Influence of tool wear on chip-like burr formation during micro-milling, and image processing based measurement of inwardly-deflected burrs

During micro-milling, the regular top-burrs usually bend in a direction laterally opposite to the milled feature. This top-burr morphology changes as the cutting edge condition progressively deteriorates with inherent tool wear. An edge-chipped tool tends to produce unusual top-burr that resembles an incompletely separated chip. Such chip-like burr also has a tendency to flow inside the micro-milled feature. This article, for the first time, explores the integral roles of worn-out tool geometry, micro-milling mechanics and process parameters on chiplike burr formation on Ti-6Al-4V during machining using 0.5 mm diameter TiAlN-coated WC-6Co tools under minimum quantity lubrication. Round-edges of the coated micro-mill progressively pass through break-in wear, steady abrasive wear, adhesive wear, coating delamination, and edge-chipping. A comprehensive analysis is presented here to explore the mechanism of chip-like burr formation considering the changes in tool geometry and corresponding variations in chip-tool-work tribological contact, cutting forces, stress distribution, burr root thickness, burr nano-hardness and surface roughness. Further, an algorithm for digital image processing is developed for efficient and reliable measurement of the burr size and corresponding inwardly-bent fraction. Subsequently, the roles of process parameters are assessed to explore the scopes of controlling the inward bending of the chip-like burrs.