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4th September 2019, Altstätten

Taking composites to new horizons

Landing of a PC-24 on the unpaved runway in Fano, Italy. © Pilatus Aircraft

Landing of a PC-24 on the unpaved runway in Fano, Italy. © Pilatus Aircraft

With a weight of only 5 tons, the new Pilatus PC-24 business jet, manufactured by Pilatus Aircraft, is light enough to take off and land on short, grassy runways. Its low weight stems from the use of components made of carbon and glass fibre. For processing these materials, Pilatus relies on state-of-the-art Zünd cutting technology.

Landing on short, unpaved grass and gravel runways was previously reserved for turboprop airplanes, but as of recently, this type of terrain is no longer off limits to the new PC-24. It can take off after just 890 metres and requires only 720 metres for landing.

How to build an airplane?

Patrick Rohrer, Pilatus’ Project Manager System Procurement, knows what it takes to successfully build airplanes. “Commitment to production location and the Swissness that goes along with it are one thing; but at least as important are state-of-the-art production cells equipped with cutting-edge technology,” he said. Key to this are permanent reduction of costs, productivity optimisation, and the ability to implement modern production technologies.

Things were different back in 1959. That's when the PC-6 Porter took off for the very first time at Stans Airfield near Lucerne, Switzerland. It was a sturdy, all-metal universal aircraft that many would refer to as a Jeep with wings – a plane with the versatility of a Swiss Army Knife. The PC-6 were still assembled by hand, which necessitated an experienced workforce and tolerances that were much greater than they are today. The company's latest aircraft type, the PC-24, consists of innumerable parts, many of them milled at tolerances in the Mμ range. Assembly is much faster now, made possible only because of the latest advances in production technologies.

Carbon fibre in aircraft

Pilatus began using carbon fibre parts early on in its history of manufacturing airplanes. Already for the PC-6, first GFRP and CFRP components were laid up by hand, albeit still in limited quantities.

In early 2019, Pilatus greatly expanded its capacity for cutting prepreg materials with a new Zünd G3 L-2500 cutting system. © Zünd

In early 2019, Pilatus greatly expanded its capacity for cutting prepreg materials with a new Zünd G3 L-2500 cutting system. © Zünd

In the aircraft industry, almost everything revolves around weight reduction. As a result, more and more parts are made from carbon and glass fibre. Major advantages of these materials are their high rigidity and toughness, as well as their wear resistance. The challenge, however, lies in balancing weight, stability, and cost. At Pilatus no load-bearing parts are made of CFRP, but the company's R&D is busy working on that. The PC-24 uses composites mainly for interior and exterior cladding. The engine casings and wingtips, too, are made of carbon fibre, as well as landing gear doors, air ducts, various pipes, covers, and trailing edges on wings.

Prepreg

The starting point for these aircraft parts is prepreg, pre-impregnated carbon fibre. Endless, pre-impregnated fibres are consolidated through pressure and high temperature.

Prepreg is delivered in rolls by refrigerated trucks and stored in freezers at -19 C. To bring the material to room temperature for processing, it is taken out of the cooler the night before. It can remain at room temperature for five to 20 days before the resin begins to react and cure. Pilatus processes around five rolls of around 90 m2 daily, or about 90'000 m2 per year.

For cutting prepreg, Pilatus has relied on Zünd digital cutting for more than 15 years. The PN-series cutter purchased at the time continues to reliably perform its duties; however, increased demand for carbon fibre components began to exceed capacity, which led to the addition of a state-of-the-art Zünd G3 L-2500 in 2019. The G3 system single-ply cuts materials for the respective components in a largely automated process and labels cut pieces with an integrated inkjet module.

The cut pieces are kitted and stored at -19° C. Using laser projectors, individual part layers can be laid out very precisely. © Zünd

The cut pieces are kitted and stored at -19° C. Using laser projectors, individual part layers can be laid out very precisely. © Zünd

Once cutting is completed, the parts are kitted and put in cold storage until further processing. Depending on rigidity and strength requirements, a component can consist of up to 350 layers.

If no DXF file is available for parts or their individual layers, a digitiser comes into play that allows for easy capture and digitisation of part templates placed on the digitising table.

Material efficiency

Another factor in Pilatus’ success has been the focus on implementing permanent productivity increases. “When dealing with cost-intensive materials such as carbon or glass fibre, material efficiency and optimisation are always a concern. We are constantly working to increase utilisation and thereby reduce waste — particularly since we still have few options for recycling,” explained Mr Rohrer.

In the meantime, waste rates have been reduced from 30% to 20%. The highly efficient nesting features in Zünd Cut Center - ZCC software play an important role in this. On one hand, cut parts are statically nested, which means parts, or rather their individual layers, are nested to create a set layout used repeatedly to complete the entire job. “Dynamic nesting, meaning parts and layers from multiple jobs are nested and combined in a single cut file, is also used whenever it makes sense,” continued Mr Rohrer.

www.zund.com

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