In order to obtain the competitiveness in the field of industrial manufacture, reduction of development period and small batch manufacture of products are required. In order to meet these requirements, many new forming processes of trial manufacturing have been proposed. Recently incremental sheet metal forming processes have been developed and have shown a possibility of effective forming processes. In these processes, the small local region of a sheet blank is incrementally deformed by moving a hemispherical head tool over an arbitrary surface. Therefore, it is possible to produce three-dimensional and non-symmetric parts directly from the CAD data. In addition, a sheet blank is stretched with drastically improved formability as compared with conventional stretch forming.
In this work, an incremental sheet metal forming process controlled three-dimensionally by computer has been accomplished. It has been shown by the experiment that a sheet blank is subject to shear-dominant deformation. Thickness strain distribution from the experiment is in accord with that derived from the analytic calculation. Therefore, a method for the improvement of formability based on assumption that a sheet blank is deformed by only shear deformation has been proposed. The uniformity of thickness throughout the deformed region is one of key factors to improve the formability of sheet metal forming process. Since the reduction of thickness results from the shear deformation, it is important to distribute the region which is deformed by shear deformation uniformly. Using the predicted thickness strain distribution, the intermediate geometry is decided in the manner that the shear deformation is restrained in the highly shear-deformed region and vice versa. This double pass forming method is found to be very effective so that the thickness strain distribution of a final shape can be made more uniform
