Cast in the same mould?

Mike Richardson


wonders whether the traditional casting and its incumbent pattern making equipment still has a key role to play in the aircraft component designs of tomorrow.

Castings have played a vital role in aircraft component manufacture from the very dawn of the industry, and from humble beginnings have provided a variety of solutions for both the power and structural needs of today's modern aircraft.

But as demand grows for low weight, high strength aircraft constructions combined with faster prototype and reduced product leadtimes, the tooling and pattern equipment required to make the next generation of casting designs must evolve. And if that wasn't enough, the advances in 5-axis CNC routing and metal forming technologies could cast fresh doubt on the traditional casting process in the future.

According to Aeromet International's marketing manager, Graham Hutchins, castings are often viewed as being too slow and expensive to produce.

“It's acknowledged that traditional casting processes cannot always compete with rapid machining technology for turnaround times,” he begins. “However, the process does offer cost-effective ways of producing complex parts rather than machining from solid or multi-piece fabrications. As a result Aeromet has proven that casting complex parts does have advantages, especially for weight saving and casting one part rather than using different suppliers for different parts.

“It would be churlish to say that there is no threat from the advanced metal forming technologies, but again they are limited in what they can achieve. There is still demand for premium quality cast products. Aeromet is well equipped to deal with this challenge head on, and through our Forming division specialising in sheet titanium hot forming, super plastic forming and diffusion bonding processes, we are able to offer customers alternative solutions. To meet the demand for stronger aluminium alloys, Aeromet has developed a more castable derivative of the A201 alloy and has secured a patent as A20X.

Hutchins notes that every company needs a niche to make them stand out, but above all else, they need to offer the customer what they want: weight and cost savings: “The supply chain has come a long way in the past few years but is still some way short of where it wants to be. Initiatives like SC21 are good models for moving forward, but need the buy-in from the whole supply chain if it's to be effective. To miss this opportunity could leave companies by the wayside.”

A sound investment

For its work within the aerospace industry, The McKenna Group manufactures precision investment cast components such as electronics enclosures, head-up displays and joysticks.

Group managing director, Don McKenna agrees that 5-axis machining from solid billets has become an increasing threat, but says there are still many complex shapes, such as large enclosures, where the removal of vast amounts of aluminium using a CNC machining centre wouldn't be economically viable.

“In these situations - particularly where cutter tool path angles may prevent it entering complex shapes - the investment casting process is ideal because the water soluble and ceramic cores used to produce these shapes are much more effectively than machining,” he observes.

“McKenna Group has a fast track process that takes the customer's tool, or a rapid prototype wax, and creates a casting within a matter of days. Whilst this isn't inexpensive, the cost is infinitely smaller to that of new tooling for the same function, or machining from solid billet on a one-off basis. The investment process allows us to produce prototypes very accurately, plus we can introduce dimensional controls to match them up to any mating components by creating a jig or fixture to set it to.”

McKenna adds that the investment casting process is very flexible and almost any part can be manufactured: “We help customers reduce tooling design costs by making the casting stronger without using additional strengthening ribs. We also minimise machining and prevent the introduction of unnecessary sharp corners. And by reviewing the dimensional tolerances, customers can eliminate other aspects of machining that can cause significant increases in cost. Customers are much smarter in how they design parts.”

A big hand for sand

Finecast Foundry on the other hand, claims its 95 grade reclaimed precision sand process provides an economical means of producing complex thin wall castings that are technically consistent to those made from investment processes.

“We produce and 5-axis CNC machine castings in a wide range of commercial and aerospace alloys, including aerospace components for engines, cockpit components, electronic chassis and interior parts for seating assemblies,” states Finecast's business development manager, David Gratton. “Our customers require castings with proven consistent dimensional stability, together with a superfine cast surface finish.”

Finecast realised that the markets were moving away from general engineering and diversified into distinct industries, so in 2007 gained AS9100 and began seeking approvals from leading independent aerospace companies looking to reduce component weight, cost and lead time.

“Finecast is the first foundry in the UK to have recently invested in a reclamation plant which enables us to reclaim 95% of sand,” Gratton continues. “We've reduced the material cost of sand and resin, while at the same time achieving a two micron surface finish similar to that of the investment process. We're the only foundry in the UK operating a 95 grade precision sand process and polishing sand grains during reclamation instead of the traditional thermo-reclaiming method.”

According to Gratton, Finecast now achieves a 2mm wall thickness on complex shapes to compete with the investment casting market in terms of component and tooling price, and manufacturing leadtime.

“It may appear the sand casting has been left behind, but things are changing. We're demonstrating that precision sand castings provide a component comparable with the investment process, not only in terms of finish and wall thickness, but also by significantly reducing production cost. Our aerospace customers are starting to see the kind of quality we can produce. It's a very promising and exciting time for Finecast at present.”

 Making the transition

Although its background is steeped in the production of automotive patterns and tooling, Hockley Pattern & Tool has become one of Europe's leading aerospace toolmakers of aluminium and Invar castings.

“Our automotive casting production experience has enabled us to make a logical transition to aerospace,” explains company director, Neil Williams. “We've actually changed the way the industry perceives cast components instead of large OEMs simply relying on the processes they've become accustomed to.”

Williams claims that once Hockley had perfected the production of cast mould tools that were up to 25% cheaper than other processes to manufacture, people began to sit up and take notice.

“A mould manufacturer wouldn't normally machine the whole mould tool from billet; they would just machine the top ‘sheet' of a fabricated tool. Where appropriate, we can manufacture our tools using the cast process which although doesn't make the tool better, means we can manufacture the tooling quicker; cheaper and can manufacture tools that would otherwise be uneconomical.

“Although the industry is fairly quiet at present, the sheer size and potential of the aerospace projects we've been quoting for are incredible. Work for aircraft programmes like the A350, CSeries and JSF are all set to ramp up. My feeling is that the aerospace manufacturing industry will soon enjoy a very busy time.”

www.aeromet.co.uk




www.mckennagroup.co.uk




www.finecast.co.uk




www.hockleypattern.co.uk

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