Research On The Effect Of Waveform Parameters On Welding Stability And Welding Formation In High Speed CMT Welding Of Aluminum Alloy

In this experiment,the electrical parameters of the welding process and the high-speed camera synchronous acquisition system are used to study the effect of the electrical parameters of the current waveform,especially the peak current Iboost,the peak current duration tboost,the base current Iwait and the peak wire feeding speed Vd,on the stability of a certain average wire feeding speed and high-speed CMT welding process and the weld formation.The experimental results show that the aluminum alloy CMT welding process window can be effectively expanded if the base current is controlled at 70 A and the peak wire feed speed,peak current duration,and peak current magnitude are properly matched.By using the method of probability and statistics,the influence of the above four waveform parameters on the probability distribution of each stage of aluminum alloy CMT welding process is analyzed.Under normal welding(welding speed 1.0 m/min)and a certain average wire feeding speed,it is found that when the peak current Iboost is less than or equal to 70 A,the heat input is low,the viscosity of the liquid metal is high,and it adheres to the end of the wire and splash phenomenon occurs during the short-circuit separation phase.The average CMT welding cycle time is basically unchanged,if the peak current duration increases.But as the peak current duration increases,the base current duration decreases by the same amount,and the welding process appears unstable when the base current duration is less than 4 ms.Changing the magnitude of the base current affects the size of the liquid droplets at the end of the wire.When the base current is too strong,the liquid droplets at the end of the wire are affected by the forward movement of the wire and the large electromagnetic force,making the welding process unstable.The change of the peak wire feeding speed affects the base current duration,and it is closely related to the welding wire retraction frequency during the welding process.Combined with the influence of the peak current duration on the welding process,the welding process window can be effectively expanded.The study also found that the average wire feed speed wfs and the actual average wire feed speed wfr during the welding process are not the same,and wfr also increases with the increasing peak current,peak current duration and base current,and decreases with the decreasing peak wire feeding speed Vd.The CMT transition frequency is basically unaffected by peak current,peak current duration,and base current,but as the peak wire feed speed Vd increases,the CMT transition frequency increases significantly.At larger peak currents and peak current durations,the droplet transition changes from a pure CMT hybrid transition into a"droplet + CMT short"hybrid transition.When the peak current is lower than 180 A or the peak current duration is less than 8 ms,the droplet transition is a pure CMT transition mode,and the hybrid transition phenomenon occurs when it is beyond the critical value.Under the condition that the peak current and the peak current duration are matched properly,large droplets are left at the end of the wire after the droplet transition,which ensures a stable welding process and good weld formation.The orthogonal test was designed to optimize the current waveform parameters of aluminum alloy CMT welding at 3.6 m/min.The comprehensive analysis method was used to evaluate the orthogonal experimental results and the influence of three parameters on the weld formation was obtained:Peak Wire Feeding Speed>Peak Current Duration>Peak Current.A well-formed weld under high-speed welding is obtained by optimizing the process parameters.The adhesion between the welding wire and the workpiece proved to be the main reason for poor weld formation under high-speed welding through the images of droplets transition.The root cause of this phenomenon is the small amount of liquid metal between the end of the wire and the front edge of the molten pool solidifies during the wire drawing process.Welding wire adhesion during high-speed welding of aluminum alloy CMT can be effectively prevented by optimizing the welding current waveform parameters and increasing the amount of liquid metal between the end of the welding wire and the molten pool.A method of a tilting torch for preventing wire adhesion is proposed.Under the condition of welding speed of 3.6 m/min,an average wire feeding speed of 6.5 m/min,a peak current of 220 A,a peak current duration of 15 ms,a base current of 70 A,and a peak wire feed speed of 20 m/min,the welding wire adhesion is effectively prevented by tilting welding torch at 70°.The welding process is stable,and a well-formed weld is obtained.