Learning Tig welding equipment details Part 1

Tig welding equipment

Tig welding equipment
Credit www.weilerwelding.com

TIG welding (GTAW or gas tungsten) is an arc welding process that operates at high temperature (over 6,000 degrees Fahrenheit) to melt and heat metals. While it is more expensive than stick welding, it is cleaner and more versatile (works on steel, aluminum, brass and many other metals).It results is high quality welds.

Tungsten inert gas Welding (TIG) is a process that uses the a non-consumable tungsten electrode to produce a weld with or without a filler material. The equipment is significantly different than MIG equipment and somewhat different than what is used for stick welding. That said, a welding machine with the right accessories can be fitted for TIG welding.

The gas tungsten arc welding process is generally not commercially competitive with other processes for welding heavier gauges of metal if they can be readily welded by the shielded metal arc, submerged arc, or gas metal arc welding processes with adequate quality.

The power source for TIG welding can be either DC or AC, but in both the output is termed a drooping, or constant current characteristic; the arc voltage/welding current relationship delivers a constant current for a given power source setting.

In TIG welding, the arc length is dependent on how consistently the welder can hold the torch above the workpiece. Arc length is directly proportional to arc voltage, so a longer arc has a higher voltage and if the arc is shortened, the voltage will decrease. Variation of arc length by 3 or 4mm can easily vary the voltage by 5V. 

By design, the TIG power source has a limited range of current and a reduced variation on changing voltage. With such a power source, the variation of current over a variation of 5V might be as little as 10A, giving almost imperceptible changes to the weld pool, making control much easier for the welder.

The arc is usually started by High Frequency (HF) sparks which ionise the gap between the electrode and the workpiece. HF generates airborne and line transmitted interference, so care must be taken to avoid interference with control systems and instruments near welding equipment. When welding is carried out in sensitive areas, a non-HF technique, touch starting or ‘lift arc’, can be used.

The electrode can be short circuited to the workpiece, but the current will only flow when the electrode is lifted off the surface. There is, therefore, little risk of the electrode fusing to the workpiece surface and forming tungsten inclusions in the weld metal. For high quality applications, using HF is preferred.

DC power source

DC power produces a concentrated arc with most of the heat in the workpiece, so this power source is generally used for welding. However, the arc with its cathode roots on the electrode (DC electrode negative polarity), results in little cleaning of the workpiece surface. Care must be taken to clean the surface prior to welding and to ensure that there is an efficient gas shield.

Transistor and inverter power sources are being used increasingly for TIG welding. The advantages are:
  • the smaller size makes them easily transported
  • arc ignition is easier
  • special operating features (e.g. current pulsing) are readily included
  • the output can be pre-programmed for mechanised operations