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There is a growing demand for flexible manufacturing techniques that meet the rapid changes in production technology, processes and innovations. Multipoint forming (MPF) is a flexible sheet metal forming technique where a reconfigurable die can be readily changed to produce various shapes. Parts produced using MPF suffer from geometrical defects such as wrinkling, dimpling and thickness variations. In this paper, a multipoint forming process using a novel mesh-type elastic cushion was proposed in order to improve the quality of the deformed sheet and to minimise the developed defects. Finite element modelling (FEM) and design of experiments (DoE) were used to study the influence of the mesh-type elastic cushion parameters such as the type and the size of the mesh, and the thickness of the cushion on the wrinkling, deviation and thickness variations of the deformed sheet. The results showed that using elastic cushion with square meshes of a size of 3.5 mm and a thickness of 3 mm reduced the wrinkling from 3.18 to 1.98 mm, while the thickness variation improved from 98 to 19 μm. Finally, the deviation from target shape reduced from 1.7848 to 0.0358 mm.

Due to the need for low-cost tooling and quality parts, a new technique has been developed which brings together the benefits of both multi-point forming (MPF) and rubber-pad forming. A significant disadvantage of MPF is the time required to adjust the heights of the pins in the upper and lower matrices and align the tools. Rubber forming achieves flexibility by replacing one of the MPF pin matrices by an elastic punch. In this study, polyurethane (PU) rubber with a Shore hardness of A90 was adopted as the elastic punch material. The punch was combined with a reconfigurable MPF die to reduce both tool cost and time to set the pins to produce doubly curved parts of acceptable quality. Experimental work has been carried out to confirm the validity of the new technique. Finite element modelling (FEM) using the ABAQUS software was applied to study stress distribution numerically in the formed parts at the end of the forming process. The amounts of wrinkling and springback were employed as criteria to evaluate the quality of the formed part and to compare the results of the current (semi-MPF) approach against full-MPF results. The major outcomes of this study were time and cost reductions of at least 50% with the added benefits that there is a significant decrease in wrinkling and springback in the final formed part even without using a blank holder.

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