MIG Tack Welding 101

admin

I while back I posted a question in here about using MIG to do tack welds for welding tubing.I went ahead and did some test welds on some .083 channel and .095 tube mild steel and wanted to see what everyone thought.  I was using .025 solid wire.The welds look like TIG and they appear to have lots of heat in the metal and would be strong in a production use.Below is what I tack welded today.  Do you think the weld is solid and can I do the same for the whole roll cage?Thanks in advance!Mike Attached Images
Reply:Mike, what is this roll cage for.  I admit they look good for uniformity, fusion, ect.  I wouldnt say they look like tig welds.  However, what does bother me is...silicon intrapment between welds.  Basically, theres them lil glass like particles that form ontop of the welds, well thats silicon.  Its a arc stabilizer and helps to make the wire more forgiving to rust, mill scale ect.  It does though form a seperation between two welds, in this case lil bitty tacks.   This could cause a fracture in a hard stress scenario.  Wondering what kind of rolly cage your wanting this for.  And I suppose more importantly you will have to determine whether the stresses are great enough.  Basically, if its were for a small lil go cart going no more than 35 mph I wouldnt worry.  But for a tractor or lets say,  I wouldnt use this.  NO way.  It might work, but you cant be sure.  And if it doesnt work, well it will just add to the carnage.    Just a thought bud.IF it Catches...Let it Burn
Reply:I pretty much agree with Chris. The weld looks a little cold in places, like on the left side of pic where wire is sticking out. The middle part of pic looks ok but I think you are concentrating too hard on making "tig" welds. You dont really need that 'stack o dimes' look to make a good weld, just good penetration
Reply:I'm wondering why you would want to do this?  .083 isn't all that thin.  You could hit it with a bead and just run it all the way around and likely achieve better results.-Heath
Reply:The reason I was trying a different approach to welding tube is because I am having trouble finding information on technique for welding tube.I am installing a roll cage in a 1/4 mile car and I have some out of position welding that needs to be done and even the in position welding it is tough to keep the tip correctly positioned while moving around the tube.MikeLast edited by malich; 12-31-2005 at 10:28 AM.Build a Barstool Racer at BarFlyRacers.com!
Reply:Mike,  yeah that will be a trouble with mig.   Racecar builders almost always do this stuff, among other things, wiht tig.  They say,  in my trade, that the smaller the pipe the tougher to weld.  With the exception of the xray its true.  The xray is a whole differnt animalIF it Catches...Let it Burn
Reply:Mike if you can stay +or- 10degrees while welding around the tube even if its only half way around then backgrind your stop and start it should be good.As for the tacking method shown in your pics,looks pretty but its not what you wanna do for a cage in a 1/4mile vehicleLance
Reply:How about just a few thoughts, opinions and points of discussion without any advice attached???   Actually more questions than anything. Without getting into sanctioning bodies, who approves what, testing and truck loads of regulation I think every so often we should be allowed to look at things from a pure duty perspective. "Will this perform for the intended purpose ?".  What's the life expectancy of a cage for a 1/4 miler anyway? One year, ten years, twenty years?  Are these cages subjected to repeated flexing, bending and twisting time after time only to fail when you need it the most?  Or are they primarly dead weight who's only purpose is to withstand the extreme forces of impact brought on by endo's and multiple rollovers? Basically a one time shot.If the sole purpose is to protect the human carcass during one dynamic event lasting ten seconds then I wonder how much difference there really is between a good weld and a crappy weld. Certainly appearance wouldn't be a high priority in my book, but it does seem to get top billing most of the time. Seems like the pulsing method or tack method we see here is going to present more problems from stress risers than cold lap. Internal risers as well as external. But then these stress risers generally manifest themselves after being subjected to constant or repeated flexing and/or twisting forces, not extreme impact. Or repeated flexing and/or twisting where unseen cracks can form and then one sudden impact.My impression is that racing events are as much a 'car show' as they are a racing event now-a-days. Events where is a guy is rated on the side by his ability to throw high dollar welding equipment and tons of talent at his cage.Blather aside, Malich is trying to acheive a good looking weld yet strong enough to withstand some tremendous forces he hopes it never gets subjected to.  Shy of buying a high priced tig, and rolling the work piece around and around so there is no 'out of position' welding there should be a way. I can impathize with the problem. I just finished up a tiny cart project for my son and grand daughter. Being able to weld out of position is one thing. Round tubing with a ton of "S" curves and complex radii coupled with numerous changes from thick to thin from the coping is quit another. A guy has to be a hot dang contortionist on top of it all. I hurt all over form rolling and twisting and cranking my neck while reaching around, over and under all at the same time.Any how thanks for letting me waste a bunch of the alphabet here.
Reply:Mike,  I read Sandy,  and I must say with extreme reservation I agree with him.  The reservation is due to the fact I am a professional welder, a contract welder and people look at what I say and they take it as scripture.   I dont like that, and not all people do, but enough do.  So if you promise to use your own thinker on this one and make your own judgements based on all youve read I will give my off the record version.  Ok,  first off Ive made welds like youve made here and they held just fine.  I think Sandy is prolly right about the welds being sufficent given the circumstances.  But alas, I dont know that with out certifying the procedure with tests to prove whether these will be sufficent.  You see, do y'all remember the No. 3 Car crash?  Dale Earnhardt died after a horrible crash.  One thing remarked, his car did hold togther, the impact was too great for his body to stand.  I guess where im going here is a lot of cars, the frame the roll cage, everything is made of chromemoly and if the pre/post heats arent done right they cause stress risers, which inturn will lead to impact cracks which instantiously cause complete failure.  Well not all do, but they are suseptable to that.  The trouble is, these welds, with enough impact, could break.  Are you going to be in a situation that yields that much impact though?   I dont know.  I dont expect you to know, but then again I also looked again at the thickness of the metal your using and find its pretty thin.  Perhaps if the impact was great enough to cause major problems to the weld, the weld is not the only thing. The strength, or lack due to wall thickness.  Not saying this is too thin, I am sayin these are considerations.  If the wall was thicker, the tacking idea would be that much worse IMO.  Given its so thin, if its heavy enough to do the job intended perhaps teh welds will work as well.  But these are uneducated assumptions on my part.  Uneducated as I have no experience or literature on the topic at hand.  I know of other areas, and I for one am no engineer to determine what is sound and what is not.  When the say is said and done youve got choices to make on your own.  One is whether you can live with the risk here.   There are many times when for my own personal use, I can live with it.  Even for my family, I can live with it.  But for other people, I cant.  This is for a number of reasons.  Not the least bit I know what I will do with something.  I cant predict that some @sshole will flip a vehicle two or three times and then on the fourth time the cage finally cracks and buckles and sues me when he knew, or should hav eknown you get a new ROPS after the first roll over!   Thats why for me personally no matter what I would make these welds as clean as possible as Ive stated in my earlier post.  But as Sandy points out, these are not the same conditions implaced on you and you are in a limited world of oppurtunity to do the same job without really putting your good posture into a heap of aches.  I do this regularly and it keeps my more spry and limber.  Plus I know how to position myself in a way thats the least painful the first time.  I want you to do some serious soul seaching,  maybe talk to your friends who do this.  Deciede how serious this is.  Like Ive said, Ive made welds with 6011, one weld ontop of the other no cleaning between passes....at all!   That was how the bosss wanted it.  I dint agree, but was told how he wanted it...Said there was no need.  ANd these were concrete batch plants, structures and tanks and batchers and conveyors.  Yet they worked.  Ok, now, what wire are you using....ER70S-6?    If so, try a roll of ER70S-3.   ITs the lowert amount of silicon and manganese and it tolerates the least amount of surface crud.  However, I dont see that a problem.  Going with the ER70S-3 will leave the least amount of crud on weld surface...less inclusions.  Now, I want you to remember, if you choose to go this route dont go,  well see this redneck from tex he told me this was just fine cause hes a contract welder and all this....no no no  I want you to say that you looked at all the variables, and all the circumstances and cite them, and say, I feel confident that were in an acceptable level of weld perfermance.  Tell them that you believe their is an acceptable tolerance.    If it is still deemed unsatisfacyory,  well I dont know.....I hope I aint confused you too much or made this too difficult.   keep us updatedIF it Catches...Let it Burn
Reply:Mike, I read Sandy, and I must say with extreme reservation I agree with him.
Reply:Well,  I will be straight wit ya here Sandy,  I figured from the start it was prolly acceptable...but like I tried to explain coverin my own butt cause I dont know.  If I was doing this job for someone else...I would do it the "proper" way whatever that means lol.   I know you do this as a hobby, and in some ways that makes you better than us for a livin' guys.  Cause when you do something you see it to his life.  Prolly makin some things do far more than it really should.  and in many cases you dont have unlimited, or seamingly unlimited resources to support the right tool for the job.  I admit Im often in a pinch,  and here recently that bit me in the leg...but usually when it comes to having the right welder fo rhte job I have that.  No problem for having enough power to do the job I need, and if I dont have enough power for a certain job,   I dont take it.  Real simple.  Hobby welders on the other hand, they may have just barelly enough, or not realy and have to find a way to squeak by cause the alternative is to get the boss involved and either beg borrow and steal a new welder, or tell her how this big investment in a welder is good for nothing on this job because you gotta hire a welder to do this job, or rent a machine cause yours aint up to the task.   I understand, Ive got friends who been there done that...some even weld for a living    But seriously, I must say that theres a lot of do's and dont's in welding.  And sometimes its hard for me, and others.  We want to tell you, hey bud I think its alright.  And we believe its true...but then were like golly but what if were wrong...so sometimes we try to go about it the right way and do like sandy suggested...consider it and consider all options.  Or we say,  nope ASME pressure vessel specifications spell out you will have no inclusiions bigger then blah blah....And yes your inclusions are bigger than that so your weld is no good.  Well yeah but this isnt a pressure vessel.  Hmmm   is subjective.  Just take into account all youe read, make your own assesment, and I guess thats all any of us can do really.  Thats what I do myself. Sometimes your right and sometimes youre wrong.  Just hope when youre wrong about something you do it on something that nobody can get hurt on.   HAPPY NEW YEAR!!!!IF it Catches...Let it Burn
Reply:Sandy and TxRed,I have reads lots and tried various things.  I feel the best approach is to burn up a few bottles of gas learning how to make either 2 to 4 passes on tube with strong welds.I was hoping there was an easier way to weld this tube, but I can see I am going to have to learn the same way I did when I started welding straight.There is a local Chassis Shop here and all they do is MIG on the mild steel cages, so I know it is possible to make strong welds and pass tech.A funny story...I spoke with a NHRA tech inspector in my area and he said and I quote "As long as the welds look pretty I am fine with that", so much said for strong welds.  I was at the World Street Nationals in 2004 and there was a guy there that actually passed tech inspection with a stick welded cage that looked like crap and the NHRA rule books specifically states a mild steel cage MUST at least be MIG welded.   What a joke....so much for the track inspectors doing their jobs..Thanks again for everyones input, this site has helped me a  lot in the past year and I have improved me welding quite a bit because of everyone here.MikeBuild a Barstool Racer at BarFlyRacers.com!
Reply:and whats wrong with teh smaw process?   I admit Im very particular with my WPS but I still gotta ask whats wrong with smaw...I know a lot of fab people try to justify wire with the statement that smaw is inferior.  However, if you take the Xcountry pipeline as an example.  You will see where they have tried to make a run with semi auto and auto prcesses.  Its a total joke.  They are having extremely high repair rates.  Its completely disgusting.  Its really easy to make a pretty mig weld.  Its a whole nothing thing to make it right.  Stick, well if it aint laid in good, its gonna show.  Some though look like hell, and they pass the picture...so you know as an amateur youre not really gonna know.  But again, it really does come back to wps.  WPS takes all guess work out, and takes it from allowin gyou to base everything on facts vs allowing individual specs to form opinions.  In the particular instance, if in fact it is what you say,  no mig welding.  That should have busted the weld.  However, if it doesnt state that, or if its stated in such a way that includes smaw, which could, then the look of the weld would only be a matter of opinion provided the weld still met the WPS standard.  The WPS will not address looks unless for some wild @ss reason.   None Ive ever seen do.  Doesnt mean we shouldnt maintain the best professiional image of our welding.  It just means it doesnt meana good weld or bad.  More importantly, the better looking your weld, usually the better your weld will be.  This isnt always true.  However, if you are good enough to pass xray tests with a crappy weld, youll do just htat much better if you clean them welds up.  Its the best way to do it IMHO.IF it Catches...Let it Burn
Reply:and whats wrong with teh smaw process? I admit Im very particular with my WPS but I still gotta ask whats wrong with smaw...
Reply:Ok Sandy,  I wont shoot.  hehe   But I will say I dissagree with the code personally.  However, oh well.  Ive heard of no grind tests, never had one myself.  The appearance thing,  well I dissagree with it as a method of eval.  I believe in visual inspec, but thats differnt from saying a pretty weld.   Ive worked on parts that if it wasnt made right there was no fixin it.  No tolerance.   You made a new one.  Sucks but its true.   Only ting I could think of is with smaw or fcaw you would have to chip.  Chipping could lead to nicks in the weld that could invariably cause stress risers.      Im just theorizing here.   But enough theorizing.  Based on what Ive read, the specification states no smaw.   Regardless of weld quality if the specification states no smaw than no smaw.    thats my story and im sticking to it.IF it Catches...Let it Burn
Reply:I'd doubt there are any real tests done any way. Not on individuals cars that is. Maybe on tubing in general or after crash results. Testing would lead to an inspectors 'acceptance' which might shift liablilty, ya know??  Probably more of a quick visual and a "looks good", leaving the responsibility of the integrity of the cage with the owner/driver. You're probably right about chipping. Chipping could lead to the need for grinding, and severe or coarse grinding could be used to disguise what type of process you used?? Dunno.Like you say, I ain't building one so it's pretty much moot point other than it is what it is.Have a good one, Get healed up there.
Reply:Thanks Sandy.   Yeah its a moot point.  And I agree with what youre saying.  My thoughts,  independatly on the chipping and all.  I never grind my welds. Ever,  well rarely.  There is the exception on an open root I grind out the wagon tracks.  Tehn I switch to a wire wheel for all the rest, or I chip and use a wire brush.  For all the 7018 passes I make no grind at all.  I dont see it being an issue.  But im theorising possibly on the thinner stuff that makes these sorts of welds I guess its possible that in some past there was an issue with people hitting the weld too hard and actually denting the face of the weld.  By doing this possiblyt there was some concern that it become a stress poiint.  Like an undercut basically.  Or a arc strike which acts as a hardned spot,  the dented spot becoming more dense then metal around it.  Its purely speculation as I have nothing back this up...I just can think of no other reason at moment.  The grinding issue, well thats hmm,  thats rooted in some old things I think.  Why exactly here I dont know.  Ive worked from AWS and API code.   Never have I used no grinding allowed.   But I know it exisits.  I dont know if its only on specific testing, or if its code specified.  I believe its also only used with a backing strip.  With a backing strip I can make xray welds with only a chipping hammer and a wire brush.  Open root, im not good enough,  or really ever bothered to practice and test out for burning it out with the hot pass.  In my line of work Ive always been able to grind out the wagon traks.   All in all my line of wrk is apples to oranges with this stuff.  Its like them tiny lil apples and them big @ss california naval oranges     But you know it all goes right.  I think to youre prolly right about the inspections, but if there were a welding procedure specification the inspectors wouldnt be held accountable to anything providing they did their job.  If they inspect it to the WPS, failure or otherwise and it passed according to the WPS the inspector is off the hook.  But then again I beleive its like you said.  Its up to the individual driver/ team to make their WPS and in that case the driver must maintain eihter a welder who is hoenst enough to be judge jury and executor of his own work, or the driver must bring in an biased spec to verify procedure has been followed to the specification the drivers engineers feel is safe.  In the case of Dale E's car, he had a top notch crew.  They had engineered WPS, a welder who was willing to follow it and an inspection procedure.  Not sure who did the inspection.  But when his car took that hit it held togetehr.  Chromemoly is a lot more difficult to weld up than mild steel, and is a lot tougher to weld up right so it holds together in such a crash.        Infortuatenly its not just weld integrity that will kill a driver.  Ok, on to my leg.  Well saw doc today.   Pulled out every other staple.  Then he told me I should take boot off at home.  Said to try walking around on the leg too.  But to start out wearing boot when I walk.  then if it works ease into no boot and will start rehab next week.  I started walking this afternoon with one crutch on the left side, left leg bad.  Then I tried walking from the bathroom...like 10 feet max  to my room no crutch.  Then I walking all the way to the bathroom and back lil later with no crutch.   Then I walked all the way to the kitchen,  walked around the kitche,  got food ate and walked back.  All with no crutch.  Im still wearing the boot to walk.  Ive been up a few more times but the short runs.   I know this sounds stupid or more detail guys but im pumped.  Like this is big achievment for me I think.   I just thank the lord that I was able to get to doc, and then after docs accessment that his nurse pushed soo hard to get me my surgery before chrismtas.   Doc kinda pushed me in...then we found out it was a whole lot worse.  He doesnt think Id have kept my leg cause of the infection and all the crud still left behind by ER.  I thank everyone for your prayers and concerns.  Its not over yet.  But im working on it          GOD BLESSIF it Catches...Let it Burn
Reply:I would wonder if the grinding comment in the rules is to avoid gouging the tubing while grinding, and just thinning down the weld by grinding too much.
Reply:Originally Posted by ttyR2I would wonder if the grinding comment in the rules is to avoid gouging the tubing while grinding, and just thinning down the weld by grinding too much.
Reply:Originally Posted by ttyR2I would wonder if the grinding comment in the rules is to avoid gouging the tubing while grinding, and just thinning down the weld by grinding too much.
Reply:x-ray and UT I think are the two methods that would do this.  Outside measurements I think might be tough.  Its tough to determine where to pull those measurements from considering the tubing isnt going to be condierably thick anyway,no more than 1/4" and on many joints it will be tough to get a straight edge in and look for any mill defects inregards to bowing or whatever.  Its a big problem if their looking for real close tolerances like that.  I dont know realy.  But again the cost of doing tests like this would far outreach the limits of the job.  So I dont know Im afriad to even venture on this oneIF it Catches...Let it Burn
Reply:peepin' this thread
Reply:I'm new here - my first post.  I am an amateur welder at best, but I am familiar with the NHRA and IHRA cage requirements.I believe the single pass, no grinding rule is because you don't need to be a certified welder to be qualified to make a roll cage.  They want to be able to see the welds, not some pretty "top coat" to assess if you "can weld."In racing, I have seen some pretty shoddy welds that look good on the outside but have little penetration (especially with MIG) and then when the car hits the wall or barrel rolls at the end of the track, you can see the results.  Saw a car 2 years ago that hit the wall, then the other wall, and rolled a dozen times at about 140mph.  Some of the bars in the cage just tore off and the driver was left virtually unprotected.  (he survived, but was airlifted to emergency)To the author of this thread, what spec are you building the car for?  Is it a simple 6 pt cage to run 10's and slower?  If that is the case they are a bit more lenient with the welds.  I know that in my backyard no tech inspector would pass the MIG-tack welded tubing made to look something like Tig.  With all the stop and starts like said above - the weld is chock full of contaminants and it would not be as strong as even a poor continuous weld.You are required to use min .118" 1 3/4" tubing for the main part of a mild steel cage.  I would use .134" because the .120" tubing often is not uniform and will not pass the sonic thickness check and if you want to upgrade the cage to run 9's or quicker, you will have to scrap it and start over.If you use chromoly, you can use .083" and 1 5/8" and .065" 1 1/2" for most of the cage but it MUST be TIG welded.Also, out of curiousity, what type of vehicle are you putting the cage into?  If it is a full frame car you can do what I just did with mine - put holes through the frame so you can drop it through the floor for access to weld.  I fit my cage very tight (touching) to the headliner so there was no way to weld it without catching it on fire.My cage is SFI 25.5 legal chromoly which means the quickest I can run is 7.50. Attached ImagesLast edited by lump; 01-07-2006 at 02:04 PM.
Reply:Nice Work!!
Reply:thanks - it was my first try - just bought the tig about 6 months ago and took an evening night class...