管材自由胀形时极限载荷及成形极限的确定

基于轮廓形状为余弦曲线及轮廓上任一质点的运动轨迹与轮廓正交的假设及材料各向异性理论,建立直观的数学模型,并借助数值计算方法,快速、准确地确定薄壁管材无模约束自由液压胀形的成形载荷及成形极限。通过对不锈钢及低碳钢薄壁管的液压胀形实验来验证理论模型及计算结果的正确性,并分析及比较胀形中的成形载荷变化规律、管材壁厚及轮廓形状的变化规律。研究结果表明,自由胀形长度l0对于极限载荷pb值的大小有较大的影响,但对极限胀形系数Kmax影响较小;基于该模型计算的极限载荷(破坏时的液压力)及成形极限更加接近实际,可用于管材液压胀形的生产中。

Determination of maximum forming pressure and bulge coefficient of thin-walled tube in free hydro-bulging

As an effective technique to manufacture thin-walled hollow structure parts,tube hydro-bulging is enjoying increasingly widespread applications in industry.Based on material anisotropy theory and the assumption that profile of thin walled tube in free hydro-bulging process of an open die is a cosine curve and any point on the profile moves tangent to the profile,mathematical models are deduced for determining the maximum pressure p_b at bursting and the maximum bulge coefficient K_(max).Free hydro-bulging experiments on tubes of stainless steel and low carbon steel are conducted to validate the models and the experimental data indicate that the theoretical models are reliable and accurate.The behavior of the forming internal pressure,the distribution of wall thickness and profile of the deformed tube are analyzed and discussed.The results also display that the maximum pressure p_b decreases with the free bulging length l_0,while the maximum bulge coefficient K_(max) is hardly dependent of l_0-value.