Reduction of diamond-coated cutting tool wear during graphite cutting

To investigate wear characteristics of diamond-coated inserts when cutting carbon based materials, lathe-turning tests were conducted using diamond-coated cemented carbide inserts and a graphite round bar at various cutting speeds in an air or a nitrogen blowing atmosphere. Tests were conducted with constant cutting length, but at different cutting speeds of 23-495 m/min. Wear to the insert was observed using a microscope after the tests. Then the wear volume was measured using coherence scanning interferometry. After cutting in air, only small wear volume was found for low speeds of 36 m/min or less and for high speeds of 328 m/min or more, but greater wear volume was found for medium speeds of 54-208 m/min. During cutting in air at high speeds, oxidation of diamond was thought to be a main wear factor because sparks were observed in the abrasion powder from the graphite round bar. Wear to the diamond-coated insert decreased with shortened time of contact to the hot graphite chips. At low speeds, the wear volume decreased concomitantly with decreased cutting speed, probably because of decreased heat generation, which is proportional to the cutting speed. For most cutting speeds investigated, cutting with nitrogen blowing produced less wear than cutting in air. The tendency was remarkable at 54-208 m/min. These results indicate oxidation as the main cause of wear to the diamond-coated insert during graphite cutting in air. Wear can be reduced considerably by cutting in an atmosphere with blowing nitrogen.