This paper is a conduct of experimental tests to investigate different effective parameters of a UNS C10100 copper/aluminum 1100 spring-back on a two-layer Ldie bending sheet through finite element simulations. The parameters are the radius and clearance of die, sheet length, thickness of each layer, different lay ups, and sheet annealing. The paper shows that the spring-back decreases with the reduction of the die clearance and radius, similar to the behavior of single-layer sheet and with the increase of the sheet length. The outcome displays a contradiction with 'no significant effect' in the single-layer sheets, previously published in other papers.Furthermore, the thicknesses of copper and aluminum are important roles to evaluate spring-back; however, there is no certain rule to decrease or increase the spring-back through changing the thickness of each layer. Moreover, this work shows the effects of stacking sequence of aluminum and copper layer on the spring-back, because of the different natural axis in each stacking sequence and also different ultimate strength of each layer. Finally, it is concluded that annealing heat treatment significantly reduces the spring-back, where the intermetallic bond hardness in the interface of Cu/Al layers and spring-back increases with the rise of annealing temperature. Experimental determination of forming limit diagram in Aluminum-Copper twolayer metallic sheets. Science and Technology of Composites, 2016. 2(4): p. 45-50. 4.Karajibani, E., R. Hashemi, and M. Sedighi, Determination of forming limit curve in two-layer metallic sheets using the finite element simulation.

This paper presents novel U-bending setups in order to investigate the effects of the curvatures created on the punch, die, or both on the spring-back/spring-go of the two-layer aluminum/copper sheets. Comparison of the new U-bending setups with the regular ones showed that the curvatures had important roles in reducing the spring-back/spring-go in the U-bending process. The results further indicated the good agreement between spring-back/spring-go and finite element simulations. Moreover, through finite element simulations, the effects of three effective parameters on reducing the spring-back/spring-go, including the curvature radius ( r) of the punch, the distance between curvature center and the fillet center ( d) in the punch, and the curvature radius at the end of the die ( R) were investigated. In achieving the desired state (90°), the results showed that the distance of curvature center from the fillet center ( d) was a more important parameter compared with the curvature radius at the end of the punch ( r) and the curvature radius at the end of the die ( R). This paper also focuses on the thicknesses of copper and aluminum as well as the stacking sequence of layers. Concerning the thicknesses of the implemented copper and aluminum change, the minimum angle of the spring-back/spring-go relative to the desired state was 75% Al/25% Cu thickness. Furthermore, the spring-back of aluminum/copper was lower than the copper/aluminum layer sheet. The effects of both thickness changing and stacking sequence of aluminum/copper layers on the spring-back/spring-go amounts of different sheets were due to the relocation of the neutral axis.