A Study Of The Plastic Forming Technology Of Thin-walled Structural Components

Compared with the conventional stamping plus welding approach,the Internal High Pressure Forming (IHPF) technology has the ability to entirely form hollow thin-walled components with complex configuration. Higher structural integrity will bring about less procedure amount,lower tooling cost,but higher specific strength,bigger specific stiffness and longer fatigue lifetime. Due to the great advancement of the hydraulic seal performance and the transducer control capability,the IHPF technology already reaches the practical level. Currently,this advanced plastic forming technology plays an important role on the lightweight issue in the automotive industry. It can be imagined that this technology is also significant for the manufacturing art improvement of the aircraft,shipping and locomotive.Centering on the tube hydroforming (THF) technology,this paper studies the methodology for the plastic forming process design and the stability of the plastic deformation.Generally,the plastic forming process design involves certain parameters,while each parameter has several cases. The discrepancy analysis demonstrates that,for the multi-factor and multi-level project design,the uniform experimental design is better than the orthogonal one. Unlike the regression analysis method,the implicit statistical inference ability of the multi-layer feedforward neural network provides a more pragmatistic way to establish the mapping relationship between the plastic deformation and the process parameters. In order to enhance the efficiency of the plastic forming process design and to overcome the drawbacks of the trial-and-error approach,on the basis of the Finite Element model of the dieless tube hydroforming under internal pressure and axial compression,this dissertation for the first time combines the uniform experimental design method with the neural network technique to design the plastic forming process parameters,which will lead to the designated deformation.Plastic wrinkling is a typical defective mode during the THF. The theoretical study on the wrinkle's onset and growth is academically valuable and useful to understand the mechanism of the THF in depth,which will make a positive contribution to the loading design. Inspired by the symmetric collapse model of thin-walled tube under axial compression and expanding its applicable material type from the ideal plastic case to the linear hardening one,this dissertation for the first time proposes a zoning model to explore the local wrinkling characteristic of the THF. According to the thin shell plastic stability theory,which is based on the plastic instability coefficients,and under the condition of the system potential minimization,this paper formulates a method to calculate the critical wrinkling loads of the THF.Besides,some IHPF-related topics,such as material properties evaluation,Finite Element simulation and loading control experimental system,are also included in this paper.