In the air

Advances in machine tool technology for the aerospace industry will be demonstrated for the first time at next month’s Farnborough Air show.

More than 900 exhibitors will attend this year’s event, organised by the Society of British Aerospace Companies. In addition to the array of military and civil aircraft will be the latest innovation in componentmanufacturing technology, a sector that is becoming increasingly competitive.

Machine tool specialists are adapting new processes to improve efficiency and production times, and they are using software more effectively to control and monitor production to achieve better results.

NCMT will be exhibiting an A380 wing rib and a rib from the A320 milled on a their new Makino MAG4 machine using the Viper (vitreous improved performance extreme removal) process. Viper was developed by Rolls-Royce four years ago in a bid to speed up component manufacture. It employs 200mm diameteraluminium oxide grinding wheels in the spindles of specially-adapted Makino machines. NCMT claims the process makes it possible to machine a set of turbine blades in 15 rather than 100 days.

Rolls-Royce retained exclusive use of Viper until recently, but it is now available to the rest of the market. NCMT marketingmanager Dave Burley said while it is still not widely used, it has huge potential. He said that with approximately 40 machinescurrently operating Viper, firms like NCMT will use Farnborough to raise awareness of the process and encourage others within the aerospace engine field to embrace the technology.

Burley claimed the high-speed Makino machines are among the most flexible and cost-effective in the industry. This is because they can produce one large, complex component very accurately in a single set-up, which eliminates the need for two sub-assemblies and reduces manufacturing lead time and cost. This, said Burley, is what will attract interest at Farnborough.

‘People want to produce parts more cost effectively. As we are unique within this process we feel we can change people’s perception of the way they make components – from the traditional method to new sector technology.’

Typically a nickel alloy is used to make aerospace engine parts because of its resistance to high temperatures. In creep-feed grinding a hardened workpiece can be machined in a single pass.

However this is a lengthy process involving very high temperatures. Viper is claimed to be capable of stock removal rates up to eight times those achievable with conventional grinding of nickel alloys.

‘The cost of machining aerospace engine components, which are typically very difficult and very costly, will be greatly reduced,’ said Burley.

Another advance making its debut at Farnborough is the product of a joint venture between Starragheckert and TTL, which claims to have developed the first fully-automated machining and polishing machine that halves the time it takes to re-process worn jet engine blades.

Turbine blades wear with the build up of deposits and aredamaged by such things as bird strikes. The result is that blades can lose their shape and the aerofoil becomes less efficient. To renew blades the tips are fettled and polished by hand to restore a technically acceptable profile.

The process has a number of drawbacks, however, such as a lack of consistency from blade to blade (the discard rate is around 20 per cent) and health and safety issues for operators such as RSI and ‘white finger’ problems. In addition, the the amount ofaircraft ‘off-wing’ time is becoming an increasingly pressing issue in the industry.

‘The combination of TTL’s adaptive machining technology and StarragHeckert’s expertise in multi-axis machining of complex forms enables blade reprocessing time to be halved, with theproduction of a more consistent aerofoil surface,’ said venture spokesman Mike Wildish.

TTL will show how the geometric data of the component – including topography, twist and angle – is captured from the aerofoil surface of a refurbished welded compressor blade. This will be achieved using a touch- trigger probe on the latest StarragHeckert STC 100 high-speed five-axis vertical machine. The programme is then prepared through TTL’s adaptive machining software and the bladere-machined and polished in a single ‘hands-off’ automated cycle.

‘The reverse engineering process can be performed with less likelihood of scrap or rejected blades,’ said Wildish. ‘By eliminating inconsistency from blade to blade, quality and performance issues are addressed with the ability to re-machine within atolerance window of 0.03mm. The complete re-machining andpolishing cycle, depending on component size, can be completed in as little as eight minutes.’

The joint venture hope to apply the process to a range of components including gas turbine, blisk, impeller and nozzle guide vane repairs, compressor blade and turbine component machining.

Another contribution to the advancement of machine processing on show will be a CNC simulation software package from CGTech UK.

Managing director John Reed said that over the last six years, an increasing number of machine tool users have moved away from the traditional CAM system, used to programme a dry run to ensure safe, viable machining. That is being replaced with a simulation to create a virtual replica of the machine tool that will cut the part and allow checks to be made for collisions and other aspects of the process.

Simulation software offers companies the ability to enhance their operation by improving the documentation process. The software contains the critical manufacturing information, especially an accurate representation of the in-process geometry, necessary to accurately document the process.

For example, in order to maintain accuracy and stay withintolerances, most manufacturers inspect parts at various times during the machining process, manually creating inspection instructions to document the results. There are many ways to create a series of inspection instructions, but in the absence of an electronic ‘in-process’ model of the part, and therefore a limited knowledge of the in-process state of material, manual methods require technical expertise and can be prone to error.

Accurate in-process geometry is necessary for efficiently creating quality inspection instructions.

‘CGTech’s latest Vericut software, version 5.4, offers a better way by automatically creating inspection instructions, complete with in-process feature dimensions, automatically created during a simulation of the machining programme. This helps establish a formal, but easy, method to create and document inspection procedures,’ said Reed.

‘With a simple template included in the program, the auto-generated reports can be customised,’ said Reed. ‘Creating the inspection sequence instructions is quick and easy because the manufacturing engineer uses the in-process, ‘as-machined’ model to graphically describe which features to inspect. To add inspection points, the user clicks on a cut feature; Vericut then identifies the feature, automatically extracts feature sizes from the electronic in-process model, and applies a standard tolerance for the measurement.’

Reed said the user can then add any additional instructions and select the measuring instrument from a list. When the inspection sequence is completed, the finished report can be saved in standard HTML or PDF format.