In recent years, the improvement of crash safety and lighter weight vehicles have become issues of highest concern in the automotive industry. To meet these requirements, the three-dimensional hot bending and direct quench (3DQ) technology has been developed. The 3DQ technology enables the formation of hollow tubular automotive parts with a tensile strength of 1470 MPa or higher. In addition, this technology facilitates the production of partially quenched automotive parts. It is possible to partially quench parts using controlled induction heat. On the other hand, there are many S-shaped automotive parts with a rectangular cross-section. In this study, the affecting factors of partially quenched S-shaped products are investigated by finite element analysis to improve energy absorption by considering production thickness and cross-sectional shape. To improve the energy absorption of S-shaped products, buckling behavior in the non-quenched straight portion is important. The effects of some major factors (notch, cross section shape and drop weight inclining angle) on the axial crash behavior of straight non-quenched products are investigated. In this study, the energy absorption per mass of a newly designed partially quenched S-shaped product with a polygonal cross section, designed using the 3DQ technology, was 530% higher than that of a conventional non-quenched product.

Crankshafts for automobile engines are usually manufactured by hot forging and machining. Since the projected area of this part is quite large, a large forging press and hence a large capital investment are required. It is expected that capital investment will be reduced by dividing and forging a crankshaft in parts that are then joined it later. This research is a study on the manufacturing method of joining this sectionally forged product by rotary friction welding (RFW) to make a crankshaft. First, we conducted a basic experiment on the joining conditions of the material by RFW and later conducted an experiment to join the parts of the crankshaft. We were able to propose a manufacturing method that results in the same strength as a normal hot forged crankshaft as well as achieve the desired angular alignment between the joined parts.