An experimental and theoretical investigation on the brittle ductile transition and cutting force anisotropy in cutting KDP crystal

As a typical brittle material, Potassium Dihydrogen Phosphate (KDP) crystal exhibits anisotropic mechanical property during processing. The most general method to produce smooth and crack-free KDP surface is single point diamond fly-cutting (SPDF). In processing KDP by SPDF, cutting direction has great influence on the cutting force and the quality of the machined surface. Thus, selecting an optimal cutting direction is of great significance in decreasing the cutting force and improving the surface quality. In this paper, influence of cutting direction on the brittle ductile transition (BDT) depth and cutting force in machining KDP crystal has been investigated. Cutting experiments are carried out on the (001), Doubler and Tripler plane of KDP crystal to find out the change law of cutting force and BDT depth related to cutting direction. Theoretical models for calculating the cutting force and conditions for achieving crack-free surface in cutting by circular edge cutter have also been established. The predicted results coincide well with the experiment results, which have proved the validity of the proposed models. The experimental results in this study can provide guidelines for optimizing the processing parameters in fly-cutting of KDP crystal, and the theoretical models can be extended to study the cutting mechanism of other brittle materials.