SAMPE Journal - July/August 2016 - 35
Feature Article
Figure 7. AFP manufacturing development for multiple
feature articles is conducted on
Polecat contoured tooling.
Results
Process Envelope Development
Flat panel assessments described earlier have
led to a number of improvements in AFP process
parameters and changes to the bagging and cure
methods used on baseline hand laid MTM®45-1
composites.
Measuring Tack. Since existing test methods did not
provide useful quantitative tack data, Lockheed
Martin developed a proprietary method to quickly
and quantitatively assess tack levels on the shop
floor before AFP begins. Several years of IM7/
MTM®45-1 tack measurement data using this
method has correlated tack levels to ambient
conditions and prepreg outlife.
First Ply Adhesion. Since the first ply is the foundation
of quality for subsequent plies it is imperative the
first ply is well adhered to the tool surface. For
this reason vacuum compaction was found to
be necessary at the completion of the first ply's
inspection and repair; whether the ply is fiber placed
with tackifier or hand laid fabric. Both methods were
employed during experimentation depending upon
whether the article was intended for mechanical
characterization (unitape 1st ply) or manufacturing
development (fabric 1st ply).
Optimized Monolithic Process Conditions. Process control
strips verified that IM7/MTM®45-1 required high
heat and compaction to achieve the desired low
bulk factor layups. A range of compaction (balance
of machine setting and roller durometer) and surface
temperature levels (combination of machine heater
output and speed) were evaluated with these strips
to establish a broad process window. While lower
speeds are not desirable as they negatively impact
efficiency, it was necessary to establish parameters
at lower speeds as some complex configurations
are speed limited due to machine movements.
Full heater output and slower speeds can cause
overheating and serve as a source of higher
SAMPE Journal, Volume 52, No. 4, July/August 2016
porosity due to wrinkles, etc. These development
efforts settled on a machine setting of 20 m/min as
the best compromise between quality and lay-up
speed on monolithic panels.
Optimized Honeycomb Sandwich Process Conditions. The
parameters established for monolithic structure did
not transition to honeycomb sandwich structure.
While the tool side lay-up used the same placement
parameters, the first four plies over honeycomb
core required change. This was because excessive
heat caused damage to the sub-plies with the
resulting blisters and wrinkles unrepairable. The
defects could not be left as they caused significant
porosity since the plies were not well consolidated
at the location of the defect.
Laser Heating. A series of studies concluded that a
single diffused beam, with beam shaping optics,
offered the best means to process OoA materials
at the highest laydown rates and the lowest void
contents.
These studies showed that the laser source,
operating at 1070 nm wavelength in the IR
spectrum, provided for accurate surface
temperature measurements near the nip point
using a pyrometer sensing at 8,000 to 12,000 nm.
These measurements were used to actively control
the power applied to the laser, thus maintaining a
uniform nip temperature at all placement speeds.
An integrated optic both shaped and focused the
beam such that the heated zone was placed just
prior to the machine's nip point. The sharp energy
drop off outside the heated zone is illustrated in
Figure 8. This capability to precisely control the
heated zone is critical for OoA AFP since high
temperatures (more than 40°C) outside the width
of the roller will lead to wrinkling of plies and the
formation of unrepairable defects in the part.
35
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 - 16
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SAMPE Journal - July/August 2016 - 18
SAMPE Journal - July/August 2016 - 19
SAMPE Journal - July/August 2016 - 20
SAMPE Journal - July/August 2016 - 21
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SAMPE Journal - July/August 2016 - 30
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SAMPE Journal - July/August 2016 - 35
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