Cutting forces and acoustic emission in the diamond turning of rapidly-solidified aluminium

Ultra-high precision machining (UHPM) is used intensively in the optical industry for a wide range of products. UHPM processes fall under the nanotechnology regime. Aluminium alloy is the common material of choice for optical moulds and surfaces. Improvements in ultra-high precision machining aim to increase productivity while maintaining acceptable tool wear rates (within five microns flank wear) and desirable surface quality (within 10 nm Ra). Newly-modified grades of aluminium alloys characterised by superior physical and chemical properties produced through rapid solidification have gained considerable traction as an alternative to traditional aluminium alloys. This paper investigates the machinability of rapidly-solidified aluminium, RSA 905, by varying cutting parameters in single-point diamond turning (SPDT) and applying monitoring techniques through force measurement and acoustic emission detection to optimise the machining quality process and provide an indication of the expected tool wear. There was a direct correlation between the level of tool wear and the corresponding acoustic signals and measured forces. Acoustic signal root mean square (RMS) within 0.12 V and average force within 0.7 N signified higher wear, above five microns, and deterioration of surface roughness, above 10 nm. Single-point diamond turning requires constant monitoring and operator intervention. Quality control is usually implemented in stages and can be as often as after every pass. A baseline was established from which a defined deviation can be used to indicate a reduction in machining quality when the workpiece and tool should be inspected and possibly replaced.