SAMPE Journal - July/August 2016 - 39

Feature Article

Figure 11. Window blinding can
increase in severity over time until
optimal process settings
are established.

the formation of other common AFP defects. In
simple applications like monolithic flat panels,
degraded tack of the material could be offset by
simply increasing the heater output (or reducing
speed). It became more challenging, however, to
effectively employ these trade-offs when placing
more complex articles.
Complex Contours
When advancing to complex contoured structures,
AFP parameters developed on flat and simple
contoured surfaces were found, in large part, not to
be successful; although the process development
used to eliminate the defects remained effective.
An added concern when fabricating complex

Figure 12. Complex curvature leads to the occurrence
of convergence gaps.
SAMPE Journal, Volume 52, No. 4, July/August 2016

contours which is not seen in simpler articles was
convergence gaps. This occurs when two courses
converge as a result of the complex geometry
resulting in an overlap of the courses (Figure 12).
To prevent unwanted increased thickness, the
machine automatically cuts one or more tows from
the edge of the course leaving a triangle shaped
gap. In some cases, this gap can run the length
of a course. The primary method of handling the
occurrence, frequency, and size of convergence
gaps is through the NC program guiding strategies
combined with lap/gap allowance.
The progression of complex contour development
articles (Figure 13) validated the three main
parameters impacting the quality of lay-ups
(including defect occurrence and severity); they are
tow tension, compaction force, and heat.
Minimizing tow tension had a significant effect
on the elimination of bridging and other defects.
Reducing tow tension was best accomplished by
modifications to the guides used to help direct and
align the tows from the spools to the nip point. Tow
tension is also impacted by changes in the NC
program.
Two general rules were followed when considering
modifying compaction parameters to improve
part quality: 1) higher durometer rollers provide
increased ply consolidation; however, they do not
conform to complex surfaces as easily, and 2) to
help increase compaction and conformity over
certain features, reducing laydown rate can be of
value, but can cause local overheating.
The two main factors controlling heat, as
discussed prior, are the machine settings and
39



Table of Contents for the Digital Edition of SAMPE Journal - July/August 2016

Contents
SAMPE Journal - July/August 2016 - Cover1
SAMPE Journal - July/August 2016 - Cover2
SAMPE Journal - July/August 2016 - Contents
SAMPE Journal - July/August 2016 - 2
SAMPE Journal - July/August 2016 - 3
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