TIG welding – how to set up the welder, how to choose the right electrode and shielding gas?
TIG welding is certainly the most versatile process. With this method, we are able to handle the widest variety of materials, even those that are heavy and toxic.
Inert gas TIG welding is also best for thin materials, thanks to the low heat input which prevents burning. It is therefore most commonly used in the welding of aluminium.
How does TIG welding work? In this method, voltage is applied to the tungsten electrode via a current-carrying wire coming from the current source. The tungsten electrode is heat resistant, so it does not burn during welding.
The biggest advantages of this welding method are the possibility to use alternating current, the best joint quality, a stable welding arc between the electrode and the material to be welded, the possibility to weld in all positions and the welding of workpieces with different thickness ranges.
The disadvantages of TIG welding include low welding speed, low productivity, expensive welding torch and relatively high welding operator experience required.
TIG welding – how does it work?
Starting with the basics, TIG welding is a method of welding with a non-fusible tungsten electrode in a shield of inert gases such as argon, helium or mixtures of these. Most commonly, however, the shielding gas that welders use in this method is argon.
The resulting welding arc between the electrode and the material melts our base material. In addition, there is no need for additional material, but if we choose to feed it (the filler material is in the form of 1m long rods with a suitable diameter) we have to do it manually.
The energy required for arc glowing is supplied by a unidirectional (direct or pulsed) welding source – so-called DC TIG or alternating current – so-called AC TIG.
Direct current with negative polarity on the electrode is used for welding almost all metals except AL, Mg and their alloys.
As far as positive polarity is concerned, in TIG welding it is not used in practice due to the fact that about 70% of the heat is released at the electrode, which will cause melting.
Aluminium, magnesium and their alloys are welded with alternating current so as to remove any oxides from the metal surface that are difficult to fuse.
TIG welding vs. MIG MAG welding – which method is better?
TIG welding is regarded as the most difficult manual welding method and is therefore not recommended for beginners. Unlike the shielded gas MIG MAG method, the welding pattern is slightly different.
The main difference between MIG and TIG welding is the electrode used to create the arc and the current source.
MIG welding uses solid welding wire, which is fed into the weld automatically by the wire feeder, while TIG welding uses a non-wearing electrode – the welding arc comes out of this electrode.
TIG welding sometimes also uses a manual filler rod.
TIG welding thus involves the generation of an electric arc using an electrode that, unlike MIG MAG welding, is not subject to wear.
Tungsten electrode for TIG welding
TIG welding is otherwise known as welding with a tungsten electrode – that is, a rod placed in a ceramic nozzle in the welding gun. Around the electrode is a shielding gas nozzle.
It is the part of the holder that will affect the quality of the whole process, so its proper selection is very important. The classification of welding electrodes depends on the composition and type of oxides present in the electrode. We can distinguish between :
- tungsten welding electrodes – made of pure tungsten
- torium welding electrodes – with the addition of thorium oxides
- lanthanum welding electrodes – with the addition of lanthanum
- cerium welding electrodes – with cerium added
- Zirconium welding electrodes – with the addition of zirconium
To make it easier for the welder to choose the right electrode, they are colour-coded, below we will present the most popular electrodes with a description of their use.
Green tungsten electrodes
This is the only electrode consisting of pure tungsten, designed for welding aluminium, magnesium and their alloys, used in AC welding.
Red tungsten electrodes
A torrefied electrode containing 98% tungsten and 2% thorium oxide. This is the most popular electrode in TIG welding due to its long life, good ignition and stable arc during welding. It is also very versatile and can be used for DC welding (with negative polarity) of stainless steels, nickel, titanium, copper and AC welding of thin aluminium components.
Yellow tungsten electrodes
The lanthanum electrode contains 98.5% tungsten and 1.5% lanthanum oxide. A versatile electrode with high arc stability, good tacking properties and recommended for high current welding. Suitable for DC and AC welding. Suitable for welding of high alloyed and unalloyed steels, aluminium, titanium, copper and magnesium alloys.
Blue tungsten electrodes
Lanthanum electrode containing 98% tungsten and 2% lanthanum oxide. A versatile electrode for AC and DC welding processes and plasma welding, recommended for automated welding. Used for unalloyed steels, high-alloyed steels, aluminium, titanium, copper and magnesium alloys.
Purple tungsten electrodes
Tungsten electrode (98.5% tungsten, 1.75% lanthanum oxide, 0.095% cerium oxide). Recommended for low to medium welding current due to very good arc ignition, used for welding steel, stainless steel, copper and brass.
Grey tungsten electrodes
Cerium electrodes containing 98% tungsten and 2% cerium. Similar in application and properties to a torrefied electrode. Can be welded with direct current DC and alternating current AC. Used for orbital welding of pipes, welding of thin sheets. Are a replacement for green electrodes. Suitable for welding high-alloyed steels, unalloyed steels, aluminium, titanium, nickel, copper, magnesium and its alloys.
White tungsten electrodes
Zirconium electrodes contain 99.10% tungsten and 0.15-0.40% zirconium. They are ideal for AC welding, retain the spherical shape of the tip, have high resistance to contamination, and form a very stable arc. Used for welding aluminium and magnesium alloys.
TIG welding – electrode diameter selection
In addition to the type of electrode itself, it is also important to remember to select the correct electrode diameter:
- 1.0 mm DC current (A) 5-80; AC (A) 10-80
- 1.6 mm DC current (A) 60-140; AC current (A) 15-90
- 2,4 mm current DC (A) 130-220; AC (A) 20-140
- 3,2 mm current DC (A) 220-340; AC (A) 30-200
- 4,0 mm current DC (A) 330-350; AC (A) 40-350
TIG welding – how to set up the welding machine?
We can carry out the TIG welding process with DC current, during this welding negative polarity is used on the electrode in order to avoid excessive heating of the material and the handle itself.
We will use AC for welding aluminium, magnesium and their alloys, this type of welding gives us greater stability and control over the welding process.
A widely used feature in TIG welding today is the ability to weld with Pulses. We then adjust the power of the welder, the frequency and the fill factor, thanks to this function we have the possibility to weld thin sheets, because we do not overheat the base material, we have an influence on the shape of the weld and the focus of the arc. TIG welding does not always require additional material.
The parameter that we set directly on the welding machine is the current intensity. We select it according to the thickness of the material as well as the electrode and the position in which we are welding. The amperage will determine the depth of fusion and the width of the weld. It should be remembered that an increase in current increases the temperature of the end of the non-fusing electrode.
What gas for TIG welding?
The most common shielding gas used in welding is argon or an argon-helium mixture. Inert, i.e. non-reactive, gases prevent chemical reactions with the molten weld pool and the heated workpiece.
The purpose of shielding gases is to protect the weld pool and consumable electrode from contamination from the atmosphere. The gas flow rate will be related to the current and the type of gas, under the most typical conditions the flow rate will be 8÷16 litres/min.
The last important step in TIG welding is to thoroughly clean the edges of the material to be welded of any impurities, which is very important for the welding process to run smoothly.
TIG welding gives us the possibility of obtaining a very clean and high-quality weld, where we do not always have to use a filler metal. The lack of spatter and the possibility of a very good control of the process makes it possible to weld in all positions, both manually and mechanised. It is not without reason that this welding is called ‘clean welding’.
