Helical Milling of Small Holes in Fully-Sintered Zirconia Ceramic with PCD Tools

Fully-sintered zirconia ceramic (ZrO2) is a typical hard-to-machine material, and fabricating small holes in this material with high precision remains a challenging task. In this study, the PCD tools and helical milling process are used to investigate this problem. First, a finite element model is established, and cutting simulations with variable thickness are carried out to identify the effect of axial depth of cut on cutting force and surface quality. The range of milling parameters for single-factor experiments is also preliminarily determined. Second, taking the milling force (F) as the evaluation index, single-factor experiments of small hole helical milling are carried out using a PCD tools to determine the range of milling parameters (spindle speed n, feed per tooth f(z) and axial depth of cut ap) for orthogonal experiments. Then, orthogonal experiments are carried out, with inner hole surface roughness (R-a) and crack width at the hole entrance (Delta(w)) taken as the evaluation indexes of machining effectiveness. The rake face wear band width (V-A) and the flank face wear band width (V-B) are taken as the evaluation indexes of the PCD milling cutter wear. Through nonlinear regression analysis and the range analysis are performed to construct nonlinear models and obtain the influence laws of milling parameters for R-a, Delta(w), V-A and V-B evaluation indexes, respectively. Finally, the optimal combination of parameters obtained from the analysis is analyzed for small hole optimization experiments, obtaining better R-a, narrower Delta(w), and longer tool service life. The obtained results provide several technical guidelines for milling small holes in Fully-sintered zirconia ceramics with PCD tools.