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WWW.AERO-MAG.COM 30 AEROSPACEMANUFACTURING | SEPTEMBER 2011
The capability and stability of equipment is a crucial factor: This includes automation via a robot, a portable power-fed machine or a hand tool
FOREVER T
DIAMONDS ARE
According to Sandvik Coromant, when it comes to drilling holes in composite materials, diamonds are a machinist’s best friend!
he increasing use of composites and composites stacked with metals has significant consequences for
the execution of optimised metalcutting operations. Their broad variation in properties, unpredictability and importance as engineering materials demands an approach of continuous improvement to ensure they are cut effectively, maintaining a competitive machining process. Even though the amount of machining needed on composite components is typically less than metal parts due to the properties of these innovative materials, successful machining is often far from straightforward. The drilling of holes dominates machining processes in composite materials and parts. Preparing the application of fasteners in composite- based frameworks and components can consume a significant amount of time. Even with unified structures reducing the
amount of assembly, hole production is still a dominant driver of efficiency, cost and safety issues. In establishing the properties of the
materials involved, testing remains a major pointer to applying the best tool and cutting data. Although tool life is the main consideration, optimising speed and efficiency is a growing, competitive issue. These are not homogeneous materials and their machinability range is larger than that of metals. A composite material needs to be identified according to its surface, structure, fibres, resin and thickness (hole depth). With stacks, the combination of metal types and thickness are the most important factors. Maintaining dimensional and finishing
control is a critical factor in tool selection, along with how much the hole needs to be pre-drilled for one or two drill-passes and whether reaming is required. Reliability is also a tool issue in that unaccepted holes usually lead to
costly corrective manufacturing measures – expensive components demand secure processes. Productivity through consistent results is the objective. The capability and stability of equipment, machine and set-up is another factor that will influence tool choice. The means involved are normally automated, power-fed or handheld in the form of a CNC machine, a robot, a portable power-fed machine or a hand tool. Cutting tools are usually dedicated to one or more of these means. The volume of holes to be produced
is a tool cost factor. It affects the choice of tool in that a large volume of holes in one type of composite needs to be made efficient with an optimised, often more expensive tool. A lower volume of holes, combined with the ability to cope with the variation in composites, components and set-ups, point to a different tool choice. With these demands in mind, the solutions at hand include diamond
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