Composites, unlike metals, are not isotropic and consist of both unique resins and fibers. Hence drilling, cutting and machining composites in any post-processing operation to get to the final part shape/configuration, is indeed different. While this short column is not intended to cover “every” little trick of the trade, it is meant to offer some advice in areas pertaining to machining, cutting, sanding and other basic operations we need today to post-process composites. Understandably we do have water jet cutting equipment and other dry cutting equipment available. However, this short column is meant to address primarily those operations that are not quite as “automated” and often require a more “hands-on” personal approach.

Machining – one of the basic operations necessary to cut things to size and to finish off edges, dimensions and other aspect of a finished assembly part. Table 1 provides a few thoughts (some very obviously very basic and more typically fall into the “well duh?” regime). However, I’ve listed them here anyway.

Table 1. Machining Composites – A Few Tricks of the Trade to Consider

Conventional fluted steel cutters certainly exist and are used in fabricating final composite parts. These are the high-speed steel (HSS) and carbide cutters that are readily available and used quite often. Cemented carbide and preferably single-crystal tools are recommended for machining glass-fiber composites. However, polycrystalline diamond (PCD) tools are more preferred due to the fact they wear less than HSS cutting tools. Table 2 shows some of the desired parameters suggested for PCD tool use.

Table 2. Recommended PCD Tool Parameters for Glass- and Carbon-Fiber Composites

Sanding operations usually fall into two categories: (a) Primary sanding for material removal and (b) Surface preparation sanding. These two areas are covered in Table 3 – along with some suggestions, warnings and common approaches.

Table 3. Sanding Advanced Composites – Some Tricks of the Trade

Finally, cutting composites may indeed produce more damage than desired if not done carefully or correctly. Table 4 points out some of the major concerns associated with “cutting composites”, particularly advanced composites.

Table 4. Cutting Advanced Composites – Areas of Concern

And, for the interested reader, a few references for additional reading:

1. DuPont Kevlar™ Aramid Fiber Processing Brochures:
a. Cutting Aramid Fibers
b. Machining: Special Cutting and Finishing
c. Machining: Cutting, Drilling and Sawing
2. Handbook of Composites (2nd Edition), S.T. Peters (Editor), Chapter 27 (Composites Machining), Kluwer Academic and Chapman & Hall, 1998, ISBN 0-412-54020-7
3. Composites: Volume 21, Introduction to Post-Processing and Assembly, F.C. Campbell (pp. 615-673, ASM International, 2001, ISBN 0-871-70703-9
4. Post Processing Treatment of Composites, M.M. Schwartz, SAMPE Publishing, 1996, ISBN 0-938-99475-1
5. Post-Processing FRP Composites: The Art of Drilling, Cutting, Machining and Getting Parts Ready to Ship, S.W. Beckwith, Composites Fabrication, pp. 52-64, October 2001.