Medicine, dentistry, and optometry encompass a broad spectrum of applications involving the direct electrical discharge machining (EDM) of medical and dental parts, tools, and implants, as well as the indirect use of EDM to produce tools, dies, and molds to create a myriad of prototype, production, and disposable parts and devices. EDM is useful in medical manufacturing for many reasons. Consider the materials typically used in this area. They include nitinol, titanium, cobalt chrome, and biocompatible or “body neutral” stainless-steel alloys, to name a few. Depending on hardness and temper, a material can be difficult to machine conventionally.

A major benefit of EDM is it can create complex shapes with high accuracy. Sharp corners, precision tapers, high L:D ratios, thin webs, and wall thicknesses are all routine in the world of EDM. Mirror-finish mold cavities for injection-molded plastic syringes and precision stainless-steel guides for bone saws are all possible thanks to EDM.

Top left: EDM can make surgical and dental hand tools comprising links, couplings, flexures, and ratchets such as shown. Top Right: These precision stainless-steel surgical saw guides were EDM’ed. Bottom right: The bone screw was EDM’ed out of titanium. Bottom left: Tiny gerotor pumps such as this are used worldwide for fluid transfer in medical, aerospace, and chemical applications. The inside rotor has one less lobe than the outer rotor. From left to right, a hardened, six-lobed trochoidal rotor (piston) rotates inside a rotating, hardened, sevenlobed case (cylinder), continually forcing the fluid ahead of it. This assembly is fitted into the valved pump body and this, in turn, is contained by the round outer case with the intake and outlets visible at 12 and 6 o’clock

Further, EDM is better suited than traditional machining to cut miniature parts. Conventional machining necessitates that holding forces overcome cutting forces. In small-parts making, simply holding or clamping parts can damage or even destroy them, while cutting pressures can bend or deflect thin sections and heat can change the material temper. EDM is a “non-contact sport,” so there is no physical force on a workpiece, greatly simplifying workholding and letting even delicate parts to be machined.

Among fast-growing applications are a vast array of surgical and dental hand tools and implements made up of links, couplings, flexures, ratchets, and other components. Other devices include closure clips and staples, insertion and spreading devices, as well as most of the tools, dies, and molds used in part production.

A good example of the use of wire EDM (WEDM) comes from a self-locking bone screw made from titanium. The EDM machine makes a series of wire-cuts radially, down the side and length of the screw, 120° apart. In use, the screw is threaded into a pre-drilled, “tap-size” hole in the bone with a hex key (the hex recess is sinker EDM’ed). The slot configuration lets a portion of the screw body flex inward when threaded under pressure. The compressed screw sections remain in tension and press outward like an expanding collet or mandrel, preventing the screw from loosening or moving.

Another interesting example of WEDM is a tiny implantable pump. All but the driveshaft of the assembly are EDM’ed. The pump is called a “gerotor” and is efficient with a long service-life. The inside rotor has one less lobe than the outer rotor. A hardened, six-lobed trochoidal rotor (piston) rotates inside a rotating, hardened, seven-lobed case (cylinder), continually forcing the fluid ahead of it. The assembly is fitted into the valved pump body, which, in turn, is contained by the round outer case with the intake and outlets at 12 and 6 o’clock.

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