A comparison of five categories of carbon-based tool coatings for dry drilling of aluminum

Due to high costs, infrastructure demands, and environmental concerns, there is motivation to move toward dry machining, i.e., machining without the use of metal removal fluids (MRFs). Aluminum, as used in light-duty engines and transmissions, is particularly difficult to machine dry because of its tendency to adhere to the tool as temperatures rise. Machining performance suffers when machining is done without MRFs. For example, tool life during drilling is reduced from > 10,000 holes/drill with MRF to about 40 holes/drill without MRF (dry). The challenge, then, is to reduce the heat build-up through improved tribological surfaces on the tool. In this study a variety of carbon-based coatings on drills were tested to determine their performance in both bench and machining tests. Coatings included metal-containing carbon, graphitic, hydrogenated and hydrogen-free diamond-like carbon, and diamond. The best coatings gave a > 100-fold improvement in performance compared to an uncoated drill.