TM 1-1500-204-23-11
(1) Boron. Boron ibers are harder than most
(3) When using diamond tools inspect cutting
conventional cutting materials (tungsten carbide, alu-
surfaces before use and replace if diamond
minum oxide, silicon carbide and tool steel) and
plating appears worn or if bare metal areas
require the hardness of diamond for cutting. Vibra-
are evident. Remove resin or other contam-
tory stress can be setup along the tungsten ilament
ination from diamond tool cutting surfaces
during machining which may result in damage to the
before use.
boron iber.
(4) Carbide tools are signiicantly heavier than
(2) Carbon. Carbon ibers are very abrasive
HSS tools and can be distinguished from
and rapidly dull high speed steel (HSS) cutters during
them by their difference in weight. When
cutting operations. Either carbide or diamond is
using carbide tools, inspect and replace if
acceptable materials to use for cutting carbon ibers.
nicks, chips or other defects are present on
Carbon ibers can be readily sanded and cut using
the tool cutting surface. Keep cutting sur-
abrasive materials. Silicon carbide is the most effective
faces free of resin buildup. Carbide tools are
abrasive material for sanding carbon ibers. During
very brittle and cutting surfaces are easily
sanding the silicon carbide particles fracture exposing
broken or chipped if dropped. Use care in
a fresh cutting surface. By contrast, aluminum oxide
handling.
abrasive dulls during sanding reducing its material
removal capability. During cutting operations, carbon
(5) Cutting forces increase considerably as tools
ibers experience a brittle fracture of the iber.
become dull. It is essential to use sharp
cutters to provide quality cuts and minimize
(3) Kevlar. Kevlar ibers are more ductile
the potential for delaminations. Replace or
and tougher than either boron or carbon. While
re-sharpen tools if excessive cutting force is
this has advantages in terms of impact resistance,
encountered during cutting operations.
it provides problems during machining. Rather than
a brittle fracture occurring during cutting operations,
(6) The use of bandsaws, table saws and radial
the Kevlar ibers split along their length resulting
arm saws for cutting generate a consider-
in fuzzing of iber ends. In addition, Kevlar ibers
able out-of-plane cutting force and should
have a relatively low compressive strength and tend
not be used on advanced composites with-
to recede into the matrix instead of being sheared off
out irmly clamped backup material. Their
during machining operations. To reduce fuzzing and
use on actual aircraft parts is impractical
produce smooth edge cuts, cutter designs attempt to
unless cutting up scrapped parts for dis-
keep the iber preloaded in tension while shearing
posal.
the iber. Sharp HSS or carbide cutters are adequate
for shearing Kevlar ibers. Unlike dust generated
(7) Prevent exit side breakout/ splintering dur-
when machining carbon ibers, Kevlar ibers tend
ing drilling. As the drill bit breaks through
to generate clumps of subibers (ibrils) which clog
the exit side of the laminate when drilling,
cutters and reduce the quality of cut surfaces.
there is a sudden decrease in resistance
to drilling and a rapid increase in feed rate.
(4) Fiberglass. While not quite as abrasive as
The increased feed rate results in exit side
carbon ibers, iberglass is still capable of dulling high
breakout and splintering of the laminate.
speed steel (HSS) cutters during cutting, machining
Reduced strength of bolted joints can result.
and drilling operations. In general, the same tooling
Use irmly clamped backup material on drill
used to machine and drill carbon iber should be used
exit sides. When drilling blind holes, use
for iberglass.
cutters designed to reduce drilling forces.
c. General Safety. These are general safety
(8) Machined holes and edges in composites
instructions to know and follow prior to executing
must be deburred. Tools and techniques
machining, drilling, reaming, or countersinking proce-
vary for composites; however, methods
dures.
include hand and power sanding. When
sanding, composite laminates should be
(1) Select the tools based on the recommenda-
sanded parallel to the iber direction. When
tions in the system speciic technical manual
deburring a hole, sand toward the center of
or Chapter 3 of this manual.
the hole. All deburring should be done with
the abrasive or tool inclined 45 degrees to
the edge. Power tools should be worked in
(2) Follow the general tool use guidelines in
the direction of tool rotation.
Chapter 3 and the material speciic guide-
lines in paragraph 6-8.
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