Methods for coating metal workpieces
Localized laser preheating and postheating zones with adjustable intensity distributions address bonding errors in high-speed laser cladding welding, enhancing the quality and durability of coated components by improving bonding and reducing defects.
Patent Information
- Authority / Receiving Office
- JP · JP
- Patent Type
- Applications
- Current Assignee / Owner
- Filing Date
- 2024-01-19
- Publication Date
- 2026-03-17
AI Technical Summary
Existing high-speed laser cladding welding methods face challenges in achieving precise and efficient preheating of workpieces, leading to bonding errors and defects like delamination, especially when coating materials like gray cast iron brake discs, due to the limitations of large-area induction heating and unpredictable temperature control.
A method involving localized laser preheating and postheating zones, using multiple laser beams with adjustable intensity distributions, allows for precise temperature control and bonding of additional material to the workpiece surface, minimizing energy input and reducing metallurgical impact.
This approach enhances bonding quality, reduces defects, and increases the service life of coated components by improving the bonding between layers and preventing delamination, while reducing process time and energy consumption.
Smart Images
Figure 2026509080000001_ABST
Abstract
Description
Technical Field
[0001] The present invention relates to the field of laser cladding welding. In particular, the present invention relates to a method and a device for coating a metal workpiece, especially a brake disc, by means of high-speed laser cladding welding.
Background Art
[0002] Methods for high-speed laser cladding welding are known from the prior art and are described, for example, in DE102011100456B4. This method achieves a significant increase in the achievable processing speed compared to conventional laser cladding welding by supplying at least one additional material in at least partially molten form to the process zone present on the surface to be processed. For this purpose, the additional material, which is initially in powder form, is heated by a laser beam at a distance from the workpiece surface, fed into the process zone, and likewise heated by the laser beam. In high-speed laser cladding welding, the feed movement, i.e., the relative movement between the surface to be coated and the processing beam, is mainly realized by the movement of the workpiece to be coated, especially by rotation. High-speed laser cladding welding can significantly increase the processing speed of the laser cladding welding process.
[0003] In high-speed laser cladding welding, also referred to as high-speed laser metal deposition (HS-LMD), most of the laser power is absorbed by the powder stream of the additional material and the metal vapor generated during the processing process. However, in order to achieve sufficient bonding between the workpiece and the coating layer, it is important that the workpiece surface has the required minimum temperature. Therefore, it is known to use induction to heat the workpiece over a large area in order to preheat the workpiece.
[0004] However, this large-scale heating is relatively complex and requires a relatively large amount of energy. In addition, the preheating temperature cannot be precisely controlled. Furthermore, for example, when preheating a brake disc made of gray cast iron by induction, the preheating temperature is limited because the surface of the brake body oxidizes if the temperature exceeds approximately 300°C. An oxidized surface negatively affects the coating process and the quality of the coating.
[0005] This invention is based on the objective of improving the coating of metal workpieces by laser deposition welding. In particular, it should be possible to avoid bonding errors (so-called delamination) between the coating layer and the coated workpiece, or between adjacent layers of the coating layer, even at high processing speeds.
[0006] Summary of the Invention The fundamental object of the present invention is achieved by the subject matter of the independent claims. Further possible embodiments of the present invention are expressed in the dependent claims, specification and drawings. Features, advantages and possible embodiments described in the specification for one of the objectives of the independent claims shall be considered at least similarly as features, advantages and possible embodiments for each of the other independent claims, and, optionally, for any possible combination of the objectives of the independent claims in combination with one or more of the dependent claims.
[0007] According to a first aspect of the present invention, a method for coating a metal workpiece by laser deposition welding is provided. The method includes, in a first step, moving, in particular rotating, the workpiece to be coated. The workpiece is preferably an automobile brake disc. The workpiece may have a base body which can essentially be made of cast iron, in particular gray cast iron. An intermediate layer made of a certain material, preferably a similarly metallic material, in particular stainless steel, can be applied to the base body on the surface of the workpiece to be coated. The intermediate layer helps, for example, to improve the bonding of the wear protection layer applied to the workpiece. Furthermore, the intermediate layer can help to stop cracking in the wear protection layer being applied. The composition of the intermediate layer can be selected depending on the material of the wear protection layer being applied.
[0008] The second step involves irradiating the surface of a workpiece with at least one first laser beam to generate at least one first irradiation zone and a second irradiation zone on the workpiece surface, wherein the second irradiation zone precedes or follows the first irradiation zone along the machining direction. The first irradiation zone may also be called a process zone. The second irradiation zone may also be called a preheating zone or postheating zone, depending on its location in the upstream or downstream area of the process zone. The machining direction is essentially determined by the movement of the workpiece. For example, when coating a brake disc, in addition to the rotation of the workpiece, the machining beam moves radially, resulting in a helical machining path. In this case, the machining direction may be tangent to the machining path starting from the center of the first irradiation zone. In addition to helical machining paths, helical machining paths or simple linear, circular, or other machining paths can also be realized. Moving the machining beam in addition to moving the workpiece is not always necessary. The workpiece surface is locally heated by at least a first laser beam in the process zone and the preheating or postheating zone.
[0009] In the third step of the process, additional material, preferably in powder form, is introduced into the first irradiation zone (i.e., the process zone). The additional material can preferably be introduced into the process zone in the form of one or more powder jets, preferably by an inert carrier gas. Alternatively, additional material in wire form may also be added. The additional material is fed into the process such that it preferably enters the first laser beam at least partially across its entire cross-section before impacting the workpiece surface at a predetermined distance from the workpiece surface, thereby preferably being heated at least partially across its entire cross-section. In this case, the additional material or at least a portion of the additional material is at least partially melted so that when it impacts the workpiece surface in the similarly heated process zone, it can rapidly bond with the material of the workpiece, creating a material bond with particularly little mixing of the materials being bonded. The focus of the powder jets supplied from several directions may be in a region of the surface of the workpiece to be coated (e.g., the surface plane), preferably above the workpiece surface. Depending on the application, the focus of the powder-fed additional material may also be below the workpiece surface, i.e., within or below the workpiece. The additional material preferably consists of a material having higher wear resistance than the base body of the component. In particular, the additional material may include an iron-containing matrix material that specifically forms a stainless steel matrix embedded with hard material particles such as tungsten carbide particles or titanium carbide particles. In the coating process, the additional material preferably forms a flat wear-protective layer on the workpiece surface. Wear protection can be increased by carbide deposits in the coating layer. When coating brake discs, the number of brake cycles and the service life of the brake discs can be increased (particularly by reducing wear during braking).
[0010] The method according to the present invention allows for precise and efficient preheating of the workpiece surface along the processing path immediately before or after the additional material collides with the process zone, thereby improving the bonding between the additional material and the workpiece surface and avoiding bonding errors. Other defects in the material structure of the coating layer, such as pore formation, can also be suppressed. Compared to large-area preheating by the prior art, the energy input to the workpiece is much more targeted. Furthermore, the temperature can be adapted very quickly to the changing thermal conditions during the coating process. In this way, the quality of the coating can also be improved. By using less energy compared to large-area heating of the workpiece to be coated, the impact on the metallurgical properties of the workpiece can be reduced. In the method according to the present invention, preferably, no significant molten pool is formed on the surface of the workpiece to be coated. The penetration depth (or impact depth) into the workpiece to be coated by at least the first laser beam can preferably be up to 20 μm, preferably up to 10 μm, and more preferably up to 5 μm. In this case, preheating the workpiece surface can contribute, in particular, to the washing and / or gas release of carbon from the workpiece to be coated, to the improvement of the wettability of the workpiece surface by the additional material, and / or to the improvement of the bond between the additional material and the workpiece.
[0011] The method according to the present invention can further provide that an inert protective gas, such as argon, helium, or an inert gas mixture, is directed through the processing nozzle of the processing head to a first irradiation zone along with at least a first laser beam, thereby shielding the welding process from reaction with oxygen from the ambient air and preventing corrosion of the coating path or the heated workpiece surface.
[0012] In the coating method according to the present invention, the resulting feeding speed, i.e., the relative movement speed between the workpiece surface and the processing beam, can preferably be at least 20 m / min.
[0013] The method according to the present invention also provides that the workpiece to be coated does not undergo any additional preheating, particularly large-area induction preheating, in addition to preheating by at least a first laser beam. By eliminating preheating time and induction preheating devices, process time and process cost can be reduced.
[0014] In a modified version, a third irradiation zone can also be generated by at least the first laser beam. The third irradiation zone is positioned to start from the first irradiation zone and face the second processing zone. For simplicity, we will assume below that the second irradiation zone is a preceding preheating zone and the third irradiation zone is a subsequent postheating zone.
[0015] The method according to the present invention can use at least two laser beams. Thus, a first laser beam can generate a first irradiation zone, and a second laser beam can generate a second irradiation zone. A third laser beam can additionally generate a third irradiation zone. The first laser beam and the second laser beam, and (optionally) the third laser beam as well, can each be designed as a sub-beam of a common laser output beam (i.e., a first sub-beam, a second sub-beam, and (optionally) a third sub-beam). Preferably, the second laser beam and / or the third laser beam have different intensities from the first laser beam in the irradiation plane (i.e., the plane of the workpiece surface or the surface plane of the coated layer). In particular, the intensity of the second laser beam in the plane of the workpiece surface can be lower than that of the first laser beam.
[0016] The second and / or third laser beams can also be supplied to the process from another beam source, for example, laterally. In this way, the laser power of the individual laser beams can be easily adjusted independently of each other. This also facilitates the positioning of the preheating beam and / or postheating beam along the processing path. Furthermore, laser beams with wavelengths different from those used in the actual coating process can also be used for preheating and / or postheating. The wavelength can be precisely adjusted to match the material-specific bonding, thus increasing the efficiency of preheating and / or postheating. Moreover, the preheating beam and / or postheating beam can be radiated onto the workpiece surface or weld bead from outside the additional material feeding section, and in particular, not affected by the powder jet of additional material arranged concentrically around the first laser beam.
[0017] As an alternative to using several separate or partial laser beams, it is also possible to use only one laser beam, preferably having an elongated, asymmetrical beam profile (e.g., elliptical or rectangular) in the processing direction, where the forward portion of the projection of the laser beam onto the workpiece surface forms a second irradiation zone, and the subsequent portion of the projection forms a first irradiation zone. An additional third irradiation zone can be added by extending the asymmetrical laser beam, which, following the first irradiation zone, reheats the generated weld bead or additional applied material to further prevent bonding errors or delamination between individual coating layers.
[0018] When using several separate or partial laser beams, the first laser beam and / or the second and / or third laser beams have a plateau-shaped intensity distribution. The described intensity distribution is present, in particular, at the beam focus of each laser beam. Alternatively, at least one of the laser beams may have a Gaussian intensity distribution. The plateau-shaped intensity distribution, also known as the top-hat distribution, has advantages over the Gaussian intensity distribution, as it allows for more uniform heating of both the workpiece surface and additional material across the entire beam cross-section of the laser beam, particularly in its edge region.
[0019] Alternatively or additionally, the first laser beam and / or the second and / or third laser beams have an intensity distribution with maximum intensity in the edge region of each laser beam. In particular, the first and / or second and / or third laser beams may each have a circular cross-section with an annular intensity distribution across the beam cross-section. Thus, the intensity is lower at the center of the beam than in its peripheral region. Laser beams with an annular intensity profile allow for more uniform heating of the workpiece surface and / or additional materials, especially powdered materials, during laser deposition welding.
[0020] The fluence applied in the second irradiation zone is preferably 0.01 J / mm². 2 ~Maximum 5J / mm 2 This is within the specified fluence range. Within the specified fluence range, the effect of laser radiation heating on the metallurgy of the workpiece to be coated can be kept to a minimum due to the low penetration depth. In particular, the preheating penetration depth may be in the range of 5 μm to 500 μm starting from the workpiece surface. Preferably, the irradiation in the second irradiation zone can be adjusted so that the preheating temperature of the workpiece in the second irradiation zone is in the range of 5% of the melting temperature of the workpiece to be coated to the maximum evaporation temperature.
[0021] The laser power of the second laser beam and / or the third laser beam can be changed during the coating process. For example, the laser power of the second and / or third laser beam can be changed by changing the resulting feed rate. The laser power of the second and / or third laser beam at the start of the coating process may also have a first value that is reduced according to specifications to compensate for process-related heating of the components during the coating process and to create the most similar possible thermal conditions throughout the entire coating process. Similar to the adjustment of the laser power of the second and / or third laser beam, the laser power of the first laser beam can also be changed as needed. In particular, by changing the laser power of the second laser beam, the preheating of the workpiece surface can be accurately and flexibly adapted to external conditions.
[0022] The total laser power of all laser beams used in the coating process may be at least 1 kW, preferably at least 8 kW. The proportion of the laser power of the second laser beam to the total power may be in the range of 0.05% to 75%, particularly in the range of 1% to 50%.
[0023] At least one of the laser beams used may have a wavelength in the range of 0.4 μm to 2 μm. The beam quality of at least one of the laser beams may be in the range of 2 mm*mrad to 500 mm*mrad. A 2-in-1 or n-in-1 optical fiber, or a single-core fiber, can be used to guide at least a first laser beam, or a laser power beam beneath the first (partial) laser beam. An n-in-1 optical fiber in the sense of this disclosure has at least one central optical guidance core region and at least one optical guidance ring region surrounding the core region for transporting the laser beam, and the optical guide regions are preferably separated from each other by cladding. When using an n-in-1 optical fiber, the power portion of the laser beam guided in the central fiber core may be at least 15% of the total power. The coating process may preferably utilize a device having a welding head equipped with welding optics, thereby focusing a first laser beam onto the process zone along with a powder gas jet containing additional material, and further focusing at least a portion of the first or second laser beam onto a preheating zone. The focal diameter of at least one of the laser beams is in the range of 1 mm to 20 mm. The laser beam can be focused onto the workpiece surface to be coated such that its focal diameter is on the surface plane of the workpiece, or offset by several millimeters above or below the surface plane. To split the laser output beam into at least first and second (partial) laser beams, corresponding optical elements (e.g., optical wedges or diffractive optical elements) can be placed in the beam path of the collimated laser output beam.
[0024] The distance from the first irradiation zone (process zone) to the second irradiation zone (preheating zone) and / or the distance from the first irradiation zone to the third irradiation zone (postheating zone) in the processing direction may be at least 0.5 times the focal diameter of the first laser beam and up to 5 times the focal diameter of the first laser beam. The first laser beam, the second laser beam, and / or the third laser beam may have the same, particularly circular, outer diameter. For example, when using 2-in-1 or n-in-1 optical fibers, overlap of the irradiation zones may be preferred in the case of an annular intensity profile of the laser beam that can be generated by using a laser portion guided to the annular fiber core of the n-in-1 fiber. The distance between irradiation zones is determined by the distance between the centers of the irradiation zones in a common plane (if there is doubt as to the surface plane of the workpiece to be coated). Preferably, the irradiation zones may be spaced apart from each other so that they are just adjacent to each other without significant overlap or significant gaps between them.
[0025] Additional material can be supplied to the first irradiation zone such that an irradiation window remains for generating a second irradiation zone and / or a third irradiation zone. In other words, powder feeding can be designed so that the second laser beam or the corresponding portion of the first laser beam for generating the preheating zone (second irradiation zone) is not obstructed by the powder flow. The same applies to the third laser beam or the corresponding portion of the first laser beam for generating the postheating zone (third irradiation zone). For example, the additional material can be fed only in a lateral direction with respect to the processing direction and / or through, i.e., from the direction following the process. If the additional material is fed in a through manner, it is understood that any postheating zone will be at least partially covered. However, concentric feeding of the additional material is also conceivable. A particularly preferred modification is one in which additional material is supplied to the first irradiation zone from several positions distributed around the first laser beam (or via individual nozzles distributed in a ring shape, or via C-shaped slot nozzles), and the powder supply is not performed in the direction of travel, and the second laser beam or a corresponding portion of the first laser beam can be directed to the workpiece surface without being obstructed through recesses present in the powder supply section. Similar recesses can be provided in the powder supply section to create a post-heating zone.
[0026] In principle, it is preferable that the additional material is blown into the process zone in powder form by a carrier gas, particularly an inert gas. The powder mass flow rate in the process according to the present invention may preferably be at least 20 g / min. Additional gas supply can be provided to avoid the oxidation process during coating. In particular, an inert gas, such as argon, can be blown through the processing nozzle, through which the laser beam also appears in at least the processing zone.
[0027] The second irradiation zone and / or the third irradiation zone can be arranged so as to be offset orthogonally from the first irradiation zone in the processing direction. This enables the curvature of the processing path to be taken into account for preheating and post-heating, especially in the case of circular, spiral or helical material application. The influence of preheating and / or post-heating on a part of the process zone or its adjacent surroundings can be adjusted via lateral variations in the preheating region and / or the post-heating region. This may be necessary when welding with track overlap, for example, when only the workpiece or only the intermediate layer is preheated.
[0028] The second laser beam and / or the third laser beam can each have a rectangular beam cross-section. The rectangular beam profile can be aligned orthogonally to the processing direction. Thereby, a uniform fluence distribution can be obtained in the preheating zone and the post-heating zone.
[0029] The second irradiation zone (preheating zone) and / or the third irradiation zone (post-heating zone) can each have a different size from the first irradiation zone (process zone). For example, for the area A2 of the second irradiation zone, 0.1*A1≦A2<A1 (A1 = the area of the first irradiation zone) can be obtained. By making the preheating spot smaller, the influence of preheating on a part of the process zone can be adjusted. This may be advantageous when welding with track overlap, for example, when only the workpiece surface or only the intermediate layer of the coating is preheated. Conversely, the following can be applied to the area A2 of the second irradiation zone: A1<A2≦3*A1. When using a preheating zone larger than the process zone, heat treatment can be performed on the previously applied coating area (especially the turn part of the spirally applied coating) while applying the powder. Furthermore, a relatively large preheating zone reduces the effort required for the precise positioning of the second laser beam relative to the first laser beam.
[0030] However, depending on the application, a configuration where the irradiation zones are of equal size may be desirable. In particular, in some cases, this can optimize the efficiency of the energy input.
[0031] In particular, the size of the projection area of the laser beam on the workpiece surface, and thus the size of the irradiation zone, can be variably adjusted.
[0032] According to another aspect of the present invention, a device for laser vapor deposition welding is provided. The device comprises a carrier unit for a metallic workpiece to be coated, the carrier unit having a moving unit for moving the workpiece, in particular for rotating it. The device further comprises a laser beam unit for providing at least one first laser beam and for generating at least one first irradiation zone and a second irradiation zone on the surface of the workpiece to be coated by means of the at least one first laser beam, the second irradiation zone preceding the first irradiation zone along the processing direction. The device also comprises a feeding unit for feeding additional material, in particular powdered additional material, to the first irradiation zone, the additional material being fed to the first irradiation zone such that it enters at least partially into the first laser beam and is thus at least partially heated before impinging on the workpiece surface in the first processing zone.
[0033] The laser beam unit preferably has an optical system which has a collimation unit and a focusing unit, as well as a beam splitter element. The beam splitter element is arranged in the beam path of the optical system between the collimation unit and the focusing unit and is designed to split the laser output beam into a first laser beam and at least one second laser beam.
[0034] The beam splitter element may be, for example, an optical wedge, a cylindrical lens, or a diffractive optical element (DOE). Faceted optical systems or microlens arrays can also be used as beam splitter elements. Optical wedges and DOEs, as well as faceted optical systems or microlens arrays, can generate separate partial beams, thereby exposing the workpiece surface to each irradiation zone. Using a cylindrical lens, an elliptical beam profile of the laser beam can be generated so that the laser beam irradiates each irradiation zone on the workpiece surface with a continuous beam spot.
[0035] The device may further include a displacement unit capable of displacing an optical element designed as an optical wedge or DOE laterally in the beam path of a laser output beam, thereby distributing laser power to the resulting laser beam.
[0036] According to a third aspect, a workpiece that can be manufactured by a coating method according to the present invention is provided. The workpiece is in particular a brake disc. The workpiece comprises a base body made of metal, in particular a base body in the shape of a disc. The base body can be made in particular of cast iron, for example gray cast iron. The workpiece further comprises at least one coating layer disposed on the surface of the base body and integrally connected to the base body, preferably with helical and overlapping coating paths. The workpiece has a mixed region having a thickness of up to 20 μm, preferably up to 10 μm, and more preferably up to 5 μm in the transition area between the base body and the coating layer. A material bond between the base body and the coating layer is formed in the mixed region.
[0037] In a preferred modification, the workpiece may have several coating layers, each having a different material composition. For example, a first coating layer may be formed as an intermediate layer made of stainless steel and applied to the surface of the base body. A second coating layer applied to the intermediate layer may consist of a matrix material in which hard material particles, such as tungsten carbide or titanium carbide, are embedded in a stainless steel matrix. Between each of the coating layers and / or between overlapping turns of such coating layers, mixed regions having a maximum thickness of 20 μm, preferably up to 10 μm, and more preferably up to 5 μm, can be formed between adjacent layers / turns. The workpiece is characterized in particular by strong and defect-free connections between the base body and the coating layers, and between adjacent coating layers (or winding paths), where the material structure and properties of different materials in the connection region have minimal influence.
[0038] The workpiece can preferably be manufactured by a method according to the present invention, according to one of the modifications described above.
[0039] The following description of preferred exemplary embodiments, in conjunction with the drawings, will help to illustrate the invention in more detail. [Brief explanation of the drawing]
[0040] In the drawing, [Figure 1] This diagram shows a schematic representation of the creation of two irradiation zones during high-speed laser deposition welding. [Figure 2] The process components in the high-speed laser deposition welding according to the present invention are schematically shown. [Figure 3] Figures 3a to 3d show schematic diagrams of different configurations for preheating and / or postheating during high-speed laser deposition welding. [Figure 4] This diagram shows schematic representations of different residence times of powder particles during high-speed laser deposition welding in process zones on the surface of a workpiece being coated. [Figure 5]The optical arrangement of the device according to the present invention for high-speed laser deposition welding is schematically shown. [Figure 6] This figure illustrates the delamination of the wear protection layer on a workpiece coated by high-speed laser deposition welding. [Figure 7] Figures 7a to 7n show schematic diagrams of further different configurations for preheating and / or postheating during high-speed laser deposition welding. [Modes for carrying out the invention]
[0041] Figure 1 schematically shows a nozzle 10 from which a first laser beam L1 and a second laser beam L2 are emitted. When the first laser beam L1 irradiates the workpiece surface (not shown), a first irradiation zone 20 is generated on the workpiece surface, and the second laser beam L2 generates a second irradiation zone 22 in a similar manner. By moving the workpiece to be coated and / or the nozzle 10 relative to each other, the laser beams L1 and L2 move in the processing direction 40 along a predetermined processing path on the workpiece surface. The powdered additive material P is also irradiated into the first laser beam L1 via the nozzle 10 so that the powder particles irradiated by the first laser beam L1 are heated and collide with the workpiece surface along the processing path in the first irradiation zone 20 (process zone). Due to the simultaneous heating of the powder particles and the workpiece surface in the process zone 20, a strong bond is formed very quickly when the powder particles collide with the workpiece surface. In principle, a complete common molten pool is not formed. The partially molten material deposition in process zone 20 then solidifies into a weld bead 30. To accelerate the coating process and simultaneously minimize the occurrence of bonding errors, the workpiece surface is preheated by a second laser beam L2 in a second irradiation zone 22 (preheating zone) during the preparation phase for process zone 20. To further improve the bonding of the material deposition (additional material P) to the workpiece, or the bonding of overlapping material deposition paths (so-called delamination defect patterns), following process zone 20, the weld bead 30 can also be heated by laser radiation in a third irradiation zone (24, see Figures 2b and 2d).
[0042] Figure 2 schematically illustrates the process steps of the coating process according to the present invention. Step S1 represents the movement, in particular rotation, of the workpiece to be coated. In step S2, the surface of the workpiece is irradiated by at least a first laser beam L1 to generate at least a first irradiation zone 20 S20, and a second irradiation zone 22 S22 on the workpiece surface, the second irradiation zone 22 preceding the first irradiation zone 20 along the processing direction 40. Furthermore, in an optional substep S24, a third irradiation zone 24 may also be generated by at least the first laser beam L1. In step S3, additional material P is introduced into the first irradiation zone 20, and the additional material P enters the first laser beam L1 at least partially before impacting the workpiece surface, thereby being at least partially heated.
[0043] Figures 3a to 3d schematically illustrate various configurations of preheating and / or postheating within the framework of the coating process according to the present invention. Figure 3a shows a configuration in which the surface of the workpiece to be coated is irradiated by two laser beams, where the projection of a first laser beam L1 onto the workpiece surface forms a first irradiation zone 20, and the projection of a second laser beam L2 forms a second irradiation zone 22 on the workpiece surface. The second irradiation zone 22 precedes the first irradiation zone 20 in the coating process along the processing direction 40. Figure 3b shows a configuration in which, in addition to the irradiation zones 20 and 22 in Figure 3a, a third irradiation zone 24 is generated by a third laser beam L3, where the third irradiation zone 24 follows the first irradiation zone 20 along the processing direction 40 to heat the additional material P applied in the process zone 40 in a controlled manner. Figure 3d also shows a configuration in which three irradiation zones 20, 22, and 24 are generated on the workpiece surface or weld bead 40. However, in contrast to the diagram in Figure 3b, the irradiation zones 20, 22, and 24 are generated by a continuous beam spot (or projection) of a single laser beam. For this purpose, the laser beam used preferably has an asymmetric beam profile in cross-section, particularly an elliptical beam profile, as shown in Figure 3d.
[0044] Figure 3c shows an irradiation configuration in a particularly preferred embodiment of the coating method according to the present invention. This irradiation configuration differs from the irradiation configuration in Figure 3a in that the laser beams L1 and L2 generate irradiation zones 20 and 22 having an annular intensity distribution. In other words, more energy per unit area is introduced to the edge regions of each irradiation zone 20 and 22 than to their respective core regions. As a result, a more uniform energy distribution is achieved across the entire width of each irradiation zone 20 and 22 along the processing direction 40 compared to irradiation with a top-hat or Gaussian intensity distribution, and therefore, more uniform heating of the irradiated surface or the powder particles of the additional material P is achieved. The example in Figure 4 further illustrates the advantages of a beam profile with an annular intensity distribution. Here, a process zone 20 is shown, with three powder particles P1, P2, and P3 distributed across the width of the process zone 20, each positioned at the front end of the process zone 20. From the figure, it can be inferred that, due to the circular process zone 20, powder particles P2 impacting the center travel a longer distance within the process zone 20 as it moves along the processing direction 40, and consequently have a relatively short residence time Δt1 within the process zone 20, and are therefore heated for a longer period Δt2 than powder particles P1 and P3 impacting the edges of the process zone, which are not heated as strongly. In the case of an annular intensity distribution of the first laser beam L1, this non-uniform energy input across the entire width of the processing track can be suppressed.
[0045] Figure 5 schematically shows the structure of an optical system 100 that can be used in a device for a coating method according to the present invention. The optical system 100 can be positioned in particular on the processing head of the device. The laser output beam L is collimated on a collimation unit 120, particularly a collimation lens, via an optical fiber cable 110, for example, a 2-in-1 fiber. A beam splitter element 130, in the form of an optical wedge, is positioned in the beam path of the collimated laser output beam L, and the beam splitter element 130, in the form of an optical wedge, is displaceable transversely to the propagation direction of the laser output beam L, thereby allowing the laser output beam L to be split into a first (partial) laser beam L1 and a second (partial) laser beam L2. By positioning the beam splitter element 130 laterally on the laser output beam L, the entire power of the laser output beam L can be directed, in particular, to the split laser beams L1 and L2. Next, the laser beams L1 and L2 are focused onto the surface of the workpiece 50 to be coated via a focusing unit 150, which is a focusing lens, thereby generating corresponding irradiation zones 20 and 22 on the workpiece surface.
[0046] Figure 5 shows a cross-section of the coating of a workpiece coated by laser deposition welding. The workpiece 50 comprises a base body 52 and an intermediate layer 54 applied to the base body 52. The coating layer 60 is applied to the intermediate layer 54. The coating layer 60 includes multiple overlapping coating tracks or overlapping turns of continuous coating tracks. The coating layer 60 shown in Figure 6 shows a bonding defect 62 between two adjacent coating layers. This defect is also called delamination. The coating method proposed herein is intended to suppress the formation of delamination 62 and bonding defects between the coating layer 60 and the workpiece 50.
[0047] Figures 7a to 7n schematically illustrate further exemplary configurations of preheating and / or postheating within the framework of the coating process according to the invention, similar to Figures 3a to 3d. In relation to the description of Figures 3a to 3d, the figures of Figures 7a to 7n are obvious to those skilled in the art, and therefore a detailed description of the individual arrangements of laser beam projections having different beam cross-sections is omitted at this time. However, it should be noted that by offsetting one or more laser beams laterally or positioning them at a certain angle on the workpiece surface (see Figures 7c to 7k), a helical course of the coating path can be considered during the preheating and / or postheating of the workpiece, and / or in at least one previous turn of the coating layer.
Claims
1. A method for coating a metal workpiece (50) by laser deposition welding, The steps include moving (S1), particularly rotating, the workpiece (50) to be coated, at least one first laser beam (L １ A step of irradiating the surface of the workpiece (50) with (S2) to generate at least one first irradiation zone (20) and a second irradiation zone (22) on the surface of the workpiece, wherein the second irradiation zone (22) precedes or follows the first irradiation zone (20) along the machining direction (40), Preferably, the step of introducing an additional material (P) in powder form into the first irradiation zone (20), wherein the additional material (P) is at least partially exposed to the first laser beam (L) before it strikes the surface of the workpiece. １ A method comprising the steps of introducing a substance into which it is at least partially heated.
2. At least the first laser beam (L １ The method according to claim 1, further comprising generating a third irradiation zone (24) formed on the surface which is coated in the opposite direction to the second irradiation zone (22) relative to the first irradiation zone (20) by means of the first irradiation zone (20).
3. The first irradiation zone (20) is illuminated by the first laser beam (L １ ) is generated by the second irradiation zone (22), and the second laser beam (L ２ ) is generated by and / or the third irradiation zone (24) is generated by the third laser beam, The second laser beam (L ２ ) and / or the third laser beam in the plane of each irradiation zone, the first laser beam (L １ The method according to claim 1 or 2, having a strength different from that of the other.
4. The first laser beam (L １ ), and / or the second laser beam (L ２ ), and / or the third laser beam has a plateau-shaped intensity distribution, the method according to any one of claims 1 to 3.
5. The first laser beam (L １ ) and / or the second laser beam (L ２ ) and / or the third laser beam has an intensity distribution having maximum intensity in the edge region of each laser beam, the method according to any one of claims 1 to 4.
6. The second laser beam (L ２ ) and / or the laser power of the third laser beam is changed during the coating process, the method according to any one of claims 1 to 5.
7. In the processing direction (40), the distance from the first irradiation zone (20) to the second irradiation zone (22) and / or the distance from the first irradiation zone (20) to the third irradiation zone (24) is the distance of the first laser beam (L １ At least 0.5 times the focal diameter of the first laser beam (L １ The method according to any one of claims 1 to 6, which corresponds to a maximum of five times the focal diameter of the said.
8. The method according to any one of claims 1 to 7, wherein the additional material (P) is supplied to the first irradiation zone (20) such that an irradiation window remains for generating the second irradiation zone (22) and / or for generating the third irradiation zone (24).
9. The method according to any one of claims 1 to 8, wherein the second irradiation zone (22) and / or the third irradiation zone (24) are offset from the first irradiation zone (20) in a manner perpendicular to the machining direction.
10. The second laser beam (L ２ ) and / or the third laser beam having a rectangular beam cross-section, the method according to any one of claims 1 to 9.
11. The method according to any one of claims 1 to 10, wherein the second irradiation zone (22) and / or the third irradiation zone (24) have a different size from the first irradiation zone (20).
12. A device for laser deposition welding, A carrier unit for a metal workpiece (50) to be coated, wherein the carrier unit has a moving unit for moving the workpiece (50), particularly for rotating it. at least one first laser beam (L １ A means of providing, and at least the first laser beam (L １ A laser beam unit for generating at least one first irradiation zone (20) and a second irradiation zone (22) on the surface of the workpiece (50) to be coated, wherein the second irradiation zone (22) precedes the first irradiation zone (20) along the processing direction (40), In particular, a feeding unit for feeding an additional powdered material (P) to the first irradiation zone (20), wherein the additional material is subjected to the first laser beam (L) in the first irradiation zone (20) before it collides with the surface of the workpiece. １ A device comprising a supply unit that can supply the first irradiation zone (20) so as to enter at least partially into the first irradiation zone (20) and thereby be heated at least partially.
13. The laser beam unit comprises an optical system (100), the optical system (100) having a collimation unit (120) and a focusing unit (140), and the collimation unit (120) and the focusing unit (140) are arranged in the beam path of the optical system (100), and the laser output beam (L) is directed to the first laser beam (L １ ) and at least one second laser beam (L ２ The device according to claim 12, having a beam splitter element (130) designed to split into ).
14. The device according to claim 13, wherein the beam splitter element is an optical wedge, a cylindrical lens, or a diffractive optical element (DOE).
15. Workpieces, especially brake discs, In particular, the disc-shaped metal base body, Preferably, the coating comprises at least one coating layer arranged on the surface of the base body with overlapping coating paths in a spiral pattern and integrally connected to the base body, A workpiece having a mixed region having a maximum thickness of 20 μm, preferably 10 μm, and more preferably 5 μm, in the transition area between the base body and the coating layer.