Endless or continuous rotation arc welding torches are a significant step forward in robotic welding operation, especially when performing radial welds. Specific industries, such as automotive, can increase productivity on parts such as instrument panels, exhausts, torque converters and fuel tank/pressure vessels because of the robot’s improved ability for radial rotation.
When robotic welding automation began, the torches had an over-the-arm weld cable dressout. The wire feeder was mounted on top of the robot or remotely mounted. A collision sensor was mounted under the wrist and a bracket tied the welding torch to the sensor. If the robot arm hit something, the collision sensor would break away. One of the biggest hurdles with an over-the-arm setup was that the bracket and weld cable got in the way of rotating the sixth axis, the axis the torch is mounted to, a full 360 degrees.
Inside the arm
Eventually, robotic through-arm technology developed where the weld cable runs inside the robot arm, the wire feeder is mounted behind the third axis and everything connects to the robot wrist. In the case where collision sensing is required, a through-arm collision sensor or a solid mounting strategy where the robot uses an on-board process for detecting collisions via monitoring of servo amperages can be used.
With through-arm robots, the bracket that limits rotation of the welding torch is removed, and the cable is held more securely.
The downside of the through-arm setup is that it still prevents full 360-degree rotation. The torch can’t rotate more than ±200 degrees on the sixth axis without damaging the weld cable because of the physical limitations associated with a multi-strand cable under torsional loads. Regardless of the better rotation characteristics, improved access to parts and ability to access faster cycles times in comparison to over-the-arm dress packages, there are still limitations on the cable.
“A through-arm setup opens up a new set of issues because of the much larger torsional load on the cable,” says Tom Graham, key accounts group manager, Abicor Binzel. “Typical cable life is roughly 15 to 18 months, but over those months, the winding and unwinding, bending and twisting of the cable eventually will break it down.”
Continuous cable stress and cable replacement is one of the more costly and time-consuming challenges of robotic welding. As the cable starts to break down, a bit of current conductivity is lost, things start heating up and the cable fails.
“With continuous rotation torches, you take the cable torsion out of the mix,” Graham says. “It allows free spinning out on the sixth axis of the robot. You can do 360-plus degrees of motion cleanly without having to put a great amount of stress on the cable. You don’t have that torsional load on the cable.”
From a cycle time standpoint, because there is no need for the cable to coil and uncoil, the welding torch can get into position much quicker. There is no need to go back to the home position.
“Higher process efficiency is achievable with the programming advantages offered,” Graham says. “You just set to position, perform the weld and move to the next position. You don’t need to worry about winding up the cable. You can just simply rotate 5 degrees to the next spot instead of having to rotate 355 degrees, for example.”
Endless rotation torches are good in high-speed automotive applications, he adds. “When you get into automotive jobs, a half second can often be the difference between meeting cycle time or not, so there are a lot of advantages from a programming standpoint that the rotating torch brings.”
Another benefit is freedom of movement in restrained locations. “You can get into tight spaces, such as welding inside of a box or a fuel tank where you have limited room,” Graham adds.
Endless rotation torches have been in the marketplace for a couple of years, but Graham believes the technology has not been universally accepted because it has pros and cons from the standpoint of how it goes into service.
“There are limitations to any application,” Graham notes. “With endless rotation products, you are primarily limited in the aspect of welding parameters, as are most air-cooled torch products. Ratings will go upwards of 500 A with varying duty cycles. With water-cooled versions coming to the market soon, you will have the ability to go after larger weldments versus standard automotive and sheet metal applications. Additionally, not every project requires continuous rotation, but it is a nice feature to have should you need it.”
Abicor’s Cyclone endless rotation torch has a modular design with an intermediate and main wrist insulator for easy access for maintenance or troubleshooting. Based on its Abirob air-cooled torch concept, it is easy to switch out the front-end pieces of the torch. Also, the same common consumables are available as for Abicor’s other air-cooled offerings, making it easier for customers.
And using the same front-end pieces as other Abicor torch packages means a common tool center-point setup is possible. This allows switching back and forth between products, endless rotation or not, with a common setup.
“Whenever you start putting a new welding torch package onto a robot, there’s potential for being off by a millimeter here or a half millimeter there,” Graham says. “That requires the end user to change their programs to accommodate the new setup. With Abicor, we have the same tool center point so you can go from an old product to a new product without affecting the tool center point. The Cyclone was designed with that in mind.”
Another differentiator is Abicor’s material selection for heat dissipation. With the continuous rotation approach, a conductive plate and brush structure is used as the means for passing electric current to the welding torch. The power cable is, in turn, connected between the wire feeder and torch module block mounted above the torch. The bearing set in the torch module along with the brushes and pressure plates work together to provide the continuous rotation feature while passing current for the welding process.
As with any moving parts, wear is a concern. As the brush or plate setup begins to wear and age, electrical resistance increases. As resistance to the current flow increases, so does heat.
“You have two contact surfaces coming together and passing current through this mechanical connection,” Graham says. “There is electrical resistance between those contact points. The amount of electrical resistance is going to vary greatly depending on the design and materials used.
“We’ve seen excellent life out of the materials selected,” he continues. “Abicor’s cycle tests and evaluations showed a robust product after many test iterations. There was little to no wear in the materials utilized, which helps provide increased longevity of the brushes and the material in and around that electrical connection.”
That, in turn, is going to provide a much more stable welding process over the long run because of low heat generation and high rate of dissipation.
In the future, Abicor plans to release a full line of Cyclone products. Versions with a collision sensor on the through-arm torches as well as a new wire brake integrated for touch sensing will be available. A water-cooled version is planned as well.
“Baseline welding is not something that would greatly benefit from a continuous rotation torch,” Graham says. “But if you’re using the full range of motion for the robot both in positioning and welding there are definite advantages to using this product.”