Development of Precision Springback Measurement and Bending System of Sheet Metal

本课题研制了两台精密的测量大塑性变形后的杨氏模量和内应力分布的仪器，并尝试由测得的杨氏模量和内应力计算回弹。测量杨氏模量的仪器由激光干涉仪和光学引伸计组成。该应力传感器由磁场发生器和基于霍尔效应的半导体磁检测器组成，实验结果表明，该杨氏模量测量仪能够以相同的精度测量试样在塑性变形开始和塑性变形20%以上时的杨氏模量，拉伸试验中伴随的应力与测得的工件磁阻成正比。结果表明，弹性模量随塑性应变的增加而减小，当塑性应变为20%时，弹性模量下降到初始值的75%。而且 ...更多信息 通过有限元模拟，利用弹性模量的变化来预测回弹值。结果表明，弹性模量变化时的回弹预测结果比仅用初始值时的回弹预测结果更准确。为了阐明塑性应变引起弹性模量变化的机理，对材料性能进行了微观测量。通过分析材料组织的横截面显微照片，测量了低碳钢板的厚度分布变化。此外，通过纳米压痕测试来测量颗粒周围的弹性模量和硬度，以测量区域材料性能的分布。结果表明，在晶界附近弹性模量降低，材料性能的降低对回弹等宏观材料性能有显著影响。针对实际的V形弯曲模具，对V形弯曲过程进行了有限元模拟。在实验室和实际的V形弯曲过程中，模拟和实验结果之间的差异进行了评估。提出了一种自适应滤波器来补偿这种差异。修改后的仿真结果存储在数据库中，并用于基于该数据库开发的智能过程控制系统。通过对几种材料的V形弯曲试验，对V形弯曲过程的人工智能控制系统进行了评价。结果表明，采用在线自适应滤波器的有限元仿真数据库对精密过程控制是有效的，并与实际过程相适应。少

In this project, we developed two precise instruments for measuring young's modulus after large plastic deformation and distribution of internal stress of the workpiece, and attempt to calculate the springback from the measured young's modulus anc stress. The instrument for measuring young's modulus consists of a laser interferometer and optical extensometer. The stress sensor consists of magnetic field generator and semi-conduct magnetic detector based on hall effect.Experimental results show that the young's modulus measurement instrument is capable of measuring young's modulus of the test piece at beginning and after more than 20% plastic deformation with the same accuracy, and the accompanying stress in the tensile test was proportional to measured magnetoresistance of workpiece. It is found that the young's modulus decreased according to increase of plastic strain, and the young's modulus decreased to 75% of initial value after deformation with 20% plastic strain. Furthermore, the … More variation in the young's modulus was applied to predict the springback value by using FEM simulation. The results show that prediction of springback with varied young's modulus was more accurate than using only initial value.In order to clarify the mechanism of the changes in elastic modulus due to the plastic strain, microscopic measurement of material properties was performed. The changes of through-thickness distribution for mild-steel sheets were measured by analyzing the cross-sectional microphotographs of material structure. Furthermore, the elastic modulus and hardness around a grain was investigated by a nano-indentation test for measuring distribution of regional material properties. The results show that the elastic modulus decrease near the grain boundary, and the decrease of the regional material properties could significantly influence on the macro material properties, such as springback value. It's caused by piled-up dislocations, which may lead to increase of spring-back.FE simulation of V-bending process is carried out for the practical V-bending die. The discrepancies between the simulated and experimental results are evaluated in both laboratorial and practical V-bending processes. An adaptive filter to compensate for the discrepancies is proposed. The modified simulation results are stored in a database and used in the intelligent process control system based on the database developed by the authors. The AI control system of the V-bending process was evaluated by bending several kinds of materials. The results show that the FEM simulation database with the online adaptive filter is effective for the precision process control, and compatible to the practical process. Less