Aachen, Germany – A new laser brake-disc-coating process developed by the Fraunhofer Institute for Laser Technology ILT and RWTH Aachen University can significantly reduce brake dust while reducing wear and corrosion which occurs in normal use.
By using “Extreme High-speed Laser Material Deposition,” known by its German acronym EHLA, it has proved possible to provide brake discs with an effective protection against wear and corrosion in a procedure that is both fast and economical.
Traditional brake discs are made of gray cast iron containing lamellar graphite phases. The virtue of this material lies in its good thermal conductivity and high thermal capacity, all for a relatively low price.
The downside is a strong propensity to corrode coupled with high material wear during service, which generates substantial emissions of fine particulate matter – brake dust. To date, it has proven difficult to provide adequate protection for brake discs by means of conventional coating processes such as electroplating or thermal spraying. The problem with such processes is that they do not produce a metallurgical bond between the cast iron and the protective coating; moreover, they are expensive and use a lot of materials.
Economic and technical advantages
A new process -EHLA – avoids these drawbacks.
“The EHLA process is ideal for use in the automotive industry, especially for coating brake discs,” explains Thomas Schopphoven, research fellow and team leader of Productivity and System Technology within the Laser Material Deposition group at Fraunhofer ILT. “Conventionally, it’s very difficult to coat brake discs, because they have to withstand high loads, and there are also economic and environmental considerations. But with EHLA, it’s now possible to apply coatings that from a metallurgical bond with the base material of the disc and therefore adhere very strongly. Unlike conventional coatings, these do not flake and chip.”
Advance on conventional processes
Coatings produced with conventional processes have pores and cracks. With the EHLA process, the coating remains intact and therefore provides longer and more effective protection for the component. This increases service life and prevents early failure as a result of damage to the surface of the brake disc. Moreover, the process is suitable for a wide range of materials. Therefore, it is possible to select an environmentally friendly coating for each specific application.
The EHLA process is a new process variant on the well-known laser material deposition, which has proved highly successful in areas such as the repair of turbine blades. EHLA does, however, have a number of decisive advantages.