Abstract
The superhard polycrystalline diamond (PCD) includes cobalt bonding, but it is difficult to remove the composited material in fabrication. Hence, an impulse-discharge is assisted by micron-scale abrasive flow to machine PCD surface. The objective is to understand how the impulse-discharge machining of conductive cobalt complements abrasive flow machining of non-conductive diamond in process. First, the rheological and bonding behaviour of loose-abrasive was analyzed in relation to electric field. Then, the surface machining procedure was modelled in relation to impulse-discharge energy, stress wave and removal force, etc. Finally, the non-conductive diamond integrity was investigated in impulse-discharge machining. It is shown that the electric field causes abrasive to aggregate and impulse-spark expansion promotes hydrated particle cluster to bond strongly and flexibly. When the resulted instantaneous stress drives loose-abrasive to flow towards the diamond surface through micron-scale removal force, the instantaneous temperature generates diamond graphitization and cobalt melting but abrasive flow improves diamond surface integrity. Although the surface electrode adhesion and residual compressive stress are higher with larger discharge energy, the diamond graphitization is reduced with grain refinement. The removal force and ratio are subject to impulse-discharge energy, electrode material and loose-abrasive size. As a result, the nanoscale-roughness surface with the material removal of 150% higher, and high diamond surface integrity can be achieved in short processing time.
Published Version
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