Compressive Instability Phenomena During Springback

Abstract

Springback in sheet metal product makes difficulties in die design because small strain causes large displacement. Especially for the sheet metal product having small geometric constraints, springback displacement may become severe. After first stage of stamping of outer case of washing machine, a large amount of springback is observed. The stamping depth of the outer case is small while stamping area is very large compared to the stamping depth, and therefore, there exists small geometric constraints in the formed part. Also, a compressive instability during the elastic recovery takes place and this instability enlarged the elastic recovery and dimensional error. In this paper, the compressive instability during the elastic recovery is analyzed using bifurcation theory. The final deformed shape after springback is obtained by bifurcating the solution path from primary to secondary. The deformed shapes obtained by the finite element analysis are in good agreement with the experimental data. The bifurcation behavior and the springback displacement for different forming depth are investigated.