To reduce environmental burden, there is a need to reduce the weights of automobile bodies and materials used. Motor cases, the subject of this study, are formed by multistage drawing. The required minimum thicknesses of motor cases vary depending on the parts because of different required properties, including rigidity. Therefore, technologies to control thickness distribution, such as partial wall thickening and thinning, are effective in reducing the weight and amount of material used. In this study, we proposed the use of a forming method to increase the thickness of a body part of a motor case, which requires a large sheet thickness. We developed an axial force application method in which a compressive load is applied in the axial direction during multistage deep drawing. We also performed numerical analysis to clarify the limit of thickening. To this end, the thickening mechanism of the developed method and the effects of different factors on the limit of thickening were examined. The developed method enabled the reduction in the amount of material used by approximately 3% for a product examined in this study.

Ultralight porous metals are attractive for reducing car weight owing to their high specific rigidity and excellent impact energy absorption. However, several problems remain with their application as car parts, such as inhomogeneity, low performance controllability, high production costs and low tensile strength. To solve these problems, a new porous metal with a lattice structure was proposed. Arranged holes, which result in ridge intersections, are cut off from a thin metal sheet by punching in the first process, and ridges are formed along a line of holes by U- shape bending in the second process. Next, the components, which are the metal sheets formed in these processes, are stacked and finally spot-welded. Since the components are mass-produced by progressive press machines with dies, a homogeneous porous structure can be fabricated inexpensively. The performance of the structure can be easily controlled by changing the metal sheet thickness and ridge shape. Tensile and bending strengths are high because there are no extremely thin cell walls. Compression and bending tests were carried out to confirm the compressive plateau stress, compressive energy absorbing efficiency and bending load-stroke relation of the material.