Composite drill: tool, process change nets 450 percent more holes per bit life.

Author:Gilpin, Andrew
Position:Cutting tool solutions

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As new composites are introduced almost daily), toolmakers are responding with effective solutions to help lower machining costs and even solve production floor management problems. As detailed by a case study below, Lockheed Martin Aeronautics Co. recently carried out a process change on its F-35 fighter development, allowing it to acquire and control cutting-tool geometries and achieve longer tool life cycles.

There is a growing demand for tool innovations to cut, shape and drill composite material applications in almost every industry sector. Composites, each presenting a unique composition and set of characteristics, are competing with and replacing traditional building materials--steel and aluminum--at a rapid rate.

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Commercial and military aircraft now incorporate a high percentage of composites, taking advantage of their utility as molded parts and structures and their extraordinary strength-to-weight ratios (see ratio table below). In Boeing's next generation commercial aircraft, the 787 Dreamliner, 50 percent (by weight) of its primary aircraft structure will be made of composites.

Inside a composite

Inherently, no two composites are the same. Their marbled internal texture is nothing like the uniformity of aluminum or steel, which can be expected to remain consistent from a drill's entry point to its exit. With composites, it's not so.

Carbon fiber reinforced polymer (CFRP) is composed of a matrix base material, reinforced with a mix of strong carbon fibers. These fibers either can be laid out in a consistent direction or opposed weave pattern. Composite layers are stacked upon others to form composite blocks, boards and molded shapes.

To add mass, foam or honeycombed core structures may be inserted between composite layers or attached to them. Layered and molded configurations are designed according to the specific need and use of the part that may be several inches in thickness.

While core layers can strengthen a composite form, composite material strength is primarily due to its ratio of extreme strength to slight weight, a ratio that translates into lighter, faster, better, for most developers and manufacturers.

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Strength to weight ratios

The CFRP strength ingredient, carbon fiber, is many times stronger than aluminum and even the hardest steel.

CFRP tensile strength ranges between 1,500 to 3,500 MPa (carbon fiber alone is shown in the chart below) as compared...

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