JEC COMPOSITES MAGAZINE - Issue #87 - March 2014 Special JEC Europe - 59

Characterization of thermoplastic
composites for hot stamp forming
This paper describes state-of-the-art characterization methods
for thermoplastic composites at high processing temperature
and provides a few examples of application in simulations of the
hot stamp forming process.

By
Bert Rietman, Senior Research Associate,
Business Development
Wouter Grouve, Research Operations Leader
Remko Akkerman, Technical Director
Thermoplastic Composite Research Center TPRC

hermoplastic composites feature
excellent stiffness and strength
properties, but they are also
recognized for their potential for fast,
robust and cost-efficient processing. An
essential advantage over their thermoset
counterparts is that thermoplastic composites can be heated and subsequently
shaped and joined. This enables emerging technologies such as overmoulding,
where a continuous-fibre-reinforced
blank is formed and subsequently overmoulded by injection in a single tool.
These advantages make thermoplastic
composites very attractive for aerospace
and automotive production, where low
weight and production costs are the main
drivers for material and process innovations. Currently, thermoplastic composites are becoming very popular and
new materials and processes are being
introduced with high frequency.
However, in order to exploit the potential of composites, material and technol-

ogy developments have to go hand in
hand with the development of design
guidelines and simulation and optimization methods. Part performance and
process feasibility can be simulated in
an early design phase and prototyping
efforts and process-induced defects can
be reduced to a minimum. In the ideal
case, product and process optimization
is not singular, but is performed through
the whole process chain. In the end, the
process-induced properties accumulated
through the process chain determine
the final product performance to a large
extent.
Detailed material knowledge and predictive simulation methods are therefore
indispensable for optimum use of the
materials' potential.

Stamp forming
The stamp forming - or thermoforming - process is extremely well-suited for
high volume production of thermoplastic
composites. In this process, a composite
blank is preheated to above the melt temperature of the thermoplastic resin and

Fig. 1: TPRC's 200-ton Pinette Emidecau Industries
(PEI) forming press (left) and doubly-curved test
geometry for formability testing (right)

is subsequently shaped in a moderately
heated tooling. This process is similar
to the well-established deep drawing
process for metallic sheets and allows for
cycle times in the order of one minute.
Typically, thermoplastic composites
are layered structures where every layer
consists of fibres in a certain architecture
embedded in a thermoplastic matrix.
For high-spec applications, continuous fibre composites with stiff glass or
carbon fibres are applied. These materials
are highly anisotropic since stiff fibres
are embedded in a weak matrix. This
behaviour is even more pronounced in

No87 March 2014 /

jec composites magazine 59

JEC COMPOSITES MAGAZINE - Issue #87 - March 2014 Special JEC Europe

Table of Contents for the Digital Edition of JEC COMPOSITES MAGAZINE - Issue #87 - March 2014 Special JEC Europe