JEC COMPOSITES MAGAZINE - Issue #82 - July 2013 - 45

crash, misuse test, noise, vibration and
durability to reach a level where the parts
are ready to be included in generic seat
structures. Environmental factors (operating temperature ranging from -30°C to
80°C and moisture) were included in the
validation plan.
This achievement shows that the simulation tools used to design reinforced
thermoplastic parts have now reached
a sufficient prediction level to engineer
complex seating parts subjected to severe
crash loads, including the effects of
temperature and humidity on the part’s
mechanical performance.

Composite backrest

Due to the need for energy absorption in a
dynamic crash event and the high impact
loads the seat back would undergo, a plastic material with higher properties than the
available glass-reinforced PA6 materials
was required. The material development
targets thus included: high elongation
while maintaining a similar strength and
stiffness to existing PA6GF35 materials,
Class A surface appearance for exposed
surfaces, colourability, improved melt flow,
good impact resistance, and maintaining
all of these properties in the operating
environment of a typical seat back. The
new material has a high elongation at break
at room temperature in dry as-moulded
conditions while retaining other mechanical properties such as tensile strength and
modulus.
As shown in Figure 4, the starting materials for the CFRT inserts are unidirectional tapes, which are simply continuous
glass fibres impregnated with a polymer.
The CFRT tapes are stacked in the required layer orientation, heated in an infrared
oven and thermo-stamped under pressure.

The formed insert is then trimmed to its
final shape. The final injection moulding
process uses a standard injection moulding
press.
The performance level of the composite
backrest was evaluated in the most severe
operating conditions of a car seat. The
key characteristics of a seat back are its
behaviour in rear crash and luggage impact
conditions.
To simulate the PA6GF35 material, a
rheology injection moulding simulation
software was initially run on the seat
back geometry, tracking and mapping the
glass fibre distribution and orientation.
The glass fibre orientations were then
utilized by the ULTRASIMTM proprietary
software to accurately model the varying
material properties of the seat back in all
dimensions. A highly detailed, non-linear
FEA model was required to accurately
model the dynamic behaviour of a seat
system in a crash scenario. Specifically for
this project, the simulation of short-fibrereinforced thermoplastics was expanded
with material data related to continuousfibre-reinforced plastics, so that it can
now reliably predict the crash behaviour
of components with a very high (fibre)
anisotropy and fibre content.
Considering the fact that mechanical
properties strongly vary with temperature
and moisture, it was decided to validate
the seat at room temperature in dry
as-moulded conditions, but also to test

Fig. 4: Three processes are used for the manufacture of the composite backrest: 1) standard stamping
of steel brackets, 2) thermostamping of CFRT inserts, and 3) over-moulding of inserts (steel and CFRT)
with PA6GF35 by injection moulding

No82 July 2013 /

Feature Automotive

A composite backrest for a front seat
was developed jointly by BASF and
Faurecia as a case study to develop
the hybrid thermoplastic moulding
(CFRT+overmoulding).
The complete trimmed backrest was
considered. The reference component
weighed 8.3 kg and was based on a standard seat design (steel frame, PU foam
pad, textile cover, plastic back panel).
The study’s goal was to develop a new
seat architecture with reduced weight
while taking advantage of the design
possibilities provided by plastics.
Therefore, the development process
moved away from the standard two-step
design, where a frame is designed first
to fulfil the safety specifications and
regulations and layers are then added
for comfort and aesthetics. The new seat
structure has a structural function while
at the same time contributing to the
seat’s comfort and aesthetics. The shell
design of the composite backrest enables
a sympathetic shape to the human
form whereas a standard steel frame
focuses on pressure. As a result, the foam
thickness required for comfort can be
reduced with the composite backrest.
In a standard seat design, the back panel
is a plastic part assembled onto the metal
frame with snap fits and/or screws. In
the composite backrest, the back panel is
directly integrated in the seat backrest as
shown in Figure 3, which eliminates all
assembly problems. Based on this shell

design, the materials were selected through
CAE analysis including integrative simulation techniques to model thermoplastic
materials accurately. The most severe crash
cases were selected to validate the concept
(rear crash with 95th dummy and luggage
test).

jec composites magazine 45

JEC COMPOSITES MAGAZINE - Issue #82 - July 2013

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