The GMAW process (part 3):

In general MIG is considered a Constant Voltage (CV) process. While welding voltage does not vary, but wire speed determines the amps. As the feed rate of the wire changes, so do the amps. Many models of welders use an inch per minute scale, and others use an amp scale. Either is correct, though wire speed is the most commonly used scale. Many small and older welders don’t have a digital readout to provide an exact reading and may only carry a 0-10 scale to allow easier adjustment, without having to think about either. Generally with these settings, the weldor operates usually by sight and ear. Small inexpensive and larger transformer based welders may have taps ( a switch with preset detent) that limits the adjustments of voltage to a specific setting. The cheapest MIG welders also use taps for wire speed adjustment. Though simple to use this can be frustrating by preventing the best setting for the weld.

Many box and large chain stores offer small transformer MIG's that are rather inexpensive, and typically yield less than professional quality welds, especially in the hands of inexperienced users. Most of these units offered for sale use taps on at least the voltage. It’s another reason why MIG has been accused of making less than adequate welds. Not having enough adjustment can make achieving the best weld quite difficult. Quite a few customers buy them not fully realizing the expense involved in providing rolls of wire, consumables, and shielding gas. Often they turn to using Flux Core wire, which pound for pound ends up costing as much or more than solid wire with shielding gas. Everlast has produced a remarkably competitive line of MIG welders that effectively deal with many of the issues surrounding achieving quality welds with MIG. Each MIG is inverter based, which allows the MIG process to be more portable than ever. The inverter design also features a step-less design for voltage and wire speed (amp) adjustment by always allowing the setting to match the material. The design also uses digital readouts for volt and wire speed, allowin precise, repeatable settings. Additionally, each unit features inductance control (arc force) which allows the user to fine tune the arc characteristics. The heavy-duty wire drive system also feeds the wire into one of the highest quality MIG guns available on the market.