DE-102024133042-A1 - Method and device for laser coating

DE102024133042A1DE 102024133042 A1DE102024133042 A1DE 102024133042A1DE-102024133042-A1

Abstract

In a method for producing a coated workpiece (110), a rotationally symmetric functional layer (170-1, 170-2) with respect to a rotational axis of the workpiece is applied to at least one surface of the workpiece in at least one coating operation using laser radiation. For this purpose, the workpiece is set into a rotational movement about its rotational axis (114), and a laser beam (LS) directed towards the surface is generated. This laser beam is guided in a beam direction at an angle of incidence (EW) onto an impact zone (ZO) in a coating area of the surface. At least one, preferably powdered, additive material is supplied to the laser beam such 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 bonds at least partially with heated material on the surface in the area of the impact zone (ZO). A relative movement between the workpiece (110) and the laser processing head (200) is generated such that, with the workpiece rotating, the impact zone passes through all positions within the coating area at least once. The relative orientation between the rotation axis (114) of the workpiece and an orientation of the laser processing head (200) is changed during at least one angular change phase of the coating operation via control signals from a control unit according to a predefined setting.

Inventors

Bernd Nagel
Claus-Ulrich Lott
Johannes Lintner

Assignees

NAGEL TECHNOLOGIES GMBH

Dates

Publication Date: 20260513
Application Date: 20241112

Claims (14)

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, the method comprising the following steps: fixing the workpiece to a workpiece spindle such that, when the workpiece spindle is rotated about its spindle rotational axis, the workpiece is substantially rotated about the rotational axis; generating a rotational movement of the workpiece about the rotational axis; 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; Feeding at least one, preferably powdered, additive material to the laser beam such 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 a relative orientation between the axis of rotation of the workpiece and an orientation 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.
Procedure 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 a 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 that at least in phases an angle of incidence of more than 20° is set, wherein the angle of incidence is in phases more than 25° or more than 30° and/or less than 45° or less than 40°.
Procedure 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.
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.
Procedure 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.
Procedure 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.
Method according to one of the preceding claims, characterized in that the laser processing head is pivoted by means of a swivel drive in response to control signals from the control unit about a swivel axis oriented transversely, in particular perpendicular to the beam direction, in order to change the angle of incidence and/or to change the relative orientation, wherein preferably the orientation of the rotation axis of the workpiece remains unchanged.
A method according to one of the preceding claims, characterized in that the The beam direction and the local surface normal define a plane of incidence, and when changing the relative orientation between the rotation axis of the workpiece and the orientation of the laser processing head, the beam direction always lies in a plane of incidence that is a radial plane of the workpiece.
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.
A method according to one of the preceding claims, characterized in that during the angle change phase, in a compensation operation under the control of the control unit, at least one of the following changes to coating process parameters is carried out: (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 the laser power, which describes which effective power of the laser is used for the interaction with the additive 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 offset focus areas; (vi) a change in the amount of additive material supplied per unit 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 filler 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 deposition rate, which indicates what quantity of coating material is applied per unit of time when forming a coating material track; (x) a change in the deposition speed, which here corresponds to the feed rate of the path movement along the track of the coating material.
A 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.
Device (100) for producing a coated workpiece by applying a rotationally symmetrical functional layer to a coating section of at least one surface of the workpiece (110) using laser radiation, comprising: a control unit (190); at least one workpiece spindle (126) rotatable about a spindle rotation axis (122) by means of a spindle drive controllable via the control unit and comprising a workpiece holding device designed such that a workpiece (110) received on the workpiece holding device is rotatable substantially 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 laser beam (LS) directed onto the surface (116) of the workpiece 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 feeding 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 in an interaction zone (222) by laser radiation of the laser beam and/or at least partially melted; 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 in 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.
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).
Device according to Claim 12 or 13 , characterized in that the control unit (190) is configured such that the device in the operating mode performs a method according to one of the Claims 1 until 11 executes.

Description

SCOPE OF APPLICATION AND STATE OF THE ART 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. 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 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. Brake discs are available in numerous different designs and configurations for a wide range of applications. Many brake discs for passenger cars 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, for example, [reference to relevant example]). US 6 161 661 A ). The EP 1 945 828 A1 such a brake disc is revealed in which the brake ring is coated on both sides with an annular wear-resistant functional layer. Besides brake discs made from a single piece, there are also multi-part brake discs (built brake discs), which can essentially consist of a brake disc hub and a friction ring supported by it (see, for example, [reference]). EP 2 245 330 B1 ). The US 7 281 769 B2 reveals a constructed 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 apply a functional layer to the surfaces of the brake section or friction ring. This layer, for example, can have a wear-reducing function due to its relatively high mechanical hardness. Alternatively or additionally, it can also provide corrosion protection. Such functional layers often consist primarily of metal or a metal-ceramic composite, e.g., with embedded carbide. A functional layer can consist of a single layer or multiple layers with different properties. 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). There are numerous proposals for the design of devices for laser coating. DE 10 2022 208 788 A1 discloses a processing machine for use in the manufacture of coated brake discs. Further examples of such devices are found, for example, in the documents EP 3 890 916 A1 , DE 10 2019 134 812 A1 , DE 10 2020 007 581 A1 , DE 10 2021 208 263 A1 or DE 10 2022 116 555 A1 revealed. TASK AND SOLUTION 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 controlled conditions. To solve this problem, 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. 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 th