Research On Wrinkling And Parameter Optimization Of Strip Metal In-Plane Bending Under Unequal Compressing

In-plane bending process of strip metal under unequal compressing, making use of the unequal deformation, can be developed into an advanced precision forming process with good flexibility, precision, high efficiency, low consumption, high forming limit and environmental friendly. The instability wrinkling and the parameter optimization are the key problems urgently to be solved in the research and development of the process. In this dissertation, a systematical and thorough investigation on the wrinkling and the parameter optimization of the process has been carried out by using rigid-plastic FEM simulation in conjunction with theoretical analysis and experiment. The new achievements made are as follows:(1) The normal and shear stress distribution is researched with the finite element code. The results are as the following: the normal and shear stress linearly diminish from external to internal on the interface between the part and the roller, and respectively reach minimum and maximum at the external and internal; the normal and shear stress slightly rise with the increase of deformation along the rolling direction, and reach the minimum at the exit; the normal and shear stress slightly rise with the increase of deformation along the rolling direction, whereas keep constant along the thickness direction of the lengthwise section, then the effect of the forming parameter such as the compress width, the loading wedge angle, the strain-hardening exponent, the strength coefficient and the friction factor on the total power, total rolling force, moment and average rolling force is analyzed. The results are as the following: energetic parameters rises linearly with the compress width, the loading wedge angle and the strength coefficient increases; energetic parameter decrease as the strain-hardening exponent increasing and the effect of the friction factor on energetic parameter may be ignored.(2) The mechanism of instability wrinkling in the process based on minimum energy principle is revealed, uniform mathematic description of the wrinkling wave on the strip of in-plane bending is established, the internal and external energy is deduced by energy method, and a uniform criteria of internal and external wrinkling is established; then how to combine the criteria with the FEM simulation system to make the numerical prediction of wrinkling into reality is also resolved in the paper. The effects of the forming parameters on the deforming result are analyzed by the uniform predict criteria. The results show as follows: as the compress width increase, external wrinkling first come into being, then internal winkling do, and finally in-plane bend occur; the loading wedge angle increase, internal winkling first come into being, thenin-plane bend do, and finally external wrinkling occur; in-plane bend is possible to occur with a increase of the strain-hardening exponent and the strength coefficient; and the effect of the friction factor may be ignored.(3) The thinking of the parameter optimization in the process is bought forward; and then the optimization objective, design variable, constraint condition and the mathematical model of the parameter optimization are proposed, the scheme of complex method combined with the fibonacci method for the process is proposed, the parameter optimization code is developed. The experiments carried out show that the developed code is reliable. The result can lay a basis for the forming parameters rapidly and exactly being decided and regulated.The achievements of this study are important to further developing the unequal deformation theory, and the plastic wrinkling theory of thin-wall component. Furthermore, it lays a theoretical foundation for generalization and industrialization of this process, also offers a new idea to the R&D of the advanced plastic processing technologies.