Significant advances have been made in understanding the behaviour of engineering materials when machining at higher cutting conditions from practical and theoretical standpoints. This approach has enabled the aerospace industry to cope with constant introduction of new materials that allow the engine temperature to increase at a rate of 10 °C per annum since the 1950s. Improvements achieved from research and development activities in this area have particularly enhanced the machining of difficult-to-cut nickel base and titanium alloys that have traditionally exhibited low machinability due to their peculiar characteristics such as poor thermal conductivity, high strength at elevated temperature, resistance to wear and chemical degradation, etc. A good understanding of the cutting tool materials, cutting conditions, processing time and functionality of the machined component will lead to efficient and economic machining of nickel and titanium base superalloys. This paper presents an overview of major advances in machining techniques that have resulted to step increase in productivity, hence lower manufacturing cost, without adverse effect on the surface finish, surface integrity, circularity and hardness variation of the machined component.

Key improvements in the machining of difficult-to-cut aerospace superalloys

Study on Elliptical Vibration Cutting

Ultrasonic elliptical vibration cutting

Machining forces, chip formation, surface integrity and shear and friction angles are important factors to understand the machinability of metal matrix composites (MMCs). However, because of the complexity of the reinforcement mechanisms of the ceramic particles, a fair assessment of the machinability of MMCs is still a difficult issue. This paper investigates experimentally the effects of reinforcement particles on the machining of MMCs. The major findings are: (1) the surface residual stresses on the machined MMC are compressive; (2) the surface roughness is controlled by feed; (3) particle pull-out influences the roughness when feed is low; (4) particles facilitate chip breaking and affect the generation of residual stresses; and (5) the shear and friction angles depend significantly on feed but are almost independent of speed. These results reveal the roles of the reinforcement particles on the machinability of MMCs and provide a useful guide for a better control of their machining processes.

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Machining of metal matrix composites: effect of ceramic particles on residual stress, surface roughness and chip formation

Machining of titanium at high cutting speeds such as from 4 m/s to 8 m/s is very challenging. In this paper, a new generation of driven rotary lathe tool was developed for high-speed machining of a titanium alloy, Ti–6Al–4V. The rotary tool was designed and fabricated based on the requirements of compact structure, sufficient stiffness and minimal edge runout. Cylindrical turning experiments were conducted using the driven rotary tool (DRT) and a stationary cutting tool with the same insert, for comparison in the high-speed machining of Ti–6Al–4V. The results showed that the DRT can significantly increase tool life. Increase in tool life of more than 60 times was achieved under certain conditions. The effects of the rotational speed of the insert were also investigated experimentally. Cutting forces were found to decline slightly with increase of the rotational speed. Tool wear appears to increase with the rotational speed in a certain speed range.

High-speed machining of titanium alloys using the driven rotary tool

The various types of rotary tool cutting operations and their performance advantage over conventional machining operations are reviewed together with the simplified or fundamental operations used to study the cutting mechanics of these novel material removal operations. The fundamental driven and self-propelled rotary tool cutting operations have been simulated as wedge tool cutting processes and their relationships to the kinematically and perfectly equivalent “classical” orthogonal and oblique cutting processes explored. Based on the modified thin shear zone cutting models the simulated driven orthogonal and oblique rotary tool cutting processes have been analysed and represented as perfectly equivalent classical oblique cutting processes accounting for all the cutting forces and energy, together with a chip transportation process, owing to the tool lateral motion along its cutting edge, which involves no additional energy. By contrast, the self-propelled oblique rotary tool cutting process has been modelled as a perfectly equivalent classical orthogonal cutting process together with chip transportation. The proposed models will be experimentally verified in the next part of this investigation.

E.J.A. Armarego

Papers

Fundamental studies of driven and self-propelled rotary tool cutting processes—I. Theoretical investigation

Computer-Aided Predictive Models for Fundamental Rotary Tool Cutting Processes

Some fundamental and practical aspects of twist drills and drilling

Mechanics of cutting model for simulated oblique rotary tool cutting processes