Mechanism Analysis And Numerical Simulation Of External Inversion Of Tubes By Axial Drawing

Inversion tubes and process have been widely applied in many industries. With the development of science and technology, more accurate inversion tubes are needed. EITAD(external inversion of tubes by axial drawing) process can be easily applied to make high precision inversion tubes efficiently .Therefore, the EITAD process has important research value.This paper has overviewed the research progress on tube inversion technology and process The advantages and disadvantages of these processes and the method of determining main process parameters have also been introduced respectively.Based on the membrane theory of axis symmetric shell,the formula of calculating tube inversion forming force was derived under the condition of non-hardening . The influence of process parameters on forming force and the variation discipline of tube thickness have been studied. The results showed that:①External inversion radius has significant influence on forming force , where there's existing an optimal inversion radius. When the radius is equal to the optimum value,the forming force will reach its minimum.②The forming force decreases as the tube radius increases,and the foming force increases as the thickness of the tube increases.③The thickness of the tube decreases during the forming process .When the curl angle reached 180°,the thickness of the tube would reach the minimum,about 83% of the original.Based on FEM software DERFORM-2D,the forming process of aluminum alloy and stainless steel tubes were simulated .The forming force variation and the flow trends of materials in the forming process had been revealed,as well as the equivalent stress and deformation state.The impact of relative tube thickness on the optimal punch radius and the impact of the width of flange at the end of the tube blank and the blank holder force on inside-out tube inversion process had been studied. The simulation results showed that:①the greater the relative thickness, the smaller the best punch radius;②The width of the flange and the blank holder force have a little effect on the forming force ,but if the flange width and the blank holder force are too small ,the flange is pulled into the die, and the forming process aborts.③EITAD process can be used to invert high-precision stainless steel tubes .Based on the results of the theory and numerical simulation , the forming process of double-wall tube with specific sizes was developed and the relative moulds were designed.