Abstract
Recent global efforts to resolve environmental issues are required in sheet metal forming. For this reason, some research projects have been focused on unlubricated processes as well as on the use of volatile lubricants. However, low formability due to poor lubrication conditions is still a matter of concern. In this study, in order to improve the friction conditions, a new algorithm for controlling blank holding force (BHF) and punch speed (SPD) was proposed. The concept is to separate the wrinkle eliminating process from drawing process. That is, the process proceeds with an extremely low BHF until a wrinkle sufficiently grows, and the wrinkle is eliminated by BHF loading without punch penetration. Its effectiveness was investigated by finite element (FE) simulation, in which two blank models (0.5mm and 1.0mm thickness) were used. As a result, the maximum forming forces decreased by 5.33%(0.5mm) and 1.55%(1.0mm) compared with those of the uncontrolled model at a constant minimum BHF. In addition, a thinner blank sheet is better for the algorithm on the basis of the result that cup height decreases and thickness distribution increases in the case of 0.5mm thickness.
