SAMPE Journal - January/February 2016 - 20

FEATURE ARTICLE

Figure 2. Schematics of the CRTM process2.

In VARTM, mold cavity is one-sided. The top is
replaced by a compliant vacuum bag. Vacuum is drawn
to compact the preform and to "draw" the resin in. As
the pressure gradient is limited, flow enhancement
layer is commonly introduced on bag side of preform
to speed up resin distribution, and sequential infusion
schemes are applied. This approach allows the rigid
side of mold to be of only moderate strength and
stiffness. Thus, large parts can be manufactured but
dimensional tolerances - particularly thickness - are
limited, bag side surface finish is poor and fiber volume
fraction is slightly lower. The resin infusion is a very
slow process and production rates are low. Volume
of discarded auxiliary material - tubing, bags, flow
enhancement media - may be significant (Figure 1).
RTM Light is more similar to VARTM than to RTM.
It replaces the vacuum bag with a compliant mold.
Commonly, the flow enhancement layer is integral part
of the product and radial infusion scheme from outside

edges is utilized. The surface quality improves relative
to VARTM, but the thickness variation and lower fiber
volume fraction are still the drawbacks and so is the
limited production rate.
Thus, the mainstream LCM variants are all relatively
slow manufacturing processes. In this paper we will
examine a newer process variation, compression resin
transfer molding (CRTM). The promise of this method
lies in the combination of the dimensional stability,
good surface quality and high reinforcement volume
fraction of RTM with much faster processing cycle.
To achieve this, reinforcement (net-shape preform)
is placed in the mold which is then partially closed
and resin is injected into the gap between the mold
and the preform. As this gap is highly permeable it
distributes the resin very quickly over the surface of
the part. Then the mold is closed, driving the resin into
preform (like compression molding), compacting the
reinforcement and squeezing the resin into remaining
unsaturated regions (Figure 2). This approach has
been successfully developed for plastic injection
molding without reinforcing fibers and is commercially
available (including simulation capability)1.
This process has significantly higher tooling
requirements than other LCM variations, and also
requires advanced preforming techniques to be
fully utilized. However, the production rates can
be increased by orders of magnitude. Despite its
potential, the current process knowledge is limited
and actual application faces some hurdles. Most of the
experimental work3-4 works with simple geometries,
not full automotive components. The more complex
shapes4 have difficulties filling with resin. Net shape
preforming is a necessity but it is rarely considered
in academic studies and experimentation as its
implementation is costly. Cure process and warpage
remain uncertain.

Figure 3. Resin infusion into automotive hood. Flow contours (left) and resin velocity orientation (right).
Results from LIMS simulation package5.

SAMPE Journal, Volume 52, No. 1, January/February 2016

Table of Contents for the Digital Edition of SAMPE Journal - January/February 2016