Q. What is the best filler material for oxyacetylene and MIG welding on patch panels? I’m looking to reduce my grinding effort, and for something that’s softer than “standard” MIG wire. I have read that part of the problem is that the MIG process heats and cools the metal quicker, which creates a harder weld than gas. Is this true?
It seems that there is more “myth” than science online when it comes to choosing the correct filler rod/wire for gas and MIG welding. I’ve even read that some folks still use coat hanger. This can’t be good! I’ve called ESAB, Harris, and Crown directly and I received a different answer from each of them. So I’ve decided to email somebody who teaches and works with metal every day to benefit from his expertise. I can’t be the only one who would like to know this!
I would like to go back to gas welding, if you confirm that there are advantages. I’m not in a hurry – heck I’m building cars, and the last thing I’m looking for is speed in patch panel welding. I’ve read that speed is probably one of the few advantages of MIG welding.
I have been using ER 70S-2 MIG wire, and have also considered MIG welding with silicon bronze filler wire. Can you comment on that? At this point, I haven’t found much of an advantage to working with 20-gauge with a MIG over the old gas torch. Ultimately, I’d like to learn TIG welding, but I am proficient with a gas torch, so I’ll stick with it for now. I need somebody to “debunk” all of this once and for all!
Via the Internet
A. Gas welding does have some advantages, although it’s not used much for patch panels these days. A gas weld is softer than either a TIG or MIG weld, which in itself is very good! Unfortunately, there are some disadvantages that accompany this seemingly great feature – one is that you will get a great deal more distortion with gas welding, and the second is that usually the size of the weld bead is so large you’ll have to either hammer it hot, or grind it flat before hammering. RG 45 is the recommended rod for gas welding mild steel. Please, readers – don’t use coat hangers!
MIG welding is a lot faster than gas welding, and it causes much less distortion, but as you suggest, the weld is so hard that it is difficult to do a lot of hammering on it, and the size of the bead will most likely require a lot of grinding before hammering. The MIG weld is hard partly because of the rapid cooling of the weld zone, and partly because of the CO2 in the shielding gas.
ER 70 S-6 is the normal alloy for MIG wire. I’ve never used S-2 wire, and although there isn’t much difference, the S-6 rod has more additives (cleaners and deoxidizers) that benefit the weld, especially in areas that have traces of rust, corrosion, paint, or other contaminants. ESAB makes an “Easy-Grind” MIG wire that is reportedly quicker to grind down, but I’m not sure it’s any softer for hammering. Maybe this is the S-2 wire!
I have met some people who use silicon-bronze filler wire for MIG welding steel panels. In Australia, this is commonly done for non-structural welds in collision repair! Bronze has only about half the strength of steel, so I don’t consider this a straight-across replacement for steel filler wire, but in certain places it might be an advantage. I wouldn’t trust it for something that needs ultimate strength, nor for a butt weld on sheetmetal.
You can certainly make a case for using a gas torch on medium or high-crown patch panels. The massive distortion makes it more challenging for low-crown patch panels, such as door bottoms, but it was done that way for decades before MIG and TIG welding became popular. The downside is that you must be an expert metalworker to get everything flat again after gas welding. Some metalmen hammer the welds while they are still glowing red to crush them flat, rather than waiting for the welds to cool and sanding the excess weld flat. Once you master this “hammer welding” technique, it works pretty well, and you can correct the shrinking from welding as you go!
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