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For the newly developed tube bending method termed “PRB,” finite element analyses (FEA) with solid elements were carried out to clarify the tube deformation mechanism in comparison with that in conventional rotary draw bending. The following results were obtained. 1 In the investigation of the strain and stress states both outside and inside the bend, it was found that plastic deformation in PRB was almost completed before the tube material entered the bend area. In rotary draw bending, plastic deformation developed in the bend area. 2 Regarding the effect of tube reduction in diameter by the pressure die in deformation of tubes, circumferential compressive deformation involving longitudinal tensile deformation is enhanced outside the bend.

Ultra high strength steels have contributed to weight reduction in automobiles. However, due to the poor formability of these materials, it is difficult to manufacture automotive parts with complex shapes using conventional sheet metal forming techniques such as deep drawing, bulging, and stretch flange forming. In this study, a bend-forming technology which enables forming of complex shapes with ultra high strength steel sheets is investigated. The target part was a front side member extension (FSM EXT) of a white body. The part has a dogleg shape and must provide adequate crashworthiness. The basic structure of the FSM EXT produced by this bend-forming technology was proposed. A bend-forming process consisting of three stages was proposed from the standpoint of commercial production. FSM EXT prototypes showed excellent crashworthiness in FEM simulations and crash tests.