Welding Digest

The welding gun is a vital piece of equipment in a robotic welding system, serving as the conduit for the welding wire, gas, and power. However, it can sometimes be an afterthought when companies implement an automated welding solution. Unfortunately, this oversight can lead to a host of problems, not to mention frustration. That is especially true for first-time users making the investment. 

The wrong robotic welding gun can also cause issues for those more experienced with robotic systems. It’s not uncommon for companies to purchase the same gun for a new robot and tooling when, in fact, it may not be the best option.

Today, most robotic welding systems are through-arm models in which the power cable runs through the casting of the robot arm. As a first step in configuring a robotic welding gun for these systems, it’s important to know the make and model of the robot, power source, and wire feeder. Each equipment manufacturer has a different interface that dictates how each piece of equipment connects with one another. 

Companies also need to determine their welding amperage and arc-on requirements for the application. This ensures that they purchase a robotic welding gun with the proper duty cycle — the amount of welding that can occur at a rated output over a period without causing damage to the gun. Robotic welding guns are available in a variety of ratings, including air-cooled models that operate at 350 or 385 A at 100% duty cycle. 

There are higher amperage water-cooled options, which are typically 400 A and above, available in the marketplace. Some of these may be rated at 100% duty cycle, while others are rated at 60%. Don’t be fooled by high amperage unless it’s at 100% duty cycle.

Hybrid options are available for companies that want the simpler construction of an air-cooled robotic welding gun with the added cooling capacity of a water-cooled one. These guns have external water lines that circulate water around the nozzle to keep the front-end consumables cooler. 

For a robotic welding gun to access the weld joints, it’s critical that the work envelope is adequate. Companies need to consider not just the size of the gun but also the space that is available when the tooling, fixtures, and parts are all in place. Joint design and weld sequencing also factor into the equation. It’s important that there is room and time for the welding gun to weld the joints in a sequence that keeps heat to a minimum. Companies should avoid heat soaking the parts, so they don’t become distorted. 

A robot integrator can conduct a 3D simulation using models provided by the robotic welding gun manufacturer through computer-aided design (CAD) to make sure the gun and neck have the proper access and reach within the given space. The CAD model can also show whether the selected gun has the correct tool center point (TCP) and can extend to the nozzle cleaning station for reaming or to a service window for consumable changeover. A service window supports safety in the operation by eliminating the need for an employee to physically enter the cell. 

Configuring the Gun

Some robotic welding gun manufacturers offer online configurators that allow companies to customize the equipment for their exact application. These configurators guide the user through a step-by-step process, providing options to choose from for each component. With or without this tool, companies need to consider what their needs are based on their upfront assessment. 

Gun mount: There are two mounting options for a robotic welding gun to protect it in the event of a collision — a solid arm mount and a clutch. If the robot or end user’s safety procedure requires external collision detection, a clutch can be added to the system. This component functions both mechanically and electrically by recognizing a collision and sending a message to the robot controller to stop the system. If procedures allow for reliance on only the robot’s collision detection, then a solid mount will suffice. 

Neck: The neck length and angle must provide the approach angle to weld parts properly and to allow for smooth wire feeding. Standard neck angles are 22, 45, and 180 deg. Through-arm robots generally use a 45-deg neck; however, that should be verified with the CAD model/simulation before implementing. Companies will also need to take into consideration the welding wire they are using. For example, aluminum wire requires a straighter neck to feed through properly since it is so soft. 

Welding cable: For through-arm robots, the make and model dictate the cable length. For conventional robots (where the cable assembly runs outside the robot arm), the gun cable length also depends on the robot make and model along with the location of the feeder. It may be remotely mounted or mounted on the robot itself. There is more flexibility with cable length for these robots, but it’s important not to use too long of a cable since this can lead to wire feeding issues. Conversely, a cable that is too short can stretch and break down quickly. 

Welding consumables: When choosing contact tips for the robotic welding gun, look at the welding process. Pulsed gas metal arc welding (GMAW-P), for example, is quite hard on contact tips due to its high-frequency waveforms. This process requires a harder tip or a contact tip specifically designed for pulsed welding. The chosen nozzle needs to allow proper access to the weld joint. A tapered nozzle works well when using smaller-diameter wire and contact tips. Higher-premium consumables are a good choice since these last longer and reduce downtime and labor for changeover. 

Liners are another factor to consider, and the welding wire being used affects the choice. Flux- and metal-cored wires tend to be stiffer and harder to feed than solid wires. They require an extra-heavy-duty liner to support the wire and gain smooth feedability as it moves toward the contact tip. A D-wound galvanized wire works well. Companies can also use this liner for solid wire with good success. 

Maintaining Efficiency

Companies invest in robotic welding systems to increase quality, productivity, and cost savings through a fast, repeatable process. To gain those benefits, every part of the system needs to be functioning optimally. Ensuring that the robotic welding gun has been configured properly before implementing the system can prevent downtime and extra expenses.

This article was written by Ryan Lizotte (project manager, Tregaskiss, Windsor, Ontario, Canada) for the American Welding Society.