Effects of tool wear on machined surface integrity during milling of Inconel 718

This study contributes to broadening the knowledge regarding the effects of cutting tool wear on the machined surface integrity characteristics during milling of Inconel 718. The surface roughness and topography, residual stress, microhardness, and microstructure of the resulting Inconel 718 after milling were evaluated under four flank wear conditions. In addition, tool wear morphology, tool lifetime, cutting force, and cutting temperature distribution were analyzed to further explain the mechanisms of surface integrity characteristics. The results of these studies show that the ball nose end mill achieves a tool lifetime of approximately 350 min. The cutting forces increase sharply with a greater tool flank wear width, while the highest cutting temperature shows a decreasing tend at a flank wear width of 0.3 mm. Higher tool flank wear width produces larger surface roughness and deteriorative surface topography. A high-amplitude (approximately −700 MPa) and deep layer (approximately 120 μm) of compressive residual stress are induced by a worn tool with flank wear width of 0.3 mm. The surface microhardness induced by the new tool is larger than that induced by worn tool. Plastic deformation and strain streamlines are observed within 10 μm depth beneath the surface. The results of this study provide an optimal tool wear criterion, integrating the surface integrity requirements and the tool lifetime for ball-end finish milling of Inconel 718.