Creation of an intelligent machining system to adapt to structural variability in safety critical titanium alloy components

Lead Research Organisation: University of Sheffield
Department Name: Materials Science and Engineering

Abstract

This work will change the way we think about machining high value titanium components - for example, turning an aeroengine shaft on a lathe. Rather than apply global rules about how much metal we can remove and how fast we can rotate the part, we will develop a technique that can monitor - in real time - the "microstructure" of the part, in order to determine how much pressure we apply with the cutting tool. Microstructure in metals is analogous to the different parts of timber - heartwood, sapwood, knots, how the grain runs - but on a much smaller scale (usually fractions of a millimetre). A master carpenter will see and feel these features of the timber by sight and touch, and instinctively work the wood with their tools in such a way as to maximise strength and/or visual appeal whilst using the least amount of effort. Such finesse has not been possible in metal working as - until now - there has not been a technique available that can "see" the microstructure.

A technique called spatially resolved acoustic spectroscopy (SRAS for short) uses lasers to generate and detect very high frequency ultrasonic waves that travel on the surface of the metal component. These waves interact with the microstructure, and this allows us to "see" it. By relating this information to knowledge of how machining the metal affects its performance - which is another part of the work - opens up the possibility of intelligently crafting the cutting process. Not only will this lead to faster machining processes and less damage, it will also mean that a map of the microstructure of the final part is available - this will be invaluable for confirming quality.

Planned Impact

Machining of titanium is highly significant in terms of product cost and throughput time, accounting for 60% of the component's total cost. Rolls-Royce spend £100 million pounds on milling operations on titanium componentry alone. Being at the leading edge of titanium component machining is an important aspect of our UK manufacturing competitiveness, demonstrated through key employers such as Rolls-Royce, BAE Systems, GKN Aerospace and Messier-Bugatti-Dowty who manufacture landing gears, bulkheads and compressor disks. Encouragingly, the UK civil aerospace sector (second only in the world to the US) shows signs of major growth: as global demand for aircraft is increasing, it could enjoy a 17% share a new market estimated to be £2.4 trillion over the next 20 years [The Engineer, June 2011].

Overall this proposal will have an important impact on the future business and jobs for the UK, particularly in the aerospace sector which currently employs over 110,000 people (second behind the USA) and a further 350,000 indirectly. With increasing demand for air travel and air cargo it is imperative that the UK strengthen their position as innovators in the industry. A recent report by Boeing stated that between now and 2032 there will be a demand for over 32,000 new airplanes the majority of which will be single-aisle to feed the low-cost carrier sector, particularly in emerging markets such as China. The report goes on to state that 85% of the planes that will exist in 2032 have yet to be built. Pressure to meet the delivery targets of many of these aircraft programmes will require higher productivity, which from a machining standpoint equates to higher surface speeds. UK manufacturers and their future cost down targets are reliant on new machining practices. In order to enhance the effectiveness and sustainability of organisations it is imperative that UK research and development provide support and confidence to these new practices, which as they stand, could promoteubsurface damage and potential deterioration of in-service properties.

This proposal intends to raise the profile and showcase the opportunities of in-situ nondestructive evaluation (NDE) for machining parameter optimisation and microstructural defects in machined components. We will demonstrate that an effective, robust technique can provide the supply chain with more confidence. The investigators and the industry partners also believe that this will lead to a change in organisational culture and practices with respect to the machining and NDE of critical components. This will lead to further confidence in manufacturing and material usage. A successful proposal will provide the UK with a technique of monitoring the machining process in-situ leading to greater yields due to less defected material and increased tool wear, which will have a significant impact on environmental sustainability.

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