Forming feasibility of complex multi-cavity parts of 316LN steel by multi-direction loading: from aspect of geometric and process parameters

Abstract

Multi-direction loading forming technology provides an effective way for green manufacturing of high-performance multi-cavity complex parts of 316LN steel, which are widely used in nuclear power pipelines. In this forming process, the material needs to undergo complex unequal deformation under a mixed stress state of tensile-shear, compression-shear and shear, flow and fill the cavity to obtain such complicated shape only from the simple cylindrical blank, thus forming defects are prone to occurring and restrict the forming feasibility, which is related to both process parameters and the geometric structures to be formed. In this paper, by considering the uniformity of deformation and temperature distribution, along with the forming load, the reasonable forming parameters were analyzed and obtained. The results showed that the deformation uniformity could be improved as the punch loading speed increased or the friction factor decreased. A lower forming load could be realized by reducing the loading speed of punches or raising the initial blank temperature. Then under the recommended process parameters, the reasonable range of geometric dimension of parts to be formed was acquired by investigating the velocity field, forming load, folding length, and damage distribution. When ratio of the branch pipe spacing to outer diameter of main pipe is Lm/D0 ≤ 0.5 or inner-outer diameter ratio of main pipe d0/D0 ≥ 0.8, the cracking would occur. When length of main pipe L0 = D0 or inner-outer diameter ratio of branch pipe is d1/D1 ≤ 0.6, both folding and cracking presented. Consequently, the acquired forming feasibility can provide guidance for the application of multi-direction loading forming process for multi-cavity complex parts.