Improvement of tool life of a commercial drill bits by cryogenic treatment while machining widmanstatten Ti-6Al-4V

Abstract

In this study, the performance of Ø 8 mm WC-Co (10%) drill bits with a TiAlN coating was tested for machining of Ti6Al4V alloy with a Widmanstatten structure. In order to improve the tool life, cutting tools were subjected to deep cryogenic treatment. In total, three groups of tools were prepared for this study. The first group was used for reference as the supplied state; the second group was subjected to 24 h deep cryogenic treatment at −196 °C, and the third group was subjected to 24 h deep cryogenic at −196 °C, additionally was tempered 2 h at 200 °C. Machining experiments were done by drilling and a set of 60 holes were drilled with each drill bit, and tool wear were observed and recorded with a stereo microscope. Additionally, Scanning Electron Microscope (SEM) and Energy Dispersive Spectroscopy (EDS) analyses were carried on to understand the tool wear better. The microhardness of Cryo-treated and tempered cutting tools hardness increased up to 20 Hv (about 1%), and the toughness value did not change significantly. Cutting performance was observed by measuring the cutting forces during drilling experiments. According to these results, deep cryogenic treatment on WC-Co-based inserts decreased cutting forces by approximately 7% compared to the reference drill bit, which affected the cutting tool life. The dominant wear mechanism was Built-up edge (BUE) formation, and cryo-treatment lowered the BUE amount 8% and cryo-treated and tempered drill bit 45% compared to the reference drill bit.