轿车顶盖冲压成形塌陷研究

Surface deflection of automotive roof in stamping forming

以实践中产生塌陷的某轿车顶盖为对象,结合物理实验、数值模拟以及板料弹塑性变形的力学本质,研究制件冲压成形的塌陷问题,分析塌陷的影响因素。研究结果表明:塌陷取决于材料特性、料厚、制件几何形状以及压边力等多方面因素;该顶盖成形后板面内的塑性变形程度小导致其形状冻结性差、制件结构刚度不足、残余压应力引发失稳,是产生塌陷的根本原因;增大压边力与板料厚度,会导致板平面的残余压应力增加且分布不均匀,使塌陷更加严重;重力也是引起塌陷的一个不可忽视的因素,可以通过优化制件形状、提高结构刚性予以解决。

By taking a car roof that presents surface deflection in practice of press working as an object, numerical simulation and physical experiments were carried out to analyze the defect and influencing factors, especially from the perspective of mechanism of plastic flow. The results show that surface defection is affected by numbers of factors,including material properties, sheet thickness, geometrical feature of panels and blank holding force（BHF）. For the car roof, surface deflection is mainly caused by insufficient shape-fix ability due to low plastic strain and lack of stiffness of the panels after forming, together with the elastic instability induced by residual compressive stress. The surface deflection increases with the increase of BHF and sheet thickness, since they incur more residual stress and lead to uneven stress distribution. Furthermore, gravity is also an affecting factor of the surface deflection, which can be eliminated by optimizing the panel shape and improving the structural stiffness.