Experimental evaluation of normalized thickness variation of superplastic cone forming

Abstract

Superplastic Forming (SPF) is the designers first choice for producing the products that have complexity as used in automobiles and aircrafts, in which the ratio of strength to weight is the major concern. SPF of sheet widely used in the manufacture of the products with more significant complexities simultaneously lighter and stronger than with any other manufacturing process. Superplastic formed products having shapes like hemispherical, conical and box results significant variation in thickness. Lowest thickness will be at the locations where the sheet contacts the die at the last. Complexity of the product, forming depth, and pressure affect the thinning. Unmitigated understanding of stress, strain rates, and strains during the forming process and the use of suitable pressures for forming can reduce this problem. In this study Lead & Tin alloy has chosen, as an exemplar material for Superplastic forming to carry out investigations. The results obtained can be applied for any other superplastic materials. The present investigation focused on studying suitable strain rates and Normalized Thickness Variation during the superplastic cone forming. Results revealed that Normalized Thickness Variation (NTV) is lower i.e., 2.27 when formed at the pressure of 3 bar, which provides an equivalent strain rate of 1.1 × 10−4 s−1. Therefore 3 bar pressure is desirable for cone forming. Results also disclosed that strain rates obtained in this investigation are in the limits of superplastic forming zone and hence no fracture happened on the conical dome due to the thinning.