Gas Metal Arc Welding or GMAW is also known as Metal Inert Gas (MIG). It is an arc welding process which produces coalescence of metals by heating them with an arc between continuous filler metal (consumable) electrode and the work. Shielding is obtained entirely from an externally supplied gas or gas mixture. Originally developed to weld aluminum, it has become one of the most popular arc welding processes.
Working Principle
This system of welding was developed to weld metals thicker than 1/4" that Tungsten Inert Gas (TIG) welding could not weld. Despite of this matter, MIG welding was limited to only thick metal applications. However, some adjustments were made and the possibilities for welding various metals were gained. This welding procedure is very close to TIG welding in that an inert shielding gas is used to protect the weld and the arc is maintained between the electrode and the work piece. The difference comes from the fact that the electrode is consumed in MIG welding. The electrode is actually a long wire that is fed through a hole in the tip of the handle that carries the current to the work piece and supplies a filler metal. The fact that the electrode is continuous makes the welds that are produced very well in quality. There is no need to start and stop to replace an electrode as in SMAW and long welds can be completed in one step. The entire process can be automated and all welding positions can be used on any thickness of metals. The process is easy to learn and there is little or no spatter and no slag is created in MIG welding which makes surface preparation for painting very easy.
Figure 1 Welding power Supply and Gas supply (left) and Welding Gun (right)
Advantages
The usage of MIG brings a lot of advantages that might not be achieved in other welding processes. These advantages really benefits and ease the usage of this welding method. Some of the advantages are listed as below;
a) Able to be welded on stainless steel, aluminium and mild steel.
b) Do not require any cleanup as the fusion is clean.
c) By using this method, it can weld metals at any positions.
d) The method is simple. First hand user will not have any problem as only one hand is require, no need to hold the filler metal.
e) Production rate is high, as the process can be continuous; the spool of filler metal will flow continuously during the welding process.
Limitations
Despite of the advantages carried out by MIG, there are several limitations which make it undesirable under certain circum stances. The limitations of MIG are listed as below;
a) More expensive and is less portable than some other types of welding, such as SMAW.
b) Requires shielding gas commonly helium.
c) The gun is large and the cable is stiff which makes welding tight spaces hard and the gun's size makes it hard to see the arc, which leads to poor welds
d) For outdoor MIG welding, the breeze must not exceed 5 miles per hour with no screen, or the shielding gas will blow away and will not protect the weld surface.
e) Not good for thick steel because it doesn’t get the proper penetration.
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