An overview of the machinability of aeroengine alloys

Machining difficult-to-machine materials such as alloys used in aerospace, nuclear and medical industries are usually accompanied with low productivity, poor surface quality and short tool life. Despite the broad use of the term difficult-to-machine or hard-to-cut materials, the area of these types of materials and their properties are not clear yet. On the other hand, using cutting fluids is a common technique for improving machinability and has been acknowledged since early 20th. However, the environmental and health hazards associated with the use of conventional cutting fluids together with developing governmental regulations have resulted in increasing machining costs. The aim of this paper is to review and identify the materials known as difficult-to-machine and their properties. In addition, different cutting fluids are reviewed and major health and environmental concerns about their usage in material cutting industries are defined. Finally, advances in reducing and/or eliminating the use of conventional cutting fluids are reviewed and discussed.

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Environmentally conscious machining of difficult-to-machine materials with regard to cutting fluids

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.

Tool wear characteristics in machining of nickel-based superalloys

Nickel-based high temperature alloys have excellent physical properties, which make them ideal for use in the manufacture of aerospace components. However, they exhibit poor machinability. Though conventional machining in industries is currently being carried out using carbide tools, there is little scope for improving the material removal rate. Machining, being a major operation, needs to be improved in order to reduce the throughput time. High Speed Machining (HSM) is a promising technique for increasing productivity in this regard. This paper mostly reviews research and development work in the machining of nickel-based high temperature alloys carried out over the last 15 years with the objective of assessing the present scenario. Emphasis is laid on Inconel 718, which is most commonly used. Both turning and milling operations using conventional and High Speed (HS) machining are reviewed herein. HSM is discussed at length in comparison with conventional machining, as it is possible to drastical...

Machinability of nickel-based high temperature alloys

https://ir.canterbury.ac.nz/bitstream/handle/10092/492/12605295_JMPT%20Tool%20Wear%20&%20Cutting%20force%20variation%20manuscript.pdf;sequence=1

M.A. Mazid

Papers

Cutting forces in the end milling of Inconel 718