Development of semi-dieless metal bellows forming process

A novel semi-dieless metal bellows forming process with local induction heating and axial compression without using any conventional dies is proposed. Firstly, the thickening of a tube is induced by local heating and axial compressive force. Secondly, the buckling of the tube occurs, producing a convoluted shape. The seamless tubes used are stainless steel SUS304 with an outer diameter of 5 mm and a thickness of 0.5 mm and 0.3 mm. The effects of compression ratio on the profiles of the bellows such as convolution height, pitch and thickness are investigated experimentally. It is found that convolution height can be controlled by compression ratio. Additionally, the mechanism of this process for fabrication of the metal bellows can be clarified by loading curve during processing. Furthermore, the validity of a two-step compression technique for improving convolution height and pitch is verified. The fundamental of the proposed technique can be confirmed as a basic key processing to fabricating metal bellows with various dimensions and small quantities.