Why not "braze" reinforcements on?, info from the "Welder's Handbook" Options

[SpecialK]

I was re-reading my copy of Welder's Handbook because my practice welds on some scrap were weak as hell when trying to weld 18ga to some 12ga (rosette welds) to beef-up my seatbelt attach points that rusted out. (IMG:style_emoticons/default/headbang.gif) Needed a break (IMG:style_emoticons/default/beer.gif) to do some research and find out what I was doing wrong.

The author, Richard Finch, is big on brazing automotive sheetmetal repairs as opposed to fussion welding (MIG, Arc, etc.), particularly when it involves pre '80 cars that weren't assembled using HSS (High Strength Steel). He says that the high temps involved in fussion welding actually weakens the surrounding metal, where as the lower temps involved in brazing doesn't. You can't braze butt joints like you'd use to attach outer body panels, but the reinforcement kits like Mark's (Engman) inner long stiffener's and Brad's 10ga beasts would actually be much stronger (at the attach points). His example is taking 1" x 5" long strips of .060" mild steel, overlapping the ends by 1" and brazing them together. In a pull-test machine it takes over 3000 lbs. to pull them apart and it's always the base metal that breaks, never the brazed joint. Since lap joints are the preferred joint when brazing, and all of the weld points (holes) on the reinforcements are essentially lap joints, wouldn't it make sense to braze in the stiffeners rather than MIG weld?

Or then there's always the possibility that everyone does braze their stiffeners in, and I'm just assuming they've been MIG'd (IMG:style_emoticons/default/slap.gif)


Kevin

[lapuwali]

Bronze welding, which is often called brazing in the US, was a very common practice in attaching mild steel tubes together to make spaceframes in the UK at least from the 50s through the 80s. Considerably less heat is involved, and thus considerably less distortion in the joint resulted. The fillet left behind also does a nice job in spreading stresses in the joint. The chief difficulty with this technique is that craftsmanship is critical. The tubes must fit together very well with very small allowance for gaps.

MIG and TIG have pretty much taken over from bronze welding these days, as both allow more slop in the fit of the joints, both are somewhat easier to do than torch welding, both are considerably faster than torch welding, but most importantly, the cost of the machines has fallen to the point that they're easily within reach of even the poorest fab shops. TIG machines, especially, used to be very expensive, and reserved only for aerospace outfits with their nearly unlimited budgets (and far higher standards).

If you have a torch and know how to use it, buying a set of bronze rods is cheap and you can practice awhile to see if you can produce good results. However, actual MIG (not just wire-feed with no gas) will produce good welds quickly and easily, esp. for something like rosette welds for attaching things like long reinforcements. If you're getting weak welds with MIG, you need to improve fit, and make sure everything is clean, clean, clean. Also, if you're having trouble with MIG, brazing is harder to do properly, so don't look there for a shortcut.