“Why do tungsten electrodes sometimes split when I am welding aluminium?”
Splitting tungsten electrodes is a common problem while welding aliminium. Someone asked me this both during Welding Week 2019 in Antwerp, and a few days later by email, It is a complex issue, because it all depends on many factors. It doesn’t always happen. Even tungsten electrodes from the same production batch can react differently. The strangest thing is that it is not type related. It occurs with gold, blue, purple, gray and also with turquoise.
Splitting tungsten electrodes: a machine problem?
With the above in mind, it seems that the splitting of tungsten electrodes is not an electrode problem, but rather machine problem. It also occurs in several brands of machines, which in turn points to a parameter problem. This means that a combination of parameters cause this problem. Because the splitting of tungsten electrodes occured irregularly, it was difficult to obtain parameters to further analyse the problem. Fortunately, the person who asked the question by email was able to answer the following questions.
- What type and diameter of tungsten electrode is used? – 2.4 mm, various types
- How is the tungsten electrode polished or welded to the tungsten electrode with a sphere? – 45 degrees, with a flattened point
- What is the balance setting? – Minus 67%
- What is the frequency of welding? – 120 Hz
- What is the set welding current? – 91 Ampere
- Which gas is welded with and how many litres per min? – Argon 4.8, with 7 litres per minute
What stands out?
The top angle is ground at 45 degrees with a flattening is unusual. The flattening should not be greater than 1.0 mm. With a top angle of 45 degrees, a flattening and an amperage of 91 amperes, the current density at the point becomes risky low, especially with alternating current. The temperature of the tungsten electrode will also remain low and this will influence the arc stability.
Due to the 45 degree electrode tip the arc spot is relatively small. It will become even smaller due to the frequency of 120 Hz. There is nothing wrong with this in itself. However, because the heat dissipation of aluminium is so great and the increased welding speed, there is a chance of hot cracks in the material. The ratio between height and width is now incorrect. This has to do with the small puddle and the very short cooling time.
With the balance control set for the frequency of 120 Hz, the plus is 33% and the minus 67%. With these parameters, you need this combination to get a proper cleaning effect.
What is the advice?
In conclusion, based on what we know, my advice is to set the balance to 25% plus and 75% minus and the frequency to 75 Hz. Grind the top corner of the electrode to 60 degrees. The tungsten electrode tip will now become slightly warmer, therefore increasing arc stability. A flattening of a maximum of 1.0 mm is allowed, but is not necessary for this relatively low current.
A frequency of 75 Hz will positively influence the welding result, but is also better for the welder. At a frequency of 120 Hz, the risk of hearing damage is much higher.
Important addition! Pay attention to the starter current setting. When using three components tungsten electrodes it should be set as low as possible. A maximum of 5 amps and preferably a little lower. The electrical conductivity of these tungsten electrodes is extremely high compared to other types. If the starting current is set too high, the tip of the tungsten electrode will split immediately at the start.
We have received feedback; after implementing the above the tungsten electrode does no longer split during welding!