1. Avoid using DC reverse welding in general welding

a）为直流反接   b）直流正接

The heat generated by the anode during DC tungsten arc welding is much greater than that of the cathode, so when welding with DC positive connection (workpiece is connected to the positive), the tungsten electrode is not easy to overheat due to the small heat generation, and the tungsten electrode of the same diameter can use a larger current. At this time, the workpiece generates a large amount of heat, has a large penetration depth, and has a high productivity. The tungsten electrode thermionic emission capability is stronger than that of the workpiece, which makes the arc stable and concentrated. Therefore, most metals (except aluminum, magnesium and their alloys) should be welded by direct current welding.

In DC reverse welding, the situation is opposite to the above, and it is generally not recommended.

2. Rectangular wave AC tungsten argon arc welding negative half-wave energization time ratio should not be too large

Rectangular wave AC tungsten arc welding can match the DC component and adjust the strength of the cathode cleaning effect by changing the ratio of the positive and negative half-wave energization time, but the appropriate minimum ratio should be selected according to the welding conditions, so that it can meet the cleaning requirements. The need of oxide film can achieve the maximum penetration and minimum tungsten loss. If the ratio is too large, a lighter cathode cleaning effect can be obtained, but the tungsten electrode will be burnt seriously, and the molten pool will become shallow and wide, which is not good for welding.

3. Avoid using sharp cone angle tungsten electrode when welding current is too large

When the welding current is large, using a tungsten electrode with a small diameter and sharp cone angle will cause the current density to be too large, causing the end of the tungsten electrode to overheat and melt and increase 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, causing the arc column to significantly expand and fluctuate, which affects the formation of the weld. Therefore, the tungsten electrode with a thicker diameter should be selected when welding with high current, and its end should be ground into an obtuse cone angle or a flat-topped cone to be used.

4. The gas flow rate and nozzle diameter should not exceed the expected range

Under certain conditions, there is an optimal range of 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. In this range, if the airflow is too small or the nozzle diameter is too large, the airflow stiffness will be poor, the ability to exclude 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, the airflow velocity will be too high. Turbulent flow is formed, which not only reduces the scope of protection, but also draws air in, reducing the protection effect.

5. Avoid excessive welding speed in gas shielded welding

The welding speed is mainly determined by the thickness of the workpiece, and is matched with the welding current and preheating temperature to ensure that the required penetration depth and penetration width are obtained. 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 high and the protective airflow is seriously behind, it may be that the tungsten extreme part, arc column and molten pool are exposed to the air, which affects the protection effect.

6. The distance between the nozzle and 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 outer elongation of the electrode 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 increases, the conical ground of the arc will become larger, and the gas protection effect will be greatly affected. However, the distance is too close, not only will affect the line of sight, and easily make the tungsten wire contact with the molten pool, resulting in tungsten clamping defects. Generally, the distance between the top of the nozzle and the workpiece is between 8-14mm

7. Avoid using contact ignition method in tungsten argon arc welding

Contact ignition, that is, the end of the tungsten electrode and the weldment are directly short-circuited, and then quickly pulled apart to ignite the arc. The reliability of this arc ignition method is poor, and tungsten is extremely easy to burn, and the metal tungsten mixed in the weld will cause the defect of "tungsten clamping". Therefore, contact ignition has many disadvantages and is not easy to use.

8. Avoid using simple welding process for argon arc welding

The welding process is too simple, and it is easy to produce obvious welding seam depressions, pores and crack defects, especially for materials with greater thermal cracking tendency. The normal welding process should be to start and close the arc under argon gas 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 method of current attenuation is used to reduce the welding current, and the heat input of the molten pool is gradually reduced to prevent cracks.

9. Avoid jumping motion of the welding torch during flat welding

Flat welding is a kind of welding position that is easier to grasp, suitable for manual welding and automatic welding. When welding, the position of the tungsten electrode and the workpiece should be accurate, and the welding gun angle should be appropriate. Special attention should be paid to the stability of the arc and the uniformity of the moving speed of the welding torch to ensure uniform penetration and width of the weld. It is advisable to use the left-hand welding method for manual welding, and the welding torch makes a uniform linear movement. In order to obtain a certain melting width, the welding torch is allowed to swing horizontally, but it is not suitable for jumping. The diameter of the filler wire generally does not exceed 3mm.

10. Avoid using aluminum and copper welding wires in hot wire tungsten argon arc welding

The resistance heat generated by the additional power source in the front section of the welding wire 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 bias and uneven melting, so it is not easy to use aluminum and copper welding wires for hot wire welding.

What are the technological characteristics of low and high frequency pulse argon tungsten arc welding?

1. During the duration of the pulse current, a spot-shaped molten pool is formed on the weldment; during the period of the pulse current stop, the base current can only maintain the stable combustion of the arc, the heat input to the weldment is significantly reduced, and the molten pool metal solidifies to form a welding spot. Therefore, the weld is composed of a series of weld points.

2. The arc is stable and the stiffness is good. When the current is small, general TIG welding is easy to arc, but pulsed TIG welding has good arc stiffness and stability, so this welding method is especially suitable for thin plate welding.

3. Low arc line energy. The pulse arc heats the workpiece centrally and has high thermal efficiency. Therefore, the average current required to penetrate the workpiece with the same thickness is about 20% lower than that of general tungsten arc welding, thereby reducing the heat input, which is beneficial to reduce the heat-affected zone and Reduce welding distortion.

4. Easy to control the weld formation. The welding pool has fast solidification speed and short high temperature residence time, so it can ensure a certain penetration depth, and is not easy to cause overheating, flow or burn-through, which is beneficial to realize single-sided welding without backing and double-sided welding and all-position welding.

5. The weld quality is good. Pulsed tungsten argon arc welding is formed by overlapping welding points, and the thermal cycle of subsequent welding points has a heat treatment effect on the previous welding point. At the same time, because the pulse current has a strong stirring effect on the spot molten pool, the cooling rate of the molten pool is fast, and the high temperature residence time is short, so the weld metal structure is fine and the dendrites are not obvious. These all make the weld performance improved.

What are the technological characteristics of high-frequency pulse argon tungsten arc welding?

The frequency range of the current is 10~20kHz. The process characteristics of this method are as follows.

①Suitable for high-speed welding

The high-frequency pulse arc has a large electromagnetic shrinkage effect and a good arc rigidity. It can avoid the bend or discontinuity of the weld bead caused by the adhesion of the anode spot during high-speed welding; avoid defects such as undercut and poor back forming. Therefore, it is especially suitable for high-speed automatic welding of thin plates.

②Big penetration

The arc pressure is large and the energy density is large, so the arc penetration capability is significantly increased.

③Good weld quality

The molten pool is subjected to ultrasonic vibration, its fluidity increases, and the physical and metallurgical properties of the welding are improved, which is conducive to the improvement of the quality of the weld.

④Suitable for large groove weld

In DC tungsten argon arc welding, if there are too many filler wires, the weld pool and the side of the groove will be poorly fused, and the weld bead will be raised and deflected to one side. When welding the next weld bead, poor melting on both sides of the weld bead easily leads to poor fusion or incomplete penetration. High-frequency pulse tungsten argon arc welding can well overcome this defect.

Many characteristics of high frequency argon tungsten arc welding are between general argon tungsten arc welding and plasma arc welding, see table

What are the technological characteristics of intermediate frequency pulsed argon tungsten arc welding?

The frequency range of the current is 10~500Hz. Its characteristic is that the arc is very stable under small current, and the arc force is not as high as high-frequency argon tungsten arc welding, so it is an ideal method for manual welding of thin plates below 0.5mm.

Source: Welding Technology, Fish Bubble Net

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