JEC COMPOSITES MAGAZINE - Issue #84 - October 2013 - 54

VARTM

Flexible permeability: a simple strategy
to simulate the VARTM process
Ahead of traditional materials, polymeric matrix composites have demonstrated their suitability for a great number of applications. This is mainly due to their low weight,
excellent mechanical properties and chemical resistance.
However, composite manufacturing processes still need
to be improved to reduce their cost and make these materials even more competitive. In that way, the benefits of
their characteristics could reach as many people as possible. Aimplas has developed a simulation methodology
based on flexible permeability that helps optimize VARTM
processes effectively.

Improvements and adaptations

esin transfer moulding (RTM)
is one of the technologies used
the most to produce composite
parts. According to AVK's 2012 report
[ 1], 120,000 metric tons of composite parts were produced in Europe
in 2012 using RTM and its derivatives, such as vacuum-assisted RTM
(VARTM). The report states that the
market for RTM and RTM parts has
fared comparatively well this year in
spite of zero growth. The substitution
of open processes and increased use
of RTM in automotive production
promise a bright future with strong
growth potential. Moreover, improvements and adaptations of the processes in this category are the focus
of a large number of research projects
to develop improved, faster production cycles, including in high-volume
automotive production.

In this type of process, a pre-shaped
reinforcement (preform) is placed inside the cavity of a mould, the mould
is closed, the resin is injected inside
the cavity, and it polymerizes. By using an optimized injection strategy,
you can get full impregnation of the
preform and a shorter delay between
the moment the cavity is filled and
the moment the resin starts to gel.
An optimum process also enables the
lowest part cost and the best mechanical properties. Mould design and raw
material selection are key parameters
to optimize the process, and the
location of the injection and venting
points greatly influences mould design. Using flow performance criteria
in choosing raw materials can also
improve the process economics.
Virtual prototyping is an effective
tool that helps to understand the flow
behaviour of resin inside a specific
mould. Simulating the RTM process

54 jec composites magazine / No84 October 2013

EnriquE Díaz EscrichE
hEaD of compositEs
aimplas

at the design stage (before manufacturing the mould) allows selecting the
raw materials and key points of the
mould so as to avoid expensive trial
and error strategies. Specific software
programs are available on the market
to handle this task. They usually offer
a user-friendly interface and running
the simulations properly does not
require a high degree of expertise. The
main difficulty is not the software itself but the precise characterization of
raw materials and, more specifically,
of preform permeability.

Permeability characterization
The characterization of permeability,
usually defined for our purposes as
how easily a preform allows a resin to
flow, has been (and continues to be) a
topic of research for long time. So far
[2], there has been no experimental
approach for permeability measurement with consistent results. When
the same preform is characterized,
different experimental set-ups yield

JEC COMPOSITES MAGAZINE - Issue #84 - October 2013

Table of Contents for the Digital Edition of JEC COMPOSITES MAGAZINE - Issue #84 - October 2013