FAA Advisory Circular 43.13-1B
Acceptable Methods, Techniques, and Practices
Aircraft Inspection and Repair
AC 43.13-1B | 3. Fiberglass and Plastics | 3. Transparent Plastics | 3-23. Forming Methods
9/8/98
AC 43.13-1B
then remove it from the mold. Smooth out any
roughness and cover it with soft cloth. It is
now ready to use to form the new part.
3-23. FORMING METHODS. (See ta
ble 3-1.)
a. Simple Curve Forming. Heat the
plastic material to the recommended tempera
ture, remove it from the heat source, and care
fully drape it over the prepared form. Care
fully press the hot plastic to the form and ei
ther hold or clamp the sheet in place until it
cools. This process may take from ten minutes
to one-half hour. Do not force-cool it.
b. Compound-Curve Forming. This
type of forming is normally used for such parts
as canopies or complex wingtip light covers,
and it requires a great deal of specialized
equipment. There are four commonly used
methods, each having its advantages and dis
advantages.
c. Stretch Forming. Preheated acrylic
sheets are stretched mechanically over the
form in much the same way as is done with the
simple curved piece. Special care must be
taken to preserve uniform thickness of the
material, since some parts will have to stretch
more than others.
d. Male And Female Die Forming. This
requires expensive matching male and female
dies. The heated plastic sheet is placed be
tween the dies which are then mated. When
the plastic cools, the dies are opened.
e. Vacuum-Forming Without Forms.
Many aircraft canopies are formed by this
method. In this process a clamp with an
opening of the desired shape is placed over a
vacuum box and the heated sheet of plastic is
clamped in place. When the air in the box is
evacuated, the outside air pressure will force
the hot plastic through the opening and form
the concave canopy. It is the surface tension of
the plastic that shapes the canopy.
f. Vacuum-Forming With A Female
Form. If the shape needed is other than that
which would be formed by surface tension, a
female mold, or form must be used. It is
placed below the plastic sheet and the vacuum
pump is connected. When air from the form is
evacuated, the outside air pressure will force
the hot plastic sheet into the mold and fill it.
g. Sawing And Drilling.
(1) Several types of saws can be used
with transparent plastics, however circular
saws are the best for straight cuts. The blades
TABLE 3-1. Typical temperatures for forming acrylic sheets.
Thickness of sheet (in.)
Type of forming
Simple curve
Stretch forming
(dry mold cover)
Male and female forming
Vacuum forming without
form
Vacuum forming with
female form
0.125
0.250
Regular acrylic plastic.
MIL-P-6886
°C
°F
°C
°F
113
235
110
230
140
284
135
275
140
284
135
275
140
284
135
275
145
293
140
284
0.125
0.250
Heat-resistant acrylic plastic,
MIL-P-5425, and craze-resistant acrylic plastic,
MIL-P-8184
°C
°F
°C
°F
135
275
135
275
160
320
150
302
180
356
170
338
150
302
145
293
180
356
170
338
Par 3-22
Page 3-17