Study On Hot Stamping Process Of High-strength Steel And Multi-field Coupled Analysis

The application of high strength steel (USS) in vehicle body is one of effectiveways to achieve lightweight vehicles and improve the safety of the vehic le’s impactresistance. However, with the enhancement of the blank’s mechanical strength, itsformability is worsened dramatically. It is difficult to accomplish the stamping of USSby traditional cold stamping process. But the hot stamping process using thecharacteristics of sheet metal thermoplastic deformation, shape the blank at a hightemperature, greatly improve the material’s formability and overcome thedisadvantages of poor formability of USS under cold stamping condition. Whichcombine the traditional sheet metal stamping process and heat treatment quenchingprocess of material. The entire process involves the heat exchange between blank,dies, cooling system and ambient. During the forming and quenching process, thestress and temperature field of the blank is changing, and along with the changes ofinternal microstructure. Therefore studing on the multi field coupled analysis methodsof hot stamping process and exploring the influences of process parameters on hotstamping process, will show great guiding significance on the establishment ofreasonable hot stamping process and its application in practice.According the changes of the heat exchange form and content during hotstamping process, the charateristics and methods of temperature field analysis to theblank transfer, stamping and quenching stage were analysed in this article. Throughthe thermal mechanical coupling simulation to the stamping process of U-shapeworkpiece by FEM software ABAQUS, the distribution characteristics and variationlaws of the temperature and stress field in metal sheet were presented and the effect ofthe main stamping process parameters including the blank initial temperature andstamping velocity on hot stamping process were also explored.On this basis, considering the fluid-solid, solid-solid conjugate heat transferproblem during the hot stamping process, a thermo-fluid-solid coupled method of hotstamping process was proposed. In this method, the pressure contact heat exchangebetween the blank and dies, internal heat transfer and thermal stress are analysed bythe structural mechanics software ABAQUS. Meanwhile the flow and heat transfer ofcooling water in the dies are analysed by CFD software FLUENT. Then both areassociated with integrated software platform MpCCI(Mesh-based parallel Code Coupling Interface). The quenching process was thermo-fluid-solid coupled analysedand the effect of cooling water velocity, temperature and holding pressure on hotstamping process was studied by numerical simulation.Finally, with high strength boron steel USIBOR1500as experiment material,establish hot stamping process according to the simulation results and trial theautomobile front pillar corner surport. Then the microstructure and mechanicalproperties of some hot stamping parts were analysed and tested. The experimentsresults show that the microstructure of the formed parts is uniform lath martensite andthe mechanics performance is greatly improved. Which verify the rationality of hotstamping process parameters, proof above numerical simulation methods can be wellused to guide the design of hot stamping process.