Which semiautomatic GMAW gun is right for the job?
October 4, 2010
From tacking operations that require short arc-on times to completing long, continuous welds on thick plate, the welding gun needs to offer the appropriate welding capacity for the job.
When it comes to choosing welding equipment, welding operators may find themselves contemplating which power source to use—and rightly so. The power source significantly affects weld quality, productivity, and overall costs of welding. But having the correct semiautomatic gas metal arc welding (GMAW) gun for the job is equally important.
From tacking operations that require short arc-on times to completing long, continuous welds on thick plate, the gun needs to offer the appropriate welding capacity for the job. For example, welding operators may not need a GMAW gun that is the same amperage as the power source. That is because often they weld only 30 to 50 percent of the time, making the use of a lower-amperage gun an appropriate option. Conversely, an overworked light-duty gun could fail prematurely. Or if a welding operation involves varied applications, the gun must be able to address the needs of all of them.
For welding applications that require short arc-on times, such as tacking or small-part welding, a light-duty GMAW gun may be the best choice (see Figure 1). A light-duty gun is typically considered one that provides from 100 to 300 amps of welding capacity. Like all guns, light-duty ones are rated according to their duty cycle, or the number of minutes in a 10-minute period that the gun can be operated at its full capacity without overheating. Generally, gun manufacturers rate their products at 60 to 100 percent duty cycle.
For applications such as welding sheet metal, general hobbyist projects, and auto repair and autobody work, a light-duty gun works well. Because light-duty guns typically have low amperage capacity, they also tend to be smaller and lighter than higher-duty ones, making them easy to maneuver even in tight areas. Most have small, compact handles that are comfortable for most operators.
Such guns often use light- or standard-duty consumables, including nozzles, contact tips, and retaining heads (or gas diffusers). These consumables generally have less mass and are less expensive than their heavy-duty counterparts. Designed for short arc-on times, the necks (or goosenecks) are made of lightweight materials such as polymer, rubber, or light aluminum armor.
The gun’s strain relief usually consists of a flexible rubber component or in some cases may be absent altogether. These features reduce the gun’s weight, but it also makes it susceptible to kinking, which may lead to poor wire feeding and gas flow. Damage to the crimped connections on some unicables can be especially problematic. If a crimped connection becomes damaged, the cable or possibly the entire gun may need to be replaced.
Generally, light-duty guns offer standard features at a low price and typically need to be replaced more frequently.
Some jobs require long arc-on times or multiple passes on thick sections. Such jobs are found in heavy-equipment manufacturing for the agriculture, construction, trucking, and mining industries. For these applications, heavy-duty guns are the best choice, as they can weld continuously on 1-inch or thicker material and in harsh environments typical in such industries (see Figure 2).
Heavy-duty guns generally are rated between 400 and 600 amps and are available in both air- and water-cooled models. The choice between a water- or air-cooled heavy-duty gun largely depends on the welding application, operator preference, and cost considerations. Water-cooled systems are more expensive and often require more maintenance. Specially treated coolant solution, rather than tap water, is necessary for a radiator cooling system because tap water can cause algae growth or scale (mineral buildup) on the gun’s internal surfaces and cable assembly.
Over time water can leak from hoses, the gun neck, or head, requiring immediate repair to prevent weld discontinuities and gun failure. However, despite the additional cost, when welding on very thick plate that requires high deposition and good weld penetration, a water-cooled gun may be required.
Heavy-duty guns—both air- and water-cooled models—often have larger handles than their light-duty counterparts to accommodate large cables designed to carry high amperages. Such guns often use heavy-duty front-end consumables that can withstand high amperages and long arc-on times.
The goosenecks on these guns are often long as well, which puts more distance between the welding operator and the hot arc. Most goosenecks have aluminum armor that protects them from damage from high temperatures and day-to-day wear and tear. An optional heat shield protects the welding operator from the heat coming from the high amperage and longer arc-on time. The shield provides a barrier between the arc and the welding operator’s hand. Adding a unicable cover also can help protect the power cable from a harsh environment.
Locking triggers help prevent operator fatigue when welding multiple passes or long, continuous joints. Other heavy-duty guns feature dual- or multischedule triggers that mount on the top or bottom of the gun, whichever the operator finds most comfortable.
In many cases, heavy-duty guns can be customized to meet the needs of the application and welder preference, including preferred handle styles, gooseneck length and angle, and unicable length.
Just like any part of the welding process, GMAW guns play an important part in obtaining the quality and performance desired. Overusing a light-duty gun can result in poor performance, while using a heavy-duty gun without cause adds unnecessary cost. If a company has multiple power sources, one gun usually can be standardized to fit them through the addition of a feeder adapter. Doing so allows for one common gun to be used throughout the operation, lessening the need to inventory multiple styles of guns and consumables.
The goal is to accommodate both the amperage and duty cycle of the application in the best way possible. Moreover, proper welding gun selection can conserve resources and help welders achieve high productivity.