Study On Surface Deflection Of Automotive Roof In Stamping Forming

For the sake of environmental protections, economic, appearance quality of theauto body et al., streamline body is widely used when body shape modeling. What ismore, sheet metal thickness of auto body panels is more thinner. Streamlined body isnot only looks beautiful, but also to reduce the damping coefficient to reduce fuelconsumption, but outer panels as roof cover, hood outer cover et al, are usuallylarge-sized and relatively flat, so there are more and more surface defects,such as,surface deflection and surface distortion in stamping forming, seriously affecting theappearance quality and assembly of the vehicle. In actual production the knowledge ofsurface deflection is still insufficient due to many influencing factors of surfacedeflection.To clarify the mechanism and contribute to effectively control, numericalsimulation are employed and physical experimental were carried out based on actualautomotive roof of Dongfeng Motor Die&Mould Co.,Ltd in this paper.①Distribution area and amount of surface deflection of roof which has beenmanufactured isunderstood.②The stamping technology of roof cover of new project, including roof andsunroof, is analyzed and understood. Its complete process numerical simulation modelsismodeled,using the numerical simulation software ETA/Dynaform. The whole formingprocess is simulated through the finite element model established for the part. Inaddition to, its mechanism is studied and influencing factors and trimming, flanging,restriking stamping technology were analyzed. The result indicates that there are manyinfluencing factors,including blank holding force (BHF),sheet metal thickness,materials and the cover’s geometrical characters and size. However, the insufficientshape-fixabilitydue to low plastic strain after forming and elastic instability induced byresidual compressive stress is the main reason of the surface deflection, spring back isanother reason of the surface deflection.③The greater is the BHF, the more serious surface deflection in drawing formingprocess. Because the increasing BHF makes residual compressive stress increase andlead to an uneven distribution.④In drawing forming process, surface deflection also will be increase with sheetthickness increasing. Its reason is that sheet thickness reduction ratio will be decreased with the sheet thickness increasing, and blank thickness strain also will be decreased.What is worse, residual stress will be increasing after unloading.⑤In trimming process, residual stress will be released and re-distribution in thepart, and so surface deflection will be influenced. However the change in the structureof parts brought about trimming process significantlyimpact on surface deflection⑥Distribution and amount of residual stress will be changed after unloading withthe change of part’s force state and structure in different stamping forming process. Andsurface deflection also will be influenced. Under the residual bending moment, surfacedeflection focused on the region of ridge and its vicinity area, and warpage on the rim.The structure of the restriking part will be changed and distribution region and amountof residual stress significantly decrease under residual bending moment in restrikingforming process.⑦The compensation scheme of the mould geometrical shape is proposed based onthe analyzed results. And surface deflection is successfully controlled within areasonable tolerance range and requirement of the vehicle assembly is satisfied.