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Welding Types

The Process

Gas shielded metal arc welding is a semi-automatic process whereby a low voltage, high current arc between the end of a wire electrode and the joint provides the heat needed for the operation. The arc and the weld are protected from atmospheric contamination by a gas shield. The shielding gases used vary according to the metal being welded e.g. Gwynedd 5 for less than 7mm mild steel.


The Operation

An electric motor feeds welding wire (the electrode) into the arc and the power source keeps the arc at a preset value leaving the welder to concentrate on ensuring the complete fusion of the joint, the welding wire is melted into the weld during the process.

The Process

TIG welding utilises an arc between a tungsten electrode and the work to fuse the joint. The electrode is not melted and any filler metal needed to build up the weld profile is added separately.

The molten metal in the weld pool, the tip of the filler wire and the hot electrode are protected from the contamination by the air by a shield of inert gas, usually Argon high purity.


The Operation

In manual TIG welding, the operator points the electrode in the direction of welding and uses the arc to melt the metal at the joint. If filler metal is required it is added to the leading edge of the weld pool.

The Process

Oxygen-fuel gas cutting is used to cut various metals. The cutting action depends upon a chemical reaction between hot iron and steel.

A preheat flame from the burning fuel gas and pre-heat oxygen is used to raise the surface of the metal to the temperature at which the reaction takes place.

The heat from the reaction melts the metal which is blown from the cut by the cutting oxygen jet.


The choice of fuel gas depends on:


Factor for Choice

Preheat Time

Cutting Speed

Fuel Gas Cost

Heating Oxygen Cost Ease of Handling
Acetylene *** *** * *** *
Propylene ** *** ** ** ***
Propane * * *** * ***


*** = best choice; * = worst choice