Ultra-Precision Cutting for ZKN7 Glass

Abstract

There is an immense need to obtain nanometric surface finish on optical glasses owing to the advantage of improved performance of the components. Thus, the use of ultra-precision machining becomes critical. According to the hypothesis of ductile machining, all materials, regardless of their hardness and brittleness, will undergo a transition from brittle to ductile machining region below a critical undeformed chip thickness. Below this threshold, the energy required to propagate cracks is believed to be larger than the energy required for plastic deformation, so that plastic deformation is the predominant mechanism of material removal in machining these materials. However, the mere use of ultra-precision machining for this brittle material would not yield mirror surface finish. Therefore, experiments were conducted using diamond cutting for machining ZKN7 glass. Based on the experimental work, a new strategy was proposed for obtaining nanometric surface finish and the cutting mechanism was studied in detail. A new method for measuring the sharpness of the cutting tools was introduced using the confocal laser scanning microscopy. Also, in this paper an alternative approach was recommended for the fracture toughness measurement of brittle materials.