Abstract
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.
Highlights
Nickel-based superalloys are widely applied in aero-engine key components because of their excellent chemical and mechanical properties at elevated temperatures [1]
This paper investigates the effects of tool wear on the machined surface integrity characteristics, including the surface roughness, surface topography, residual stress, microhardness and microstructure, during ball-end milling of Inconel 718
The tool flank wear width has three typical stages of initial running into wear, middle steady wear, and final sharp wear
Summary
Nickel-based superalloys are widely applied in aero-engine key components because of their excellent chemical and mechanical properties at elevated temperatures [1]. Various works have focus on investigating the effects of cutting parameters and tool wear on the machined surface integrity of nickel-based superalloys. High thermal gradients tend to generate tensile stress and softening phenomena at small depths below the surface, whereas the extrusion effect produced by mechanical loads contribute to induce compressive residual stress and work hardening [21,22,23,24]. Aspinwall et al [27] and Soo et al [28] found that when milling with new and worn tools, the surface tensile residual stress of Inconel 718 increased with tool wear due to the dominant thermal effects. The machined surface integrity characteristics under various flank wear conditions were examined based on the surface roughness and topography in the surface, residual stress, microhardness, and microstructure in the subsurface. The cutting force and temperature were analyzed to further explain the mechanisms of surface integrity characteristics
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