Miller's Auto-Set function...
Miller's Auto-Set function is perfect for novices. Simply dial in the wire diameter and material thickness and you're ready. It makes set-up easy for novices, though it has a manual mode with infinite voltage control too. It's available on the 140, 180, 211 and 212 machines.
Both MIG and TIG require shielding gases, unless you use a gasless flux core MIG wire, which produces its own shield for the welding process, but we wouldn't recommend buying this type of MIG welder if you plan on doing any serious work with it. MIG welding uses Argon, as well as Argon mixes, such as 1 to 5 percent Oxygen, 3 to 25 percent CO2 or an Argon/Helium mix, while TIG uses Argon, Argon and Hydrogen or an Argon/Helium mix. It all depends on what metal you are welding as to which shielding gas is required. Helium is most often added to increase welding speed or penetration.
While there's a common misconception that anyone can MIG weld (we've all seen bubblegum or pidgeon-poo welds and were probably responsible for some when we were learning to MIG weld!), it's definitely easier than TIG welding, which takes practice and is an acquired skill, albeit very satisfying when you get it right. The superior quality of TIG welds, the precise control offered by the process, and even the appearance of the finished product, seeing as our hobby is as much about appearance as function, means a TIG welder wins over a MIG for chassis fabrication.
The benefits of MIG welding are that it's way easier to weld vertically or even upside down with MIG, less operator skill is required, long welds can be made if distortion isn't a factor, and it's easier to learn. Benefits of TIG welding are superior quality welds, precise control of heat input, it's spatter-free and offers low distortion and minimal cleanup. It also looks great!
Whether you're learning to MIG or TIG, you're going to have to master the machinery, though most MIG welders these days carry a chart inside the casing where the wire spool mounts, guiding you to the correct wire speed and heat settings for the thickness of metal you're planning to weld. TIG welding is more complicated and until recently the bewildering array of knobs and switches on a TIG welder meant you had to really know what you were doing to set the machine up. Miller has made things easier with the introduction of not only its 212 Auto-Set MIG, on which you simply set the wire size and metal thickness before welding, but also with the revolutionary Diversion 165 AC/DC TIG, on which you just set the material type and thickness. We've used the latter at Miller's Southern California facility during one of their training days, and actually preferred it to the considerably more complex and expensive Dynasty 200, finding it easier to use (for a novice-I may have been MIG welding for 25 years but can count the times I've TIG welded on both hands) though the latter is designed more for industrial use admittedly. The Diversion 165 also offers fingertip control of the heat input, thanks to the amperage control on the Weldcraft LS17 torch, though a more regular (for TIG) foot pedal can also be used.
I attended the training session with the intention of learning to TIG weld aluminum, as I was about to start fabricating an all-aluminum roof for my roadster pickup, and the Diversion 165 proved ideal However, Miller also has a spool gun which allows their newer MIG welders to easily convert to weld aluminum too, which I had previously used and found to be a great tool. This is compatible with, and easily attaches to, the 212 Auto-Set and Millermatic 252 as well as Miller's Passport Plus, and by simply switching to Argon shielding gas you're ready to tackle welding aluminum. In fact on the 252 the machine automatically detects which gun you're using when you pull the trigger. Speaking of Miller's Passport Plus, it's a compact MIG welder that not only contains a gas bottle and 8-inch spool of wire inside a 45lb package, but it can be plugged into either 115 or 230 V power using Miller's Multi-Voltage Plug for a truly portable welder. Probably not what you need in your shop but ideal for working up ladders or down holes!