Criteria for Selecting a MIG Gun
MIG welding is considered among the easiest welding processes to learn and is useful for a variety of applications and industries. Since the welding wire constantly feeds through the MIG gun during the process, it doesn’t require frequent stopping, as with stick welding. The result is faster travel speeds and greater productivity.
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, in a range of thicknesses. In addition, it produces a cleaner weld that requires less cleanup than stick or flux-cored welding.
To maximize the benefits this process offers, however, it is imperative to select the right MIG gun for the job. In fact, this equipment’s specifications can significantly impact productivity, downtime, weld quality and operating costs — as well as welding operators’ comfort. Here is a look at different types of MIG guns and some key factors to consider when making the selection.
What’s the right amperage?
It is important to select a MIG gun that offers adequate amperage and duty cycle for the job in order to prevent overheating. 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; lower-amperage guns tend to be smaller and easier to maneuver, so they are more comfortable for the welding operator.
When evaluating a gun’s amperage, it is important to consider the shielding gas that will be used. Most guns in the industry are tested and rated for duty cycle according to their performance with 100 percent CO2; this shielding gas tends to keep the gun cooler during operation. Conversely, a mixed-gas combination, such as 75 percent argon and 25 percent CO2, makes the arc hotter and therefore causes the gun to run hotter, which ultimately reduces duty cycle. For example, if a gun is rated at 100 percent duty cycle (based on the industry-standard testing with 100 percent CO2), its rating with mixed gases will be lower. It is important to pay attention to the duty cycle and shielding gas combination — if a gun is rated at only 60 percent duty cycle with CO2, the use of mixed gases will cause the gun to operate hotter and become less durable.
Water- versus air-cooled
Deciding between a water- or air-cooled MIG gun depends largely on the application and amperage requirements, welding operator’s preference and cost considerations.
Applications that involve welding sheet metal for only a few minutes every hour have little need for the benefits of a water-cooled system. On the other hand, shops with stationary equipment that repeatedly weld at 600 amps will likely need a water-cooled MIG gun to handle the heat the applications generate.
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 then returns to the radiator, where a baffling system releases the heat absorbed by the coolant. The ambient air and shielding gas further disperse the heat from the welding arc.
Conversely, an air-cooled system relies solely 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. By comparison, water-cooled guns range from 300 to 600 amps.
Each system has its advantages and disadvantages. Water-cooled guns are more expensive upfront, and can require more maintenance and operational costs. However, water-cooled guns can be much lighter and more flexible than air-cooled guns, so they can provide productivity advantages by reducing operator fatigue. But because water-cooled guns require more equipment, they can also be impractical for applications that require portability.
Heavy- versus light-duty
While a lower-amperage gun can be appropriate for some applications, be sure it offers the necessary welding capacity for the job. 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 heavier-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. They 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. As a result, care should be taken to prevent kinking that may impair wire feeding and gas flow. Also note, overworking a light-duty MIG gun can lead to premature failure, so this type of gun may not be appropriate for a facility that has multiple applications with various amperage needs.
At the other end of the spectrum, heavy-duty MIG guns are 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 that are required to deliver these 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 are often longer as well, to put more distance between the welding operator and the high heat output from the arc.
Fume extraction guns
For some applications and welding operations, a fume extraction gun may be the best option. Industry standards from the Occupational Safety and Health Administration(OSHA) and other safety regulatory bodies that dictate allowable exposure limits of welding fumes and other particulates (including hexavalent chromium) have led many companies to make the investment. Similarly, companies that seek to optimize welding operator safety and attract new skilled welding operators to the field may want to consider these guns, as they can help create a more appealing work environment. Fume extraction guns are available in amperages typically ranging from 300 to 600 amps, as well as various cable styles and handle designs. As with all welding equipment, they have their advantages and limitations, best applications, maintenance requirements and more. One distinct advantage to fume extraction guns is that they remove the fumes at the source, minimizing the amount that enters the welding operator’s immediate breathing zone.
Fume extraction guns can, in combination with many other variables in the welding operation — welding wire selection, specific transfer methods and welding processes, welding operator behavior and base material selection — help companies maintain compliance with safety regulations and create a cleaner, more comfortable welding environment.
These guns operate by capturing the fumes generated by the welding process right at the source, over and around the weld pool. Various manufacturers have proprietary means of constructing guns to conduct this action but, at a basic level, they all operate similarly: by mass flow or the movement of material. This movement occurs by way of a vacuum chamber that suctions the fumes through the handle of the gun and into the gun’s hose through to a port on the filtration system (sometimes informally referred to as a vacuum box).
Fume extraction guns are well-suited for applications that use solid, flux-cored or metal cored welding wire as well as those conducted in confined spaces. These include, but are not limited to, applications in the shipbuilding and heavy equipment manufacturing industries, as well as general manufacturing and fabrication. They are also ideal for welding on mild and carbon steel applications, and on stainless steel applications, as this material generates greater levels of hexavalent chromium. In addition, the guns work well on high amperage and high deposition rate applications.
Other considerations: Cables and handles
When it comes to cable selection, choosing the smallest, shortest and lightest cable capable of handling the amperage can offer greater flexibility, making it easier to maneuver the MIG gun and minimize clutter in the workspace. Manufacturers offer industrial cables ranging from 8 to 25 feet long. 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 welded is very large or if welding operators must move around corners or over fixtures to finish the task at hand. In these cases, where operators are moving back and forth between long and short distances, a steel mono coil cable might be the better choice. This type of cable doesn’t kink as easily as standard industrial cables and can provide smoother wire feeding.
A MIG gun’s handle and neck design can impact how long an operator can weld without experiencing fatigue. Handle options include straight or curved, both of which come in vented styles; 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 operator can rotate the neck to place the trigger on top or on bottom.
In the end, 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 arc-on time and productivity — and, ultimately, increase the profitability of the welding operation.