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EP-4493351-B1 - METHOD TO PRODUCE A COATED BRAKE DISC USING MULTI-LASER HEADS

EP4493351B1EP 4493351 B1EP4493351 B1EP 4493351B1EP-4493351-B1

Inventors

  • SPATZIER, Joerg
  • COSKUN, Mehmet, Kemal
  • ZIKIN, Arkadi
  • NAJAFI, HOSSEIN

Dates

Publication Date
20260506
Application Date
20230307

Claims (3)

  1. A method to produce a coated brake disc, the method comprising the steps of: - providing a brake disc with a first and a second friction surface, - coating at least part of the first friction surface by a laser cladding process, wherein for the laser cladding process at least three laser and processing heads are used and at least during part of the laser cladding process the laser and processing heads are used simultaneously at different locations of the first friction surface, characterized in that during at least part of the laser cladding process the brake disc is rotated around its rotation axis and the distance of the lasers and processing heads to the rotation axis at the beginning of the part of the process is chosen to be the same and then the distance is simultaneously changed in such a manner that at any time within the part of the laser cladding process each one of the at least three laser and processing heads has the same distance to the rotation axis as the others of the at least three laser and processing heads.
  2. The method according to claim 1, characterized in that the angular position of the lasers and processing heads is described as φ i for i = 1 … n and that the lasers and processing heads are positioned in such a way that the following condition is fulfilled: φ i = φ 1 − 2 π ⋅ i − 1 / n for i = 1 … n if n is the number of the lasers and processing heads.
  3. The method according to claim 2, characterized in that the deposition start of the i th laser and processing head is delayed until the brake disc is rotated by an angle of 2 π ⋅ i − 1 / n

Description

The present invention relates to a method for layer cladding of friction surfaces of brake discs with more than one laser and processing heads (LPH) performing the cladding process simultaneously at different locations on the same friction surface, according to the preamble of claim 1 (see for example DE 10 2019 132191 A1). Requirements driven by the market to increase the life time of brake discs together with tightening fine dust emissions regulations, as one of the main pollution elements in the vehicle is the braking system (disc and pad), have led to an increasing demand for brake discs with a durable corrosion resistance and reduced fine dust emissions to the environment. A method to increase wear and corrosion resistance and to reduce fine dust emissions of brake discs is to apply a corrosion and wear resistant coating onto the friction surfaces of brake discs. The coating applied to these surfaces combines the advantageous properties of cast iron as a base material, like affordability, good thermal conductivity and mechanical stability at high temperatures with the benefits of the coating like increased corrosion and wear resistance compared to the base material. A prior art approach as outlined in EP1336054A1 reveals a brake disc coated with a metallic non-ceramic coating that shows higher oxidation and wear resistance than the cast iron core, the process being used for the coating is plasma-, flame- or wire-coating. As described in DE102014006064A, the application of a cermet coating, consisting of a metallic matrix with oxide-ceramics, on the friction surface further improves corrosion and wear resistance. In order to overcome issues with infiltration corrosion, the application of a nitride-, carbide- and oxide-layer in between the brake disc substrate and the functional top coating can be applied. Furthermore, an intermediate Nickel-based layer to improve the adhesion of the functional top coating may be applied using thermal spray. One of the challenges with thermally sprayed coatings on cast iron brake discs is that the graphite in form of lamellae and/or spherical particles present at the surface to be coated leads to a low adhesion of the coating as well as water dissipating through the coating or in between the brake disc substrate and the coating leads to rust. Both effects may eventually lead to delamination of the coating. In order to overcome this, WO2022003189A1 reveals that by using a laser cladding process for coating iron-based substrate materials containing graphite, such as brake discs, graphite lamellae and/or spherical particles on the surface of the substrate can be melted or even evaporated during the coating process. However, graphite particles melting or evaporation during the laser cladding process lead to local defects and locally reduced adhesion. Subsequently the application of an angle ranging from 10° and 45° between an axis perpendicular to the substrate surface and the laser beam is revealed. The advantage of this approach is that on one hand, the adhesion of the coating on the substrate can be increased and on the other hand, laser power levels and thus deposition rates can be increased compared to a process using a laser beam being perpendicular to the substrate to be coated. As the deposition rates and thus the time to coat a brake disc friction surface are primarily related to the power of the laser, the application of a bond-coat and a protective layer using a high-speed and high-power laser is proposed in another prior art approach. With this approach, processing times of below 110 seconds for the laser cladding of a whole brake disc of a standard size (outer diameter 288 mm; inner diameter 163 mm) can be achieved. To be able to achieve that, high-power lasers of with a power of over 20 kW are required. Using high-power lasers is therefore a reasonable way to scale up the laser-cladding process of brake discs for mass production scenarios. However, the usage of a high-power laser results in a harm of optical components and the nozzle due to reflection of heat back to the laser and process head. This has a negative impact on the component lifetime and process stability in terms of powder feed rate to the part.. In addition to this, the high power of the laser beam may lead to a deformation of the brake disc due to thermal effects. Reducing the power of the LPH on the other hand would increase the laser cladding process time to clad a standard brake disc surface. The application of the coating using laser cladding on a friction surface of a brake disc can be performed with the LPH moving radially from the axis of the brake disc towards the outer diameter of the friction surface whilst at the same time the brake disc is rotated around its centerline. In this case, the spot of the laser beam describes a spiral on the surface to be coated. In order to produce a smooth surface an overlap between adjacent lines of coating has to be implemented. If for example the widt