Influence of Contact Interface Friction on Plastic Deformation of Stretch-Bend Forming

The contact interface friction between the specimen and the mold during the stretch-bend is a complex interactive process. Friction causes the uneven distribution of tensile stress on the specimen, which affects the plastic flow of the forming material and the spring-back after forming. In this paper, the analytical model of frictional shear stress and tensile stress distribution in the contact mold segment of the stretch and bend synchronous loading stage was established. The influence law of friction coefficient and contact mold angle on the stress–strain distribution of the specimen contact mold segment was discussed. The effect of key factors affecting the friction state of the contact interface (mold surface roughness and contact mold angle) on the shrinkage deformation of the cross-section and the tensile deformation gradient of the specimen was analyzed by equivalent stretch-bend forming experiments. The results showed that the smaller the surface roughness of the mold was, the better the friction state of the contact interface was, the plastic deformation of the specimen was more uniform, and the difference between the section shrinkage and elongation of the contact mold segment and the suspension segment was smaller. Reducing the contact mold angle of the stretch-bend can bring down the tensile stress difference at both ends of the contact mold segment of the specimen so that the section shrinkage and tensile elongation of the contact mold segment and the suspension segment tend to be consistent.