Resin Transfer Molding

Question 1

RTM involves the creation of reenforced plastics, or fiber _____________ and is known for having high _______________ ratios

Answer 1

fiber composites, strength to weight

Question 2

RTM is a relatively _____ class of materials (since
_______) and an example is _______, a tough composite
based around __________ fibers

Answer 2

new, 1950, Kevlar, aramid

Question 3

Composites are different than anything we
have studied so far because the material is
_______during the manufacture of the part

Answer 3

Created

Question 4

In RTM, fibers are first placed in a ____________followed by the _________ of a thermosetting plastic resin that makes a ____________ matrix around the fibers

Answer 4

mold, injection, continuous

Question 5

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

Answer 5

1970, good, low

Question 6

Other composite part manufacturing methods are:
o ___________ production (low production volumes)
o __________ winding (large, rotationally symmetric shapes)
o _____________
o ___________
o ____________

Answer 6

Hand layup, Filament, Press forming, protrusion, autoclaving

Question 7

Other composite methods use ________________ which is uncured resins are ______________________ with fibers.

Answer 7

Pre-preg. pre-impregnated

Question 8

The properties of a composite will depend on:
o The properties of the fibers and the __________
o The volume fraction of __________
o Fiber orientation

Answer 8

resin, fibers,

Question 9

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

Answer 9

Unidirectional, perpendicular

Question 10

Typically fibers are oriented in several ____________ e.g. 0/90 cross-ply or +/- 45 degrees), but can also be oriented _____________

Answer 10

Several directions, randomly

Question 11

What is the typical volume percentage of fiber in RTM?

Answer 11

20-60%

Question 12

The fibers are inherently brittle, so they will not ________________

Answer 12

deform plastically

Question 13

The high strength of fibers allows them to compete with metals, but with the added benefit that the fiber volume and orientation can be ___________________________

Answer 13

customized to requirements

Question 14

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

Answer 14

Load, impact

Question 15

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 _______________

Answer 15

drapability

Question 16

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 ____________

Answer 16

Mold, pressure difference, cure, de-molded

Question 17

RTM cycle times are typically on the order of _____________, but can be considerably longer with some ____________

Answer 17

1 hour, epoxy resins

Question 18

RTM resins are __________ (~________ Pa.s), so they
require considerable pressure to be injected into the
mold

Answer 18

Viscous, 0.2

Question 19

_______________equation is used to calculate flow
through a porous medium (i.e., the fiber mats)

Answer 19

d’Arcy’s

Question 20

Typical pressures for RTM are in the ______bar range

Answer 20

1-6

Question 21

The ___________is a thermo-setting plastic that enters as a
viscous liquid and then ____________ during the process

Answer 21

Resin, cures

Question 22

There are two main classifications of resins: _____________ and
_______________

Answer 22

epoxies, polyesters

Question 23

Epoxies are mixed with a __________ and the ratio between epoxy and hardener must be controlled to achieve the desired
__________

Answer 23

hardener, ductility

Question 24

Polyester resins are mixed with a “___________” compound
(usually _________________) and a small amount of ___________
to act like a catalyst

Answer 24

starter, hydrogen peroxide, cobalt

Question 25

The more ____________ the faster the resin reaction takes place.

Answer 25

Starter

Question 26

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

Answer 26

quicker, exothermic, dissipated

Question 27

______________ are generally favored for RTM, except in
________________ applications where _________ are used for their
toughness

Answer 27

Polyesters, high performance, epoxies

Question 28

________________are another type of resin that are gaining
popularity as a compromise between epoxies and polyesters and ___________________ are beginning to be developed.

Answer 28

Vinyl esters, Bio-based

Question 29

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.

Answer 29

Additives, retardants, clear coat

Question 30

Two common issues with RTM are:
1. Variation in fiber _______________
2. __________________

Answer 30

Volume Fraction, internal Runners

Question 31

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

Answer 31

overlapping, permeability,

Question 32

Decreased permeability from patches produces “________________” that are not fully impregnated by the resin
which results in a _________________

Answer 32

dry spots, rejected part

Question 33

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

Answer 33

Sharp Corners, outside, inside

Question 34

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

Answer 34

Pressure-Controlled

Question 35

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

Answer 35

Volume Controlled RTM

Question 36

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.

Answer 36

Resin Infusion