Tungsten Electrodes <-> Welding Result

Preliminary Note:

Precondition for a good welding result is the use of a good weld current source with characteristics like HF-ignition, exact setting of weld current, impulse equipment and an adequate current load (duty cycle).

An additional requirement is the use of the correct inert gas (according to DIN EN 439).
For TIG-welding only inert gases may be used (WIG-Schweißen dürfen nur inerte Gase (low oxygen gases, not reacting with ambient air). Most common is Argon of purity grades "pure" (quality 4.6) or "ultra pure" (quality 4.8).
As feature it is recommended to weld with a low hydrogen content, since hydrogen causes a reduction of residue oxygen content in the weld seam.

For manual welding it us recommended to use Argon with 2 % hydrogen content, for automatic welding Argon with up to 5 % hydrogen. In any case the material compatibility must be ensured.

The optimal gas defense during welding is extremely important. A content of oxygen (even if very low) may result - on the one hand - in oxidation of the electrode (blue coloration) and - on the other hand - in weld failures due to oxygen inclusions. Draft air (for instance due to a strong exhaust) shall in any case be avoided.

Moreover it should be taken care of, that all connections from gas bottle to tip of electrode are gas tight, avoiding any suction of oxygen from ambient air into the line system. The ceramic around shouldn't be too small, so that the electrode (and the weld seam) will be well protected bey the inert gas. The electrode shouldn't stick out from the ceramic more than 5 mm.

The inert gas flow must be dosed correctly. A gas flow too low results in mixing with the ambient air. But a gas flow too high will draw oxygen due to turbulences to the weld seam.

After completion of welding the electrode (as well as the weld area) shall be rinsed with inert gas until the material has cooled down to < 300 ° C.

Generally an inert gas flow of approx. 6 - 8 l/min and a post-purge period of min. 30 sec. is recommended.

All information are recommended values and do not claim to be complete.

Factors for a good welding result

Following factors have to be regarded for a good welding result:

Type of tungsten electrode
Diameter of electrode
Distance of electrode to workpiece
Clean and correct grinding angle of electrode tip

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Types of Tungsten Electrodes:

For the selection of the correct electrode the most common types of electrodes are listed below with their short description and colouring. Tungsten is used as electrode material due to its high melting point of ~ 3.400° C.

By mixing oxides with pure tungsten (doping) the characteristics and the life time of electrodes can be influenced.
The essential attribute of electrodes (according to DIN EN 26 848) are listed also.

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