Experimental and theoretical research on drilling epoxy granite using coated and uncoated carbide spiral drill bits

Abstract

Hard materials with superior physical and mechanical properties, such as epoxy granite, are used in the base of machine tools and precision instruments, where vibration damping properties of epoxy granite has been used. However, epoxy granite drilling is still in its incipient stage of research, due to its heterogeneity, anisotropy and brittleness. The main objective of this study is to analyze the effects of the drilling process parameters, i.e. drilling forces and torques, wear and surface roughness during the drilling process of epoxy granite. It was studied diamond drill bits, twist drill bits with brazed carbide plates, spiral solid carbide drills (with different apex angles of 110°, 120° and 130°). Also were studied spiral solid carbide drill bits coated with (TiAl)N and solid carbide spiral drill bits coated with (TiAl)N + NbHfTi. The experimental data showed that, forces acting on the flank face are greater than the forces acting on rake face of the drill bits. It was also concluded that, coating the carbide spiral drill bits with (TiAl)N + NbHfTi has improved tool life in comparison with uncoated spiral solid carbide drill bits and the spiral solid carbide drill bits coated with (TiAl)N. Wear of uncoated drill bits takes place faster (1.5–2 times) than coated drill bits with (TiAl)N, and up to 3–4 times faster than the drill bits with (TiAl)N coating + NbHfTi treatment.