Cai Zhongyi

Optimum path forming technique for sheet metal and its realization in multi-point forming

Abstract A technique to shape sheet metal along an optimum forming path is proposed in order to achieve the most even deformation distribution in the final products and to avoid failures such as wrinkling and tearing. In multi-point forming technology, by adjusting the relative position of each element in an element group, one can change the forming path so that one may implement the deformation of the sheet metal along the optimum path. On the basis of the theory of minimum plastic work, the optimum forming path is described in the paper. To establish a desired forming path, a method to generate a forming surface is developed, the method being based on the representation of an objective surface with c1 continuous by an 18 d.o.f. triangular element. Sheet forming tests are performed to evaluate the effect of the technique presented, the test results demonstrating that when deformed along an approximate optimum forming path the forming limitation of metal sheet is raised obviously, comparing with that of deformation along a common path.

Principle and theoretical analysis of continuous roll forming for three-dimensional surface parts

Continuous roll forming (CRF) is a novel forming process for three-dimensional surface parts, in which a pair of bendable forming rolls is used as sheet metal forming tool. By controlling the gap between the upper and lower forming rolls, sheet metal is non-uniformly extended in the longitudinal direction while it is bent in the transverse direction during the rolling process. As a result, longitudinal bending is gained and a doubly curved surface is formed. With the rotations of the forming rolls, the sheet metal is deformed consecutively, and a three-dimensional surface part is shaped continuously. In this paper, the mechanism of the three-dimensional surface formation in CRF is set forth. Through theoretical analysis of the CRF process, the governing equations for the bending deformation in rolling process are presented. Based on the simplification on the deformation and material model, the formulation to calculate the longitudinal bending deformation is derived, and the methods to design the compression ratio and the roll gap are given, the effects of compression ratio of rolling and the width of blank sheet on the longitudinal bending curvature are analyzed. The forming experiments on typical surface parts and measured results show that forming results with good precision can be obtained by CRF process.

Digitally Adjustable Tooling Technology for Manufacturing of Aircraft Panels

Digitally adjustable tooling using multi-point forming methodology is a flexible manufacturing technology for aircraft panels. It includes multi-point press forming and multi-point stretch forming which are used in the forming of three dimensional aluminum alloy panels and multi-point positioning tool which is used in subsequent assembly operation. The deformation mechanism of the multi-point die less forming and positioning technology were analyzed with commercial FEM codes. The forming defects such as dimpling and spring back in forming were investigated and the preventing measures were proposed. The factors which affect the performance of multi-point positioning tool were given. Based the simulation results, three types of prototypes were developed under the supporting of EC 6th programme project DATAFORM.