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Study on the characteristics of heat transfer and flow of stainless steel GTAW weld pool

Author: LiRiSheng
Tutor: WangHong
School: Taiyuan University of Science and Technology
Course: Materials Processing Engineering
Keywords: GTAW stainless steel double ellipsoid heat source model flowfield temperature
CLC: TG402
Type: Master's thesis
Year: 2014
Downloads: 9
Quote: 0
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Abstract


GTAW is joining technology that arc heat is used as the heatsource,welding pool and near the metals protected by inert gas,and the flow ofwelding pool metal affect the quality of welded joints directly.A double ellipsoidheat source model is adopted using Fluent fluid software in the paper. A3-dimensional transient numerical model for GTAW pool was created tosimulate flow and temperature fields under the action of a moving heatsource.Research the effects of welding parameters on the weld pool shape,temperature field and flow field.The mechanism of the molten pool fluid flow isanalyzed under buoyancy,electromagnetic force,surface tension and thecombined action of buoyancy,electromagnetic force and surface tensionseparately. Compare and analyze the difference of GTAW pool fluid flow andheat transfer under the condition of different welding current,welding speed,andthe same heat input.The simulated results are compared with the experimentaldata for welding pool of1Cr18Ni9Ti stainless steel,showing that both are well inaccordance with each other basically.It is the model built that could meet therequirements.Use Gambit to build the model and divide grid,write the source term of theheat source and the electromagnetic force in C language.It is taken into accountthe effect of surface tension,electromagnetic force,buoyancy, etc on weldingpool, temperature field and flow field.In the thesis adopt0Cr18Ni9stainless and1Cr18Ni9Ti stainless steel simulated.Simulation results show that when the current is220A,voltage20V andwelding speed4mm/s in the numerical simulation of GTAW pool,buoyancyforce that makes liquid metal flow from the center to the periphery has a veryweak influence on pool shape,and maximum flow velocity in welding pool is9.85mm/s．The high temperature metal is drived by the electromagnetic force toflow from the weld pool periphery toward the center,transferring the more heatto the bottom.Maximum flow velocity in welding pool is0.134m/s.While the surface tension temperature coefficient is negative,maximum flow velocityin welding pool is0.394m/s,the metal moving from the center to theperiphery.But the direction of fluid flow on the condition of positive surfacetension temperature coefficient is the opposite.The direction of fluid flow in thecombined force is in agreement with individual negative surface tension,themaximum flow velocity in welding pool reaches0.427m/s,which makes nodifference with that under the negative surface tension.The role of buoyancy and negative surface tension for the molten poolmakes the pool wide and shallow,but that of electromagnetic force and positivesurface tension is on the contrary.Each group of the surface tension in twogroups is greater than another force.When buoyancy,electromagnetic force andsurface tension work together,surface tension plays a leading role in it.It is poolform performance that is wide and shallow.Other conditions being constant, thebigger the welding current changes, the deeper the molten pool gets with a widerwidth;the greater the welding speed changes,the shallower and narrower themolten pool becomes.And under the condition of the same heat input, along withthe increasement of welding speed and current, the depth and width grow largeras well.

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CLC: > Industrial Technology > Metallurgy and Metal Craft > Welding, metal cutting and metal bonding > Welding general issues > Welding heat transfer process
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