Tool wear and surface integrity of inconel 718 in dry and cryogenic coolant at high cutting speed

Abstract

The high speed machining of Inconel 718 represents a significant challenge. This is attributed to the excessive heat generated during the chip formation process, which elevates the cutting tool temperature and accelerates tool wear. The heat generated can shorten the tool life and lead to dimensional inaccuracies. In severe cases, this circumstance can result in product damage. During the milling process, the use of conventional cutting fluids to control heat generation may not be sufficiently effective. This is due to the inability of these fluids to fully penetrate the cutting zone. Such a situation can lead to the development of health and environmental problems. To overcome this dilemma, a cryogenic cooling unit using liquid nitrogen (LN2) was developed to cool the tool–chip interface. This cooling technique is not only more efficient, but also environmental friendly. This paper presents the experimental investigations conducted to assess the effectiveness of cryogenic cooling for the milling of Inconel 718 in comparison to the dry cutting process. This comparison embraced tool wear rate, mechanism wear, cutting force, surface roughness and microstructure changes. The experiments involved the use of PVD coated with TiAlN/AlCrN ball nose tungsten carbide for varying cutting speeds ranging between 140–160m/min, a feed rate of 0.15–0.20mm/tooth, and a radial depth of cut of 0.2–0.4mm. The axial depth of cut was kept constant at 0.3mm. The results revealed that the cryogenic cooling process is more effective than dry cutting for reducing tool wear, lowering the required cutting force, improving surface roughness, lessening deformation of microstructure changes at the sub-surface level, and eliminating contamination of the machined part. Notch wear and flaking near the depth of the cut zone are the predominant types of tool failure during the machining of this kind of material. In comparison to dry machining, the utilization of the cryogenic technique reduces the cutting force to 23%, and improves the surface roughness to a maximum of 88%. This can be attributed to the capacity of LN2 machining to provide better cooling and lubrication through the reduction of heat generation at the cutting zone. The machined surface roughness obtained of less than 0.2µm could fulfill the demands of the aerospace industry for the finishing of precision components.