Argon Arc Welding

In any industry of the modern Steel-Age existence of welding technology is a must. And MMAW (Manual Metal Arc Welding), SM AW (Stick Metal Arc Welding), and GTAW (Gas Tungsten Arc Welding) are firmly established. This is because of their flexibility, utility in all positions and locations and easy availability of the consumables required for various types of welding’s.

In most of our industries the jobs for welding are being done using various types of stick or coated electrodes.

But the industrialists of the present day are increasing their productivity with a view to combating competition—both from internal and international markets—especially when the industry worldwide is becoming more and more competitive and industrial management is continuously seeking new ways and means to reduce cost and improve quality control.

Under the situation, users want to modernize their machines to run faster, longer and more efficiently. And they are seeking various advantages of Automatic and Semi-Automatic welding processes—MIG/MAG, TIG, GTAW or Gas-shielded Arc Welding—which are most modernized Machine Tools of Welding Technology. Argon Arc or Gas-shielded Arc welding is the most popular among them.

Now, let us consider inert gases and their utilisation in welding science. An inert gas is, as its name suggests, an inactive gas. It is used to protect the molten pool from the atmospheric air at the time of welding. Important inert gases are Helium and Argon. They are used with other Shielding-gases.

The Shielding gases may be classed into two groups

(1) Gases soluble in or reacting with metals. These are Hydrogen, Carbon dioxide, Nitrogen etc.

(2) Inert gas like Helium and Argon.

Argon and Carbon dioxide are the most widely used. Argon is obtained as a by-product in the separation of air to produce oxygen. Argon is supplied in steel-drawn cylinders under a pressure of 150 atmospheres. Purified argon contains 97-98 per cent argon, while commercial argon contains 13-14 per cent nitrogen.

It is convenient to consider that the application of gases which involve shielding the arc with argon, helium and carbon dioxide (CO2) and mixtures of argon with oxygen and CO2, helium are essential.

Argon is used as a shielding gas because it is chemically inert and forms no compounds. Commercial grade purity of argon is about 99.996% and obtained by fractional distillation of liquid air from the atmosphere. It is cheaper and is therefore used for commercial purposes.

Argon in commercial purity state is used for metal welding purpose. Argon with 5% hydrogen gives increased welding speed and penetration in the welding of stainless steel and Nickel alloys.

Helium may be used for aluminium and its alloys and copper. But Helium is more expensive than Argon and, due to its lower density, a greater volume is required than Argon to ensure shielding. A small variation in arc length causes greater changes in weld conditions.

The mixture of 30% Helium and 70% Argon gives fast welding speeds. The mechanised D.C. welding of aluminium with Helium gives deep penetration and high speeds.

Automatic Argon-arc welding has been successfully employed for welding thin stainless steel, aluminium and its alloys. The Argon-Arc Process may use either non-consumable or consumable electrodes. With a non-consumable electrode, the arc is maintained between a tungsten electrode and the ‘Work’. A shield of Argon is projected around the electrode.

The arc burns between a tungsten electrode and the work-piece within a shield of the inert gas argon, which excludes the atmosphere and prevents contamination of electrode and molten metal. The hot tungsten arc ionizes argon atoms within the shield to form a gas plasma consisting of almost equal numbers of free electrons.

Unlike the electrode in the manual metal arc process, the tungsten is not transferred to the ‘Work’.

The heat source in the inert gas arc welding process is an electric arc between a tungsten electrode and the parent metal. The electrode is shielded by a stream of inert gas—argon or helium—which eliminates the necessity of adding flux.A.C. is generally used with tungsten electrodes, and D.C. with the consumable metal arc electrode. This process is used for welding light alloys, some non-ferrous metals—especially aluminium, copper and their alloys, and also stainless steel.

With a consumable electrode, the arc is maintained between a metal electrode and the ‘Work’. Steel is widely welded by the Semi-automatic C02 shielded arc process. In aircraft industry Argon arc welding is used in a large scale even though it is a costly welding. Before its use the argon should be dried by passing through caustic or silica-gel

It has been successfully employed for welding thin stainless steel, aluminium and its alloys, copper and its alloys, nickel and its alloys, titanium, zirconium, silver, etc. The gas-shielded tungsten arc process enables these metals and a wide range of ferrous alloys to be welded without the use of the flux. This is a great advantage in all such welding’s.