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Hot Rods Welding Shrinkage Help

Discussion in 'The Hokey Ass Message Board' started by Fortunateson, May 28, 2014.

  1. Fortunateson
    Joined: Apr 30, 2012
    Posts: 4,037

    Fortunateson
    Member

    Was trying to weld in a patch on a fender for the first time. Took my time and skipped around. I thought it was going well but when finished there was some major shrinkage along a vertical seam; I guess I didn't wait long enough. I tried tapping out the shrinkage but the mig welds cracked in a couple of spots. tried annealing them to stretch out the damage but it really didn't improve hte situation much. So I'm sending pout an SOS for advice. I have access to oxy/actelyne once my bottle comes back from a free fill up. Help "Oh Masters of Metal".
     
  2. gimpyshotrods
    Joined: May 20, 2009
    Posts: 18,143

    gimpyshotrods
    ALLIANCE MEMBER

    What metal gauge? What amperage? What wire size? What shielding gas? What shielding gas flow rate? How big of a panel was the patch? How far apart were your tacks? Did you do a continuous weld, or a series of overlapping tacks? How tight was the fit on the replacement panel? What was the largest gap that you tried to fill? Were all surfaces surgically clean, on both sides, before you welded?
     
    Buick59 likes this.
  3. anthony myrick
    Joined: Sep 4, 2009
    Posts: 7,718

    anthony myrick
    Member

    every thing gimpy said effects your weld especially cleanliness and the gap size. Less gap means a smaller weld and less heat. Also hammer and dolly as you weld. This puts less stress on the weld when finished. When you " tapped " the weld did you hammer and dolly directly on the weld or just beat from the backside? This will usually cause cracks to form next to a mig weld. Some pics may help to diagnose as well.
     
  4. Fortunateson
    Joined: Apr 30, 2012
    Posts: 4,037

    Fortunateson
    Member

    Well here comes most of the info...

    I believe the metal is 20 gauge, the greatest gap was approx. the thickness of a dime (as suggested by Matt Joseph a well respected restorer), very clean, wire was .23 gauge, patch was approx. 4"x8", tacked about 2.5" to 3' apart but skipped around a lot so initially they would have been even further apart, allowed to cool to the touch before next nearby tack, continuous weld bead when tacks were about 1/2" to 3/4" apart, flow rate ?(don't remember), amperage was the slowest on a Century 180 welder, and co/argon mix.

    I didn't hammer the tacks as I went only after all welding was complete which caused a little bit of cracking. annealed the area afterward and didn't see much change after I tapped the annealed area. Stopped as I didn't want to cause more grief. I will appreciate constructive critisism on my welding technique but i'm really looking for help to stretch out the shrunken area. One thought i had was to zip cut the problem weld area, hammer/dolly the area back too where I want it and re-weld going even slower Thoughts?
     

  5. Muttley
    Joined: Nov 30, 2003
    Posts: 18,452

    Muttley
    Member

    PM this guy, he knows all about shrinkage.

    [​IMG]
     
    ABONES likes this.
  6. You have to stretch the weld back. Since you used a mig, you need to grind down the weld, both sides. Careful not to grind into the surrounding metal. Remember that grinding causes more shrinkage than welding sometimes. Then get out your hammer and dolly. With firm pressure with the dolly right at the weld, use the hammer with crisp snapping blows right on the weld. Hammer on dolly technique. This will stretch the metal with every blow.
     
  7. Maladjusted
    Joined: Sep 9, 2010
    Posts: 56

    Maladjusted
    Member

    I Was In The Pool!
     
  8. pbr40
    Joined: Aug 10, 2008
    Posts: 808

    pbr40
    Member
    from NW Indiana

  9. Practice on some junk before you do a good fender.
     
  10. jlaird
    Joined: Nov 25, 2007
    Posts: 26

    jlaird
    Member

    You will get shrinkage no matter how fast or slow you go. 65standard hit the nail on the head. This is the technique I use with great success:

    1. Tack the piece in. Leave about a 1/16th gap. A MIG will fill this in nicely giving you full penetration. Tack every inch.
    2. After you are done with the above step, grind down the tack welds on both sides. Now using hammer on dolly, make any adjustments to make sure your patch is flush with the surrounding metal.
    3. After the patch is flush, fill in one of the inch areas by making repetitive tacks. To fill an area an inch long, you are going to do about 5 tacks.
    4. After you are done with that inch area, grind down both sides with a course 50 grit 2" disc on an angle grinder. Grind down to right before you get to the parent (surrounding) metal. Now repeat with a 80 grit disc down flush. Remember, you HAVE to do both sides or your hammer/dolly work will do nothing.
    5. Ok, after the weld is flush, put a straight edge on it. I use a little 6" metal ruler. You will notice that the weld area dips down. You are using the ruler so you can check your progress as you hammer and dolly.
    6. Your hammer should have a slight crown and your dolly should match the contour of your sheetmetal as closely as possible. Put the dolly on the back side and give it a good 15 blows. Make sure you are hitting right on the weld. You should not be putting in dents in the metal, but you should be able to see scuff marks where you are hitting. This will tell you if you are hitting in the correct spot. Also, listen to the noise the blow is making. You will know when you are making contact correctly with the dolly because it will make a higher pitched noise than when you miss.
    7. Check your work with the ruler again. You should have completely removed the dip in the metal. If not, hammer and dolly again. If you are missing the dolly, not striking on the weld, or have not ground down the weld, none of this is going to work. You will not take out shrinkage.
    8. Now repeat the process until you go out of your mind!

    This definitely takes practice, but once you get it, its a great feeling to be able to know how to manipulate metal! Let me know if you have any questions.
     
    fortynut likes this.
  11. black 62
    Joined: Jul 12, 2012
    Posts: 1,895

    black 62
    Member
    from arkansas

    just finished a 4 by 12---pretty much what jlaird said---it is never to late to hammer and dolly ...
     
  12. Fortunateson
    Joined: Apr 30, 2012
    Posts: 4,037

    Fortunateson
    Member

    I was actually going to reference that episode when I wrote the original post. In both cases (George and my welding) embarassment occurs!
     
    Last edited by a moderator: May 28, 2014
  13. Fortunateson
    Joined: Apr 30, 2012
    Posts: 4,037

    Fortunateson
    Member

    That is basically exactly what I did except that I didn't grind down as I went along. Next time 'll try that. I did use the ruler/straightedge to check for the shrinkage and it was quite evident but a good reference for progress. Both sides were ground down and annealed to compensate for the hardness of Mig welding. I guess I didn't stick at it long enough, partly because I didn't want to bugger it up.

    As far as going out of my mind that happened years ago; I've been teaching for 33 years!
     
  14. jlaird
    Joined: Nov 25, 2007
    Posts: 26

    jlaird
    Member

    Oh yeah, I never really answered your question since you already finished welding. The easy way is to find a friend with a pneumatic planishing hammer. That might be a far shot, so like black62 said, make sure everything is ground and hammer away. It's going to be more difficult and take longer to do after fully welding it, but doable. The reason why you hammer as you go along is so you can make the job much more manageable. Little at at time...
     
  15. Fortunateson
    Joined: Apr 30, 2012
    Posts: 4,037

    Fortunateson
    Member

    Josh,
    Thanks a hell of a lot. I just did about 15 minutes worth of hammering and most of the shrinkage has gone. Stopped as I didn't want to go beyond what I want. I'll get back at it in an hour; slow and steady. I do have a Harbour Freight type planishing hammer on a stand and maybe I'll finish offwith that. I REALLY appreciate your help and the whole HAMB concept of helping others learn. You know, I think I may get back into my mind.
     
  16. jlaird
    Joined: Nov 25, 2007
    Posts: 26

    jlaird
    Member

    Fortunateson, it's my pleasure! Glad things worked out for ya.
     
  17. Buick59
    Joined: Mar 3, 2001
    Posts: 1,994

    Buick59
    Member
    from in a house

    A copper backing plate helps dissipate the heat too. I use one where ever I can fit it behind the seam to be welded.
     
  18. gimpyshotrods
    Joined: May 20, 2009
    Posts: 18,143

    gimpyshotrods
    ALLIANCE MEMBER

    All of the above. I keep my gaps about the thickness of the wire that I am welding with.
     
  19. Great explanation Josh.
     
  20. Falcon61wagon
    Joined: Mar 15, 2014
    Posts: 131

    Falcon61wagon
    Member
    from Indiana

    So what advice can be given for welding in quarter panels?


    Posted using my Big THUMB on a small screen!
     
  21. prpmmp
    Joined: Dec 12, 2011
    Posts: 1,075

    prpmmp
    ALLIANCE MEMBER

  22. prpmmp
    Joined: Dec 12, 2011
    Posts: 1,075

    prpmmp
    ALLIANCE MEMBER

  23. Mike51Merc
    Joined: Dec 5, 2008
    Posts: 3,856

    Mike51Merc
    Member

    Yeah, because shrinkage in your junk is better than shrinkage in your fenders.
     
  24. Falcon61wagon
    Joined: Mar 15, 2014
    Posts: 131

    Falcon61wagon
    Member
    from Indiana

    I was referring to the I inability to hammer and dolly on a quarter panel or certain areas on a car that can't be reached.


    Posted using my Big THUMB on a small screen!
     
  25. BarryA
    Joined: Apr 22, 2007
    Posts: 643

    BarryA
    Member

    Wherever possible I would try to make the back side accessible, even if this meant cutting out some inner structure for access, or removing the panel entirely or maybe just enough to get a spoon behind the weld. You'd need to justify the extra work in each situation depending on the potential problems (and work) an undressed weld might throw into the mix. I also tend to favour Tig or gas for the better workability of the weld.
    I would likely reach for the Mig on areas where there is no other option as there would be less total heat going in. I would take a lot of care getting voltage and feed setup for as little build up as possible to avoid additional heat from grinding. Bumping the immediate area to slightly below the true surface and using a small amount of filler or lead.
    I 'd also be wary of doing this in low crown areas where oil canning from the shrinkage might be more likely, with no way of stretching the weld to sort it out....
     
  26. MP&C
    Joined: Jan 11, 2008
    Posts: 2,361

    MP&C
    Member


    Regardless of appearance, all body panels will have crown in at least one direction to help hold the shape of that panel. A flat sheet of metal has no support and will flap in the breeze, so ALL panels will have crown somewhere. If we were to look at the horizontal weld seam along the top of the quarter in a cross-section view (top-down) you would see that despite appearing flat, that panel actually has crown from front to back. It looks like a slight arc. Now, anytime you apply the heat from welding, you are going to get a shrink as that weld cools. When we weld one dot at a time (using the MIG), each and every dot is going to pull at the metal around it, from all directions, causing a shrink. Once you've added all those shrinks from all those weld dots together, along the entire weld seam, it adds up to a substantial amount of shrink such that what used to look like an arc is now more closely resembling a straight line. This is why the panel is pulling inward, the crown is shrinking. If this seam were in the middle of the panel, it would appear as a more pronounced valley. As to the gap question, I prefer no gap at all. The weld seam has a tendency to shrink, and the use of a gap between will permit more movement as this shrinking occurs. This risks losing more crown and will require more effort in planishing to restore the panel's crown. If you can properly set up the welder with more heat, you don't need any gap to get a full penetration weld.

    As to how I address the weld dots, lets look at this again:
    I have found that due to the manner in which each weld dot shrink pulls from ALL directions, you will have better luck in planishing to remove said shrinking effects if you can planish the weld dots while they are singular, sitting all by their lonesome. This will more effectively STRETCH that weld dot back out in all directions. And by stretching as you go, you eliminate the panel being pulled into a valley as your picture shows. As far as tacking the panel, you would want to start your tacks at one end and work toward the other. I know many people will tell you to skip around to minimize heat buildup, and I have been one of those. But if you tack one end and then move to the opposite end, you run a greater risk that one panel may have more material than the other. Once things get all tacked up, this results in a panel bulge on one side of the weld. So tacking from one end and working progressively to the other will help to eliminate this by being able to align the panels together as you go. Now that the panel is tacked and weld dots are spaced about (2 or 3"), go back and planish each weld dot individually, to add a bit of stretch. At this point, I use a 3" cutoff wheel to grind down the dots to just above flush. This gets them out of the way for planishing the next sets of dots, and by leaving them just above flush, you can do the final cleanup with a roloc sander all at once. by trying to grind things down to perfectly smooth after each, you run a greater risk of inadvertent sanding of the metal to the sides of the welds, which may thin and weaken the panel. So I hold off on this until the end. For your grinding disc, I prefer to use cutoff wheels about 1/16 thick. This gives a much smaller contact area than most any other method, so you will have less heat buildup from the grinding process. Here is a link showing the grinding method on a plug weld, again, sanding on a weld seam I would wait until the end.

    [video]

    Once these initial welds are planished and ground down just above surface, then continue, adding a weld between each one until your welds are spaced about 1" apart. At this point (still planishing and grinding after each time) instead of hitting the center between for weld location, start overlapping by about 1/3 of the last welds. By overlapping, you will have less risk of missed spots or pin holes. Continue with the weld, planish, grind, repeat until the seam is done. I typically weld from start to finish using weld dots only, none of the longer passes at the end, in order to keep everything consistent throughout the process.

    For the cutoff wheels, I spend the extra coin and get ones rated for stainless steel. This makes them last longer and put less of that brown haze in the air that you see from the cheap HF or swap meet specials. By the time you figure out the cost of how quickly the cheap ones wear away, you haven't saved a thing. With the bulk of the welds being removed by a cutoff wheel, we are only dressing what little remains of the weld and blending that into the parent metal. I use a 60 or 80 grit roloc, that should be as coarse as you need to go.

    There are a few different considerations in locating weld seams on low crown panels, such as the quarter panel or a door skin. In most cases, as mentioned above, a seam horizontally through the middle of the panel is just asking for trouble as there is little shape (strength) in the panel to resist any movement/distortion from the shrinking, and why a weld here normally results in a severely caved in valley. (given no planishing to counteract the shrinking). For the most part one would put the weld up as high as possible, as most quarters have more shape toward the top where the quarter slopes inward to help resist movement and distortion. It also puts the seam up where most if not all is better accessible for planishing. That is the normal scenario.
    In other cases, where the panel is blocked by an inner wheelwell or other structure that prevents/discourages planishing the weld. In this case, one can be creative in making a dolly on a stick, say a piece of steel flat bar that would fit in the void, welded to a pipe to allow better reach. I've also employed the assistance of my nephew in remote cases where his youth permitted more of a contortionist approach over what my body refuses to do anymore. This is also why it is important to planish those weld dots individually, and then grind them out of the way, front and back. This way two people can better work together on either side of a panel to planish out the welds, and find the correct weld dots in doing so. Next, you have the option of removing the outer wheelwell to better address an exterior panel that everyone will see, and then replace the wheelwell after you are satisfied with the metal bumping and finish work on the quarter.

    Next, you can use features of the panel in your favor. Here is a lower replacement panel that I fabricated for the bottom of a 55 Chevy wagon lift gate, that has had no planishing performed, and looks to be virtually flawless...

    [​IMG]

    [​IMG]

    [​IMG]

    [​IMG]

    [​IMG]

    Any imperfection are slight enough that epoxy primer will take care of them. But as you can see, the panel where the weld travels through has a crown that protrudes outward in the horizontal plane, and inward in the vertical plane. So the shrinking forces tended to counteract each other, and the panel stayed exactly where it was. The weld's limited length also help out to limit the shrinking effects. So this shows a good example of using panel profiles in weld placement to limit distortion/panel movement while using the mig.
     

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