Page 159 - CITS - Welder - Trade Theory

WELDER - CITS

This type of power source is used in GMAW & SAW process. With a flatter output slope the welder can control
the molten pool and electrode melt rate by making small changes in the arc length. Control of the molten pool and
electrode melt rate are most important when welding in the horizontal, vertical and overhead positions.

Working Principle of GMA welding:
In this welding process, an arc is struck between a continuously fed consumable bare wire electrode and the base
metal. The heated base metal, the molten filler metal and the arc are shielded by the flow of inert/non inert gas
passing through the welding torch/ gun. (Fig 2)

Fig 2

If an inert gas is used to protect the arc produced by a consumable metal electrode, this process is called Metal
Inert Gas Welding (MIG).
When carbon-dioxide is used for shielding purposes, it is not fully inert and it partly becomes an active gas. So
CO2 welding is also called as Metal Active Gas (MAG) welding
Advantage & Limitations of GMAW over other welding process-
Advantages: Welding is economical due to less edge preparation and no stub loss. Produces joints with deep
penetration. Thin and thick materials can be welded. It can be used for welding of carbon steels, alloy steel,
stainless steel, copper and its alloys, aluminium and its alloys. Welding in all positions can be done.Deposition
rate is more. No solid flux is used. So needs no cleaning of slag after each run. Reduced distortion
Disadvantages and Limitation
Welding equipment is costly, more complex and less portable. Since air drifts may disturb free flow of the shielding
gas, GMAW may not work well in outdoor welding.
Applications: This process can be used for welding carbon, steel alloy steels, stainless steel, aluminium, copper,
nickel and their alloys, titanium etc. Light and heavy fabrication work. This process is successfully used in ship
building fabrication of pressure vessels and automobile industries.

Wire feed units- types- application, limitation care and
maintenance

Objectives: At the end of this lesson you shall be able to
• describe the wire feeder.
• explain the wire feeder application
• explain the wire feeder care maintenance.

The wire feeder is the part of the MIG/MAG welding set up that:
i Controls the speed of the wire electrode and pushes this wire from the feeder through the welding torch to the
work piece.
ii Provides the path for welding current to be passed from the welding power source through the interconnecting
lead to the feeder and then to the welding torch.

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CITS : C G & M - Welder - Lesson 49 - 60