Method for coating a surface

Abstract

The invention relates to a method for coating (1) a surface (2) by means of a laser coating device (3), wherein the method involves at least the following steps: a. providing a main body (4) having a surface (2) to be coated; b. providing a laser optical unit (6); c. moving the surface (2) to be coated relative to the laser optical unit (6); and d. providing filler metal (8) and carrying out a coating process by means of heating the provided filler metal (8) by means of laser light (7) from the laser optical unit (6) in order to join a web-like first welding trace (9) to the surface (2) to be coated, wherein step c. is carried out during a coating process according to step d. The method is characterised primarily in that the first welding trace (9) is created in step d. with an overlap (13) with itself of less than 10% of the trace width (12) or without an overlap (13) on the surface (2) to be coated, and a further welding trace (10, 11) is applied at the earliest following completion of a relative 360° turn between the surface (2) to be coated and the laser optical unit (6). By way of the method proposed herein for coating a surface, an improved welded joint is achievable with no or little loss of time.

Description

[0001] Process for coating a surface

[0002] The invention relates to a method for coating a surface by means of a laser coating device, wherein the method comprises at least the following steps: a. providing a base body with a surface to be coated; b. providing laser optics; c. moving the surface to be coated relative to the laser optics; and d. providing welding filler material and carrying out a coating process by heating the provided welding filler material by means of laser light from the laser optics to connect a web-shaped first welding track to the surface to be coated, wherein step c. is carried out during a coating process according to step d. The method is characterized in particular in that the first welding track in step d.with an overlap of less than 10% of the track width or without overlap on the surface to be coated, and a further welding track is applied at the earliest after completion of a relative 360° turn between the surface to be coated and the laser optics. The invention further relates to a laser coating device.

[0003] Additive manufacturing processes are becoming increasingly attractive for large-scale production. The goal of additive coating processes is usually to provide a base body with a coating that is more suitable for the respective application. This opens up the possibility of using a base body made of a mechanically and / or thermally more suitable material and / or that can be manufactured more cost-effectively. This is well known, for example, in the field of brake discs, cylinder barrels in engine blocks, and pistons for exterior applications.

[0004] Among the additive manufacturing processes are the local coating processes, i.e. those that deliver coating material to the processing point in a timely manner, and among these are laser spraying and laser cladding, for example the extremely high-speed laser cladding [EHLA] as it is known, for example, from the

[0005] Laser coating processes, as known from DE 102011 100 456 A1, are advantageous in many respects. This allows a mostly thin layer to be applied to the surface of a base body within a very short process time, with low energy consumption, efficient use of powder material, and high bond quality. This, in turn, can save material depending on the application. Especially in the area of ​​components subject to high thermal stress, such as brake discs, the material difference between the base body and the coating to be applied is large, and weldability is critical. The welding process must therefore be carried out within a very narrow process window.

[0006] Based on this, the present invention is based on the object of at least partially overcoming the disadvantages known from the prior art. The features of the invention are derived from the independent claims, for which advantageous embodiments are presented in the dependent claims. The features of the claims can be combined in any technically reasonable manner, whereby the explanations from the following description as well as features from the figures, which comprise additional embodiments of the invention, can also be consulted for this purpose.

[0007] The invention relates to a method for coating a surface by means of a laser coating device, wherein the method comprises at least the following steps: a. Providing a base body with a surface to be coated; b. Providing laser optics which is movable relative to the provided base body and by means of which laser light for connecting a welding filler material to the surface to be coated can be provided in a focused manner; c. Moving the surface to be coated relative to the laser optics; and d. Providing welding filler material and carrying out a coating process by heating the provided welding filler material by means of laser light from the laser optics to connect a web-shaped first welding track to the surface to be coated, wherein the first welding track has a predetermined track width and comprises provided welding filler material, wherein step c.during a coating process according to step d.

[0008] The method is characterized in particular in that the first welding track in step d. is produced on the surface to be coated with an overlap of less than 10% of the track width or without overlap, and a further welding track is applied at the earliest after completion of a relative 360° turn between the surface to be coated and the laser optics.

[0009] In the following, reference is made to the specified axis of rotation whenever, without explicit indication to the contrary, the axial direction, radial direction, or the direction of rotation and corresponding terms are used. Ordinal numbers used in the preceding and following descriptions serve only to clearly distinguish them and do not reflect the order or ranking of the designated components. An ordinal number greater than one does not necessarily imply that another such component must be present.

[0010] It was determined that the application and introduction of laser energy causes such a temperature change on the surface of the substrate that the quality of the weld deteriorates. Because cooling options are limited in this area, and liquid cooling is only possible with considerable effort, the achievable cooling performance is limited.

[0011] A method is proposed here which saves time for cooling without causing a disadvantage in process times. This is achieved by applying the individual weld tracks at a distance from one another on the surface to be coated and not in the desired overlap of the weld tracks in the final state, or with regard to a respective layer and its final state. Such an overlap is, for example, up to 90% [ninety percent], preferably 60% [sixty percent] to 80%. With only a slight overlap of less than 10%, it is necessary to place at least one additional weld track between these two slightly overlapping weld tracks.Due to the small overlap and thus a small amount of material, in an advantageous embodiment this overlapping material is melted again and thus any insufficient connection between the welding traces and / or the surface to be coated is improved.

[0012] The method is designed for coating a surface of a base body, wherein the surface to be coated is preferably provided with a coating over its entire area using a welding filler material and the thermal energy of laser light from the laser optics.In one embodiment, such a base body is made, for example, of a gray cast iron material, preferably lamellar gray cast iron, and the coating formed from the welding filler material is made of a steel, for example stainless steel or tool steel, with a high proportion of additives, such as carbon [C], chromium [Cr], molybdenum [Mo], vanadium [V], titanium [Ti], tungsten [W], manganese [Mn], boron [B] and / or niobium [Nb]. In one embodiment, the welding filler material is already provided on the surface to be coated as a so-called powder bath (selective laser welding), and in another embodiment, the welding filler material is fed into the welding process in-situ, preferably via a nozzle. In a preferred embodiment, the above-mentioned extremely high-speed laser cladding [EHLA] is used.

[0013] First, in step a., a base body is provided, for example, clamped in a workpiece holder, wherein a surface to be coated is aligned as required. In step b., which takes place at the same time as or before step a., laser optics are provided, which are usually supplied with laser light from an external laser source. The laser optics can be used to suitably focus the laser light, for example in extremely high-speed laser material deposition [EHLA] with a laser focus just above the surface to be coated. The base body or the surface to be coated and the laser optics are movable relative to one another, wherein preferably the surface to be coated is movable in a fixed plane and the laser optics itself is alignable relative to it and / or movable along a further spatial axis relative to the surface to be coated.A corresponding laser coating device has an actuator device, which usually has a plurality of individual actuators or feed axes.

[0014] In step c, the relative movement between the base body and the laser optics is now carried out, for example, by the actuator device of the executing laser coating device. In one embodiment, for example, the surface to be coated is moved relative to the laser optics in such a way that a weld track is created.

[0015] In step d., welding filler material is now provided, whereby this, as already described above, is either already held on the surface to be coated before the welding energy is supplied by means of the laser light or is fed in situ into the laser focus of the laser optics. Due to the movement and the welding process before steps c. and b., a web-like first welding track is applied to the surface to be coated and connected to it. In a preferred embodiment, the welding filler material is partially melted or completely melted and at the same time a molten pool is formed on the surface to be coated, so that an excellent bond quality is achieved between the welding filler material and the surface to be coated.

[0016] Here, it is proposed that a first weld track be created that has little or no overlap with itself, so that the first weld track does not create a final coating. Rather, additional weld tracks are necessary to achieve a final coating result. It should be noted at this point that a coating is often created from multiple layers, with each additional layer being formed from weld tracks applied to a previously applied complete layer consisting of multiple weld tracks.

[0017] A further weld track is applied with a considerable delay, which then has a greater overlap than the first weld track with itself. For example, a further weld track is applied with the final desired overlap of, for example, 40% [forty percent] to 60%. With a meandering weld track, an outward path, a transverse path and a return path are thus first created, and then another transverse path of the first weld track is created, before a further weld track with a greater overlap is placed next to the already created portion of the first weld track. Overall, this process control therefore results in only a slight time delay due to the time offset between the start of the application of the first weld track and the subsequent weld tracks.

[0018] In one embodiment, the method proposed here can achieve an overall time saving because, as a result of the improved weld joint, an intermediary layer, a so-called adhesion layer or buffer layer, can be dispensed with.

[0019] It is further proposed in an advantageous embodiment of the method that in step c. the laser optics rotate relative to the surface to be coated about the rotation axis and are moved radially with respect to the rotation axis, and in step d. the first welding track is generated spirally, a further welding track is applied during step d. at the earliest after a full relative rotation of the surface to be coated.

[0020] In this embodiment, the surface to be coated is a rotating surface (preferably a rotationally symmetrical surface) on which the weld marks are created in a spiral shape. In one embodiment, the spiral shape is created using circles (with a constant radius over a segment section) with one or more offset jumps. In another embodiment, the spiral shape is approximately an ideal spiral.

[0021] In this embodiment, a further weld track is only applied once a full relative rotation of the surface to be coated has been completed, i.e., the first weld track has already completed a complete revolution on the surface to be coated. As already mentioned above, a further weld track is then applied to the surface to be coated with a greater overlap than the first weld track itself (preferably with the final overlap).

[0022] It is further proposed in an advantageous embodiment of the method that, analogously to step a. to step d., one or more further welding tracks are applied to the surface to be coated, wherein at least one of the welding tracks forms an overlap with the first welding track which is equal to or greater than 40%, preferably greater than 60%, of the respective track width.

[0023] Here, it is proposed that the additional weld tracks be applied in the same way as the first weld track, with the additional weld tracks being arranged relative to the first weld track in such a way that an overlap with the first weld track or the next adjacent weld track is formed. By now, with appropriate process control, the first weld track and the base body have cooled down sufficiently to create an excellent weld connection between the additional weld track of the first weld track and the surface to be coated. In one embodiment, the overlap is, for example, 80% [eighty percent] or even 90% of the track width.

[0024] In a further advantageous embodiment of the method, it is proposed that a subsequent welding track is only applied after the previously generated welding track has been completely completed. Here, it is proposed that the subsequent welding track is only applied when the previously generated welding track has been completely applied to the surface to be coated. For example, in the case of a spiral-shaped welding track that is applied from radially outside to radially inside or vice versa, the subsequent welding track is only applied to the surface to be coated when this spiral has been applied from the starting point (e.g., radially outside) to the end point (e.g., radially inside) and is thus completed.

[0025] It should be noted that the coating of the surface to be coated is not yet complete with the creation of the first weld line; at least one more weld line still needs to be applied to the surface to be coated. The same applies to the completion of each layer in a multi-layer coating structure.

[0026] In a preferred embodiment, all of the weld traces in the final state form a complete coverage of the surface to be coated. Alternatively, a desired (partial) coverage of the surface to be coated is achieved. In both embodiments, a partial coverage of the surface to be coated is created by the first weld trace, in such a way that the remaining partial surfaces are covered by the at least one subsequently applied weld trace. A desired overlap of all of the weld traces is taken into account. It should be noted that part of the surface to be coated is not necessarily still visible if not all of the weld traces necessary for a desired overlap have yet been applied.

[0027] It is further proposed in an advantageous embodiment of the method that steps a. to d. are carried out several times simultaneously to simultaneously produce a plurality of first welding tracks, wherein the simultaneously produced first welding tracks in step d. are produced without overlapping with themselves and with an overlap with each other of less than 10% of the track width or without overlapping on the surface to be coated.

[0028] In this embodiment of the method, a plurality of laser optics are provided, which are configured to simultaneously generate multiple weld tracks on the surface to be coated. Such simultaneously generated weld tracks are referred to herein as first, second, and subsequent weld tracks, respectively, according to their chronological sequence. It should be noted that the respective weld tracks with the same ordinal number do not necessarily have to begin and be applied at exactly the same time, nor do they have to be spatially adjacent to one another. Nevertheless, during simultaneous generation, there is a period of simultaneous generation of sections of the weld tracks with the same ordinal number.

[0029] In the case of spiral-shaped weld tracks, for example, the first weld tracks are applied radially offset from one another without overlapping with the immediately adjacent one or with a slight overlap (for example, less than 10% [ten percent]) on the surface to be coated. In one embodiment, the weld tracks of the same ordinal number are applied offset from one another (by, for example, 90° [ninety degrees of 360°]) on the surface to be coated and have the same overall length from the starting point to the end point. Alternatively, the weld tracks begin differently offset from one another and / or have a different length between their respective starting point and end point. In one embodiment, all weld tracks created on the surface to be coated have the same length between the starting point and the end point.In one embodiment, a weld trace is applied only over a partial section (for example in a dead end formed by previous weld traces or subsequently formed weld traces).

[0030] It is further proposed in an advantageous embodiment of the method that a distance between two adjacent sections of the first welding track produced by means of the method is equal to or greater than twice, preferably three times, the difference between the track width and the desired overlap of welding tracks in the final state of the coated surface.

[0031] Here, it is proposed that, regardless of the number of initial weld tracks (see previous description), the distance between the initial weld tracks be twice the difference between the track width and the desired overlap of all weld tracks, which corresponds to the final state (of the respective layer) of the surface to be coated. Alternatively, the distance is greater than twice, preferably exactly three times, or even a factor greater than three times. In a preferred embodiment, the respective factor is an integer and corresponds to the number of weld tracks in the final state.

[0032] It should be noted at this point that, in the case of a plurality of initial weld marks and subsequent weld marks, as described above, the ordinal number also refers to their simultaneous creation, i.e., the time of creation. It should be noted that the desired minimal overlap of the initial weld mark with itself and the desired final overlap of all weld marks determine the number of successively applied weld marks, provided that these, like the initial weld mark, are also to be created consecutively.

[0033] In an embodiment with a single first welding track, the distance to the generated adjacent section of the same first welding track is defined. In an embodiment with multiple first welding tracks, the distance to the generated adjacent section of the next adjacent first welding track is defined. In a rotational base body, the distance is defined in the radial direction to the axis of rotation. In a meandering course of the welding track, the distance is defined transverse to the center line or longest extension of the respective welding track, for example between two sections of the welding track which run parallel to one another in an x-direction and whose track width extends in the y-direction. A transverse connection between the parallel sections of the meander has no distance to another transverse connection, and another has at least no smaller distance.It should be noted that a non-spiral weld track does not necessarily form a meander. Alternatively, several weld tracks, preferably running parallel to one another (e.g., curved, jagged, and / or wavy), are formed, preferably applied simultaneously to the surface to be coated using a plurality of laser optics.

[0034] It is further proposed in an advantageous embodiment of the method that the surface to be coated is cooled during or after step d., preferably by means of air cooling and / or activated heat conduction.

[0035] In this embodiment, in addition to cooling the generated welding track due to the time delay until the next welding track (overlapping by equal to or more than 10% of the track width) is generated, active cooling is used, namely air cooling (i.e., convection) and / or activated heat conduction. This activated heat conduction not only utilizes material conduction, but also actively dissipates the heat within the material via a fluid. Such an activated heat conduction is formed, for example, by a so-called heat pipe, in which an enclosed coolant evaporates at the end providing cooling and liquefies again at the end dissipating heat.Alternatively or additionally, a cavity or a line for a circulating liquid and / or a coolant is formed in a component of the laser coating device (for example the workpiece holder).

[0036] In a further advantageous embodiment of the method, it is proposed that the base body be that of a brake disc, with a friction surface being formed on the surface to be coated. In this embodiment, the base body is that of a brake disc, for example, a cast body, on whose surface (to be coated) a friction surface is created by means of a coating. For example, such a brake disc is designed for a motor vehicle and has an inner and an outer friction surface, each of which is designed to interact with a brake pad.

[0037] According to a further aspect, a laser coating device is proposed, comprising at least the following components:

[0038] - a laser optic;

[0039] - a feeding device for feeding welding filler material;

[0040] - a workpiece holder for holding a base body with a surface to be coated; and

[0041] - an actuator device for moving the laser optics, and preferably the feed device, relative to a base body received in the workpiece holder, wherein the laser coating device is configured to carry out a method according to an embodiment as described above, wherein the laser coating device is preferably configured for extremely high-speed laser deposition welding.

[0042] The laser coating device is a selective laser deposition welding machine, a laser spraying machine for thermal coating, or a laser welding machine, for example for deposition welding, preferably for the aforementioned extremely high-speed laser deposition welding [EHLA]. The coating, for example for surface finishing, is carried out using a material that is supplied as a welding filler material in the form of a wire, (liquefied) droplet, or (solid) powder via the feed device. The welding filler material is liquefied or kept in liquid form by means of the laser light of the laser optics, i.e., melted or only partially melted on the outside and / or introduced into a molten pool formed by the laser light in the surface to be coated, thus bonding it to the surface to be coated at the atomic or molecular level.

[0043] The laser optics are fed from and / or comprise one or more laser sources. The laser beam or the multiple laser beams of the laser optics are bundled onto one or more laser focuses, wherein the energy density (intensity) for the desired (maximum) thermal input is preferably present only in this area when, controlled by a control device, a predetermined power limit or more power is emitted by means of the laser optics. The laser focus has a spatial extent, for example with a diameter (in a plane parallel to the surface to be coated) of 1 mm [one millimeter] to 12 mm, for example from 1.2 mm to 8 mm, particularly preferably from 3 mm to 4 mm. It should be noted that the area depends on the power of the laser beam used and should have an increasing diameter with increasing power for a desired energy density on the surface to be coated.In one embodiment of the coating method executable with the laser coating device, the intersection point or interface between the laser focus of the laser optics and the surface to be coated is formed outside the area of ​​the highest intensity of the laser beam. However, for simplicity, this intersection between the laser beam and the surface to be coated is referred to here as the laser focus, because, at least in laser cladding, this intersection point or interface is effective for melting the filler material or for thermally treating the surface.

[0044] It should be noted that in one embodiment of the coating method, as explained above, the surface to be coated is a surface of the fixed workpiece (i.e., the base body), which in one embodiment is arranged on the workpiece with the surface to be subsequently coated, for example, within the surface to be coated. Such a surface of the fixed workpiece is referred to here for simplicity as the surface to be coated. In another embodiment, the surface of the fixed workpiece is a surface outside of an area to be coated (for the desired function), for example, in the case of a brake disc or a piston, on the continuous and / or identically aligned surface for the respective function, but outside the functional surface, i.e., outside the braking surface or the sliding surface.Alternatively, the surface to be coated with the laser optics is arranged in a section that is not continuous with and / or aligned with the functional surface, but rather, for example, on a surface that is angled and / or offset relative to it. This is, for example, a shoulder or, in the case of a brake disc, its cylindrical outer peripheral surface, and in the case of a piston, one of its cover surfaces. In an advantageous embodiment, the coating method processes a region of the functional surface to be coated.

[0045] The feed device for welding consumables is configured, for example, for wire or powder material. A powder nozzle for transporting powder material for powder buildup welding has one (e.g., lateral) or multiple outlets and / or an annular gap outlet, wherein the powder material is transported by means of a gas stream (e.g., air or an inert carrier gas). The powder material is thus conveyed as a powder stream along a powder trajectory by means of the shape of the at least one outlet and (at least approximately) the speed of the gas stream. A more complex feed device for welding consumables or a more complex gas jet must be referred to as a powder focus.The powder focus is defined, for example, in a design coaxial with the laser beam by a conical arrangement (or extending along an imaginary conical surface) of the plurality of nozzle channels (powder ring as an imaginary ring line through a plurality of points and / or line segments) or by a ring nozzle (circumferential powder ring). Due to the conical structure, the coaxial powder ring tapers concentrically to a powder focus. After passing through the powder focus, the powder gas jet diverges along the propagation direction (of the laser beam). In one embodiment, the powder focus is to be aligned relative to the laser focus. The workpiece holder is designed to clamp, i.e., fix, a workpiece (i.e., the base body), whereby a defined spatial axis, for example, a central rotational axis, of the workpiece can be precisely aligned.Typically, the base body is already finished, except for the coating to be applied or, if necessary, other minor post-processing steps. Precise positioning is therefore necessary. This is preferably supported by a gripper arm and defined gripping surfaces on the workpiece and / or appropriate measuring technology. For example, the workpiece holder includes a detection device for imbalances, whereupon clamping can be corrected or, if balancing of the workpiece has not yet been carried out or may still be added (e.g., within the scope of permissible regulations), at least appropriate material removal or material deposition can be carried out. For a rotating workpiece, the workpiece holder is, for example, a chuck.For a workpiece without a rotational axis or which is unsuitable for rotary machining, the workpiece holder is, for example, a tool table with appropriate fixing elements. The workpiece holder itself is preferably integrated into a fixed, possibly adjustable, machine coordinate system (at least within the scope of an adjustment tolerance).

[0046] The actuator device is designed to position the laser optics (or their laser focus) and, if applicable, the feed device for welding filler material (or their powder focus) relative to the workpiece or its surface to be coated. The actuator device comprises at least one actuator, preferably a plurality of actuators, for translationally and / or rotationally moving the laser optics and, if applicable, the feed device for welding filler material and / or the base body. For example, if a brake disc is used as the base body, the actuator device rotates the brake disc about its axis of rotation (fixed in the workpiece holder) and guides the laser optics and the feed device for welding filler material radially, resulting in an (at least approximately) spiral shape of the application track.In addition, a movement axis aligned perpendicular to the surface of the base body is often provided. This axis is intended for base bodies of different sizes and / or for the possibility of clamping the base body collision-free into the workpiece holder of the device for the laser coating process and / or for convenient maintenance or replacement of the laser optics and the feed device. In a preferred embodiment, the actuator device (per spatial axis) can only be moved with sufficient precision for the coating process, for example, in the range of a few millimeters, preferably from 0.1 mm [one-tenth of a millimeter] to 1 mm.

[0047] The laser coating device is configured to carry out the method for coating a surface of a base body, as described above. In an advantageous embodiment, the laser coating device is configured for the aforementioned extremely high-speed laser deposition welding (EHLA). This combines the high deposition speed with the necessary cooling of the weld tracks, which is beneficial for material pairs that are difficult to weld. In one embodiment, this can also result in time savings compared to conventional deposition methods using EHLA because an intermediary layer, a so-called adhesion layer or buffer layer, can be dispensed with.

[0048] The invention described above is explained in detail below against the relevant technical background with reference to the accompanying drawings, which show preferred embodiments. The invention is in no way limited by the purely schematic drawings, whereby it should be noted that the drawings are not to scale and are not suitable for defining proportions. It is shown in

[0049] Fig. 1 : a laser coating device in a schematic view with a base body;

[0050] Fig. 2: a (rotational) base body in a plan view;

[0051] Fig. 3: a sectional view of a brake disc with weld marks; and Fig. 4: a motor vehicle with brake discs in a schematic plan view. Fig. 1 shows a laser coating device 3 in a schematic view with a base body 4 (i.e., workpiece). The base body 4 is clamped here by means of the workpiece holder 20 of the laser coating device 3 and is, for example, a brake disc 17. For this purpose, the base body 4 has a surface 2 to be coated (upper as shown) and optionally an opposite rear side 22 (lower as shown). In the state shown, a layer can be applied to the surface 2 to be coated for coating 1 the surface 2 of a base body 4. For this purpose, the base body 4 is clamped in a workpiece holder 20 of the laser coating device 3 and held precisely positioned by the latter.In this exemplary embodiment, the workpiece holder 20 is, for example, a chuck with a rigid rotational axis 5, and the base body 4 is aligned coaxially with the rotational axis 5. The rotational axis 5 is thus aligned perpendicularly to the surface 2 to be coated. In the exemplary embodiment shown, the workpiece holder 20 is optionally driven by a rotary drive 23, so that the base body 4 can rotate about the rotational axis 5. The base body 4 can preferably be repeatedly and precisely adjusted to coordinates by the rotary drive 23 according to a coordinate system. In this exemplary embodiment, the rotary drive 23 is part of the actuator device 21.

[0052] As shown, a coating unit 24 of the laser coating device 3 is positioned above the base body 4. The coating unit 24 comprises a laser optics system 6, a control device 25, and a feed device 19. The laser optics system 6 is configured to emit laser light 7 in the form of a laser beam, wherein the power output of the laser light 7 can be controlled by the control device 25. The control device 25 is configured such that the power output of the laser optics system 6 can be raised or lowered in synchronization with the feed movement of the actuator device 21. In this exemplary embodiment, a welding filler material 8 (here purely optionally a powder material) is focused by the feed device 19 in the form of a cone in a powder focus 26.When aligned correctly, the powder focus 26 overlaps with the laser focus 27 of the laser optics 6 just above, with an offset 28, the surface 2 to be coated. The laser optics 6 is formed by a single-beam or multi-beam laser beam (preferably in a protective gas atmosphere). The coating unit 24 shown is configured, for example, for precise high-speed coating using EHLA. As shown, in this exemplary embodiment, a purely optional measuring device 29 (shown here as a camera) is arranged to the left of the coating unit 24, which, for example, transmits data to the actuator device 21 for detecting a point and / or a pattern and the relative position to the machine coordinate system 30 of the laser coating device 3.The coating unit 24 (here purely optionally itself) is movable relative to the base body 4 radially with respect to the rotation axis 5 (feed) by means of a horizontal actuator 31 of the actuator device 21. Furthermore, the coating unit 24 can be moved vertically (i.e., parallel to the rotation axis 5) by means of a vertical actuator 32 of the actuator device 21.

[0053] The coordinate systems shown here are purely optionally represented as Cartesian coordinate systems, with the z-axis pointing upwards in the image plane, the x-axis pointing to the left in the image plane, and the y-axis pointing out of the image plane. The data and the actuator coordinates 33 (here shown purely symbolically in the horizontal actuator 31) of the actuator device 21 are processed in the control device 34 or in a computer 35 (here shown purely schematically with a processor 36 and a memory 37), used for control, and compared with one another. In this exemplary embodiment, an adjustment device 38 is provided (purely optionally), which comprises a first adjustment unit 39, which here acts (indirectly) on the feed device 19 in the horizontal direction in the image plane (i.e., the x-direction or the radial direction relative to the rotation axis 5 of the base body 4) to the laser optics 6.Preferably, the first adjustment unit 39 also includes an adjustment direction out of the image plane (i.e., in the y-direction or in the direction of rotation relative to the rotation axis 5 of the base body 4). Purely optionally, the adjustment device 38 further includes a second adjustment unit 40, by means of which the laser focus 27 can be aligned. This second adjustment unit 40 is shown here acting (horizontally) (preferably also in both the x-direction and the y-direction) on the laser optics 6, preferably directly on the laser focusing lens.

[0054] Fig. 2 shows a (rotary) base body 4, for example a brake disc 17 according to Fig. 1, in a plan view of the surface 2 to be coated, wherein three spiral welding tracks 9, 10, 11 (for example their center lines) are indicated purely schematically for better understanding. Each of the welding tracks 9, 10, 11 begins (or ends) at the outer edge 41 of the base body 4 and ends (or begins) at the inner edge 42. In this schematic representation, the beginning and the end of the equally long welding tracks 9, 10, 11 are offset from one another by 90° [ninety degrees out of 360°]. In order to completely cover the surface 2 to be coated, additional welding tracks must be provided accordingly.

[0055] In a possible interpretation of this representation in accordance with the designation, the welding tracks 9, 10, 11 shown overlap 13 with each other due to their track width 12, which is not shown here (compare Fig. 3). Thus, to completely cover the surface 2 to be coated, at least one further welding track is missing, which in turn begins (or ends), for example, offset by 90° between the third welding track 11 and the first welding track 9.

[0056] In another possible interpretation of this illustration (not in accordance with the designation), the welding traces shown are all first welding traces 9, which were applied simultaneously to the surface 2 to be coated. The further welding traces 10, 11 are then placed (preferably in an analogous manner) between these shown first welding traces 9. It should be noted that here too, in order to completely cover the surface 2 to be coated, at least one further first welding trace 9 is required, which, for example, is again offset by 90° between the welding trace 11 at approximately 9 o'clock in the illustration (referred to here as the third according to the previous interpretation) and the welding trace 9 at approximately 3 o'clock in the illustration (referred to here as the first).

[0057] Fig. 3 shows a schematic sectional view of a brake disc 17 with welding tracks 9, 10, 11 on its surface 2 to be coated. The proportions are not to scale, and the welding tracks 9, 10, 11 and the produced coating 1 are exaggerated. In this exemplary embodiment, a complete (i.e., final) produced coating 1 is already shown on the rear side 22, which is further ground here (purely optionally) and from which a friction surface 18 is formed. On the surface 2 to be coated (the upper one as shown), a first welding track 9 can be seen on the outer edge 41 and three further ones up to the inner edge 42, which preferably belong to a common spiral track (for example, in an analogous manner to that shown in Fig. 2).With a (purely optional approximately 80%) overlap 13, a second welding track 10 is shown adjacently and, in turn, a third welding track 11 is shown overlapping the second welding track 10, which for the sake of clarity are only designated here in the group at the outer edge 41, but are arranged overlapping adjacently in all further sections 15 of the first welding track 9.

[0058] The difference 16 results from the desired overlap 13 and the set track width 12, both of which are purely optional but preferably constant for all welding tracks 9, 10, 11 and over the entire extent of the respective welding track 9, 10, 11. The distance 14 shown between the (here radially) adjacent sections 15 of the respective welding tracks 9, 10, 11 (here purely optionally removed from the center line of the first welding track 9 at the outer edge 41 to the next inner section 15 of the same welding track 9) is a multiple of this difference 16 and is clearly exaggerated. For example, this schematic representation lacks further first welding tracks 9, second welding tracks 10 and third welding tracks 11, which are inserted in the (radial) gap between the shown groups of sections 15 of the three welding tracks 9, 10, 11.Alternatively or additionally, in the final state (as shown on the rear side 22), sufficient additional welding tracks are applied radially adjacent and / or overlapping after the third welding track 11 to completely fill the (radial) gap shown. It should be noted that, for the sake of simplicity, a single-layer coating structure is shown here. Preferably, however, a final coating 1 consists of a plurality of layers, which are preferably applied in a similar manner to the previously applied welding tracks 9, 10, 11.

[0059] Fig. 4 shows a schematic plan view of a motor vehicle 43 with brake discs 17. The motor vehicle 43 has four wheels 44, each pair of wheels 44 arranged opposite one another on a common wheel axle. In this example, each of the wheels 44 has a brake disc 17, with the wheel 44 and brake disc 17 being connected in a torque-resistant manner.

[0060] For example, on each of the two axially opposite sides of the brake disc 17, a coating 1 (see Fig. 3) is applied to the surface 2 of the (rotating) base body 4 to be coated by means of the laser coating device 3 shown in Fig. 1. A pair of brake pads 45 is arranged on each of the brake discs 17, wherein the brake pads 45 are firmly connected to the vehicle body. To decelerate the motor vehicle 43, a respective brake pad 45 is pressed against the respective brake disc 17 (each or individually controlled). The braking energy is largely transferred to the respective brake disc 17 as waste heat, which is why the coating 1 is subjected to high temperatures, high shear loads, and high pressure. This coating 1 must withstand this load.

[0061] With the method for coating a surface proposed here, an improved weld can be achieved with little or no loss of time. List of reference symbols produced coating 34 control device surface to be coated 35 computer laser coating device 36 processor base body 37 memory rotation axis 38 adjustment device laser optics 39 first adjustment unit laser light 40 second adjustment unit welding filler material 41 outer edge first welding track 42 inner edge second welding track 43 motor vehicle third welding track 44 wheel track width 45 brake pad overlap distance between adjacent sections difference brake disc friction surface feed device workpiece holder actuator device back side rotation drive coating unit control device powder focus laser focus offset measuring device machine coordinate system horizontal actuator vertical actuator actuator coordinates

Claims

Patent claims Method for coating (1) a surface (2) by means of a laser coating device (3), the method comprising at least the following steps: a. Providing a base body (4) with a surface (2) to be coated; b. Providing laser optics (6) which are movable relative to the provided base body (4) and by means of which laser light (7) for connecting a welding filler material (8) to the surface (2) to be coated can be provided in a focused manner; c. Moving the surface (2) to be coated relative to the laser optics (6); and d.Providing welding filler material (8) and carrying out a coating process by heating the provided welding filler material (8) by means of laser light (7) from the laser optics (6) to connect a web-shaped first welding track (9) to the surface (2) to be coated, wherein the first welding track (9) has a predetermined track width (12) and comprises provided welding filler material (8), wherein step c. is carried out during a coating process according to step d., characterized in that the first welding track (9) is produced in step d. with an overlap (13) with itself of less than 10% of the track width (12) or without an overlap (13) on the surface (2) to be coated, and a further welding track (10, 11) is applied at the earliest after completion of a relative 360° turn between the surface (2) to be coated and the laser optics (6). Method according to claim 1, wherein in step c.the laser optics (6) rotates around the rotation axis (5) relative to the surface to be coated (2) and radially relative to the rotation axis (5). is moved, and in step d. the first welding track (9) is generated spirally, a further welding track (10, 11) is applied during step d. at the earliest after a full relative rotation of the surface (2) to be coated. Method according to claim 1 or claim 2, wherein, analogously to step a. to step d., one or more further welding tracks (10, 11) are applied to the surface (2) to be coated, wherein at least one of the welding tracks (10, 11) forms an overlap (13) with the first welding track (9), which overlap is equal to or greater than 40%, preferably greater than 60%, of the respective track width (12). Method according to claim 3, wherein a subsequent welding track (10) is applied only after completion of the previously generated welding track (9). Method according to one of the preceding claims, wherein Step a. to step d. are carried out several times simultaneously for the simultaneous production of a plurality of first welding tracks (9), wherein the simultaneously produced first welding tracks (9) in step d. are produced without overlap (13) with themselves and with an overlap (13) with each other of less than 10% of the track width (12) or without overlap (13) on the surface (2) to be coated. Method according to one of the preceding claims, wherein a distance (14) between two adjacent sections (15) of the first welding track (9) produced by means of the method is equal to or greater than twice, preferably three times, the difference (16) between the track width (12) and the desired overlap (13) of Welding traces (9,10,11) in the final state of the coated surface (2). Method according to one of the preceding claims, wherein the surface (2) to be coated is cooled during or after step d., preferably by means of air cooling and / or activated heat conduction. Method according to one of the preceding claims, wherein the base body (4) is that of a brake disc (17), wherein a friction surface (18) is to be formed on the surface (2) to be coated. Laser coating device (3) comprising at least the following components: - a laser optics (6); - a feeding device (19) for feeding welding filler material (8); - a workpiece holder (20) for receiving a base body (4) with a surface (2) to be coated; and - an actuator device (21) for moving the laser optics (6), and preferably the feed device (19), relative to a base body (4) received in the workpiece holder (20), wherein the laser coating device (3) is set up to carry out a method according to one of the preceding claims, wherein the laser coating device (3) is preferably set up for extremely high-speed laser deposition welding.

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