For optimal product
performance we suggest following these basic RULES of
design.
VACUUM
FORMING
This method is
the most commonly used technique for forming plastics
sheets into custom shapes. It is also the most economical
method.
Dimensions
- Tolerances:
Please see the sheet titled
"Standard Manufacturers' Tolerances"
for guidelines.
Draft Angles:
Draft on male
(positive) molds should be 2° - 5°, maybe
0° to ½ ° in special circumstances. Draft
on female (negative)
molds may be 1° - 4° depending on texture
of mold and surface finish. Draft angles are necessary
to prevent the part locking onto the molds.
Radii and Fillets:
Radii
and Fillets are required on most vacuum formed parts.
They should never be less than the minimum part thickness.
They should be 2-4 times the expected wall thickness when
extra strength and thickness of parts are required.
Pockets and Indents:
Pockets and Indents,
as a rule of thumb, the depth of a pocket or
indent should be equal to or greater then the smallest
width of pocket. This would provide for the greatest material
distribution.
Example: if Length = 1" and Width = 1.5" then
Depth should be 1" or less
Material Thickness:
Material starting
thickness will always be thinner when the part is formed
and will vary upon the general size, height, depth of
pockets and other complexities. If you have any questions
on starting thickness specifications or any other design
consideration, please contact the C&K Plastics' sales
engineering people.
PRESSURE
FORMING
Pressure forming
is used where the injection molded look is desirable,
namely greater definition, variety of surface textures,
smaller radii, molded vents or pockets. It is generally
more expensive than vacuum forming, but tooling costs
are only a fraction of other methods. Molds that are female
(negative) should be aluminum and preferably water-cooled.
Parts designed for short runs or prototype may be made
of epoxy or wood, depending on complexity of the shape
and depth of draw.
Dimensions - Tolerances:
Please see the
sheet titled "Standard Manufacturers' Tolerances"
for guidelines.
Draft Angles:
Draft angles
for female (negative) aluminum molds should be 2°
- 6° to prevent lockup of part in mold. Deep parts
or complex configurations, texturing on the tool side,
may require more draft angle.
Radii and Fillets:
Radii and Fillets
may be less than in vacuum forming. Sharp corners may
be attained on shallow draw areas. Keep in mind that larger
fillets and radii make stronger, stiffer parts and create
thicker corners.
Pockets and Indents:
Pockets and Indents,
as a rule of thumb, the depth of a pocket or
indent should be equal to or greater then the smallest
width of pocket. This would provide for the greatest material
distribution.
Example: if Length = 1" and Width = 1.5" then
Depth should be 1" or less
Material Thickness:
As in vacuum
forming, material starting thickness will thin when part
is formed. However, the amount of thinning will depend
upon shape, size, depth of draw, radii and fillets. For
any special design considerations in pressure forming,
please contact C&K Plastics' sales engineering people.
STANDARD
MANUFACTURERS' TOLERENCES
Tolerances will
vary from part to part, depending on the materials, size,
shape, numbers of cutouts and other configuration possibilities.
