Atsushi Tomizawa

Development of finite element analysis method for three-dimensional hot bending and direct quench (3DQ) process

The automotive industry has been focusing on developing lighter vehicles to improve fuel economy and crash safety. In order to meet these requirements, Three Dimensional Hot Bending and Direct Quench (3DQ) Technology has been developed, which enables a manufacturer to form hollow tubular automotive parts with a tensile strength of 1,470 MPa or over. 3DQ is a type of consecutive forming that allows bending and quenching at the same time, with a tube feeding device, an induction heater, a cooling device, and a bending device. In this research, a coupled thermomechanical-metallurgical finite element analysis (FEA) method has been developed to investigate the deformation behavior and to predict the forming capability of 3DQ. In the developed FEA procedure, the temperature distribution was calculated with electro magnetic and heat transfer analysis, and the flow stress was defined by transformation models and linear mixture rule. An experimental formula was used to track the ferrite-austenite transformation, a...

Formable Range in Three-Dimensional Hot Bending and Direct Quench Process: ―Development of Three-Dimensional Hot Bending and Direct Quench Technology 2 nd Report―@@@―3次元熱間曲げ焼入れ技術の開発 第2報―

A three-dimensional hot bending and direct quench (3DQ) process that enables the fabrication of automotive parts having hollow tubular structures with an ultrahigh tensile strength and a three-dimensional complex shape has been developed. This 3DQ process is a tube bending process that uses an induction heater, a cooling device, and a robot. In this research, a formable range in 3DQ was investigated. The main results are as follows: (1) When the width of the heating area is large, the ratio between the circumferential and axial stresses of the tube during deformation is almost constant irrespective of the bending radius, yielding a notable change in cross-sectional height. On the other hand, when the width of the heating area is narrow, the stress ratio approaches 0.5 (plane strain) with decreasing bending radius, reducing the change in cross-sectional height. (2) Twist forming with a small cross-sectional shape change is possible in 3DQ. (3) Wrinkling limit strain is almost proportional to (t/Lp)2 for a rectangular tube and to (t/D)2 for a circular tube, where t, Lp, and D, are the thickness, the length of the plane in the inner side of bending, and the diameter of the tube, respectively. (4) The localization of a high-temperature area increases wrinkling limit strain.