Superplastic metal forming

Abstract

Part I of this paper describes the phenomenon of superplasticity in metals and the behaviour of superplastic alloys in simple tension. The advantage of using these materials in forging processes and the possibility of developing, for superplastic alloys, vacuum forming, pressure forming and blow-moulding techniques similar to those used in the plastics industry is investigated. It is shown that many of the tensile processes for forming superplastic materials are inherently unstable but that the effects of instability can be reduced by appropriate control of the rate of forming. Part II describes experiments in which tubes and sheet of superplastic tin-lead eutectic alloy were formed using various pressure-forming techniques; these include free forming of tube, forming a tube into a die, production of a bottle from a backward extruded pre-form, stretch-forming sheet both freely and into a female die and the drawing of a very deep cup using pressure-augmented deep drawing. The material used is a true superplastic alloy which deforms superplastically at low strain-rates at room temperature.