Predictive Modelling of Cutting Force and its Influence on Surface Accuracy in Ultra-high Precision Machining of Contact Lenses

The successful application of contact lenses is heavily dependent on their form accuracy and surface integrity. Cutting forces play a key role in the diamond turning of contact lenses as they have direct influence on their form accuracy and surface integrity. In addition, the cutting forces are also important for other aspects of diamond turning of contact lenses such as tool wear. Therefore, the prediction of cutting forces in contact lens manufacturing is deemed essential for the sake of high quality optical surfaces. One way to manage the effect of the cutting force and reduce its negative effect on surface finish could be realised through optimisation and modelling techniques. There are several factors that affect the extent of the cutting force developed in diamond turning. An example of these factors is the selection of cutting parameters. The establishment of a statistical model for the reliable prediction of cutting forces which is linked to a specific optical quality characteristic could be a way for understanding the behaviour of cutting force and its effect. In this study, a cutting force model based on response surface statistical method is developed for reliably predicting the values of cutting force based on its relationship to cutting parameters in the high-precision machining of contact lenses. The model obtained from fifteen experimental tests determines the effects of cutting speed, feed rate and depth of cut on force and how various combinations of parameters affect cutting force and thus surface quality. Results indicate that feed rate is a significant factor in the generation of high cutting force and low surface roughness. The study concludes that high feed rates and high cutting speeds cause an increase in cutting force and thus adversely affect the quality of the diamond-machined surface in the high precision machining of contact lenses.