Stability Analysis And Forming Control Of GTAW Process With Filler Wire Based On Probe Sensing

The introduction of process sensing and quality monitoring mechanism in gas tungsten arc welding(GTAW)is conducive to improving the automation and intelligence level of this welding method.There have been many researches on information sensing and control of GTAW process status,forming morphology or weld imperfection,while most research focuses or monitoring objects are weld pool or electric arc,and the effect of filler metal intervention on the process is usually ignored.To this end,an electrical signal sensing method using the filler metal as probe is proposed for the GTAW process with filler metal in this study,that is,the probe sensing method.Based on this,the effect mechanism of filler metal on arc stability,the dynamic behavior of filler metal and the evolution of sensing signals are explored,the relevant characteristic signals are extracted,and the real-time feedback control of liquid metal transfer state and weld surface height is conducted.Firstly,the monitoring idea,implementation schemes and sensing principle of the probe sensing method are described,the experimental sensing system is designed,and the software interface is developed,thereby realizing the simultaneous acquisition of multiple electrical signals and the external adjustment of wire feed parameter,etc.Secondly,a high-melting-point metal probe is employed instead of filler metal to exert targeted interference on the arc,and the static and dynamic interference mechanism of the filler metal that is also a conductor to the arc is clarified.The intervention of probe metal destroys the minimum energy state of the arc,resulting in an increase in the overall average electric field strength,thereby increasing the arc voltage;the effect of probe metal on different areas of the arc is inconsistent,and the probe voltage can reflect the electrical characteristics of the local area of the arc;as the interference increases,the ionization degree of the arc near the anode side will decrease and it will first become unstable,thus making the electrical characteristics of the local area of the arc different;in the dynamic reciprocating disturbance,when the sudden change of the arc conduction cross-section and the gradual change of the ionization degree in the local area have opposite effect on the probe voltage and the latter has sufficient time to manifest,the probe voltage will reach the extreme point before the arc voltage.And then,the liquid droplet transfer behavior and sensing signals during the GTAW with filler wire are analyzed,and it is found that the probe voltage significantly contains the time information of the existence of the short-circuit liquid bridge,which can be used to detect the liquid droplet transfer mode.Based on high-speed camera and image processing,the dynamic behavior of the droplet is analyzed.It is found that after a certain volume of droplet completes the transfer,the feed of welding wire will make the probe signal approximately linearly changed,and the droplet oscillation will cause the signal to fluctuate up and down.Wavelet transform is used to analyze the time-frequency characteristics of the droplet oscillation,and the result shows that the probe voltage can reflect the droplet oscillation more significantly and sensitively than the arc voltage.Finally,the characteristic signals that characterize the liquid droplet transfer state and the weld surface forming height in the wire-filling GTAW process are extracted respectively,and the fuzzy controller and PID controller are designed.The preliminary real-time control of the droplet transfer stability and the forming height of weld surface is performed.The results of control experiment show that the information sensing and control system studied is effective.