Problems with welding aluminum

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I'm having a prob with welding aluminum, got a SIP Migmate 170, and have been welding steel for over 20 years with no troubles.  Needed to weld some ally about 4mm thick and the machine is one minute doing an OK job then next minute is an utter pig. I'll put a piece of scrap in the vice and do a run that's fine, then i'll do another one and the wire is melting at the tip and fusing with it. One time a large blob form and arced with the shield/work piece burning a large piece away, ruining the shield. I always clean the ally with a stainless brush, use a teflon liner in the torch, 100% argon gas. I 've slowed/speeded up the wire feed, increased/decreased the power, but can't work out what's up. HELP! The machine isn't over heating. I though maybe the + & - are mixed up but the ground lead is definitely - and the torch is +.  I have spent hours trying to work out why it is so erratic, when I put steel wire back in it's fine.
Reply:MIG is tough to do alum., I've never done it for that reason, plus I have TIG machines. I'm sure someone will chime in when doing alum. w/ MIG. Good luck.John -  fabricator extraordinaire, car nut!-  bleeding Miller blue! http://www.weldfabzone.com
Reply:The first thing that comes to mind is wire feed problems.  Since aluminum wire is so soft compared to steel, it is difficult to feed and binds up or galls in the liner or feed mechanism.  This is why spool guns and push/pull systems like the Cobramatic were developed.Try optimizing feeding by cleaning the entire drive system.Adjust the feed roll pressure just tight enough not to slip, not so tight as to deform.Try holding gun with liner stretched straight, minimizing any curves that would cause binding.Maybe the above with help, at least it may give an clue if feeding is the problem.There are special gun liners for aluminum, I think Teflon rather that coiled wire.See the lincoln site, there are a bunch of short articles that may give you some ideas on how to solve your issue.http://lincolnelectric.com/knowledge...es/results.asphttp://lincolnelectric.com/knowledge...compactmig.asp
Reply:It sounds to me like you may have a couple things going on.  MIG on aluminum is difficult - especially so if you don't have a spool gun.  As said above check your feed system for cleanliness and tension.  You definately HAVE to keep the line as straight as humanly possible from the machine to your work piece.  You'll have to position your machine such that it is possible - as far away as you can.  Aluminum is very difficult to push up a liner.  Next is that aluminum is a very efficient conductor of heat.  As your piece heats up you need less and less heat.  So the heat setting you start a weld with and is working fine will all of a sudden melt through.  That's one of the reasons it's so much easier with TIG because you just back off on the pedal as your weld progresses.  When I was doing aluminum with my MIG I'd have to weld about 1/2-3/4" and then stop and let it cool for a bit before continuing on - otherwise I'd blow through (this is on 1/8" alum angle).  Good luck - I just took the plunge and bought a TIG welder and I'll NEVER go back to MIG on aluminum!
Reply:Thanks guys, I will check out the drive feed tomorrow, I use a teflon liner, which has stopped the wire damaging at the drive wheel, but what is bugging me most is how erratic it is welding. I can do a really nice weld on the bench, I go to do a second one and the machine has had a brain storm and sends the arc into the torch and away from the work piece fusing the wire into the end of the tip. I have not had this prob when welding steel. I am spending more time fixing the welder than I do welding with it!
Reply:Originally Posted by pulserThere are special gun liners for aluminum, I think Teflon rather that coiled wire.[/url]
Reply:you need to keep the welding lead as straight as you can and not a lot of tension on your wire feed rollers sorry I didn't read all the post and just said some stuff that some else did mig welding Aluminum is no were as easy as steel it takes time and practice and you don't need a spool gun to to it right Tig is easier  but not very thing aluminum can be welded with tig I repair aluminum tipping trailers at work and with mig it takes around 20 mins to weld 40 ft(allowing for getting up and moving ) tig would take for ever and you also need special tips for aluminum than steel a 1.2 aluminum tip is different to a 1.2 steel tipthis a piece I maded for a friends boat that is all mig weld ally Last edited by wello; 10-04-2006 at 07:20 AM.Creative metal Creative metal Facebook
Reply:Thanks for all the replies, I checked everything and someone mentioned on another site about the tip size. A .8mm tip is too small for using with .8mm alloy. Doesn't tell you that in the manual  The greater expansion of aluminium requires a larger tip bore to stop it binding, (OK when cold, so I didn't guess that the heat would have made that much difference),  I didn't have any 1mm pits so I drilled out a .8mm size to internal size of 1.2mm. Works a treat.Had a look at spool guns as I had never heard about them before and was surprised about the cost, here is one on Ebay £304, the welder cost me £299. http://cgi.ebay.co.uk/SEALEY-SPOOL-O...QQcmdZViewItemLast edited by Dave Daytona; 10-07-2006 at 07:12 AM.
Reply:Hi Dave,the SIP migmate welders have an inherent weakness in their construction causing uneven wirefeed due to the wire feed motor being feed directly from a winding on the main welding transformer. This leads to fluctuating motor speed as the welding arc strikes.This welders are popular in britain/Europe, and searcing for SIP migmate wire-feed on e.g www.mig-welding.co.uk will give you more information and some suggestions of improvements. I have also modified and fixed the wire-feed problem on my own SIP migmate 150 DP (gas/gasless).I have posted complete instructions on my homepage in case you would like to do similar modifications on your migmate.http://hobbymechatronics.com/project...ess-mig-welder-Bjorn--------------------------------------------www.hobbymechatronics.com
Reply:I was going to say it was a problem with your tip heating up and jamming the wire but looks like you figured that out already.  Do yourself a favor and stock up on the right size tips, your going to need them.Have we all gone mad?
Reply:If you're using  .035 wire, you can use an .039 tip to help keep it from hanging up in the tip.I don't know if your machine can burn it or if your project's material thickness is enough for it, but 3/64 wire feeds better than .030 and .035. cause it's thicker and thus stiffer.  You can use .052 tips with 3/64 (.047) wire.If you can get a spool gun for your machine, get one.  It's alot easier than messing with feeding the wire through a push mig torch.MM350P/Python/Q300MM175/Q300DialarcHFHTP MIG200PowCon300SMHypertherm380ThermalArc185Purox oaF350CrewCab4x4LoadNGo utilitybedBobcat250XMT304/Optima/SpoolmaticSuitcase12RC/Q300Suitcase8RC/Q400Passport/Q300Smith op
Reply:I'm too late, but I was going to say "bigger tip".My name's not Jim....
Reply:Too late???The thread's 3 years old!    The best laid schemes ... Gang oft agley ...
Reply:Originally Posted by MoonRiseToo late???The thread's 3 years old!
Reply:I see now, a newb revived it.My name's not Jim....
Reply:Originally Posted by BoostinjdmI see now, a newb revived it.
Reply:Originally Posted by Dave DaytonaThanks guys, I will check out the drive feed tomorrow, I use a teflon liner, which has stopped the wire damaging at the drive wheel, but what is bugging me most is how erratic it is welding. I can do a really nice weld on the bench, I go to do a second one and the machine has had a brain storm and sends the arc into the torch and away from the work piece fusing the wire into the end of the tip. I have not had this prob when welding steel. I am spending more time fixing the welder than I do welding with it!