Yushin Servo Robot Improves Worker Safety
by Doreen Demers
Robotic Industries Association
Productivity and profitability are the benefits most often associated with molding robots, while one of the most important—safety—is sometimes overlooked. One large, automotive custom molder, however, installed a Yushin servo robot with the specific objective of protecting workers from a hazardous situation. And while the installation is entirely successful in that regard, the company simultaneously increased productivity as a side-benefit.
Con-Met, a.k.a. Consolidated Metco, Inc., Portland, OR, runs three permanent mold and die casting facilities, in addition to two plastics molding plants, including one in Bryson City, NC. With 163,000 feet of manufacturing space, the plant molds parts for the automotive and trucking industries, on 19 Toshiba injection molding machines ranging from 120 to 1,950 tons. Among its trucking contracts, Con-Met recently began molding a headliner for Freightliner Corp. Class 8 trucks. The polycarbonate part weighs 20 pounds, and measures roughly 30" x 72" x 1/4". Con-Met could not simply eject this large, thin-walled cosmetic part without sacrificing surface quality and dimensional integrity. During the early production phase of the job, an operator had to crawl between the platens of the 1,950-ton press and manually remove the part. Lanny Bullock, Maintenance Manager for Con-Met, said, "Manual part removal certainly increased the machine cycle, but we were most concerned about operator fatigue and safety. Even though there are many safeties on today's injection molding presses, it made us uneasy to see our operator standing there between the platens, and then weaving back out with the part. Once we had this job running, our first priority became automating part removal."
Con-Met is committed to systematically increasing its in-house capabilities in molding robotics and the automation of secondary operations, to improve operating efficiency and safety. The company had already achieved success with a Yushin VNII-850S servo-driven traverse robot on applications for smaller parts. An even larger 4-axis model would be required to remove the truck headliner. This style of robot was chosen not only for its ability to handle the specific application at hand, but also for its flexibility to handle a broad range of future part removal and positioning requirements over the life of the injection-molding machine.
The company installed a Yushin VN-II servo-drive traverse robot with an additional A-axis capable of rotating the part a full 180° around a vertical axis. Con-Met chose a servo robot because it provides a continuous range of axis movement which can be digitally programmed to meet the exact motion requirements of any part removal situation.
In this case, the robot arm descends between the mold halves as the press opens, then kicks forward to grab the part with several vacuum cups. While kicking back to pull the part from the mold, the A-axis rotates 45°, so that the part can then be lifted straight out between the tiebars. The robot then traverses over the side of the press and lowers the part onto a conveyor, which delivers it to an operator, who fixtures it for degating.
Bullock says he plans to modify the operation soon, so that the robot places the part directly in the degating fixture. With 0.004" repeatability, the Yushin robot is capable of meeting this precision positioning requirement. In addition, the robot's controller is designed to make program changes easy to implement. It includes many pre-programmed sequence options, and presents instructions, prompts, and error messages in plain English, bringing the programming of new sequences within the capabilities of most operators.
Con-Met is very pleased with this system, which has trimmed about 25 seconds from a 180-second molding cycle—roughly a 14 percent improvement. "We have seen an increase in production," said Bullock, "but even more important, we have provided our operator with an extra margin of safety." Bullock also noted that overall press cycle times have become more consistent, because the robot now controls the operation. This means that melt temperature is also more consistent, with reduced chances of part warpage or other quality problems.