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From the internet: "assuming your joint is designed properly and you have an experienced welder performing the work, your welded joint will be as strong as the

• deelowe 6y ago
  The "weld is stronger than the base metal" argument is often repeated on the internet, but it's overly simplistic. Welded joints don't usually fail at the seam (a.k.a the weld). Instead, they fail near the seam where the base metal has been stressed due to thermal expansion/contraction and heat treating. It is correct that when done properly, everything should be fine, but I wouldn't trust the vast majority of body shops to have access to welders who would do it "properly."
  • glenstein 6y ago
    This doesn't make it any more clear whether weld repair poses a practical danger for most people in most circumstances. If it's the case that metal stress near the point of welding is the where it's more likely to fail, that still doesn't tell me how much more likely to fail. For all I know it could be the weakest part but still such a trivial difference as to pose no concern. And the point about welders leaves a dangling, open ended implication that invites anyone reading the sentence to just go ahead and assume that poor weld jobs leading to immenent danger are happening all the time. But are they? Or is that just being noted as a hypothetical possibility? I'm having a hard time telling whether a possible or probable danger is being asserted here.
    • jacquesm 6y ago
      Welding is like programming. Everybody with half a brain and some skills can weld. But proper welding is an art form, and the difference between the two levels is many years of work and study. So for most people welding like that is not in the cards, but a trained and meticulous professional can do miracles (or close to miracles). It starts to get really interesting when you start hanging stuff from your welds, for instance when building an overhead crane.
      • throwaway0a5e 6y ago
        Welding is just practice, practice, practice. Like everything else. Welding lifting rings onto stuff is not really a high bar. High quality welds are easy if the materials you're dealing with are easy. Stuff that is exotic, expensive and hard to work with is the stuff that takes real skill because it's really hard to get a ton of practice at those things (there's only so much magnesium alloy that needs welded) so you need a lot of skill and experience in varied circumstances to do a high quality job from the get go. I can weld and I can dick around in a bash shell but I'm much better at the one that is my current day job that I do for ~40hr a week.
        • jacquesm 6y ago
          You only know how good your welds are once you've seen them destructively tested. What looks good may not be all that good. A really good welder will be able lay bead after bead after bead with very consistent quality and material characteristics.
          • throwaway0a5e 6y ago
            It's hard to look at someone else's weld and know if it's good because lord knows what they did under there (if it's externally bad there's some pretty obvious signs). It's easy to lay a weld and know that it's good from a combination of how you did it and how it came out. If you know what you're doing then a bend test just confirms what you already knew. X-rays keep honest welders honest. For "easy" material combinations you can get away with a surprising amount of corner cutting and still pass a bend test. Good welds aren't hard. A community college will have you passing a bend test on an overhead weld in a semester and doing the same for pipe in two but it will all be in steel and a limited variety of consumables and processes. Those kids might be masters of 7018 but hand them some aluminum electrodes and they'll be lost. Good welds the first or nearly the first time on material + consumable combo on which you only burn say 10lb a year is what really takes practice.
    • deelowe 6y ago
      The vast majority of welders do not possess the skills to properly repair an automobile frame. There's no way I'd trust a body shop to repair my car's cast frame with weld on replacement pieces.
  • jacquesm 6y ago
    Yep. Thermal hardening is a thing and if a weld isn't properly annealed post work then there is a good chance that it will fail right next to the weld itself. This is taken as proof that the weld is stronger than the material that's been welded but actually it is more often than not proof that the weld wasn't properly thermally treated. Once you do that though, it is actually true, and even then you may see stress cracks next to the weld if the change in thickness is too abrupt. You need to gradually thin down or you'll get a focal point for stresses.
• bch 6y ago
  They are the part of the frame that fails, but they’re also at joints, which is where stress collects. I’d be interested to see failure modes for lugged (silver soldered) frames vs TIG welded vs pressed/glued or other bonded joins of tubed (no monocoque) frames.
• hansvm 6y ago
  Frames do fail at or around welds though, especially for even mildly exotic metals beyond plain low-carbon steel. I've had them break before, and it makes for a long walk home.
• TylerE 6y ago
  That is true in steel, but not aluminum. Because of how thermally conductive it is it doesn't work the same way.