Numerical Simulation Study On Curved Surface Forming Technology Of Push-Pull Stretch Equipment

In order to meet the market requirement of three-dimensional surface parts with large-size and large curvature radius,and the traditional stretch forming process still has technical problems,a flexible stretch forming process was proposed in recent years.The flexible stretch forming process is characterized by the flexibility of clamps,a sheet metal can more easily conform to the contour of the die,material utilization is increased,and the forming defects such as wrinkles,stress concentration and cracks and so on are decreased.Based on the flexible stretch surface forming process,a push-pull stretch surface forming process is proposed in this paper.Push force of the rodless cavity of the hydraulic cylinder converts to pull force for stretching sheet metal,which is the most important feature of this process.In this paper,the numerical simulation method is applied to analyze the forming process,which provides technical support and theoretical basis for the application of push-pull stretch equipment in the field of curvature surface stretch forming.The main contents and conclusions of this paper are as follows:(1)The structural and key components of the push-pull stretch equipment were studied;the kinetic characteristic and the forming force in forming process are compared between flexible stretch forming process and push-pull stretch forming process.The characteristics of the push-pull stretch forming process were summarized.(2)The model parameters such as material properties,contact,friction and boundary conditions were determined,the finite element model of push-pull stretch equipment was built.The shape characteristics,plastic strain,equivalent stress,thickness distribution and forming track of the forming surface parts were analyzed;the feasibility of the push-pull stretch equipment was verified;The wrinkling,stress concentration of forming surface parts were discussed.(3)The effect of clamps discretization on the forming result of forming surface parts in the push-pull stretch forming process were studied.The results show that: as the clamps discretization increase,more parts of material can be independently stretched and rotate with the clamps,so the sheet metal can preferably conform to the contour of the die.In the effective forming zone of the forming surface part,the deformation is more uniform with the clamps discretization increase;in the transition zone,The concentration phenomenon of the deformation is obviously improved with the clamps discretization increase,and the quality of forming surface part is improved.(4)The typical loading modes were introduced in the push-pull stretch forming process;By numerical simulation,the effect of different loading modes on the forming surface parts results were studied,the results show that: under the minimum stretch elongation loading mode,the stress and strain concentration of the forming surface part basically disappear in the effective forming zone;In the transition zone,the concentration of stress and strain were significantly improved in the front of outside clamps.In terms of the overall distribution of the forming surface part,the stress and strain of forming surface part in the whole loading mode are the minimum and the thickness is the maximum,but the forming uniformity is the worst.In the minimum stretch elongation loading mode,the stress and strain of forming surface part are the maximum and the thickness is the minimum,but the forming uniformity is the best.(5)To study the effect of clamps discretization on the forming surface parts results in different loading mode,the experimental results show that: compared with the whole load mode and the equivalent stretch elongation load mode,the average stress,strain and thickness difference of forming surface part are minimum in the minimum stretch elongation load mode.By analyzing the average deformation difference in the two directions,the effect of clamps discretization on the forming distribution in the whole loading mode is maximum;the effect of clamps discretization on the forming distribution in the minimum stretch elongation loading mode is minimum.It is verified that: in the push-pull stretch forming process,the appropriate loading mode is selected,a surface part with better quality can also be obtained under the condition of low clamps discretization.