2015 Volume 56 Issue 657 Pages 885-890
When processing microparts, the effects of grain size on the surface roughness and dimension must be considered. There are several reports and papers on quality improvement using ultrafine-grained steel because there are a variety of grain deformations. However as the material grain size is reduced, the material hardness and tensile strength increase, and the number of grains are simultaneously increased during one process. Purpose of this study is to clarify the stabilization element of sheared surface. Firstly, microhole piercing using a small stamping machine with an environment-temperature-control unit is examined for two different grain sizes. The clearance between the punch and die is varied between narrow and wide. Then the hole condition is observed by EBSD under different observation modes. The effects of grain size on process effected zone in different micropiercing conditions are discussed. As a result, the selection of an appropriate clearance is necessary for different grains sizes in consideration of the product quality and tool life.
