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JUL/AUG 2013  

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News/Features: EDM Notes

Micro sinker EDMing requires part manufacturers to optimize a host of areas to achieve success, such as applying new technology, developing new machining parameters, mastering electrode production and managing electrode wear.

Figuring out micro-sinker-EDMing is no easy task. As electrodes shrink, challenges grow, including maintaining the proper spark gap, minimizing electrode wear and determining the correct power settings. Plus, experienced EDMers know that using graphite electrodes can turn your hands black.

When micromachining, a wire EDM offers distinct advantages. It can cut complex contours, meet tolerances of ±0.0001" and impart surface finishes of 0.18µm Ra and finer. Also, in a properly executed operation, the wire never touches the workpiece, eliminating cutting forces and enhancing accuracy.

While writing this column on wire EDMing best practices, we learned that the term “best practices” has fallen out of favor. Earlier this year, Forbes magazine editors included it in a collection of 45 phrases they called “the most annoying business jargon.” They also judged best practices “the single most pompous confection the consulting industry has ever dreamed up.”

Effectively controlling the spark energy of an EDM’s power supply is critical to meeting cycle-time and part-accuracy requirements for all sinker EDM applications. But it’s especially important when micro-sinker-EDMing because a lack of control causes more electrode wear, and—in the fine-feature micro world—when you lose a little, you lose a lot.

Theoretically, any insulating liquid can be used as a dielectric fluid when EDMing to allow the spark to cross the gap between the electrode and workpiece, and vaporize material.

MicroEDMing has made major strides in recent years, both in terms of the equipment used to perform it and the quality of parts shops are able to make using the process. MICROmanufacturing asked several experts for their thoughts on the most important improvements made in microEDMing over the past 5 years. They identified several, from machine design to electrode materials to wire-threading capability.

When it comes to micro moldmaking, there’s only one good way to create the smallest cavities and other features, according to Dennis Tully, president of Miniature Tool and Die Inc., Charlton, Mass. “Using sinker EDMs, we can make feature sizes smaller than anything we’ve managed to successfully produce using other removal methods,” he said. “With conventional milling, there are limitations on how low you can go on cutter size.

Electrical discharge machines have been used commercially for more than 30 years, with the tool and die industry being the first to adopt the technology. Since then, other manufacturing sectors have steadily added EDMing to their parts-producing capabilities.

Small-hole EDMing is performed with a spinning electrode. Shown is a 0.040"-dia. hole being EDMed in a 0.5000"-dia. ball bearing.

Preparing start holes is a critical micromachining operation. One common method is sinker EDMing start holes prior to running a wire EDM operation. Appropriate electrode preparation and workpiece fixturing are vital to the successful machining of a start hole. The following case study examines how microscale start holes were machined in a challenging application.

Magnified view of finished holes after wire EDM process. All photos courtesy Makino.