Research On The Forming Characteristic Of Dual-Phase Steel For Automobile And Its Effect On Strain Path

Energy crisis, environmental pollution and low carbon emission reduction have urgentrequirements on vehicle lightweight. Recently, steel sheet for automobile has graduallydeveloped to the direction of high strength. According to the study, the automobile bodymass will decrease by12%when the steel sheet thickness reduce by0.1mm. This showsthat steel sheet with high strength is of great significance to automobile lightweight.In a series of developed advanced high strength steels (AHSS), advanced high strengthDP steel is widely used in automobile structure because of its good comprehensive formingcharacteristic. Dual-phase steel has perfect comprehensive forming characteristic, anddecreases the mass of automobile body effectively while maintaining the strength. However,due to the differences of chemical constituent and microstructure, the mechanical propertiesand the stamping performance of dual-phase steel are greatly different from theconventional high strength steel. Therefore, dual-phase steel is prone to some formingqualities problems by traditional forming process.To solve these problems, first of all, some physics experiments and numericalsimulations, such as tensile test, simulation cupping test and free bending test, were used ondual-phase steel DP600and high strength low alloy steel. The differences of basicmechanical properties, bulging performance and resilience between dual-phase steel sheetand conventional high strength low alloy steel sheet were analyzed. Then, the constitutiverelations of the two materials are established, and the accurate reflection of numericalsimulation to the strain path of stamping process was verified.Focus on strain path of stamping process, some common strain paths were classifiedby numerical simulation. Analyzed the surface characteristics of the panels, and the law ofthe different surface characteristics corresponding to the strain path were summed up. Thestamping characteristics which could reflect the common stain paths including singledrawing stain path, double drawing stain path, plane stain path and bilinear stain path weredesigned.Author carried out numerical simulation of the stamping process under theconditions of different materials and process parameters. The effects of materials andprocess parameters on strain path were studied by regression orthogonal test, and thesensitive factors of strain path changes were discussed, the way of improving the stamping quality of dual-phase steel sheet by controlling the strain path was obtained finally. Bysimulating two-phase steel stamping forming process of the different wear state, theeffects of wear state on two-phase steel stamping forming process were studied.The paper presented an idea of changing the strain path to control the forming qualityby controlling the process parameters, and verify the feasibility of the method. Thisresearch has an important significance to the promotion and application of the dual-phasesteel.