If you real any welding books, you will find that MIG welding is really called GMAW (Gas Metal Arc Welding). But everybody calls it MIG.
Note that flux core welding uses a different polarity than gas shielded welding. This is important, not switching the polarity will give poor results. My little Lincoln SP-135T welder requires 3 change to switch from gas shielded welding to flux core:
Many people give up on flux core because they don't get the polarity right.
MIG welding (with gas) is done with what is called reverse polarity, which is electrode (torch) positive, work (clamp) negative.
Flux core (gasless) welding is done with straight polarity, which is electrode (torch) negative, work (clamp) positive.
I have yet to find a truly satisfying explanation of why this is so important. Perhaps the best explanation that I have heard is that the electrons flow from the negative to the positive, and cause heat build up at the positive side.
Some people will tell you, you must have a 220 volt machine, but this is not true for the jobs most people are wanting to do.
Although I am probably going to buy a 110 volt unit like the Miller 140, I recognize the virtues of having a 220 volt unit (like the miller 180, or Hobar Handler 187), but the convenience of the 110 unit (it does need a 20 amp dedicated circuit) carries the day for me. It means that I can throw it in the truck and go help out a buddy who doesn't have a special circuit for it. It will also do everything that I want to do with it at this point in time. Pushed to the limit, a 110 volt welder can weld 1/4 or even 5/16 metal. Flux core wire instead of gas is recommended to increase heat and penetration. You will need to go slow. A 220 volt unit will do these big jobs smoothly and with ease.
The cheap welders at places like Harbor-Freight may be wire-feed, but are not MIG.
They are designed for flux core wire only, which is fine for many jobs.
Here is some great advice from a post by Brian Martin on www.hotrodders.com
The MIG is used in EVERY SINGLE auto manufacturers welding reqirements for sheetmetal. It is used in EVERY SINGLE welding requirements set by nationally known orgianizations such as ICAR and ASE. It is THE standard of the autobody industry. It is not only the "standard" it is the ONLY welder seen. TIG isn't even mentioned, gas torch isn't even mentioned for welding sheetmetal.
On which "cheap welder", A Miller 130 135 or 140 is a FINE 110V welder and will set you back about 800 bucks with the gas tank and all. In my opinion, it is as cheap as I am going to get. Anything cheaper than that (new) is just not worth spending the money on. As for the gas bottle: My suggestion is to buy the biggest one you have room for. DON'T CHEAP OUT and buy a little bottle thinking you don't use it much bla bla bla. A small bottle STOPS your progress and just plain wastes time. I bought small bottles for my torch, STUPID, I now have to go get larger ones. My MIG has an 100 CF or something like that on it. It will last literally a year or more. THAT is what I am talking about baby, work instead of going to fill bottles.
Now I have never used this exact welder, the 140. But I assume by reading the description that it is simply a 140 amp version of the 130 and 135 welders that we have at work. We have about 8 of them. This is at a shop with a bunch of guys using them. If you have ever seen what "shop tools" look like around the average bodyshop you would understand that these welders are some tough buggers to last in this environment. They work day after day, week after week year after year without so much as a whimper. We replace a gun now and then, or switches in the gun, THAT is it, PERIOD. We fill the tanks and put wire in them along with the contact tip and use them day after day, they are TOUGH little welders.
We weld light frames even with them. They are certainly big enough for EVERY SINGLE COMPONANT on a unibody car or ANY car or truck body.
If you are going to be welding sheet metal 99% of the time, this is the welder for you. For that 1% where you need a 200 amp 220v welder, rent it or borrow it. There is no need to buy a 220V. If you plan on welding up a frame or something for your rod, get a 220v you will be glad you did. Plan on spending about three or four hundred bucks more.
There is some commonly heard (but erroneous) story that Miller owns Hobart. This is not true. Both Miller and Hobart are owned by a parent company ITW (Illinois Tool Works), but they are different plants in different locations. Thinking of Hobart as Millers low end line is wrong, although they are aimed at somewhat different markets. Millers are aimed at a commercial market, and tend to be a bit more "high end" than the Hobarts, but both are fine machines.
Tom's Welding pages / email@example.com