Study on Thinning of a Boron-Doped Polycrystalline Diamond Wheel-Tool by Micro Rotary W-EDM Approach

Abstract

This study presents a novel approach for using a micro rotary wire Electrical Discharge Machining (micro w-EDM) to thin the grinding-edge of a wheel-tool made from boron-doped polycrystalline composite diamond (PCD). For thinning the PCD, two discharge circuits (a Resistance-Capacitance (RC) circuit and a transistor) were used as power sources to obtain a grinding-edge of less than 10 µm in thickness and high surface quality. The wheel-blank is vertically mounted on a spindle and while rotating is thinned by micro w-EDM along a planned computer numerically controlled path. Experimental results verify that boron-doped PCD can be successfully thinned down to 5 µm in edge-thickness. The study shows it is possible to break (cut) diamonds of 10-µm grain size, leaving smooth surface-exposed diamonds at the cutting edge of the wheel tool. The dimensional and geometrical accuracy of the wheel-tool can be exactly controlled. Raman analysis reveals graphitizing of the PCD caused by local high temperature spark erosion at a peak of 1593 cm-1 in RC discharge circuit machining. The peak at 1332 cm-1 for the transistor circuit method indicates diamond sp3 structure. The surface degenerating layer produced by transistor circuit machining gives a suitably thin grinding edge with exposed diamond grains.

Electrical discharge machining of polycrystalline diamond: A review

“…42,43 Also, the extremely high temperature generated by the discharge sparks could lead to severe changes in the diamond structure, one of which is the graphitization of diamond inside the PCD, which can significantly improve the conductivity of the workpiece through the formation of a conductive layer on the top surface of PCD workpiece. 44–46 Sparking, as such, can also take place at the conductive diamond surface directly 47 to remove the diamond material in the form of graphite.…”

Successful fabrication of a convex platform PMMA cell-counting slide using a high-precision perpendicular dual-spindle CNC machine tool

“…When the diamond wheel-tool is formed by spark erosion, the polycrystalline composite diamond melts, and even partially evaporates due to the extreme temperatures of the process. However, discharge frequency is only 33 K Hz or less in RC circuits (Chen and Chang 2012), resulting in a longer pulse time. This leads to molten cobalt and carbon in the diamond matrix having enough time to uniformly precipitate and distribute on the PCD surface.…”