In order to predict the forming limit in warm/hot sheet hydroforming, the warm/hot sheet hydrobulging test of aluminum alloy sheets were carried out by elliptic bulging die with the long shaft diameter Φ100 mm, short axis diameters Φ100,Φ90,Φ80,Φ60和Φ40 mm respectively under the conditions of four different temperatures at 300, 210, 150 ℃, RT (room temperature) and two different pressure rates at 0.0045, 0.045 MPa·s-1. The experimental data were calculated and collated, and the forming limit curves (FLCS) in tensile-tensile stress deformation zone were obtained by the correlation formula of ultimate strain. Combined with the quadratic polynomial curve fitting method, material constants of fitting function were calculated, and a prediction model equation was established to predict metal forming limits, plot forming limit curves (in tensile-tensile stress deformation zone), and give a guidance to warm/hot sheet metal hydrobulging test.
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