JEC COMPOSITES MAGAZINE - Issue #104 - April/May 2016 - 58

multimaterial
The assembly of configuration 2 was also
tested in endurance. The test started with
the conditions used in seat validation tests
(30,000 cycles), as shown in table 1, and
the torque value and number of cycles were
progressively increased to reach -500/+250
N·m and 2 million cycles without failure.
The sample tested in endurance with 2 million cycles was then tested for its torque
at failure, showing that the value had not
decreased after endurance testing.
The CMT pins concept is very robust
and effective. Therefore, it was decided to
develop a seat prototype integrating this
technology.

Seat backrest prototype
A composite seat backrest side member was
developed to demonstrate the performance
of an assembly combining a textured steel
disk with a composite part. The demonstrator's geometry was integrated in the
prototype as much as possible.
The design of the seat side member is
shown in figure 9. The part is made of an
organic sheet (1) as the main structure, an
overmoulded section (2), a metal disk (3)
anchored in the composite and overmoulded, a steel recliner mechanism (4), and a
steel flange (5).

The assembly's concept is similar to that
of the demonstrator, where the composite
triangle is replaced by 1, the steel triangle
is replaced by 5 and the shape of the metal
disk is adapted to the part geometry.
The moulding technology used to manufacture the seat side members was optimized
as a one-shot process rather than a two-step
process. The resulting manufacturing process included the following steps:
- Preparing a metal insert (3) with either
CMT pins or collars;
- Laser welding the recliner mechanism
(4) onto the metal insert;
- Placing the assembly in an injection
mould. Thermo-stamping and backinjecting (2) the organic sheet (1) in one
step;
- Laser welding the metal flange (5) onto
the other side of the recliner mechanism.
A picture of the moulded part is shown
in figure 10. The side members were then
assembled with steel cross-members and
the prototypes were assembled by adhesive
bonding. The assembled backrest is shown
in figure 11.
The backrest was tested for resistance to a
rear force at the centre of the upper cross
member, as shown in figure 12. The force at
failure was around 7000 N and was similar
to the performance of a standard steel
backrest. The failure did not occur at the
interface between the metal insert and the
composite but in the composite, above the
metal insert.
The part was also tested in endurance for
20,000 cycles with a load of +0/+900 N at
the centre of the upper cross-member with
a 150 mm offset. No damage was observed
on the backrests.

Prospects

Fig. 9: Seat side member concept for the prototype

Fig. 10: Seat side member prototype

The one-shot thermo-stamping/overmoulding process is very attractive for the
automotive sector because it combines the
advantages of injection moulding (fast cycle
time, high level of automation, industrial robustness) and composite processing (continuous fibres with high mechanical properties). The LIMECO project demonstrated
that additional features can be integrated
in the moulding process by placing a metal
insert in the mould. The metal insert can
be macro-textured, e.g. with CMT pins or

58 jec composites magazine / No104 April - May 2016

Fig. 11: Hybrid seat backrest prototype. Metal
cross-members are adhesively bonded onto the
composite side members

Fig. 12: Testing the backrest

holes with collars, to promote the anchoring of the metal insert in the composite and
yield structural joining between the metal
insert and the composite structure. Several
applications can be developed in the field
of seats, but also in the field of automotive bodies in white or structures for other
industries. n
References
[1] Renault, T. Thermoplastic composites
for automotive seats, JEC Composites
Magazine, 82, pp. 61-64, 2013.
[2] Schierl, A. The CMT Process, a revolution in welding technology. Weld World,
49(9):38, 2005.
[3] Ucsnik, S., Scheerer, M., Zaremba, S., &
Pahr, D. H. Experimental investigation of a
novel hybrid metal-composite joining technology. Composites, pp. 369-374, 2010.
Contact:
thierry.renault@faurecia.com

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