高盒形件多道次变薄拉深工艺机理研究及数值模拟模型确立

盒形件有限元模拟通常采用壳单元进行建模,由于薄壳单元在计算中忽略了厚向应力,因此在多道次拉深成形及变薄拉深成形工况下的适用性存在质疑。以3003H14高盒形件多道次变薄拉深为研究对象,利用Dynaform并结合LS-DYNA有限元软件进行数值模拟,对比壳体单元与实体单元的模拟计算数据,通过分析外观模拟结果和Levy-Mises增量理论中瞬时本构关系系数的模拟数据,得到单元类型对薄板多道次变薄拉深成形模拟计算精度的影响规律。利用实际工程中的毛坯尺寸样本数据对建立的盒形件拉深毛坯尺寸计算程序进行训练,从而实现了盒形件拉深工艺毛坯尺寸预测软件的开发。此外,在明确建模方法后,结合实体单元有限元模拟结果研究板料在变薄拉深过程中材料的减薄与增厚的机理,揭示了材料流动规律。研究表明:实体单元模拟计算结果与实际更接近。若以坯料单元在工序前后的理论变形厚度的百分比差值作为变形程度衡量指标,当变形程度为0~11.1%时,两种单元计算差异为0.5%~27.8%;当变形程度为24.2%~34.9%时,两者计算差异为44.4%~79.3%。经多道次变薄拉深后,金属材料增厚区域多发生在凸缘及长边与短边交界处的圆角上;在模具的限制作用下,减薄区域多发生在底部圆角,长边与短边区域都有一定减薄;除工序1外,其他各个工序长边侧直壁平均厚度比工艺设计的理想值大1.00%~2.02%,短边侧直壁平均厚度比工艺设计的理想值小0.86%~12.90%。

Research on the Mechanism of Multi-pass Ironing Drawing Process of High Box-shaped Parts and Establishment of Numerical Simulation Model

The finite element simulation of box-shaped parts is usually modeled by shell unit. The applicability of the thin shell unit in multi-pass deep-drawing forming, and multi-step ironing process conditions is questionable because they ignore the thick-directional stresses in the calculation. This paper takes 3003H14 high box as the research object, and uses Dynaform and LS-DYNA finite element software to conduct numerical simulation. The simulated results of shell element and solid element are compared and the instantaneous constitutive relationship coefficients of Levy-Mises increment theory are analyzed. Then the influence law of element type on simulation calculation accuracy of multi-pass thin sheet deep drawing is obtained by the above methods. The development of the blank size prediction software for the box-shaped parts drawing process is achieved by training the established box-shaped parts drawing blank size calculation program using the sample data of blank sizes from actual engineering. In addition, after the modeling method was clarified, the mechanism of material thinning and thickening during the ironing process of the sheet is studied in combination with the solid unit finite element simulation results, and the material flow law is revealed. The study shows that the solid unit simulation calculation results are closer to the actual one. If the percentage difference of the theoretical deformation thickness of the billet unit before and after the process is used as a measure of the degree of deformation, when the degree of deformation is 0-11.1%, the difference between the two unit calculations is 0.5%-27.8%. When the deformation degree varies from 24.2% to 34.9%,the calculated difference is 44.4% to 79.3%. After the multi-stage ironing draws, the thickness of the metal material has occurred in the rounded corners of the flange and the long side and the short side. The thinned region occurs in the bottom round of the bottom,and both of the long side and the short side area are thinned under the limitation of the mold. After multiple thinning and drawing, the thickening area of the metal material mostly occurs on the flange and the rounded corners at the junction of the long and short sides.Under the restrictive effect of the mold, the thinning area mostly occurs at the bottom rounded corners, and both of the long and short sides are thinned. Except for process one, the average thickness of the straight wall on the long side of each process is 1.00%-2.02%larger than the ideal value of the process design, and the average thickness of the straight wall on the short side is 0.86%-12.90%smaller than the ideal value of the process.