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This paper is motivated by the fact that machining of Inconel 718 involves rapid tool wear and poor surface integrity. We investigate the performance of ceramic cutting inserts in turning of Inconel 718 by virtue of two different assisted machining conditions, plasma preheating- and cryogenic cooling-assisted technologies. The plasma nozzle placed in front of the cutting zone is used to soften the materials before machining. The liquid nitrogen flow located in the cutting area is used to reduce the cutting temperatures in the contact area. The cutting experiments are set for reducing tool wear and improving surface integrity, including surface roughness and micro-hardness beneath workpiece surface. With these two assisted techniques, the tool wear including flank wear and notch wear and the surface microstructure including surface roughness and micro-hardness are assessed and compared with conventional machining. Tool wear reduction and surface integrity improvement can be obtained with these two assisted technologies in turning of Inconel 718 with ceramic cutting inserts. The main causation of notch wear of the ceramic cutting inserts may be the hardened layer beneath the surface. By comparing these two assisted cutting techniques with opposite effects on the cutting tool and workpiece, it has been found that the surface roughness is reduced by 50 %, the micro-hardness is smaller, and the tool life is extended up to more than 40 % over conventional machining. [ABSTRACT FROM AUTHOR]

This work is motivated by a fact that an excessively worn tool will continue to be used in practical machining of difficult-to-cut materials, such as nickel-based superalloys. Quantitative comparison of worn tool temperature variations with a sharp tool shows great practical significance. A thermal model is presented to describe the coated tool temperature variation in dry milling of nickel-based superalloys for a turbine blade. The influence of flank wear is considered according to the rapid tool wear. In the proposed model, both heat fluxes into the tool from the rake face and due to flank wear are calculated to estimate the tool temperature distribution at different tool states. Feed rate optimization at the convex and concave surfaces of blade based on the force constraints is employed to investigate its influence on heat generation and tool temperature rise. A comparative experiment for dry milling of an Inconel 718 turbine blade is carried out to validate the model. Considering a set of experimental data and the output of the numerical simulations in the present work, a key global heat transfer coefficient (HTC), working as a partitioning coefficient which determines the heat amounts flowing into the chip and the tool, respectively, is assessed through an inverse procedure. This comparison indicates a good agreement in both trends and values. With the alternative method, an accurate simulation of the tool temperature variation can be achieved by the assessed global HTC which is used as an input in the FE model. As the influence of tool wear should be considered, this work can be further employed into the feed rate scheduling guidance in machining complex parts. [ABSTRACT FROM AUTHOR]

The alumina-based ceramic cutting tools are a kind of promising tools used in machining of heat-resistant-super-alloys, such as nickel-based super alloy, due to its high wear resistance, low thermal expansion and good oxidation resistance up to above 1000�°C. Sharp temperature rise mainly caused by excessive plastic deformation as well as the friction in machining of nickel-based super alloys is considered to be the key for rapid tool wear, especially the notch wear, which is the predominant type of catastrophic failure mechanism for the round type ceramic cutting tools. In this study, the wear mechanism of alumina-based ceramic cutting tools during dry turning of Inconel 718 is experimentally investigated. Based on the observation of tool wear, an attempt by employing the hardened layer beneath the workpiece surface is made to explain the occurrence of notch wear. Consequently, a predictive model of notch wear depth considering the influence of work hardened layer is developed. Series of cutting tests are used to validate the proposed notch wear model, and the result indicates that the proposed model is feasible. The contribution of this work can guide the effective control of tool wear by reducing the work hardened layer through the optimization of processing parameters. [ABSTRACT FROM AUTHOR]

Abstract: Nickel-based superalloy is widely employed in aircraft engines and the hot end components of various types of gas turbines with its high strength, strong corrosion resistance and excellent thermal fatigue properties and thermal stability. However, nickel-based superalloy is one of the extremely difficult-to-cut materials. During the machining process, the interaction between the tool and the workpiece causes the severe plastic deformation in the local area of workpiece, and the intense friction at the tool–workpiece interface. The resulting cutting heat coupled with the serious work hardening leads to a series of flaws, such as excessive tool wear, frequent tool change, short tool life, low productivity, and large amount of power consumption etc., in which the excessive tool wear has become one of the main bottlenecks that constraints the machinability of nickel-based superalloys and its wide range of applications. In this article, attention is mainly focused on the tool wear characteristics in the machining of nickel-based superalloys, and the state of the art in the fields of failure mechanism, monitoring and prediction, and control of tool wear are reviewed. The survey of existing works has revealed several gaps in the aspects of tool self-organizing process based on the non-equilibrium thermodynamics, tool wear considering the tool nose radius, thermal diffusion layer in coated tools, tool life prediction based on the thermal–mechanical coupling, and industrial application of tool wear online monitoring devices. The review aims at providing an insight into the tool wear characteristics in the machining of nickel-based superalloys and shows the great potential for further investigations and innovation in the field of tool wear. [Copyright &y& Elsevier]