The purpose of this research is to develop technology to make complex-shape closed-section parts from sheet blanks. Closed-section parts with large expansion of circumferential length are expected to be manufactured by such forming technology. In this work, the effect of the deformation path is investigated in the forming of horn tubes, curved circular tubes, and curved conical tubes. These tubes are formed by three processes (U-shaping, curving, and closing). The main conclusion based on the results of finite element (FE) analysis is as follows. The parameter α = κ _B1/ κ _B2 is proposed as a universal parameter that indicates the difference between deformation paths. κ _B1 is the longitudinal curvature at the bottom of a U-shaped section of the sheet after the U-shaping process. κ _B2 is that after the closing process. It is clarified that the strain induced during forming can be organized relatively by using parameter α. With an increase in parameter α, stretch strain at the sheet edge of section of each tube increases. On the other hand, compression strain at the bottom of the section decreases.

A cup forging method has been developed using discontinuous carbon-fiber-reinforced thermoplastic. Two types of billet have been prepared for the forging. Unidirectional thermoplastic carbon fiber chips of 20 mm length and 10 mm width were randomly laminated and compressed into a circular cylinder. Another billet was made from laminated unidirectional thermoplastic carbon fiber fan-shaped sheets. A forging die was designed for making side holes and side grooves in the cup forging process. In a forging experiment, a cup with side holes and a side groove was forged from discontinuous carbon-fiber-reinforced thermoplastic. Carbon fiber sheets were compressed by the head of the punch and made to flow into the side wall of the cup. Test specimens cut from the side wall of the cup showed a flexion strength of about 400 MPa with a 90 MPa standard deviation. Further study on the relationship between the fiber structure in the billet and that in the forged cup will be necessary to reduce the deviation of the strength of the forged cup.