Performance of diamond inserts in ultra-high precision turning of Cu3Cr3Zr alloy

Copper–chrome–zirconium (Cu3Cr3Zr) alloys can be used in the optics industry to make mould inserts for injection of thermoplastic optical parts such as lenses and windows. The fabrication of optical mould inserts is usually achieved by diamond turning in order to obtain necessary optical surface finish and high form accuracy. This study was undertaken to investigate the tool wear characteristics when ultra-high precision machining of Cu3Cr3Zr with mono-crystalline diamond inserts. In this work, standard non-controlled waviness diamond inserts having nose radius of about 1.5 mm, rake angle of negative 5°, clearance angle of 5° and included angle of 60° were used to produce a flat mirror of 50-mm diameter. Wear patterns occurring on the tool flank and rake faces were observed. Diamond tool performance is discussed in terms of possible wear mechanisms. In addition, the tool wear is associated with the acoustic signals emitted during machining. The preliminary results from the SEM analysis show that abrasive wear is a dominant mechanism especially at low feed rates. The study yields some recommendations on the best combination of machining parameters that will result in maximum material removal rates with relatively smallest possible damage to the tool edge.