SAMPE Journal - July/August 2022 - 43

Figure 3. Photomicroscopy of CF/thermoplastic tape
supplied and utilized for previous HH-ATP studies
(2007) by Accudyne Inc, and NASA, showing excessive
porosity and surface roughness.
serve as a solution to replace existing production
capable AFP heads, because the area-compactors
would not conform to complex-contour parts
or tight radii associated with a wing skin or spar,
respectively. The developmental HH-ATP head
was used at Accudyne to study the heated and
cooled compaction process of multiple CF/
thermoplastic materials including: the amorphous
thermoplastic, LaRC 8515 polyimide with a Tg
of ~270°C; and various other semi-crystalline
polyaryletherketones, including: polyether ether
ketone (PEEK), polyether ketone ketone (PEKK),
as well as PIXA, PIXA-M, PIXA-M1, Avimid® K3B,
Avimid® R1-16, and PETI-5 tape. Despite the
poor quality of most of the supplied tape in these
previous studies3,6
, the low-warpage, HH-ATP
fabricated laminate quality was excellent; OHC
strengths following in-situ placement using the
LaRC HH-ATP head were 76 to 94 percent of those
from in-situ placed, post-consolidated autoclaved
laminates3
. The measured mechanical properties
of in-situ placed laminates were almost equal to
laminates post-autoclave-consolidated after insitu
placement. Based on the results at the time it
was concluded that to reach mechanical properties
equivalent to autoclave processed laminates, HHATP
would benefit from further equipment, process,
and especially incoming tape material quality
development. In work performed in 20087
three
versions of AS4/ PEEK tape were acquired from
multiple industry suppliers and characterized to
assess their potential use with the HH-ATP process.
One of the explanations for the property disparity,
especially in the lowest performing materials, was
the quality of the supplied CF/thermoplastic tape
utilized in this study. At the time, the AS4/PEEK
(APC-2) and an AS4/PEKK tape were supplied with
quality sufficient for consolidation in an autoclave
with an elevated temperature and pressure cycle.
An autoclave cycle provides sufficient time under
pressure and above the melt temperature for the
viscous polymer to flow sufficiently to establish
intimate contact, fusion between plies, and for
porosity found in these supplied materials to be
evacuated from the laminate, or at a minimum,
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the porosity already present in the supplied tape
does not expand under autoclave pressure. The
level of quality of these supplied tape materials was
insufficient to fabricate quality laminates during
the more rapid HH-ATP process, where intimate
contact, fusion-bonding, and void consolidation
between the incoming and substrate ply occurs in
seconds as opposed to longer times (up to 1 hour)
in an autoclave process. The microscopy of the
7.62 cm (3 in) wide AS4/PEEK tape supplied for the
lowest performing laminates tested are shown in
Figure 3. The 7.62 cm wide tape was cut into smaller
sections and the sections of tape stacked in potting
solution prior to polishing and photomicroscopy.
In other words, each of the images in Figure 3 are
of three sections of stacked tape, not a processed
composite laminate. The significant improvements
in commercially supplied tape quality are discussed
further in the results section of this paper.
Laser Assisted Thermoplastic AFP
As discussed above, the NASA and Accudyne
developed approach to HH-ATP of thermoplastic
composites is not likely to meet the rigors of the
composites structure production environment.
The current approach in industry for AFP of
thermoplastics appears to be the retrofit8,9
highly capable existing AFP heads developed for
placement (tacking) of thermoset tape materials
at temperatures ranging from 25 to 70°C and at
advertised speeds of up to 1270 mm/s (3000 in/
min). Thermoplastic AFP processing requires much
higher tape heating temperatures (300-400°C)
than thermoset AFP and ideally the tape material
heating occurs directly ahead of the compaction
roller nip-point where the incoming material
meets the pre-placed substrate tape (Figure 1). As
an alternative to the HGT heating source discussed
above, lasers and flash lamp technologies have
been developed and added to existing AFP machine
heads to quickly heat the materials to these higher
temperatures (Figure 4). Laser systems inherently
have very quick response times to commands
from the AFP head CNC control. Also, because the
spot size is precisely controlled, residual heat is
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SAMPE Journal - July/August 2022

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