Background to the project was the very significant weight saving and thus improved fuel economy and reduced emissions which can come about through the use of Ti alloy components in some airframes and spacecraft and in aero engines.
The project aimed at enhancing strategic international co-operation between China and Europe in the field of casting large titanium aero structure components. The consortium consisted of EU and Chinese partners.
The COLTS project aimed at making a step-change for casting of large Ti components by overcoming some key challenges in the casting process. Such a step-change is critical if the production of large Ti components is to meet the requirement in cost reduction by end-users, the requirement of CO2 reduction and raw material waste reduction in every step of component manufacturing process by the end-users and by society.
This step change involved the development of the centrifugal casting process by which the filling of thin sections of large Ti structures was improved so that significantly fewer and smaller defects will be present in the component and a significantly higher production yield rate will be achieved. Further development will be carried out to improve the gravity casting process which is important for casting asymmetrical components such as Ti airframes.
Those developments were closely coupled with the development of computer modelling in terms of better understanding and predicting liquid filling of the mould, defect formation and distribution, control of the dimensional accuracy of the cast component together with the development of a stronger wax and optimum ceramic mould material if required in order to meet the component dimension tolerance specified. The micro structure and mechanical properties including that of heat treated and welded castings must be optimised. If successful, this project will lead to significant cost reduction in producing large Ti components, removal the USA monopoly of supply of aero engine Ti casings and significant reduction of CO2 and of Ti raw material wastage incurred in current manufacturing processes. It will also lead to more application of light Ti structures in aerospace and space, thus weight and fuel reduction by making Ti structure commercially viable.
The specifications and properties of the cast components were defined in WP2 and were produced by IMR and BIAM (partners 9 and 7a) in WPs 3 & 4. Because Rolls-Royce left the consortium, a generic cylinder instead of an actual aero engine casing was specified as one of the castings, but this was not viewed as satisfactory by CAE as the only relevant final product for an aero-engine. BIAM have therefore defined the design for a specific aero-engine casing; casting of this is already being modelled by Tsin (partner 10). BIAM have noted that this cost an additional 30keuros.
IMR have produced three castings of the generic cylinder and samples from these have been examined and tested by them and more extensively by ESA and by the IRC (partners 3 and 1). Although considerable numbers of quite large casting defects were observed in the first and second cylindrical castings initial observations have suggested that the third cylinder was significantly improved in terms of reducing the number of large pores, but because this casting used a lower speed of rotation of the mould during centrifugal casting there was a higher density of small pores. IMR intend to introduce some further modifications - guided by the modellers in WP6 (partners 4 and 10) - into the next cast cylinder including reverting to a revolution speed of 200 revs/min during centrifugal casting and inverting the casting to improve the mould filling. In addition they investigated the influence of mould pre-heat temperature on the microstructure and properties. The work so far has shown a very coarse microstructure and thus downgraded properties. It is considered that both of these problems (imperfect filling and coarse microstructure) will be eliminated, or at worst dramatically reduced, in the next casting. The alloy composition will be corrected in the next casting and the changes (higher Al and O) are in the sense that would increase the strength. It is planned to deliver the next improved casting, after HIPping it, for display at the 24 month meeting in Barcelona in September/October 2012. After this meeting the HIPped casing will be assessed in terms of dimensions, microstructure and mechanical properties. These observations will define if an additional generic cylinder has to be cast.
The casting work being done by BIAM has also progressed to schedule and sections of gravity-cast doorframe have been delivered to the IRC Birmingham for property, microstructure assessment. This has required production of ingots by BIAM as well
The most significant potential impacts of COLTS to end-users are the reduction in weight through the improvement in the properties of cast Ti6Al4V components and a narrowing in the scatterband of these properties; the reduction in cost of the manufacture of large components through a reduction in the quantity of materials and the improved fly-to-buy ratio associated with reduced machining.
Innovating for the future:
- Promoting more sustainable development