SAMPE Journal - July/August 2016 - 38

Feature Article
in Figure 9. To minimize the tool surface dryness, six
different tool preparation methods were explored.
In addressing the bridging defect, multiple
modifications to the numerical control (NC) program
and other settings were considered. In addition,
reducing speed in zones containing joggles
increased roller compaction benefits, although it
did lead to the IR heater dwelling over the region,
increasing the risk of overheating. With some
process settings, this excessive dwell time was
found to lead to sub-ply damage, in some cases
causing the plies to lift off of the tool surface at the
feature location. Once the plies lifted from the tool
surface, the tension of the current tows being placed
prevented the lay-up from returning to its original
position of conformance. Selecting the correct
combination of heat and machine speed was,
therefore, critical to achieving good compaction
and feature conformance while not overheating
and causing sub-ply damage. Optimized process
settings have been established which have led to
joggle trials panels with well consolidated ramp
plies and excellent tool side surface quality as
shown in Figure 9.

reduce bridging at core ramps (Figure 10). The
primary factors focused on were the following: tack
levels of the material, compaction forces, and tow
tension. One of the elements impacting the tack
of the material is the heat settings of the machine.
As discussed previously, heat settings directly
over the core differ from the optimized settings on
monolithic laminates since the core material acts as
a thermal insulator. The high heat settings desired
on monolithic structure caused blistering of the film
adhesive and/or plies below; making core structure
more challenging to lay-up using OoA materials.
Other factors found to directly impact the quality
of the placed core ramps was roller width and
durometer, and tension in the tow path. Smaller
rollers reduced the distance between the roller
ends and allowed for better conformance to highly
contoured surfaces. Lower durometer rollers
improved the ability of the roller to conform to the
ramped surface feature. Minimizing tension in the
tow path was also found to play a critical role in
reducing bridging defects, including the insertion of
radius fillers in the laminate-to-ramp transition area
to reduce the severity of the transition geometry.

Optimized Core Ramps. Another feature evaluated on
flat surfaces was encapsulated core structure.
Processing encapsulated core begins with the
definition of the core geometry. Both the core ramp
angle (nominally 20°) and the shape of the corners
are of important consideration. Conical corners, as
opposed to square corners, are preferred. The sharp
edge of the square corner resulted in increased
bridging and wrinkling of the tows. Moreover, the
conical corners allowed the machine to maintain a
higher speed due to lesser abrupt movements of
the AFP head.
Once the geometry of the core was established,
the emphasis turned to maturing techniques to

Simple Contours
The impact of concave and convex geometry on
process settings was the focus of the efforts on midscale simple contour parts. Using a simple concave
tool measuring 2 × 2 m (Figure 5), tow paths with
multiple radii were evaluated to ascertain when the
window blind defect begins with IM7/MTM®451. On most radii, the window blind defect did not
always immediately appear, but as shown in Figure
11, began to emerge after placement was complete
and continued to manifest over time.
In addition to window blind defects the advent of
contour to our test articles was found to increase

Figure 10. Development of improved
AFP process parameters at
core ramps leads to
minimized bridging and
other defects.

38

SAMPE Journal, Volume 52, No. 4, July/August 2016



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
SAMPE Journal - July/August 2016 - 4
SAMPE Journal - July/August 2016 - 5
SAMPE Journal - July/August 2016 - 6
SAMPE Journal - July/August 2016 - 7
SAMPE Journal - July/August 2016 - 8
SAMPE Journal - July/August 2016 - 9
SAMPE Journal - July/August 2016 - 10
SAMPE Journal - July/August 2016 - 11
SAMPE Journal - July/August 2016 - 12
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SAMPE Journal - July/August 2016 - Cover3
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