Andy Dingley wrote:
On 28 Aug 2003 20:12:13 GMT, wrote:

what effect does the polarity have in MIG welding?

Same as any process - the +ve electrode gets hotter

For MIG welding in spray-transfer mode, it's important to have the
wire running hot and the torch +ve, or else you won't get a spray
(which leads to globular transfer, poor penetration, and premature
baldness)

If you're using dip transfer on thin sheet, then it doesn't matter
which way you run it. Besides which, the voltage (and thus the power)
is lower anyway. For cored wire, running the wire over-hot can
disrupt the shielding effect of the generated gas - but even then,
thin sheet isn't fussy.

Thanks for the explanations, I'm working on fairly thin material so it
would seem that polarity isn't all that critical.


MIG keeps the same polarity for all metals. TIG uses a -ve torch, to
stop the tungsten melting. Welding aluminium (or magnesium) with TIG
(but _not_ MIG) uses AC, to get a "scrubbing" action on the weld pool
to break up the oxide film.

Well my instructions definitely say:-
+ve torch for using MIG with gas.
-ve torch for using MIG gasless with cored wire.
This is a SIP 130DP, specifically designed to be used for both gas and
gasless MIG welding. It's also marked up on the welder itself.

--
Chris Green )