Research On Ultrasound-assisted Laser-Metal Inert Gas Hybrid Welding Of Aluminum Alloy

Laser-metal inert gas(MIG)hybrid welding is a high-efficiency welding method to realize aluminum alloy joining.However,the welds formed using this method suffer from defects such as coarse grains and high porosity.The key to solving this issue is to improve solidification and crystallization of welding pool.Ultrasound is introduced into the laser-MIG hybrid welding process of aluminum alloy,as a result of its unique nonlinear effects,such as cavitation effect and acoustic flow effect,and we refer to this process as ultrasound-assisted laer-MIG(U-L-MIG)hybrid welding.According to the working characteristics of ultrasonic and welding,a hybrid welding torch with ultrasonic vibration and arc welding function was designed and optimized,and the U-L-MIG hybrid welding platform was constructed.The influence of the acoustic geometry parameters on the state of the sound field was studied by means of the numerical calculation method,and the effect of the acoustic radiation force was revealed by combining the water-droplet detachment and the standing wave levitation of expandable polystyrene spheres(EPS).According to the working principle of the U-L-MIG hybrid welding method,it is necessary to improve on the basis of the ultrasonic vibration system and design a hybrid welding torch.The basic dimension of the ultrasonic vibration system was calculated by the traditional analytical solution method,and the ultrasonic vibration system which was matched with the operating frequency of the ultrasonic drive power supply was obtained by the finite element method.The ultrasonic vibration system was improved,and the welding requirements of wire feeding,cable connection and gas flow protection were realized.Based on the laser platform,the construction of U-L-MIG hybrid welding system was completed.Based on the Navier-Stokes equation and the component transport equation,the flow field under different nozzle patterns was calculated to further optimize the hybrid torch.In order to study the characteristics of acoustic field in radiation space,based on the simplified two-dimensional model,finite element method was used to calculate the influence of acoustic geometric parameters,including the height and inclination of the radiating surface,on the sound pressure of acoustic field.The result indicated that the simulated sound pressure distribution was highly sensitive to the height and inclination of the radiating surface.The sound pressure decreased as the height of the radiating surface increased from a maximum value at the resonance height,and decreased as the inclination of radiating surface increased.In addition,based on the principle of acoustic focusing,a concave spherical radiating surface was proposed.The relationship between the radius of curvature of the concave spherical surface and the sound pressure of the acoustic field was studied by the finite element method.The acoustic focusing effect was best when the radius of curvature was 19.5 mm.The water-droplet detachment results qualitatively verified the distribution of ultrasonic radiation force(URF)in the sound field.The EPS levitation position in the standing wave field was basically consistent with the minimum of the relative time average potential of the URF.The confirmatory test results were in good agreement with the numerical results.The effect of radiation space temperature on sound pressure was studied.With the increase of temperature,the density of medium decreased,the velocity of sound propagation increased,and the amplitude of sound pressure decreased.To explore the feasibility of U-L-MIG hybrid welding method,the influence of height of acoustic radiating surface on voltaic arc was studied in the traditional direct current welding mode.The arc projection diameter enlarged obviously under the action of ultrasound.The arc length were slightly different,but the results of variance analysis showed that ultrasound had no significant effect on arc length,and the change of arc length could be attributed to random factors.In pulse welding mode,the influence of ultrasound on droplet transfer and electrical parameters was studied.The droplet transfer period and form had no obvious effect under ultrasonic action,and the ultrasound had no obvious effect on the current and voltage of the whole welding process.