SAMPE Journal - July/August 2016 - 28

Feature Article
Out-of-Autoclave Fiber Placement Developments
R. W. Koon and S. C. Parsons
Lockheed Martin Aeronautics Company, Marietta, GE

K. A. Povlitz and S. R. Jirik
Lockheed Martin Aeronautics Company, Palmdale, CA
Abstract
Fiber placement of Out-of-Autoclave (OoA) epoxies presents unique challenges to high rate automated fabrication of composite
structures. Development efforts by Lockheed Martin Skunk Works® on MTM45®-1, in particular, have shown that, as compared to
autoclave materials, fabrication of high quality OoA structures by fiber placement requires significant modifications to the hand lay-up
prepreg form, higher temperature placement conditions, and close attention to material tack and outime levels. Recent efforts using
Skunk Works® Ingersoll Mongoose AFP machine have fabricated a variety of MTM45®-1 articles from test panels, to elements, to
complex wing skin structures, all of which have led to the formation of improved placement parameters. The lessons learned from
these efforts have highlighted which changes in machine design and process parameters will have the greatest impact on improving
the quality and cost of future OoA fiber placed structures.
Introduction
The aircraft industry's emphasis on reducing the
cost of composite structures has accelerated the
development and application of Automated Fiber
Placement (AFP). AFP's cost savings potential stems
from reductions in labor costs through automation,
its suitability to fabricate larger unitized assemblies,
and its ability to place pre-impregnated (prepreg)
plies at rates far in excess of the manual lay-up
process. Much of the development and production
use of AFP technology has been in the fabrication
of autoclave cured composites. As designs for
such composite structures increase in size, both
the cost of tooling and autoclaves to accommodate
them becomes prohibitive for all but the largest
production programs (e.g. 787). As an industry
leader in the manufacture of advanced prototype
aircraft, Lockheed Martin Skunk Works® has
recognized the cost savings opportunities offered
by the development of toughened out-of-autoclave
(OoA) epoxy materials. Looking to leverage these
cost benefits, we have invested in facilities and
conducted AFP process development on Cytec's
IM7/MTM®45-1 epoxy. This paper provides an
overview for materials and manufacturing personnel
of this development effort.
Challenges with AFP of OOA Materials
The current state-of-the-art in OoA epoxy
materials (e.g. MTM®45-1 and Cycom®5320-1) are
tailored for the hand lay-up process by employing
the combination of low flow resins and a prepreg
format that retains dry fibers within the tows. These
intentional air paths augment vacuum extraction
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of air and volatiles during the early stages of the
cure1,2. This approach allows the limited pressures
of the vacuum only cure to consolidate the prepreg
stack without needing to retain the volatiles in
solution as can only be accomplished at high
(autoclave) pressures.
Lockheed Martin established early on that this
form of the material was not suited to the AFP
process. First, the prepreg was difficult to slit and in
some cases could not be provided by the material
supplier in slit tape form. Dry fibers located in the
tows restricted the ability of the slitter to provide
uniform slit widths and also resulted in the rapid
formation of fuzz balls within the AFP head leading
to a significant increase in down-time for head
cleaning. Second, AFP processing of the hand layup product was found to "seal" off the dry fiber air
paths at even the lowest compaction force settings
entrapping the air already in place and any volatiles
seeking to escape from the lay-up.
Net Thickness Tape
The solution to this material product form
challenge was achieved by applying an AFP material
technology originally established for autoclave
materials. In-situ fiber placement technology
(first developed for thermosetting materials under
Navy sponsored programs) employs nearly void
free prepreg, called net thickness tape, and high
temperature and compaction pressure placement
conditions offered by the AFP machine to
consolidate the prepreg during the fiber placement
process2-5. The need to consolidate the prepreg
stack in the autoclave is negated and the oven
SAMPE Journal, Volume 52, No. 4, July/August 2016

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