Resin Transfer Molding Flashcards
RTM involves the creation of reenforced plastics, or fiber _____________ and is known for having high _______________ ratios
fiber composites, strength to weight
RTM is a relatively _____ class of materials (since
_______) and an example is _______, a tough composite
based around __________ fibers
new, 1950, Kevlar, aramid
Composites are different than anything we
have studied so far because the material is
_______during the manufacture of the part
Created
In RTM, fibers are first placed in a ____________followed by the _________ of a thermosetting plastic resin that makes a ____________ matrix around the fibers
mold, injection, continuous
RTM first deployed commercially in ____________ and has:
o Production volumes up to 10,000 per year
o __________ form freedom
o good potential for functional integration
o ___________ part counts
1970, good, low
Other composite part manufacturing methods are:
o ___________ production (low production volumes)
o __________ winding (large, rotationally symmetric shapes)
o _____________
o ___________
o ____________
Hand layup, Filament, Press forming, protrusion, autoclaving
Other composite methods use ________________ which is uncured resins are ______________________ with fibers.
Pre-preg. pre-impregnated
The properties of a composite will depend on:
o The properties of the fibers and the __________
o The volume fraction of __________
o Fiber orientation
resin, fibers,
When all fibers are aligned in same direction, it is called a _____________(UD) composite, but this is rarely done because the matrix will split if loaded in the _____________ direction
Unidirectional, perpendicular
Typically fibers are oriented in several ____________ e.g. 0/90 cross-ply or +/- 45 degrees), but can also be oriented _____________
Several directions, randomly
What is the typical volume percentage of fiber in RTM?
20-60%
The fibers are inherently brittle, so they will not ________________
deform plastically
The high strength of fibers allows them to compete with metals, but with the added benefit that the fiber volume and orientation can be ___________________________
customized to requirements
RTM parts can be customized to match the ______________ it is
expected to carry and materials can be tuned to optimize
price, performance or be especially strong in ________, for example
Load, impact
In RTM, fibers are often woven or stitched together
which introduces additional considerations such as how tight the fibers should be woven together and their _______________
drapability
In the RTM process,
The fibers (and any inserts) are placed in the ___________. Then resin is driven into the mold by a _______________. Next, the mold is set aside to ____________. Finally, the product is ____________
Mold, pressure difference, cure, de-molded
RTM cycle times are typically on the order of _____________, but can be considerably longer with some ____________
1 hour, epoxy resins
RTM resins are __________ (~________ Pa.s), so they
require considerable pressure to be injected into the
mold
Viscous, 0.2
_______________equation is used to calculate flow
through a porous medium (i.e., the fiber mats)
d’Arcy’s
Typical pressures for RTM are in the ______bar range
1-6
The ___________is a thermo-setting plastic that enters as a
viscous liquid and then ____________ during the process
Resin, cures
There are two main classifications of resins: _____________ and
_______________
epoxies, polyesters
Epoxies are mixed with a __________ and the ratio between epoxy and hardener must be controlled to achieve the desired
__________
hardener, ductility
Polyester resins are mixed with a “___________” compound
(usually _________________) and a small amount of ___________
to act like a catalyst
starter, hydrogen peroxide, cobalt
The more ____________ the faster the resin reaction takes place.
Starter
Polyesters set much __________ than epoxies, but it is important to be careful because setting is an ___________ process and if the heat isn’t ___________, the reaction is sped up, creating a runaway situation
quicker, exothermic, dissipated
______________ are generally favored for RTM, except in
________________ applications where _________ are used for their
toughness
Polyesters, high performance, epoxies
________________are another type of resin that are gaining
popularity as a compromise between epoxies and polyesters and ___________________ are beginning to be developed.
Vinyl esters, Bio-based
For Resins, It is possible to put _________________ such as flame ___________________ and pigment. It is also common to apply a gel coat or a _________________ resin to the mold before the fiber mats are placed which creates a nice surface finish on the part.
Additives, retardants, clear coat
Two common issues with RTM are:
1. Variation in fiber _______________
2. __________________
Volume Fraction, internal Runners
To account for variation in fiber volume fraction, it is not uncommon for fiber mats to be laid in patches with some of the patches __________________ which decreases the
_______________ of the mat, making it more difficult for the resin to flow through
overlapping, permeability,
Decreased permeability from patches produces “________________” that are not fully impregnated by the resin
which results in a _________________
dry spots, rejected part
Internal Runners involve sections with too few fibers (often
near___________________). In this case, resin flows on the ______________of the fibers leaving the _______________ fibers not fully impregnated
Sharp Corners, outside, inside
In this method, two rigid mold halves are clamped together and resin is injected at constant pressure.
o Typical projects are flat, single-curved or mildly double curved
o Sizes can range from .1m to 6m
o Thickness range from about 1mm to 20mm
o A notable application are car bumpers
Pressure-Controlled
This method is essentially the same as the pressure Controlled method, but now the injection speed (and thus Volumetric Flow Rate ) is controlled
o Pressure gradually rises during the process
o More complex to control injection time, but allows for
more optimization and for easy automation
o Good choice for high volume production
Volume Controlled RTM
This method is also called vacuum bagging or
vacuum infusion and requires just one half of a mold that is covered with a vacuum bag.
o A vacuum is pulled and the bag is pressed onto the part
o Resin is then pulled in through injection tubes
o Sealing can be difficult and only the side that makes contact with them mold has good surface properties.
Resin Infusion
