Top Factors and Considerations for MIG (GMAW) Gun Selection

How do I choose a MIG gun?

Selecting a MIG gun should be done with just as much attention to detail as the welding power source itself. Think of it as the human body: an injured toe inhibits our ability to perform basic functions such as walking. The gun is just as critical to the quality of the weld itself and the productivity of your operators. There are also important considerations when selecting a MIG gun that may help you lower your operating costs. Let's take a look at common types of MIG guns and considerations for selecting the gun that’s right for you.

Choose wisely: Types and varieties of MIG guns

The choice of a MIG gun goes beyond just air- or water-cooled models. There are five basic MIG welding gun options; here's what you need to know about each:

Air Cooled: Air-cooled guns use ambient air and shielding gas to dissipate excess heat. The power cable on an air-cooled gun contains more copper to help prevent the cable insulation from melting or burning. As a result, air-cooled guns are heavier and less flexible compared to water-cooled guns in most cases. Air-cooled systems, however, are less expensive as they do not require an independent radiator cooling system and extra hoses that are associated with water-cooled systems. The simpler design of air-cooled setups makes them easier to operate, assemble, maintain and support. Air-cooled MIG welding guns are typically available in a wide range of amperages, between 150 and 600 amps.

Water Cooled: Water-cooled MIG gun systems require a radiator cooling system that circulates water, the ambient air and shielding gas to dissipate heat from the gun. However, water-cooled gun cables are lighter and more flexible because the cable contains less copper compared to air-cooled systems. Water-cooled MIG guns are typically available in 300- to 600-amp ranges.

Push-Pull: These guns are particularly helpful when welding soft alloys such as aluminum, small diameter stainless, silicon bronze and cored wires. They are available in both air- and water-cooled designs. Push-pull guns are an excellent option when welding far away from the power source — some push-pull guns are capable of working more than 50 feet away (although 15- to 35-foot distances are more common and preferred). This is not always ideal, but is helpful when accessibility is an issue. Push-pull systems feature a push motor at the feeder that works in conjunction with a pull motor on the gun, effectively allowing the wire to feed through the liner with minimal resistance. The feeder and the gun must be compatible for these systems to work. Push-pull guns are typically available in gooseneck and pistol-style grip to meet application demands and operator preference.

Spool Gun: Spool guns improve feeding of soft wires by locating a small spool of wire, typically about 1 pound and 4 inches in diameter, on a pistol-grip style gun. Because spool guns only need to feed the wire a few inches before it hits the weld puddle, they eliminate the potential problems created by pushing soft wires through a regular gun, such as birdnesting. This type of gun is particularly helpful with welding aluminum. A spool gun is best suited for occasional MIG welding at low amperages, such as MRO.

The key to a spool gun is flexibility. Duty cycles are typically lower, but spool guns offer a cost effective entry point into MIG welding. It can be used with any power source with a 14-pin connection, including some engine drives. So, you don’t need to buy new power sources to get into MIG welding aluminum in most cases.

Fume Extraction Gun: Fume extraction guns capture the fume right at the gun and connect back to a high-vacuum fume extraction system. Typically rated up to about 400 amps, these models have become more efficient and user friendly with features such as adjustable extraction control (so as not to disturb shielding gas flow while still providing excellent fume extraction), a smaller vacuum chamber (for ease-of-handling) and improved neck designs for better joint access.

These MIG welding guns provide extra defense against welding fumes, such as those encountered when welding certain varieties of stainless and galvanized steels, and when welding with wires and steels containing high levels manganese.

Flux-Cored Guns: While the same machine can typically be used to run both MIG and flux-cored wires, a MIG gun is not recommended to run the flux-cored process. Flux-Cored welding is typically hotter and rougher on front-end consumables. There are, however, consumable conversion packages that will allow you to run flux-cored wires on a standard MIG gun. Otherwise, if you plan to run the flux-cored process, invest in a dedicated flux-cored gun.

Top considerations for gun selection

1. Application: Whether you choose an air- or water-cooled MIG welding gun often comes down to operator preference. High-amperage pulsed MIG applications typically rely on water-cooled systems, as do applications that run larger diameter wires (1/16-in. and up). Applications with smaller diameter wires (.035-, 3/64-in.) tend to more often use air-cooled guns. Companies that run a helium mix tend to prefer water-cooled systems as helium runs hotter than other gas mixes. In general, water-cooled guns also help consumables last longer because the tip, nozzle and diffusers all run cooler. This creates less downtime and increases cost savings.
   
   Also, are you welding in the shop or in the field? Air-cooled MIG guns are more practical for outdoor use because they require fewer parts, simplifying transport, set-up and parts management. Water-cooled systems make more sense in stationary applications because of the required water-cooling system and hoses.
   
   As mentioned before, when welding with softer wires, push-pull and spool guns provide greater support to prevent feeding problems.
   
   
2. Amperage Ratings/Duty Cycle: One of the most common mistakes is to buy a gun with the wrong duty cycle. Guns rated at 600 amps will more than cover almost any application you can think of. However, the added size, weight and cost of a gun with that high of a rating may exceed your needs and fatigue the operator. A gun rated at 150 or 200 amps will cost less, be lighter and easier on the operator, but won’t be suitable for extensive welding on applications that may require 300-400 amps. As new work comes in that requires MIG welding at higher amperages, you may find yourself buying a higher-amperage gun anyway.
   
   It’s a delicate balance: you may weld at 400 amps, but a gun rated at 300 amps/100 percent duty cycle may work because you realistically will not be welding 100 percent of the time. The average “arc-on” time for a welding operator over an eight-hour day is roughly 30 minutes for each hour. Consider your welding application and determine, based on average amperage and arc on time, what MIG gun will be best.
   
   
3. Cost: Water-cooled systems offer a higher cost of implementation due to the added components (e.g. cooling system, hoses). This means there are more parts and components that may be prone to downtime. On the other hand, as previously stated, water-cooled systems help consumables last longer, helping reduce those associated costs.
   
   Push-pull guns are ideal for welding soft wires and will provide greater performance and productivity than using a push-only system. However, these need to be coupled with compatible wire feeders and systems, potentially increasing the cost of implementation. If you infrequently weld with these wires, a spool gun may prove to be a wise choice because it will work with most of the welding systems you already own (provided they have a 14-pin connection) and will not require you to buy new equipment in most cases
   
   
4. Components/Consumables: A welding system is only as strong as its weakest part. Here are a few things to look at when specifying a MIG gun:

a. The back end: A heavy, sturdy power pin designed to seal the connection tightly helps prevent problems such as electrical resistance, overheating, gas leakage and poor conductivity. Look for a rigid strain relief at the connection between the power cable and the wire feeder. This will prevent kinking and improve feeding. Also, select a MIG welding gun with multiple, interchangeable plug options. A gun that can be matched with multiple feeders allows you to standardize on one type of gun and consumable. This helps to reduce equipment costs, minimize inventory and simplify the entire process.

b. The liner: There are three key factors when looking at liners: make sure there is a good gas seal and/or solid o-ring connection at the back of the liner to prevent gas leaks; choose liners with durable jacketing or coating to prevent additional gas loss, and select a liner designed for your diameter wire. Also, look for a liner that is easy to remove and replace to minimize downtime. Push-pull guns use unique liners designed specifically for this type gun, usually made of teflon or a type of plastic.

c. The power cable: A cable that is too light for your application can cause the gun to overheat and may lead to poor welding performance. On the other hand, a cable that is too large can be cumbersome and cause clutter on the shop floor. A good rule of thumb is to use the smallest and shortest cable possible without limiting your welding needs. Smaller cables reduce operator fatigue, minimize clutter and help prevent excessive coiling that can lead to poor wire feeding.

d. Trigger options: Triggers are the only moving part on a MIG welding gun that can fail due to mechanical motion. Look for a strong, reliable trigger that is easily serviceable to help minimize downtime for component changeovers. Also, choose a gun that gives you the most appropriate trigger option for your application: standard, locking, dual pull and dual schedule switches are all available through most manufacturers. These options allow your welding operators to work with the trigger set-up that best suits them and the application. It will also further increase productivity by making welding more comfortable.

e. Neck and handle options: MIG welding guns are available with fixed, rotatable and flexible necks of different lengths and angles to provide flexibility when welding in various positions or tight quarters. Rotatable necks allow you to weld out-of position more comfortably without changing your gun handle or sacrificing quality. Operators can easily adjust flexible necks to fit different positions, and they save time and money for changing out and/or inventorying expensive specialty guns for a given application. Also, 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/duty cycle rating needs. Similar to the power cable, a smaller gun handle makes it easier for you to weld. Also, a ventilated handle can reduce heat and increase your comfort and productivity.

f. Consumables (nozzles and tips): Less expensive consumables do not always translate into cost savings. Ultimately, you get what you pay for. By selecting a consumable based on longevity instead of price, you can reduce costs for replacement parts and for changeover time. You will likely spend more money upfront for such consumables, but more durable consumables can help reduce overall operating costs in the long run by increasing productivity and reducing downtime. It is also important to look for heavy duty tips and nozzles that provide good conductivity and gas coverage to help ensure good arc starts, less spatter and less rework and clean-up.

As you can see, the choice is much more complicated than simply picking the least expensive or most powerful gun that matches your machine. Careful consideration of your welding process, operator preferences and performance/comfort will lead you to the right MIG welding gun.