Trailer frame repair

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Well, first of all let me say that the MIG competition and all of your posted pics make me feel so inadequate.  I have soooo much learning to do.A friend has a trailer made from an old pick-up truck.  The frame has been notched, bent and welded to bring the frame together for the hitch.  The weld on one side is cracked.  The original weld was done with O-A and I suspect insufficient penetration.I plan on grinding the original weld off and a “V” into the crack.Now, finally, my question the owner of the trailer wants to O-A weldit I want to FCAW it.  She is fairly experienced with O-A.  I feel that I will get a better bond with FCAW than O-A.  There just seems to be so much steel there to suck all the heat away.Your learned opinions would be greatly valued.Please (pretty please).Oh, All my welding is outside hence FCAW, I have a Lincoln 3200HD (315T)
Reply:Well there is a lot to consider here.  Number 1...is your insisting on a FCAW-ing this going to jeprodize a friendship?Number 2...might she like trying out your welder? (do I hear the word convert?).Number 3...getting a better weld means being able to produce a better weld, is this going to be a problem?  Note, there is nothing inherently wrong with OA, except for the fact that you are welding a frame that probably has some type of hardening process done to it...and, the heat affected area will be larger using that process.  You might try to convince her by having a little test.  Both of you weld a piece of metal comparable in composition, size and in the same position you plan to weld on the trailer.  Then place each weld into a vice and beat the holy crap out of both welds and see which is better.  Agree before hand to use the welding process (and weldor) that holds up better.  You could also offer to let her use the welder and see if she ends up with the better FCAW welds.  If so, use the lincoln and let her do the welding.Diplomatic and scientific, what more could anyone want. Last edited by smithboy; 08-22-2005 at 02:27 PM.Smithboy...if it ain't broke, you ain't tryin'.
Reply:Thank you Smithboy   , no problem with jeapardy here, we've been friends since before she was born (y' know the way women calculate age!)I just ordered 300' of 2x2 steel tubing for her so no covert plans to try out my toy.  She IS going to use it no @#$% choice!  Oh, it's my O-A too.Talked to her a short time ago and I have to let her read this thread.Again thanks for the response.Gordon,Last edited by Pentawelder; 08-22-2005 at 03:58 PM.
Reply:O/A welding with good penetration and a minimal HAZ is difficult indeed.  Butt-weld a couple of pieces together with each process, mount it in the vice and then beat on it with a hammer.  Whichever process holds up better is the one that should be used.  Or in fewer words, I agree with what smithboy said.  With all that said, a very skilled O/A welder with the right tools can do a better job on thicker material than FCAW with no chipping required afterwards.  However, FCAW is ideally suited for welding moderately thick materials with higher productivity and more variable weldor skill.  This is probably why the 4x4 guys use ready-welder alternator style rigs rather than portable O/A rigs on the trail.I am almost, but not completely certain that truck frames are comprised of mild steel in it's unhardened state.-Heath
Reply:Well I'm going to throw in some thoughts too. The frame may have very well cracked do the to either constant flexing at that bend/angle joint or from the constant hammering from road vibration or both. There are  a gazzillion of those pick-up bed trailers out there all built the same, so like you say, it could have been less than a quality weld to begin with.  The point being 'duty' should always be a consideration when choosing a weld method. There has/was never a whole lot wrong with O/A welds to start with other than the discomfort and time it takes to do it. O/A just got shoved aside in lieu of quicker easier more time efficient methods. There can be a very large haz, yes, but that would tend to produce a large 'soft' zone, in which case you'd think any cracks that develop would show up along the perimeter of that or right along the leading edge of the weld where the hard weld meets the softer annealed parent metal. One slight consideration is the characteristics of the more common flux cores. Part of their good performance as self shielding wires on dirtier metals is because of the addition of a little extra manganese. Manganese tends to work harden. Each successive layer (multi-pass) tends to increase the percentile of manganese contained in the weld material plus counts as a 'working'. A thin section that constantly flexes would also constitute as 'working'.  Most manufacturers of the e71t-gs specifically list it as single pass, so if you plan on filling then filling and filling, think about it.. Most list the e71t-11 as multi-pass and the manganese % is a little less but the manganese content is still something to think about. That said, flux core has done many miles of perfectly fine work. There are tons of iron out there being held together just great using flux cores.
Reply:In addition to what Sandy has mentioned...,  If the cracking has occured where the frame may have been cut/notched and bent, some additonal shaped support pieces (on top and bottom of C channel) can be added to stiffen and strenghten those areas, sort of to act like a gusset.Here in the Great White NorthMosquitoes can't fly at 40 below