Size effect on the springback of CuZn37 brass foils in tension and micro W-bending

With the ever-increasing demands on miniaturization, the requirement on good forming quality and high dimensional accuracy of micro parts is dramatically motivated. As a decisive factor affecting the accuracy of micro-bent parts, the springback is significantly influenced by size effects. In order to explore size-effect associated springback behaviour and evaluate the forming quality of micro-bent parts, an experimentally-based investigation on the influence of foil thickness, grain size and their interactive effect on the springback behaviour of CuZn37 brass foils with different thicknesses and grain sizes was carried out. The experimental results obtained via micro tensile tests revealed that the yield strength, Young’s modulus and elongation had a close correlation with the thickness to average grain size ratio. A micro W-bending process was used to perform the bending tests. Both springback and negative springback phenomena were observed. It was found that how size effects may influence the amount of springback would depend on the springback behaviours, e.g. positive springback or negative sprinback, etc. In addition, scatter phenomenon of the springback behaviour was analyzed quantitatively. An increased scatter was observed for the 50 μm thick specimens when the thickness to average grain size decreased, whereas an inverse tendency of the decreased scatter of the negative springback was found for the 75 and 100 μm thick specimens with increase of the grain size. Finally, forming quality of the W-shaped micro-bent parts was assessed