techview
Technology that Silences Warranty Concerns
O
ne of the highest warranty concerns for all auto- motive OEMs is noise in the form of brake squeal. This noise comes from vibrating frequencies that
are generated due to the friction between brake disks and brake pads and is exacerbated by components like calipers, knuckles, etc. Among a myriad of solutions, some feasible options for mitigating or eliminating noise occurrences involve increasing damping, and modifying resonant frequencies and/ or geometry of components. Damping can be achieved either by active system damping or material damping. Material damping involves internal friction generated in
response to a vibratory stress. Magneto-mechanical damp- ing (MMD) is one of several material damping mechanisms that helps generate internal friction by movement of magnetic domains. Not all materials have magnetic properties, but ferromagnetic materials such as iron, cobalt and nickel as well as paramagnetic materials like aluminum and titanium do. When the magnetic domain structure and alignment of these parts are adjusted, changes in the domain walls take place and internal friction is generated causing MMD. Though MMD is very applicable to the grey iron brake rotors, there have been limited efforts over the years to study and apply this towards decreasing brake noise.
In 2012, Rassini and the University of Windsor saw this miss-
ing research as an opportunity to partner together and develop methods that increase and optimize the contributions of MMD in brake disks, through electrical and magnetic processing. Benchmarking of all available processes provided an opportu- nity to understand the important process variables and develop a potentially cost-effective method. Based on the results, prototype equipment was manufactured in 2014 that generates the appropriate current signal to provide the optimal range of process variables for consistent damping improvements. Process development is currently underway to provide a simple method in creating a magnetic fi eld around the rotor in a production environment. The intent is to process the rotor in line or offl ine, either as a casting or a machined part, in less than a minute. Successful manufacturing of the proto-
Mauricio Gonzalez
Engineering Director Rassini
Plymouth, MI
type machine has proven a simple and feasible way to further implement this technology for production. To date, damping improvements ranging between 10– 45% have been achieved after processing, depending on the material grades (cast iron). MMD improvement was found to be highly dependent on the material microstructure and ma- terial characteristics being studied. Other variables included the chemistry of product, microstructure, graphite size and distribution, pearlite lamellae, alloys and eutectic cell size.
It will be production feasible in late 2016.
Additionally, dynamometer noise tests, which measure the
frequency and amplitude of brake squealing, were conducted to ensure the damping improvement translated into noise reduction. The fi nal results found that parts with damping im- provement of more than 30% showed 95% noise occurrence elimination, while parts with lesser improvements showed a reduction of up to 70%.
The equipment to generate the optimal signal is a proto- type and is still undergoing extensive research and tests in the lab. Once all the process parameters are optimized and perfected, it will be production feasible in late 2016. While signifi cant steps have been made in this process, the level of brake noise will remain a key initiative for automo- tive OEMs and suppliers alike. A crucial next step will be the industry’s commitment to developing and improving new and existing technologies that will only further advance these efforts until an end goal of supplying noise-free brakes to customers is reached.
Mauricio Gonzalez is an engineering leader and strategic thinker with more than 20 years of experience. For the past nine years he has served as the engineering director for Rassini, a Mexican industrial company engaged in the design and manufacturing of suspension and brake components for the automotive industry.
41 — Motorized Vehicle Manufacturing 2015
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