February 7, 2012
Following a few guidelines when selecting and using GMAW equipment and consumables can help improve productivity and quality in your welding operation.
Gas metal arc welding (GMAW) involves more than just arc-on time. Welding operators also need to be mindful of other factors that contribute to the overall productivity and quality of their welding operation, such as joint preparation, weld parameters, and part fit-up (Figure 1).
Selecting the proper GMAW gun, consumables, and shielding gas also are critical to achieving good results. Unfortunately, welders often are confused as to how these components affect the welding operation. The reality is 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.
When it comes to GMAW guns, bigger isn’t always better. In fact, selecting a larger-amperage gun than is 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-min. timeframe. 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 instead of a 400-amp model if the actual arc-on time does not exceed the amperage-to-duty-cycle ratio. The benefit is that the lower-amperage gun generally costs less — and it also weighs less, which can help reduce wrist fatigue that can cause downtime. The lower-amperage GMAW gun still can be operated at the appropriate capacity while also being easier to maneuver – a factor than may help you improve weld quality and lessen rework too.
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 poor wire feeding.
Next, consider selecting a gun with a small handle (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 also might want to consider looking for a specific neck style for your application. Many GMAW gun manufacturers offer fixed, rotating, and flexible necks in various lengths and angles that allow 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. Trigger options include standard style, locking, and dual schedule. Regardless of the style, look for sturdy triggers that will withstand work-site abuse and can be replaced easily should one of the mechanics fail.
Shielding gas prevents exposure of the molten weld pool to oxygen, nitrogen, and hydrogen contained in the air atmosphere to protect the weld from contamination and defects. The type you use affects everything from 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 also allows you to use a spray transfer process, which increases welding speed in many cases. Argon also produces a narrower penetration profile that is useful for fillet and butt welds.
If you’re welding a nonferrous metal — aluminum, magnesium, or titanium — you must use 100 percent argon. In some cases, oxygen or helium is used in the GMAW process, but this is not as common.
Consumable service life varies dramatically from application to application, but there are steps you can take to make them last longer.
First, use the correct contact tip for the wire size you have, and make sure it fits securely with the gas diffuser. A solid connection between these components helps ensure good conductivity and minimizes overheating, which makes them last longer.
Inspect the gun’s nozzle on a regular basis for spatter and clean as necessary. Use a pair of welding pliers or a nozzle-cleaning tool as specified by the consumable manufacturer.
Be sure, too, that you have the appropriate type of consumables for your application. For instance, applications above 300 amps 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 tension) that may cause the wire to wear out the contact tip prematurely.
Cutting a GMAW liner (Figure 2) too long can cause it to become misaligned with the gas diffuser. Conversely, cutting a liner too short may lead to debris buildup between the liner and gas diffuser. Both instances can lead to poor wire feeding, weld quality issues, and premature contact tip failure.
To prevent these problems, 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 poor consumable performance.
Burnback (Figure 3) is a frequent cause of premature contact tip failure, a common cause of downtime in a GMAW application. 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 stickout for your application, and maintain a correct contact-tip-to-work distance.
Check electrical connections regularly, and replace worn work leads or cables that can also cause burnback.
Make sure to maintain the correct drive roll tension and install your liner properly. Both precautions minimize erratic wire feeding that could lead to burnbacks.
Storing and handling GMAW consumables properly help them last longer and perform better. Never store your GMAW consumables loose in a bin, because doing so can create scratches that attract spatter and lead to premature failure. Instead, keep them in their original packaging until you are ready to use them. Storing them in this manner also protects the components from contaminants such as dirt or oil.
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 potentially entering the weld puddle.
Like any welding process, GMAW has many factors to consider to achieve the best results. Make sure that you don’t overlook the importance of your GMAW gun, consumables, and shielding gas. Being mindful of the selection process, storage and handling, and installation, among other things, is beneficial to both your productivity and your bottom line in the long run.