Progressive microforming of pin-shaped plunger parts and the grain size effect on its forming quality

Progressive microforming of bulk microparts by directly using sheet metals has been developed to address the issues of preformibillet positioning, transportation and ejection in microforming, and it has potential to be used for making complex pin-shaped microparts with high productivity and material utilization. In this research, a progressive microforming system with blanking and extrusion operations to make two types of pin-shaped plunger parts by using brass sheets was developed, and the grain size effect was investigated from the aspects of deformation load, dimensional accuracy, microstructural evolution and surface quality. It is revealed that the grain size effect results in the deviation of punch stroke and the variation of part dimension. The formation and characteristics of shear band and dead metal zone are related to velocity gradient and strain accumulation. The forming defects including micro cracks, micro pits, uneven surface and longitudinal surface texture easily occur on the body and tail feature, and micro voids appear with the coarse-grained material. The circular surface, however, shows the desirable quality with each grain size. All these findings provide a basis for mass production of complex pin-shaped microparts by progressive microforming and enrich the knowledges from deformation behavior and product quality assurance aspects. (C) 2019 The Authors. Published by Elsevier Ltd.