General Principles weldingtheory
TIG (Tungsten Inert Gas) welding also known as GTA (Gas Tungsten Arc) in the USA and WIG (Wolfram Inert Gas) in Germany, is a welding process used for high quality welding of a variety of materials, especially, Stainless Steel, Titanium and Aluminum.
Power Source
TIG welding can be carried out using DC for Stainless Steel, Mild Steel, Copper,
Titanium, Nickel Alloys etc. and AC for Aluminum and its Alloys and Magnesium.
Further information on the TIG Welding Process follows information on equipment
used in this document.
The Power Source is of a transformer design with or without a rectifier, with a drooping characteristic (constant current power source). The output is generally controlled by either a moving core within the main transformer of the power source or by using electronic control of power thyristors.
DC power sources could be of 1 phase or 3 phase design, with an inductor to provide a smooth output. AC and AC / DC Power Sources are of a single phase design.
Output Control weldingtheory
In TIG output voltage is not controlled by the power source ( as with MIG ), but is determined by the process and output welding current. Welding current is normally controlled by either a moving core in the main transformer or by electronic power components. Moving Core Control : - The main drawback of this method of control, is its slow response to change when required and due to the mechanical movement remote controls ( such as foot control ) are so difficult and expensive to provide, that it is thought of as not possible.
Electric Power Control : - This system has many advantages over the previous system. The possibility to have a remote control of welding current, so the operator can raise or lower the output as required while welding.
Equipment
● DC or AC / DC Power Source
● TIG Torch
● Work Return Welding Lead
● Shielding gas supply line, ( normally from a cylinder )
● Foot Control Unit ( common option
Arc Starting Circuit
HF : - Sparks of high tension jump across the gap between electrode and workpiece rapidly to carry the welding current across to start welding in DC TIG welding, this will stop once the arc is struck, in AC TIG welding, this will normally continue to keep the arc alive as the AC output changes from a Positive half cycle to a Negative half cycle and back again.Lift Arc : - The electrode is touched onto the workpiece, the TIG Torch switch or foot control switch is operated, the equipment circuits detect a short circuit on the output and allow only a very low current typically 5 - 8 amps to flow. The electrode is lifted off the workpiece, the equipment circuits now detect a voltage between electrode and workpiece and welding current strikes across that very tiny gap as the electrode lifts off and welding continues.
Scratch Start : - The electrode is scratched or dragged and lifted off the workpiece, much the same as striking an electrode in MMA ( Stick ) welding.
Using the HF method. No cross contamination from electrode and workpiece takes place as they never touch, with Lift arc correctly set and used, only minimal cross contamination occurs because of the low current when electrode is in contact with workpiece, scratch start TIG is a low cost option for general TIG welding, but cross contamination can occur.
AC Waveform Balance weldingtheory
A pot can be fitted, when welding in AC mode the positive half cycle cleans the oxides on the Aluminum and the Negative half cycle produces weld penetration during welding self rectification occurs and causes an imbalance of the waveform, a balance control allows the operator to adjust the amount of time the cleaning or penetration takes in each cycle.