Difference between mig n tig on ally

[andy m]

Maybe a stupid question, but what are the differences between mig and tig on aluminium I'm thinking about m/cycle tank work, is mig a no goer, I am aiming to tig but just curious. I believe if I was to be doing heavier guage work that didn't need to look too pretty then mig is fine ?? is that it or am I missing something??
Early days still on the course so learning, bear with me...Thanks.

 

[wyn]

With mig the very start of the weld is likely to be "cold" and not completely fuseing the two bits together resulting in leaks.

 

[Rrunnach]

If appropriate, use of run on plate will avoid cold start problems. With run off, at end of weld, thus avoiding craters............

 

[andy m]

Not recommended on tank work then ?? unless run on extra plate ??

 

[hotrodder]

M/cycle tank work, forget MIG. TIG or oxyfuel is the way forward and in many respects oxy fuel is the best choice although it's a bit swings and roundabouts between the two

The size/shape of bike tanks puts the material thicknesses used kinda into the MIG is more hassle than it's worth category.
Thicker material would make MIG easier but add unnecessary weight and make them harder to shape i.e. to take advantage of a faster/cheaper welding process you make things more difficult/expensive and slower everywhere else
Because they need shape for aesthetics/structure etc there's typically more joints than with something made from simple folded pieces all of which make run on/off tabs impractical... lots of tacking + the shape of the things

If we were talking bigger tanks (static/marine etc) then the shortcomings of MIG are reduced/worth working around i.e. material is gonna be thicker which means more weld metal is needed... tacks can be feathered to fix cold start issues and run off tabs are easier to set/make more sense because we're into much longer joints etc where the higher speed of MIG can be taken advantage of

 

[andy m]

Thanks, it's all falling into place now. Just a minefield of which tig to use. Will be experimenting at home for a while so needs to be 13 amp. I have another thread re welders.

 

[agrimog]

a quality synergic mig will easily out perform a tig set on motorcycle tank work, tig is slow and difficult to lay down a precise bead without a lot of experience on thin, 1-1.5mm alluminium, a properly set up synergic pulse mig will lay on a bead that is almost impossible to tell apart from wire fed tig (efectivly what it is) in the hands of a moderatley skilled user, synergic migs are taking over in the production industry for this reason