Compression molding is a process where a preheated polymer material is placed into a heated mold cavity. The mold closes with force to push the material against all areas of the mold. Heat and pressure are applied to cure the material into the shape of the mold cavity. Both thermoset and some thermoplastic materials can be molded in this way. The process is used to make large, intricate parts for various applications like electronics casing, appliances, automotive parts, and more. Key factors for success include the amount of material, heating time and technique, applied force, and cooling time and technique. Common materials molded are epoxies, urea formaldehyde, melamine formaldehyde, and phenolics.

1. Plastics
Compression Molding
Energy meter
casing
Plates
Tray
Buttons
Electric wall receptacles
Hair brush handle
Mirror body

2. Compression molding
• Compression molding is a process in which a molding polymer is squeezed
into a preheated mold taking a shape of the mold cavity and performing
curing due to heat and pressure applied to the material.
• The method is used mostly for molding thermosets, but some
thermoplastics parts may also be produced by compression molding.
• Compression molding is a method of molding in which the molding
material, generally preheated, is first placed in an open, heated mold cavity.
Bemis
Radio cases

3. Compression molding
• The mold is closed with a top force, pressure is applied to force the
material into contact with all mold areas, while heat and pressure are
maintained until the molding material has cured.
• The process employs thermosetting resins in a partially cured stage, either
in the form of granules, putty-like masses, or preforms.
• The advantage of compression molding is its ability to mold large, fairly
intricate parts.
Milling machine
adjustment wheel
Dinnerware

5. Compression molding
• The method uses a split mold mounted in a hydraulic press
• Compression molding process involves the following steps:
• A pre-weighed amount of a polymer mixed with additives and fillers
(charge) is placed into the lower half of the mold.
• The charge may be in form of powders, pellets, putty-like masses or pre-
formed blanks.
SoleAppliances housings

6. Compression molding
• The charge is usually preheated prior to placement into the mold.
• Preheated polymer becomes softer resulting in shortening the molding
cycle time.
• The upper half of the mold moves downwards, pressing on the polymer
charge and forcing it to fill the mold cavity.
Pot handles
Hockey stick

7. Compression molding
• The mold, equipped with a heating system, provides curing (cross-linking)
of the polymer (if thermoset is processed).
• The mold is opened and the part is removed from it by means of the ejector
pin.
• If thermosetting resin is molded, the mold may be open in hot state – cured
thermosets maintain their shape and dimensions even in hot state.
Front bumper

8. Compression molding

9. Compression molding

10. Compression molding

11. Compression molding
• If thermoplastic is molded, the mold and the molded part are cooled down
before opening.
• Compression molding cycle time is about 1-6 min, which is longer than
injection molding cycle.
• The method is suitable for molding large flat or moderately curved parts.
Dice
Poker chips

12. Compression molding
There are four primary factors in a successful compression molding
process:
• Amount of material
• Heating time and technique
• Force applied to the mold
• Cooling time and technique
Spoilers
Plug
Helmet ear flaps

13. Compression molding
Materials commonly processed by compression molding are:
• Epoxies (EP)
• Urea Formaldehyde (UF)
• Melamine Formaldehyde (MF)
• Phenolics (PF)
Socket
Switch
Fender
Scoops