Study On Swing Arc Narrow Gap MAG Welding Process Of Thick High Strength Steel

When welding high-strength steel,there are mainly problems such as poor welding joint quality and low welding efficiency.Narrow gap welding can effectively improve the quality of welded joints and increase welding efficiency.However,narrow gap welding has the problem of sidewall not fusion,so how to solve the problem of sidewall not fusion has always been the focus of research.Therefore,this paper adopts the swing arc technology to increase the heat input of the sidewall to solve the problem of sidewall non-fusion.The influence law of forming is finally applied to the high-efficiency welding of thick plates of Q690 high-strength steel with a narrow gap of 80mm and a deep groove.This article first optimizes the design of the swing arc narrow gap welding gun,and builds the welding experiment system at the same time.The system is mainly composed of the swing arc narrow gap MAG welding system,high-speed camera acquisition system and current and voltage acquisition system.The welding experiment system provides a good foundation for the experiment.The effect of different shielding gas composition on the droplet transfer law of narrow-gap MAG welding with swing arc was studied.By comparing the droplet transition form and current and voltage changes under different shielding gas composition,the welding droplet transition law of different shielding gas composition is obtained,and the best shielding gas under this process condition is determined,the composition is 80%Ar+20%CO₂.The influence of swing arc welding parameters on the formation of narrow gap MAG welds is studied.It mainly discusses the influence of welding speed,wire feeding speed,swing amplitude and swing speed on welding formation.With the increase of welding speed,the smaller the penetration depth and penetration width,the larger the wire feeding speed,the greater the penetration and the penetration width.Large;the swing amplitude mainly affects the welding width of the weld.In a certain range,the increase of the swing amplitude will cause the weld width to increase first and then decrease;the swing speed mainly affects the stability of the welding process,and the speed is too fast.The swing device is abnormal;finally,the appropriate process parameters are obtained.The swing speed is 61°/s,the welding speed is150mm/min,the wire feeding speed is 7m/min,and the swing amplitude is 3.2mm.Orthogonal experiments are used to obtain data samples,and a narrow gap welding process prediction model based on BP neural network is constructed,and the model is optimized by genetic algorithm to verify the reliability of the model.Through model prediction and analysis,the optimized welding parameters were obtained:welding speed 150mm/min,wire feeding speed 7.5m/min,swing amplitude5.5mm,welding test was carried out on a narrow gap 80mm deep groove,and a well-formed welded joint was obtained.The microstructure and mechanical properties of the Q690 high-strength steel narrow-gap welded joints were analyzed,and the structural characteristics of the welded joints were observed by metallographic microscopy.The base material area is lath-shaped bainite,and the weld area is granular bainite.and acicular ferrite,the heat-affected zone is lath-shaped martensite and a small amount of bainite;at the same time,the welded joints have been tested for microhardness,tensile and impact.There is no obvious softening in the affected area.The tensile strength is relatively high.The overall average tensile strength of the joint is 827.4MPa.The impact toughness at low temperature is analyzed.The impact energy of the weld area is 62J,which is greater than the standard value(47J at-40?).