The Joint Strike Fighter (JSF) Program is
not only cutting edge, but cutting costs too.
Image: iStockphoto

Defence is an expensive business. Strike aircraft weapons systems, for example, don’t come cheap. But their necessity, and these strained economic times, means more research is being put into reducing their cost of production.

So what on the surface is a conventional cost-cutting exercise – to reduce titanium machining costs and improve productivity – also has important ramifications for an international military project led by the US.

Run by the US Department of Defense, the Joint Strike Fighter (JSF) Program is looking to not only produce the next generation of defence aircraft for the US military and its allies, including Australia – which has a $16 billion tentative order for 100 F-35 JSFs – but to also make them more affordable.

An important aspect of achieving this is being able to reduce the cost of machining titanium alloys. Their high strength-to-weight ratio, the ability to retain that strength at high temperatures, and high corrosion resistance compared with other alloys has long made this metal attractive to the aerospace, marine, chemical, petroleum and biomedical industries.

However, titanium alloys are difficult to machine, even with modern cutting technology. This is due to of a number of factors:

• the way the alloy changes shape when machined;
• its low thermal conductivity, which makes it difficult to remove heat from the cutting region, increasing the temperature and contributing to a chemical interaction with the cutting tool’s material; and
• the alloy’s low elastic modulus, which means the material is easily deformed during machining.

Added together it means that it takes longer to machine titanium alloys compared with other metals and tools are worn out faster, resulting in high machining costs.

Tackling this problem – the resolution of which would have benefits for manufacturing worldwide – is Australia’s CAST Cooperative Research Centre (CRC). The CRC, which includes Swinburne University of Technology, conducts industry-driven research into the use of aluminium, magnesium, titanium, cast iron and steel.

Its CEO, George Collins, says the CAST CRC has been working to reduce titanium production costs for several years, and has been funding Swinburne to work on the laser-assisted turning of titanium. “It was a ‘blue sky’ project for us and one of only two strategic research projects we fund. But it caught the attention of Lockheed Martin.”

US-based Lockheed Martin is the global security and IT consultancy responsible for delivering on the goals of the US Defense Department’s JSF program.

Dr Don Kinard, Lockheed Martin’s technical operations deputy for F-35 global production operations, says titanium alloys are widely used on the F-35 Lightning II, a strike fighter being developed by the JSF Program.

“Machined and forged titanium parts are used routinely in high temperature areas such the engine compartment, where aluminium alloys cannot operate efficiently,” Dr Kinard says. “Titanium is also used in other structural F-35 applications, where it saves sufficient weight to justify the increased production cost.

“For example, the use of machined/forged titanium parts is more pronounced on the F-35 carrier variant because of the high loads which that airplane encounters during carrier landings.”

Interested in the results Swinburne’s Professor Milan Brandt was getting – including that lasers make it possible to quicken the turning process at the same lathe power, while improving the finished product’s surface integrity thereby maintaining its strength and corrosion-resistance properties – Lockheed Martin paid a visit while in Australia touring local research capability.

Professor Brandt says Lockheed Martin was interested in the laser-assisted turning project, but wanted to know if the same results could be gained from laser-assisted milling.

It is a question that Professor Brandt’s team – which includes his Industrial Research Institute Swinburne colleagues Dr Shoujin Sun, Girish Thipperudrappa, Andy Moore and PhD student Nancy Yang – is now half-way through answering via another CAST CRC project, one that is funded by Lockheed Martin.

The research team uses a laser to heat the material surface, with a beam directed in front of the cutting tool, allowing the material to be cut with greater ease.

Experiments vary the laser power, machining speed and depth of cut. “We want to find out why the reduction in cutting forces occurs with the heat of the laser and at what distance from the cutting tool,” Professor Brandt says.

So far, results for milling are as positive as those of laser-assisted turning. “But we need to do more experiments and see how we could integrate a laser and the cutting tool. That’s the long-term objective and ultimate aim of the Lockheed Martin work – to deliver the technical data needed to design an all-in-one machine.”

Professor Brandt says the idea to use lasers came from previous research on ceramics, another hard-to-machine material. “All we are trying to do is translate that to titanium. If we can increase the removal rate and increase tool life, then we can reduce the cost of machining and using titanium.”

The research also allows for his team to examine the fundamental science behind laser-assisted titanium machining – and already Dr Sun has a new theory on titanium cutting.

“At the end of the day it is all leading to machining titanium faster but maintaining a quality surface. Our objective is to increase the understanding of the cutting process and translate that into practical information.”

The F-35

The Royal Australian Air Force has placed a tentative order, worth $16 billion, for 100 of the Lockheed Martin F-35 Lightning II joint strike fighters.

The F-35 is a supersonic, multi-role, fifth-generation stealth fighter. Three variants derived from a common design, developed together and using the same infrastructure worldwide, will replace at least 13 types of aircraft for 11 nations initially, making the Lightning II the most cost-effective fighter program in history.