Understanding robotic guns

From high volume, low variety manufacturing facilities to low volume, high variety fabrication shops, robotic GMAW arc welding has become increasingly popular due to the potential weld quality and productivity improvements it can provide. Not only do these benefits make it an attractive investment for growth and profitability, but they can also provide companies with a competitive edge.

Just Add Water

Water-cooled robotic GMAW guns offer excellent advantages for applications that require welding at higher amperages for prolonged periods of time. These guns provide high amperage capacity—generally 300 to 600-plus amps—and are capable of managing a duty cycle within the 60 to 100 per cent range. They are designed for welding on thicker materials (typically 1/4 in./6.35 mm and greater), making them a good choice for applications in heavy equipment manufacturing or other similar industries. As a rule, the larger the overall size of the weldment, the greater the chances the application will require a water-cooled GMAW gun.

To prevent overheating, water-cooled robotic GMAW guns rely on a supply of water or coolant from an external source. These sources include circulators or chillers, which tend to add to the overall cost and maintenance requirements of the system. The coolant travels through a water hose in the gun’s cable bundle (also containing the power cable, wire, and gas and water return hoses) and circulates up through the gooseneck to the consumables. For very high amperage applications, there are also water-cooled nozzles that are capable of circulating the coolant around the nozzle, but these are more expensive than standard ones.

As mentioned previously, water-cooled power cables (found in the cable bundle) have approximately one quarter of the copper found in an air-cooled unicable; thus, water-cooled unicables quickly fail if the water s

upply is interrupted. This factor is a disadvantage of water-cooled robotic GMAW guns, as the parts can be expensive and time consuming to replace should they become damaged.

Routine maintenance of the cables within the cable bundle can also be difficult, as they are all in close proximity to one another. And because these guns have internal water chambers in the gooseneck, that part is inherently weaker than the gooseneck on an air-cooled robotic GMAW gun and much more likely to bend in the event of a collision. Still, for high amperage applications that require high capacity cooling to protect the gun during long periods of welding, dealing with these disadvantages still make having a water-cooled robotic GMAW gun worthwhile.

An Option In Between

For companies that weld multiple thicknesses of base materials and require both high and low amperage capabilities from a gun, a hybrid air-cooled/water-cooled robotic GMAW gun is a good option. These guns have a durable gooseneck like an air-cooled model, but offer the higher cooling capacity of a water-cooled GMAW gun. They feature exterior water lines that run along the outside of the gooseneck to the nozzle, as opposed to through the gooseneck like water-cooled GMAW guns have. Hybrid air-cooled/water-cooled robotic GMAW guns typically offer 300 to 550 amperage welding capacity at 60 percent duty cycle (using mixed gases).

Hybrid air-cooled/water-cooled robotic GMAW guns also have features that provide easier maintenance compared to a true water-cooled product. For example, the water lines run independently of the power cable and are more accessible than with a standard water-cooled GMAW gun, so these guns do not need to be taken off of the robot for maintenance. Plus, if there are issues with water circulation, these guns can rely on the underlying air-cooled unicable to provide enough current-carrying capacity to avoid a catastrophic failure such as destroying a power cable or other components. Overall, the features of the hybrid air-cooled/water-cooled GMAW gun help provide a lower total cost of ownership for the gun.

One limitation is the limit to duty cycle. For applications that require continuous duty cycles, these GMAW guns would not be the best choice

and a water-cooled product may have to be deployed.

Protecting the Assets

Regardless of which robotic GMAW gun is right for a given application, good preventive maintenance is critical to ensuring product longevity and reducing unscheduled downtime. In particular, most robotic GMAW gun manufacturers recommend using a nozzle cleaning station to prevent spatter buildup that can lead to quality issues or downtime (and costs) related to consumable changeover. Checking for loose connections along the length of the robotic GMAW gun—from the power pin to the nozzle—is also key to preventing quality issues or damage that could cause the gun to fail prematurely.

Remember, choosing the appropriate robotic GMAW gun to suit the requirements of the application is essential for optimizing the return on investment. Using the right robotic GMAW gun also provides for a more reliable system and can help manage the total cost of ownership, particularly by minimizing performance issues, costly repairs, unscheduled downtime and premature failures. In the end, it takes less time and money to protect a robotic GMAW gun with preventive maintenance procedures than it does to take the gun offline for repair or to replace it. CM

Robert Ryan, P.Eng., MBA,  is product manager, Automation Group, Tregaskiss, Windsor, ON.

www.tregaskiss.com