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RESIN
TRANSFER MOLDING
In recent years, resin transfer molding, or RTM, vacuum-assisted RTM,
VARTM, and its derivative processes have been gaining popularity in the
aerospace, infrastructure, automotive, and military industries. In fact,
RTM was originally introduced in the mid 1940s but met with little commercial
success until the 1960s and 1970s, when it was used to produce commodity
goods like bathtubs, computer keyboards, and fertilizer hoppers.
Overview of Resin Transfer Molding Section:
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Schematic
showing typical RTM set-up.
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Resin Transfer Molding (RTM) is a low pressure molding process,
where a mixed resin and catalyst are injected into a closed mold
containing a fibre pack or preform. When the resin has cured the
mold can be opened and the finished component removed.
A wide range
of resin systems can be used including polyester, vinylester, epoxy,
phenolic and methyl methacylates etc, combined with pigments and
fillers including aluminium trihydrates and calcium carbonates if
required.
The fibre pack
can be either, glass, carbon, arimid, or a combination of these.
There are a large variety of weights and styles commonly available.
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The Advantages and Benefits of using RTM:
- Moldings can be manufactured to close dimensional
tolerances
- Components will have good surface finish on
both sides
- Selective reinforcement and accurate fibre management
is achievable
- Ability to build-in fibre volume fraction loadings
up to 65%
- Uniformity of thickness and fibre loading, resulting
in uniform shrinkage
- Inserts may be incorporated into moldings
- Tooling costs comparatively low compared to
other manufacturing processes
- Uses only low pressure injection
- Low volatile emission during processing
- Ability to produce near net shape moldings,
reducing material wastage
- Process can be automated, resulting in higher
production rates with less scrap
- Ability to mold complex structural and hollow
shapes
- Low resultant voidage in molded components
- Ability to achieve from 0.5mm to 90mm laminate
thickness
Possible Resin Types To Be Used
Vinylester, Polyester, Polybutadiene, Epoxy, Polimide, Bismaleimide
The selection of a manufacturing technique for producing polymeric composite
parts must be based on consideration of a number of factors, including
the size and shape of the part, microstructural control, reinforcement
and matrix type, required performance, market economics, and so on.
RTM appears uniquely capable of satisfying the low-cost/high-volume 500-50,000
parts per year of the automotive industry as well as the higher performance/lower
volume 50-5,000 parts per year of the aerospace industry.
Moreover, variations of the RTM process make it well suited for the production
of large, complex, thick-sectioned structures for infrastructure and military
applications. For example, the glass-fiber / vinyl-ester bridge deck and
the lower hull of the Army Composite Armored Vehicle (CAV). The automotive
industry has used resin transfer molding (RTM) for decades. The resin
transfer molding process is fairly simple: A two-part, matched-metal mold
(or tool) is made. A preform is placed into the mold, and the mold is
closed.
The resin is then pumped under low pressure through injection ports into
the mold and follows predesigned paths through the preform. Both the mold
and resin can be heated as needed for the application.
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Reources: Plastech
Thermoset Tectonics - Email: rtm@plastech.co.uk
- Southern Illinois University
- Brigham Young University
(BYU)
- Michigan State
University
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