Effect of ultrasonic and low frequency vibrations on friction coefficient at die radius in deep drawing process

In the deep drawing process, the friction between sheet metal and die can be reduced by ultrasonic vibration (UV) or low frequency vibration (LFV), and the forming performance can be improved by the surface effect. In this study, a new friction test apparatus to determine the effect of both UV and LFV on the friction coefficient in the die radius region was designed and fabricated. The apparatus can realize UV and LFV conditions by switching the vibration exciters. New, simplified theoretical models with combined types of vibration were proposed, including flexible friction model and vibration superposed model. Using these models, the reduction mechanism of the macroscopic friction coefficient was investigated, and the corresponding mathematical expressions were derived. The theoretical results showed that the reduction ratio of the macroscopic friction coefficient (RMFC) is a function of only two parameters: the dimensionless relative velocity ratio and the wrap angle. Several groups of tests were conducted on three materials, stainless steel 304, brass CuZn40 and aluminium 1060, under UV and LFV conditions, and validated the theoretical results. Tests under UV conditions obtained higher RMFC values than those under LFV conditions, but caused more wear and adhesion.