New developments in composite hole-making

Machining has a new challenge in an evolving material area: composites. Although these materials are not difficult to machine, today’s challenge lies in making holes to tighter quality limits with greater efficiency and security, particularly when the composites are stacked with metal layers. This has called for a different approach, with solutions that are highly dedicated for specific applications.

Dedicated drills

The use of carbon fibre reinforced plastic (CFRP) is increasing, not only in the aerospace industry but in other sectors too, notably automotive and defence. Large amounts of holes for fasteners are needed, and product safety means quality has become a competitive issue. However, drilling CFRP can lead to different material-specific defects such as delamination and splintering. Furthermore, when the same cutting tool has to drill through metal stacks, such as aluminium or titanium, the need for solutions dedicated to the application become even more important as the tool has to cope with completely different, sometimes demanding machinability, chip formation and evacuation issues.

The amount of machining needed on CFRP and CFRP/metal stacked components is typically less than conventional metal components, but due to the material properties, they can be more demanding to machine to critical specifications. Drilling CFRP involves fracturing the fibre part of the material but to obtain ‘clean’ cuts, a different approach is needed in tools and methods. As poor conductors of heat that fail to produce chips, heat produced when machining composites becomes an issue as there is a risk to the resin part of the material at elevated temperatures. Composites are therefore more able to indicate weaknesses in the machining process than metals. Their broad variation in properties, unpredictability and their growing importance as a component material, needs continuous improvement to maintain a competitive machining process.

Plan ahead

Planning production involves establishing a close description of the application for it to become a successful machining process. Data required should include: the number of holes to be machined; hole size; depth and tolerance; the manufacturing equipment or machine type being used; the stability of the set-up; and the material properties. It is also vital to gather any documented experience from machining similar materials and to enlist the support of an experienced tool supplier with good products.

A dedicated cutting tool that is correctly specified and applied is the key to achieving satisfactory holes. This will also minimise dust contamination when machining CFRP and CFRP/metal stacked components. The hole quality indicators traditionally visiAir Jordan XXXI Low