pre/post flow setting for my pulse aluminum mig

admin

Ok i haven't really played to much with pulsed mig so i got a few question.The boss wants me to start repairing our transport fuel cells, mostly fixing leaks and putting patches. These tankes are made of 1/8" aluminum.currently they are tig welded which would be the smart thing to do but my boss is cheap so mig it is.back to my question my machine has a pre flow setting of 0-5 seconds and a post flow setting of 0-10 seconds. what do you look for when setting the flow.I normally weld aluminum on normal mig mode but i figured pulsed mig would cause me less problems!
Reply:You need some small amount of preflow time to push the air out of the gun cable to ensure that undiluted shielding gas reaches the work piece before the arc is started.  How much time does this take? who knows, maybe 2 seconds.  If you have porosity at the weld start, it may be due to inadequate preflow time.You need some postflow to protect the puddle/crater as it cools after the arc is extinquished.  Of course if you pull the gun away from the crater immediately, post flow won't do much good.  How much postflow? You tell by looking at the weld, is it contaminated, at more postflow time.