Compounds and Composite Materials - PEEK Biomaterials - page 41

type of process is being used to manufacture CFR
PEEK intramedullary nails.

geometry of the part being made and has an appro-
priate split line to open it.
A plunger is inserted into the barrel until it is in
contact with the rod. It is then pushed along under
considerable force, pressing the material into the mold
in which the material takes up the shape of the cavity.

3.5.2.4 Hot Forming
Composite Flow Molding
“Composite flow molding,” developed by ETH
Zurich [32,33] and commercially applied by Icotec in
Switzerland, is a high-pressure molding process in
which a piece of continuous fiber-reinforced
composite material (usually a length of pultruded
rod) is transformed by heat and pressure directly into
the shape of the required artifact. This has the
advantage of producing very-high-strength
composite parts such as screws, plates, and pins.
It is best described using a number of process steps
( Fig. 3.25 ).

Step 3 d Follow-up pressure and cooling

The mold is cooled under pressure, whereupon the
PEEK matrix cools, crystallizes, and solidifies,
creating a stiff composite part, which is then de-
molded below the glass transition temperature

(143 C).
A key feature of this process is that, unlike injection
molding, it is able to use continuous fiber-reinforced
PEEK with high fiber loading (60 e 65% by volume).
This means that the mechanical strength and stiffness
of the final device can be optimized to take the fullest
benefit from the superb properties achieved with
combination of carbon fiber and PEEK polymer.
Examples of parts manufactured using this process
are shown in Fig. 3.26 , courtesy of Icotec AG
(Switzerland). These parts include two translaminar
pins for the spine, a bone plate (snake plate), and
a bone screw. In polished cross-section the arrange-
ment of fibers in the screw follows the helical direc-
tion of the threads as shown in Fig. 3.27 , yet at the
same time other fibers in the center are oriented along
the axis of the screw; in between, there is a transition
zone. This fiber arrangement occurs naturally and is
as a result of the flow paths that the fibers take as they
flow into the mold cavity under pressure, which is

Step 1 d Loading

The pultruded rod (with continuous, axially
aligned carbon fibers) is cut to length and placed on
a heated barrel. The barrel is a plane cylinder; there is
no screw in the barrel as there is with injection
molding and extrusion. The barrel is electrically
heated to above T m , the melting point of PEEK, to
soften the polymer matrix.

Step 2 d Shaping

A steel mold is placed at the output end of the
heated barrel. This carries the impression of the final

Figure 3.26 Composite flow molded parts (translami-
nar pins, snake plate, and screw). Photo courtesy of
Icotec AG.

Figure 3.25 Composite flow molding process

sequence. Courtesy of Icotec AG.