平面应变板料拉弯成形回弹理论分析

SPRINGBACK OF SHEET METAL AFTER PLANE STRAIN STRETCH-BENDING

  • 摘要: 基于平面应变假设,采用服从Hill平方屈服准则和指数强化材料模型,建立了板料拉弯成形回弹量预测的理论模型。应用该模型计算了一个拉弯成形回弹实例,分析了单位宽度切向拉力、凸模圆角半径、摩擦因数及各向异性参数对板料回弹量的影响。分析结果表明,只有当中性层偏移距离超过板厚的四分之一时,增大切向拉力才能有效地控制板料回弹量,而且弯曲半径越大,增大切向拉力控制板料的回弹量越为有效,然而拉力不能无限制的增大,它的计算准则为板料最外层的等效应变应不大于极限应变。同时还表明,摩擦因数对板料回弹量的影响随切向拉力的增大变得更为显著,而各向异性参数对板料拉弯成形回弹量的影响也较为明显。与有限元数值模拟预测结果的对比表明,理论模型预测板料拉弯成形回弹量与有限元数值模拟结果很接近。

     

    Abstract: For the springback problem of sheet metal stretch-bending, a mathematical model was proposed based on Hill’s yielding criterion, exponential hardening and plane strain assumption. The model was validated by a stretch-bending example. The effects of stretching force per unit width, die profile radius, friction and anisotropy on the springback were studied. The results from the proposed model indicate that only if the shift distance of neutral surface exceeds one-fourth of sheet thickness, the increase of stretching force can control the springback effectively. Furthermore, the larger the bending radius, the more effective the increase of binder force in controling the sheet springback. However, the stretching force cannot increase without limit. Its calculation criterion is that the effective strain at the outer sheet layer is not greater than the material limit strain. It also shows that with the increase of stretching force, the friction has much larger influence on the sheet springback. Besides, the anisotropy also has effect on the sheet springback of stretch-bending. Comparison with FE simulation results shows that the predicted results by the mathematical model consist well with those by FEM.

     

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