Selecting the Right Gun for MIG Welding Is Key to Achieving the Best Results

The MIG welding process offers many benefits for various applications and industries, including fabrication, manufacturing and general maintenance. It’s one of the easiest welding processes to learn and offers good control on thin metals. Because MIG welding uses a spool to constantly feed a wire through a welding gun, it doesn’t require frequent stopping as with stick welding. This feature makes it an efficient process that offers faster travel speeds and productivity benefits.

The versatility and speed of MIG welding also make it a good option for all-position welding on various metals, including mild and stainless steels and aluminum, in a range of thicknesses. In addition, it produces a cleaner weld that requires less cleanup than stick or flux-cored welding.

Selecting the right gun for the job is important to achieving good results and realizing the benefits MIG welding can provide. The choice of gun can have a significant impact on productivity, downtime, weld quality and operating costs, not to mention welding operator comfort.

 Selecting the right gun for the job is important to achieving good results and realizing all of the benefits MIG welding can provide. The choice of gun can have a significant impact on productivity, downtime, weld quality and operating costs, not to mention welding operator comfort. This article discusses the options to consider in selecting the appropriate MIG gun for the job.

Selecting the right amperage
Amperage and duty cycle rating are both important considerations, but keep in mind that when it comes to amperage, bigger isn’t always better. Selecting a larger amperage gun than necessary for an application can cost money upfront and cause operator discomfort due to the increased weight, which can result in unnecessary downtime.
Welding operators are often better off selecting the smallest amperage gun possible for the application, to provide them with a lighter-weight, more flexible gun that can reduce fatigue and associated downtime. Lower amperage guns also typically cost less.

Duty cycle refers to the number of minutes in a 10-minute period that a gun can be operated at its full capacity without overheating. For example, a 60 percent duty cycle means six minutes of arc-on time in a 10-minute span. Because most welding operators don’t weld 100 percent of the time, it is often possible to use a lower amperage gun for a welding procedure that calls for a higher amperage one.

A lower amperage MIG gun should still be capable of operating at the necessary capacity, while also offering the benefit of being easier to maneuver. That improved maneuverability can help improve weld quality and reduce the need for rework.

Choosing between light- and heavy-duty guns
While a lower amperage gun is appropriate for some applications, be sure the gun offers the necessary welding capacity for the job. Overworking a light-duty MIG gun can lead to premature failure. It’s also important to consider if a facility has multiple applications that make it necessary to have a gun that can handle various amperage needs.

A light-duty MIG gun is often the best choice for applications that require short arc-on times, such as tacking parts or welding sheet metal. Light-duty guns typically provide 100 to 300 amps of capacity, and they tend to be smaller and weigh less than higher duty guns. Most light-duty MIG guns have small, compact handles as well, making them more comfortable for the welding operator.

Light-duty MIG guns offer standard features at a lower price but typically need to be replaced more frequently. They also often use light or standard duty consumables (nozzles, contact tips and retaining heads), which have less mass and are less expensive than their heavy-duty counterparts.
The strain relief on light-duty guns is usually composed of a flexible rubber component and in some cases may be absent, causing the opportunity for kinking that may lead to poor wire feeding and gas flow. Also, some unicables on light-duty MIG guns have crimped connections and may not be able to be repaired, requiring replacement of the cable or possibly the entire gun. Welding operators should watch for these potential issues.

At the other end of the spectrum, heavy-duty MIG guns are often the best choice for jobs that require long arc-on times or multiple passes on thick sections of material, including many applications found in heavy equipment manufacturing and other demanding welding jobs.
These guns generally range from 400 to 600 amps and are available in air- and water-cooled models. They often have larger handles to accommodate the larger cables necessary to provide the higher amperages. The guns frequently use heavy-duty front-end consumables that are capable of withstanding high amperages and longer arc-on times. The necks often are longer as well, to put more distance between the welding operator and the high heat output from the arc. 

Cooling options: air vs. water
When using a heavy-duty MIG gun, choosing between a water- or air-cooled model depends largely on the application and amperage requirements, operator preference and cost considerations. Applications that involve welding sheet metal for only a few minutes every hour have little need for the benefits a water-cooled system can provide. Whereas shops with stationary equipment that repeatedly weld at 600 amps likely will need a water-cooled system to handle the heat of the application.
A water-cooled MIG welding system pumps cooling solution from a radiator unit, usually integrated inside or near the power source, through hoses inside the cable bundle and into the gun handle and neck. The coolant returns to the radiator where a baffling system releases the heat absorbed by the coolant. The ambient air and shielding gas further disperses the heat from the welding arc. Water-cooled guns range from 300 to 600 amps.

An air-cooled system relies on the ambient air and shielding gas to dissipate the heat that builds up along the length of the welding circuit. These systems, which range from 150 to 600 amps, use much thicker copper cabling than water-cooled systems.

Each system has advantages and disadvantages. Water-cooled guns are more expensive up-front and can require more maintenance and operational costs. However, water-cooled guns also are much smaller and lighter than air-cooled guns, so they can provide productivity advantages due to reduced operator fatigue.
Because water-cooled guns require more equipment, they can be impractical for applications that require portability.

Options for handles and cable selection
A MIG gun’s handle, neck and power cable design can all impact how long an operator can weld without experiencing fatigue. Handle options include straight or curved — both of which come in vented styles — and the choice often boils down to welding operator preference. A straight handle is the best choice for operators who prefer a trigger on top, since curved handles for the most part do not offer this option. With a straight handle, the neck can be rotated to place the trigger on top or on bottom. In heavy-duty applications, some welding operators drape the power cable over their shoulder, and in those cases a trigger on top is more accessible.

When it comes to cable selection, smaller, shorter and lighter power cables can offer greater flexibility, making it easier to maneuver the equipment and avoid clutter in the workspace. Manufacturers offer cables ranging from 8 to 25 feet long, and shorter cables often contribute to better feedability of the wire. The longer the cable, the more chance it can get coiled around things in the weld cell or looped on the floor and possibly disrupt wire feeding. However, sometimes a longer cable is necessary if the part being welding is very large.

Other options to consider are the addition of a heat shield, which protects the welding operator from the heat output of a high amperage MIG gun and allows for longer arc-on time. Adding a unicable cover can protect the power cable from a harsh environment.

A side note on self-shielded flux-cored guns
Just as with standard MIG welding, self-shielded flux-cored welding (FCAW-SS) can offer high productivity and quality advantages in certain fabrication applications, while also providing easier training and operation.

Many of the considerations for selecting a FCAW-SS gun are similar to those for selecting a standard MIG gun. Amperage and duty cycle ratings and the application requirements remain among the most important elements to consider in selecting either type of gun.

Here are some issues to keep in mind for self-shielded FCAW-SS gun selection:

•    Operators can choose between a fixed liner and a replaceable liner, which (as the name suggests) can be replaced if it becomes clogged or damaged.

•    Guns with fixed liners typically have external trigger leads, while guns with replaceable liners commonly have trigger leads internal to the power cable, which prevents catching on surrounding equipment. This can be a consideration for applications that require welding around hard corners or fixtures.

•    Trigger options include standard or dual-schedule to allow welding operators to increase or decrease wire feed speed at the gun with the flip of a switch.

The value of comfort
Minimizing fatigue, reducing repetitive motion and decreasing overall physical stress are key factors that contribute to a safer, more comfortable and more productive environment. Choosing a MIG gun that offers the best comfort and operates at the coolest temperature allowed by the application can help improve productivity and, ultimately, the profitability of the welding operation by increasing arc-on time.