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CFRP gets tough love from microtools

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Carbon-fiber-reinforced plastic (CFRP) is a corrosion-resistant and lightweight material used in everything from paintball guns to Formula One racecars. The composite material has an “ultimate tensile strength” approximately four times that of steel and unrivaled strength-to-weight ratio, meaning it’s not only stronger than alternative materials, like aluminum, but you also need far less of it by weight to do the same job.

Tiger Woods has CFRP in his golf clubs; the Boeing 787 Dreamliner has a CFRP skeleton; and, if you’re a superhero, you’ve probably got a CFRP crime-fighting suit hanging in your closet.

But CFRP is difficult to machine because it’s made of carbon fiber and epoxy resin. Not only is CFRP extremely abrasive, it’s prone to nasty things like delamination and fracturing. Think of it as machining fiberglass with a bad attitude. And the smaller the tool, the greater the challenge it is to keep that tool sharp and in one piece.

Given those challenges, machining costs for CFRP must be astronomical, right? “Not necessarily,” said Earl Benton, executive advisor for CFRP manufacturer Toray Composites (America) Inc., Tacoma, Wash. “There are always trade-offs. You have to look at it in the context of the total life-cycle cost.”

According to Benton, the machining challenges posed by CFRP are offset by its longer service life and the reduced number of manufacturing steps required to turn it into a useful product.

Compare a CFRP airframe to a traditional airframe, for example, where the different aluminum components must be joined with mechanical fasteners. “By using composites and utilizing cold-bonding or secondary bonding techniques, you can eliminate a lot of fasteners,” he said. This means less machining, lower assembly costs and a cheaper, stronger and longer-lasting airplane.

Anyone who flies loves the thought of a better plane, but that doesn’t help you cut this stuff. So how do you drill microholes in the material equivalent to Superman’s tights?

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