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This paper presents a new material technology that can achieve both crashworthiness and weight reduction of the vehicle body. This new technology is based on three fundamental approaches. One is a technique for evaluating high-speed material deformation characteristics related to the crush behavior of energy-absorbing structures. A second is the material concept of high tensile steel featuring both increased material strength and higher strain-rate sensitivity in order to improve its energy-absorbing capacity. We have found 590N/mm2-class dual-phase (DP) steel consistent with this concept. The third is a technique for estimating the crush behavior of body structures, taking into account the plate thickness reduction and work hardening distribution resulting from the press-forming process. Finally, it was shown that the use of DP steel results in a 15% reduction in the weight of absorbing structures without affecting crashworthiness.

A double-action hydraulic forming simulator (“Simulator”) has been designed to investigate sheet forming processes accurately and systematically. The new machine allows precise control of several process variables. In this study, the Simulator and new scale-model fender dies have been employed for experiments to evaluate the effects of the Blank Holding Force (BHF) control in sheet forming. By the experimental approach, it has been made clear that quality defects of panels formed by stamping processes, such as wrinkles, surface distortion, and fracture, can be suppressed by increasing or decreasing the BHF during the operation. The two simple BHF control patterns, the increasing method and the decreasing method, are effective enough to improve the quality of products and are practical for industrial application.

Surface roughness of steel sheet for automotive use is one of the most important control items, because the surface roughness influences image clarity of painted surface, press formability and easiness in handling during manufacturing and processing of steel sheets. Laser texturing technology is introduced into a roll finishing process of cold rolling, and new type of regular surface roughness profile can be processed on the surface of steel sheets. Effective application method of this technology is investigated at the present day. In Japan, Laser-textured dull steel sheets are used for outer-panels of automotive body as the first application. And image clarity after painting of outer panels has been successful in improving. Nowadays, Laser texturing technology is actually used for manufacturing the high image clarity steel sheets, and they are manufactured in large quantities. Another application of Laser texturing technology is for the inner parts which require pressformability.