Hand Lay-up Flashcards
. What does a wet hand lay-up process entail?
Cutting dry cloth to fit details of part/shape, wetting out those layers with desired
resin and laying material into a mold or as a sheet. The layup can be placed in
vacuum bag to gain some pressure on the material to make the part more dense.
What are some limitations to the hand lay-up process?
i. Exposed to volatile organic compounds due to open mold,
ii. One smooth surface, with Poor surface quality on other,
iii. More difficult to control of part thickness, leading to inconsistency in parts
quality
iv. Challenge to control of void fraction, and fiber content,
v. Labor intensive, as it is not clean process.
What is the average Standard Atmospheric Pressure (at sea level):
101325 Pa
equivalent to 1.01325 bar, 760 mmHg (torr), 29.92 inHg and 14.696 psi
Why do we use vacuum bagging for some hand lay-up parts? What does vacuum
bagging do?
Vacuum bagging compresses the part, removing excess resin from part; increases
the volume fraction of fiber. Both these phenomena help to make a stronger
composite.
What are the functions of the following materials:
Gel coat Peel Ply Separator Bleeder Breather Tacky Tape Caul Plate
Gel coat - a material used to provide a high quality finish on the visible surface of
a fiber-reinforced composite material. Gel coats are modified resins which are
applied to molds in the liquid state.
Peel Ply - perforated film that is placed immediately on top of or under the
composite laminate removed just before bonding or painting operations to provide
clean, bondable surface
Separator - Non-perforated film that is placed between laminate (and peel ply, if
used) and tool (tool surface preparation may make film unnecessary). Porous or
perforated film is placed on top of laminate (and peel ply, if used, or peel ply
alone may serve this function). Porous or perforated film allows volatiles to
escape from laminate and excess resin to bleed from laminate into bleeder plies
during cure.
Bleeder – extra fiberglass materials that absorbs excess resin from laminate
during cure (resulting in desired fiber volume)
Breather - cotton like fabric that goes on top of a part in vacuum bagging. It is
used to put an even pressure on the part once the vacuum starts.
Tacky tape – Sealant tape between bagging material and part mold to allow
vacuum to be drawn and hold. Usually a not volatile tape.
Caul Plate – A steel, aluminum, glass piece used apply a more uniform pressure
across part, ensuring a smooth, non-wavy surface.
Can you make high quality parts using hand lay up and vacuum bagging? Answer
this question both in terms of mechanical properties and aesthetics.
Yes, but it is
hard. Mechanically it will be weaker for you cannot control part thickness as
easily or make a high fiber content part. Aesthetically, only one side is usually a
clean Class A surface, with the other side showing poor surface quality reproducing the surface of caul plates or bagging materials. It is also labor
intensive but achievable. Desirable to post cure parts for better strength.
What is prepreg? What are its limitations?
Cloth that has been impregnated with predetermined amount of uniformly
distributed thermoset or thermoplastic resin and used directly to layup part. The
thermoset prepreg must remained chilled till use, with limited out of freezer time
and has a product shelf life
What is debulking with respect to prepregs?
When layers of a prepreg are used to achieve a certain part thickness, some air
bubbles can get trapped in between the layers. One way to manage them out is to
use a vacuum bag after every 2-3 layer to cause compression of the layers and
removes the air.
What are some concerns in stacking prepreg layers to construct a laminate?
Maintain proper fiber angle from ply-to-ply, eliminate trapped air between plies,
One chance only in lay-up stack the plies together, Only “matrix joints” allowed
in plies with a Gap size should not exceed 0.03 in. or 0.76 mm, One ply may
require more than one piece of prepreg
