Diamond tool wear during ultra-high precision machining of rapidly solidified aluminium RSA 905

Aluminium alloys such as AA 6061-T6 are used to create forming optical surfaces in mould cavities for the injection of plastic optical components. However, 6061-T6 aluminium is characterised by its coarse microstructure which results in inconsistent performance of the cutting tool in terms of tool wear. In this study, a modified grade of 6061 aluminium, called RSA 905, is diamond machined. RSA 905, which enjoys a finer microstructure achieved using a rapid solidification melting process, is diamond turned at different feed rates and a constant cutting speed and depth of cut. This paper reports on the tool wear mechanisms encountered when turning the rapidly solidified aluminium grade using mono-crystalline diamond inserts on an ultra-high precision machining centre. The cutting speed and depth of cut were set at 2000 rpm and 25 μm, respectively. The tool wear on the flank and crater surfaces was observed using scanning electron microscopy. In addition, acoustic signals emitted during machining were acquired to monitor the tool wear. Although the RSA 905 alloy possesses an increased ultimate strength, its diamond-machinability is found to be high and tool wear is absolutely low even after relatively high cutting distances. However, the tool wear measurement results show that the tool wear tends to be more intensive at the middle value of the feed rate.