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Cutting Tool Specialists
Carbon Composite Cutting Solutions
The development of Carbon Fibre Composites and their introduction into the aircraft and related industries, where weight and strength of materials are essential requirements, has demanded a reappraisal of the conventional cutting tools. New geometry is essential to avoid delamination in composite materials. Special emphasis has been placed upon the machining activities in drilling, reaming, countersinking, routing/milling and slitting.
The rivet is the main fastening method for component assemblies
, therefore it is important that
good quality holes are produced, because of the use of different material laminates, i.e. Carbon,
For Carbon-Aluminium and Carbon-Titanium different types of drills must be used. The carbide tipped drill GT100/GT200 (fig 1) is most commonly used for drilling carbon only. It can be supplied in relatively small diameters with long flute and overall lengths. These drills can be supplied to drill H8/H11 standard holes but should be changed after approximately 50 to 60 holes to avoid delamination or poor quality.
DRILLING
Another type of drill commonly used in the UK is the dagger drill (fig 2). Early experiments proved it was the best drill for machining unbacked carbon, because of its ability to reduce delamination and at the same time giving a quality sized hole. The drill is manufactured from solid tungsten carbide and because of the dagger point geometry, the cutting forces are much reduced at the centre. It must be remembered that dri
lled holes in Carbon Fibre always shrink slightly after machining, so allowances must be taken into account at the planning stage, before drills are ordered. It must also be remembered that when drilling laminates the Carbon shrinks but the Aluminium and Titanium elements do not. When drilling Carbon laminates it is necessary to drill a pilot hole using a solid carbide two flute drill which has a split point geometry and an angle of 130deg. The point geometry is normal for drilling Titanium and is quite acceptable for Carbon. The solid carbide tri flute drill is then used to open the pilot hole to a size prior to reaming (fig 3).
Gandtrack Ltd, Unit 8, Gladstone Business Park, Gladstone St, Moorhey, Oldham, OL4 1AX England.