Abstract
Superplastic Forming (SPF) process has many unique advantages over conventional forming operations including ability to produce complex thin shapes and significant cost and weight savings potentials. However, the SPF may result in excessive thinning at certain locations and a non-uniform thickness profile. To address these issues, the two-stage SPF process was developed to improve the uniformity of thickness distribution. In this work, two techniques were considered to improve the final thickness distribution of a complex shape, namely, the license plate pocket potion of an automobile decklid outer panel. These two techniques are the reverse free bulging and sheet preforming. The commercial finite element code, ABAQUSTM, was used to model the two-stage SPF process of an aluminum alloy AA5083 sheet at 450 °C. The study concluded that reverse free bulging did not result in improvements in the thickness profile compared with that obtained from the single-stage SPF. However, the sheet preforming technique, with an engineered preform cavity, resulted in an almost uniform thickness distribution for the superplastically formed part.
Highlights
Superplasticity is the ability of certain type of materials to exhibit large tensile deformation prior to fracture
The study concluded that reverse free bulging did not result in improvements in the thickness profile compared with that obtained from the single-stage Superplastic Forming (SPF)
The forward SPF stage, the gas pressure was applied at the top of the AA5083 sheet, forcing it to take the shape of the license plate pocket die cavity under a constant strain rate of 0.001 1/sec
Summary
Superplasticity is the ability of certain type of materials to exhibit large tensile deformation prior to fracture. An interesting approach to improve the thickness profile of superplastically formed parts is preforming It was concluded by (Johnson, Al-Naib, & Duncan, 1972) that multistage operations that take advantage of the high friction conditions of SPF were the most effective at producing improved thickness uniformity. Abu-Farha and Nazzal (2010) imposed a pre-thinning reverse bulging step before the forward SPF stage Their results showed that the reverse free bulging approach improved the thickness profile and decreased the severe thinning with specific part geometries and materials. The sheet was initially bent into a V-shaped groove prior to the gas forming work They found that preforming of the V blank creates a uniform length of line and improved the thickness profile of the final part. We will develop a finite element method predictive tool of the process and suggest certain process guidelines that would overcome some of the limitations of the SPF process
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