Challenges in the micro-EDM world

Say “EDM” and most manufacturing folks think mold, tool and die work. Yet sinker, wire and hole-popping EDMs are often employed in conjunction with, or as alternatives to, traditional part-making processes, such as milling and turning.

EDMing is generally much slower than chipmaking processes, which limits its use to parts where the metal is too hard, the geometry too difficult or part features too small for conventional cutting tools.

This microprobe uses the “prespark” electrical fields generated during EDMing to build 3D models of the workpiece. Image courtesy SmalTec International.

Some parts, especially those in the medical and semiconductor industries, meet all three criteria and arrive on the doorstep of someone like Eberhard Bamberg, president of Viteris Technologies LLC, Salt Lake City. Bamberg designs, builds and operates micro-EDMs and defines “micro” as anything smaller than 0.0004″ (10µm). And while his definition is more restrictive than what most in the EDM community consider micro (objects smaller than 1mm), Bamberg’s equipment addresses the more common problems associated with micro-EDMing, starting with the electrode.

“From a mechanical point of view, getting the right tension on a wire measuring 0.002″ and smaller is extremely challenging,” Bamberg said about the typical wire size the company uses. “There’s almost no margin for error, especially with tungsten, which is what we typically use in this range.”

In addition to gentle methods of wire handling, Viteris also needed to develop its own spark generators, because the current-carrying capacity of electrodes in this size range is limited—a little too much on-time or amperage microspike and the wire is likely to blow apart.

An array of ultrasmall brass springs created with 0.0004″-dia. tungsten wire, one-tenth that of a human hair. Image courtesy Viteris Technologies.