Internal crack formation in cross wedge rolling: Fundamentals and rolling methods

Material fracture is a serious problem in cross wedge rolling (CWR). Finding new solutions for material fracture prevention in CWR processes presents a technological challenge for researchers these days. This paper presents a new approach to the problem of material fracture, which investigates a not previously undertaken aspect concerning the influence of the cross wedge rolling method on the development of internal cracks. CWR rolling methods in which two tools are used (two flat wedges, two roll wedges, roll wedge-concave segment, two concave wedges) were analysed. In addition, the effect of the number of moving tools on material fracture in CWR is investigated. Material fracture is predicted by a novel hybrid fracture criterion. In this paper, FE simulations were used to determine the value of the hybrid fracture criterion. Experimental studies were used to validate the built numerical model. The conducted research has shown that with the increase in the ovalization of the cross-section of the rolled forging, which depends on the rolling method and the number of moving tools, the degree of damage to the forging increases. The highest degree of damage occurs during the flat wedge rolling method, in which only one wedge is moving. The lowest degree of damage occurs when rolling with two moving concave wedges. The most important conclusion of the study is that changing the rolling scheme from the least favourable to the most favourable one allows to reduce the degree of forgings damage twice.