Experimental and numerical study of the size effect on compound Meso/Microforming behaviors and performances for making bulk parts by directly using sheet metals

Meso/microforming of bulk multi-scaled parts and components by directly using sheet metals is an efficient approach to realizing mass production of meso-/micro-scaled bulk structures with good productivity and low cost. This process is promising with the large-scaled application potentials. In this unique deformation-based meso-/micro-scaled manufacturing, size effect arises due to the size scaling up and down of the extrinsic and intrinsic parameters of materials and forming systems, which further induces different mechanical responses and deformation behaviors in meso/microscale from those in macroscale. In this research, a compound microforming system for a blanking-heading process was developed to produce plug-shaped bulk parts by directly using copper sheets as a case study. Different punch-die clearances and grain sizes of specimen were employed to study the interactive effects of geometry and grain sizes on the microforming process and the micro-formed part. Through numerical simulations and experimental measurements of the final parts, the influences of size effect on microstructural evolution, geometrical precision and surface defects of the meso-/micro-formed parts and the load-stroke relationship were comprehensively investigated. The results reveal that when punch-die clearance equals grain size, the maximum ultimate shear stress of blanking and the highest burr are obtained. The larger grain size and punch-die clearance increase the material loss and reduce the bulge diameter of the produced parts. Three shear bands and three dead metal zones were identified on the cross-section of parts, and various defects including sunken area, pits, crack and surface damage were observed on the surface of the parts. These findings facilitate the production of plug-shaped microparts in the aspects of process monitoring and product qualities control and enrich the understanding of sheet-metal bulk forming in this progressive and compound meso/microforming.