The MIG welder is a common welder, using GMAW, it is very effective at what it does. The electrode wire gets fed through a welding gun, and at around the same time, shielding gas glows through, which is used to protect the weld while it cools down and settles. The is basically the GMAW process.
Carbon dioxide is most commonly used for this type of welding because it is the cheapest and it creates a great weld. Also used is Argon which creates a good mixture with carbon dioxide, and creates less spatter which means a cleaner weld overall. To get the best welds with aluminium, using argon gas alone is the best method.
Over other processes of welding the GMAW method has many advantages such as the welding gun itself which has a control on the trigger which will position the electrode without accidentally hitting one of the arcs. Once you have positioned the gun in the right place all that left to do is put your helmet on and pull the trigger.
Alternating current will not give you a steady arc when welding, which is why MIG welders use a DC current. Using the inert shielding gases makes the welds smooth and clean with no slag to chip off. MIG welding is best used for thinner metals and weld sheet metal, because they can be welded at much lower power than other welders.
Creating clean welds with a MIG welder is helped by the control you have over the voltage and the speed the wire comes through to the welder. The tension of the electrode is variable also which is very handy.
Using a MIG welder for FCAW (flux cored arc welding) means you will not have to use shielding gas. You can switch the polarity of the arc for the flux cored wires. For better effect and cleaner welds it is recommended that the electrode has a hollow core filled with FLUX.
For some more details on mig welders and where to get them from, then visit Welding Supplies.