There are two varieties of wire-feed welders: flux-cored welders and MIG (metal inert gas) welders. Both use the resistance of electrical current passing through the wire to produce the heat for welding. MIG welders use shielding gas — usually a carbon dioxide or Argon/CO2 mix for steel — from a cylinder to prevent the rapid oxidation of the metal due to the extreme heat of welding. The flux-cored process is also known as FCAW (flux cored arc welding) and MIG welding is also called GMAW (gas metal arc welding). Flux-cored wire produces its own shielding gas as the core material (flux) vaporizes.
The MIG process produces cleaner welds with less spatter and smoke than flux-cored welds. This makes MIG welding well suited for sheet metal work, such as auto body repair. MIG welding works best indoors protected from windy conditions that can blow the shielding gas away from the weld area. If you plan on welding stainless steel or aluminum, you’ll need to buy a MIG welder or a wire-feed machine that can be retrofitted to MIG.
MIG welding is more expensive than flux-cored welding because the machines cost more and you must buy a gas cylinder. However, any MIG welder can also be used with fluxcored wire. Unless your shop is wired for 230-volt service, a 115-volt unit is the best for home use. Plan on spending at least $450 for a MIG welder and $120 for a small cylinder and gas. For a supplier, check under “Welding” in the Yellow Pages.
Standard flux-cored wire welders start at around $200, but $350 will buy you a more capable machine, such as one that can be converted to MIG by adding a gas regulator. Fluxcored wires are typically larger and therefore hotter than MIG wires, so the welds penetrate deeper — a real advantage when using thicker stock such as the steel rod we used for the table project. You can also weld in almost any position with flux-cored wire, and the metal doesn’t need to be cleaned as thoroughly as it does with MIG welding.
All arc welders, including wirefeed machines, have a duty-cycle rating. Most smaller wire-feed welders typically have a 20-percent duty cycle based on a 10-minute cycle. That means the unit can weld continuously for two minutes and must then cool down for eight. The duty cycle is often based on an output amperage that reflects typical usage, not necessarily the peak output of the welder. For instance, a 130-amp unit might have a duty cycle based on 90 amps. At full power, the duty cycle is lower; with lower amperage, the duty cycle is higher.