Mig vertical and overhead certification test questions

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Hello Everyone, new user posting for the first time. I work in the sheet metal trades and need to take a certification test coming up, but in practicing I am having some issues. I need to weld an 8" bead vertical-down and then overhead on 18g and 1/8" black iron, and then again on 304 stainless, 1/8" only. I'm using a 110v Lincoln 140c with .035 wire and 75% argon 25% co2, and for the stainless using stainless wire and tri mix gas. There have been former employees who passed on this machine so I know it is possible. Anyway, I am fairly experienced, I have shop fabrication and field experience, and my welding looks real good. The problem is I am having issues getting full penetration on the black iron, and haven't even begun practicing on the stainless. I know this machine is a little under powered, but I have it maxed out, I have been able to achieve the penetration the test is looking for but need to gap the metal 1/8" or more, and it's a real hit or miss as to either too much or not enough gapping. Again with the overhead it is real finnicky, if i gap the metal too much I am burning through right away, not enough and I am not getting the penetration needed to pass. I know others have passed with little to no thought on how much to gap the metal, if at all. So I am looking for insight from maybe some of you who have taken this test or maybe generally just have more experience. What am I doing wrong here? Any tips, tricks, techniques will be helpful. I am travelling slow and using a nice even weave, and the machine sounds good, but obviously there is something I am doing wrong. The beads look beautiful but when you flip the plate over the seam is still visible. We do have a larger 220 machine (antique) that I have access to but I've had the same results with it. I'm not as familiar with it, the wire speed dial is wicked touchy and I would rather stick with the one I'm more familiar with .Last edited by robc917; 03-06-2015 at 05:18 PM.
Reply:I guess where I would like to begin is I need to know the proper amount of gap i should be using in my test plates, both for the 18 gauge and the 1/8", also would it be acceptable to do any kind of bevelling? It is only going to be one pass
Reply:Hi Rob, welcome to the forum    I am by no means a great sheetmetal welder but will try till someone better posts. First an 1/8" gap on 18 Ga seems huge. I would think that a tight fit will give you best results on 18 Ga and perhaps 1/16" for the 1/8". You should be able to get good penetration with that setup and minimal gap.
Reply:Hey Bausman, thanks for the welcome, and thanks for the response! Yeah Let me clear that up, the 18 gauge I was going with a tight fit, no gap, but couldn't get penetration all the way through. The proctor wants to see the two pieces fused together on the back side, so there is no remaining seam. I was able to get passing results with a gap but to be honest I was estimating my measurements. The 1/8" pieces I was gapping quite a bit (again, to be honest here I wasn't using a tape) but needed almost 1/8th of gap (eyeball) to get full penetration. The guy I work with said something similar to your response, no gap on the 18 gauge and just a slight gap on the 1/8th (maybe the thickness of the wire) but in trying this I can to no means get the penetration this way. I always start with the vertical down weld, and I've even travelled so slow that the puddle begins to teardrop but still nothing. Maybe it's technique?? The only way I can get it is with a (huge) gap and basically fill it in with a weave technique. Then it becomes difficult to not burn through when I have to switch to overhead. It's hard to pull him off of what he's doing to come see what I am doing wrong, but the guys upstairs are pushing pretty hard to schedule this cert test, but it's useless if I'm not going to pass.Unfortunately over the weekend I am not able to practice as the equipment is located at my work. But I know from here on out what I really need to do is make up a bunch of test pieces and actually measure the gap so at least I can be accurate on that end. I am still open to comments, suggestions, anything I can bring with me tomorrow to practice after work. If anyone has any questions or if there is something I didn't explain very clearly please don't hesitate to ask. I looked online for this test and was unable to find it. But It's a vertical down and then an overhead (one pass) on each of the metals, and then again on stainlessLast edited by robc917; 03-08-2015 at 09:10 AM.
Reply:Sounds like your settings may be a bit cold as you should be able to "blow through" 18 Ga with no problem. A good starting point would be 1 ampere for every .001 material thickness : 1/8" material = .125" = 125 amps. If you are using .035" wire, use 1.6 to figure the wire speed for .125 metal. 125 x 1.6 = 200 inches per minute. Then adjust voltage. Also .035 wire seems like a lot for 18 Ga. If you have the option use .023-.030. Oh, and the stainless will run about the same speed but less voltage. Although like I stated I don't weld much gauge material but assume if you are not getting enough penetration turn up the heat.I also looked for that test but found nothing on it. Is this an AWS test or in shop?
Reply:Not sure if this helps, but I've done lots and lots and lots of butt welds on 18/20 gauge sheet metal and have never been able to get full penetration without gapping, 0.040" is decent, anything less and the shrinkage will pull the pieces together and prevent complete penetration through the back, you'll see a little hairline where the joint is.Does the weld have to be in one non-stop complete pass? Its really tough not to burn through on stuff that thin, downhill is probably your best bet. I prefer to tack every 1/2", then start in the middle of a tack and weld straight across to the next tack, skip a few inches, then do the same. in your case it may not be relevant, but skipping around keeps the warpage under control. For really thin stuff (20 gauge) i will lengthen the stickout as well when i notice the weld is looking like its about to burn through, and grind down the tacks before welding up the gaps between them. My experience with gauge welding has been mostly for automotive restoration so all of these welds get ground down, but these techniques work well for me even with gauge steel up to 14 gauge. I've always found it difficult to try to run a straight bead for more than a few inches on 18 gauge and thinner without burning away an edge. Lengthening your stickout might help, and I always use 0.030" wire for this.
Reply:Thanks Bausman and Jieve for the replies! Bausman I know what you're saying about the blow-through, I have this welder cranked up all the way, which on this unit is "J", the wire speed is numerical, but I have it at about 3 1/2, which sounds and welds nice and hot. (I haven't calculated the IPM at this point) If gapped I can get the penetration but in doing so I am walking a thin line of burning through, which I can easily control until I get to overhead it gives me trouble. Tight fit I can't get any penetration. Also on the larger 220 unit I have the same results, and I have cranked that one way up. As far as the test, it's my belief that this  is an AWS test, the guy who is coming in to perform the test is from an outside source. That's all I really know. Jieve, to clear things up, it does have to be one continuous pass, vertical down. Also it has to be .035 wire, I have no option on this. Actually I normally run .030 on this machine but the test specifically calls for .035 so I have a little spool of that to practice with. I can tack the two pieces together at the beginning and end but that is it. Warping is not a concern in this test (I don't believe), he is looking for penetration imperfections on the back side. The stainless they take and I believe do an x ray test, but the black iron is a visual test from the back side, and then he bends it in a vise. I will know pass or fail on the black iron portion before he leaves. Overhead I can do it any way I like but again it is a one pass deal. I'm gonna try to make it in for some practice time tonight, first and foremost I'm going to prep up some test plates and clean them up real good, I have a few other ideas as well, along with noting my gaps, I'll keep you posted on what I find. Thanks again for the help!
Reply:Ok just a quick follow up...I was able to get in and run a few practice beads yesterday, and had some better success this time. On the 18 gauge I'm getting good penetration with 1/32" - no gap using a lot of heat and a lot of wire speed. On the overhead I am getting good results except with a whole number less heat and half a number less wire speed. Then on the 1/8" I am indeed using a 1/8" gap, using a piece of metal to gauge the gap I am filling the void as I work down. For the overhead I found a 1/16" gap works with a half number more wire speed. (as stated before this machine's dials go 1 thru 10 for the wire speed and A thru J for the voltage) Now here's a few questions for you welding Gurus: First, it seems like (and judging by my settings) that it is easier to get better penetration in overhead rather than vertical down (less heat required, etc). Is this true? I.e. I have to travel faster in overhead to avoid burning through. Also a curveball question: I was using .030 initially to dial in these settings, until I realized I need to be practicing on .035 (stupid mistake), so once I switched to .035 my wire speed had to be cranked DOWN from the wire speed settings I was using with .030. Is that correct? Finally, when I switch to stainless, I believe someone said to use less voltage than on black iron. When I weld stainless I usually weld hotter than black iron, so any tips there?
Reply:Not sure about the black iron/stainless question, but with a larger wire diameter you will need less wire speed for the same current. For a pretty close estimate of amperage at different wire feed speeds for different wires, check out Lincoln's gmaw guidebook. There are curves of wire speed vs. amperage for their stainless, aluminum and carbon steel wires. I've tested and found them to be pretty accurate. In case you read through the welding procedures listed there, just fyi the welding procedures (wfs and voltage) in the handbook didn't match their own curves for 0.035". I wrote lincoln about this and their response was that the procedure tests and curves were done at separate times with different stickouts ... I've tried to duplicate the procedure values and couldnt get anything that high, even with the gun shoved into the joint. But the curves themselves are pretty close. I've tested the 0.030", 0.035" and 4043 0.035". At least it'll help with an understanding of the effect of the parameters.Last edited by Jieve; 03-10-2015 at 11:51 AM.Reason: mistake