SAMPE Journal - July/August 2022 - 14

FEATURE / THREE-DIMENSIONAL STITCH PATHS
stitching path capability for wind tunnel blades,
aircraft structures, spacecraft structures, and other
composite structures with highly curved surfaces
was the motivation for formal development of the
process to define and program these nonlinear
stitching paths at LaRC. In the following sections of
this paper, an overview of the stitching capabilities
at LaRC is presented, followed by the development
of the 3D stitching path definitions required to
stitch the complex paths, and finally, conclusions
related to the stitching path development and
definitions are presented.
ISAAC FACILITY
Stitching of composite material structures at
LaRC is performed at the Integrated Structural
Assembly of Advanced Composites (ISAAC)
facility. The ISAAC facility houses a robotic system
designed to facilitate the development of new
technologies related to aerospace composites
manufacturing22
. The robotic system is a six-axis
industrial robot capable of accommodating a
variety of end effectors. A 41-ft-long linear rail and
a vertical rotator provide two additional degrees
of freedom. The workcell and operator station are
enclosed within an International Organization
for Standardization (ISO) Level 7 clean room that
provides positive control over airborne particulates
and enables consistent temperature and humidity
to be maintained23
. The ISAAC robotic system is
shown in Figure 2 with the original head capable
of performing AFP using up to 16 spools of one
quarter-inch wide tows of material. Since the initial
installation of the ISAAC facility, several additional
heads have been incorporated onto the system to
increase functionality.
Because of the success of previous work
conducted on stitched composites under LaRC
programs, two stitching heads were added to
the capabilities of the ISAAC facility to continue
development of stitching technology and
application to composite structures. Incorporating
the stitching heads required coordination between
multiple vendors. The stitching end effectors,
the machines that perform the stitching process,
were manufactured by PFAFF Industriesysteme
und Maschinen GmbH Branch Office KSL (KSL)*
(Lorsch, Germany) through DAP America*
(Norcross, GA). The two end effectors comprise a
double-sided end effector and a single-sided end
effector. The double-sided end effector uses one
needle and one thread to create a chain stitch to
join layers of fabric. The double-sided end effector,
termed the RS566 (Figure 3), was primarily an offthe-shell
design and requires access to both sides
of the preform by the end effector. The single-sided
end effector uses two needles, an insertion needle
and a catcher needle, and one thread to create
a modified chain stitch to join layers of fabric
that can include more complicated structural
arrangements. This single-sided end effector,
termed the RS535 (Figure 4), was modified based on
past experience with its use during the ERA project
and only requires access to one side of the preform
by the end effector. Development of the RS535
modifications was facilitated by input from the
stitching expert at The Boeing Company (Boeing),
who provided stitching development and support
throughout the ERA project. LaRC engineers
worked with KSL, the needle manufacturer and the
Boeing stitching expert, who provided information
based upon the experience developed during
the ERA project, to develop improvements to the
stitching end effector and the catcher needle. The
different chain stitch patterns produced by the two
stitching heads are shown Figure 5.
Figure 2. ISAAC robotic
system and ISO 7 clean room.
14 | SAMPE JOURNAL | JULY AUGUST 2022
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