GMAW

GMAW METAL ARC WELDING PROCESS

It is an ARC welding process in which fusion is produced by heating the work along with an electric arc between the continuous filler metal electrode and the weld pool.

It employs a constant voltage (CV) power supply, and use either short-circuiting Spray method for transferring work from globular, or electrode to metal, and can be operated in semi-automatic or automatic mode also.

Since shielding gas is used in this process, no flux is required. Shielding gas is used to avoid atmospheric contamination from the molten weld pool.

gmaw welding process

Shielding Gases

gas metal arc weldingगैस मेटल आर्क वेल्डिंग

The argon, helium or their mixtures may be used as shielding gas whereas the co2 welding method, Carbon dioxide is used as the shielding gas, the basic details are as follows:

Materials Shielding gas
Al, Mg, Cu, Ni, Ti Argon
Al, Mg, Cu Helium
Mild steel Carbon-di-oxide(CO2)
Copper Nitrogen
Al, Low alloy, Carbon steel, Stainless steel Argon+(1 to5%)Oxygen
Al, Cu, Ni, and alloys Argon+Helium
The function of Shielding gasses The helium and CO2 help to increase the penetration whereas the argon gas reduces spatter loss.

Welding Operation

Before start

 

Before breaking the arc, the gas and water flow is inspected by the operator. Current and wire feed speeds are determined and electrical connections are checked. The arc can be struck in two ways. 
First method The first method involves switching on the current and shielding gas flow and as a common practice to grab the arc the electrode is scratched against the job.
Second method In the second method, the electrode is to be in contact, which is withdrawn and then swept to advance the welding, but before the arc is broken, the gas, water, and current are turned on.

The electrode length is estimated to be approximately 15 mm from the torch before the arc strike. During welding, the torch is about 10-12 mm away from the work and the arc length should be kept between 1.5 to 4 mm. Arc length is needed to keep constant using the principles. Self-adjusting arc, and self-controlled arc, respectively, in semi-automatic (manually operated) and automatic welding sets.