1. DC reverse welding method shall not be used in general welding
a) It is DC reverse connection b) DC positive connection
During DC TIG welding, the heating capacity of the anode is much greater than that of the cathode.
Therefore, when DC positive connection (workpiece positive connection) welding is used, the tungsten electrode is not easy to overheat due to its small heating capacity, and a large current can be used for tungsten electrodes with the same diameter.
At this time, the workpiece has large calorific value, large penetration, high productivity, and the extremely hot electron emission capacity of tungsten is stronger than that of the workpiece, making the arc stable and concentrated.
Therefore, DC Positive welding should be adopted for most metals (except aluminum, magnesium and their alloys).
The situation of DC reverse welding is opposite to the above, and it is generally not recommended.
2. The proportion of negative half wave energization time of rectangular wave AC TIG welding shall not be too large
Rectangular wave AC TIG arc welding can generate DC component and adjust the strength of cathode cleaning by changing the proportion of positive and negative half wave energization time, but the appropriate minimum proportion shall be selected according to the welding conditions, so that it can not only meet the needs of cleaning oxide film, but also obtain the maximum penetration 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 burned seriously, and the molten pool will become shallow and wide, which is unfavorable to welding.
3. Sharp cone angle tungsten electrode shall not be used when welding current is too large
When the welding current is large, the use of fine diameter sharp cone angle tungsten electrode will make the current density too large, cause the end of the tungsten electrode to overheat and melt and increase burning loss.
At the same time, the arc half point will also extend to the conical surface at the end of the tungsten electrode, making the arc column expand obviously and drift unsteadily, affecting the weld formation.
Therefore, tungsten electrode with thicker diameter should be selected during high current welding, and its end should be ground into blunt cone angle or flat top cone to be used.
4. The gas flow and nozzle diameter shall not exceed the proper range
Influence of nozzle size and gas flow rate on protection effect
Under certain conditions, there is an optimal matching range between 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, too small air flow or too large nozzle diameter will lead to poor air flow stiffness, weak ability to eliminate surrounding air and poor protection effect;
If the air flow is too large or the nozzle diameter is too small, turbulence will be formed due to too high air flow speed, which will not only narrow the protection range, but also involve the air and reduce the protection effect.
5. Excessive welding speed shall not be adopted for gas shielded welding
The welding speed is mainly determined by the thickness of the workpiece and cooperates with the welding current and preheating temperature to ensure the required penetration and width. However, in high-speed automatic welding, the influence of welding speed on gas protection effect should also be considered, and excessive welding speed should not be used.
Because the welding speed is too high, the protective air flow is seriously backward, and the tungsten extreme part, arc column and molten pool may be exposed to the air, thus affecting the protective effect.
6. The distance between nozzle and workpiece shall 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 radian.
When the extended length of the electrode remains unchanged, changing the distance between the nozzle and the workpiece changes both the arc length and the state of gas protection.
If the distance between the nozzle and 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 nozzle top and the workpiece is 8-14mm.
7. Contact arc striking method shall not be adopted for TIG welding
Contact arc striking, that is, the end of the tungsten electrode is directly short circuited with the weldment, and then quickly opened to ignite the arc.
The reliability of this arc striking method is poor, the tungsten electrode is easy to burn, and the metal tungsten mixed into the weld will cause the defect of “tungsten inclusion”.
Therefore, contact arc striking has many disadvantages and is not easy to use.
8. Argon arc welding shall not adopt simple welding process
The welding process is too simple, which is easy to produce obvious weld depression, porosity and crack defects, especially for materials with large tendency of thermal crack.
The normal welding process should be to start and stop the arc under argon protection, so as to avoid the oxidation of tungsten electrode and weld metal and affect the weld quality.
At the same time, the current attenuation method is used to reduce the welding current and prevent cracks by gradually reducing the heat input of the molten pool.
9. During flat welding, the welding gun shall not jump
Flat welding is a kind of welding position that is easy to grasp, which is suitable for manual welding and automatic welding.
During welding, the position of tungsten electrode and workpiece shall be accurate, and the angle of welding gun shall be appropriate. Special attention shall be paid to the stability of arc and the uniformity of moving speed of welding gun, so as to ensure the uniformity of weld penetration and width.
During manual welding, the left welding method should be adopted, and the welding gun should move in a uniform straight line.
In order to obtain a certain melting width, the welding gun is allowed to swing horizontally, but should not jump.
The diameter of the filler wire generally does not exceed 3mm.
10. Aluminum and copper welding wires shall not be used for hot wire TIG welding
The resistance heat generated by the additional power supply in the front section of the welding wire can heat the welding wire to a predetermined temperature, so as to improve the welding deposition speed.
However, for aluminum and copper, due to low resistivity and large heating power supply, resulting in excessive arc magnetic bias blowing and uneven melting, it is not easy to use aluminum and copper welding wires for hot wire welding.