Finite Element Analysis On Warm Forming Of Dual-Phase Steels Laser Tailor-Welded Blanks Based On Thermo-Mechanical Coupled Method

Dual-phase(DP) Steels Laser Tailor-welded Blanks(TWBs) have been put into use in the automotive industry for the purpose of the lightweight of auto body in recent years. Compared with other sheet steels,DP steels TWBs lag very far behind in widely application due to their poor formability at room temperature.The warm sheet metal forming process has been widely used for mass production of various components because the warm forming process is superior.Therefore,it can also be used in forming of DP steels TWBs to improve the formability.The elastic-plastic finite element method is applied to sheet forming at warm temperature and proved to be effective.However,the elastic-plastic finite element method for cold forming cannot be directly adopted for the numerical simulation of warm forming processes because of the lack of consideration of the effects of deformation temperature on mechanical properties of DP steels TWBs.Based on the warm uniaxial tensile test of DP steels TWBs,thermo-mechanically coupled finite element analysis(FEA) is performed for DP steels TWBs by combining finite element simulation techniques of TWBs with thermo-mechanical analysis,and the finite element simulation is applied to the non-isothermal cylindrical deep drawing process of DP steels TWBs.The main contents of this paper are as follows:1) True stress-strain curves for welding zone are acquired from the theoretical formula expressed by the results obtained from the uniaxial tensile test of base material and TWBs with vertical weld beam.A Finite element analysis of tensile test is performed for DP steel TWBs with vertical weld beam using the true stress-strain curves mentioned above.The material property of welding zone is also studied.The comparison of simulation results with experimental data at several elevated temperatures showed the validity of modeling of TWBs,provided that the material parameters of welding zone are available.Finite element simulations are applied to the cylindrical deep drawing of DP steels TWBs with same thickness to establish the coupled thermo-mechanical finite element model of warm forming for DP steels TWBs.2) Based on the stress-strain behaviors of base material and weld beam at several elevated temperatures,a coupled thermo-mechanical finite element analysis of warm forming is performed for DP steels TWBs by the coupled simulation of plastic deformation and heat conduction.The effect of process parameters of non-isothermal deep drawing on formability of TWBs is investigated by the finite element simulation.The effect of non-isothermal deep drawing process on formability of welding zone is also studied by the analysis of thickness distributions of the wall in different forming conditions.An optimal warm forming process is determined finally by the investigation of the effect of different die-punch temperature combinations on formability of warm forming TWBs using two different non-isothermal deep drawing processes.