Process adaptability and efficiency enhancement of electrical discharge machining for polycrystalline diamond hardbanding profiling

Abstract:

To address the low bulk stock-removal efficiency and severe grinding-wheel wear encountered during the mechanical grinding and profiling of superhard composites such as polycrystalline diamond （PCD） hardbanding， an experimental study was conducted into the process applicability and efficiency enhancement of electrical discharge machining （EDM） for PCD hardbanding profiling. Unlike hybrid processes in which electrical discharge and mechanical actions occur simultaneously within the same machining zone， and electrical discharge grinding using a rotating wheel electrode， the proposed method arranges electrical discharge machining and mechanical grinding as sequential， independent operations and allocates the machining allowance across three stages： EDM roughing， profile grinding with a 60-grit wheel， and finish grinding with a 400-grit wheel. The investigated PCD hardbanding consisted of thermally stable polycrystalline diamond （TSP） blocks embedded in a metal matrix. Firstly， the EDM responses of the metal-matrix material and TSP material were characterized separately. The EDM parameters for machining the composite surface were then optimized. Finally， the hardbanding was profiled by EDM and subsequently finished by mechanical grinding， and the combined process was comparatively evaluated against pure mechanical grinding and pure EDM alone. The results showed that pure mechanical grinding produced a surface roughness of 2.63 μm， but its mass removal rate was only 0.20625 g/h， resulting in limited machining efficiency. EDM achieved a mass removal rate of up to 1.23053 g/h， demonstrating substantially higher stock-removal efficiency. Although the EDM-processed surface exhibited a roughness of 16.62 μm and could not directly satisfy the surface-quality requirement， subsequent mechanical grinding with a small finishing allowance increased the overall mass removal efficiency by 160.2% compared with pure mechanical grinding， while reducing the surface roughness to 2.92 μm， a level close to that achieved by pure mechanical grinding. These results demonstrate that， after appropriate parameter optimization， EDM can be effectively applied to the high-efficiency profiling of superhard composites used in PCD hardbanding. The proposed process provides a technical reference for machining PCD hardbanding on drillpipe tool joints used in deep-well drilling.