Choosing GMAW Gun Consumables Wisely

Simple ways to save money and reduce downtime

By Andy Monk

May 4, 2011

Choosing liners, contact tips, and nozzles.

Everyone is trying to save money these days. From implementing lean practices to repairing equipment instead of purchasing new, companies are seeking ways to reduce costs without sacrificing quality. Selecting the right gas metal arc welding (GMAW) gun consumables for your welding application can help.

Not only can the right consumables minimize unscheduled downtime for changeover, but they also can reduce the need to rework weld defects caused by a poorly performing contact tip, nozzle, or liner. The bottom line? You can spend more time welding, gain greater productivity, and lower your costs.

Following are some suggestions for selecting the most appropriate GMAW gun consumables for your application and ways you can best care for them.

Lineup for the Best Performance

Liners are responsible for guiding the welding wire from the wire feeder, through the gun cable, and up to the contact tip. They typically are composed of steel coils, but also can be made of nylon or Teflon®, the latter of which is used for welding with aluminum wire.

Selecting a liner is a relatively straightforward process. You need to match the liner’s inside diameter (within a specific range) to the diameter of wire you are using. For example, if you are welding with a 0.035-in. wire, you can use a liner that measures between 0.035 and 0.045 in. in diameter.

Making this match helps prevent wire-feeding problems that can lead to poor arc stability, birdnesting (a tangle of wire that prevents the wire from feeding), and weld defects. Also, using premium-quality liners is best, as these maintain a more consistent inside diameter than less expensive ones, and also provide better feeding performance.

To prevent shielding gas leaks that can increase costs and jeopardize gas coverage of your welding puddle, make certain that the back of your liner has a good O-ring connection and that you select a liner with a durable coating.

Replace the liner at a regularly scheduled time, and always follow the manufacturer’s recommendation for trimming and installation. Liners that are poorly trimmed, worn excessively, or are kinked from use can easily cause wire-feeding problems or an erratic arc that leads to poor weld quality. A poorly chosen liner causes excessive spatter that will require postweld grinding, minimizing throughput and adding to your overall costs.

Some manufacturers offer partial liners that replace only the most commonly worn part of the liner (along the length of the GMAW gun) instead of the entire liner. These partial liners help reduce downtime for changeover as they usually take about half the amount of time to install compared to a full-length liner.

Tips for Making the Right Contact

Liners that are poorly trimmed, worn excessively, or are kinked from use can easily cause wirefeeding problems or an erratic arc that leads to poor weld quality.

While they may look like a small and perhaps insignificant part of the overall welding system, contact tips play a critical role in helping achieve good weld quality, reducing costs for downtime, and minimizing rework.

In addition to helping direct the welding wire to the weld puddle, contact tips are responsible for transmitting the current to the wire to initiate the arc.

The contact tip you select should correspond with the diameter of welding wire you are using. Typically, contact tips are available to accommodate wire diameters from 0.023 to 0.125 in.

Depending on the type of joint your application requires, you may need to select a tapered contact tip. These contact tips are good for applications that have restricted joint access, but they tend to be a bit more delicate than nontapered contact tips. They should be coupled with a tapered nozzle.

If joint access is not a factor in your application, however, choosing a nontapered contact tip is the best option as it has more mass and will last longer.

Various manufacturers offer either threaded or nonthreaded styles of contact tips.

Threaded contact tips are the most common and, as their name implies, they are held in place in the gas diffuser by threading or twisting them.

Nonthreaded contact tips drop into the gas diffuser. This tip style can be rotated when it starts to wear on one side (called keyholing). This creates a new wear surface, extends the life of the contact tip, and prevents arc instability that can in turn lead to spatter and rework.

Nonthreaded contact tips also tend to be easier to change out after a burnback, which is the formation of a weld in the contact tip. It most often occurs when the contact tip is placed too close to the workpiece or wire-feed speed is too slow.

Regardless of whether you choose a threaded or nonthreaded contact tip, it is important that you install it according to the manufacturer’s recommendations. Doing so will help ensure a good electrical connection and, with it, reliable welding performance and quality.

Contact tips generally are available in small or large sizes and in standard or heavy-duty variations.

If you are welding on high-temperature applications (generally, 300 amps and higher), you should select a large contact tip, as it has greater mass and provides better cooling capacity than a smaller contact tip.

For high-amperage applications that also require prolonged welding, heavy-duty contact tips can provide greater conductivity, improve arc starts, and last longer.

Lighter-amperage applications (typically, below 300 amps) are well-suited for small, standard contact tips.

To ensure the best welding performance, inspect the contact tip for spatter buildup on a regular basis and replace as needed. Waiting too long to replace a damaged contact tip can lead to arc irregularities and poor weld quality, not to mention unscheduled downtime for replacements, which can cut into your productivity and cost you money.

Know Your Nozzles

The contact tip you select should correspond with the diameter of welding wire you are using.

Depending on your application, a variety of nozzle styles are available to choose from. Like contact tips, nozzles are an important part of creating good weld quality and reducing costs. The main function of the nozzle is to direct shielding gas to the weld. For that reason, you want to select a high-quality nozzle that is capable of providing smooth gas coverage and resisting damage like dents and scratches. 

Usually, nozzles are made from either brass or copper. Brass nozzles provide good protection against spatter, while copper nozzles withstand heat better, particularly on heavy-duty applications.

You can choose from two main styles of nozzles — threaded and nonthreaded — as well as a variety of different shapes and sizes.

Threaded nozzles tend to maintain a more secure connection than nonthreaded, which protects against shielding gas leaks that can lead to weld defects like porosity. These nozzles also help keep the contact tip centered for greater accuracy.

Nonthreaded nozzles, however, are easier to change over.

Nozzles come in small and large sizes and with various inside diameter measurements, often from 3/8 to 5/8 in. Ultimately, the best option for any application is to use the largest nozzle possible that still gives you access to the joint. Doing so provides greater gas coverage to protect against contaminants. For restricted joints, however, you will need to use a small, tapered nozzle that allows you to place the contact tip close to the weld puddle.

Or, if you have a high-amperage application that requires a high gas flow rate, select a large-diameter nozzle, because it provides the best shielding gas coverage.

Some GMAW consumable manufacturers offer nozzles that keep the contact tip at a fixed position: flush, recessed, or extended. Each has distinct attributes.

For example, if you are welding in a short-circuit transfer mode, a nozzle that keeps the contact tip flush to the end of the nozzle, or is slightly extended, helps minimize the spatter that tends to be generated in this welding process. Similarly, when welding with solid wire in spray-arc transfer or pulsed-spray mode, having a nozzle that keeps the contact tip slightly recessed can help the contact tip operate at cooler temperatures and provide greater shielding gas coverage.

For all styles and sizes of nozzles, regular inspection for spatter is crucial to achieving good gas coverage.

Also, careful handling and storage of these consumables is important. Always wear gloves when changing out nozzles to prevent debris and oils from adhering to them and entering the weld puddle. To prevent damage, keep them in the original packaging until you are ready to use them.

Remember, choosing the right nozzle, contact tip, or liner for your GMAW application can go a long way in reducing unnecessary downtime and lowering your overall costs.

For more information, visit www.bernardwelds.com.