Other common medical applications using WEDM range from the standard and custom wire-cut serrations found on specialty grippers, forceps, hemostats, and gripping tools that rely on flexures to the precision, straight, serrated, and scalloped cutting edges of scrapers, biopsy tools, and rotating cutters used to clear blocked arteries.

Dental and orthodontics also rely heavily on EDM. Except for the arch wires, almost all components of stainless steel orthodontic braces are investment cast. The cavities for these master models are typically produced in hardened mold steels in a sinker (ram or vertical EDM) to tolerances of +/- 0.0002 in. with good surface finishes. Special tools are needed to fit, adjust, or remove these dental braces. In production, the entire tool is wire-cut from a larger blank using two relatively simple 2D programs and a single 90° index. Polishing and plating operations finish the device. Thousands of such parts are required by dentists and orthodontists worldwide every year.

1. EDM works well in the production of surgical staples. 2. Gerotor pumps are made using EDM. Here, the pump’s intake port is on the left and the discharge port on the right. Both the (grey and the yellow) bodies rotate, but on different centerlines. During rotation, the expanding pockets create a vacuum causing fluid to be drawn into the pump (9 o’clock). As rotation continues, the pockets expand and eventually reach their maximum volume (12 o’clock), at which point the fluid becomes sealed-off from the inlet side of the pump. Further rotation causes the pocket volume to decrease, forcing the fluid out through the discharge port (3 o’clock). 3. This stainless-steel surgical instrument used in spinal repairs has made back surgery much less invasive. Many of the components in this complex assembly were made using EDM, without which this design would not have been feasible. Photo courtesy of MacKay Manufacturing, www.mackaymf.com Select figures to enlarge.

In a different slant, EDM prototyping is a good way to economically create first parts to better understand a design. Imagine you are inventing a new kind of surgical staple. The device is about 5-mm square and 0.5-mm thick and the material is aircraft-grade 6Al4V titanium, which is almost impossible to hold and mill conventionally. The requirements for excellent edge-quality and sharp details rule-out laser-cutting and abrasive waterjet. In an easily executed EDM process, five “stacks” of eight parts or 40 identical prototype staples are wire-cut from a solid block of material and are ready for testing in only 3 hours, 40 minutes or 51⁄2 minutes each.

Should changes in geometry or dimensions be necessary, just edit the program accordingly and in under four hours, you have a completely new batch of 40 parts in under four hours. Or, make four program edits and cut five different versions or dash numbers of the same part. In production, the stack height and length can be increased to produce more parts without interruption. Additionally, the use of a coated wire for increased speed might be an option.

Thanks to:
Accelent, MA
Bedra GmbH, DE
MacKay Mfg, WA
Makino Inc, OH
Spectrum Mfg, IL