The Research Of Numerical Simulation Of Single-side Double Spot Welding For Stainless Steel

At present stage，resistance spot welding is widely used in China tomanufacture stainless steel body of rail vehicle. Because nucleationprocess is not easy to observe, welding time is short and welding processinvolves the interaction of electric,thermal and force，so the formationprocess of nuclear has a lack of complete theoretical knowledge. Numericalsimulation is an important method to research the resistance spot welding,which can be used to simulate the influence factors and analyze the spotwelding process. It has important theoretical guiding significance forimproving the quality of joint. At present,most of the numerical simulationof resistance spot welding is limited to double-side single spot welding,and the study of single-side double spot welding is rare.But single-sidedouble spot welding is widely applied in the actual production as its highproduction efficiency,so it is necessary to simulate the process.The paper simulates the single-side double spot welding process of304stainless steel with2mm thickness.Analyze nucleation process and temperaturefield,stress field,strain field with ANSYS. Through measuring the nuclearsize of experiment validates the rationality of the mathematical model.The preloading determines the initial conductive contact area. Thispaper establishes preloading contact finite element analysis model ofsingle-side double spot welding and obtains stress field、strain fieldand contact condition of contact surface. The result show: the axialstress of contact area is compressive stress. The largest axial stresson the interface between electrode and workpiece. The axial stress isgradually decreased with the increasing of the radial coordinate. Theaxial stress drops fast at the edge of the interface between electrodeand workpiece and changes gently between two workpieces. Contact radiusbetween two workpieces is obviously bigger than the interface between electrode and workpiece. Compare the influence of electrode pressure andspherical radius on the contact pressure and contact area. Based on theinterface contact condition at the end of preloading,simulate the ohmicheating of single-side double spot welding.Using birth-death unittechnology to deal with the contact area, and set the contact resistanceas a function of temperature.Because the nugget is formed under the actionof heat and force,it is necessary to build two finite element models.Thethermoelectric coupling model is used to simulate temperature field andthe thermal-force coupling model is used to simulate stress field andstrain field.Using direct coupling method, a model analysis result asanother model analysis load in order to achieve the purpose of the couplingbetween the two physical fields.Get temperature field distribution in theprocess of resistance spot welding,discuss formation and growth processof nuclear and get the size and shape of nuclear.Analyze the reason ofnuclear offset to the up workpiece.The simulation results show that:atthe end of ohmic heating,the pressure stress between two workpieces cometo the minimize.The molten area happens axial compression deformation andoutside the plastic deformation gradually transition from compressiondeformation to the tensile deformation, eventually form plastic metalring in the surface.At pressure-maintained,nuclear rapidly solidification keeping ellipsoidunder the action of heat dissipation of cooling water and the electrodeand workpiece surface.At the end of the unloading cooling,the shape ofisotherm changes from ellipsoidal to square.Eventually becomes parallellines perpendicular to the radial, and distribute sparsely.