Innovative Machining of Tungsten

Abstract

Fossil fuels continue to be the main source of electricity production in many countries while dominating the global energy systems. Despite the increasing concerns about the effects of climate change, arising from electricity production and consumption, there has been no substantial move away from these energy sources. Renewable energy sources have not proven to be reliable, although there is a massive investment in them in various parts of the world. While nuclear fission has been a dependable source of energy since the 1950s, there are critical issues surrounding its safety. However, nuclear fusion has the potential to be a reliable and safe alternative energy source which does not result in any harmful environmental emissions.

Fusion research is advancing into materials which can withstand the extreme conditions inside the reactor. Tungsten is an ideal material in this type of environment and forms the bulk of the core components in the reactor. However, the manufacturing of tungsten poses a challenge, especially in terms of producing complex-shaped components in the reactor. Machining remains the most promising manufacturing route for tungsten despite some advances in its additive manufacturing. The machining of tungsten is extremely difficult owing to its properties including its high strength and hardness as well as its high ductile-to-brittle transition temperature, which limits its workability.

This research investigates the effects of various methods and combination of cutting parameters which have the potential to improve the machining of tungsten. Specifically, the effects of thermal assisted machining and tungsten disulphide nano lubrication are compared to traditional dry and flood cooling environments. A literature review was conducted, and a methodology has been developed and implemented to realise the objectives of the research.

The major contribution of this research is in providing information on the effects of various cutting parameters, including the cutting speed and the rake angle of the cutting tool, in the milling of tungsten. Information is also provided on the effects of different cutting environments including thermal assisted machining and tungsten disulphide nano lubrication in comparison with flood cooling and dry machining. The investigations range from bending moment/cutting force and tool wear to surface topography and surface integrity analyses. Furthermore, with the exceptional difficulty in machining tungsten, machine learning methods are used for cutting tool condition monitoring to detect and predict the tool state.

The research mainly demonstrates that tungsten disulphide nano lubrication achieved comparable performance to dry machining, although producing a superior surface finish and introducing the least degree of sub-surface residual stresses. On the other hand, thermal assisted machining and flood cooling are ineffective in the milling of tungsten, owing to the accelerated rate of wear of the cutting tool.

Date of Award	26 Jun 2024
Original language	English
Awarding Institution	University of Bath
Supervisor	Alborz Shokrani Chaharsooghi (Supervisor) & Alexander Lunt (Supervisor)