MIG welding—The basics and then some

Practical Welding Today July/August 2004
July 13, 2004
By: Marty Rice

Whether it's used in the shop, field, or the garage hobby shop, MIG is a great process.

Man welding with Lincoln Electric power source.

Photo courtesy of The Lincoln Electric Company.

"You ran much MIG?" the foreman asked. "Yeah (I lied), quite a bit." Heck, I didn't even know what MIG was! I had been welding a couple of semesters at a vocational college and had gotten pretty good with stick welding. So Phil Newell, the head instructor who used to scream in my ear, "Relax your hand. Watch the puddle." sent me to apply for an entry-level welding job.

The job was flat welding thin-gauge steel. The foreman took me to a testing area and showed me the MIG machine. He then gave me four pieces of thin-gauge tubing and told me how he wanted them welded. He said he'd be back in about 20 minutes to check on me. After he walked out, I contemplated what I should do. Should I tell him I didn't know diddlysquat? Should I run out, jump in my truck, and tear outta there?

A Humbling Experience

I picked up the MIG gun and didn't realize I was pressing the trigger. I was looking at the machine, trying to figure out the settings, when something touched my leg. About 10 feet of wire had run out of the gun! I madly tried to break it off by bending it back and forth. After about a hundred bends, I looked down at the table and saw a pair of wire cutters. "So that's what they do, they cut it off," I thought.

After wadding up the wire and hiding it under the machine, I decided to try and weld the tubing. As soon as I started the arc, POW! A big hole opened up in the tube. What the heck! I pulled the trigger again and immediately blew out another big hole in a second tube. I grabbed the other two tubes, tried welding them, and, you guessed it, more big holes.

About that time the foreman came walking in. I swear, that was 25 years ago and I can still see the exasperated look on his face like it was yesterday. "Not too good, eh?" I meekly whispered. "Naw, I would say it's more like not worth a &%$#(#*#!!!" the foreman politely replied. Have you ever seen a TV show in which someone is embarrassed and shrinks down to about one inch? Well, that really happened to me.

The foreman told me to come back when I had learned MIG, and he'd give me another chance. What's ironic is I could have learned MIG well enough to work at that job site in just a couple of days, had I know it wasn't a stick welding job.

Fundamentally Speaking

MIG is one of the easiest processes to learn. Most people can learn to run good beads with MIG in just a few hours. Now don't get me wrong here. Remember, I am all about the basics in my articles. The keep-it-simple-stupid theory is my style. There is a lot more to MIG welding than just learning to run beads, but in this article, I'm talking fundamentals.

When did MIG start? MIG came about during World War II. It was developed to help produce weapons and equipment faster. It was then used in the postwar booming economy, mostly in shops and factories.

What is MIG? MIG stands for metal inert gas. In stick welding the flux on the electrode melts and forms a gas to shield the puddle from the atmosphere. The atmosphere has hydrogen, nitrogen, oxygen, and other gases that will cause weld defects if allowed to get into the weld pool.

In MIG, a spool of solid-steel wire is fed from the machine, through a liner, then out of a contact tip in the MIG gun. The contact tip is hot, or electrically charged, when the trigger is pulled and melts the wire for the weld puddle. This is accomplished in several ways. This article discusses short-circuitwelding.

In short-circuit welding, small droplets of molten wire, heated when short-circuited, flow together to make a puddle as they touch the base metal. Inert gas flows out of the gun and keeps the weld puddle shielded from the atmosphere. Thus, metal inert gas. Inert means the gas will not combine with another element; so inert gases, like helium and argon, were used.

An Identity Crisis

Then it was discovered that carbon dioxide, which is not actually an inert gas, worked well also. Then someone figured, now we can no longer call it MIG, so let's call it gas metal arc welding (GMAW). That's all well and good for whoever decided to do that, but welders in the shop and field said, "No, kind sir, we respectfully will still call it MIG." (Probably not quite that nicely spoken.) Everyone I know still calls the process MIG.

MIG usually is used in shops and factories, because out in the field, the wind displaces the shielding gas, which, ironically, is there to displace the wind. You have to be careful MIG welding in close quarters, because some of the shielding gases, such as argon, can displace the oxygen in your brain or collapse your lungs, causing you to wake up dead!

MIG can be used in the field. However, wind blocks, usually made of plastic sheets, must be built around the welder.

Automatic and Semiautomatic

MIG can be used automatically or semiautomatically. An example of automatic MIG is a robotic arm welding car frames at an auto assembly plant. Semiautomatic is when an operator holds the MIG gun and manipulates the weld pool.

In automatic MIG, an operator sets up and watches the machine. An experienced welder is the preferred operator, because he has the right touchand knows what it means to be in the welding zone. (In the zone is when you become one with the process of the weld metal becoming one with the base metal, grasshopper. In other words, you are seeing that you're putting down a good bead as you weld.) Anyone can run a bead. A good welder sees the bead tie-in, and makes sure it is uniform.

MIG at Home

What's neat about MIG is that you can put a machine in your garage and weld up a storm. MIG welding is very popular, because it is easily learned and because you can do and make many things with it. In my adult community education classes, people learn MIG so they can do everything from making yard art to restoring 1957 Chevy pickups with Corvette engines.

A plethora (did you like that five dollar word?) of MIG machines are available People are always asking if I know where they can get a good MIG welding machine for about a hundred bucks. Sure, and although it won't work worth a dang for welding, at least you can use it as a good boat anchor.

A good machine costs at least $400 to $500. You can buy a cheaper machine, but you'll get what you pay for.

Now the nice thing about a good, small machine is that you can plug it right into 110-V outlets in your garage. However, make sure you have a 50-amp fuse—or whatever the manufacturer tells you—or you'll blow out your electricity. (Ask my wife how I figured that one out!)

A warning about buying one of these small machines: Do notlet your neighbors see it. If they do, you will have everyone and their brothers coming by. "Hey, I'll bring you some steel and you can make me a smoker! That way it's practically free." (Never mind that it'll take you 20 hours of tedious labor to get it done.) You'll be surprised how many new friends you'll gain when you acquire a MIG welding machine. It's kind of like owning a pickup truck when someone needs to move.

MIG Advantages

  1. High productivity, because you don't have to stop to change rods or chip and brush the weld frequently. (No checking watch, counting money, smoking cigarette, talking to buddy.)
  2. Easy to learn and makes great-looking welds.
  3. Almost no cleanup.
  4. Can weld on stainless, mild steel, and aluminum.
  5. Can weld in all positions.

MIG Disadvantages

  1. Can't check watch, count money, smoke cigarette, or talk to buddy as often.
  2. Requires a cumbersome bottle of shielding gas.
  3. Costs money for consumables, such as tips and nozzles.
  4. Isn't worth a dang on paint, rust, or dirty surfaces.
  5. Not good for thick steel, because it doesn't get the proper penetration.

Next time we'll talk about the different processes, safety, gases, consumable costs, wire diameters, techniques, and projects for MIG.

By the way, once I learned MIG, I never went back to apply for that job. They didn't pay that great anyway!

Marty Rice

Marty Rice

Contributing Writer
High School Career Center in Texas
Marty Rice is a welding instructor at a high school career center in Texas. He is an honorary member of the Ironworkers Local 263.


Questions for the author can be e-mailed to vickib@thefabricator.com

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Practical Welding Today

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