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 promote subsurface 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.
 
Description Titanium alloys compressor disks are used in gas turbine engines and are safety critical parts that are manufactured through multi-step forging and machining processes. We have successfully developed an in-process non-destructive evaluation approach for generating a digital fingerprint of a titanium disk during the machining (turning) process. This approach converts the forces exerted on the machine tool through a mathematical algorithm into a the grain structure of the disk. Such information can be used to determine features in disk that will be prone to premature failure during service. In addition, the approach can be developed in future to remove time-consuming and costly NDE processes, such as chemical etching and manual inspection.
Exploitation Route Although the approach has been used on compressor disks, it can be applied to other critical parts that require extensive machining, such as landing gear components, fan disks, off-shore titanium parts and hip joints.
Rolls-Royce are now keen to develop the approach developed through this programme as a non-destructive evaluation technique for critical rotating parts. The intention is apply for ATI funding with tool insert manufactures and material suppliers.
Sectors Aerospace

Defence and Marine

Energy

Manufacturing

including Industrial Biotechology

Transport

 
Description Findings been used to predict the mechanical properties of a titanium replacement hip joint. Three hip joints from different suppliers were machined and the techniques developed through this programme was used to identify features that could impact on the service performance of the components.
First Year Of Impact 2023
Sector Aerospace, Defence and Marine
Impact Types Economic

 
Description PhD project - Rolls-Royce plc 
Organisation Rolls Royce Group Plc
Country United Kingdom 
Sector Private 
PI Contribution Conducting research into the digital fingerprinting of safety critical rotating parts, such as aero-engine compressor disks using the force feedback technique developed in the programme.
Collaborator Contribution Partners are providing unique testing and training opportunities for postdoctoral researchers.
Impact still too early
Start Year 2023
 
Description PhD project - Sandvik Coromant 
Organisation Sandvik Coromant
Country Sweden 
Sector Private 
PI Contribution Started to investigate the effects of different material workpieces from a range of processing routes to determine whether different machine tool coatings can be applied to the tool inserts to enhance tool wear rates.
Collaborator Contribution Provision of materials and expert analysis and characterisation facilities.
Impact Still too early
Start Year 2023
 
Description PhD project SECO TOOLS 
Organisation SECO Tools
Country United Kingdom 
Sector Private 
PI Contribution Carried out machining research trials on new tooling inserts for aerospace alloys.
Collaborator Contribution Provided materials and carried out unique testing and analysis.
Impact Still too early
Start Year 2023
 
Description Presentation at Conference 
Form Of Engagement Activity A talk or presentation
Part Of Official Scheme? No
Geographic Reach International
Primary Audience Industry/Business
Results and Impact Presentation on force feedback approach as non-destructive evaluation approach for detecting defects in safety critical parts.
Year(s) Of Engagement Activity 2022