In the January-February 2007 issue of the SAMPE Journal we discussed the various industry
highlights of resin infusion technology that has occurred over the last few decades. The purpose
of this column is to take a brief look at some over the process definitions and important process
variations that pertain to this rather broad manufacturing technology.

Resin infusion overall is a very broad manufacturing field in that one often sees what might be
termed “an alphabet soup” of acronyms pertaining to well over 40-50 processes that are often
considered part of this technology. Classically resin infusion traditionally has meant a process in
which a structural reinforcement preform (e.g. the fiber portion and other peripheral things like
fittings) is loaded ahead of time into a mold and then the resin portion is added by some infusion
methodology afterwards. The resin then “infuses” into the space between and around the
structural reinforcement and is cured in place once infusion is complete.

The process of resin infusion technology, while not universally accepted, often is divided into
two distinct categories based on the manner in which the resin is infused into the preform and
mold cavity:
• Resin Transfer Molding (RTM) – resin is introduced into the mold and preform at a
higher than atmospheric pressure
• Vacuum Infusion Process (VIP) – resin is introduced into the mold and preform at
lower than atmospheric pressure

VIP is often referred to in the industry by another term, Vacuum-Assisted RTM (or VARTM).
Hence, in brief RTM=positive pressure and VIP=vacuum as the manner in which resin is moved
through the unsaturated preform. I am not aware that anyone has actually gone down the list of
40-50 available process variations to line them up within these two categories, but most of the
known ones do tend to fall into one or the other.

One might ask “why are there so many resin infusion variations out there?” Personally I see two
reasons: process innovation and marketing. Process innovations has led to a wide number of
advances in this field and are legitimate variations of improving the process or developing a
process to meet structural or design needs. For example, SCRIMP™ was developed to more
rapidly infuse very large and complex structures, by taking advantage of flow through porous
media quickly over large surface areas such that infusion traveled the minimum distance (e.g.
through the thickness). Resin Film Infusion (RFI) is another innovation example is which the
resin is preloaded into the tooling as “prepreg resin sheets or film-like tiles” and the preform
added on top. Autoclave pressure, temperature-time sequencing and vacuum draw typical of
conventional prepreg operations are all used to cause the resin to flow through the minimum
thickness direction and subsequently cure numerous complex parts. Marketing has also
accounted for a large number of these 40-50 variations. In some cases the variations have a bit
of minor tweaking of a resin infusion process. On the other hand the process is often just a
minor tweaking of the “alphabet soup acronym” for company marketing benefit. While one sees
the term VARTM or VIP fairly often as generic terms, one also sees terms like VARI, VRTM, etc.

Needless to say, there are some variations that seem to have one foot in the RTM bucket and
one foot in the VIP bucket. Sure, there are hybrids within the resin infusion process as there are
in any other manufacturing category. For example, TERTM (Thermal Expansion RTM) and
RARTM (Rubber Assisted RTM) may utilize either a resin infused into the primary preform
structure by an RTM or a VIP method, but the next step after resin infusion is created by the
internal structure within the part or tooling. TERTM relies on an expanding core material
(caused by the increase to the cure temperature) to provide preform/resin compaction within the
tooling. The expanding core material then squeezes out excess resin and drives the preform to
a net higher fiber volume while conforming nicely to the inner tooling surface. RARTM, on the
other hand utilizes rubber insert materials conveniently placed within the mold cavity. These
rubber inserts expand tremendously (because of their thermal expansion mismatch), and with
nowhere to go within the closed mold, squeezes out excess resin and again drives the
composite structure to much higher fiber volumes. The rubber material is often referred to as a
“pressure intensifier.”

Consequently there are numerous paths one might travel in order to process their composite
part via “resin infusion processing.” There are differences in tooling required, preform selections,
flow media resources, core materials, rubber pressure “intensifiers”, resin pumping or vacuum
pump equipment, resin viscosity selection approaches, etc. But we will save this discussion for
another issue.