Tool Failure Mechanism in High-Speed Milling of Inconel 718 by Use of Ceramic Tools

Abstract

A series of high-speed milling tests of Inconel 718 were carried out utilizing SiAlON ceramic tools, and the transitions of the cutting edge geometry and cutting forces were investigated. Through the experimental investigations, it was confirmed that the cutting edge is worn rapidly and a round shape is formed at the initial stage of machining. The radius of the round cutting edge becomes considerably large with respect to the uncut chip thickness, and thus the ploughing process is dominant in ceramic milling like general micro cutting operations. Based on the observed phenomena, a quasi-mechanistic model for cutting force prediction was proposed, where the measured cutting edge geometry and the contact stress distribution at the toolworkpiece interface are taken into account. The estimated cutting force by the proposed model showed a good agreement with the measured one. Minimizing the estimation error in the cutting forces, contact stresses of the cutting edge to the workpiece are identified. Stress field analysis using the estimated contact stresses revealed that the large tensile stress instantaneously generates around the stagnation point. This mechanism may contribute to the generation of the rake face flaking, which determines the end of the tool life.