Cutting to the chase with composites

The use of composite materials is growing in the manufacturing industry and correct cutting methods are vital to reaching full machining potential.

BOEING’S new 787 Dreamliner marks a turning point for the commercial aerospace industry as it moves away from tradition and paves the way of the future.

The 787 is the first large commercial aeroplane made almost entirely from carbon fibre composite materials and is an example of the growing popularity of composites. Using composites is known to provide economic gains as they are lighter, stronger, require less maintenance and produce a better fuel economy.

While the composite industry in Australia remains relatively small, Dr Paul Falzon, Program Manager for Manufacturing and Test at the Cooperative Research Centre for Advanced Composite Structures (CRC-ACS) believes it is steadily growing.

“As the demand for high performance, reduced weight and better corrosion resistance materials grows, the move towards composite materials grows,” said Falzon.

He says that as more and more Australian manufacturers choose to work with composites, it is vital they understand the different skills sets required and the different cutting tools needed to take full advantage of the material.

“It requires either an up-skilling of current staff, or an introduction of new staff with skill sets you need because machining a composite is a completely different skill and process.

“It also means all capital equipment would need to change and for a company wanting to do that, it should probably look toward buying a facility that specialises in composite manufacture to expand its industry.”

While the aerospace industry is the largest in Australia to be using composites, a number of other manufacturers have embraced the materials.

Jason Theobald, Productivity Engineer at Sandvik Coromant Australia says composites are now a crucial production ingredient in the automotive, rail and transport, energy, electronics, bicycle and sporting industries.

“The Australian composite industry is in its infancy but Australia, as with the rest of the world, is seeing that composite materials can offer great advantages over metallic components. Carbon fibre is stronger than steel, lighter than aluminium and as stiff as titanium,” he said.

Composite materials have a lower density than metals meaning they will often outperform metals in stiffness and strength. With corrosion resistance and enhanced fatigue resistance, composites are also less likely to fail as a result of repetitive loading.

Theobald believes these could be some of the reasons why Boeing opted to create an aeroplane where composites make up 50% of the total structural weight.

“Pressure is being put on the aircraft manufacturers to make planes more fuel efficient. One way to do this is to reduce the weight of the aircraft. The use of carbon fibre reinforced plastics (CFRP) has gone a long way to reducing the weight of the aircraft,” he said.

Despite this, both Falzon and Theobald agree that the use of metal remains more popular in Australia, largely due to its ease of machining.

According to Falzon, metals are ductile and therefore more damage resistant; they are easier to join, have better bearing performance and are less damaging to cutting tools.

“Composites need to be machined by an abrasive process so using conventional cutters that are used for metals will not necessarily work with composites,” said Falzon.

“Also composites are insulating materials so they generally don’t take the heat away from the cutter and the cutters themselves can get very hot. You don’t want your composites hot because that could be detrimental to the material itself.”

Cutting composites requires abrasive wear resistant cutting tools, with diamond coating or polycrystalline diamond (PCD) tools the most popular. While the best tool to use is determined by the fibre type in your composite, Theobald advises that while more expensive, PCD tools are generally best.

“A lower cost solution is uncoated carbide or diamond-like coated (DLC). These tools are cheaper to purchase but are not always the most cost effective solution, more often than not, the more expensive PCD or diamond-coated tool will give a lower cost per hole,” he said.

Safety and maintenance

Cutting composites generates a fine dust rather than the traditional swarf produced when machining metal, which can pose health and safety risks as well as cause equipment to malfunction.

“There are two ways to address dust generation: one is by adding a lubricant or water into the cutting process and the second is to have some sort of dust extraction system or vacuum,” said Falzon.

Carbon fibre dust also has the potential to infiltrate mechanical electrical systems, causing them to short out, he adds.

The abrasive nature of machining composites can also cause damage to cutting tools.

“Composites are more damaging to your cutting tools than metals. They wear faster; they need to be replaced sooner and if they’re not replaced can introduce further damage into your composite parts,” Falzon said.

Theobald adds that due to the multi-layered fibre nature of CFRP materials, splintering, fraying and delaminating are issues of concern.

“When drilling these materials, as the drill enters and exits the hole, there is a tendency for the material to splinter or delaminate. Drills that are designed to impose lower axial forces will help to reduce this,” Theobald said.

While both Falzon and Theobald believe there is a strong tradition for using metal in Australia, they are optimistic for the future of composites.

“With the emerging aerospace market, we will see an increase in the machining and use of composites within Australia. Is there a big market? That remains to be seen,” Theobald said.

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