Method and device for laser coating

Abstract

In a method for producing a coated workpiece (110), in at least one coating operation a functional layer (170-1, 170-2) which is rotationally symmetrical with respect to an axis of rotation of the workpiece is applied to at least one surface of the workpiece using laser radiation. For this purpose, the workpiece is set in rotational motion about the axis of rotation (114) thereof, and a laser beam (LS) directed onto the surface is generated, which is guided in a beam direction at an angle of incidence (EW) onto an impingement zone (ZO) in a coating region of the surface. At least one, preferably powdered, filler material is supplied to the laser beam in such a way that the filler material is heated and / or at least partially melted in an interaction zone by laser radiation of the laser beam, and bonds at least partially to heated material on the surface in the region of the impingement zone (ZO). A relative movement between the workpiece (110) and the laser machining head (200) is produced such that the impingement zone passes through all positions within the coating region at least once when the workpiece rotates. A relative orientation between the axis of rotation (114) of the workpiece and an orientation of the laser machining head (200) is changed during at least one angle-change phase of the coating operation by means of control signals of a control unit according to a specification.

Description

[0001] P 62112 WO 10 November 2025

[0002] - 1 - TK

[0003] Method and device for laser coating

[0004] SCOPE OF APPLICATION AND STATE OF THE ART

[0005] The invention relates to a method for producing a coated workpiece in which, in a coating operation, a rotationally symmetric functional layer with respect to a rotational axis of the workpiece is applied to at least one surface of the workpiece using laser radiation, and to a device suitable for carrying out the method.

[0006] A preferred application is the production of coated brake discs. A brake disc is the part of a disc brake that is fixed to the wheel and against which the brake pads, attached to a brake caliper, act to decelerate rotational movement. A brake disc is generally point-symmetrical or rotationally symmetrical about an axis through which the brake disc's axis of rotation passes. A ready-to-use brake disc has a friction ring that surrounds a hub section. The more or less flat surfaces of the friction ring form the actual braking surfaces or friction surfaces, which, in the form of a circular ring, enclose the axis of rotation. The hub section, often cup-shaped, serves to attach the brake disc to a receptacle on the vehicle's wheel hub.

[0007] Brake discs are available in numerous different designs and configurations for a wide range of applications. Many passenger car brake discs are manufactured from a single piece of cast material and feature an inner hub section with a more or less raised axle mounting or hub. Some brake discs, particularly those for commercial vehicles, often have a radial projection or flange with mounting holes for wheel bolts at an axial distance from the disc-shaped section containing the brake ring (see, e.g., US 6161,661 A). EP 1 945828 A1 discloses such a brake disc in which the brake ring is coated on both sides with an annular, wear-resistant functional layer.

[0008] Besides brake discs manufactured from a single piece, there are also multi-part brake discs (built-up brake discs), which can consist essentially of a brake disc hub and a friction ring supported by it (see, e.g., EP 2 245 330 B1). US 7 281 769 B2 discloses a built-up brake disc with a wheel mounting flange (see also, e.g., DE 19647391 A1). The manufacturing process of a coated brake disc comprises one or more coating operations to coat the surfaces of the brake section or the friction ring with a functional layer, which, for example, due to its relatively high mechanical hardness, can have a wear-reducing function. Alternatively or additionally, a corrosion-inhibiting effect may also be present. Often, such functional layers consist essentially of metal or a metal-ceramic composite, e.g.,with embedded carbide. A functional layer can have a single layer or several layers with different properties.

[0009] Functional layers or coatings on brake discs and other components are now frequently produced using laser radiation, for example, by laser cladding. In conventional laser cladding, a component surface is melted using a laser beam, and a filler material, preferably in powder form, is added to the resulting molten pool. The powder is also partially or completely melted in the molten pool, so that after the molten powder material and the surface solidify, a metallurgically bonded, and in particular, melt-metallurgically bonded, material layer is formed. When metallic material is applied, the cladding process is also referred to as "Laser Metal Deposition" (LMD).

[0010] There are numerous proposals for the design of devices for laser coating. DE 102022 208 788 A1 discloses a processing machine for use in the production of coated brake discs. Further examples of such devices are disclosed, for example, in documents EP 3 890 916 A1, DE 102019 134 812 A1, DE 102020 007 581 A1, DE 102021 208263 A1, and DE 102022 116555 A1.

[0011] TASK AND SOLUTION

[0012] Against this background, an object of the invention is to provide a generic method and a generic device that can be used to produce high-quality functional layers or coatings on workpieces with significantly different geometries without requiring complex design modifications. In particular, it should be possible, if necessary, to coat even difficult-to-access sections of the workpiece surface under controllable conditions. To achieve this object, the invention provides a method with the features of claim 1. Furthermore, a device with the features of claim 12 is provided. Preferred embodiments are specified in the dependent claims. The wording of all claims is made clear by reference to the content of the description.

[0013] According to a first aspect, the invention provides a method for producing a coated workpiece in which, in at least one coating operation, a rotationally symmetric functional layer with respect to a rotational axis of the workpiece is applied to at least one surface of the workpiece using laser radiation. Typically, the workpiece has a rotationally symmetric mass distribution with respect to the rotational axis, and the functional layer is rotationally symmetric with respect to this rotational axis. Workpieces with a rotationally symmetric mass distribution are frequently required where the workpiece is rotated about its rotational axis during intended use, possibly at relatively high speeds. A typical example is brake discs for motor vehicles of all kinds.

[0014] To carry out the process, the workpiece is attached to a workpiece spindle of a coating device in such a way that, when the workpiece spindle rotates around its axis of rotation, the workpiece rotates around the workpiece's axis of rotation. A suitable workpiece holding device can be provided on the workpiece spindle for this purpose. To perform the coating operation, a rotational movement of the mounted workpiece around the axis of rotation is generated; thus, the coating is applied while the workpiece is rotating.

[0015] In the laser-assisted coating process, (at least) one laser beam is generated and directed onto the surface to be coated. For this purpose, laser radiation emitted from a laser source is guided by the beam-shaping optics of a laser processing head in a specific direction at a defined angle of incidence onto an impact zone within the coating area of ​​the surface. The coating area is the region of the surface to be provided with the functional layer. Within the scope of this application, the angle of incidence is defined as the angle between the direction of the incident laser beam and a local surface normal in the impact zone.

[0016] The method further comprises the introduction of at least one filler material to the laser beam such that the filler material is heated and / or at least partially melted by the laser beam's radiation within an interaction zone and bonds, at least partially, to the heated workpiece material on the surface, either by fusion or otherwise, in the area of ​​the impact zone. Preferably, a powdered filler material is used. Powder particles enter the laser beam's field of view and are thereby heated, with the heating extending predominantly to or even exceeding the melting temperature, so that the powder particles are at least partially transformed into the molten phase. The interaction zone typically comprises the laser beam's focus region and / or areas of increased laser beam power density near the focus region.The focus area can be located near the surface, similar to conventional laser cladding, so that the majority of the added filler material melts only in the weld pool. It is also possible – similar to the EHLA process – that the interaction zone and / or the focus area is located at a certain distance from the surface, so that at least a portion of the filler material is at least partially melted before contact with the workpiece and, in this molten state, comes into contact with the workpiece surface and / or any weld pool that may be present there, and melts there.

[0017] In this process, a relative movement is generated between the workpiece and the laser processing head in such a way that, with the workpiece rotating, the impact zone gradually passes through all positions or locations of the coating area to be coated at least once.

[0018] Due to the workpiece's rotation, the impact zone moves along a feed path at a feed rate, creating a track of coating material behind it. The motion parameters can be adjusted so that adjacent track sections partially overlap, resulting in a continuous functional layer. This relative movement can be achieved solely by moving the workpiece, particularly by rotating it around its axis of rotation, while the laser processing head remains stationary. It is also possible to stationary the workpiece and move the laser processing head simultaneously. A combination of laser processing head and workpiece movements is also possible.For example, when coating rotationally symmetrical surfaces, the workpiece can be rotated around its axis of rotation and the laser processing head is simultaneously moved radially to the axis of rotation so that a spiral path of the coating material is created.

[0019] A special feature of the process is that the relative orientation between the rotation axis of the workpiece and the orientation of the laser processing head or the beam direction is changed during at least one angle change phase of the coating operation via control signals from a control unit according to a specification.

[0020] According to another aspect of the invention, a device is provided that is structurally suitable for carrying out the method and is configured for this purpose in at least one operating mode. A device of this type has corresponding means for realizing the process steps. As a computer numerically controlled device, it has a programmable control unit that, based on control software, can control the controllable components of the device to realize specific process sequences. The controllable components include at least one workpiece spindle, which is rotatably mounted in a spindle carrier and which can be rotated about its spindle rotation axis by means of a spindle drive controllable via the control unit.The workpiece spindle has a workpiece holding device which is designed such that a workpiece held on the workpiece holding device can be rotated essentially about the axis of rotation of the workpiece when the workpiece spindle is rotated about the spindle rotation axis.

[0021] Furthermore, the device comprises at least one laser processing head, controllable via the control unit, with a steel forming optic for receiving laser radiation from a laser source and generating a laser beam directed onto the surface of the workpiece. The laser beam is aligned so that it can be guided in a specific direction at an angle of incidence onto an impact zone of the surface. Furthermore, devices for feeding at least one additive material to the laser beam are provided in the manner already described. In particular, this additive material can be in powder form. The devices can then accordingly include powder storage and powder conveying devices. The device also comprises a motion system for generating relative motion between the laser processing head and the workpiece in the manner described above.The motion system, controllable via the control unit, comprises one or more drives for generating movements of the driven components and, if necessary, guide systems for guiding these movements. The relative movement should proceed in such a way that, during a coating operation with a rotating workpiece, the impact zone passes through all positions of the coating area at least once.

[0022] In order to be able to carry out the method according to the claimed invention in at least one operating mode, the motion system and the control unit are configured such that, in one operating mode, the relative orientation between the rotational axis of the workpiece and an orientation of the laser processing head can be changed during a coating operation according to a predefined setting. This predefined setting can be implemented by a corresponding program module in the control unit.

[0023] The phrase "during a coating operation" here preferably refers to a period of time in which the laser beam is switched on and additional material is supplied, so that material is applied to the workpiece.

[0024] An angle-change phase often extends over only a fraction of the duration of a coating operation, thus including phases in which the angle (i.e., the relative orientation between the workpiece's axis of rotation and the laser processing head's orientation or beam direction) does not change. However, an angle-change phase can also extend over the entire duration of a coating operation, resulting in a continuous change of the angle.

[0025] This novel functionality creates additional, technically advantageous degrees of freedom for the laser-assisted coating of certain workpiece types.

[0026] Due to the additional degrees of freedom of a controlled movement of the laser processing head, the method and the device can be used for different designs of brake discs and other components without retooling.

[0027] In particular, this creates the possibility of better adapting the local angle of incidence for the impact zones and the resulting coating properties to the shape of the surface to be coated, or of predefining it within certain limits depending on the surface shape. Furthermore, if necessary, difficult-to-access areas of complex workpiece surfaces can be reached more effectively if the relative orientation can be selectively changed during the coating operation.

[0028] According to a further development, the relative orientation is adjustable such that the angle of incidence varies depending on the position of the impact zone. This allows different positions within the coating area to be coated at different angles of incidence. Preferably, the angle of incidence is varied by at least 3 degrees or at least 10 degrees depending on the position of the impact zone within the coating area. The range of change or variation of the angle of incidence can also be larger, for example, 15° or more, 20° or more, possibly up to 30° or up to approximately 40°, and rarely beyond.

[0029] It is quite possible that, at least temporarily, an angle of incidence greater than 20° is set, whereby the angle of incidence may temporarily exceed 25° or 30° and / or be less than 45° or less than 40°. Even larger angles of incidence may also be achieved.

[0030] In some embodiments, the surface of the workpiece to be coated is nominally flat, and the workpiece is attached to the workpiece spindle in such a way that the surface is oriented perpendicular to the spindle's axis of rotation. An example of this variant is the coating of brake discs with an annular coating area.

[0031] The coating area can extend radially from an inner edge to a radially more outwardly located outer edge. The inner edge can lie on the axis of rotation, resulting in a closed circular area being coated, which contains the axis of rotation at its center and is bounded by the outer edge of the coating area. In other cases, for example when coating brake discs, an annular coating area is applied, so that the inner edge of the functional layer lies at a radial distance from the axis of rotation and the outer edge of the functional layer lies at a greater radial distance from the axis of rotation.

[0032] One process variant, particularly useful for coating brake discs, involves varying the angle of incidence during the angle-change phase by continuously or incrementally reducing it from the inner edge to the outer edge of the coating area. Such process variants can be advantageous, for example, when the workpiece geometry near the hub section, such as a flange at the end of the hub section, prevents access to the coating area from above. In such cases, the laser processing head must be tilted significantly relative to the workpiece's axis of rotation to reach the inner edge of the coating area without colliding with the workpiece.

[0033] This variant is based, among other things, on the following considerations. In principle, it is possible for the laser processing head to be oriented with respect to the surface to be coated such that the laser beam is essentially oriented in the normal direction to the surface, i.e., perpendicular to the surface. Devices and methods have also been described in which the laser head is oriented at an angle to the workpiece's axis of rotation such that the beam direction is oblique to the surface normal, with the angle of incidence being, for example, in the range of 3° to 10°. With oblique radiation incidence, the surface normal and the beam direction each define a plane, which is also referred to in this application as the "plane of incidence." This oblique radiation incidence can potentially prevent disturbances to the coating process caused by laser radiation reflected from the surface to be coated.However, once a preset angle of incidence is set, it remains constant throughout the entire coating operation of a flat surface.

[0034] In contrast, according to a further development of the invention, the angle of incidence is deliberately and intentionally varied automatically and controlled by the control unit of the coating device in such a way that different angles of incidence and thus different coating conditions are provided for different radial positions, i.e. for different distances from the axis of rotation, and are then automatically implemented by the device during operation.

[0035] It is quite possible that, at least temporarily, an angle of incidence greater than 20° is set, whereby the angle of incidence may temporarily exceed 25° or 30° and / or be less than 45° or less than 40°. Even larger angles of incidence may be achieved, e.g., up to 50° or more.

[0036] In some embodiments, the beam direction and the local surface normal define a plane of incidence, and when the relative orientation between the workpiece's axis of rotation and the laser processing head's orientation changes, the beam direction always lies in a plane of incidence that is a radial plane of the workpiece. However, this is not mandatory. The tilt can also be oriented tangentially, so that a finite tangential angle exists between a radial plane of the rotating workpiece and the beam direction. A tilt can contain components in both the radial and tangential directions.

[0037] The applications of the claimed invention are not limited to coating brake sections of brake discs and other essentially flat workpiece surfaces. In some embodiments, the surface of the workpiece to be coated is a substantially rotationally symmetric circumferential surface of the workpiece, i.e., a surface that extends radially around the workpiece's axis of rotation. The circumferential surface is preferably designed such that an angle varies between a local surface normal and a radial direction in the axial direction of the workpiece. The workpiece can, for example, be a bearing ring for a rolling element bearing. On the annular base body of the workpiece, a raceway with a concave cross-section for the rolling element(s) is formed in the outer circumferential surface.If the goal is to coat the rolling element raceway, for example to increase the service life of the rolling bearing, a variant of the process and the device can be used. This involves changing the relative orientation between the workpiece rotation axis and the alignment of the laser processing head so that, for example, a thicker and / or stronger coating is applied to the more heavily loaded bottom area of ​​the circumferential groove than to the axially adjacent edge areas of the circumferential groove.However, if necessary, it is also possible to perform the coating operation in such a way that the laser processing head has the same relative orientation with respect to the surface normals of the surface to be coated at all positions over the axially oriented cross-section of the circumferential groove, so that the layer properties of the layer do not vary or hardly vary in the axial direction of the groove, even though work is carried out at different points of impact of the laser beam with different angles of incidence.

[0038] According to a further development, the laser processing head is pivoted about a pivot axis oriented transversely, and in particular perpendicularly, to the beam direction by means of at least one pivot drive in response to control signals from the control unit, in order to change the angle of incidence and / or the relative orientation. The suitability of the device for this method variant can be achieved by mounting the laser processing head pivotably about at least one pivot axis on a frame component of the device, and by including a pivot drive in the motion system for pivoting the laser processing head about the pivot axis in response to control signals from the control unit. Two independent pivot axes can be provided, which are preferably orthogonal to each other.

[0039] A swiveling movement of the laser processing head is also possible by synchronously controlling several machine axes of the motion system (interpolating axes).

[0040] According to a further training, the desired change in the angle of incidence and / or a desired change in the relative orientation is achieved solely by pivoting the laser processing head around a swivel axis. This allows the orientation of the spindle rotation axis to remain constant with respect to the machine coordinate system, so that the design of the workpiece holder and rotation does not need to be modified compared to many conventional designs. Alternatively, it would also be possible to keep the orientation or tilt angle of the laser processing head constant in the machine coordinate system and to make the workpiece spindle bearing pivotable, so that the orientation of the spindle rotation axis (rotation angle) of the workpiece spindle can be changed drive-controlled during the coating operation. It is also possible to adjust both the tilt of the spindle rotation axis in space and / or...within the machine coordinate system, as well as the orientation of the beam direction, can be varied by swiveling the laser head.

[0041] A coating operation can be performed such that during the angle-change phase, only the angle of incidence is changed according to a predefined parameter, while other process parameters, such as the working distance between the laser processing head and the surface to be coated, laser power, powder flow, workpiece spindle speed, and / or track offset, remain unchanged. Theoretically, the layer thickness should increase with a smaller angle of incidence, as efficiency is improved. The energy in the system also changes because the reflection properties change. This can also lead to changes in the powder and / or the melt pool. This can potentially create a gradient layer in which one or more layer properties change continuously as a function of the angle of incidence in the radial direction, for example, the layer thickness, the surface structure of the layer, etc.

[0042] Since the application conditions typically change significantly due to a change in the angle of incidence, influencing the achievable layer thickness and / or other layer properties, a further development provides that at least one compensation operation is performed during the angle change phase under the control of the control unit, which at least partially mitigates or compensates for the influence of the change in the angle of incidence on the layer properties.

[0043] In some applications, the aim is to maintain layer properties as constant as possible across the entire coating area, e.g., across the entire braking section, such as layer thickness. This can be achieved during the angle change phase through suitable compensation measures or operations (one or more in combination). It is also possible to set a profile of layer properties using at least one compensation operation, i.e., specific location-dependent differences in the layer properties. According to a further development, it is provided that during the angle change phase, at least one of the following changes to coating process parameters is carried out in a compensation operation under the control of the control unit:

[0044] (i) a displacement of the laser processing head with a movement component oriented parallel to the beam direction to compensate for fluctuations in the working distance between the laser processing head and the surface to be coated;

[0045] (ii) a change in the focus position of the laser beam along the beam direction; (iii) a radial position change, which is preferably taken into account with the feed movement;

[0046] (iv) a change in laser power that describes the effective power of the laser used for interaction with the filler material;

[0047] (v) a change in the distribution of energy in the laser beam, in particular the energy distribution between the annular outer region and the core region of the laser beam and / or the distribution over two or three offset focal regions (bifocal distribution, trifocal distribution) which may precede or follow the main beam;

[0048] (vi) a change in the quantity of additive supplied per unit of time, in particular a change in the powder mass flow rate;

[0049] (vii) a change in the powder utilization rate, which describes what proportion of the powdered additive material introduced into the laser beam is used for layer formation; (viii) a change in the track offset, which describes the radial distance or offset between two immediately adjacent sections of the track of coating material;

[0050] (ix) a change in the application rate, which indicates the quantity of coating material applied per unit of time when forming a coating material track;

[0051] (x) a change in the application speed, which here corresponds to the feed rate of the path movement along the track of the coating material.

[0052] A process can be designed such that a workpiece passes through the machine or device multiple times at different angles for partial areas of the surface to be coated (e.g., a disc). At least one interruption of the laser beam during the angle change can be provided, followed by a restart of the welding process. Preferably, the "Extreme High-Speed ​​Laser Material Deposition" (EHLA) process or a variant thereof is used to achieve high deposition rates. EHLA is a variant of laser cladding in which the melting of the deposition powder does not occur on the surface of the object to be coated (e.g., brake disc), but rather before the material reaches the surface. This allows relatively thin layers to be produced at relatively high speeds.This method was developed at the Fraunhofer Institute for Laser Technology ILT and the RWTH Aachen University (see DE 102011 100456 A1).

[0053] Other laser-based coating processes can also be used, for example, those that operate without the formation of a melt pool by the laser radiation, where impacting, at least partially molten powder particles fuse directly with the hot, but not yet molten, workpiece surface. It is also possible to perform a complete coating operation using a melt pool.

[0054] According to a further development, the method and the device are used to coat a workpiece in the form of a brake disc, in particular a brake disc for use in the commercial vehicle sector, for example on the brake of a truck (lorry).

[0055] Preferably, the brake disc has a disc-shaped section with an annular coating area and a substantially cylindrical or otherwise rotationally symmetrical inner hub section, which has a radially outwardly projecting flange at an axial distance to the disc-shaped section with the coating area, wherein an outer circumferential surface of the flange has a radial distance to the axis of rotation that is greater than an inner radius RI of the coating to be applied, so that an outer section of the flange partially covers the coating area at an axial distance.

[0056] The method and apparatus can be used, among other things, to coat one-piece brake discs whose workpiece body is made from a single casting. Besides brake discs made from a single piece, there are also multi-part brake discs (built-up brake discs), which can consist, for example, essentially of a brake disc hub and a friction ring supported by it (see, e.g., EP 2 245 330 B1). US 7 281 769 B2 discloses a built-up brake disc with a wheel mounting flange (see also, e.g., DE 19647391 A1). The method and apparatus can be used, among other things, to coat the friction ring of a built-up brake disc before it is joined to the brake disc hub, e.g., by welding.

[0057] BRIEF DESCRIPTION OF THE DRAWINGS

[0058] Further advantages and aspects of the invention will become apparent from the claims and from the description of exemplary embodiments of the invention, which are explained below with reference to the figures.

[0059] Fig. 1 schematically shows an embodiment of a coating machine for producing a coated workpiece by laser-based application of a coating;

[0060] Fig. 2 schematically shows the coating of a brake disc for use in the commercial vehicle sector, for example on the brake of a truck;

[0061] Fig. 3 shows in the upper part a top view of the coated side of a brake disc with two ring zones of different layer properties after completion of a coating operation and in the lower part a vertical section through such a brake disc;

[0062] Fig. 4 shows a schematic diagram to illustrate a selection of possible processing scenarios and the changes in the angle of incidence used;

[0063] Fig. 5 schematically shows a coating operation to create a wear-resistant functional layer on the circumferential concave rolling element raceway of a bearing ring of a rolling bearing.

[0064] DETAILED DESCRIPTION OF THE EXECUTION EXAMPLES

[0065] Figure 1 schematically shows an embodiment of a device 100 for producing a coated workpiece by applying a coating to at least one surface of the workpiece using laser radiation. The device 100 is configured as a coating machine for coating workpieces 110 in the form of brake discs. The term "coating" generally refers to something tangible, namely a functional layer applied by the coating process, which may consist of one or more superimposed layers. The act or process step of coating is also occasionally referred to as coating.

[0066] A brake disc has a base body 112, made, for example, of gray cast iron, with a central hub section 111, which serves to attach the brake disc to a vehicle axle, and an annular brake section 115, which encloses the hub section. The mass distribution of the base body is rotationally symmetrical about the axis of rotation 114 of the brake disc. The brake section has two axially opposite, parallel surfaces 116, 117. These are each to be provided with a coating or functional layer 170 that is rotationally symmetrical with respect to the axis of rotation, the free surface of which, after subsequent grinding, is to serve as the friction surface of the brake disc.

[0067] In this example, the circular braking surfaces on both sides are to be coated using a modification of high-speed laser cladding.

[0068] The coating machine 100 is configured as a numerically controlled rotary transfer machine with two workstations. All functions are implemented via control commands from a control unit 190, which can be located locally (on or next to the machine) or remotely, e.g., in another room.

[0069] The coating machine has a rectangular machine coordinate system (MCS) designated with lowercase letters x, y, and z, featuring a vertical z-axis and horizontal x- and y-axes. These coordinate axes x, y, and z are distinct from the controlled, driven machine axes, whose drives are controlled by the coating machine's control unit 190. These machine axes are designated with uppercase letters. A machine axis can be either a translational or a rotational axis.

[0070] In the example case, the capital letters X, Y, Z each denote translational axes and A, B, C each denote rotational axes with: A: rotation about the x-axis, B: rotation about the y-axis, C: rotation about the z-axis.

[0071] For transporting the brake discs between the workstations, an internal transport system is used with a rotary table or turntable 150, which is mounted on or in the machine base so that its rotation is limited (e.g. over approx. 180°) or unlimited and can be rotated around the vertical axis of rotation by means of a rotary table drive.

[0072] The device has two diametrically opposed workpiece spindles 126, which are supported by the rotatable part of the rotary table and can be rotated about a vertical spindle rotation axis 122 by means of a spindle drive. The speed of the workpiece spindles is infinitely variable. The direction of rotation can also be set via the control system.

[0073] A brake disc is mounted on the workpiece spindle in a horizontal orientation, i.e., with its rotation axis vertically aligned ("turntable arrangement"), and clamped in a rotationally fixed manner such that the rotation axis 114 of the brake disc is coaxial with the spindle rotation axis 122. There are also embodiments in which the workpiece rotation axis is oriented horizontally or obliquely to the vertical.

[0074] On the front side shown on the right in Fig. 1 is a loading and unloading station 130. A brake disc is mounted on a workpiece spindle there. The mounting can be achieved, for example, by clamping it to a workpiece holding device (e.g., a clamping device such as a mandrel) on the workpiece spindle in such a way that the brake disc is clamped or clamped in a rotationally fixed manner and the axis of rotation of the brake disc is coaxial with the spindle's axis of rotation. A rotationally fixed connection to the workpiece spindle can also be achieved by holding the brake disc down or clamping it from above.

[0075] A brake disc loaded in this way is then transported to a processing position in a coating station 120 by rotating the rotary indexing table 150 by 180° clockwise. During the rotation, the rotational speed is already increased so that the brake disc arrives at the processing position at a high speed, possibly at its target speed. In this station, the upper side of the braking section of the brake disc is coated.

[0076] The single-sided coated brake disc is then transported by 180° rotation to the loading and unloading station 130, from where it can be unloaded, for example, by means of a robot or other handling equipment, or manually.

[0077] A brake disc to be coated can then be mounted on the workpiece spindle that is now free, so that, except during changeover times, both workpiece spindles are occupied by brake discs and are each in different phases of processing or coating. The coating of the other side is carried out later in an analogous process on the same or a similar coating machine. It is also possible to set up a coating machine with more than two workstations, e.g., with four workstations (loading and unloading station, first laser processing station for the first side, turning station, and second laser processing station for the second side (see DE 102022208788 A1)).

[0078] The device comprises, at its coating station 120, a laser processing head 200 controllable via the control unit 190, which contains a focusing beam shaping optic 210 that receives laser radiation from a laser source and shapes it into laser radiation LS. This laser radiation is directed in a beam direction 212 at an angle of incidence EW onto an impact zone ZO in the coating section of the surface in a more or less focused form, heating it locally. The angle of incidence is the angle between the beam direction 212 and a local surface normal NOR in the impact zone ZO.

[0079] The device 100 further comprises means 230 for supplying at least one powdered additive material into the area of ​​the emitted laser radiation in such a way that the additive material, supplied in the form of powder jets 233, can be heated and / or at least partially melted by the laser radiation in an interaction zone 222 and, in this state of matter, comes into contact with the surface 116 heated by the laser radiation. The means include a powder feeder 232 for conveying powdered additive material. In the powder feeder 232, the powder is mixed with a gas, in particular an inert gas such as nitrogen or argon, to generate a powder gas stream for conveying the powder. In a distributor component 234, the powder gas stream is distributed into several feed tubes and then flows into the exit-side section of the laser processing head.This device features a multitude of powder guide channels whose longitudinal axes lie on a common conical surface, the apex of which coincides with the optical axis 221 of the beam shaping optics 210. Powder jets emerge from these channels during operation. Alternatively, an annular nozzle can be provided, which directs powder from all sides towards the first laser beam. The laser processing head preferably has shielding gas supply devices for supplying shielding gas to the area of ​​the impact zone ZO. In alternative versions, each injector has its own feeder, or the nozzle is an annular gap nozzle, and the powder is mixed within the annular gap nozzle.

[0080] The device 100 further comprises a motion system 160, controllable via the control unit 190, with several coordinately controllable machine axes for generating a relative movement between the laser processing head 200 and the workpiece 110. The relative movement is designed such that, during a coating operation with the workpiece 110 rotating, the impact zone ZO passes through all radial positions between an inner edge RI and an outer edge RA of the coating section, the impact zone ZO moving in a feed direction at a feed rate along a (spiral) feed path, leaving a track of coating material behind it.

[0081] The entire assembly of the laser processing head 200 is linearly displaceable via the Y-axis (translational machine axis for generating a linear movement in the y-direction using an electric motor, see double arrow Y). A controllable Z-axis enables linear movement in the vertical direction parallel to the rotation axis 112 of the workpiece (or parallel to the z-axis of the machine coordinate system). Furthermore, the laser processing head 200 is mounted on a frame component of the device so that it can pivot about a swivel axis SAX (corresponding to the A-axis) running parallel to the x-axis of the machine coordinate system. The motion system includes a swivel drive 192 (drive of the rotary A-axis) that can be controlled via the controller for pivoting the laser processing head 200 about the swivel axis SAX in response to control signals from the control unit 190.In addition, there is a rotary B-axis with which the laser processing head can be pivoted around a parallel Zury axis oriented swivel axis SAY in a drive-controlled manner.

[0082] Due to its swivel capability, the laser processing head, or rather the direction of the laser beam LS, can be aligned parallel to the workpiece's axis of rotation 112, or tilted at an adjustable angle to the axis of rotation. When swiveling solely via the A-axis, the swivel can occur in a plane perpendicular to the swivel axis SAX and containing the workpiece's axis of rotation 114. This plane is a radial plane of the brake disc. When swiveling via the B-axis, the swivel can occur in a plane perpendicular to the swivel axis SAY. This plane can also contain the workpiece's axis of rotation and is then a radial plane. Alternatively, the swivel plane can be positioned at a distance from the radial plane and is then a tangential plane of the brake disc.

[0083] In other embodiments, the motion system comprises a multi-axis industrial robot, at the end of which the laser processing head is, among other things, pivotably mounted.

[0084] When coating brake discs or other flat workpieces where the coating area is freely accessible from above across its entire radial width from the side of the laser processing head when the workpiece is mounted, the laser processing head is typically tilted slightly to avoid potential problems with reflected laser radiation. For this purpose, the laser processing head 200 is pivoted a few degrees around the pivot axis SAX by the swivel drive 192 before the coating operation begins, for example, by approximately 5° to 10°. This tilt then remains constant.

[0085] However, there are also components with a relatively complex design, such that the coating area is not continuously accessible from above and / or has interfering contours that require a specific orientation of the laser processing head. Fig. 2 schematically shows, as an example, a brake disc 110 for use in the commercial vehicle sector, for example, on the brake of a truck. The brake disc comprises the disc-shaped part that has the surface 116 to be coated. Within the annular coating area, the brake disc has a substantially cylindrical inner hub section 111, which, at an axial distance AX from the disc-shaped section with the brake ring, has a radially outwardly projecting collar or flange 113, which here contains mounting holes for wheel bolts.

[0086] The outer circumferential surface of the flange has a radial distance AR to the axis of rotation 114 that is greater than the inner radius RI of the coating to be applied, so that an outer section of the flange partially covers the coating area at an axial distance. The brake disc can be manufactured in one piece, for example from a cast material, or it can be assembled as a brake disc from several separately manufactured parts.

[0087] Figure 2 illustrates a potential problem when coating such complex workpieces. If the laser processing head 200 is tilted slightly in the usual way, so that the angle of incidence of the laser radiation is in the range of approximately 5° to approximately 10°,

[0088] If the angle of incidence is 20° or higher, and the laser processing head exits at the normally maintained working distance AA to the coating surface, a collision between the laser processing head and the flange section 113 would occur if one were to attempt to coat the entire coating area up to its inner edge RI with the inclined laser processing head (see left inset figure). The currently common angles of incidence are usually in the range of approximately 3° to approximately 20°, rarely higher. Larger angles of incidence, e.g., up to 40° or even up to 45°, can certainly be set, but limitations and quality losses must be expected at larger angles of incidence. These include, for example, more complex reflections, reduced powder efficiency, a more wavy coating surface, more overspray (unused powder), etc.

[0089] The problem that internal areas of the coating area are difficult to access in the undercut region could be solved, for example, by using a laser processing head with angled optics instead of the proven laser processing head (with a straight optical axis). This angled optics would be inserted radially into the space between the disc-shaped section and flange 113 and, by deflecting the laser beam and the powder, ensure that the entire coating area can be coated with the same angle of incidence across its entire radial extent. Such special optics, which can fit into the available installation space or adapt to the contours of the brake disc, are generally available.However, tests have shown that it then seems to be advantageous to work with lower laser powers, so that it can be difficult to produce the coating with the desired properties in terms of homogeneity of the structure, adhesion to the substrate, surface quality, etc.

[0090] One way to avoid such problems would be to tilt the laser processing head so steeply that the area of ​​the inner edge RI could also be coated (see right-hand inset figure, laser processing head with solid lines), and then to coat the entire coating area between the inner edge RI and the outer edge RA at this angle of inclination. However, since the complex structure that requires a higher angle of inclination or angle of incidence is only present in a part of the coating area adjacent to the inner edge RI, limitations resulting from an excessively high angle of inclination would not be necessary across the entire radial width of the coating area.

[0091] The inventors have found that significantly better overall properties can be achieved by operating the coating process in such a way that relatively large angles of inclination or incidence are used in the inner area near the inner edge RI, and that the process then transitions to smaller angles of incidence as soon as this is possible without collision with the workpiece. Since the complex structure, which requires a higher angle of inclination or incidence near the axis of rotation, is only present in a radial sub-region of the component, the associated limitations are only acceptable in this sub-region. In a general formulation, this aspect of the invention therefore provides for the relative orientation between the axis of rotation 114 of the workpiece 110 and an alignment of the laser processing head 200.to change the beam direction during at least one angle-changing phase of the coating operation such that the angle of incidence varies depending on a radial position of the impact zone ZO according to a specification.

[0092] For the exemplary coating process of a truck brake disc, a distinction can be made between the undercut side and the freely accessible side of the brake ring. This distinction can involve various parameters, such as the tilt angle of the laser processing head and the associated angle of incidence. On the freely accessible side (surface 117), parameters optimized for the coating material in the process can be applied across the entire radial width of a friction ring. For example, the tilt angle can be chosen to be relatively steep (e.g., between 3° and 20°), and the other parameters, such as laser power, track offset, application method, etc., can be adjusted. This can positively influence the coating result and the properties of the finished coating 170-1 with regard to layer structure and layer properties.Among other things, relatively low angles of incidence can be used to ensure that the surface of the coating shows no or only slight waviness compared to coatings with larger angles of inclination.

[0093] The side of the friction ring facing the flange (surface 116) with the complex workpiece contour can then be coated with parameters adapted for this task. In the example shown in Fig. 2 (right-hand inset), the laser processing head 200 can be set with such a large tilt angle or angle of incidence EW that the coating 170-2 can be applied up to the inner edge RI at this angle. It is then possible to work with constant tilt angle settings over the entire radius of the coating area using these settings, i.e., with a relatively high angle of incidence. An advantage of this approach would be relatively homogeneous coating properties across the entire radial width of the coating area.However, this approach usually also means that the quality of the entire coating is essentially determined by the quality that can be achieved in the most inaccessible area.

[0094] Another approach is to change the relative orientation between the axis of rotation and the workpiece, or the angle of incidence EW, during the coating operation, at least during one angle-change phase, so that the angle of incidence EW becomes a function of the radial position of the corresponding impact zone. In other words, different tilt angles can be set for different radial ranges by controlling at least one of the swivel drives during the coating operation to change the tilt of the laser processing head 200. This is shown schematically in the right-hand part of Fig. 2. The solid line shows the laser processing head at maximum tilt (corresponding to the largest angle of incidence EW required here), while the dashed line represents the same laser processing head coating impact zones located further out.Here, the laser processing head is angled much more steeply, so that the usual angles of incidence can be used, for example in the range of approximately 3° to approximately 20°.

[0095] The change in the tilt angle of the laser processing head 200 or the change in the angle of incidence of the laser during the coating operation has the consequence in the design of the motion system of the laser processing machine that the working distance AA, i.e. the distance measured along the beam direction of the laser beam between the exit of the laser processing head and the coating surface, also changes with the tilt angle, because the laser processing head is in principle pivoted around the pivot axis and accordingly the exit describes a circular path which moves away from the surface to be coated as the tilt angle increases.

[0096] Preferably, compensation measures (one or more in combination) are provided to achieve relatively small fluctuations in layer quality despite different tilt angles. In particular, distance compensation can be provided in which an axial relative position between the laser processing head 200 and the workpiece 110 is changed synchronously with the tilt of the laser processing head so that the laser processing head is raised or lowered parallel to the z-axis to optimize the working distance AA for each tilt angle. Additionally, adjustment of the horizontal position and / or speed can be provided.

[0097] Alternatively or additionally, it is also possible to vary the effective laser power depending on the radial position of the impact zone, for example, by changing the laser power proportionally or at least in the same direction as the working distance AA, i.e., increasing it when the working distance increases. Alternatively or additionally, the amount of filler material supplied per unit time can also be varied. The compensation measures (one or more) can be carried out continuously from a specific starting point or in stages.

[0098] To illustrate a possible design of a coated brake disc 110, Fig. 3 shows in the upper part a top view of the coated side of the brake disc after completion of the coating operation and in the lower part a vertical section. The coating area was produced in a single coating operation. Starting from the inner edge RI, a first annular zone R1 with a first radial width and first layer properties was produced, and immediately adjacent to it, a second annular zone R2 with a second radial width and second layer properties was produced. The annular zones merge directly into one another in the radial direction, so that a continuous coating 170 is created in the radial direction. In this example, the inner annular zone R1 was produced with a larger angle of incidence EW1 than the outer annular zone. The angle of incidence remained constant within each annular zone.As a result, the finished brake disc in this example may have an inner ring zone with a slightly greater layer thickness than the outer ring zone. These differences in layer thickness can be leveled out during a subsequent grinding operation.

[0099] It would also be possible to create a gradient layer in which the angle of incidence is continuously changed from a first value at the inner edge to a second value at the outer edge. The resulting coating would then have continuously varying layer properties in the radial direction.

[0100] It is also possible to control the coating process so that, when coating both sides of a workpiece section, the layer thicknesses differ between the top and bottom surfaces. This can be used, for example, to specifically counteract workpiece deformation caused by the coating process and the associated heat generation. The parameters for the top and bottom surfaces can be set independently.

[0101] The process is often carried out in such a way that the layer properties are essentially the same throughout the coating area, so that, for example, the same specific layer thickness is present everywhere. This can be specified as a target parameter during programming.

[0102] To illustrate a selection of possible processing scenarios and the changes in the angle of incidence used, Fig. 4 shows a schematic diagram where the radial position RPOS, i.e., the radial distance of the impact zone from the tool's axis of rotation, is plotted on the X-axis, and the corresponding angle of incidence EW is plotted on the Y-axis. The coating area begins at the inner edge RI, radially away from the axis of rotation (RPOS = 0), and ends radially outward at the outer edge RA. In the example cases, the process parameters are coordinated so that the impact zone progresses along its intended helical path at a constant feed rate. For this purpose, the workpiece rotational speed and the Y-axis feed rate for the radial movement are coordinated; the powder flow should remain largely constant.

[0103] Curve K1 represents a case similar to the one described, where, starting from the inner edge RI, the beam direction or the laser processing head is initially steeply inclined to avoid a collision with the flange section of the brake disc. The position of the switching radius RU is calculated such that, starting from this radial position, the laser processing head can be optimally positioned with a small inclination relative to the surface without colliding with the workpiece. Accordingly, a constant angle of incidence, smaller than in the inner area, is used continuously between the switching radius and the outer radius RA. This allows for the creation of two nested ring zones, each with constant layer properties within its own ring zone. The layer properties of the ring zones can differ from one another.A process can also be controlled in such a way that different generating properties are used, but the quality of the layer properties is the same or very similar.

[0104] Similar scenarios can also be used in the coating of workpieces, where the change in inclination is not chosen for collision reasons, but to create, for example, a coating subdivided into two or more ring zones on a flat brake disc.

[0105] Curve K5 shows a variant where the transition between a relatively larger and a relatively smaller angle of incidence does not occur in steps or within a very short time (i.e., abruptly or instantaneously) as in curve K1, but rather relatively slowly during the radial outward movement. The angle-change phase WVP5 lies here temporally between a preceding and a subsequent "constant phase." This refers to a period of the coating operation in which the angle of incidence does not change during the coating process. In the processing operation represented by curve K2, the process starts at the inner edge of the coating area with the largest angle of inclination, which then decreases continuously to progressively lower values, with the angle of inclination asymptotically approaching the final angle of inclination at the outer edge.

[0106] In the coating operation according to curve K3, the angle of incidence is continuously reduced from the inner edge with a uniform rate of change relative to the radial position until it reaches the lowest value, which occurs at the outer edge RA.

[0107] Curve K4 is a simple example of a processing operation where the angle of incidence of the coating operation reaches its smallest value in the region of the inner edge RI and increases linearly outwards with increasing radius. In this way, a gradient layer can be created where the layer properties change essentially linearly from the inside to the outside.

[0108] To further influence the radial profile of the layer properties (including essentially constant layer properties of the entire coating), one or more coating process parameters can be varied during the angle change phase under the control of the control unit, in particular at least one of the following coating process parameters:

[0109] (i) the powder utilization rate, which describes what proportion of the powdered filler material introduced into the laser beam is used for layer formation; (ii) the laser power, which describes what effective power of the laser is used for interaction with the filler material;

[0110] (iii) the spatial distribution of the laser energy within the laser beam or in the impact zone

[0111] (iv) the track offset, which describes the radial distance or offset between two immediately adjacent sections of the track made of coating material;

[0112] (v) the application rate, which indicates the quantity of coating material applied per unit of time when forming a coating material track;

[0113] (vi) the application rate, which here corresponds to the feed rate of the web movement along the track of the coating material. The process parameters can be varied during the angle-change phase with different objectives. For example, the coating can be applied in such a way that the layer thickness remains essentially constant over the entire radial extent despite changes in the angle of incidence.

[0114] If necessary, the coating can be applied in such a way that the thickness of the applied coating material changes in a targeted manner in the radial direction.

[0115] In the embodiments described above, workpieces in the form of brake discs are coated. A brake disc is an example of a workpiece that has a base body with a rotationally symmetric mass distribution about an axis of rotation of the workpiece. Other workpieces can also be coated, e.g., bearing rings for rolling bearings or workpieces with Dic-Othungen running surfaces.

[0116] For illustrative purposes, Fig. 5 schematically shows the processes involved in coating a rolling element raceway of an inner ring for a rolling element bearing. The ring-shaped workpiece 510 is rotationally symmetrical with respect to its axis of rotation 514 and has a circumferential groove 511 with a substantially semicircular cross-section on its outer circumferential surface. In the assembled state of the rolling element bearing, the concave inner surface 516 of the groove serves as the raceway for a rolling element, which here has the form of a ball, but can also assume other shapes. The workpiece is attached to the workpiece spindle 526 of the laser processing device by means of an internal clamping mandrel, with clamping elements of the mandrel bearing against the cylindrical inner surface of the bearing ring.The device includes a laser processing head 600 at its coating station, which can be controlled by a control unit and which may be similar or identical in design and function to the laser processing head of the first embodiment. The axis 612 defines the orientation of the laser processing head and is identical here to the optical axis of the focusing optics. The direction of the laser beam runs parallel to this axis. The motion system of the device is designed such that the laser processing head can be pivoted back and forth about a pivot axis SAX1 over a relatively large angular range of more than 90°, in particular more than 120°, preferably between 140° and 180°, by means of a pivot drive connected to a control unit. The pivot axis SAX1 can be a virtual axis; the laser processing head 600 can, for example, be guided by an arc guide.In this example, the swivel axis SAX1 is located close to the workpiece, between the exit end of the laser processing head and the workpiece surface 516, at or near the center of curvature of the rolling element raceway to be coated. The laser processing head can be tilted by a few degrees (e.g., from 3° to 10°) relative to the swivel plane oriented perpendicular to the swivel axis (out of the drawing plane), so that laser radiation reflected back from the workpiece cannot fall onto radiation-sensitive areas of the laser processing head.

[0117] To produce the coating 570 on the concave inner surface 516 of the groove, the workpiece 510 is set into relatively rapid rotation about its axis of rotation 514 by rotating the workpiece spindle 526. The laser processing head 600 is pivoted slowly back and forth between the reversal points of its swivel range, either once or several times. The orientation of the laser processing head, or rather the orientation of the beam direction (dashed line 612), changes accordingly to the curvature of the rolling element track, such that the angle of incidence remains essentially constant at close to zero degrees across practically the entire width of the concave rolling element track, allowing the entire rolling element track to be coated with essentially the same radiation incidence. The working distance also remains constant.The speed of change of the swivel angle is adapted to the rotational speed of the workpiece so that the tracks with coating material lie close together or partially overlap with an essentially constant track offset, so that a closed functional layer is created.

[0118] After the functional layer has been created, a finishing operation can follow to smooth the initially relatively rough surface of the functional layer to the desired roughness level.

Claims

Patent claims 1. A method for producing a coated workpiece, in which, in at least one coating operation, a rotationally symmetric functional layer with respect to an axis of rotation of the workpiece is applied to at least one surface of the workpiece using laser radiation, the method comprising the following steps: Attaching the workpiece to a workpiece spindle in such a way that, when the workpiece spindle is rotated about its spindle rotation axis, the workpiece is essentially rotated about the axis of rotation; Generating a rotational movement of the workpiece around the axis of rotation; Generating at least one laser beam directed towards the surface, wherein laser radiation emitted from a laser source is guided by a beam shaping optic of a laser processing head in a beam direction at an angle of incidence onto an impact zone in a coating area of ​​the surface, wherein the angle of incidence is the angle between the beam direction and a local surface normal in the impact zone; Supplying at least one, preferably powdered, additive material to the laser beam in such a way that the additive material is heated and / or at least partially melted in an interaction zone by the laser radiation of the laser beam and at least partially bonds with heated material on the surface in the area of ​​the impact zone; Generating a relative movement between the workpiece and the laser processing head such that the impact zone passes through all positions within the coating area at least once when the workpiece is rotating, characterized by the following step: Changing the relative orientation between the rotation axis of the workpiece and the alignment of the laser processing head during at least one angular change phase of the coating operation via control signals from a control unit according to a specification.

2. The method according to claim 1, characterized in that the relative orientation between the axis of rotation of the workpiece and an orientation of the laser processing head is changed such that the angle of incidence varies depending on the position of the impact zone in the coating area, wherein preferably the angle of incidence varies by at least 5 degrees or at least 10 degrees and / or an angle of incidence of more than 20° is set at least in phases, wherein the The angle of incidence is, at times, more than 25° or more than 30° and / or less than 45° or less than 40°.

3. Method according to claim 1 or 2, characterized in that the surface of the workpiece to be coated is a nominally flat surface and the workpiece is attached to the workpiece spindle in such a way that the surface is aligned perpendicular to the spindle rotation axis.

4. Method according to one of the preceding claims, characterized in that the workpiece is a brake disc with an annular coating area extending radially from an inner edge to a radially more outward outer edge, and that the relative orientation is changed such that the angle of incidence varies depending on a radial position of the impact zone within the coating area according to a specification.

5. Method according to claim 4, characterized in that the angle of incidence is varied during the angle change phase in such a way that the angle of incidence is reduced continuously or in steps from the inner edge to the outer edge of the coating area.

6. Method according to claim 1 or 2, characterized in that the surface of the workpiece to be coated is a substantially rotationally symmetric circumferential surface of the workpiece, wherein preferably an angle between a local surface normal and a radial direction varies in the axial direction of the workpiece, wherein preferably the workpiece is a bearing ring for a rolling element bearing and a raceway for rolling elements with a concave cross-section is formed on an outer circumferential surface, wherein preferably the relative orientation between the workpiece rotation axis and the coating operation is carried out such that the laser processing head has the same relative orientation with respect to the surface normal of the surface to be coated at all positions over the axially oriented cross-section of the circumferential groove.

7. Method according to one of the preceding claims, characterized in that the laser processing head is oriented transversely, in particular perpendicularly to the beam direction, by means of a swivel drive to change the angle of incidence and / or to change the relative orientation in response to control signals from the control unit. The pivot axis is pivoted, preferably while the orientation of the workpiece's axis of rotation remains unchanged.

8. Method according to one of the preceding claims, characterized in that the beam direction and the local surface normal define a plane of incidence, and that when changing the relative orientation between the axis of rotation of the workpiece and the orientation of the laser processing head, the beam direction always lies in a plane of incidence which is a radial plane of the workpiece.

9. Method according to one of the preceding claims, characterized in that during the angle change phase, at least one compensation operation is performed under the control of the control unit, which at least partially compensates for the influence of an angle change on the layer properties, in particular such that layer properties remain essentially constant over the entire coating area.

10. Method according to one of the preceding claims, characterized in that during the angle change phase, at least one of the following changes to coating process parameters is carried out in a compensation operation under the control of the control unit: (i) a displacement of the laser processing head with a movement component oriented parallel to the beam direction to compensate for fluctuations in the working distance between the laser processing head and the surface to be coated; (ii) a change in the focus position of the laser beam along the beam direction; (iii) a radial position change, which is preferably taken into account with the feed movement; (iv) a change in laser power that describes the effective power of the laser used for interaction with the filler material; (v) a change in the distribution of energy in the laser beam, in particular the energy distribution between an annular outer area and a core area of ​​the laser beam and / or the distribution over two or three focal areas offset from each other; (vi) a change in the quantity of additive supplied per unit of time, in particular a change in the powder mass flow rate; (vii) a change in the powder utilization rate, which describes what proportion of the powdered additive material introduced into the laser beam is used for layer formation; (viii) a change in the track offset, which describes the radial distance or offset between two immediately adjacent sections of the track of coating material; (ix) a change in the application rate, which indicates the quantity of coating material applied per unit of time when forming a coating material track; (x) a change in the application speed, which here corresponds to the feed rate of the path movement along the track of the coating material.

11. Method according to one of the preceding claims, characterized in that a workpiece in the form of a brake disc is coated, in particular a brake disc for use in the commercial vehicle sector, preferably on the brake of a truck, wherein preferably the brake disc has a disc-shaped section with an annular coating area and a substantially cylindrical or otherwise rotationally symmetrical inner hub section, which has a radially outwardly projecting flange at an axial distance to the disc-shaped section with the coating area, wherein an outer circumferential surface of the flange has a radial distance to the axis of rotation which is greater than an inner radius of the coating to be applied, so that an outer section of the flange partially covers the coating area at an axial distance.

12. Device (100) for producing a coated workpiece by applying a rotationally symmetric functional layer to a coating section of at least one surface of the workpiece (110) comprising using laser radiation; a control unit (190); at least one workpiece spindle (126) which is rotatable about a spindle rotation axis (122) by means of a spindle drive controllable via the control unit and has a workpiece holding device which is designed such that a workpiece (110) received on the workpiece holding device is rotatable about the rotation axis (114) of the workpiece when the workpiece spindle is rotated about the spindle rotation axis; at least one laser processing head (200) controllable via the control unit (190) with a beam shaping optic (210) for receiving laser radiation from a laser source and for generating a beam onto the surface (116) of the workpiece directed laser beam (LS) such that the laser beam can be guided in a beam direction (212) at an angle of incidence (EW) onto an impact zone (ZO) of the surface (116), wherein the angle of incidence is the angle between the beam direction (212) and a local surface normal (NOR) in the impact zone (ZO); Devices (230) for supplying at least one, preferably powdered, additive material to the laser beam (LS) under control by the control unit (190) such that the additive material is heated and / or at least partially melted in an interaction zone (222) by laser radiation of the laser beam; a motion system (160) controllable via the control unit (190) for generating a relative movement between the laser processing head (200) and the workpiece (110) such that the impact zone (ZO) passes through all positions of the coating area at least once during a coating operation with a rotating workpiece, characterized by the fact that the motion system (160) and the control unit (190) are configured such that in an operating mode a relative orientation between the rotation axis (114) of the workpiece and an orientation of the laser processing head (200) can be changed during a coating operation according to a specification.

13. Device according to claim 12, characterized in that the laser processing head (200) is pivotably mounted on a frame part of the device about at least one pivot axis (SAX, SAY) and the motion system comprises a pivot drive (192) for pivoting the laser processing head about the pivot axis in response to control signals from the control unit (190).

14. Device according to claim 12 or 13, characterized in that the control unit (190) is configured such that the device performs a method according to one of claims 1 to 11 in the operating mode.

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