A method according to any one of the preceding claims, wherein: The first laser beam (51) and / or the second laser beam (52) has a reduced intensity in a core region relative to an edge region.

8. The method according to any one of claims 1 to 6, wherein: The first laser beam (51) and / or the second laser beam (52) has a plateau-shaped intensity distribution.

9. A method according to any one of the preceding claims, wherein: The first laser beam (51) and the second laser beam (52) are generated by beam splitting from the same laser output beam (50) in the same optical component, wherein the beam splitting is produced in particular by means of a wedge, a cylindrical lens and / or a diffractive optical element (DOE).

10. The method according to any one of claims 1 to 8, wherein: The first laser beam (51) and the second laser beam (52) are provided by two separate laser beam sources, in particular by means of two separate laser optics, wherein the second laser beam (52) is supplied to the second irradiation zone (102) outside the light channel (3).

11. A method according to any one of the preceding claims, wherein: A protective gas is guided in the light channel (3), by means of which the first irradiation zone (101) and / or the second irradiation zone (102) are protected from the influence of ambient oxygen.

12. A method according to any one of the preceding claims, wherein: The filler material (60) is introduced into the first irradiation zone (101) by means of a powder injector.

13. A jet nozzle (1) for laser cladding in a feed direction (2), the jet nozzle having - an optical channel (3) for guiding at least one laser beam (50, 51) directed onto a workpiece (100); and a powder unit (7) arranged outside the light channel (3) for guiding at least one filler (60), in particular a powder, which is to be applied to the workpiece (100); in, The jet nozzle (1) is configured and arranged to carry out a method according to one of the preceding claims.

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