Worth Considering:
Vacuum Chucks for Electric Discharge Machining

NIST Team Develops, Tests Prototype; Concept Free for Adoption by EDM Suppliers, Users

Choosing the right tool, goes the indisputable maxim, can reduce even the most demanding manufacturing jobs to manageable proportions. In the case of electric discharge machining, the ideal tool for certain high-precision cutting jobs could very well be a straightforward vacuum-chuck technology. Better yet, the technology—an inexpensive combination of workpiece holder and pump add-on—is available for adoption, at no cost, from the National Institute of Standards and Technology.

The concept of adding a vacuum chuck and a vacuum-creating aspirator pump (common equipment in chemistry labs) to EDM equipment was born of equal parts necessity and frustration. A team of NIST and university scientists and an instrument maker wanted to eliminate the time-consuming chore of making elaborate fixtures for large, thin parts and for parts vulnerable to distortion by vises, clamps, or other two-surface clamping methods. The team came up with a surprisingly simple, single-surface clamping approach that overcomes many limitations of standard tooling. Used in the NIST machine shop, where one-of-a-kind scientific equipment is fabricated, the vacuum chuck met the inventors’ performance requirements. On the basis of their experience, team members believe their idea has merit for a range of EDM applications.

Expected Benefits: Anticipated advantages of a vacuum chuck for EDM equipment include:

• simplified holding of otherwise hard-to-hold workpieces,
• no tooling marks,
• fewer setups,
• faster cycle times,
• higher yields, and
• expanded capabilities of EDM equipment.

Innovation at a Glance: At its most basic, the NIST innovation is largely a matter of plumbing. The team plumbed an aspirator—the source of vacuum for various laboratory filtering techniques—into an EDM system. A tube situated after an existing pump, which is part of the EDM apparatus that continuously drenches the workpiece with an insulating (dielectric) fluid, siphons off a portion of the circulating fluid. As the liquid shoots down the tube, it creates a vacuum in the hose that connects the tube to the workpiece holder. The suction created by the vacuum holds the workpiece firmly in place. Closing a valve on the tube allows air to enter the chuck, breaking the vacuum and freeing the workpiece.

Akin to using machinable chuck jaws in a lathe, a vacuum chuck in EDM equipment can be faced off in the same setup as the work piece. This increases the accuracy of EDM processing.

Is It Practical? EDMs usually are equipped with one or more plumbing circuits that filter and feed dielectric fluid. Many circuits run continuously, at pressures and flows adequate for an aspirator.

Will the Chuck Hold? Vacuum chucks are rarely used in milling, turning, and other machining operations that typically exert high cutting forces. In the case of EDM, however, tooling forces are minimal—below the threshold of the vacuum created by a pump of sufficient capacity. Best of all, an aspirator-enabled vacuum chuck accommodates continuous, 24-hour-a-day machining.

Can the Vacuum Technology Withstand Water and Debris? Yes. Unlike piston pumps and membranes that also can be used to create a vacuum, an aspirator is insensitive to even large volumes of water. Dirt and grime, normally present in a machining environment, do not affect performance.

How Much Would It Cost? Incorporating an aspirator into the design of a commercial EDM machine probably would require an uncomplicated design change. To retrofit existing machines, the innovators estimate, plumbing an aspirator in a manner akin to the set-up in the picture might run several hundred dollars, including the cost of the aspirator.

Is the Vacuum Chuck Technology in the Public Domain? A federal technology agency, NIST works to provide U.S. industry with the world’s best technical infrastructure. The NIST laboratories supply companies and R&D organizations with measurements and a host of related tools and services that are used in many economic sectors and technology areas. Part of the Commerce Department, NIST aims for broad use of its outputs. Intending to make the invention widely available for private-sector examination, NIST has placed the vacuum chuck technology in the public domain.

To Learn More: Organizations or individuals interested in learning more about the concept of adding a vacuum chuck and aspirator pump to electric discharge machining equipment should contact the NIST members of the team that developed and implemented the technology:

Paul Brand, (301) 975-5072; paul.brand@nist.gov
Dwight Barry, (301) 975-6502; dwight.barry@nist.gov

Created: 6/21/02
Contact: inquiries@nist.gov

Return to Fact Sheet Page