A definition of forming limit is given with minimum centerline radius min R before wrinkling for NC bending process of thin-walled tube. Based on the developed FEM wrinkling prediction system TBWS-3D, an effective searching algorithm of wrinkling limit is proposed and forming limit can be obtained conveniently. Thus influence laws of main forming parameters on wrinkling limit are investigated and revealed. Measures to improve forming limit is put forward consequently. The achievements may help to both practice of thin-walled precise tube bending and research of plastic wrinkling.

Thin-walled tube bending processes may produce a wrinkling phenomenon if the process parameters are inappropriate, especially for tubes with large diameter and thin wall thickness. How to predict this phenomenon rapidly and accurately is one of the urgent key problems to be solved for the development of this process at present. In this paper, a wrinkling wave function is proposed and a simplified wrinkling prediction model to predict the minimum bending radius for tubes is established based on thin-shell theory, forming theory, the energy principle and wave function. The minimum bending radius calculated according to the method established is in agreement with data reported in the literature. Furthermore, effects of parameters on the minimum bending radius are also analyzed: (1) the influence of bending angle on the minimum bending radius is negligibly small; (2) the effect of geometrical dimensions and material properties of tubes on the minimum bending radius is significantly large; (3) the minimum bending radius becomes larger with the original radius and strength coefficient of tubes increasing, whereas with the wall thickness and strain hardening exponent decreasing. The results are helpful to the design and optimization of the relevant processes in practice.

The development of aero-space, automobile, and high-technology industries requires the development of advanced plastic processing technologies in order to manufacture parts with light weight, high strength, high precision, high efficiency and at low cost, with a short period and a friendly environment, and with intellectualization and digitization. There are key problems urgently to be solved in the research and development of advanced plastic processing technologies, and FEM numerical simulation in combination with physical modeling and theoretical analysis has been playing a more and more important role in this field. This paper reports the state-of-the-art of some advanced plastic processing technologies and their numerical simulation in the authors'laboratory, including the unequal deforming and in-plane bending process of strip metal, free deformation under dieless constraint and axial compressive precision forming process of tube, wrinkling and spring-back prediction and the NC bending precision forming process of thin-walled tubes, and precision forming laws and a complicated massive forming process such as blade forging with a damper platform.

A simple and efficient method has been proposed in order to determine the dynamic speed boundary condition caused by the guide rolls for developing the 3D-FE model of cold ring rolling process rapidly. The concept of the motion track of guide rolls has been put forward firstly and an optimal motion track and track type are given by simulation. Meanwhile, an effect of the guide rolls on the ring tilting and ring circularity was simulated and analyzed. The result shows that the simulation results are in good agreement with experiment results from the literature.

Research on precision forming laws of complicated blade has been a challenging issue on international frontiers of plastic forming areas. The precision forging laws of the blade with a damper platform have been obtained by using 3D FE simulation and physical modeling. The laws involve in the deforming characteristics of the tenon, damper platform, middle blade body, and tip blade body, such as the unevenness of deformation and material flow, the branch-flow of material, material flow characteristic of the blade body and rotation forming characteristic of the damper platform. The research may serve as a guide to the optimization design of relevant process and dies.