EFFECT OF THIN FILM COATINGS ON DRILL BIT

Abstract

In view of the lack of reliable predictive wear theories, this paper was set up to study, experimentally, the effects of PVD surface
coatings namely TiAlN, TiN+TiAlN, AlCrN on carbide twist drill bit by drilling the mild steel as work material. The use of
coatings for cutting tools is nowadays widespread, however, wear mechanisms are not always understood, and a clear
relationship between coating’s laboratory characterisation and operational machining performance are seldom assessed. The
possibility of correlating the laboratory characterisation results with real tools operational performances would be a key issue in
reducing development costs of innovative coatings. High oxidation resistant coatings, such as TiAlN, are used extensively in
global manufacturing for reducing production costs and improving productivity in such aggressive metal-cutting operations. In
this investigation, the performance of uncoated, TiAlN, TiN+TiAlN and TiN+AlCrN coatings was assessed on DIN6357K Carbide
twist drill bit used to machine mild steel. As part of the study, the experimental method was used to characterise the performance
of the twist drill bit by measuring of the progression of major flank wear. It showed that a multi layer TiN+TiAlN coating and
uncoated drill bit failed to outperform TiAlN and AlCrN coated twist drill bit when machining mild steel under aggressive
machining conditions. In the case of the TiAlN and AlCrN coated twist drill bit, an improvement in the tribological interaction
between the coatings and the workpiece and also increased oxidation resistance resulted in a significant reduction in material
transfer at the cutting edge. The above results are discussed in terms of the major flank wear.