Study On The Influence Factors And Control Method For Surface Lowof Exterior Auto-panels

With the increasingly competitive environment for domestic automobilemanufacturing techniques, every large automotive makers put forward higherrequirement for the Manufacturing Quality of automotive body. To exteriorauto-panels, not only the formability quality should be ensured, but also thesurface quality should be ensured. With the development trend of integration forexterior auto-panels and the thickness of sheet becoming thinner, qualityproblems like surface low becomes more serious.Surface low attracts a lot of automotive makers’ attention. t the same time,it became one of the focus problems of academic research. At present, due to lackof experience and theory study, there are no mature prediction method andevaluation index for surface low, which limited the standard of products,die-design and technological process. In this paper, the influence factors andcontrol method on surface low for exterior auto-panels are studied. The rulesand effect of materials, stamping parameters and geometry of panels on surfacelow are illustrated.Effective surface low evaluation methods are proposed and amethod of surface lowcontrol by tool surface compensation is advanced.In order to prove the accuracy of the simulation, a sample panel with a doorhandle feature is stamped and measured in experiment to be compared with thesimulation result by setting material model, element model and boundaryconditions reasonably. Four surface low evaluation methods are introduced.After comparing the experiment and simulation result by different evaluationmethods, the accuracy of simulation result is proved. The advantages anddisadvantages of different evaluation methods are analyzed and summarized.The rules and effect of materials, process factors and geometry of panels onsurface low are illustrated based on the bending theory of thin plates andhardening behavior of materials. Material factors include sheet thickness,hardeningexponent and strengthcoefficient. Process factors include blank holderforce, draw beads, radius of punch and local negative gap. Geometry factorsinclude draw depths of left and right ears, transition radius of left and right earsand the length of left and right ears.In order to control surface low, take the sample panel with a door handle feature and the sample panel of cylindrical shallow shell as examples,a method ofsurface lowcontrol by tool surface compensation is advanced. Tool surfacecompensation is a method to control the surface defect by changing the elementsnodes of tools. This method bases on numerical simulation. After compensatingfor several times, the reasonable tool surface mesh is gained. It can control thesurface low result in the bending moment by controlling the stress throughthickness direction. It provides the solution to control the surface low in thedesign of the forming tools. Finally, surface low problem of an exteriorauto-panel during stamping step is solved by tool surface compensation. So thepracticability of tool surface compensation is proved.Consequently, it is to guidethe solving of surface low on exterior auto-panels.