Forming characteristics analysis and springback prediction of bi-directional trapezoidal sandwich panels in the multi-point bend-forming
Forming characteristics analysis and springback prediction of bi-directional trapezoidal sandwich panels in the multi-point bend-forming
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DOI：
10.1007/s00170-018-2316-z
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发表时间：
2018-09-01
影响因子：
3.4
通讯作者：
Zhang, Xi
中科院分区：
文献类型：
--
作者：
Liang, Xiao-Bo;Cai, Zhong-Yi;Zhang, Xi
弯曲成形是一种高效、经济的曲面夹芯板制造方法，成形特性和回弹预测是制造精密产品的关键。本文采用数值模拟、解析分析和成形实验相结合的方法，对双向梯形夹芯板多点圆柱弯曲成形过程进行了研究。分析了夹芯板成型初期的变形特点、规律及成型缺陷。采用半解析法结合有限元法推导了核心层的等效弹性常数。在此基础上，建立了在成形范围内计算弯矩和预测回弹的理论模型。结果表明，面板焊接区的应力明显低于悬空区。通过改变斜面与平台的夹角，核心细胞主要发生变形，细胞层的变形主要发生在过渡表面区域。在弯曲成形过程中，韧窝和平直面效应是最常见的成形缺陷。影响成形缺陷的主要因素是面板厚度和弯曲半径。夹层板的回弹量与等效板的回弹量相近。回弹小的成形精度容易控制，回弹率随弯曲曲率半径的增大而增大。理论模型与实验回弹误差小于1.0 mm，验证了理论预测模型的准确性。
Bend-forming is an efficient and economical method to manufacture curved sandwich panels, and the major concerns for fabricating precise products are forming characteristics and springback prediction. In this paper, numerical simulation, analytical approach, and forming experiments were conducted to assess the multi-point cylindrical bend-forming process of bi-directional trapezoidal sandwich panel. Analysis was performed on the deformation characteristics, regularity, and forming defects of sandwich panel in the early stage. And afterwards, equivalent elastic constants of the core layer were deduced by the semi-analytic approach combined with finite element method (FEM). On this basis, a theoretical model was established to calculate bending moments and predict springback within formable range. The results indicate that the stress of face sheet in the welded area was obviously lower than that in the suspended area. The core cell was primarily deformed by changing the angle between the inclined plane and the platform, and the deformation of the cell layer mainly occurred in the transition surface area. The dimple and straight plane effect are the most common forming defects during the bending process. The main factors that affect the forming defects are face sheet thickness and bending radius. The springback amount of the sandwich panel approximates the equivalent thickness plate. Thus, it is easy to control the forming precision for small springback, and the springback ratio increases with the increase of bending curvature radius. The springback in theoretical model and experiment has an error of less than 1.0 mm, verifying the accuracy of the theoretical prediction model.