Study On Deformation Rule And Thickness Thickening Of Tube Necking Process Under Non-uniform Temperature Field

The precise and quick forming process can realize material and energy saving is one of the important development trend of plastic forming. Tube precise forming process has become one of the most important forming and production method of hollow structural components, and this process is consistent with the trend of material and energy saving, green manufacturing and near net shape forming. Tube precise hot necking process is one of the main forming process of hollow structural components. The structural components have high requirements on forming size and thickness, however the available papers have little research on this field.Warm and hot necking process of 20Mn2 alloy steel has been selected as the research object in this paper. The mechanical characteristics of 20Mn2 alloy steel under the condition of hot forming process was studied, and the constitutive equation of warm and hot forming process was established. Considering the critical necking coefficient and thickness thickening, the tube variable temperature field necking process(TVTFNP)was studied. The necking force formula was deduced through the theoretical study. The simulation of TVTFNP was realized through user-routine technology in commercial FEM software and the process was applied to the forming of the rear axle. The creative results are as follows:The 20Mn2 alloy steel deformation behavior and the constitutive equation under warm and hot conditions were obtained by hot compression test. According to the requirements of the TVTFNP, the non-uniform temperature field was gained by secondary development of the DEFORM software. The contrast analysis between uniform and nonuniform temperature necking process was studied.The necking force formula, which is based on Arrhenius hyperbolic sine function, was deduced by slab method. Based on instability criterion, the influences of variable process parameters and linear temperature slop on critical necking coefficient were studied through theoretical calculation and numerical simulation. The effects of different forming parameters on tube thickness thickening were studied through orthogonal experiment and numerical simulation, major and minor relationship of parameters were also determined. Considering two aspects of decreasing necking coefficient and tube thickness thickening, the determination principles of forming parameters in TVTFNP under linear temperature field were summarized and analyzed. The new method was proposed and used in this paper, this method can decrease the necking coefficient and control the tube thickness thickening and distribution by changing the tube's temperature field.Three forming steps was put forward according to the characteristics of the rear axle. Numerical study was carried out for each step, the metal flow law and the necking load change were revealed. The influence of different parameters on forming law, tube thickness thickening and workpiece attachment were analyzed. The selection ranges of key process parameters were determined by optimization, meanwhile, the metal streamline and die stress were also analyzed.The TVTFNP of rear axle was verified by industrial test, and the axle, meeting the requirements of length and the wall thickness in the drawings, has been gained. The new process with less heating time and less steps has greatly simplified the existing rear axle extrusion forming process and realized the precision quick forming process of rear axle. The forming defects of the new process were analyzed, accordingly, the improvement measures were also proposed.