Magnetic chuck attracts moldmaker

June 1, 2001
Forget all the clamps and straps when EDMing mold parts, says a shop using magnetic workholding.

Forget all the clamps and straps when EDMing mold parts, says a shop using magnetic workholding.

Magnetic workholding from Hermann Schmidt is an integral part of Ivanhoe Tool & Die's automated EDM operations.

A System 3R robotic handling system holds Hermann Schmidt magnetic chucks for automatic loading and unloading.

Ivanhoe Tool & Die uses Charmilles ram EDMs equipped with System 3R robots to burn parts for plastic injection unscrewing molds.

There was a time when shops doing EDM were warned about using any kind of magnetic workholding because it could adversely affect flush and operating conditions. But those days are gone thanks to the advanced technology of not only today's EDMs but also the magnetic systems themselves. As a result, the workholding method is slowly replacing cumbersome setups and providing shops, in particular moldmakers, with easy-to-use, streamlined, and ready-for-automation systems.

One such moldmaker benefiting from magnetic workholding is Ivanhoe Tool & Die in Thompson, Conn. The shop specializes in the design and building of plastic injection "unscrewing" molds that produce parts with threads. Some examples include caps for shampoo, liquid detergent, and soft drink bottles. As part of its production process, the shop burns everything from cavities to cores on two fully automated ram EDMs equipped with magnetic workholding.

What Ivanhoe uses are fine-pole magnetic chucks for palletized referencing systems. The chucks, from Hermann Schmidt of East Hartford, Conn., have macro reference plates affixed to their undersides. The plates adapt to Ivanhoe's System 3R Workman robots, which keep two Charmilles Roboform EDMs supplied with electrodes and parts.

In total, the shop has thirty-two 6 6-in. Herman Schmidt chucks, or pallets — 16 for each EDM. Once loaded with workpieces, these pallets are stored in the robot systems until it is time to burn. The setup provides around-the-clock operation for Ivanhoe.

"Without magnetic workholding," says Warren Salvas, EDM supervisor at Ivanhoe, "parts would have to be clamped or strapped onto plates. And we would be unable to automate our EDM operations."

Also, because these are fine-pole magnetic chucks, they let users burn parts closer to the chuck surface without interrupting the EDM operation. Instead of increased power, these magnets secure parts using more poles, which does not inhibit flushing.

"It used to be," adds Peter Schmidt, vice president at Hermann Schmidt, "that shops would have flushing through their magnetic chucks. This often involved connecting lines to the chuck, which limited any kind of automated pallet changing."

Ivanhoe's square-shaped magnetic chucks have rails mounted on all four sides. These rails are referenced to the chuck's center, and the X, Y, and Z dimensions on all of Ivanhoe's chucks are matched to within 0.0002 in. Accurately located rails and matched dimensions let Ivanhoe situate its parts in four corners and probe just one chuck instead of all 32. "They are all exactly the same," says Schmidt. "Everything on the chucks is flat, parallel, and square — and coupling them with the 3R system adds repeatability." The moldmaking shop loads multiple pieces on its magnetic pallets, trying to stay with an even number or as many as will fit. Sometimes this amounts to 30 pieces on one pallet or as little as one or two, says Salvas. Ivanhoe's previous magnetic chucks were round and had only two rails. In addition, they weren't fine pole, so parts got pulled in and removing them was difficult, says Salvas. But what was also detrimental was that they were over 2-in. thick, meaning the shop lost some of its Z-axis travel on the EDMs. With the Hermann Schmidt pallets measuring 1 1 /2-in. thick, the shop gains back some of that lost travel.

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