T&W Stamping in Ohio wanted to automate one of the most labor-intensive parts of its metal fabricating process: the tending of resistive welders. This is a tricky application to automate due to the welding equipment's electro-magnetic pulse that blank out robots' servo motors. But the company came up with a solution that paid for itself in less than four months, delivered a 40 percent increase in efficiency and freed up three operator functions.
"Using collaborative robots to tend resistive welders? To the best of our knowledge, this was not something anyone in the industry had done before," says Juan Rodriguez, Director of Automation with Crum Manufacturing, a Certified Systems Integrator of Universal Robots.
Installing the UR5 cobot to tend the resistive welders has freed up three operator functions at T&W Stamping. Frank Fowler is now programming the UR5 and conducting product inspection.
He was working with T&W Stamping in Youngstown, Ohio, a contract manufacturer primarily for the heavy-duty truck market who was in need of a reliable automation solution.
"We had just received a contract from a large customer of ours to manufacture powertrain brackets," says Craig Sivak, Executive Vice President & General Manager, T&W Stamping. "Volume on it wasn't huge -- about 40,000 parts per year -- but each part has eight weld nuts, so that's 320,000 welds that we would otherwise have to do manually."
Sivak and his team decided to investigate whether collaborative robots could handle the task. "With a cobot, we could keep our existing layout as we didn't need additional guarding around the cobot due to its built-in safety system," he says.
Universal Robots' UR5 cobot handles a 52 second cycle that includes picking up the part from the inbound conveyor, presenting the part to two welders, and placing the finished part on the outbound conveyor.
While it is common for large industrial robots to perform resistive welding, Rodriguez explains why this is not an application that small collaborative robots have historically handled.
"Resistive welders set off an EMP (eletro-magnetic pulse) that blanks out any kind of electronics in a certain radius. That's not an issue with traditional robots with big C-clamp end-of-arm tools where the robot is extremely far away from the point of strike," he says. "But with a small cobot that you try to fit nicely into an existing cell? That's a very different story."
Crum Manufacturing overcame this obstacle by grounding the robot and adding a non-metallic material to the custom-made end-of-arm-tooling which distanced the robot farther from the welder. Being able to use collaborative robots for this tricky task was not the only pleasant discovery at T&W Stamping.
"As our engineers gave us the initial quotation for the Universal Robot itself, we were stunned at the cost," says Sivak. "When looking at some of the larger robots, they're six figures; we were expecting a much larger number."
As the UR5 presents the part to the welder, a nut feeder shoots out a bolt to be welded to the part.
T&W Stamping was able to implement the entire cell for 30 percent less than the company would have spent on eight separate fixtures to position the part to present it to the welder. The contract manufacturer also freed up three operator functions, that are now doing more value-added tasks. "We're in the neighborhood of 40 percent more efficient than we normally would have been," said Sivak who also did the ROI calculations. "When we factored in the cost savings that we didn't have in the other fixtures -- and more importantly, the labor dollar and benefits saved with less operators -- payback was less than four months."
Vision-Guidance Ensures Exact Welds
"The UR cobot picks the part up right on the datum point, which is very important because it's being the fixture for the part itself," explains Sivak. "Once the UR robot picks up the part, it knows exactly where each and every hole location is."
The part handled in the cobot application is a heavy gage bracket for a Class 8 truck powertrain. It has 8 nuts welded onto it.
The part picking is guided by a vision camera from Cognex above the conveyor. With that guidance, the UR5 places the part in the first of two resistive welders, which carries out the first four welds as weld nuts are placed on the part by a vibratory nut feeder.
After the first four welds are performed, the UR5 rotates the bracket and moves it to the second welder that completes the final four welds. The 52-second cycle concludes as the UR5 moves the part to a second Cognex camera above the outbound conveyor that checks that the part has all eight weld nuts, that they're in a correct position, and that they all have threads.
Product Consistency with No Downtime
T&W Stamping runs eight-hour shifts, five days a week. The UR5 typically operates at 60 percent capacity and has been in operation for more than two years.
"The benefit that we see from installing the UR robot really is consistency. It does a fantastic job," says Sivak. "We haven't had any production issues or downtime with it. If we didn't have the robot, there would be four operators in that cell managing the eight fixtures to get the weld nuts on that part."
Now just one operator is needed to tend the cell. The operator, who had no prior robotics experience, took a three-day training course in how to operate and program the UR5 and is now in charge of product inspection and cobot operations.
Vision guidance provided by Cognex cameras ensures the UR5 picks up each bracket on the datum point and that each weld is performed correctly.
Developing the robot cell for T&W is an accomplishment Juan Rodriguez does not hesitate to call a homerun. "These resistive welders are more than 30 years old. Being able to find a way to interface these with brand new cobot technology is a big win both for us and the company," he says. "We will definitely see more integration of Universal Robots with resistive welders and with welding equipment altogether."
T&W Stamping has now started to look at new tasks that cobots could handle.
"We produce oil pans with components resistance-welded into them. Because of the size and configuration of the part, it would be very difficult to automate with resistance welders," says Sivak who is instead looking at MIG welding. "Our intention is to use a UR robot to fixture the components into the part, as well as put a torch on one and do the MIG welding with that," he explains. "This will be a new process for the robot as opposed to what it's doing today, as it will actually be doing the welding itself."
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