Ten Taboos Of Argon Tungsten Arc Welding - Industry News

01 In general welding avoid the use of DC reverse welding method
The caloric value of the anode is much higher than that of the cathode in DC tungsten argon arc welding. Therefore, the tungsten electrode is not easy to overheat due to the small caloric value in DC positive welding (workpiece positive welding). The tungsten electrode with the same diameter can use a larger current. At this time, the workpiece heat is large, deep penetration is also large, high productivity, tungsten pole thermal-electron emission capacity is stronger than the workpiece, so that the arc is stable and concentrated. Therefore, most metals (except aluminum, magnesium and their alloys) should be welded with direct current joint. The situation of DC reverse welding is contrary to the above, which is generally not recommended.
02 The ratio of negative half wave conduction time in rectangular AC tungsten argon arc welding should not be too large
Rectangular wave AC tungsten-argon arc welding can be done by changing the ratio of positive and negative half wave current time to match the DC component and adjust the strength of cathode cleaning. However, appropriate minimum ratio should be selected according to welding conditions, so that it can not only meet the needs of cleaning oxide film, but also obtain the maximum penetration depth and the minimum tungsten loss. Though the ratio is too large, it can get light cathode cleaning effect, but it will cause serious burning of tungsten electrode, and the welding pool will become shallow and wide, which is unfavorable to welding.
03 When the welding current is too large, do not use tapered tungsten electrode
When the welding current is large, the use of thin diameter taper tungsten electrode will make the current density too large, resulting in overheating and melting of the tungsten electrode end and increase the burning. At the same time, the arc half point will also extend to the tungsten terminal cone, so that the arc column is obviously extended, drift instability, affect the weld forming. Therefore, the tungsten electrode with a larger diameter should be selected for high current welding, and its end should be ground into a blunt cone Angle or a cone with a flat top to be used.
04 Gas flow and nozzle diameter should not exceed the proper range
Under certain conditions, the gas flow and nozzle diameter have an optimal matching range. For manual argon-arc welding, the corresponding nozzle diameter is 5-20mm when the flow rate is 5-25L/min. In this range, the airflow is too small or the nozzle diameter is too large, will make the airflow stiffness is poor, the ability to exclude the surrounding air is weak, the protection effect is not good; If the airflow is too large or the nozzle diameter is too small, the airflow speed will be too high and turbulent, which not only reduces the protection range, but also makes the air involved, reducing the protection effect.
05 Excessive welding speed should not be used in gas shielded welding
The size of the welding speed is mainly determined by the thickness of the workpiece, and the welding current, preheating temperature, etc., in order to ensure that the required penetration depth and width. However, in high-speed automatic welding, the influence of welding speed on gas protection effect should be considered, so it is not suitable to use too large welding speed. Because the welding speed is too high, the protective airflow may be seriously deviated, and the tungsten extreme part, arc column and molten pool may be exposed to the air, thus affecting the protective effect.
06 The distance from the nozzle to the workpiece should not be too large or too small
The distance from the nozzle to the workpiece reflects the relative length and radian of the electrode. When the electrode extension length is constant, changing the distance from the nozzle to the workpiece not only changes the arc length, but also changes the state of gas protection. If the distance between the nozzle and the workpiece is enlarged, the conical surface of the arc will be enlarged, and the gas protection effect will be greatly affected. But too close, not only will affect the line of sight, and easy to make tungsten wire and weld pool contact, resulting in tungsten clamping defects. Generally, the distance between the top of the nozzle and the workpiece is between 8-14mm.
07 Tungsten argon arc welding should not use contact arc initiation method
Contact arc initiation, that is, direct short circuit between the end of the tungsten pole and the weldment, and then quickly pull apart to ignite the arc. The reliability of this method is poor, the tungsten pole is easy to burn, and the metal tungsten mixed into the weld will cause the "clamping tungsten" defect. Therefore, contact arc initiation has many disadvantages and is not easy to use.
08 Argon arc welding should not adopt simple welding process
The welding process is too simple, easy to produce obvious weld sag, porosity and crack defects, especially for materials with a larger tendency of thermal crack. The normal welding process should be arc starting and arc retracting in argon to avoid the oxidation of tungsten electrode and weld metal, which will affect the quality of weld. At the same time, the current attenuation method is used to reduce the welding current, and the heat input of the weld pool is gradually reduced to prevent the crack.
09 Skip movement of the torch is avoided during flat welding
Flat welding is easy to master a kind of welding position, suitable for manual welding and automatic welding. During welding, the position of the tungsten pole and the workpiece should be accurate, and the Angle of the welding gun should be appropriate. Special attention should be paid to the stability of the arc and the uniformity of the moving speed of the welding gun, so as to ensure the uniform penetration depth and width of the weld. Hand welding time to adopt the left welding method, welding gun to do uniform linear motion. In order to obtain a certain width, the welding torch is allowed to swing sideways, but not jumping. The diameter of the filler wire is generally not more than 3mm.
10 Do not use aluminum or copper wire for hot wire argon tungsten arc welding
The resistance heat generated by the additional power supply in the front section of the welding wire can be heated to a predetermined temperature, so as to improve the welding coating speed. But for aluminum and copper, due to the small resistivity, requires a large heating power supply, resulting in too large arc magnetic bias and melting uneven, so hot wire welding is not easy to use aluminum, copper wire.