Making the cut: tools for machining composites

Composite machining 4Many issues for cutting composite materials must be resolved as their applications multiply.

Manufacturers of large structures often need to remove weight from the product, which has pushed the greater use of composite materials. Leading the way are aircraft structures, wind turbine blades, Formula One monocoque cabins and, increasingly, structures on cars. The Jaguar F-Type has carbon-fibre wind mirror covers, bonnet louvres and a variant has a carbon-fibre roof.

The aerospace sector is the largest customer for composite machining solutions

The growth of carbon-fibre applications  has driven new machining technologies for composites. Machining techniques, cutting tool designs and workholding solutions have been refined, but the biggest area is cutting tool design, with a growing  range of tooling companies introducing new designs to overcome the problems of machining composites, which behave very differently to metals. Layers, or plies, of fibre and resin bonded together react differently when placed under the force of a cutting tool.

“The biggest difference is in the chip formation mechanism, which you have no control of for composites, as the material shatters,” said Dr Kevin Kerrigan, composites machining technology lead at the Advanced Manufacturing Research Centre (AMRC)  with Boeing near Rotherham. Dust is the predominant feature when composite machining, as the cured epoxy resin layers disintegrate and throw up micro-sized particles.

The challenge for tool designers is to create a geometry that first deals with the chip formation mechanism and then the damage you encounter with fibre (FRP) or glass-reinforced plastic (GRP).

Damage mechanisms  can vary with  the bonding of two different materials, the epoxy plastic and the fibre itself. Under mechanical stress, these layers can separate or delaminate.

“Delamination is one of the biggest challenges for tool suppliers, in that there are so many damage types and every application has a different requirement,” said Kerrigan. “The tool designer  has to design a product for the customer’s own needs.
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July 2, 2015



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