Tool wear characteristics in high-speed milling of graphite using a coated carbide micro endmill

Abstract

High-speed milling using a coated carbide micro endmill is one of the dominant precision manufacturing techniques for graphite electrodes in the die and mould industries. The abrasive and frictional properties of graphite result in severe tool wear in high-speed milling processes. In this paper, a carbide micro endmill with an AlTiN coating is used in the high-speed milling of graphite. The endmill is thoroughly examined using a scanning electronic microscope and the wear and failure mechanisms are deduced. It is found that all the worn areas increase almost linearly with tool displacement, and flank wear is the dominant wear pattern in the steady wear stage. In the initial stage, premature coating delamination and edge microchipping occurred. The steady wear stage occurred with the creation of abrasive and erosion wear mechanisms. Tool failure occurred owing to the creation of coating delamination failure, severe chipping, and impact fatigue spalling. Polishing abrasive wear is the primary wear mechanism of the endmill. No major diffusion of elements occurred during the tool wear. Increasing the feed-per-tooth level and cutting speed facilitated the tool performance in terms of reducing tool wear and improving productivity.