Table 1 – Typical welding current ranges for different tungsten electrode diameters in TIG welding.
Preparation – grinding the tungsten electrodes – tip, round, or cut tip?
After you have decided on an electrode type, the next step is the choice of the grinding method. The three most common methods of grinding the tungsten electrodes are point, round point, or cut point.
A round tip is normally used for pure tungsten electrodes labeled green and is recommended for alternating current (AC) welding with sinusoidal current waves and for conventional TIG welding machines with rectangular current waves. To properly shape the tip of the tungsten electrode, simply use the recommended alternating current for a given electrode diameter (Table 1) and a round tip will form at the end of the electrode. The diameter of the rounding formed should not exceed 1.5 times the diameter of the electrode (e.g. the electrode with a diameter of 1.6 mm must not have a round tip with a diameter of approx. 2 to 2.5 mm exceed). A larger ball at the tip of the electrode can reduce the stability of the arc. In addition, the round tip can fall off and contaminate the weld seam.
Preparation – grinding the tungsten electrodes
In TIG welding with inverter welding devices with direct or alternating welding current, the tungsten electrodes are ground to a point or a sharpened point. To avoid contamination of the electrodes, we recommend using special grinding wheels for grinding tungsten. Diamond cutters are best for this.
When grinding the thorium-tungsten electrodes, make sure that they are suctioned off and ventilated, as the dust produced during grinding is poisonous and harmful to health. Follow the manufacturer’s warnings, instructions, and safety data sheets.
The electrode is ground parallel to the grinding wheel so that the grinding marks run lengthways to the electrode, which ensures a stable arc and reduces the possibility of welding contamination.
We also recommend that you grind the tungsten electrode as centrically as possible, because the more centrically it is ground, the more stable the arc is, on which the arc quality also depends.
The cone at the end of the electrode should not be larger than 2.5 times the electrode diameter. For example, with a 1.6 mm electrode, the cone should be about 4 mm long. Electrode ground in this way guarantees better ignition and more precision in the arc.
If you are welding a thin material with a very low current (from 0.1 to 1.00 mm) it is best that the electrode is ground to a point. In this case, the point-ground tungsten electrode ensures the maximum concentration of the arc and thus prevents excessive heat transfer to the weld seam. In practice, this means less bending of the workpiece.
It is not recommended that you use a pointed tungsten electrode with higher welding currents, as increased welding current can cause the tip of the electrode to fall off and contaminate the weld. When welding at higher currents, it is best that the electrode tip is smoothed and ground. So, sharpen the electrode as described above, then lightly sand the top of the tip. The flat surface at the end of the electrode prevents tungsten from being transferred across the arc and prevents the formation of a ball.
Of course, there are also special electrode grinders for grinding tungsten electrodes, but due to the high prices and their unavailability, these are only mentioned here. If you follow instructions for choosing and preparing the tungsten electrodes, you can get great results even without special machinery and equipment.
How the arc and the binding behave depends on the bevel angle. An acute angle causes the penetration to be deeper, while an obtuse angle causes the penetration to be shallower with the same welding current. However, in order to achieve a good welding result and to reduce the load on the tip, the guideline value is that the tip of the electrode can be blunted by approx. 10% of the electrode diameter after grinding (2.4mm = approx. 0.24mm blunt). For the length, the diameter of the electrode is approx. Times 1 – 1.5. So the length of a 1.6 mm electrode is 1.6 – 2.4 mm.