Optimization of design parameters using a response surface method in a cold cross-wedge rolling

Abstract

Cold cross-wedge rolling process is utilized to enhance the surface hardness and the strength in a round shaped part. Main geometrical design parameters in a cold cross-wedge rolling die are the forming angle, the spreading angle, and the die height. General defects in this process are an excessive slip on the surface and a hole generation at the center point which is usually called as the Mannesmann hole defect. The friction coefficient and geometrical design variables affect occurrences of an excessive slip and/or a central hole generation. In this paper, effects of the forming angle and the friction coefficient on the initiation of the Mannesmann hole defect are analyzed by using a response surface method. Integrals of four different ductile fracture models are compared with a history of the effective plastic strain at the central point. It reveals that the maximum effective plastic strain at the point can be utilized to determine the initiation point of the ductile fracture in the cold cross-wedge rolling process. Optimization of design parameters for prevention of the Mannesmann hole defect initiation is carried out using a response surface method. As results, that the forming angle of 25° and the spreading angle of 1° can be proper design conditions with the prevention of occurrences of internal hole defect and an excessive slip. Optimum design specification is testified by the experimental result.