GTAW welding
(TIG welding)

TIG welding process

This process, in which a non-consumable solid tungsten electrode is used to conduct the electric current, uses an inert shielding gas to facilitate current transmission.

TIG welding is used for welds that must have an excellent visual appearance with a reduced number of machining operations after welding; this requires a correct preparation and cleaning of the edges to be welded. The filler rods must have mechanical properties similar to those of the material being welded.

Both argon and helium can be used as shielding gas in this welding mode. Normally argon is used both because of its lower cost and because it tends to stabilize the electric arc, making it easier to operate; some welding operations include the use of helium (or argon-helium mixtures) because it favors a greater penetration of the bath and a higher feed rate.

2. Execution of the TIG welding process

  1. Selection of current type.
  2. Power source selection.
  3. Torch consumable selection.
  4. Protective gas selection.
  5. Selection of input material.
  6. Welding execution.

2.1. Selection of current type.

Direct current – Direct polarity:

It is the most used and allows welding most of the materials. For this purpose, the TIG torch is connected to the negative pole and the ground to the positive pole; it allows limited electrode wear because most of the heat is concentrated on the part being welded.

This polarity is used for welding materials with high thermal conductivity, such as copper, but also in the welding of steels.

The diameter of the electrode changes according to the chosen welding current.

Direct current – Direct polarity with pulsed current:

Allows better control of the weld pool. It ensures a reduction of the thermally affected zone, with less deformation, less danger of gaseous inclusions and hot cracks.

By increasing the frequency, a more stable and concentrated welding arc is obtained, allowing higher quality welds to be obtained on thinner materials.

Welding in Alternating Current:

It is used in the welding of aluminum (and its alloys) and magnesium with high currents.

During the positive cycle the oxide covering the material is broken, while during the negative cycle the electrode cools down favoring a good penetration, because the heat input into the piece to be welded increases.

By varying the wave balancing (Balance) it is possible to control the relationship between the cleaning current and the arc penetration current.

The preparation of the electrode foresees the rounding of the angles of the tip due to the high heat input during welding which, subsequently, also deforms due to the electric arc thus taking a circular tip shape.

Pulsed TIG

Pulsed Arc is the variation of current between 2 levels set at a certain frequency. The total control over the frequency and working intensities with Pulsed Arc facilitates the welding of thin thicknesses, the application in root beads, the penetration in pipes and thick thicknesses with chamfered edges, as well as the possibility of joining materials with poorly aligned joints.

This is possible due to the increase of the welding speed with a significant reduction of the heat input to the joint (Thermal Input) which gives us a very reduced and controlled HAZ (heat affected zone) and deformations caused by the heat.

2.2. Power source selection.

Depending on the material, we will select direct or alternating current power sources (aluminum) and we will adjust the power of the equipment according to the thickness to be welded. In addition, the alternating current favors the pickling of the oxide layer of aluminum alloys, and can be used for welding low thicknesses.

Fe/Inox 30 A/mm
Cu 70 A/mm
Al 40 A/mm

 

2.3. Consumable selection.

Consumable selection (Tungsten)

The shape of the electrode tip will directly affect the stability of the electric arc. It is preferable to select an electrode as thin as possible, concentrating the electric arc and reducing the molten pool.

The sharpening, in case of direct current, should be between 1.5 and 2 times the diameter of the electrode. With a length of 2 times the diameter and being tapered longitudinally to facilitate current transmission.

Depending on the electrode selected, we will obtain different performances.

2.4. Selection of protection gas.

Argon

  • Its high density increases protection. Being heavier than air, it tends to cover the weld area well. It is recommended for welding in overhead positions.
  • Low ionization energy resulting in easy priming, very stable and low energetic arcs, making it ideal for small thicknesses.
  • More economical.
  • Low thermal conductivity that concentrates the heat in the central zone of the arc to obtain beads with good penetration.

Helio

  • Due to its low density, a very high flow rate is required for a correct protection, resulting uneconomical because we use between 2 and 3 times more than that required with Argon.
  • ionization energy that produces more unstable arcs and high thermal input, favoring welding at high speeds, in automated applications and in large thicknesses.
  • High thermal conductivity that generates wider beads with greater penetration.

Hydrogen

  • Increases heat input, increasing the width and penetration of the weld bead.
  • It allows to increase the speed of displacement.
  • In proportions lower than 5% addition, it should never be used in carbon steels, low alloy steels, or ferritic stainless steels since hydrogen can produce figuring in these materials.

Nitrogen

  • Increases heat input, increasing the width and penetration of the weld bead.
  • Allows to increase the scrolling speed.
  • Low cost.
  • It is almost exclusively used for welding copper and its alloys.

2.5. Selection of filler material.

In thicknesses of less than 3 millimeters and with proper edge preparation, filler metal is not always necessary.

It should be of the same nature as the base metal, verify that it is free of moisture and select the appropriate diameter according to the thickness to be welded.

3. TIG welding applications

The TIG process can be used for welding all materials including aluminum, magnesium and oxidation-sensitive materials such as titanium, zirconium and their alloys.

It is ideal for responsibility welding in the petroleum, chemical, food, nuclear power generation and aerospace industries due to its high weld quality, high metallurgical purity and good defect-free surface finish.

Its low deposition rate prevents it from being economical in materials thicker than 8 millimeters, recommending in these cases the welding of root beads with this process and the rest of the passes with another process of higher productivity.

Advantages:

  • Obtaining stronger and more ductile strands.
  • Deformation reduction.
  • Clean and uniform welds.
  • Smoke and projection reduction.
  • Good surface finish = reduced finishing operations = lower production costs.

Disadvantages:

  • Need to provide continuous gas flow = increased cost.
  • It requires highly skilled labor, which also increases costs.
  • It is reserved for joints with special surface finish and precision requirements.

4. TIG WELDING Equipment

Gala Gar has a wide range of products for this type of welding, click on the following link to see it:
See TIG Welding Equipment.