mike 109444
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Hummmm Not easy to explain 9by me!) but basically Mig are jsut a DC power supply all be it a very high current low voltage one. In most AC to DC power supplies the raw DC coming from the rectification can vary with load. If an inductor (choke)and sometimes a large capacitance is added to the out put this resist the tendency for the out put to vary. When you have miged in the past I guess you like me have mainly done thin sheet metal (<2.0mm). When welding metal this thin you would be using dip transfer. This is where once the arc is established the wire is constantly feeding into the weld pool (dipping) when you increase the thickness of metal being welded you would up the power and feed rate of wire and then get to globular transfer. This is when the wire feeding in to the weld is transferring as globs of metal. Next stage up is MORE POWER as Mr Clarkson would say 
and more wire feed and you get to spray transfer. Watch any of the ship building welders and you will notice that there welding sounds different from welding car body work! This is where the wire being feed in to the weld is melting at such a rate/power that it melts the second it leave the tip and is carried as a stream of metal particles. To try and get the mig to supply a suitable voltage and maintain the arc the inductor (choke) resist the reflected voltage that comes from getting a DC voltage to arc. On some bigger migs you may see the ground clamp on the welder has several (3 usually) sockets it can be used in. These are varying levels of inductance (choke) for different thicknesses of metal.
The above is probable not the best description.
But the attached manual is a good read on some of the technical side of mig welding
and more wire feed and you get to spray transfer. Watch any of the ship building welders and you will notice that there welding sounds different from welding car body work! This is where the wire being feed in to the weld is melting at such a rate/power that it melts the second it leave the tip and is carried as a stream of metal particles. To try and get the mig to supply a suitable voltage and maintain the arc the inductor (choke) resist the reflected voltage that comes from getting a DC voltage to arc. On some bigger migs you may see the ground clamp on the welder has several (3 usually) sockets it can be used in. These are varying levels of inductance (choke) for different thicknesses of metal.The above is probable not the best description.
But the attached manual is a good read on some of the technical side of mig welding
