Besides amperage capability range, the machine's performance is also evaluated for continuous rated output, which is expressed in terms of its "duty cycle." The duty cycle is the number of minutes out of a 10-minute period that a welding machine can operate at the rated output. This standard helps buyers make a direct comparison between welders. To better understand how duty cycle ratings are applied specifically let's look at two different sizes of welders. A typical machine for home or shop use might have a total output range of 30 to 140 amps. If it were rated for an output of 90 amps at a 20 percent duty cycle that would mean that it can weld continuously at 90 amps for two minutes and then must cool down during the remaining eight minutes to prevent overheating. A second example might be a heavier semi-industrial-type unit that's also popular for more serious personal users. If it has 30 to 300 amp welding range and duty cycle of 40 percent at 250 amps it can weld continuously at 250 amps for four minutes and then must cool down during the remaining six minutes to prevent overheating. As welding output decreases, duty cycle increases. For example the 40 percent duty rating at 250 amps would increase to a 60 percent duty cycle when welding at 200 amps. Ambient temperature also impacts duty cycle. For example, if a machine achieves its rating at 104 degrees Fahrenheit then the machine becomes de-rated to some extent when welding at ambient temperatures of greater than 104 degrees.
Stick welding is also known as shielded metal arc welding. Stick welding is a manual arc welding process that uses a consumable electrode, or stick rod, that is coated in flux. The filling metal material is obtained from the electrode core, while the flux coating produces shielding gas and a layer of slag, both of which protect the weld from atmospheric contamination.
The second type of welding we are concerned with is commonly called MIG, or gas metal arc welding. It is also sometimes referred to as wire welding. MIG welding is a semi-automatic process that creates an arc between a continuously fed wire electrode, which provides the required filler material, and the part being welded.
There are two types of MIG welding. A specialized machine can do both types. In one, externally supplied shielding gas from a gas cylinder protects the molten weld puddle from contamination. The shielding gas and wire are both fed through a MIG "gun" and they begin flowing when the operator squeezes the trigger. A big advantage to gas-shielded welders is that there is no residual coating because the gas dissipates after the procedure is completed. Because in standard MIG welding the weld is protected from contamination by a continuously fed protective gas there is no slag to chip and far less smoke. The downside of gas-shielded welders is that they can't be used outside in windy conditions because the wind can disperse the gas before it provides the required protection.
MIG welding can also be accomplished using one of two types of flux-cored wire. In one case, instead of a gas being applied from an external source a flux contained within the tubular electrode wire core creates the shielding gas when heated by the arc. The self-shielded gasless-type of MIG welder does not need any secondary shielding gas and they are commonly used for do-it-yourself or home service. The other type is the gas-shielded flux-cored wire MIG welder. It requires an externally supplied shielding gas. Both types of flux-core wire cover the top of the weld with a hard slag coating that must be chipped off prior to painting or subsequent weld passes. Another advantage of MIG welding is that it is the easiest welding process to learn.