Superhard versus superhard

Toolmakers combine technologies to meet growing demand for PCD (Poly-Crystalline Diamond) tools. The cutting edge geometries and final dimensions of cutting tools are typically produced on CNC tool and cutter grinders. Tools with PCD cutting edges, however, pose a challenge. Grinding PCD pits the hardest known substance (diamond) against an equally hard grinding wheel. The resulting virtual standoff consumes excessive time and wheels.

“In PCD grinding, what you are doing is taking two substances of equal hardness and trying to have one remove the other, as result you end up having an almost one-to-one wear, which becomes very expensive.”

Electrical Discharge Grinding (EDG), is an efficient and accurate way to remove PCD when manufacturing or regrinding PCD tools. One way to limit expense is removing PCD via electrical erosion, in the form of either Electrical Discharge Grinding with a tungsten-copper disc or with a wire-EDM. The cobalt binder in PCD acts as a conductor for the electrical energy. The main benefit of using an EDG or a wire EDM to shape PCD tools is cost savings: you are using a noncontact, electrical charge to remove material instead of wearing down a diamond wheel.

PCD cutting edges can be shaped via Electrical discharge grinding (EDG) with a tungsten-copper disc. The cobalt binder in the PCD tool conducts the electrical energy, and the electrical charge removes the diamond material without any hard contact. 
Wire EDM can offer an advantage compared to rotary erosion because it can create small inside radii and other complex tool features that a rotary disc can’t. On the other hand, the rotary electrode is a thick, stiff piece of tungsten copper that, unlike a wire, does not offer any deflection. It is much more rigid erosion, and all things being equal, you have a faster material-removal rate.