Numerical Analysis For Contact Pressure And Surface Damage In Dual-Phase Steel Sheet Stamping

Advanced high strength steel(AHSS) is widely used in auto-bodystructures and safety components for its high specific strength andcrashworthiness. However, AHSS forming demands more blank holderforce and forming force in stamping than mild steels, and it is usuallyformed in small die radius to improve parts size accuracy, which lead tosevere blank surface damage and tool wear as a result of increasedinterface contact pressure between blank and forming tools. Surfacedamage can be costly due to increased stoppages and tool maintenance,and poor part quality. So it is important to investigate the relationbetween contact pressure distribution and surface degradation. Revealingthe changing law of contact pressure with various factors is also vital tocontrol and alleviate surface damage.Surface damage of dual phase steel blank in sheet metal forming isinvestigated by finite element method. Contact pressure distribution andevolution in various parameters is obtained from channel formingstamping finite element model Finally, N-W curve is constructed to provide guide for surface damage control, in which frictional work (W) iscalculated using simulation result and critical stamping parts number (N)is obtained from channel forming test. The following efforts areperformed:(1) Acquisition of interface contact pressure in sheet metal forming ofdual phase steelConsidering the acquisition of interface contact pressure is difficultin real experiment, the contact pressure is gained from simulation model.So channel forming model is built, which is the typical representative ofsheet metal forming. And contact pressure distribution and evolution isformed in a whole punch stroke.(2) Changing law of contact pressure in key parametersContact pressure level in stamping has relation to friction pair,lubrication conditions, and process parameters and so on. The effect ofmaterial property such as strength grade, and process parametersincluding holder pressure, die radius, friction coefficient and draw-beadto contact pressure distribution and evolution are investigated.(3) Prediction method of surface damage based on frictional workBlank surface damage is the combined result of friction pair materialand process conditions. Frictional work can represent the general effect ofprocess conditions better than contact pressure. And frictional work canbe a bridge between simulated test and real production. N-W curve is constructed to realize the prediction of dual phase steel surface damage,in which friction work is calculated by finite element method and criticalstamping parts number.Through this research, dual phase steel blank surface damage insheet metal forming is investigated from the angle of contact pressure andfrictional work. And surface damage prediction method is formed, whichcan provide technical guide for surface quality control.