1. Do not use DC reverse welding in general welding
During DC tungsten arc welding, the calorific value of the anode is much greater than that of the cathode, so when using DC positive connection (workpiece positive) welding, the tungsten electrode is not easy to overheat due to its small calorific value, and the tungsten electrode 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, and the productivity is high. The tungsten electrode has a stronger thermionic emission capability than the workpiece, so that the arc is stable and concentrated.
Therefore, most metals (except aluminum, magnesium and their alloys) should be welded by DC positive welding. The situation of DC reverse welding is the opposite of the above, and it is generally not recommended.
2. The ratio of the negative half-wave energization time of rectangular wave AC tungsten arc welding should not be too large
Rectangular wave AC tungsten arc welding can make the DC component consistent and adjust the strength of cathode cleaning by changing the ratio of positive and negative half-wave energization time.
However, the appropriate minimum ratio should be selected according to the welding conditions, so that it can not only meet the needs of cleaning the oxide film, but also obtain the maximum penetration depth and minimum tungsten electrode loss. If the ratio is too large, a lighter cathode cleaning effect can be obtained, but the tungsten electrode will be seriously burned, and the molten pool will become shallow and wide, which is not good for welding.
3. When the welding current is too large, avoid using tungsten electrodes with sharp cone angle
When the welding current is large, using a tungsten electrode with a small diameter and a tapered angle will cause the current density to be too large, causing the end of the tungsten electrode to overheat and melt and increase the burning loss.
At the same time, the half point of the arc will also extend to the conical surface of the end of the tungsten electrode, which will cause the arc column to expand significantly and become unstable, which will affect the formation of the weld. Therefore, a tungsten electrode with a larger diameter should be used for high-current welding, and its end should be ground into an obtuse taper angle or a taper with a flat top to be used.
4. The gas flow and nozzle diameter should not exceed the proper range
Under certain conditions, the gas flow rate and nozzle diameter have an optimal fit range. 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 diameter of the nozzle is too small, turbulence will be formed due to the high airflow velocity, which will not only reduce the protection range, but also involve air and reduce the protection effect.
5. Gas shielded welding should not use excessive welding speed
The size of the welding speed is mainly determined by the thickness of the workpiece, and is coordinated with the welding current and preheating temperature to ensure the required penetration depth and width. However, in high-speed automatic welding, the influence of welding speed on the gas shielding effect should also be considered, and excessive welding speed should not be used.
Because the welding speed is too large, the protective air flow is seriously deviated, and the top of the tungsten electrode, the arc column and the molten pool may be exposed to the air, thus affecting the protective 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 and arc. When the extension length of the electrode remains unchanged, 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 from the nozzle to the workpiece is increased, the conical ground of the arc 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 make the tungsten wire contact with 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. Tungsten argon arc welding should not use the contact arc ignition method
Contact arc ignition, that is, the end of the tungsten electrode and the weldment are directly short-circuited, and then quickly pulled away to ignite the arc. The reliability of this arc ignition method is poor, the tungsten electrode is easy to burn, and the metal tungsten mixed into the weld will cause the "tungsten inclusion" defect. Therefore, contact arc ignition has many disadvantages and is not easy to use.
8. Avoid using simple welding process in argon arc welding
The welding process is too simple, and it is easy to produce obvious weld depressions, pores and crack defects, especially for materials with a high tendency to thermal cracking.
The normal welding process should be to start and end the arc under argon protection, so as to avoid oxidation of the tungsten electrode and the weld metal, which will affect the quality of the weld. At the same time, the welding current is reduced by the method of current decay, and cracks are prevented by gradually reducing the heat input of the molten pool.
9. The welding torch should avoid jumping motion during flat welding
Flat welding is a welding position that is easier to master, suitable for manual welding and automatic welding. When welding, the position of the tungsten electrode and the workpiece should be accurate, the angle of the welding torch should be appropriate, and special attention should be paid to the stability of the arc and the uniformity of the moving speed of the welding torch to ensure that the penetration depth and width of the welding seam are uniform. In manual welding, the left-hand welding method should be used, and the welding torch should move in a uniform straight line.
In order to obtain a certain melting width, the welding torch is allowed to swing horizontally, but should not jump. The diameter of the filler wire generally does not exceed 3mm.
10. Do not use aluminum and copper wires in hot wire tungsten arc welding
The resistance heat generated in the front section of the welding wire by the additional power source can heat the welding wire to a predetermined temperature, thereby increasing the welding speed. However, for aluminum and copper, due to the small resistivity, a large heating power supply is required, resulting in excessive arc magnetic deflection and uneven melting, so it is not easy to use aluminum and copper welding wires for hot wire welding.
