Application Research For More Efficient Aircraft Machining

Aircraft production is active and expected to ramain that way. According to Boeing figures for the whole market, in the next 12-15 years 27,000 cargo and large passenger aircraft will be built. Boeing broke its own order record in 2007 with five weeks to spare, and its current backlog of orders stands at approximately 3,000 commercial airliners. At present production rates that's over five years of 737 production, four years of 777 production and nearly six years of production of the 787. Airbus has also scaled-up production recently from 32 aircraft per month to 44, and yet more orders are waiting in the wings for Airbus or Boeing to seal. Air France/KLM, British Airways and Air India have all been in the market for more aircraft, and this doesn't even consider the legacy US carriers such as American, Delta and United, which are sitting on huge fleets of older planes that will have to be replaced sooner rather than later if they want to remain competitive. Not only that, defense contracts of the Eurofighter and the JSF (Joint strike fighter) must also be added.

Cutting tool supplier Sandvik Coromant has developed new products and techniques for specific aerospace machining applications. The company is a partner of the Advanced Manufacturing Research Centre in Sheffield, UK, a 60-million-euro collaboration between world leaders in the aerospace supply chain and international academic institutions. Boeing has a 10-year commitment of involvement to invest in research and development at AMRC, to aid the development of value-added manufacturing solutions.

Sandvik Coromant uses the AMRC to prove concepts and provide confirmed data to help address real customer applications. A recent example concerns the machining of structural aircraft parts, all of which feature pockets. Sandvik Coromant and AMRC came up with 25 practical ways to generate these pockets before further development identified the most feasible five methods in terms of productivity, efficiency and tool life. These were transferred to Sandvik Coromant’s Application Research Centre in Sweden to produce the company’s guide to Titanium Milling.

Sandvik Coromant has had an Application Research Centre in Sweden for many years, but since as European aerospace industry has grown the company has also established a specialised facility at its UK headquarters in Halesowen, called the Aerospace Application Centre (AAC).

As a result of different research programs conducted at the two centres, the company has developed application guides for machining heat-resistant superalloys (HRSA) such as Inconel 718, titanium milling and blade machining, as well as many ongoing studies regarding composites.

Regarding HRSAs, one of the crucial factors is tool material. A high degree of insert hot hardness, the right level of insert toughness and sufficient adhesion of the insert coating are the primary requirements, and the company has built many of its solutions around these considerations. For example, the company now offers two Sialon (silicon, aluminium, oxygen, nitrogen) ceramic grades for profiling and pocketing HRSAs: tough and predictable CC6065 is an economic alternative to whisker ceramics in intermediate stage machining, while CC6060 is the notch resistant first choice for open profile machining.

The extensive research platform adopted by Sandvik Coromant is a differentiating factor in the marketplace, bringing consistency and robustness to the manufacturing process. Sandvik engineers can state with confidence the expected tool life for individual aerospace applications in line with specified depths of cut and feed rates. From this information, accurate job costing can be achieved.

And it’s not just the cutting tool that is assessed. The size and shape of toolholders also have to be carefully considered to avoid any collisions with the workpiece or workholding equipment. Expensive aerospace components can be scrapped by a toolholder hitting the workpiece.

The evaluation process involving a new or existing machined part is applied in five stages:

1. Customer provision of drawings and information such as plant list and materials used

2. Development by Sandvik Coromant of an optimised tool layout, application methods and the business case to proceed

3. Development of the programming strategies based on customer machines

4. Process simulation and verification

5. Actual machining of customer components and confirmation of savings specified in the business case

Thanks to this process, a titanium fitting that previously required two operations to produce in a combined machining cycle time of 614 minutes, now only takes 199 minutes. The solution has since been applied to 10 component variants offering annual savings of 300,000 euros for an implementation cost of around 3 per cent.

Similarly, multiple operations on an engine component that were resulting in a combined cycle time of 480 minutes have been reduced to a single operation that takes just 53 minutes to complete. Elsewhere, an airframe structural component has seen cycle times slashed from 1,030 minutes to 350 minutes, delivering savings worth 110,000 euro per year. The right tooling solutions can provide the opportunity for this kind of return on investment.