The effects of machining residual stresses on springback in deformation machining bending mode

Hybrid machining-forming technology is a combination of two thin-structural machining and incremental forming manufacturing processes. A group of complex geometry parts in which a thick region is connected to a thin wall region can be manufactured through this technology with certain advantages. The parts made by this technology require less raw material compared to the ones created by means of machining. The major problem with this technology is the dimensional and geometric inaccuracy of its products which is mainly due to springback. The main purpose of this research was to study the effects of machining parameters and residual stresses induced by the machining primary stage on the subsequent springback after the forming stage. It was found by experiments that the parameters of cutting speed, axial depth of cut, mode of milling and milling path had a minor effect on springback. However, the workpiece fracture during the forming stage was observed to be sensitive to the prior machining feed rate. Both finite element simulations and experimental results confirmed that the compressive machining residual stresses increased with an increase in the machining feed rate. The compressive residual stresses postponed the onset of fracture at the workpiece lower end during the forming stage. Therefore, we could approach the forming tool closer to the bottom of the wall during forming and, as a result, springback decreased considerably.