Biomedical Engineering Reference
In-Depth Information
2.6 Machining
Table 2.4
Properties of a 0.5-mm PEEK
Monofilament
Often for prototype designs or short production
runs, it is not economically viable to manufacture an
injection molding tool. Under such circumstances, it
is common to use compression molding or to
machine PEEK-OPTIMA polymer materials to form
components. PEEK-OPTIMA polymer may be
machined and finished using the same techniques
and equipment as for other engineering thermo-
plastics. However, because of the excellent physical
properties and wear characteristics of these mate-
rials, it is advisable to use carbide or diamond tipped
tools and bits. Machining and finishing operations
on polymeric materials are prone to propagating
molded-in or residual stresses. Before machining, it
is recommended that components formed from
PEEK are annealed to relieve stress. During
machining or finishing, further stresses may be built
up within the material by localized heating at the
cutting point. Therefore, if a large amount of
machining and finishing is to be carried out on
a component, a second annealing procedure may be
required.
The thermal conductivity of all polymeric mate-
rials is lower than that of metals; hence, heat build-up
during machining is rapid. It is advisable that
a cooling fluid is used to remove some of the heat
generated by working the material. Water or air jet
cooling is generally recommended for medical grade
PEEK polymer-based materials. A summary of the
suggested machining conditions for PEEK-OPTIMA
has been provided by Invibio
[10]
.
Typical
Value
Material Property
Energy to break
1.24 J
Tensile load at 2% elongation
1.18 kg
Tensile load at 5% elongation
1.77 kg
Tensile load at 10% elongation
2.66 kg
Tensile load at break
5.81 kg
Elongation at break
22.0%
Knot strength
2.42 kg
of fully amorphous PEEK films becomes more
challenging.
PEEK monofilament can be produced by extrusion
followed by drawing of the PEEK extrudate.
Drawing the polymer provides orientation within the
fiber prior to heat setting. The resultant monofilament
is tough, highly oriented, and has a controlled
diameter, which will retain its set form above the
glass transition temperature of the material. Typical
properties of a PEEK monofilament are shown in
Table 2.4
. PEEK monofilaments are distributed as
multifilament yarns (
Fig. 2.13
) and can be woven into
more complex three-dimensional shapes.
2.7 Summary
As detailed in this chapter, there are various
synthetic routes involved in the production of
polyketone-based materials. These routes have been
developed to overcome the initial challenges in
relation to polyketone manufacturing, resulting in the
consistent production of polymers for medical
applications. It should be noted that the synthetic
chemistry used in PAEK manufacture has a major
influence on the thermal stability of the polymer in
processing operations and on the leachable and
volatile content of these polymers. Therefore, the
manufacturing route has the potential to alter the
biocompatibility of PAEK materials. The progress in
manufacturing has been extended to processing
where established methods have been developed to
Figure 2.13
Spool of
technical grade, multifilament
PEEK yarn.
