Numerical Simulation And Experimental Investigation On The Plastic Formation Of Automotive V302 Subframe

In recent years,tube hydroforming technology has been widely used in automobile and aerospace industries due to the increasing lightweight parts demand.Under the premise to guarantee the performance,the subframe manufactured by tube hydroforming technology has the advantages of more uniform wall thickness distribution,less forming process,higher strength and rigidity,better dimensional and shape accuracy.In this study,finite element(FE)models were adopted to analyze the forming process of the complex geometry and spatial curved axis of the cross and longitudinal beams of the subframe,which included the rotary bending,pre-forming and hydroforming.The influences of process parameters on wall thickness distribution and the forming defects were studied through FE analysis.Eventually,the cross and longitudinal beams of the subframe with high dimensional and shape accuracy were manufactured successfully through the actual forming experiment.Two reasonable plastic forming process schemes were made by analyzing the shape characteristic of cross and longitudinal beams of the subframe.Comparing with the two schemes in terms of the manufacturing cost and the convenience of die installation,two-cavity in one mould and adding process supplement section were selected as the forming method of longitudinal beams of the subframe.Also,the basic processing parameters of the hydroforming were determined including: the radius,thickness and length of the tube blank,the initial yield pressure,the calibration pressure and clamping force.The material parameters of SPH440 were obtained through uniaxial tensile tests,and on this basis,the constitutive model was established.FE simulations of bending,pre-forming and hydroforming on cross and longitudinal beams of the subframe were conducted,by FE analysis software DYNAFORM 5.9.2.The influences of process parameters on the wall thickness distribution and the cross section distortion were studied through the variation of the process parameters such as relative bending radius,displacement of the upper die,loading path and friction coefficient.For the cross beams of the subframe,the numerical analysis results showed that the minimum thinning rate of the bent tube reached 6.59% if the bending radius was set to 250 mm and mandrels were used in bending process.In the pre-forming process,no distortion appeared in the cross-section when the displacement of pre-forming upper die was set to 40 mm.In the hydroforming simulation,the maximum thinning rate and thickening rate could be controlled to 13.81% and 27.45% through a combination of loading path 4 with friction coefficient 0.05.For the longitudinal beams of the subframe,the minimum thinning rate of the bent tube could be controlled to 11.50% if the bending radius was set to 120 mm and mandrels were used in bending process.In the hydroforming simulation,through a combination of loading path 5 with friction coefficient 0.05,the maximum thinning rate and thickening rate could be controlled to 14.90% and 24.94%.The devices were designed to form the cross and longitudinal beams of the subframe,which mainly included pre-forming die,hydroforming die,and seal punch.Firstly,the experimental researches of the cross and longitudinal beams of the subframe were preformed based on the simulation results.Secondly,the wall thickness distribution of the typical section of the parts after bending,pre-forming,hydroforming were analyzed.Finally,the defects in the actual hydroforming process were discussed.