GMAW guns: More than a commodity

6 gun components that can make a difference

THE FABRICATOR® SEPTEMBER 2006

September 12, 2006

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Many welders think of GMAW guns as just a commodity. However, all of the parts in a GMAW gun have a direct impact on the time it takes to make a weld and its quality.

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Many welders often think of a gas metal arc welding (GMAW) gun as a mass-produced, unspecialized product—a commodity—when purchasing a GMAW system. More costly components, such as the power source, wire feeder, and shielding gas, generally take precedence, and the gun often becomes an afterthought. Unfortunately, that afterthought can lead to poor weld quality and higher operating costs.

Because the GMAW gun is responsible for delivering the current, electrode, and shielding gas to the weld puddle, it plays a critical role in achieving quality welds. Closely examining your application and selecting a gun specifically designed for your needs can be an economical way to improve weld quality and increase productivity.

Are You Using Too Much Gun?

The first question to ask is, Am I using too much gun? A common misconception dictates that if a welding procedure calls for 400 amps, then you need a gun rated at 400 amps and 100 percent duty cycle. You certainly can weld at 400 amps for eight hours straight and never set that gun down, but in reality, moving parts, tacking, and related activities comprise a day's work. In fact, the average arc-on time for a welder in many companies during an eight-hour shift can be as little as 45 minutes to one hour.

You may be able to buy a smaller, less expensive gun with a lower duty cycle rating and still achieve the same results. For example, switching from a 400-amp gun with 100 percent duty cycle to a 300-amp gun with a 100 percent duty cycle often can provide equal performance.

Switching to a smaller gun also can lower equipment costs (lower-amperage guns cost less) and reduce operator fatigue and downtime—a smaller gun generally means less weight, better maneuverability, and increased comfort. A smaller gun also may be able to help establish a healthier work force by reducing injuries such as carpal tunnel syndrome, which often is associated with using heavy guns.

Shorter power cables on your gun also can help minimize downtime and lower costs. Shorter power cables are less expensive and help prevent wire feeding problems by minimizing unnecessary coiling. Using the shortest power cable possible for your application—one that will meet your amperage and duty cycle requirements— also can offer better maneuverability.

A Closer Look at Gun Components

Amperage isn't the only consideration related to choosing the right GMAW gun for your application. Six main components on a GMAW gun can translate into better productivity and savings when given careful consideration.

  1. The Back End—Examine the power pin that connects the gun and power cable to the wire feeder. A loose connection between the gun and the feeder can cause electrical resistance throughout the entire system, leading to overheating that can damage either the gun or the wire feeder. It also can cause gas leakage and poor conductivity that can lead to an erratic arc and poor weld quality. A heavy, sturdy power pin designed to seal the connection tightly helps prevent these problems and the downtime and rework associated with them.

    Choose a gun with a supportive strain relief at the connection between the power cable and the wire feeder. It can prevent the power cable from kinking and provide good wire feeding, a stable arc, and quality welds—each of which add up to less rework and more welding time.

    Especially in shops that run different brands and styles of feeders, select a gun with multiple interchangeable plug options. A gun that can be matched with different feeders allows you to standardize on one style of GMAW gun throughout your shop and stock one brand of accompanying consumables. This standardization helps reduce equipment costs and minimize inventory, not to mention the time that goes into stocking and maintaining numerous parts.

  2. The Liner—Liners are one of the most critical components of a GMAW gun because many feeding problems originate with this component, and replacing them is one of the biggest culprits of downtime and maintenance problems. The liner also can be a source of gas leakage, which wastes costly shielding gas and leads to insufficient protection of the weld puddle, resulting in rework and added cleanup.

    First, make sure you have a good gas seal or solid O-ring connection at the back of the liner to help prevent gas leaks. Also, choose liners with a durable jacket or coating to prevent additional gas loss through the steel liner coils.

    Next, select a liner designed specifically for your wire diameter. Liners that either are too large or too small can cause poor wire feeding that can lead to an erratic arc and poor weld quality. The liner size needs to match wire size, usually within a specific range; for example, you can use a 0.035-inch wire in a 0.035-in. to 0.045-in. liner. Adhering to these parameters will help ensure proper wire feeding and improve weld consistency.

  3. The Power Cable—A good rule of thumb is to use the smallest and shortest cable possible without limiting your welding needs. Smaller, shorter cables reduce operator fatigue, minimize clutter, and help prevent excessive coiling that can lead to poor wire feeding. As with other components, make sure that the power cable fits tightly into the wire feed system to maintain proper conductivity.

  4. The Trigger—The trigger is the only moving part on a GMAW gun that can fail because of mechanical motion. Look for a strong, reliable trigger that can be serviced easily to help minimize downtime for component changeovers. Also, choose a gun that gives you the most appropriate trigger option for your application, such as standard, locking, dual-pull, and dual-schedule switches. These options allow you to work with the trigger setup that best suits you and the application and will help increase productivity by making welding more comfortable.

  5. The Neck and Handle—GMAW guns are available with fixed, rotatable, and flexible necks in different lengths and angles to provide flexibility when welding in various positions or tight quarters. Rotatable necks, for instance, allow you to weld out of position more comfortably without changing your gun handle or sacrificing quality. Flexible necks can be adjusted for different positions, which saves changeover time and eliminates the need to inventory specialty guns for each application. Choose a neck with good armor (hard plastic or metal) to protect it from damage that could lead to shorts and failures in the gun

    When looking at handle options, consider lightweight, comfortable styles that will meet your amperage and duty cycle rating needs. Similar to the power cable, a smaller handle makes it easier to weld. Also, a ventilated handle can reduce heat and increase comfort and productivity.

  6. Consumables (Nozzles and Tips)—By selecting a consumable based on longevity instead of price, you can reduce costs for replacement parts and for changeover time. Nonthreaded, large-base contact tips that fit securely to the diffuser provide good electrical conductivity and heat transfer. Also, look for machined tips, nozzles, and diffusers that don't have burrs or other inconsistencies that can lead to erratic arc and short consumable life.

It's also important to look for heavy-duty tips and nozzles that provide good gas coverage to help ensure good arc starts, less spatter, and less rework and cleanup.



Bill Giese

Contributing Writer
Bernard
449 W. Corning Road
Beecher, IL 60401
Phone: 708-946-2281

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