Servorobots can handle the hot stuff in thermoset insert molding

Semco Plastic Co. Inc., a St. Louis-based custom molder, can tell you the problems resulting from manually handling inserts are intensified when hot thermosets are involved. Semco Plastics also can tell you automated insert loading is a good solution. By installing servorobots in a difficult thermoset molding application, its cycle times are now both quicker and more consistent. Part quality has improved, and the chance of mold damage has been reduced while scrap has fallen by 8.5 percent. Of greater importance, operators can work more safely and more comfortably.

"We've achieved significant cost savings directly related to improved machine timing," says Charles Voelkel Jr., vice president of production at Semco. "Previously, the press cycle was driven by the operator. Now it's driven by the robot, which is much faster and absolutely consistent."

Founded in 1944, Semco operates a 250,000-sq-ft facility, serving markets that include hardware, appliances, consumer goods, medical, and outdoor products. The company has in-house engineering and tooling capabilities, 25 presses ranging from 55 to 1000 tons for thermoplastics and thermosets, and it performs value-added secondary operations like machining, assembly, decorating, and packaging.

Semco molds a variety of phenolic handles for high-temperature applications. The handles, each with a cosmetic upper surface and a deeply ribbed back, are produced in sizes up to 17 inches long and weighing more than 11 oz. Four blind-hole threaded brass inserts are molded into each part, two at each end. The parts are molded on three Van Dorn 286-ton hydraulic clamp machines. Total shot sizes range up to 34 oz.

Operators originally loaded the eight inserts per mold by hand. Because the molds are maintained at a temperature of 420F, the operators wore gloves, which made insert handling difficult and slowed the process down. Semco achieved just 45 to 50 cycles per hour with cycle times averaging anywhere from 72 to 80 seconds.

According to Voelkel, even though Semco's operators are skilled and conscientious, they did not always place the inserts accurately, hampered as they were by the gloves and the discomfort of working close to the hot molds. Inserts not properly bottomed in their recesses would occasionally fall out as the mold closed and could cause mold damage. Furthermore, the resin's residence time in the barrel varied with the operator's work pace, resulting in irregular melt temperatures and uneven part quality. Thermoset parts are not directly recyclable, so every bad part was a loss, including the inserts, which cost $.10 each.

Robots to the Rescue
Semco selected an all-servo VN-350 from Yushin America. The company already owns 12 Yushin robots used for some of its thermoplastic molding. Yushin's engineers designed special double-ended end-of-arm tooling (EOAT) for part removal and insert loading, plus separate pre-loading stations for the inserts. Special insulating plates were fabricated and installed in the robots' risers to isolate them from the heat of the molding machines.

Now, an operator manually places the inserts in the pre-load station. This occurs outside the machine's safety gates during mold close, so the operator is safe and has ample time to do it right and inspect the work. The servorobot traverses over the machine's guarding and acquires the inserts from the pre-load station. Acquisition is confirmed with verification circuits on all grippers.

The robot then moves back, waits for the mold to open, descends, grips the molded parts, and kicks back to extract them from their cavities. On the stationary mold side, the end-of-arm tooling engages hardened docking pins, ensuring proper alignment as the robot places the inserts into the mold recesses. The robot then releases the inserts, rises out of the mold area, and deposits the molded parts on a conveyor, which delivers them to the operator for flash removal and packing. Maintenance requirements are minimal, and the robot's mold programs are stored on integrated-circuit data cards, so operators simply choose the right program from a menu during mold changeovers. Nevertheless, Semco sent maintenance technicians to Rhode Island for training at Yushin. They came back with a greater level of expertise and a deeper understanding of how to optimize robot functioning.

"People must be properly trained to back up a servorobot and get the maximum payback out of it," Voelkel explains. "You can't just buy a robot and think it's going to run itself." Semco has trained five in robot programming, ensuring that it is a widely distributed skill and not a specialty. As any custom molder can appreciate, business dictates frequent changeovers. So if you're thinking of automating, Voelkel says easily programmable and versatile servorobots like his are the way to go whether the parts are piping hot, like his, or cool, like yours.