| A modified analytical model for the bulge forming process was made by reflecting the microstructural evolution and applied to the superplastic bulge forming of Ti-6Al-4V alloy. Bulge forming of Ti-6Al-4V alloy sheets with a fine grain size(2.5㎛) was conducted at 900℃ with three different strain rates, e.g., 2.5×10^(-4)s^(-1), 5×10^(-4)s^(-1) and 1×10^(-3)s^(-1), respectively. It was found that the grain growth rate of uniaxially tested specimens was quite different from that of biaxially bulge formed specimens. After incorporating the biaxial grain growth rate into the modified analytical model, bulge farming process was successfully controlled at desired strain rate. Also, the prediction by the modified model for thickness distribution agreed well with the experimental results. |
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