Arc Behavior And Characteristic Of Tungsten-consumable Indirect Arc Welding

In traditional arc welding, the welding torch and the base metal act as the two electrodes of the arc. For some special occasions such as requiring the high deposition rate of the weld and small amount of fusion of the base metal, the heat input into the base metal is difficultly controlled because the base metal directly absorbs the arc heat. The large fusion of the base metal goes beyond the welding requirements and this restricts the application of the arc welding. For example, depositing Cu alloy onto steel is often applied in aviation, aerospace and weapon facture for improving the electric conductivity, thermal conductivity and surface hardness. To prevent the segreation for the mutal fusion between Fe and Cu, it is required that the fusion of the steel be decreased on condition that the high deposition ratio is ensured, and then the deposition weld with low dilution ratio be obtained.The tungsten-consumable indirect arc welding method has been presented. The base metal does not contact with the welding power source and the two output terminal connects with the consumable electrode and tungsten electrode of the weld power source. There is angle between the two welding torch and the indirect arc is generated between the two torches. The weld is created with the resultant droplets continuously transferring onto the base metal. This method can restrict the heat input into the base metal to the maximum extent while guaranteeing the deposition rate of the welding wire. The steady indirect arc and continuous metal transferring have been realized. These provide the basis for studying the arc behavior and application with the tungsten-consumable indirect arc welding.Take the Cu welding wire for example, the metal transfer behavior of the tungsten-consumable indirect arc welding is observed by high speed camera and the electrical signal is also acquired. The deposition of Cu onto steel substrate process experiment is conducted by this method. The macrostructure and the microstructure are observed. The droplet flying velocity and its impact force are calculated. By using the infrared temperature tester,the droplet temperature is obtained and its heat content is calculated.Result showed that: using constant voltage (CV) weld power source and the constant current (CC) weld power source can both realize continuous metal transfer. When using the CV power, the metal transfer frequency increases with the increase of the wire feeding speed. In 16-20V, the metal transfer frequency and its directionality can keep getting better. When using the CC power, the position of the tip of the welding wire changes from the lateral below the tip of the tungsten to the lateral upon the tip of the tungsten. The metal transfer frequency increases with the increase of the welding current. When the welding current goes beyond 140A, the metal transfer mode changed from globule transfer to spray transfer. Before metal transferred from welding wire, the indirect arc can climb to the interface between the welding wire and the droplet, decreasing the arc fluctuation.The arc shape presents inverted triangle. In different statistic characteristic of the weld power source and different parameters, the arc shape presents different patterns. When the tip of the welding wire is situated on the top left side of the tungsten, the arc shape presents Y shape; when the tip of the welding wire is situated on the left side of the tungsten, the arc shape presents heart shape; when the end of the welding wire is situated on the bottom left side of the tungsten, the arc shape presents pencil shape. The fluctuation of the arc voltage and the welding current correspond with the change of the arc shape. By using the CV power, the fluctuation of the arc is bigger than that by using the CC power.The indirect arc is composed of the cathode zone, the anode zone and the arc column zone. The arc column zone is also been composed of arc core zone and arc flame zone. According to the characteristic of the indirect arc, the whole indirect arc is also composed of consumable arc zone near the consumable electrode and the non consumable arc zone near the tungsten electrode. The convergence of the two zone produced heart arc shape, which can rapidly melt the welding wire. The integrated action by the magnetic field, the hedging between the cathode flame and the anode flame get into inverted triangle arc shape. The indirect arc is stabilized for the addition of the tungsten, the arc self-regulation. When using the Cu welding wire, the CC power is more suitable.The droplet is acted on by the gravity force, surface tension force, electromagnetic force, plasma force and arc force. The arc is situated on the right side of the droplet, and easily climbs to the welding wire. The electromagnetic force increases. The driving component of the arc force also increases,which increases extrusion on the droplet and then decreases the surface tension force.The droplet transfer rate is measured. When the welding current exceeds 140A the droplet transfers quickly. With the increase of the welding current, the impact force onto the base metal reaches the peak and then the impact force drops a little and then stabilized. With the increase of the welding current, the temperature of the droplet gradually fall and then remaining 1200℃. The heat content of the droplet metal is about 30% of the general energy of the arc. This proves that the method can decrease the heat input into the base metal effectively.The indirect arc heat mainly provides the fusion of the welding wire, and the indirect arc force mainly acts on the metal transfer. The tungsten-consumable indirect arc welding has been successfully applied on depositing CuSi3 onto 30CrMnSi steel. No obvious defect is observed and the dilution ratio is decreased at a minimum of to 0.12%. The segreation is restrained for low heat input into the base metal. This method is also successfully applied onto welding 0.6mm thin zinc coated steel plate. Small amount of fusion of the steel also proves that this methods'characteristic of decreasing heat input into the base metal.