Ultra-High Precision Machining of Optical Mould Inserts
Metal cutting techniques that result in surface roughness in the ranges of few nanometres and form accuracy in the sub-micron region are categorised as ultra-high precision machining (UHPM). In this technology, diamond inserts are used to shape components from various non-ferrous materials by lathe operation. These components are usually optical objects such as flats, convex and concave lenses made from aluminium, copper alloys, silicon, germanium, etc. Diamond turning can also be used to produce mould inserts for plastic optics injections. Optical injection moulds are usually made from high strength aluminium such as AA 6061 and beryllium copper alloys. These materials are easily machined by diamond tools. However, for high requirements mould inserts used for glass moulding, the mould inserts must be made from ultra-hard materials such as tungsten and silicon carbides. UHPMof these materials can be achieved using ultra-high precision grinding spindles. This presentation will highlight the capabilities of precision engineering when makingoptics and mould insert manufacturing. Optical components, including freeform,with form accuracy of about 0.1 um and surface roughness of 1 nm can be produced with diamond machining. Currently, we are busy investigating the process of diamond turning when machining a special grade of aluminium produced by rapid solidification and spin melting. This aluminium grade which enjoys elevated tensile strength (600 MPa) can be used as a mould material for injecting plastic optics.
Keywords - Optical mould inserts, diamond turning, ultra-high precision grinding