GMAW Guns, Consumables and More: Common Questions Answered

Gas metal arc welding (GMAW) involves more than just arc-on time. Welding operators also need to be mindful of other activities that contribute to the overall productivity and quality in the welding operation, including proper joint preparation, following correct weld parameters and ensuring good part fit-up. Selecting the proper GMAW gun, consumables and shielding gas is also critical to achieving good results. Unfortunately, it is not uncommon for there to be confusion as to how these components affect the welding operation. The reality is, however, that they can have a significant impact on downtime and costs, not to mention operator comfort. The goal is to make sure that impact is positive.

Following are answers to some common questions about GMAW guns, consumables and shielding gas to help you select the best ones for your welding operation and manage them in a way that provides optimal results.                                                                                                                                                                       

How do I determine what amperage GMAW gun I need?
When it comes to GMAW guns, bigger isn’t always better. In fact, selecting a larger amperage gun than needed for your application may cost you money in the long run and lead to discomfort, which results in unnecessary downtime. Duty cycle is defined as the amount of arc-on time within a 10-minute period, so a 20 percent duty cycle would constitute two minutes of arc-on time in a 10-minute time frame.  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. For example, in many cases you could use a 300-amp gun model in place of a 400-amp gun model, since actual arc-on time often does not exceed the amperage to duty cycle ratio of a 300-amp gun. The benefit is that the lower amperage gun generally costs less money — and it also weighs less, which can help reduce wrist fatigue, commonly associated with downtime. The lower amperage GMAW gun will still be capable of operating at the appropriate capacity, while also offering the benefit of being easier to maneuver – a factor than may help you improve weld quality and lessen rework, too.

Welding operators need to be mindful all activities that contribute to the overall productivity and quality in the welding operation, including GMAW gun, shielding gas and consumable selection.

Besides amperage, what else should I consider when selecting a GMAW gun?
There are several factors to consider when choosing your GMAW gun. After determining your amperage needs, you should also look for features like a rigid, strong strain relief. Strength in this area between the power pin and cable can help minimize kinking, which often leads to an unstable arc and/or poor wire feeding. Next, consider selecting a smaller handle gun (but one that can still meet your amperage needs), as it may help reduce wrist fatigue and be easier to maneuver into complex joints. You may also want to consider looking for a specific style of neck for your application. Many GMAW gun manufacturers offer fixed, rotating and flexible necks in various lengths and angles, allowing you to reach joints more easily. Regardless of the style of neck you choose, you should find one with good armor to protect it against damage that could lead to electrical shorts or premature failure. Finally, select a GMAW gun with a comfortable and easy-to-service trigger. Typically, you will be able to find a variety of trigger options, including standard style, locking or dual schedule. Regardless of the specific style, look for sturdy triggers that will withstand work site abuse and that can be easily replaced should one of the mechanics fail.

What type of shielding gas is best for my application?
Shielding gas prevents exposure of the molten weld pool to oxygen, nitrogen and hydrogen contained in the air atmosphere, in order to protect the weld from contamination and/or defects. The type you use can impact everythingfrom the penetration profile to arc stability and the mechanical properties of the finished weld. If you need deep weld penetration, particularly on thick materials, carbon dioxide (CO2) is a good choice and it is also the least expensive. This gas, however, does tend to create spatter and is limited to use in short circuit welding. Adding 75 to 95 percent argon to the CO2 can provide better arc stability and puddle control, both of which reduce spatter compared to straight CO2. This mixture will also allow you to use a spray transfer process, allowing you to weld faster in many cases. Argon also produces a narrower penetration profile that is useful for fillet and butt welds. If you’re welding a non-ferrous metal — aluminum, magnesium or titanium — you’ll need to use 100 percent argon. In some cases, oxygen or helium is used in the GMAW process, but it is not as common.

How can I make my GMAW consumables last longer?
Consumable service life can vary dramatically from application to application. There are a few steps you can take to make them last longer, however. First, use the correct contact tip for the size wire who have and be certain it fits securely with the gas diffuser. A solid connection between these components helps ensure good conductivity and minimize overheating, making them last longer. Also, inspect your nozzle on a regular basis for spatter and clean as necessary. Use a pair of welding pliers or a special nozzle-cleaning tool for the job, as directed by the consumable manufacturer. Be sure, too, that you have the appropriate type of consumables for your application. Applications above 300 amps, for instance, can often benefit from heavy-duty consumables, which have greater mass and can dissipate heat more readily. The result, in many cases, is longer service life. Finally, set the drive roll tension on your wire feeder so that the wire feeds properly. Doing so prevents deformities in the wire (in the case of too high of tension) that may cause the wire to wear out the contact tip prematurely.

The liner (shown in the center of the handle) can be a common source of wire feeding problems. Always trim and install it according to the manufacturer's recommendations.

What is the proper way to trim and install my GMAW gun liner?
Cutting a GMAW liner too long can cause it to become misaligned with the gas diffuser. Conversely, cutting a liner too short may lead to debris build-up between the liner and gas diffuser. Both instances can lead to poor wire feeding, weld quality issues and premature contact tip failure. To prevent this problem, always follow the manufacturer’s instructions for installation, making certain that the liner is free of any burrs or short edges after you trim it. A smooth cut helps ensure smooth and consistent feeding of the welding wire. Some manufacturers offer a liner gauge to help you determine the proper length for your particular liner, while others print markings on the outside of the weld cable to show when the liner is twisted, allowing for more accurate trimming. If your gun does not have these markings, make sure the cable is fully extended when inserting the new liner. Remember to wear gloves when handling the liner and avoid dragging it on the ground. These precautions help prevent debris from being introduced into the GMAW gun and causing weld contamination and/or poor consumable performance.

How can I protect my contact tips from burnback?
Burnback is one of the most common causes of downtime in a GMAW application and is a significant cause of premature contact tip failure. Proper equipment setup is one of the key defenses to protect your consumables. First, be sure that you have established the appropriate contact tip recess and wire stick out for your application, and that you maintain a correct contact-tip-to-work distance. Check electrical connections regularly and replace worn work leads or cables, as faulty ones can also cause the problem. Make sure to maintain the proper drive roll tension and install your liner properly, too. Both precautions minimize erratic wire feeding that could lead to burnbacks.

Proper equipment setup is one of the key defenses to protect consumables against burnback and reduce downtime associated with contact tip changeover.

What’s the best way to store and handle my GMAW consumables?
Storing and handling GMAW consumables properly not only helps them last longer, but also perform better. Never store your GMAW consumables loose in a bin, since it can cause scratches on them that attract spatter and may lead to premature failure. Instead, keep them in their original packaging until you are ready to use them. Doing so will also protect the components from contaminants such as dirt or oil. Finally, always wear clean gloves when handling or replacing contact tips, nozzles and diffusers. Again, it helps prevent dirt, oil or other contaminants from adhering to them and also potentially entering the weld puddle.

Like any welding process, GMAW has many factors to consider in order to achieve the best results. Make sure that you don’t overlook the impact of your GMAW gun, consumables and shielding gas as part of those. Being mindful of the selection process, storage and handling, and installation, among other things, can be beneficial to both your productivity and your bottom line in the long run.