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.
Because of the poor effect of lubricant in microscale dimensions, tribological issues in microforming are encountering further severe problems in the enhancement of performance in microforming operation. Therefore, as an approach to enhancing the tribological performance of the microdie surface, in the present study, we applied surface texturing on the microdie with the expectation of the wear-debris-ejecting effect. A microtextured surface was realized by using metallic masks during the deposition of diamond-like carbon (DLC). To characterize the basic tribological property of textured DLC film, the ball-on-disk tribology test was carried out. Furthermore, a system for in-situ observation during microbending was developed to characterize the practical applicability of surface texturing in the microforming operation. The textured DLC film showed a lower coefficient of friction than that of the nontextured DLC surface. Additionally, we demonstrated that surface texturing promoted the wear-debris-ejecting effect during the microforming operation.