Size effect in micro multi-point sheet forming
The influence of size effects on material behaviour is very significant with the trends towards miniature and portability. Based on a new constitutive relation which includes the punch size, the process of micro multi-point forming for sheet metal was modelled by dynamic finite element software. It is used to study the influence of size effects on surface quality and thickness behaviour. It has been found that the top surface has good quality when the grain size and the punch size are kept constant. When the thickness is under 0.6 mm, the surface quality is better with increasing thickness but the effect of the grain size is small; when the thickness is larger than 0.6 mm, the surface quality decreases with increasing thickness and grain size. It was also found that the surface quality would be better with small punch. As to the thickness, there is a new result that when the thickness is less than 0.6 mm, the center of sheet is much thicker than the edge. For larger grain size and punch size, the sheet thinning is more significant.