SAMPE Journal - July/August 2022 - 46

FEATURE / HIGH-RATE AIRCRAFT MANUFACTURING
Initial ICAT Process Characterization
Experiment
The first ICAT processing characterization trial
was conducted to verify the heating capability
of the Electroimpact® VSS laser heating system.
An abbreviated processing design of experiment
(DoE) was performed to determine, or improve
the understanding of, the relationship between
the ICAT processing parameters of material
temperature, tool temperature, and placement
speed on the quality of the interface formed
between the tape plies during the process. The
compaction load of 1.1 kN (250 lbs) was selected
and fixed based on input from Electroimpact®
and their experience with placing thermoplastic
laminates for other customers. This value is high in
comparison to the compaction loads used during
thermoset AFP to tack plies but well within the
capability of commercially available AFP heads.
To conserve the slit-tape materials, the flat panels
placed in the first ICAT processing trial were only
six plies thick [0°/0°/+45°/-45°/0°/0°]1
and were
intended to provide 0° on 0° plies for thermocouple
placement and measurement while also providing
off-axis plies, which are assumed to be the worstcase
scenario for heating and establishment
of intimate-contact during placement.
The
processing parameters studied in this first ICAT
processing trial are listed in Table 1.
Each run, or trial, listed in Table 1 corresponds
to an ICAT placed 15.24 cm x 10.16 cm (6.0 in x 4.0
in) six-ply unsymmetric, unbalanced panel. For
the PEEK material processing trials, the maximum
tape heating temperature of 500°C was targeted
to be well below the reported 2% mass-loss
decomposition temperature of 575°C10
, while high
enough to maintain the tape surface temperature
above TM through the compaction zone beneath
the AFP head roller. Likewise, the maximum laser
heating of the surface of the LM-PAEK® material
processing panels was maintained at or below 450°C
based on the understanding of its degradation
occurring at 557°C11
. The onset of polymer
decomposition is suspected to be well below the
2% mass-loss temperature reported and hence the
reason for ongoing thermal characterization of this
material property at NASA. The heated tool used
in these processing experiments has a maximum
temperature capability of up to 300°C and for these
initial trials the tool temperature was varied but
kept in the lower range with the idea that lower
tool temperatures would be more acceptable to
the production floor at an aircraft OEM. However,
higher tool temperatures may be required and
investigated in future experiments to determine
effects on polymer crystallization and resulting
mechanical properties. The temperature of the
substrate ply heated by the incident laser spot is
understood to scale linearly with the heated tool
temperature. The uniformity of the tool surface
temperature was measured prior to placing the
first ply using the FLIR camera mounted on the
Electroimpact AFP head. The resulting eleven
panels were intended for cross-section and
evaluation by photomicroscopy, and the results of
this first trial were used to determine the processing
parameters to fabricate thicker mechanical test
panels in the next ICAT processing experiment
trials discussed below.
The second set of ICAT process characterization
experiments conducted as a part of this current
work were intended to fabricate mechanical
Table 1. Processing parameters of the first ICAT processing characterization experiments.
46 | SAMPE JOURNAL | JULY AUGUST 2022
www. sampe.org
http://www.sampe.org
SAMPE Journal - July/August 2022

Table of Contents for the Digital Edition of SAMPE Journal - July/August 2022
