The Basic Types of Welding - Part I

[567chevys]

Anyone who performs body repairs soon realizes that learning how to weld is essential if one is going to get serious about this type of work. Here is a brief overview of the most commonly used welding methods.

We know that any metal will start to melt if its temperature is raised high enough. In welding, two pieces of metal are put together at a point, with the welder using some extra metal to help produce the joint. After the weld is made and the metal cools, you end up with what appears to be one continuous piece of metal.

There are two basic methods to heat the metal sufficiently in order to produce a weld: electricity or high-temperature bottled gas.

Brazing is the easiest method of holding two pieces of metal together. Like fusion welding described above, two pieces of metal are held together and a bronze rod is melted using a flame. This holds the metal together fairly well, something between super glue and a fusion steel weld. For brazing, you can use either bottled gas or electricity to produce your heat. Note that brazing is fairly expense, primarily because of the cost of the bronze rods. Note too that "bronze" is only a descriptive phrase to describe the metal used for fusion in brazing. A "bronze" rod is actually made of the same substances as bronze or brass: copper and/or tin or zinc.

Electric arc welding equipment is the least expensive to purchase and the easiest to set up. This equipment includes the following: a transformer, or welding machine that changes regular household current to that needed for welding; and two heavy-duty cables leading from the transformer, one which has a welding rod and hand grip on the end and the other that has a grounding clamp that attaches to the work piece. The welder grips a steel welding rod with the handgrip/holder. When the power is ON, s/he touches the rod to the place on the piece where the weld is desired. This completes an electrical circuit. A bright electric arc jumps between the work piece and welding rod, and melts the steel at the end of the rod and at the point near the end of the rod on the piece. The weld then takes place. Arc welding is not good for welding thin metal because it usually melts right through it. (Direct-current arc welders are less prone to do this.) Use arc welding for general welding like brackets rather than body panel.

Carbon-arc brazing employs a special adapter at the end of the arc welder cable, which consists of two rods of carbon. The welder manipulates the two rods, which burn against each other as the arc forms. This forms the flame. A brazing rod is then fed into the area and the weld occurs.

Oxy-acetylene welding is the mainstay of auto body and repair people. A special torch mixes acetylene and oxygen to produce a very hot flame. The flame creates a pool of metal at the joint, and when this happens, a thin steel rod is fed in. The rod then melts and forms a fair thickness of metal around the joint. Do-it-yourself repair people are more often using this setup because handy kits are now available with smaller gas cylinders for convenience. Gas welding does not burn through metal panels and is good for brazing.

See Basic Welding - Part II/Welding Safety

[chevynut]

I think these days a 110V MIG (wire feed) welder is the easiest and most cost-effective welding to learn for bodywork. I personally would never use oxy-acetylene welding anymore because of the high amount of heat involved. It causes significantly more warpage to the panels because of the much larger HAZ (heat affected zone) which results in more shrinkage of the metal at the weld. Some swear by TIG welding for bodywork, but the metal has to be VERY clean to successfully TIG weld old steel. TIG welding can result in a smaller weld bead than MIG, and some say it makes a softer weld that can be more easily planished (stretched with hammer and dolly). But TIG is much harder to learn than MIG, and the equipment is more expensive.

[BAM55]

I swear by tig welding body panels. Tig does a beautiful job and I since I have a tig now I will always tig my panels. Metal Finishing is much easier due to the low bead profile, softer tig bead, and more control over the heat. That being said if I had to have one welder a mig would be it. I could live without a tig its a luxury item, but my mig welder is my work horse, my old faithful buddy when in times of need.

[chevynut]

Bam55, how do you deal with the contamination with old metal? I tried to TIG my new quarters on, but kept getting the "volcano" no matter how clean I made the old steel. I used MIG, and I'm not sure I agree about a harder weld bead like some people claim. The metal is the exact same composition, and both processes have to get hot enough to melt the metal. I don't see why MIG would cool faster like some claim either. I do agree that the weld bead is a lot smaller with TIG, or at least it CAN be. I just think MIG is a lot easier to use for sheetmetal. I my have to try TIG again on another project.

[BAM55]

Chevynut when I tig sheetmetal I have shiney metal after have cleaned it I do not have the issues you described. I know what your talking about though. If I can't get the metal clean with sanding by hand or disk. I use phosphoric acid to clean it and then I sand the residue to shiny metal. Now I do agree with you the mig is way easier that is for sure and I really could not live without my mig.

What I like about tig welding sheetmetal is the less grinding and doing hammer and dolly work on the haz is more satisfying. You can hammer to your hearts desire without worrying about cracking a weld like with mig weld. If you hammer a mig too much its a brittle weld and may crack and tig doesn't. I have hammered a mig tack and it cracked I have never cracked a tig bead.
That said I would still mig a quarter because I don't see the benefit of tig welding sheet metal if you don't have access to the back of the panel for hammer and dolly work. Fenders and things like that turn out great.