Effect of manufacturing processes on the natural frequency, surface roughness and dimensional tolerances of GCI brake discs

Abstract

Automotive component manufacturing involves various processes that can affect the performance of components. Cast articles, such as brake rotors made from gray cast iron (GCI), often have residual stresses owing to cooling variations during solidification. These stresses can cause significant material property degradation and compromise geometric tolerance requirements. Residual stresses can distort GCI rotors during machining and FNC processing when the rotors are heated above the stress-relief temperature, resulting in disc thickness variation (DTV) and increased vibrations during braking owing to lateral runout (LRO). Thermal processing through stress-relieving operations can help eliminate or reduce the residual stresses. This study examined the effects of stress-relief (SR) heat treatment on the natural frequency, damping properties, surface roughness, and geometric tolerances of gray cast iron brake rotors before and after FNC processing. The results indicated that brake discs of similar sizes exhibited no notable difference in their mean resonant frequencies, regardless of whether they underwent prior treatment before FNC processing. The post-FNC damping Q-factor of the brake discs was generally lower than the pre-FNC Q-factor, regardless of disc size and previous treatments. Analysis of the data from the post-FNC discs revealed that the SR discs displayed significantly higher average DTV values (6.3%) than the NA discs, regardless of disc size. The study findings suggest that the surfaces of the FNC-treated discs exhibited increased roughness, regardless of whether they underwent stress-relieving or natural aging before FNC processing. The surface roughness of all treated discs after FNC exceeded the specified Ra value of 2.5 µm. Additionally, FNC processing of stress-relieved discs resulted in an LRO improvement of 30–42% compared to their naturally aged counterparts.