Questions for the experienced Aluminum MIG welders

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I am trying to dial in settings and develop consistent technique for MIG welding different aluminum joints, and have some questions for those much more experienced than I.  I know there are some guys on here that do amazing work building trailers, etc. day in and day out, hopefully you can give me some advice.  I am using a Millermatic 211 with a beefed up Spoolmate 100 (HD barrel and tips, essentially a 3435 spoolgun with 100 motor), ground clamp is a copper tweco.  To get current/voltage values, I’ve been using the Maxal Aluminum GMAW guide and online Miller Calculator.  Wire is 4043 Superglaze 0.035”, metal is 1/8” and 3/16” 6061-T6/T651 flat bar.  The coupon sizes I’ve been using are 2”x3”. I’ve been setting up the machine with fluke meters since I’ve found the chart values from the machine to nowhere near correspond to the values given in the maxal guide or miller’s website.  For 3/16” fillets I’ve tuned the machine to 24V, 140-145A and for 1/8” 23V, 125-130A.  240V input.Just for curiousity’s sake, I measured the absolute max I could get out of the machine and it corresponds somewhat with Lincoln’s 0.035” 4043 curves, I was able to get 160-165A at 24.6V on 240V. When using the above settings for fillet welds on 3/16”, I have been tacking the pieces together at the end of the fillet weld so that the arc force doesn’t end up blowing out the end of the joint (a problem I’ve had).  Finishing the joint on the tack reduces the crater size and keeps the edge intact.  Contact tip to work distance is about 1”, Argon set to 30 cfth, very slight push angle, maybe 10 degrees. I move in a straight line with a 4 steps forward, 1 step back motion (no weave, no circles).  I clean the joints first with acetone, then a stainless wire brush.  I start at the right edge, dwell until the arc is stable, then start moving slowly for the first ½”, then move at a normal constant speed with the motion described previously.  On 3/16” the beads come out looking pretty decent.  However, I’ve been struggling with 1/8”. The main problem tends to be undercut and slight melting out of the back.  The 125-130A settings (somewhere around 350 ipm) do well for starting the bead, even on cold metal.  (I tried the chart settings, they were a joke, looked like birdsh*t).  However, once I’m about 1.5” into the 3” fillet I start getting bad undercut and the welds look ok but a little mushier than I’d like.  It seems sometimes I’m able to lay good beads, and other times I’m not. So my questions are: 1)Do these settings sound reasonable for the joints and thicknesses I’m working with?2)It’s clear the settings are a bit hot for the 1/8” (I even turned it down from Maxal’s recommended 24V for 4043).  Could it simply be that my coupons are too small to serve as good examples? I’ve measured the temps with a surface probe, they’re around 250-300F after 30 seconds, maybe they’re just getting too hot to lay consistently good beads?  I’m thinking working on something like a trailer where there is a lot more metal would provide much more of a heat sink.3)Does my technique sound reasonable? Does anyone have any tips for changing anything, maybe better ideas for preventing blowout of the end of the joints? I’ve tried welding 2” square x 3/16” tubing to flat 3/16” plate and blew out the edges if I didn’t tack the corners beforehand. 4)I’ve noticed that when laying down the first pass, I don’t get as clean, smooth flowing welds as I get on a second or third pass.  I’m guessing this is either due to leftover surfaces oxides (I try to scrub as much as possible), or the effects of pre-heat.  I will run some tests, but just curious what the pros say it is?5)Any other ideas on what I might change to improve?I’ve read just about everything I could get my hands on about aluminum MIG until now.  One thing worth mentioning is that when comparing the settings a lot of noobs to aluminum MIG use (mostly described in forum posts) as well as the welding charts inside the welders, they seem to be woefully below handbook/welding guide voltage/amperage recommendations.  Curious what the take is from the pros regarding this discrepancy? Is it a result of the BS marketing hype (i.e. you too can weld 3/8" steel with this 90amp MIG welder)?Thanks for any input. The first pic: 1/8" fillets. Looking closely you can see the undercut along the top edge of the welds.Second pic: 3/16" fillets. The lower fillet in the pic is what I'm going for, although it did have a tendency to blow out the end of the joint.Third pic: 3/16" square tube to 3/16" flat bar. Cold start on the right, didn't dwell long enough and let the puddle flow out, but blew out the end on the left. I think the porosity was caused but the lack of cleanliness of the part that blew out. Attached Images
Reply:The small coupon size is a lot of it. Also you have to really move once the weld heats up. Try just a push instead of backing up, as that builds extra heat. Your angle of travel and gas flow sounds right. Volts seem high for 1/8".
Reply:MJD thanks for the response. Maybe I'll try to get some 1/8" x 2" square tube for some practice, been picking the metal up from a local job shop and they've been giving me a good deal but the stuff still ain't cheap, and its the first pass welds i'm most interested in, meaning it takes a lot more prep time for one joint than I get welding practice. Or make bigger coupons and let them cool a little more. The volts recommended by maxal for 1/8" aluminum fillets with 4043 is 24V, i actually turned it down from there because of the undercut. Millers calculator says 21-22V, but doesnt specify the aluminum alloy, and 5356 should be run a couple volts lower than 4043. Maxal's starting point for the same joint with 5356 is 22V. I didnt want to turn it down too much more from the guidebook values, my first assumption would be that any weld issues would be my technique and not their settings. But good hear it may not be me.
Reply:Millers parameters on the machines are listed for 4043. On the mm252 chart it shows 20.0 volts and about 380 for wire speed on .035 4043 wire.
Reply:IMO, your test piece size is too small. An AL weld will always be different at the start on cold material. With only having 3" to run this is what's happening:1st inch: Oh wow, look at that, what do I do now?2nd inch:  Ok, how come it looks different now then when I started?3rd inch:  Jeez, that went fast! and I almost blew the stop out! (the piece has heated up so much that your settings don't mean much anymore)I would make them 6 X 3 or so. A 6" fillet is about all that (maybe) a novice can handle after lots of practice. Just tack the back side of the test piece with a couple of bird turds and go. Let the piece cool before you weld the back side. Waiting different lengths of time also aids in understanding what the value of preheat is. Go to your recycler and buy scrap plate and tell him you'll return it weighing more than when you got it. Be prepared that you get less for it in return than what you paid but it's a LOT cheaper than new. I don't pay much attention to settings. I have three 30A guns and every one of them work at a different IPM setting, even on the same power source. When you understand and can feel what's 'right' you will do the same. Therefore, practice, practice and then practice some more. Take your fillets and do simple bend tests; that will show you a lot about what a good weld is. When I have my little bug-sprayer mig machine stretched out with a 50' extension cord on some dock that already has a dicey AC circuit, you better believe the settings will be considerably different than at the bench. Of course, this is only my opinion so FWIW!Last edited by Yofish; 03-07-2015 at 06:03 PM.
Reply:Guys thanks for the responses.MJD: that's interesting, I looked in Lincoln's GMAW aluminum guide under the welding procedures and its the same chart as in the maxal guide, specs starting parameters as 24V and 130-140 amps with 4043. In another chart it says 20-24V for 0.030"-0.047" (non specific) but says use the high side of voltage for 4043. I'm surprised the 252 chart says something totally different. Yofish: thanks for the invaluable information. I'll check out a local scrap recycler a see what i can get, then make the pieces bigger. Hopefully that will give me a better idea of if the settings are ok and can work on technique from there. I did go through one spool in 2 days just practicing fillets and i've got 3 more on the way.
Reply:The 252 setting seems cold, but there is a pretty wide range on aluminum. Fillet or butt weld is a big difference on 1/8".
Reply:The best advice I can give you is create your own table. Reference thickness, surface area, preheat and amperage and then record the characteristics of the weld.Why?Because every weld on AL is different.Even the same thickness and the same weld is different if you are welding a 4x8 sheet vs a 1x1 piece.BUT, there is a kinda procedure I follow:1) Preheat moderates the influence of the part heating up. Therefore your settings will always do better at the beginning and end of the weld. I always preheat if I want a good weld.2) I set the heat input for penetration. You have to watch to see what works...not just make a pretty bead, but join the parent metal pieces. No one can tell you this from a picture of your weld unless you cut it in half and show it in cross section. To me that's the hard part about MIG. It can look pretty but not be very strong.3) Then I perfect the wire speed, by sound and feel. It should give you a nice consistent sizzle. Your beads show this property, so i assume you're on this already.Not that I'm perfect my any means, but that is what I've found that works for me.Chay
Reply:Chay thanks for the tips. Creating something like a table is exactly what I'm doing, I'd like to get settings and technique dialed in for a number of different joints and metal thicknesses and have all of the info for reference. Avoiding lack of penetration takes precedence for me over pretty beads, hence my hesitation to turn down the heat too much. But I really want to get something consistent that just comes automatically without thinking too much about it, has good penetration and looks good. Once i get some bigger scrap I'll experiment with the pre-heat. As mentioned above after the first pass these small pieces get a bit too hot, so I get what you're saying about the joint size difference. Will try to do some more controlled temp experiments with a surface probe and see what I can come up with.