Experimental research and numerical optimisation of multi-point sheet metal forming implementation using a solid elastic cushion system

There is a growing demand for flexible manufacturing techniques that meet the rapid changes in customer needs. A finite element analysis numerical optimisation technique was used to optimise the multi-point sheet forming process. Multi-point forming (MPF) is a flexible sheet metal forming technique where the same tool can be readily changed to produce different parts. The process suffers from some geometrical defects such as wrinkling and dimpling, which have been found to be the cause of the major surface quality problems. This study investigated the influence of parameters such as the blank holder force, coefficient of friction, elastic cushion thickness and radius of curvature, on the quality of parts formed in a flexible multi-point stamping die. For those reasons, in this investigation, a multi-point forming stamping process using a blank holder was carried out in order to study the effects of the wrinkling, dimpling, thickness variation and forming force. The blank holder force is an important parameter in the multi-point forming process, mainly because of wrinkle and sheet springback prevention. The aim was to determine the optimum values of these parameters. Finite element modelling was employed to simulate the multi-point forming of hemispherical shapes. Using the response surface method, the effects of process parameters on wrinkling, maximum deviation from the target shape and thickness variation were investigated. The process parameters yielding the best product quality characteristics were obtained. By using variable blank holder force in comparison with constant blank holder force, it is possible to significantly improve the multi-point process; and in terms of product quality, it is possible to achieve optimal blank holder force in the whole sheet MPF process. These results were compared with the numerical simulation results of the multi-point forming for hemispherical shapes using a blank holder and it was found that using cushion A90 led to reduce wrinkling and maximum deviation.