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EuroBrake 2022: Rotor coatings session overview

The Rotor coatings session will take place on Tuesday May 17th and will be chaired by Matthias Leber of Porsche AG and David Bryant of University of Bradford.

Topics and speakers for the session include:

Serial process development and industrialization of laser-based hard coated brake discs

Phillip Utsch, HPL Technologies GmbH (WECODUR)

Brake discs play a significant role in converting the vehicle’s kinetic energy into heat energy that is dissipated through conduction and convection. The automotive industry has been looking for many years to develop lightweight brake discs to reduce vehicle weight and subsequently improve fuel efficiency.

In addition, the reduction of particulate emissions from the braking system is becoming a target, not least due to the more stringent emission regulations worldwide. In recent years, metal matrix composite (MMC) coatings for rotors have been reported to be a sustainable solution for those issues.

Besides technological issues, the problem of a reproducible, cost-efficient coating and finishing process has not been solved so far. WECODUR® offers a way out of this dilemma and presents a turnkey solution for the integrated high-speed laser cladding and grinding coated brake discs.

The presentation will give detailed insights into the technology of both, cladding and grinding as well as into the consequent quality assurance strategy for a automotive serial production. Test bench result for brake performance and NVH Behaviour will be presented along with a cost break down for series production.

Friction performance of an alumina-based coating on cast iron brake disc

XueyuanNie, University of Windsor

This study presented an alumina-based coating prepared using a plasma electrolytic aluminating (PEA) method. The technology addressed the important topics of brake wear reduction and improvement of corrosion resistance, especially important for electrical vehicles (EV). A commercial EV cast iron brake disc with the alumina-based coating was tested with two modified AK Master dynamometer tests under SAE Brake Dynamometer Standards J2522.

In the first test, the number of stops in the Fade sections were reduced from 15 to 6 to maintain the test temperature below 500 °C. Such Fade tests were repeated two times. Weight loss of tested brake disc and pads were then measured. After measurements, the tested components were installed back to the dynamometer to run additional normal Fade (sections 9 and 14, 15 stops each with temperature up to 580 °C) and Recovery (sections 10 and 15) tests. The Characteristic Value coefficient of friction (COF) during testing was around 0.38-0.48. The COF was quite stable at 0.33-0.35 in all Fade sections.

In the first part of the dynamometer test, the brake pads lost weight of 6.1 g (inboard) and 6.8 g (outboard) while the tested brake disc lost a weight of 2 g. After the additional test, the weight loss on the top of the previous test was 4.5 g and 3.7 g for inboard and outboard pads, respectively, and the disc only lost 0.5 g more. Comparing to a tested stock disc baseline, typical pad and disc weight loss were 21 g and 14.5 g. The significant reduction in wear is attributed to adhesive friction mechanism instead of abrasive wear behaviour.

Laser cladding in brake disc coating – from application development to industrialization for mass production

Hossein Najafi, Oerlikon

Laser cladding technology has been identified as one of the most promising technologies in brake disc coating and reducing the particle emission problem from brake discs. It can provide corrosion and wear resistance as well as a very high mechanical resistance through metallurgical bonding with the substrate. In addition to the technical advantages, laser cladding technology brings economic and supply chain advantages. The process efficiency is higher than 90% and is suitable for the scaling up and industrialization phase. The developed materials used in the laser cladding process are cost-effective, and the process requires minimal masking or preparation. It can also be fully automated using robots and set production lines.

In this regard, we have developed a single-layer solution, i.e. DiscCover® Beam using a dedicated laser cladding powder for brake disc application, i.e. Metco®Brake powder. The developed powder is perfectly weldable on cast iron substrates without any pre-processing or pre-heating.

From the application development point of view, the developed solution for brake disc coating has technical and quality advantages compared to other coating technologies. First, it can provide the required corrosion and wear resistance over such a thickness of 150-300 µm as a single-layer solution. Secondly, it can produce a coating with minimal heat input and carbon pick up from the substrate resulting in deformation in the disc and cracking in the coating. Finally, it also enables good metallurgical bonding with the substrate which guarantees no coating delamination during the operation.

In regard to industrialization for mass production scenarios, the economic advantages of laser cladding technology are far ahead of the competing technologies as well. The process can be scaled up with more laser power, higher process speeds, and powder flow rates in addition to possible innovative machine designs to shorten the coating cycle time. These features are ideal for continuous processes. Present work is intended to provide up-to-date information on the latest trends in laser cladding technology on brake discs from application development to industrialization for mass production scenarios.

Fine dust reduction by coating of brake discs using the high-speed laser metal deposition technology

Marco Göbel, TRUMPF Laser- und Systemtechnik GmbH

Due to introduction of new EURO 7 standard the by cars emitted fine dust particles must be reduced significantly. The by tires and brake discs emitted fine dust particles contribute to approx. 30-35% of the overall fine dust emission by gas or diesel driven cars. Since the total fine dust emission must be reduced by more than 90% (in comparison to EURO6) the coating of brake discs will become critical for gas or diesel driven cars. Even for electrified vehicles fine dust will be produced by brakes discs if the vehicle must come to a complete and safe stop. Further development of the High-Speed Laser Metal Deposition (abrev. HS-LMD) process has made this coating technology even more attractive for the automotive industry.

High-Speed Laser Metal Deposition is already used for a broad range of applications: wear resistant layers on small valves, corrosion resistant coatings for very long shafts used in hydraulic systems, etc. Even additive manufacturing of rotational symmetric geometries – such as seal lips or a shoulder on a shaft – are feasible.

For automotive industry HS-LMD are already being investigated for a broad range of applications. Using HS-LMD, a laser beam is melting powder particles, which are fed coaxially into the laser beam, before these particles hit the substrate. Using a laser as heat source, heat input into workpiece can be minimized and fast thermo cycles can be achieved. This allows for a very low dilution of additive into workpiece – typically < 10µm – and high feed rates between 100-500 m/min. Layers generated by this process can be locally adjusted in thickness between 50-300 µm per layer. Since each layer is metallurgically bonded to the substrate or the layer before, multi layers or multi-material approaches are feasible. This feature can be used to achieve functionally graded material or to apply metallurgically bond coatings on hard-to-weld alloys such as cast iron.

In this paper we will show recent results of the development of HS-LMD, which will make the process even more robust for such highly innovative mass production applications. At the same time the productivity has been scaled towards high productivity. These new developments involve new laser-based systems technology that also utilizes beam shaping for the first time.

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