Innovative ways to grip the ungraspable

Among vises, collets and chucks, there’s no shortage of reliable methods to secure workpieces for machining. Still, some parts are simply hard to hang on to. Clamping too aggressively on thin walls and delicate geometries causes warpage and accuracy problems and may lead to scrap. Fortunately, a number of workholding suppliers have developed innovative ways to grip the ungraspable.

IBAG North America, North Haven, Connecticut, is one. President Bill Popoli said using a Witte Ice-Vice Freeze Chuck can be an effective way to clamp thin, flat parts when other methods fail. “We offer two types. The first works much like an ice hockey rink, where coolant is circulated through a flat chuck and back to a refrigeration system. You spray the face with a little water mist, set the parts on and energize the system.”

Blue Photon’s photo-curable adhesive and patented gripper system is strong enough for a variety of machining applications. Image courtesy of Blue Photon Technology and Workholding Systems

Freezing takes around a minute, he said, depending on the size and quantity of the parts. Yet the custom-made system is admittedly expensive. A lower-cost alternative is an icing chuck that uses the Peltier effect. It works by applying electrical current to an internal thermocouple device, rapidly cooling the device and the surrounding area. Chucks with a 250mm × 150mm working area are available. There’s also a system that uses compressed air and the Venturi effect to rapidly cool the chuck surface.

With an accuracy of ±3μm and holding power up to 150 N/cm², ice chucks are surprisingly robust but create no external forces that may cause workpiece distortion. It’s possible to cut pockets in the surface of the chuck, making it easy to position parts, Popoli noted.

“We also offer an alloy that can be used to encapsulate parts prior to machining,” he said. “It’s a white metal with a melting point of around 170º F. You set the part in a potting fixture or premachined cavity, pour the melted alloy around it and machine as usual. It’s a good, low-cost solution for low-volume production of thin-walled or irregularly shaped workpieces.”