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Final Report Summary - RAPOLAC (Rapid production of large aerospace components)

The objective of the RAPOLAC project was to investigate the additive Shaped metal deposition (SMD) process and develop it for use in production, where it could be particularly useful for manufacturing large, fully-dense components, or for adding features to already-existing parts. The SMD technology was initially developed by Rolls-Royce plc, but was not widely adopted for commercial production for several reasons. The TIG welding process had to be manually controlled by a skilled technician, and there was little understanding of the material properties of the parts produced by such an innovative process.

The system and process were modelled and research was carried out to determine stable parameter windows for welding the common aerospace alloy Titanium-6Al-4V and to discover the mechanical and microstructural properties of the resulting depositions and any differences in machining strategies required. Methods of automating the deposition were also investigated and the developed controller was integrated with the cell. Finally, the cost and environmental benefits of the process were compared to traditional manufacturing techniques for a number of parts. This report describes the work done by the partners to bring about the successful conclusion of the project.

The individual goals of RAPOLAC were chosen to address the problems facing the aviation industry today as set out in the sixth framework work programme. These were to:
- reduce the lead-time for new parts;
- lower manufacturing costs;
- significantly reduce the cost of inventory ;
- reduce emissions and harmful materials.

SMD meets all these criteria, as parts can be built directly from the CAD model, with no need to wait for tooling and features can be added or removed from the component as required. It will lower manufacturing costs for low-volume or one-off parts and inventory can be reduced to the wire needed for deposition. The only emission of the process is Argon, which can be safely vented to the atmosphere. However, SMD has not been widely adopted for commercial production because it had to be manually controlled and the resultant material properties were not well understood; in other words, the accuracy and repeatability of the process were barriers to take up.

The main objective of RAPOLAC was to develop the SMD process for use in production to the point where it can reliably and repeatedly produce component geometries. This meant finding stable parameter windows which would produce material with known properties, developing a controller so that the cell could be left unattended and presenting a business case for SMD. The scientific and technical objectives of the project were:
- reduction of 60 % in the lead-time necessary to produce new parts, through the elimination of tooling and the use of SMD parts as manufacturing prototypes, particularly affecting SMEs working on small batches of parts;
- reduction in the cost of manufacturing final products by 40 %, through the reduction in raw material usage, finish machining and machining products and the elimination of tooling;
- reduction in the cost of inventory held of 90 %, since the only inventory held is wire. Parts are stored as programs and then built to order.

To achieve these goals, RAPOLAC had three main research strands:
- process modelling at micro- and macro- scales;
- investigation of part microstructure and material properties;
- process control.

With the exploitation of the results leading to another two strands:
- integration of the process controller;
- development of a business case for SMEs.

The main outputs of RAPOLAC were:
- stable parameter sets for the materials chosen;
- known material properties for a given parameter window and part geometry;
- a prototype control system integrated with the main SMD cell;
- a cost and environmental comparison of SMD and traditional production processes;
- a business plan for SMD;
- example parts with different geometries for dissemination purposes.

A Design of experiments (DoE) approach was used to organise the work and to ensure that the maximum amount of data was gained from each trial. This allowed stable parameter windows to be found and the mechanical and microstructural properties of parts deposited with these parameters were investigated. The consortium investigated methods of monitoring and hence controlling the deposition to allow the cell to be automated. Thermo-metallurgical models were developed which can predict microstructure and stresses and were integrated with the results from the DoE approach to create and SMD calculator which can be used to predict properties from input parameters or to offer parameter options which will produce the required material properties.

Early on in the project, the common aerospace alloy Ti-6Al-4V was chosen as the main focus of the project as SMD is most beneficial for components made from expensive alloys where there is high material waste. Standardised test pieces (walls, cylinders and beads as well as more complicated dissemination pieces) and procedures were defined which would allow the results of different trials to be compared and which would enable partners to obtain the maximum amount of information. Suitable geometries and dimensions were chosen for testing which could be produced from a single SMD bead. Various methods of monitoring the weld were used (thermocouples, pyrometers) to provide information to the controller and to validate the thermomechanical models developed.

The parts developed for dissemination purposes were used to measure the cost and environmental implications of the process. Due to constraints on part size imposed by the robot reach, deposition times and cost, the dissemination parts are scaled down versions of standardised geometries which had the added advantage of making them more portable. However, comparisons are carried out for full-sized parts.

The benefits of SMD depend on many factors such as material used, part geometry, batch size and current method of manufacture. During RAPOLAC, comparisons were made for low-volume aerospace parts where around 95% of material stock is removed and which require large tooling to produce. Using traditional methods, there is a nine-month lead time to create such parts, but with SMD they can be produced in under a month. This makes SMD ideal for prototyping, and one-off or short production runs.

The consortium carried out life-cycle analysis for SMD parts, taking into account wire production and transportation and waste from finish machining as compared to production of forgings and subsequent machining. The parts used for the calculation were standard-feature engine-casing parts. Although wire production is less environmentally friendly and more expensive than the creation of ingots, because less material is used, overall there is net environmental and cost gain for the SMD component; it required only half the energy to produce and CO2 and NOx emissions were reduced by 20 % over the whole manufacturing chain. This makes SMD competitive for parts where a large amount of material is removed from the stock, or for small batches which require expensive tooling, such as low-volume parts or spares. SMD can also be used in conjunction with tradition processes to add features to the stock or to add material to out-of-conformance forgings or castings. It is envisaged that the main market for SMD will be in this area. A website (please see online) for the project was launched in time for the kick-off meeting. The website has been updated on a monthly basis in this period. A RAPOLAC YouTube channel has been set up and RAPOLAC pictures have been posted on the popular photo -sharing site, Flickr, and tagged. Videos have been produced showing the operation of the SMD cell, modelling and robot operation. A longer video was also produced summarising project results. These are available on the website through YouTube and on the RAPOLAC channel. They are also being shown on the Sheffield MANTRA lorry.

Related information

Reported by

University of Sheffield
Western Bank
S10 2TN Sheffield
United Kingdom
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