Taboos of Tungsten Inert Gas Arc Welding Process
1 Avoid using DC reverse welding in general welding
During DC tungsten inert gas arc welding, the heat generated by the anode is much greater than that of the cathode. Therefore, when using DC positive connection (workpiece positive connection) welding, the tungsten electrode is not easy to overheat due to its low heat generation. Tungsten electrodes of the same diameter can use a larger current. At this time, the workpiece generates a large amount of heat, the penetration depth is also large, the productivity is high, and the tungsten electrode’s thermal electron emission ability 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 DC positive connection. The situation is the opposite of the above when DC reverse welding is used, and it is generally not recommended.
2 Avoid using too large a proportion of the negative half-wave power-on time of rectangular wave AC tungsten inert gas arc welding
Rectangular wave AC tungsten inert gas arc welding can unify the DC component and adjust the strength of the cathode cleaning effect by changing the ratio of the positive and negative half-wave power-on time.
However, the appropriate minimum ratio should be selected according to the welding conditions so that it can meet the needs of cleaning the oxide film and obtain the maximum penetration depth and the minimum tungsten electrode loss. Although a larger ratio can achieve a lighter cathode cleaning effect, it will cause serious burning of the tungsten electrode, and the molten pool will become shallow and wide, which is not conducive to welding.
3 Avoid using a sharp cone angle tungsten electrode when the welding current is too large
When the welding current is large, using a thin diameter sharp cone angle tungsten electrode will make the current density too large, causing the end of the tungsten electrode to overheat and melt and increase the burning.
At the same time, the arc half point will also extend to the cone surface at the end of the tungsten electrode, causing the arc column to expand significantly and drift unsteadily, affecting the formation of the weld. Therefore, when welding with a large current, a tungsten electrode with a thicker diameter should be used, and its end should be ground into a blunt cone angle or a flat-top cone for standby use.
4 Avoid gas flow and nozzle diameter exceeding the proper range
Under certain conditions, there is an optimal matching range for gas flow and nozzle diameter. For manual argon arc welding, when the flow rate is 5-25L/min, the corresponding nozzle diameter is 5-20mm.
Within this range, if the airflow is too small or the nozzle diameter is too large, the airflow stiffness will be poor, the ability to remove the surrounding air will be weak, and the protection effect will be poor;
If the airflow is too large or the nozzle diameter is too small, turbulence will be formed due to the high airflow speed, which will not only reduce the protection range, but also cause air to be drawn in, reducing the protection effect.
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5 Avoid using too high a welding speed for gas shielded welding
The size of the welding speed is mainly determined by the thickness of the workpiece, and is coordinated with the welding current, preheating temperature, etc. to ensure the required melting depth and melting width. However, in high-speed automatic welding, the influence of the welding speed on the gas protection effect must also be considered, and it is not advisable to use too high a welding speed.
Because the welding speed is too high, the protective airflow is seriously backward, which may be that the tungsten extreme end, arc column and molten pool are exposed to the air, thus affecting the protection effect.
6 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 of the electrode extension length and arc. When the electrode extension length remains unchanged, changing the distance from the nozzle to the workpiece not only changes the size of the arc length, but also changes the state of gas protection.
If the distance from the nozzle to the workpiece is increased, the arc cone will become larger and the gas protection effect will be greatly affected. However, if the distance is too close, it will not only affect the line of sight, but also easily cause the tungsten wire to contact the molten pool, resulting in tungsten inclusion defects. Generally, the distance between the top of the nozzle and the workpiece is between 8-14mm
7 Avoid using the contact arc initiation method for tungsten inert gas welding
Contact arc initiation means directly short-circuiting the end of the tungsten electrode with the weldment, and then quickly pulling it apart to ignite the arc. This arc initiation method has poor reliability, the tungsten electrode is easily burned, and the metal tungsten mixed in the weld will cause “tungsten inclusion” defects. Therefore, contact arc initiation has many disadvantages and is not easy to use.
8 Avoid using a simple welding process for argon arc welding
The welding process is too simple, which is prone to obvious weld depressions, pores and cracks, especially for materials with a greater tendency to thermal cracks.
The normal welding process should be to initiate and end the arc under argon protection to prevent oxidation of the tungsten electrode and weld metal, which will affect the quality of the weld. At the same time, the current attenuation method is used to reduce the welding current, and cracks are prevented by gradually reducing the heat input of the molten pool.
9 Avoid jumping movement of welding gun during flat welding
Flat welding is a welding position that is easier to master and is suitable for manual welding and automatic welding. During welding, the position of tungsten electrode and workpiece should be accurate, the welding gun angle should be appropriate, and special attention should be paid to the stability of arc and the uniformity of welding gun moving speed to ensure uniform and consistent weld depth and weld width. It is advisable to use left-hand welding method during manual welding, and the welding gun should make uniform linear movement.
In order to obtain a certain weld width, the welding gun is allowed to swing horizontally, but it is not advisable to jump. The diameter of the filler wire is generally not more than 3mm.
10 Avoid using aluminum and copper welding wires for hot wire tungsten arc welding
The resistance heat generated by the additional power supply at the front end of the welding wire can be used to heat the welding wire to a predetermined temperature, thereby increasing the welding deposition speed. However, for aluminum and copper, due to their small resistivity, a large heating power supply is required, which causes excessive arc magnetic blow and uneven melting, so hot wire welding is not easy to use aluminum and copper welding wires.
Post time: Jan-14-2025
