Composite brake discs have become a state-of-the-art solution for mass reduction in the entire braking systems. Replacing a massive cast iron disc by a combination of a friction ring made of cast iron and a hub made of other material can lead to a lighter design due to lower density or material thickness.

Aluminium is still one of the most desired materials for visible parts of brake systems - not only due to its low mass density. For luxury and sports cars, design and attractive look remain very important factors, determining the customers' purchasing decisions. Thus, the objective was to combine an attractively looking aluminium surface with a robust, safe and scalable concept applicable for luxury and sports cars.

The main challenge is to make the connection withstand the hard thermo-mechanical test condition, including high temperatures and torques during abrupt braking events. Due to differences between thermal properties of cast iron and aluminium, disconnection of both parts is not the only problem the disc has to face. Different heat capacities and expansion coefficients could lead to unwanted restraints or unnatural deformation as possible reasons for a pre-mature failure.

A cooperation of experts in metal forming and casting has become a base for a lightweight concept with a cast iron friction ring and a sheet metal hub made of aluminium. The connection between both parts is set by forming the aluminium outwards into the friction ring, acting as a die. The concept has been tested by means of the FEM simulation and real dynamometer trials. The result is a robust design with minimized undesirable thermal and mechanical interaction between the hub and the ring.

The next phases of the project comprise the design optimization and preparation for further performance tests, including trials in a real vehicle.

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Kamil Zawalich, Development engineer, Erdrich Umformtechnik GmbH; Dr.-Ing. Matthias G. Müller, ERDRICH Umformtechnik GmbH; Mr. Ulrich Lorenz, ERDRICH Umformtechnik GmbH; Mr. Wilfried Strauß, Fritz Winter Eisengießerei GmbH & Co. KG; Mr. Tobias Müller, Fritz Winter Eisengießerei GmbH & Co. KG