The welding current of tungsten inert gas arc welding is usually selected based on the material, thickness, and spatial position of the workpiece. As the welding current increases, the penetration depth increases, and the width and excess height of the weld seam slightly increase, but the increase is small. Excessive or insufficient welding current can cause poor weld formation or welding defects.
The arc voltage of tungsten inert gas welding is mainly determined by the arc length. As the arc length increases, the arc voltage increases, the weld width increases, and the penetration depth decreases. When the arc is too long and the arc voltage is too high, it is easy to cause incomplete welding and undercutting, and the protection effect is not good.
But the arc cannot be too short either. If the arc voltage is too low or the arc is too short, the welding wire is prone to short circuiting when it touches the tungsten electrode during feeding, causing the tungsten electrode to burn out and easily trapping tungsten. Therefore, the arc length is usually made approximately equal to the diameter of the tungsten electrode.
When the welding speed increases, the depth and width of fusion decrease. When the welding speed is too fast, it is easy to produce incomplete fusion and penetration. When the welding speed is too slow, the weld seam is wide and may also have defects such as weld leakage and burn through. During manual tungsten inert gas welding, the welding speed is usually adjusted at any time based on the size, shape, and fusion situation of the molten pool.
1. Nozzle diameter
When the nozzle diameter (referring to the inner diameter) increases, the flow rate of protective gas should be increased. At this time, the protected area is large and the protective effect is good. But when the nozzle is too large, it not only increases the consumption of argon gas, but also makes it difficult to observe the welding arc and welding operation. Therefore, the commonly used nozzle diameter is generally between 8mm and 20mm.
2. Distance between nozzle and weldment
The distance between the nozzle and the workpiece refers to the distance between the nozzle end face and the workpiece. The smaller this distance, the better the protection effect. Therefore, the distance between the nozzle and the weldment should be as small as possible, but too small is not conducive to observing the molten pool. Therefore, the distance between the nozzle and the weldment is usually taken as 7mm to 15mm.
3. Extension length of tungsten electrode
To prevent the arc from overheating and burning out the nozzle, the tungsten electrode tip should usually extend beyond the nozzle. The distance from the tungsten electrode tip to the nozzle end face is the tungsten electrode extension length. The smaller the tungsten electrode extension length, the closer the distance between the nozzle and the workpiece, and the better the protection effect. However, if it is too small, it will hinder the observation of the molten pool.
Usually, when welding butt joints, it is better for the tungsten electrode to extend a length of 5mm to 6mm; When welding fillet welds, it is better to have a tungsten electrode extension length of 7mm to 8mm.
4. Gas protection method and flow rate
In addition to using circular nozzles to protect the welding area, tungsten inert gas welding can also make the nozzle flat (such as narrow gap tungsten inert gas welding) or other shapes according to the welding space. When welding the root weld seam, the back weld seam of the welded part will be contaminated and oxidized by air, so back inflation protection must be used.
Argon and helium are the safest gases to inflate the back during welding of all materials. And nitrogen is the safest gas for back inflation protection when welding stainless steel and copper alloys. The gas flow rate range for back inflation protection of general inert gas is 0.5-42L/min.
The protective airflow is weak and ineffective, and it is prone to defects such as porosity and oxidation of welds; If the air flow rate is too large, it is easy to generate turbulence, the protection effect is not good, and it will also affect the stable combustion of the arc.
When inflating the pipe fittings, appropriate gas outlets should be left to prevent excessive gas pressure inside the pipes during welding. Before the end of the root weld bead welding, it is necessary to ensure that the gas pressure inside the pipe is not too high, in order to prevent the welding pool from blowing out or the root from being concave. When using argon gas for backside protection of pipe fittings during welding, it is best to enter from the bottom, allowing air to be discharged upwards and keeping the gas outlet away from the weld seam.