Effect of tool wear on the surface integrity of Inconel 718 in face milling with cemented carbide tools

Abstract

Nickel-based superalloys are known for their high-temperature performance regarding oxidation, creep and fatigue resistance. For this reason, they are widely used as structural components in the aerospace industry. However, because of these properties, they are difficult to machine, and normally a rigorous control of the surface integrity and residual stresses are required to avoid structural premature failures. Residual stresses are present in all mechanical components regardless of the manufacturing process applied, and they are either of thermal or mechanical origins. In machining several variables affect the residual stresses, but the tool quality is one that is most influential. The present work studies the influence of the wear of coated cemented carbide tools on the surface integrity of Inconel 718 alloy in the face milling process. Tools with different stages of wear were tested under finishing, roughing, and moderate machining conditions. During milling tests, the machining forces and cutting temperatures were monitored, the latter by two different techniques, using a thermal camera and with J-type thermocouples welded on the workpiece surface close to the cutting region. The surface roughness, microhardness, and residual stresses were measured after each machining test. The results showed that there is a close relationship between the tool wear and the residual stresses that varied from compressive to tensile stresses – the latter being of thermal origin. A direct relationship between tool wear and machining forces and cutting temperature were also observed.