Depends an aweful lot on an aweful lot of things: thickness of steel/wire/draught/amperage etc. On 1mm sheet I'd say 6 or 7 would be a good starting point. There are those that would argue that good MIG welds and CO2 are mutually incompatable.
As a result of reading this thread I realised I didn't know, so looked in the tutorial and nothing on setting up the gas (I've always done it by trial & a lot of errors).
Could the more experienced members throw in some data that could be turned into a table of recommended initial gas flows, power settings, etc for different materials.
I think it would be invaluable to beginners & very useful for the rest of us, who get the odd “exotic” rush job once in a blue moon.
Co2's alright. A bit spattery, not as nice as argon mix, but until not so long ago it was the standard shielding gas for MIG.
Danouse - I wouldn't rely on 7Lpm for TIG. It depends on an awful lot of things - like your ceramic size for starters (although it is a fair standard for anything up to 150A or so).
For mig - again gun/nozzle size will make a difference to the gas requirement. On any larger torch, 10Lpm would certainly be a good starting point. On those wee hobby type migs, rather less would be suitable i'd have thought.
For tig gas volumes etc, and plenty more info, look here
Just got this off Wiki
Perhaps most importantly, the four primary variations of GMAW have differing shielding gas flow requirements—for the small weld pools of the short circuiting and pulsed spray modes, about 10 L/min (20 ft³/h) is generally suitable, while for globular transfer, around 15 L/min (30 ft³/h) is preferred. The spray transfer variation normally requires more because of its higher heat input and thus larger weld pool; along the lines of 20–25 L/min (40–50 ft³/h).[16]