JEC COMPOSITES MAGAZINE - Issue #104 - April/May 2016 - 55

multimaterial

Multimaterial joining of steel inserts with
continuous fibre-reinforced thermoplastics
Macro-textured metal inserts were successfully integrated in a onestep thermo-stamping/overmoulding process to yield highly structural assemblies. The technology, which has the potential for massproduced applications in the automotive industry, was demonstrated
by the LIMECO partners on a composite seat backrest side flange
with an integrated steel recliner mechanism. LIMECO (Links Metal
Composites) is a collaborative project of the IRT Jules Verne.

ntroducing composites into mass-produced vehicles involves solving material
and processing problems and finding
suitable joining technologies to create multimaterial structures. The joining technologies currently available to assemble metals
and composites in structural applications
are very limited and do not allow their
introduction into mass-produced cars.
The LIMECO (Links Metal to
Composites) project, conducted from
2012-2015, is one of the first projects of the
IRT (Technical Research Institute) Jules
Verne in Nantes, France. The project focused on the design, testing, and validation
of structural multi-materials joining. The
selected materials were steel and thermoplastic composites (polyamide). The only
moulding processes considered for this
project were thermoplastic injection and
thermo-stamping. The joining technologies
developed were overmoulding, adhesive
bonding, and mechanical assembly methods, and their combinations in synergy.
Welding technologies were not considered.
The IRT Jules Verne members that took
part in the project are IRT Jules Verne,

Faurecia (three business groups), Compose
Tools, Cetim, and Ecole Centrale Nantes.
Compose Tools designed and manufactured the moulds used in the project. The
demonstrators were manufactured and
tested by CETIM. Faurecia designed and
manufactured the seat prototype. Ecole
Centrale Nantes and IRT Jules Verne developed the multimaterial joining simulation,
but this work is not presented in this article.

Macro-texturing of metal inserts
An automotive seat backrest was used as a
case study for the project. A key challenge
for a composite seat is to find a way to join
a standard steel recliner mechanism onto
the composite backrest. Previous work
was presented in JEC Magazine, but the

Fig. 1: Demonstrator made of two triangles (steel
and composite) with a steel recliner mechanism
in-between. The left sketch shows the organic
sheet (yellow), the overmoulded plastics (grey)
and the steel recliner (brown)

Thierry renaulT,
Senior experT CompoSiTeS, FaureCia
and projeCT leader aT irT juleS Verne

solution was not optimized in terms of
weight and cost [1].
A demonstrator was designed to evaluate
and compare several solutions for joining
a steel recliner mechanism and an organic
sheet plate (continuous fibre fabric impregnated with a thermoplastic resin). The
recliner mechanism is basically a steel disk
80 mm in diameter but the disk is not perfectly flat. It is designed to be laser welded
onto a steel part (the welded area has the
shape of a ring a few millimetres in width).
The assembly has to resist a 2500 N·m
torque. The two technologies most used
for multimaterial joining are mechanical
fastening and adhesive bonding. Due to the
functionality of the recliner and the fact that
it is made of hardened steel, it is not possible
to design a mechanical joint (with either
screws or rivets) to assemble the mechanism
onto the composite without degrading its
function. Moreover, due to its geometry, it
is not possible to design an efficient adhesive bond: the contact area is too small for
adhesive bonding and the surface is not
flat. To solve the problem, it was decided
to laser-weld the recliner mechanism onto
a steel disk that would then interface with
the composite. Now, the challenge is to
limit the weight of this interface part by
keeping its surface as small as possible.

No104 April - May 2016 / jec

composites magazine

Table of Contents for the Digital Edition of JEC COMPOSITES MAGAZINE - Issue #104 - April/May 2016