| The triple advantages of plasma arc welding,cable wire GMAW hybrid welding and pulse current are combined with plasma arc welding + cable wire GMAW hybrid welding,which is a new high efficiency and energy saving and high-quality welding method.Among them,the penetration ability of plasma arc is strong and can form a larger depth of penetration.The cable wire GMAW arc energy is concentrated and the welding efficiency is high.The use of pulse current for welding helps to control the heat input and also stirs the pool to improve welding quality.It can be used in a variety of industrial fields and has important engineering application value.However,the study of heat transfer and pool behavior mechanism of plasma arc welding + cable wire GMAW hybrid welding is still in the preliminary stage.Therefore,the method combining numerical simulation and experiment is adopted in this thesis,and the molten pool fluid behavior of plasma arc welding + cable wire pulse GMAW hybrid welding of 304 stainless steel is studied in this thesis,and the theoretical basis is provided.Heat transfer and fluid dynamics are comprehensively considered in this thesis,and FLUENT numerical analysis model is established.The double ellipsoid-cone heat source model was used to represent the plasma arc welding heat transfer model,the double ellipsoidal heat source was used to represent the GMAW arc heat transfer,the droplet heat transfer was considered,and the electromagnetic force,buoyancy force,surface tension,iso-ion flow force and other forces on the molten pool were also considered.Based on FLUENT software,the temperature field and flow field of molten pool in the process of hybrid welding were studied,and the influence of the change of GMAW welding current,pulse current and welding speed on the fluid behavior of molten pool was studied.Based on the simulation model,firstly,the influence of GMAW constant current and welding speed on the fluid behavior of plasma arc + cable wire GMAW hybrid welding pool was studied.The plasma welding current was fixed to 100 A,the welding speed was fixed to 30cm/min,and the GMAW current was adjusted to 150 A,175A and 200 A.It is found that with the increase of GMAW current,the width of molten pool increases,which are 11.81 mm,11.93 mm and 12.08 mm,respectively.The penetration depth was also increased continuously,which were 3.35 mm,3.52 mm and 3.78 mm respectively.The residual height formed by metal stacking was increased to 3.96 mm,4.09 mm and 4.26 mm,respectively.The flow rate of liquid metal in the molten pool is also increasing,and the behavior of molten pool fluid is more obvious.When the welding speed is adjusted to 20cm/min,30cm/min and 40cm/min,it is found that with the increase of welding speed,the volume of the welding pool is continuously reduced,and the welding width is 11.89 mm,11.81 mm and 11.52 mm,respectively.The penetration depth is 3.53 mm,3.35 mm and 3.28 mm,respectively.The residual height is 3.99 mm,3.95 mm and 3.87 mm,respectively.The flow rate of liquid metal in the molten pool becomes slower and the behavior of molten pool fluid becomes smaller,which is mainly caused by the heat input of the molten pool.Secondly,the influence of the variation of GMAW pulse current and welding speed on the oscillating behavior of plasma arc welding + cable wire pulse GMAW hybrid welding pool was studied.The plasma welding current was fixed at 100 A,the welding speed was fixed at 30cm/min,and the average pulse current of GMAW was adjusted at 150 A,175A and 200 A.It is found that with the increase of GMAW pulse current,the melting widths are 10.57 mm,10.69 mm and 11.19 mm,respectively.The penetration depth is 2.58 mm,2.79 mm and 2.96 mm,respectively.The residual height is 3.66 mm,4.07 mm and 4.12 mm,respectively.The liquid metal flow speed in the molten pool is accelerated,and the liquid behavior in the molten pool is obvious.When the welding speed was adjusted to 20cm/min,30cm/min and 40cm/min,the temperature field and flow field of the molten pool were studied,and several moments were selected for comparison.It is found that with the increase of welding speed,the flow velocity of liquid metal in the molten pool also decreases,which is mainly caused by the heat input of the molten pool.Compared with the constant current,the pool volume is reduced,and the melting width is 12.06 mm,10.57 mm and 10.48 mm,respectively.The penetration depth is 2.85 mm,2.58 mm and 2.52 mm,respectively.The residual height is 3.36 mm,3.66 mm and 3.43 mm,respectively.It is found that with the increase of current,the melting width,depth and residual height of the constant current are all larger than that of the pulse,because the total heat input of the constant current arc to the molten pool is greater than that of the pulse.However,the velocity of the pulse flow field is greater than that of the constant current,which is mainly because the pulse current has a stirring effect on the molten pool,which accelerates the fluidity of the liquid metal in the molten pool,and the behavior of the molten pool fluid is more obvious.Finally,plasma arc welding + cable type welding wire composite GMAW welding constant current mode and pulse mode of experiment was carried out,the measured value of the shape of weld after welding and the simulation value was used to carry out comparison,found that the numerical simulation to get slightly deep than the measured value,the depth of molten melt more than width,and height ratio slightly smaller measurements,the error is within 5%,molten pool shape size in good agreement with the test results,The accuracy of simulation results is verified and its reliability is improved.In this thesis,the theory of plasma arc welding + cable wire GMAW hybrid welding is studied,the theoretical basis of hybrid welding process is provided,and the industrial application of plasma arc welding+ cable wire GMAW hybrid welding can be effectively promoted and has a broad application prospect. |
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