Simulation Of Fluid Dynamics Behavior And Solidified Structure In Welding Pool

An one-phase continuum mixture model which is suitable for calculating fluidflow, temperature field and liquid fraction field on the problems of solid/liquid phasetransformation for multi-phase systems by solving a set of conservation equationsand supplementary equations is established by combining fluid flow dynamicalequations and porous medial flow equations. Energy boundaries and momentumboundaries are listed. Fluid dynamics behaviour that is occurred by driven forces isstudied by using software PHOENICS3.3. A new algorithm method is developed,which evidently speed up the iterative convergence rate. Fluid flow and temperaturefields in a moving welding pool of 1Cr18Ni9Ti stainless, LF6 aluminium alloy andultra-fine grain steel are simulated. Effects of surface-active element－oxygen andsulfur on flow patterns in welding pool are studied. And then simulate grainsgrowing in the weld pool of 1Cr18Ni9Ti stainless and LF6 aluminium alloy underdifferent welding parameters by using GBE model and Visual Basic language. Thesimulated results are agreed well with the experimental results. The numerical simulation of TIG welding process when the current is 150A andwelding speed is 3.33mm/s has indicated that in the condition of individualbuoyancy force the driven flow is very weak, and the maximum velocity is on theorder of 10mm/s. The electronic magnetic force causes fluid motions that increasethe depth of the pool, and the maximum velocity is on the order of 10mm/s. Thesurface tension is the major driven force in the pool. The sign of the surface tensiontemperature coefficient affect the shape of the weld pool. The negative value ofsurface tension temperature coefficient for causing near surface fluid moving fromthe centre to the periphery results in a fairly shallow and wide pool, and the positivevalue of surface tension temperature coefficient for causing near surface fluidmoving from the periphery to the centre results in a very deep pool. The flowpatterns would be complex when the sign of surface tension temperature coefficient - III -北京工业大学工学博士学位论文is varied. The maximum velocity is on the order of 1.0m/s. The simulated and experimental results of TIG welding of 1Cr18Ni9Ti, LF6and ultra fine grain steel show that several vortexes could be obtained undercombing conditions of buoyancy, electromagnetic, surface tension and surfacetension is the governing factor which control the fluid pattern. The velocity dependson the magnitude of the surface tension temperature coefficient. The thermalconductivity has a great effect on the fluid flow. The shapes deform seriously whenthe thermal conductivity is small such as 1Cr18Ni9Ti and deform slightly when thethermal conductivity is large such as LF6. The vortex strength driven byelectromagnetic force is relative to the current, thermal conductivity and weldingspeed. The electromagnetic force would be weak at high welding speed and largethermal conductivity under the same current. The sign of the surface tension temperature coefficient changes the fluid flow inA-TIG welding pool apparently. The increase of elements content and the decreaseof surface temperature can extend the region of positive surface tension temperaturecoefficient. As the content exceed a critical value, the positive surface tensiontemperature coefficient controls the flow pattern completely. Positive and negativesurface tension temperature coefficient would be existed at the same time in the poolwhen the content is less than this value. The critical value would be different withdifferent welding parameters. Isotherms arrange closely near the maximum surfacetension and the temperature gradient is the largest in the surface pool. Surface-activeelements change surface tension temperature coefficient from a negative value to apositive value, can cause significant changes in depth/width (D/W) ratio of the weldpool. When the oxygen content increases,...