Investigating the Effect of Tool Coating on Cutting Forces and Tool Wear During Micro-Milling of Polycarbonate Glass

Abstract

Polycarbonate glass is one of the most widely used materials in the optical industries for making impact resistance lenses. Besides optical applications, polycarbonate glass has found applications in automotive and biomedical industries. The objective of this study is to investigate the effect of tool coating on the reduction of tool wear and cutting forces during micro-milling of polycarbonate glass. Both numerical modeling and experimental investigation have been carried out to investigate the effectiveness of various tool coatings on the carbide tool in minimizing the cutting forces, and hence tool wear. A series of experiments were conducted using CNC micro-milling of polycarbonate glass by varying feed rate, depth of cut, and tool coating. The three types of cutting tools used in this study were uncoated, titanium nitride (TiN) coated, and titanium aluminum nitride (TiAlN) coated tungsten carbide tools. The cutting forces have been recorded using the Kistler force dynamometer and the tool wear were analyzed using scanning electron microscope (SEM). It was found that all tools had reduced instances of failure, chipping, and abrasion at a moderately higher feed rate and depth of cut. Both very low and high feed rate were found to result in comparatively higher tool wear. The cutting forces increased with an increase of depth of cut, except for the TiAlN coated tool in some instances. With the increase of feed rate, the cutting forces gradually increased or stayed relatively constant across all depths of cut. It was found that the TiAlN coated tool reduced the amount of tool wear and cutting force across all feed rates and depths of cut. There is also a critical depth of cut around 0.3–0.5 mm and feed rate around 576–768 mm/min that reduced the amount of tool wear for the micro-milling of polycarbonate glass. Finally, the numerical modeling and simulation results of cutting forces were found to be in good agreement with the experimental cutting forces and the validated FEM models were then used to predict the cutting forces for higher spindle speed.