GMAW WELDING PROCESS

GMAW WELDING PROCESS

GAS METAL ARC WELDING (GMAW)
In this process, an arc is maintained in a stream of inert gas between a consumable electrode and the workpiece. The arc heats the work and melts the electrode, which thus supplier filler metal for the joint.   The power sources used are direct current with electrode positive.   The metal transfer is irregular if the electrode is negative or if the alternating current is the use of whilst effective welding of aluminum is only possible if the workpiece is negative so that oxide film is removed by the action of the arc cathode.

The shielding gas is normally argon, but argon-oxygen mixtures containing up to  20% oxygen are sometimes used for welding austenitic stainless steel in order to obtain an improved weld profile in welding carbon steel and for the sheet metal may be better and cheaper.
As with GTAW welding, there is a small degree of atmosphere contamination of the shield, requiring the use of de-oxidized sires for carbon steel, copper, nickel and  Cu-Ni alloys. Deoxidants for carbon steel and copper are Si and Mn, whilst for Cu-Ni alloys, titanium and aluminum are used. If they lack de-oxidants, weld made in these metals is porous.
GMAW welding is used for high alloy steel, AI, Cu, Ni, and their alloys. The process is of special value for AI, Cu, and their alloys because of the limited range of coated electrodes available for these materials. It is complimentary to TIG welding, being mainly useful for thicker materialand for fillet welds.

The GMAW process uses four modes to transfer metal from the electrode to the workpiece. Here all mode of transfer depends on the welding process &  the welding power supply.

Short-circuit Transfer - Here electrode touches the workpiece and creates a short circuit, causing the metal to transfer.
Globular Transfer - weld metal transfers across the arc in large droplets (usually larger than the diameter of the electrode)
Spray Transfer Mode - a spray of tiny molten droplets across the arc
Pulse Spray Transfer – Here all play “cycle of power supply” which  between a high spray transfer current and a low background current, this allows for fast cooling of the weld pool during the background cycle.

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