Need Advice for Mig Open root

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Hey guys, i am new here and in desperation for some advice. I have been attempting to pass a flat open root test in Mig welding for the past week and have been unsuccessful so far.  My main problem is my root pass.  I get a nice looking bead with full penetration each time i weld, but then when it comes time to bend my test, it breaks like glass. The cap for each test i have done has never broken, not even a crack.The setup on my machine is 0.035 wire, 18-19 volts, 200-250 wire speed for short circuit transfer.   Gas mixture is 80 % argon, 20 % CO2, or so i'm told by the instructor.My plates are beveled at 45 degrees, with a 1/8'' gap. The landing is 1/8''. I have tried push work angles and perpendicular work  angles.I have tried large, slow c motions in my welds, and have tried small c motions, making  very tight beads. I have examined the root pass and have found no porosity, cracks, inclusions or undercut. I show each root pass i have done to my instructor and he says it looks good. (Yeah, good enough to break like glass.)Any advice you may have for me would be greatly appreciated, i am at a loss on what to do.
Reply:Do you know why it broke?Edit:- I had better not leave you hanging like that!  If the landing is an eighth of an inch thick, then the total thickness is such that you must bring the pieces up to about 150 degrees to allow the first pass (root) to gain penetration. The preheat will also dry off any surface moisture. The cold first pass will crack everytime, whereas a preheated identical pass will bend.That's my opinion and I am sticking to it.Last edited by tanglediver; 08-13-2009 at 12:15 AM.City of L.A. Structural; Manual & Semi-Automatic;"Surely there is a mine for silver, and a place where gold is refined. Iron is taken from the earth, and copper is smelted from ore."Job 28:1,2Lincoln, Miller, Victor & ISV BibleDanny
Reply:Originally Posted by tanglediverDo you know why it broke?Edit:- I had better not leave you hanging like that!  If the landing is an eighth of an inch thick, then the total thickness is such that you must bring the pieces up to about 150 degrees to allow the first pass (root) to gain penetration. The preheat will also dry off any surface moisture. The cold first pass will crack everytime, whereas a preheated identical pass will bend.That's my opinion and I am sticking to it.
Reply:Yup, i already grind the plate on the backside.  I  haven't heard about preheating the plates before, but i usually get my plates right after they have been cut, and they are pretty warm. I have changed the way i grind my welds and root and i also now let my pieces cool naturally instead of putting them in front of a fan.  A classmate told me i was concentrating too much on penetration and not enough on tie in. So I'll focus more on that and see what happens.
Reply:Cycling between overheating and fast cooling could be the cause of the cracking.   Maybe use lower machine settings, do only one pass at a time, let it sit and cool naturaly a bit between passes and eliminate the fan.   If you can get one of those digital laser temp guns then you can see what the temps are and how long to cool it and when to stop putting in passes.   I don't have a temp gun so don't remember what the numbers are supposed to be, but I seem to remember 500-700 as being the target temp range?  I'm sure Lloydeo can tell us exactly what it's supposed to be, he knows all this stuff well.MM350P/Python/Q300MM175/Q300DialarcHFHTP MIG200PowCon300SMHypertherm380ThermalArc185Purox oaF350CrewCab4x4LoadNGo utilitybedBobcat250XMT304/Optima/SpoolmaticSuitcase12RC/Q300Suitcase8RC/Q400Passport/Q300Smith op
Reply:We have been doing the same test as you and i got my to pass with no land and 1/8 root opening 3/8 plate ran miller inverter 304 at 17-18 v and around 2-250 ipm  and 25 cph on the c25 gas and used the c motion.. You will pass if you do it all right..
Reply:Originally Posted by GraydevilWe have been doing the same test as you and i got my to pass with no land and 1/8 root opening 3/8 plate ran miller inverter 304 at 17-18 v and around 2-250 ipm  and 25 cph on the c25 gas and used the c motion.. You will pass if you do it all right..
Reply:Switch to 1/16" - 3/32" land.  Your 1/8" land is too thick for adequate penetration.  Your root passes are probably cracking because you're getting cold lap and just laying the metal over top the root face, and not fusing them together.Stay on the leading edge of the puddle.  your root pass shouldn't require much if any gun manipulation.  Too much manipulation is spreading your available heat into the bevel walls, and not into the root face, where you need it.Oh, and your 90° work angle or push work angle are not doing you any good when it comes to penetration.  You're probably getting a nice flat bead, because the puddle freezes really quick when you push.  You should be using about a 15° drag travel angle.  You'll get more penetration on the back side, and concentrate the heat in the puddle.  This will help you tie into the bevel and get 100% fusion.  In my opinion, pushing with MIG is fine with sheet metal, but on heavier plate, that soaks a lot more heat, you have to use a drag travel angle, combined with the right travel speed, gun manipulation, and machine settings to get good fusion on the root pass.You'll have to experiement with travel speed and machine settings to find what works for you. Originally Posted by ArsenalHey guys, i am new here and in desperation for some advice. My plates are beveled at 45 degrees, with a 1/8'' gap. The landing is 1/8''.
Reply:Well i have some improvement on my root. The last one i welded didn't break in half.  I have a couple small cracks, which will prevent me from passing. The next one i try i will use the drag angle you suggested.  I'll also  decrease the size of my landing and gap as well.  Should i still use the c motions with the drag, or just drag it in a straight line?The environment i am in isn't cool at all.  I'm down here in Dallas, Tx and its nice and hot in the lab each day.  I really haven't been letting it cool between passes. I'll take that info into consideration and look for a temp gun this weekend. Thanks for the advice guys, i will let you know how it turns out. Attached Images
Reply:Arsenal,Is your instructor holding you to perfection, or to a specific code?  AWS has standards for what is acceptable, and your photo looks to me like it might pass muster.  I think the AWS D1.1 standard is no single defect larger than 1/8" and the combined total must be less than 3/8"; but don't hold me to that in court. There are also exceptions for edge defects, unless there is clear evidence of a discontinuity(like cold lap or a slag inclusion, etc).If your instructor is looking for perfection(which is not necessarily a bad thing) you're almost there. The bend strap magnifies the weld appearance, and I can see some variation in the width of your root pass.  It's wider on the right side of the strap than on the left side.  Something about your technique is not 100% consistent.  Travel speed, work angle, gun manipulation, root face, root opening, etc.  What did you change to get the result shown in the photo?Benson's Mobile Welding - Dayton, OH metro area - AWS Certified Welding Inspector
Reply:I changed my travel speed and gun manipulation. I also focused more on tieing in my plates than penetration, since i was getting enough penetration on my previous tests anyway.  I had to stop and restart due to my keyhole getting too big. Once i restarted, i probably traveled a little faster than i did before.  My instructor does ask for perfection on our welds.
Reply:Arsenal,I think you might want to go with a globular transfer arc on the root pass. Short circuit transfer is prone to lack of fusion on thicker metal. The globular transfer arc will be hot enough for fusion on the root pass, and with the intermittent glob there will be that moment where the puddle has just a fraction of a second to chill a little. This is a more controlled and cleaner way to weld than short circuit. My opinion is that it is almost always better to push with mig; especially on heavier metal, with spray arc. Experiment. I like a 15 to 25 degree angle on the push. The penetration is a result of amps, wire speed, travel speed and arc type. I would only drag on the last pass, and be tempted to go with a spray arc.Your teacher probably already covered this, but, if you have a little stick out with the tip, you will have a more control than if it is back into the nozzle to much.Last edited by maarty; 08-15-2009 at 12:56 AM.
Reply:Maarty,I have to make a couple observations after reading your comments.  You're the first person I've met who intentionally uses settings to give globular transfer with solid wire MIG.  Usually there's too much spatter, which leads to lost time in cleanup.  I've never tried it, but I confess I have a hard time imagining that you won't get excessive reinforcement on the root side of the joint.  I'd love to see a photo of an as-welded  MIG weld root pass made flat using a globular transfer modeI suspect that arsenal's instructor has them intentionally learning to weld this joint with short circuit transfer becase the other arc transfer modes can't be run out of position.  You can't put an open root pass in vertical or overhead with globular or standard spray transfer arcs(pulsed spray perhaps being an exception)If I'm right, Arsenal's instructor won't accept a test plate that isn't welded using short circuit arc settings.  Because that defeats the preparation he's giving them in learning to make the same weld in the vertical and overhead positions.  If I'm wrong, please clear up what you're trying to accomplish in your class, arsenal.Lastly, I agree with you when you said you'd push the puddle when using spray arc.  But again, I suspect he has to weld this all the way out with short circuit transfer.  I believe he's going have to make this same weld out of position, eventually. Originally Posted by maartyArsenal,I think you might want to go with a globular transfer arc on the root pass. Short circuit transfer is prone to lack of fusion on thicker metal. The globular transfer arc will be hot enough for fusion on the root pass, and with the intermittent glob there will be that moment where the puddle has just a fraction of a second to chill a little. This is a more controlled and cleaner way to weld than short circuit. My opinion is that it is almost always better to push with mig; especially on heavier metal, with spray arc. Experiment. I like a 15 to 25 degree angle on the push. The penetration is a result of amps, wire speed, travel speed and arc type. I would only drag on the last pass, and be tempted to go with a spray arc.Your teacher probably already covered this, but, if you have a little stick out with the tip, you will have a more control than if it is back into the nozzle to much.
Reply:I have actually used globular on my cap in the past and it held pretty strong. Haven't tried it on the root pass however.  My instructors did tell me that they want me to weld using short circuit, so i had to stop using globular. Globular makes a pretty good popping noise, which will lead to anyone nearby coming around and asking me what the heck im doing, lol.I may weld a practice piece with globular on the root  just for kicks and post a pic of it.But for my tests, gotta use Short Circuit. I had a classmate claim he passed his flat running a straight bead on the root, but used a whipping motion, back and forth like with a 6010 rod. This guy does exaggerate from time to time, but it would be interesting if that did work.
Reply:Just try it. I find globular to have excellent control features, and far less spatter than short circuit arc. When I run globular it makes a soft and ryhthmic ffft ffft ffft sound, not a popping sound.I would also recommend experimenting with different fit ups; a little tighter on the root, with a smaller landing; a little wider etc. I wonder also about the 90 degree fit up. On open V welds my plates are cut at about 37degrees, to achieve an included angle of 75 degrees.I suggest if you haven't done this, to fit up at least ten test plates; so that there is a continuity and freshness in your learning curve, as you experiment with different feed, amperage and travel speeds.Last edited by maarty; 08-15-2009 at 05:50 PM.
Reply:So i changed the size of my gap and landing and got these results on my root. Attached Images
Reply:Arsenal,That looks really good!! Very nice. Tell me what you did differently this time. And lets see the face and root bend samples.
Reply:I turned up my volts to around 20, wire speed at 250. Had a smaller landing and gap.  It does look good, root tie in will be my main concern. I will finish up this plate tomorrow.
Reply:What was the puddle manipulation like; did you hold it steady or whip it back and forth a little? It looks like you whipped it a little. What did the arc look like? How much stick out did you have with the tip from the nozzle? You pushed, not pull, right? Lets see how you do in the other positions; especially vertical.
Reply:Just a quick question.  What are the things in the yellow boxes?  see photo.I can't tell from the photo, but are they lack of fusion(LOF) discontinuities?  Or just spots where the glassy slag popped off of the weld?Looks like you're making progress.  But check those things I marked in the photo.  If they're LOF, you may be favoring one side of the joint at times.  As Maarty asked, what was your travel angle and work angle when you ran the pass?I'd ask what the travel speed was too, but if you're like me then time seems to stand still while I'm welding.... Attached ImagesBenson's Mobile Welding - Dayton, OH metro area - AWS Certified Welding Inspector
Reply:Looking at your pics from the top of the weld,  I see a lot of gouging from the bevel cut.  This could be causing some problems and inconsistencies in your weld.  How are you prepping the joint?  If I saw something like that,  I'd grind the face until it was smooth.  It still seems that your settings are a little low.What brand and classification of wire are you using?Esab Migmaster 250Lincoln SA 200Lincoln Ranger 8Smith Oxy Fuel setupEverlast PowerPlasma 80Everlast Power iMIG 160Everlast Power iMIG 205 Everlast Power iMIG 140EEverlast PowerARC 300Everlast PowerARC 140STEverlast PowerTIG 255EXT
Reply:i had a bend test yesterday and it passed!Those spots you saw were glassy slag that popped off.On travel speed, i try not to go too fast and not too slow. I try to find the right speed to get good penetration and not end up with a keyhole.On the stickout, i had my contact tip level with the nozzle. The stickout was probably a little over half an inch.I pushed while doing a c motion, making sure to tie in and pause a little in the middle to get penetration.I did well enough on my horizontal practice pieces to take a test. So i welded one and the pieces are ready for bending tomorrow. Horizontal feels a lot easier than flat for some reason.
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Reply:Originally Posted by Arsenal Originally Posted by maartyIn a couple of spots on the picture with the root face, the weld looks a little narrower than the rest. I have to wonder if that is where you made your fit up tacks?Also, are you running a globular arc? There seems to be confusion with some people about what that is:With a short circuit arc the wire is feeding straight into the puddle and the arc is relatively short; it has a loud ripping of fabric sound.With a spray arc the current and wire speed are high; the arc has a V or cone shape, and a strong steady vvvvvv sound is made; the puddle is large, and the weld bead looks very smooth.A globular transfer arc is hotter than short circuiting; the arc starts to fan out a little (as in, not tight and narrow) Because of the higher heat the wire burns back a little, and then jumps the gap and joins the puddle. This does not mean that you have a ball of molten metal that hangs at the melt off point for very long. With a good globular arc the molten ball transfer happens at a relatively rapid rate of say, 3 to 5 per second; with a ffft ffft ffft ffft soundThe globular arc is a hybrid of short circuit and spray, but it does need fine tuning. Experiment with having a fast transfer, and then a low speed transfer. There are two ways you can do this; vary the wire speed, and vary the current. Tweak both of these variables and you will have an arc that is unbelievably smooth, low spatter and controllable.I was welding outside corners on electrical box lids once, and inside of this old Linde wire feeder, at the back was a chart of volts, amps and fit ups with metal thicknesses. I just followed the instructions, and started to weld; the welds were so smooth that the grinding department had almost nothing to do. The foreman was even surprise when I showed him the chart. Anyway that was the first time I ran a globular arc, just over 30 years ago.