Numerical Simulation And Analysis Of The Resistance Spot Welding Process On Ultra-high Strength Hot-stamped Steel

Through advanced hot stamping technology，the high strength boronalloy steel with homogeneous austenite phase becomes ultra-high strengthhot-stamped steel after rapidly quenching heat treatment. The hot-stampedsteel, with the advantages of high strength and hardness because of its finelath martensite microstructure, is playing a more and more important role tomeet the requirements of lightweight and safety in a utomotive industry.Meanwhile, resistance spot welding (RSW) process is widely used for joiningthin sheet steels in the automotive industry due to its advantages in weldingefficiency and suitability for automatic production. However，RSW processon the hot-stamped steel is a complex process and it is very difficult to obtainthe insightful information of the welding process through the experimentsalone. Building finite element numerical model and numerical simulationmethod provide a valuable way in st udying the spot welding process.Numerical simulation can not only save experimental time and cost but alsocan provide theoretical guidance for studying the weldability and practicalprospect for searching suitable welding parameters. In this study，a coupled axisymmetric finite element model is built tosimulate the RSW process of BR1500HS hot-stamped steel with1.5mmthickness by the finite element analysis software，SORPAS. The ConstantCurrent Transformer (CCT) curve of the hot-stamped steel is simulated bythe material property software，JMatPro. Via simulation，the dynamic dataincluding temperature field，welding thermal curve are quantitativelycalculated and the influences to the welding field with variation of thewelding parameters are studied. The information of the welding nugget size，microhardness of the weld joint，the metallographic structure distribution ofthe weld joint after welding，et al are simulated. The mechanism of thewelding soften zone is also discussed in this study.The hot-stamped steel is nowadays wildly used in the automotiveindustry to produce the body-in-white structure components with enhancedcrash resistance and geometrical accuracy. In the production process，it needsthe hot–stamped steel to have good resistance spot weldability with differentsteels especially the mild steel. In this paper，the RWS process on thehot-stamped steel with2.0mm thickness and HC260LAD+Z mild steel with0.8mm and1.5mm have been investigated, respectively. Via simulating theRSW process on the hot-stamped steel and mild steel by SORPAS software，the temperature distribution of the welding area is studied and weld spatterconditions are simulated and validated by comparing them with experimentalresults. Via adjusting the welding parameters assist in numerical simulation，appropriate welding parameters are achieved. The mechanic properties of the welding joints in optimized parameters are compared with those of notoptimized. Moreover，some methods of solving the phenomenon of the weldnugget migration in the RSW process on different steels are explored in thispaper.