Tungsten Inclusion is the most occurring weld imperfection, mainly caused by the
absorption of tungsten fragments in weld puddle. This problem is associated with
tungsten inert gas welding process where an erroneous weld
attempt with defected electrode may result in tungsten entrapment. Parameters like voltage, welding current, shield gas composition and even the welding modes must be
rectified in order to achieve inclusion free welds. Because TIG is the most strenuous arc
process and that is why, high level of skills are required to perform with. Below is the exposition of common reasons
for weld tungsten inclusion and their practicable solutions.
Electrode Dipping
The exposure of electrode in weld pool, makes the particles of tungsten to detach. These particles after set apart from the
electrode gets surrounded in the weld pool. This contamination may have
deleterious effects on weld properties. In such situation high skills are
required to avoid tungsten entrapment into the weldment by;
- Holding the gun at a distance so that electrode may not have contact with weld puddle.
- The electrode must be away from the weld pool.
- Using high-frequency start-up mode, to fulfill the requirement and condition of above two steps.
Contact between the filler and electrode
Problem of Tungsten inclusion may also arise when the filler rod makes contact with the high temperature electrode. In this way contaminated weld
metal is fed that contains metallic (tungsten) segments. In order to prevent
any such contact, it is a recommended practice to hold the rod slight away from the electrode tip.
Unsuitable current settings
In TIG welding, current settings are associated with
electrode size. Specific current is set for specific electrode size. If the
current is adjusted at high end, overshooting the limit for specific electrode
size, a lot of spatter may result. Spattering also contaminates electrode
and consequently the weld puddle gets tungsten pieces. To prevent both
spattering and inclusion, one must adjust the correct welding current.
Interrupted Gas shield
Interruption in gas shield supply causes many problems to
happen. As it is stated above, spattering results in electrode contamination while spattering may be caused by improper shield/covering. Therefore shielding
characteristics need to be improved in order to avoid any process of adulterating.
On the other hand, current of air may also interrupt the supply of gas causing
oxidation of electrode. Gas shielding must be adequate, heavier and stronger enough, to reduce the interruption of air in the arc zone. One of the beneficial features of TIG gun, is the provision of extended
gas flow, even after the weld current is switched off. This feature is quite
helpful to avoid any electrode and wed metal contamination, facilitating the solidification mode.
Gas Composition
Selection of gas composition for shielding is the foremost
element in attaining quality welds. Gas shield prevents the entrapment of atmospheric gases that
may react with the weld metal. Gas supplies not only protection but also helps
to keep the arc stable. Normally inert gases argon, helium and argon-helium
mixture are being used for their best results. Other compositions with other gases may
also be applied but they don't give such satisfactory results as compared to the inert gases. In order to achieve
best quality results, it is recommended to adjust suitable composition of gases depending on the weldable material.
Futile electrode
A nonfunctional electrode may also result in the entrapment of
tungsten particles into the weld metal. The electrode cannot work effectively if it is not properly
coupled with the torch. Same is the case when a damage electrode is inserted. Before
fixing the electrode in torch, following are the points that must be considered;
Choice of electrode size for the specific job is chiefly dependent on welding current. Too higher the current for a given size of electrode, may induce problems. For this correct adjustment of current is recommended for given electrode size. Moreover too high stick-out can heat up the electrode and influence the outcome. So an electrode must be extended out at specified distance from the torch collet, according to the requirements.
- Make sure electrode has no fissure and small gaps on it.
- Electrode is properly ground
- Clamp the electrode tightly in the electrode.
Choice of electrode size for the specific job is chiefly dependent on welding current. Too higher the current for a given size of electrode, may induce problems. For this correct adjustment of current is recommended for given electrode size. Moreover too high stick-out can heat up the electrode and influence the outcome. So an electrode must be extended out at specified distance from the torch collet, according to the requirements.
Last comments
- Tungsten Inclusion is typically caused due to manual mistakes by a welder.
- Welding inspector must check related points during qualification.
- Retrain the welder if not working well.
- Adjust the allowable welding current for specific electrode size.
- Ensure the correct placement of electrode in gun.
- Prevent any contact with electrode tip and avoid contamination.