As an exhibitor at WESTEC this year, I was amazed by the number of times I was asked the same question: “How do I machine CFRP?”
It’s a question I often field as the sales director of Diamond Tool Coating. But the frequency with which it was asked during WESTEC suggests that the use of Carbon Fiber Reinforced Polymers (CFRP) is rapidly transforming every facet of the manufacturing sector.
Seven years ago the question of ‘how best to machine CFRP’ was very much on the minds of the engineers at large aerospace companies. These companies invested millions of dollars in testing to find solutions that are now being used in projects approaching full-scale production, including Lockheed Martin’s F-35 and the Boeing 787.
One solution that was discovered as a result of testing was the combination of customized tool geometry and CVD diamond coating.
What Is Diamond Coating?
Many coatings are referred to as “Diamond”, but several important distinctions can be made between three main types: Poly Crystalline Diamond (PCD), amorphous diamond or Diamond Like Coating (DLC) and Chemical Vapor Deposition (CVD) crystalline diamond coating.
PCD consists of diamond crystals held in a cobalt matrix. This material is produced as small tips that are brazed onto the leading edge of cutting tools. Amorphous diamond is a carbon based coating ranging in hardness from 500 to 5,500 Vickers. Crystalline diamond coating is grown in a CVD hot filament vacuum chamber, producing a coating with a hardness of 9,000 to 10, 000 Vickers.
Unlike PCD-veined tools, CVD diamond coating consists of 100% natural diamond. And because the coating protects the entire surface of carbide tools, complex geometries can be quickly designed and tested for specific applications.
The most difficult to machine composite material is made up of dense resins with fiber layers stacked in a single direction, as opposed to a cross-hatch pattern. In addition, a Titanium or Aluminum back plate is often paired with the composite in what is referred to as a composite stack.
The natural properties of CVD diamond significantly increases tool life and performance when machining this type of composite: Its high hardness and high fracture toughness resists chipping and cracking, while its low coefficient of friction dissipates heat and eliminates build-up edge. The coatings smooth surface is also capable of cutting fibers cleanly and producing fine finishes in metal.
To ensure that the maximum benefit of the coating is employed, it is important to consult with tooling engineers, who can recommend or customize tool geometries. This is especially true for applications requiring tight tolerances.