SAMPE Journal - January/February 2023 - 35

INTRODUCTION
The share of thermoplastics is constantly growing
in the field of commercial aerospace applications1
.
Thermoplastics are lightweight, relatively cheap,
easy to process and their properties can be altered
through addition of fillers. Thermoplastics are
often used in aircraft interior segments1
.
In order to be certified for the use in
commercial aircraft, thermoplastics must fulfill
strict requirements regarding traceability during
production specified by the Federal Aviation
Administration (FAA) as well as flammability, smoke
and toxicity requirements (FST). Polyetherimide
(PEI), commonly known as Ultem (Saudi Basic
Industries Corporation, Riad, Saudi Arabia), and
polyphenylsulfone (PPSU) are among the qualified
materials due to their inherent FST resistance2
.
Fibre-reinforced types of PEI and PPSU exhibit
excellent mechanical properties, which are crucial
for a long service-life in commercial aircraft.
Pre-series and functional prototypes are
essential during product development. It is
common practice to reduce iteration loops by
using prototypes and pre-series that come as
close as possible to the serial part. Therefore,
manufacturers need flexible and cost-effective
production methods at this stage of the product
development process. Rapid prototyping methods
fulfill these requirements. For thermoplastics, these
technologies include Fused Filament Fabrication
(FFF) and selective laser sintering (SLS)3
. Other
rapid prototyping methods for plastics include
Stereolithography (SLA) and Polyjetting, both
of which are based on UV-hardening thermoset
resins.
Thermoplastic parts produced through FFF
or SLS possess a certain degree of anisotropy as
a result of insufficient interlayer bonding4,5
rapid prototyping systems and materials are
currently certified for use in aerospace applications.
Only Stratasys Ultem 9085 Filament fulfills FST
requirements and other standards set by several
regulatory administrations. However, this filament
is only qualified for use on one specific additive
manufacturing system6
. It is worth noting that
even parts manufactured using the FAA-certified
Ultem 9085 filament are still subject to significant
anisotropy7
. SLS currently offers only a small range
of materials. Few fibre-reinforced SLS powders are
available today, none of which are based on PEI or
PPSU. Thermoset prototyping technologies such
as SLA or Polyjetting are currently not qualified for
application in commercial aircraft.
Ideally, pre-series parts are produced from the
same material and through the same qualified
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JANUARY FEBRUARY 2023
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SAMPE JOURNAL |
35
. Few
process as intended for serial production. If
isotropic mechanical properties, good surface
quality, aerospace certification and an unlimited
range of materials are crucial for the intended part,
injection molding remains as the most suitable
manufacturing method. Injection molds are
commonly CNC-milled from steel or aluminum
blocks. However, even rapid CNC manufacturing
methods result in high costs per part for small preproduction
batches of up to 100 parts. Depending
on the desired output number, tooling costs can
make up 90% or more of the total costs. The lead
time for CNC-milled metallic molds typically
amounts to at least three weeks.
Combining additive manufacturing methods
with traditional injection molding can significantly
reduce the costs-per-part. This rapid tooling
approach uses
additively manufactured mold
inserts that are mounted in a metallic master
mold. SLA is best suited for this approach since
it guarantees the smoothest surfaces, finest
details and highest dimensional accuracy of all
additive manufacturing methods for plastics8
However, due to their limited thermal conductivity,
.
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SAMPE Journal - January/February 2023

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