Method and device for laser cladding with a primary and a secondary laser energy

Abstract

The present invention relates to a method for laser cladding along a feed direction (2) by means of a jet nozzle (1) comprising a light channel (3) for conducting at least one laser beam (51, 52), which is directed at a workpiece (100), and comprising a powder unit (7) which is located radially outside the light channel (3) and which is provided for carrying at least one filler material (60), in particular powder, which is to be applied to the workpiece (100), the method comprising the steps of: directing a first laser beam (51) at the workpiece (100) in order to produce a first irradiation zone (101) and directing a second laser beam (52) at the workpiece (100) in order to produce a second irradiation zone (102), the second irradiation zone (102) being located upstream of the first irradiation zone (101) in the feed direction (2); and introducing the filler material (60) into the first irradiation zone (101), the filler material (60) at least partially entering the first laser beam (51) before hitting the workpiece (100), and being at least partially heated as a result; wherein a secondary laser energy which the second laser beam (52) introduces into the second irradiation zone (102) is greater than a primary laser energy which the first laser beam (51) introduces into the first irradiation zone (101). The invention also relates to a jet nozzle.

Description

[0001] Method and device for laser cladding with a primary and a secondary laser energy

[0002] Technical area

[0003] The present invention relates to a method for laser cladding along a feed direction and a jet nozzle for laser cladding.

[0004] State of the art

[0005] Laser cladding is used in repair, coating, and / or 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 published patent applications DE 10 2011 100 456 A and DE 10 2018 130 798 A1. Furthermore, published patent application DE 10 2022 100 173 A1 discloses a method for additive manufacturing in which a first laser beam from a nozzle unit and a second laser beam from a separate head are directed onto a workpiece in order to additively apply a powdered build material.

[0006] A functional layer can be applied to a workpiece using laser cladding. This generally increases the load-bearing capacity of the workpiece processed using laser cladding compared to an unmachined workpiece. The functional layer can serve, for example, as a wear-resistant layer. The application of the functional layer can be based on a diffusion process, partial melting and / or melting of a workpiece surface, the application of a filler material, and subsequent cooling, so that a matrix structure with hard material particles is firmly bonded to the material surface. Laser cladding influences and changes the internal material structure of the workpiece and the material being applied. This can, under certain circumstances, result in deficiencies in the internal material structure, for example, cracks and / or lack of fusion.It is also possible that the hard material particles form an alloy with the matrix material, leading to embrittlement of the matrix structure and thus of the applied functional layer. These deficiencies can therefore impair the desired increase in load-bearing capacity. They are generally microscopic in nature, which is why they and their underlying cause are difficult to identify.

[0007] Description of the invention

[0008] Based on the known prior art, it is an object of the present invention to provide an improved method and an improved beam nozzle for laser material deposition along a feed direction. The invention aims in particular at applying the filler material to the workpiece in such a way that the imperfections in the internal material structure are reduced or even avoided and the welding quality of the applied functional layer and the workpiece as a whole is increased. The imperfections can be lack of bonding between the material surface and the applied functional layer or between individual applied functional layers. The imperfections can also be pores, i.e. air inclusions, that occur within the applied functional layer or between the applied functional layer and the material surface.Pores may occur more frequently, particularly if the material surface is a cast material. Deficiencies may also include cracks, particularly those running vertically to the material surface within the applied functional layer. Deficiencies may also arise from powder particles, particularly carbides, of the powdered filler material dissolving in a matrix material of the powdered filler material, thus forming an alloy, which leads to embrittlement of the matrix material. The invention further aims, in particular, to provide a reliable blasting nozzle that enables process-compliant application of the functional layer. The invention may further aim to design the blasting nozzle in such a way that it ensures reliable and precise laser cladding over very high cycle counts.

[0009] The object is achieved by a method and a jet nozzle having the features of the independent claims. Advantageous further developments emerge from the subclaims, the description, and the figures. Accordingly, a method for laser material deposition along a feed direction using a jet nozzle is proposed. Laser material deposition can be a method for high-speed laser material deposition (HS-LMD). The feed direction is the direction along which the jet nozzle moves relative to a workpiece. It can result from a movement, in particular a rotational movement, of the workpiece, from a movement of the jet nozzle, or from a superposition of both movements. The workpiece can be a rotationally symmetrical workpiece, such as a brake disc, a hydraulic cylinder, a printing roller, or a plain bearing.The jet nozzle has a light channel for guiding at least one laser beam directed at a workpiece. The light channel can be a hollow channel that runs through the entire jet nozzle along a longitudinal direction. In addition to the laser beam, a process gas can also be guided to the workpiece surface through the light channel. The jet nozzle further has a powder unit, arranged in particular radially outside the light channel, for guiding at least one filler material, in particular a powder or alternatively a wire, wherein the filler material is to be applied to the workpiece. The powder unit can be located radially outside the light channel, starting from the longitudinal direction of the jet nozzle, and can be part of an external structure that surrounds the light channel. The powder jet can guide a powdery filler material consisting of hard material particles, in particular carbides, and a matrix material.The powder unit can be the part of the blasting nozzle intended to guide the powdered filler material directly or indirectly. The powder unit can have injector guides into which powder injectors can be inserted. It can also have an annular gap within which the powdered filler material is guided.

[0010] The method includes the step of directing a first laser beam onto the workpiece to create a first irradiation zone. The first laser beam can be used to heat and, in particular, at least partially melt the filler material and the workpiece. The thermal energy conveyed by the first laser beam, hence the primary laser energy, can thus be used to melt the filler material and the workpiece in the manner desired for laser cladding. The first irradiation zone can therefore be referred to as the process zone, because this is where the intended process of applying the functional layer to the workpiece takes place.

[0011] The method further includes the step of directing a second laser beam onto the workpiece to create a second irradiation zone. The second laser beam can be used to preheat the workpiece. The thermal energy transported by the second laser beam, hence the secondary laser energy, can thus be used to preheat the workpiece or the base to be coated prior to melting. The second irradiation zone can therefore be referred to as a preheating zone because the base to be coated is preheated here. The second laser beam can be directed such that it interacts only negligibly or not at all with the filler material before it impacts the workpiece.

[0012] The second irradiation zone is located upstream of the first irradiation zone in the feed direction, so that the first irradiation zone follows the second irradiation zone. The second irradiation zone can be located directly upstream of the first irradiation zone, so that the time between preheating and melting is as short as possible.

[0013] The method further includes the step of introducing the filler material into the first irradiation zone, wherein the filler material at least partially enters the first laser beam before impinging on the workpiece and is thereby at least partially heated. Heating the filler material by the first laser beam can improve the melting behavior of the filler material onto the workpiece. The filler material can be introduced circumferentially around the first laser beam, for example, along a partial circle or a partially elongated hole.

[0014] According to the invention, a secondary laser energy that the second laser beam introduces into the second irradiation zone is greater than a primary laser energy that the first laser beam introduces into the first irradiation zone. The higher secondary laser energy can be obtained from a higher irradiance of the laser beam (in W / cm 2). It can also be caused by a laser wavelength that has a higher absorption on the workpiece. This can happen in particular using diode laser radiation, which is around 800 nm for aluminum and around 515 nm or 450 nm for copper. The thermal energy introduced into the preheating zone therefore exceeds the thermal energy introduced into the process zone. The invention thus deviates from the principle widespread in the field that more energy is to be expended for the actual process, namely the deposition, than for an accompanying phenomenon, namely preheating. In this way, the thermal input into the filler material can be large enough to promote melting, but without running the risk of hard material particles forming an alloy with the matrix, which has been identified as the cause of a brittle, cracked matrix.

[0015] The invention is therefore based on a heat management system in which less energy is applied to heat and partially melt the filler material before it impacts the workpiece than for preheating the workpiece. By preheating the workpiece to a relatively high degree using higher secondary laser energy than primary laser energy, heat transfer from the heated filler material to the workpiece after its application is reduced. The reduced heat transfer from the filler material, for example in the form of molten powder, to the workpiece can mean that neither in the first irradiation zone nor in the second irradiation zone is a melt pool, in particular a homogeneous melt pool, absolutely necessary to ensure that the functional layer is applied to the workpiece without any deficiencies.With correspondingly high secondary laser energies, it is also possible that a melt pool can form on the workpiece surface as early as the second laser beam, i.e., before the powder jet hits the workpiece. Furthermore, the reduced primary laser energy can result in the filler material in the process zone only being partially preheated. The direct energy input to the filler material and the hard material particles it contains is thus relatively low compared to the indirect heat input from the preheated workpiece into the filler material. The indirect heat input enables a gentle, uniform bond between the filler material and the workpiece, and possibly a previously applied layer, with a lower temperature gradient.This gentle and uniform manufacturing reduces the risk of hard material particles forming an alloy with the matrix material and thus contributing to a brittle and / or cracked functional layer.

[0016] The first laser beam and / or the second laser beam can use a disk laser or a fiber laser as the laser source. A diode laser can also be used. 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 respective laser beam can be designed such that it can be guided to a processing head via an optical fiber. Due to large usable fiber diameters, the laser beam can be satisfactorily coupled into a comparatively large ring and core portion of a multi-clad fiber, as described in more detail below, for example, when the brilliance of the diode emitters, bars, or stacks is limited. The laser source can have a laser power of between 2 kW and 100 kW.If the workpiece is a brake disc, the laser power can be between 8 kW and 50 kW, and if it is a plain bearing, the laser power can be 2 kW. The laser beam can be directed essentially orthogonally onto a surface of the workpiece to be machined. The powder jet can be inclined with respect 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 the powdered material to be applied to the workpiece more efficiently. In one embodiment, the second laser beam has a higher laser power and / or a higher irradiation intensity in W / cm compared to the first laser beam. 2 and / or an increased cross-sectional area in the unit cm 2The increased secondary laser energy compared to the primary laser energy can be geometrically achieved by carving out a larger area from the laser output beam for the second laser beam. It can also be achieved by using different laser sources for the first and second laser beams. Using an adapted focusing lens, the cross-sectional area of ​​the first and / or second laser beams can be adjusted. This helps prevent cracking and / or bonding defects through optimized thermal treatment.

[0017] In one embodiment, the ratio of secondary laser energy to primary laser energy is greater than 11:10, in particular 5:4, and more particularly 3:2. It has been found that these ratios provide an optimal balance between sufficient heating of the filler material and subsequent melting by the first laser beam, and sufficient thermal energy in the second irradiation zone. This prevents alloying of hard material particles into the surrounding metallic material.

[0018] In one embodiment, 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 a central control unit of the laser system and a local control unit of a processing 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.

[0019] 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 rotational axis. 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. An offset direction of the translational movement can cause a translation orthogonal to the rotational axis, which can accordingly affect a trajectory of a powder layer track. The rotational movement can be very high compared to the translational movement.

[0020] The rotational movement and the translational movement overlap to form a feed movement such that a powder layer track with a radial track width is applied to the workpiece along a spiral trajectory. This enables surface powder coating 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 rotation axis, with the distance from the rotation axis increasing if the material is applied from radially inward to radially outward, or decreasing if the material is applied from radially outward to radially inward.The rotational movement results from a rotational speed, while the translational movement results from 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.

[0021] An offset between two adjacent spiral flanks of the spiral trajectory is smaller than the track width, so 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 at least the nearest radially outer powder layer track. In particular, a first individual track of the powder layer track can be superimposed by several, for example three, four, five or six further tracks of the powder layer track to form a powder layer. Accordingly, 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, i.e. overlapping powder layer tracks, have a higher powder layer thickness than two powder layer tracks whose offset is greater than their radial track width.

[0022] In one embodiment, the ratio of track width to offset is greater than 2:1, particularly 5:1 or even 15:1. This ensures an appropriate layer thickness of the applied functional layer. The ratio of track width to offset allows adjustment not only of the resulting layer thickness of the functional layer, but also of the process speed of the laser deposition welding. The above ratios enable a reliable, sufficiently thick functional layer with efficient processing times.

[0023] In one embodiment, the radial overlap and the feed movement are such that the second laser beam, during deposition along the spiral trajectory, reheats a previously applied powder layer track in order to promote its welding behavior through post-processing, in particular reheating. The second irradiation zone created by the second laser beam, i.e. the preheating zone, can thus simultaneously create a reheating zone for an adjacent spiral flank. The second irradiation zone thus not only promotes the deposition of a single track, but also contributes to a gentle cooling phase, i.e. a cooling phase with a low temperature gradient, of the adjacent spiral flank.

[0024] In one 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, 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 an intensity in the core region of the laser beam, so that the powdered filler material is exposed to the higher intensity of the edge region upon entering the interaction zone. By aligning the at least one powder beam at an angle to the laser beam, the interaction path with the laser beam varies across the cross-section of the powder beam. Due to the reduced intensity in the core region, the individual powder particles are supplied with essentially homogeneous energy while the interaction path varies.In other words, an intensity maximum at the edge of the laser beam leads to a more uniform distribution of fluence per powder particle, thus expanding the process window toward higher laser powers while maintaining stable weld quality. The following applies to the intensity distribution of the laser beam in the focal plane: iedge — Icenter > 0.

[0025] In one 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 shape. The plateau- or top-hat-shaped intensity distribution describes a sudden increase in intensity at the edge of the laser beam to the intensity maximum, which is maintained essentially across the entire width of the edge region before the intensity suddenly drops again towards the core region of the laser beam. The plateau- or top-hat-shaped intensity distribution in the edge region of the laser beam promotes a reduction in the roughness of the applied material layer compared to a Gaussian-shaped intensity distribution.At at least one point within the interaction zone, the intensity in the core region of the laser beam can be at most 90%, preferably at most 50%, even more preferably at most 10%, of the intensity maximum in the edge region of the laser beam. The intensity distribution with reduced intensity in the core region of the laser beam can increase the process window with regard to the variability of the laser power used. In particular, with the described intensity distribution in the focal plane, laser powers > 4 kW can be used while simultaneously maintaining the weld quality because more laser power is used to preheat and / or melt the powder for coating the workpiece. The power in the core region of the laser beam can, at least at one point within the interaction zone, be, for example, between 7% and 9% of the laser power of the entire laser beam.In the core region, it can also be between 5% and 7%, in particular approximately 6% of the total laser beam power. According to an alternative variant, the power in the core region can be reduced to a minimum, in particular to 0% of the total laser power.

[0026] In one embodiment, the first laser beam and the second laser beam are generated by beam splitting from a common laser output beam in a common optical system. This simplifies the construction of the laser system and enables a space-saving arrangement. The beam splitting is achieved in particular by means of an optical wedge, a cylindrical lens and / or a diffractive optical element (DOE). A facet optic or a microlens array can also be used as a beam splitter element. By means of the optical wedge and the DOE, as well as by means of a facet optic or a microlens array, separate partial beams can be generated, by means of which the workpiece surface is exposed to the respective irradiation zone.The cylindrical lens can be used to generate an elliptical beam profile of the laser beam, so that the laser beam irradiates the respective irradiation zones on the workpiece surface with a continuous beam spot. Furthermore, a displacement unit can be included, by means of which the optical element, designed as an optical wedge or DOE, can be displaced laterally in the beam path of the laser output beam to distribute the laser power to the resulting laser beams.

[0027] In one embodiment, the first laser beam and the second laser beam can be provided from two separate laser beam sources, in particular by means of two separate laser optics, with the second laser beam being supplied to the second irradiation zone outside the light channel. Thus, the provision of the laser beam itself can take into account the intended irradiation energy of the respective irradiation zone.

[0028] In one embodiment, a protective gas is supplied into the light channel, by means of which the first irradiation zone and / or the second irradiation zone are shielded from ambient oxygen. The protective gas can surround the first laser beam and / or the second laser beam in a ring shape to prevent unwanted oxidation in the first irradiation zone and / or the second irradiation zone.

[0029] In one embodiment, the filler material is introduced into the first irradiation zone using powder injectors. The powder injectors can be embedded in corresponding injector guides in the powder unit of the blasting nozzle. The powder injectors enable high precision in the process-oriented supply of the filler material. The desired separation of the powder focus and the preheating zone by the second laser beam can be achieved particularly efficiently with the powder injectors.

[0030] The disclosure further relates to a jet nozzle for laser material deposition along the feed direction. The jet nozzle has a light channel for guiding at least one laser beam directed onto a workpiece. The workpiece can be a rotationally symmetrical workpiece, such as a brake disc, a hydraulic cylinder, a printing roller, or a plain bearing. The light channel can be a hollow channel that runs through the entire jet nozzle along a longitudinal direction. In addition to the laser beam, a process gas can also be guided to the workpiece surface through the light channel. The jet nozzle further has a powder unit, arranged in particular radially outside the light channel, for guiding at least one filler material, in particular a powder or a wire, to be applied to the workpiece.The powder unit can be located radially outside the light channel, starting from the longitudinal direction of the jet nozzle, and can be part of an external structure that encloses the light channel. The powder jet can guide a powdered filler material consisting of hard material particles, in particular carbides, and a matrix material. The powder unit can be the part of the jet nozzle intended to guide the powdered filler material directly or indirectly. The powder unit can have injector guides into which powder injectors can be inserted. It can also have an annular gap within which the powdered filler material is guided.

[0031] The jet nozzle is configured and intended to carry out the method according to the disclosure. It can be coupled to a control unit that specifies the primary laser energy and the secondary laser energy in such a way that the application of filler material with the heat management optimized according to the disclosure is enabled.

[0032] In one embodiment, the jet nozzle is manufactured using an additive manufacturing process, in particular powder bed melting. For this purpose, the jet nozzle can be made of copper or a copper alloy, in particular a copper-chromium-zirconium alloy. This is suitable for additive manufacturing processes on the one hand and ensures sufficient strength, thermal conductivity, and heat resistance to withstand the process requirements on the other. In powder bed melting, the material to be processed is in powder form. A laser beam heats the powder along the intended geometry, liquefying the powder and bonding it together. Powder bed melting can be implemented, for example, as selective laser melting ("SLM") or selective laser sintering ("SLS"). The jet nozzle can be made of a non-ferromagnetic and / or non-ferromagnetizable material.

[0033] The features disclosed contribute, partly individually and partly in combination, to overcoming the deficiencies in laser cladding mentioned at the outset.

[0034] Short description of the characters

[0035] Preferred further embodiments of the invention are explained in more detail in the following description of the figures. In the figures:

[0036] Figure 1 is a schematic view of a jet nozzle in a laser cladding process with a first irradiation zone and a second irradiation zone;

[0037] Figure 2 is a schematic view of a laser optics for generating the first irradiation zone and the second irradiation zone;

[0038] Figure 3 is a microscopic view of a functional layer applied by conventional laser deposition welding methods and a functional layer applied by the method according to the disclosure;

[0039] Figure 4 shows a schematic plan view of a brake disc onto which a powder layer track was applied along a spiral trajectory; Figure 5 shows a schematic cross-section through a brake disc onto which a first powder layer track (top) and further powder layer tracks (bottom) were applied;

[0040] Figure 6 is a schematic plan view of a brake disc onto which a first powder layer trace (left) and further powder layer traces (right) have been applied;

[0041] Figure 7 is a perspective view of a blasting nozzle from above into which powder injectors are inserted;

[0042] Figure 8 is a perspective view of a jet nozzle from below; and

[0043] Figure 9 is a schematic view of an interaction between a filler material and a first laser beam and a lack of interaction between the filler material and a second laser beam.

[0044] Detailed description of preferred embodiments

[0045] 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.

[0046] Figure 1 shows a jet nozzle 1 for laser material deposition along a feed direction 2. The feed direction 2 is the direction along which the jet nozzle 1 moves relative to a workpiece 100. It can result from a movement, in particular a rotational movement, of the workpiece 100, from a movement of the jet nozzle 1, or from a superposition of a movement of the workpiece 100 and the jet nozzle 1. The feed direction 2 and the correlating feed movement can be constant throughout the process. Alternatively, they can vary depending on the respective process stage. The workpiece 100 can be a rotationally symmetrical workpiece, such as a brake disc, a hydraulic cylinder, a printing roller, or a plain bearing.

[0047] The jet nozzle 1 has a light 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 derived from the same laser source or, alternatively, from two different laser sources. The light channel 3 has a lateral surface 4, within which the laser output beam 50 is guided. An external structure 5 is located radially outside the light channel 3. In the region of an end of the jet nozzle 1 facing a workpiece 100, a nozzle mouth 6 forms a powder unit 7. Injector guides 8 can be formed within each of which a powder injector 9 can be inserted.

[0048] The first laser beam 51 is directed onto the workpiece 100 and forms a first irradiation zone 101. The second laser beam 52 is also directed onto the workpiece 100 and creates a second irradiation zone 102. The second irradiation zone 102 lies upstream of the first irradiation zone 101 in the feed direction 2. A filler material 60 is introduced into the first irradiation zone 101 by the powder unit 7, wherein the filler material 60 at least partially enters the first laser beam 51 before striking the workpiece 100 and is thereby partially heated. A secondary laser energy that the second laser beam 52 introduces into the second irradiation zone 102 is greater than a primary laser energy that the first laser beam 51 introduces into the first irradiation zone 101.

[0049] The laser output beam 50, which is composed of the first laser beam 51 and the second laser beam 52, can therefore emerge from the beam nozzle 1. When irradiating a workpiece surface (not shown), the first laser beam 51 creates the first irradiation zone 101 on the workpiece surface, and the second laser beam 52 creates the second irradiation zone 102 in a similar manner. By a relative movement of the workpiece 100 to be coated and the beam nozzle 1, the laser beams 51, 52 are moved in the feed direction 2 along a predetermined processing path over the workpiece surface. Furthermore, the powdered filler material 60 is irradiated into the first laser beam 51 via the beam nozzle 1, so that powder particles are heated by the first laser beam 51 and impinge on the workpiece surface along the processing path in the first irradiation zone 101, which is also called the process zone.Due to the simultaneous heating of the powder particles and the workpiece surface in the process zone 101, a solid bond is formed very quickly when the powder particles hit the workpiece surface. In this case, a partial melt pool can be formed instead of a full melt pool. The partially molten material deposit in the process zone 101 solidifies in the aftermath to form a track in the form of a weld bead 61. In order to accelerate the coating process and at the same time minimize the occurrence of bonding errors, the workpiece surface is preheated in the run-up to the process zone 101 by the second laser beam 52 in the second irradiation zone 102, which is also called the preheating zone. To further improve the bond of the material deposit of the filler material 60 to the workpiece 100 orTo join overlapping material deposit paths, the weld bead 61 can be further heated in a third irradiation zone following the process zone 101, which 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.

[0050] Figure 2 schematically shows the structure of a laser optics unit 110 that can be used in a laser system with the beam nozzle 1. The laser optics unit 110 can, in particular, be arranged in a processing head of the laser system. The laser output beam 50 is collimated onto a collimation unit 112, in particular a collimation lens, via a fiber optic cable 111, for example with a 2-in-1 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 displaceable transversely to the propagation direction of the laser output beam 50 and can thus split the laser output beam 50 into the first laser (partial) beam 51 and the second laser (partial) beam 52 in a process-appropriate manner.For example, by laterally positioning the beam splitter element 113 in the laser output beam 50, the total power of the laser output beam 50 can be specifically divided between the partial laser beams 51, 52. For example, the first laser beam 51 can carry 30% of the energy of the laser output beam 50, while the second laser beam 52 can carry 70% of the energy of the laser output beam 50. The laser beams 51, 52 are then focused onto the surface of the workpiece 100 to be coated via a focusing unit 114, in particular a focusing lens, and in doing so each generates a corresponding irradiation zone 101, 102 on the workpiece surface.

[0051] Figure 3 shows a cross-section of the coating of a workpiece 100 coated by laser deposition welding. The workpiece 100 comprises a base body 80 and an intermediate layer 81 applied to the base body 80. A functional layer 82, which has powder particles embedded in a matrix material, is applied to the intermediate layer 81. The functional layer 82 comprises several overlapping powder layer tracks, as described further below. The functional layer 82 according to the upper illustration in Figure 3 shows bonding defects 83 between the powder particles and the matrix. In the upper illustration, the primary laser energy exceeded the secondary laser energy during laser deposition welding.The coating method proposed here is intended to counteract the formation of bonding defects, as shown in the lower illustration in Figure 3, in which the secondary laser energy exceeded the primary laser energy during laser deposition welding. Figure 4 shows the workpiece 100 in the form of a brake disc with a hub cup. The brake disc is provided on a workpiece holding unit that moves the workpiece 100 along a rotational movement 115. Furthermore, the workpiece holding unit and / or the jet nozzle 1 is provided with a translation unit that causes a translational movement 116 of the jet nozzle and / or the workpiece holding unit. The rotational movement 115 and the translational movement 116 overlap to form a feed movement along the feed direction 2. In this process, a powder layer track 62 is applied to the workpiece along a spiral trajectory 63.Due to the feed motion, an offset 64 exists between two adjacent spiral flanks of the spiral trajectory 63. The dimension of the offset 64 will be discussed further in connection with Figure 5.

[0052] Figure 5 shows the workpiece 100. In the upper image, a first powder layer track 62 with a track width 65 was applied as a single track. As the laser deposition process continues, the powder layer track 62 is applied to the workpiece 100 along the spiral trajectory 63. The offset 64 between two adjacent spiral flanks is selected such that it is smaller than the track width 65, so that the powder layer track 62 forms a radial overlap 66 along the spiral trajectory 63. The ratio of the track width 65 to the offset 64 in the present example is 4 to 1, so that four partial tracks are applied to the single track from the upper image in the lower image. The radial overlap 66, in combination with the division of the primary laser energy and the secondary laser energy according to the disclosure, has the advantage that a previously applied powder layer track 62, for example the single track from the upper image, is reheated when the overlapping track is applied.This postheating promotes the solidification of the applied functional layer 82 and results in higher weld quality. The overlap 66 welds over a previously welded track and favorably remelts it.

[0053] Figures 6a and 6b show the workpiece 100 in the form of a brake disc in a top view. In Figure 6a, the powder layer track 62 is still a single track. The powder layer track 62 has a track width of 65. In Figure 6b, the laser deposition welding process is further advanced. In addition to the single track from Figure 6a, three further tracks are indicated which were applied to the workpiece 100 along the spiral trajectory 63. The offset 64 between two adjacent spiral flanks of the spiral trajectory 63 is less than the track width 65. Accordingly, the radial overlap 66 forms between adjacent spiral flanks. The ratio of the track width 65 to the offset 64 can be greater than 2 to 1, for example 3 to 1 or 4 to 1. As soon as the entire spiral trajectory 63 has been applied, the functional layer 82 covers the base body 80. In the case of the brake disc, the friction surface as the base body 80 is provided with the HS-LMD coating as a functional layer.This reduces the particulate matter pollution associated with braking.

[0054] Figures 7 and 8 show an embodiment of the jet nozzle 1 for laser material deposition along the feed direction 2. The laser output beam 50 emerges from the light channel 3 with the lateral surface 4. The light channel 3 can also be adapted to guide a process protective gas at a radially outer section to shield a process zone and prevent oxidation. The light channel 3 is surrounded by the outer structure 5, which has the nozzle mouth 6, which in turn contains the powder unit 7. The powder unit 7 can, for example, have a plurality of injector guides 8, into each of which a powder injector 9 can be inserted. As an alternative to the individual injector guides 8, the powder unit 7 can have a powder annular gap channel (not shown). The filler material 60 is directed onto the workpiece 100 via the powder unit 7 and, for example, the powder injectors 9 arranged therein.The laser output beam 50 heats the workpiece 100 such that a molten pool forms at least partially on a material surface. The distribution between the primary laser energy and the secondary laser energy, as disclosed, contributes to avoiding deficiencies in the functional layer 82. The first laser beam 51 heats the filler material 60. As the molten pool cools, the welded functional layer 82, for example, a wear-resistant layer, forms from the hard material particles and the matrix material. The welded functional layer 82 makes the material surface more resistant and increases its load-bearing capacity.

[0055] A flange section with a coupling ring 10 can be connected to the blasting nozzle 1, which fastens the blasting nozzle 1 to the connected unit, for example, the laser optics 110 or the process adapter. The powder injectors 9 are inserted into the injector guides 8 of the powder unit 7. The filler material 60 is conveyed by means of the powder injectors 9 and applied to the workpiece 100 with the focus, which can be adjusted in particular. The individual powder injectors 9 can apply different powder foci than one another. Alternatively, the powder injectors 9 can be directed at the same focus point. The powder injectors 9 are arranged in the designated injector guides 8 of the powder unit 7 in a powder section 11. Adjoining the powder section 11 in the circumferential direction is a powder-unit-free feed section 12 which is free of powder injectors 9.Furthermore, an inlet nozzle 13 is inserted into a coolant inlet, and an outlet nozzle 14 is inserted into a coolant outlet. These connect a coolant inlet and a coolant outlet of the jet nozzle with a coolant circuit of the laser system. The nozzle mouth 6 has a curved funnel shape. The injector guides 8, into which the powder injectors 9 can be inserted, are formed within the individual curvatures. In the feed direction 2, the light channel 3 is elongated in a manner deviating from a circular shape in order to guide the first laser beam 51 and the second laser beam 52 as disclosed, thus contributing to the disclosed advantages.

[0056] Figure 9 shows the blasting nozzle 1, from which the first laser beam 51 and the second laser beam 52 emerge. A powder jet emerges from each of the injector guides 8 and interacts with the first laser beam 51. According to the disclosure, the second laser beam 52 serves to preheat the workpiece surface. The second laser beam 52 is provided upstream of the first laser beam 51 in the feed direction 2. To avoid interaction between a powder jet and the second laser beam 52, the powder-unit-free feed section 12 is provided in the region of the nozzle mouth 6, in which feed section no filler material 60 is conveyed to the workpiece surface. A cross-sectional area of ​​the light channel 3 running orthogonally to the longitudinal direction of the blasting nozzle 1 is elongated in the feed direction 2, deviating from a circular shape. This elongation favors the first irradiation zone 101 being designed as a process zone and the second irradiation zone 102 as a preheating zone.In other words, orthogonal to the longitudinal direction of the jet nozzle 1 is a cross-section, part of which is the shape of the light channel 3. This cross-section can be elongated in the feed direction 2 and can be axially symmetrical along the feed direction 2 and point-symmetrical about a center point of the cross-section of the light channel 3. A minimum cross-sectional area of ​​the light channel is predetermined by a dimension, in particular a diameter, of the laser beam. Compared to the minimum dimension, the cross-sectional area is elongated along the feed direction.

[0057] Where applicable, all individual features presented in the embodiments may be combined and / or interchanged without departing from the scope of the invention.

[0058] 1 jet nozzle 63 spiral trajectory

[0059] 2 Feed direction 64 Offset

[0060] 3 Light channel 25 65 Track width 4 Shell surface 66 Radial overlap

[0061] 5 External structure

[0062] 6 nozzle mouth 80 base body

[0063] 7 Powder unit 81 Intermediate layer

[0064] 8 Injector guide 30 82 Functional layer 9 Powder injector 83 Connection error

[0065] 10 coupling ring

[0066] 11 Powder section 100 Workpiece

[0067] 12 Feed section 101 first irradiation zone

[0068] 13 Inlet nozzle 35 102 second irradiation zone 14 Outlet nozzle 110 Laser optics

[0069] 111 Fiber optic cable

[0070] 50 Laser output beam 112 Collimation unit

[0071] 51 first laser beam 113 beam splitter element

[0072] 52 second laser beam 40 114 focusing unit 60 filler material 115 rotational movement

[0073] 61 Weld bead 116 Translational movement

[0074] 62 powder layer track

Claims

Claims 1. A method for laser deposition welding along a feed direction (2) by means of a jet nozzle (1) which has a light channel (3) for guiding at least one laser beam (51, 52) which is directed onto a workpiece (100), and which has a powder unit (7) arranged in particular outside the light channel (3) for guiding at least one additional material (60), in particular powder, which is to be applied onto the workpiece (100), the method comprising the steps: Aligning a first laser beam (51) onto the workpiece (100) to generate a first irradiation zone (101) and aligning a second laser beam (52) onto the workpiece (100) to generate 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; wherein a secondary laser energy that the second laser beam (52) introduces into the second irradiation zone (102) is greater than a primary laser energy that the first laser beam (51) introduces into the first irradiation zone (101).

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 compared to the first laser beam (51).

3. Method according to one of the preceding claims, wherein a ratio of the secondary laser energy to the primary laser energy is greater than 11:10, in particular 5:4, further in particular 3:

2.

4. Method according to one of the preceding claims, further comprising the steps Controlling a workpiece holding unit on which the workpiece (100) is arranged, so that a rotational movement (115) moves the workpiece (100) about a rotational axis; and Controlling a translation unit such that a translation movement (116) moves the jet nozzle (1) and / or the workpiece holding unit in an offset direction that is substantially orthogonal to the rotation axis; wherein the rotation movement (115) and the translation movement (116) overlap to form a feed movement such that a powder layer track (62) with a radial track width (65) is applied to the workpiece (100) along a spiral trajectory (63); wherein an offset (64) of two adjacent spiral flanks of the spiral trajectory (63) is smaller than the track width (65), such that the powder layer track (62) forms a radial overlap (66) along the spiral trajectory (63).

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

1.

6. Method according to one of claims 4 or 5, wherein the radial overlap (66) and the feed movement are such that the second laser beam (52) reheats a previously applied powder layer track during application along the spiral trajectory (63) in order to promote its welding behavior by means of post-processing.

7. Method according to 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 compared 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. Method according to one of the preceding claims, wherein the first laser beam (51) and the second laser beam (52) are generated via a beam splitting from a common laser output beam (50) in a common optics, wherein the beam splitting is generated in particular by means of an optical 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 from 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. Method according to 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 shielded from ambient oxygen.

12. Method according to one of the preceding claims, wherein the introduction of the additional material (60) into the first irradiation zone (101) is carried out by means of powder injectors.

13. A jet nozzle (1) for laser material deposition along a feed direction (2), comprising a light 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 material (60), in particular powder, to be applied to the workpiece (100); wherein the jet nozzle (1) is configured and provided to carry out the method according to one of the preceding claims.

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