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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.

Since galvannealed steel sheets (GA) are widely used for automobile body parts, they require excellent features such as press formability, resistant spot weldability and phosphatability. We have focused on improving the press formability of GA since the late 1990s, and have developed a new type of surface modified GA which has a lower friction coefficient than conventional GA. The developed surface modified GA based on mild steel is now used by all automakers in Japan, especially for those parts such as side panels that are difficult to form. This paper describes the features of the surface modified GA.

Sheet hydro-forming was applied to hydro-form a door outer panel using different steel grades. The effect of mechanical properties and the forming conditions on panel properties such as thickness profile and cross-sectional shape accuracy were investigated by both experimental sheet hydro-forming and FEM forming analysis. 590MPa T.S. steel grade was successfully formed with improved dent resistance compared to the conventional 340MPa T.S. steel grade. On the other hand, the results of the FEM forming process analysis showed that the pre-forming conditions were important in controlling the fracture formation during forming and to improve dent resistance, which successfully led to the best forming condition.

New highly ductile AHSS steel grades with tensile strength greater than 980 MPa have been developed with the aim of combining high strength and excellent formability. The new jetQ-Family offers high local and global ductility while still fulfilling standards for resistance towards hydrogen embrittlement and weldability. These improved properties are based on their specifically engineered microstructure, which utilize the TRIP-mechanism in a strengthened matrix. This work shows how the microstructure plays a significant role for the tensile testing as well as hole-expansion. Based on the increased yield strength a better crash performance compared to conventional DP steel grades can be attained. The local ductility is demonstrated with excellent hole expansion ratios and high resistance to sheared edge failure. In combination with improved bending angles and thickness strain at fracture a robust process for manufacturing of components can be achieved.

Although reduction of the thickness of materials used in the automobile body is important for weight reduction, reducing the thickness of outer panels deteriorates dent resistance and surface distortion. To investigate the potential for weight reduction, the factors which influence the surface distortion and dent resistance properties were evaluated quantitatively with the aim of securing these properties. The materials used in these experiments were a tensile strength (TS) 340MPa grade bake hardenable (BH) steel sheet, which is often used in door outers, and a TS 440MPa grade BH steel sheet for outer panels. Surface distortion increases as a result of higher yield point (YP). It is possible to suppress the increase in surface distortion by increasing the blank holding force (BHF) in press forming. However, because this reduces the BHF range to the forming limit, application of low YP material is considered to be more advantageous for suppressing surface distortion.