The Effect of Backing Profile on Cutting Blade Wear during High-Volume Production of Carbon Fiber-Reinforced Composites

Carbon fiber sheet molding compound (SMC) is an attractive material for automotive lightweighting applications, but several issues present themselves when adapting a process developed for glass fiber composites to instead use carbon fibers. SMC is a discontinuous fiber material, so individual carbon fiber tows must be chopped into uniform rovings before being compounded with the resin matrix. Rotary chopping is one such method for producing rovings, but high wear rates are seen when cutting carbon fibers. Experiments were performed to investigate the wear progression of cutting blades during rotary carbon fiber chopping. A small rotary chopper with a polyurethane (PU) backing and thin, hardened steel blades was used to perform extended wear tests (120,000 chops, or until failure to reliably chop tows) to simulate the lifespan of blades during composite material production. Backings of different hardness were tested, as well as several intentionally profiled backings with grooves machined into their surfaces. The key measure of blade wear was obtained by examining the side face of the blade under a microscope and measuring the maximum depth of its crescent-shaped wear pattern while butted against a flat datum edge. Cutting-edge rounding progression was also examined by comparison of abraded regions, and parallels between this work and previous observations are drawn. Blade wear rates were found to decrease as backing hardness increased, as harder backings were more prone to forming grooves naturally during fiber chopping. Intentionally grooved backing rolls were seen to have little effect on wear rates as compared to plain backings, also due to the tendency of backings to form grooves naturally.