Compression molding involves placing a thermosetting plastic material directly into a heated metal mold. The material is softened by heat and forced to conform to the shape of the mold. The plastic is subjected to heat and pressure in a single stroke using a hydraulic press with heated platens. The temperature and pressure applied depends on the plastic's properties. Once molded, the excess material is trimmed off as flash and the hardened part is ejected from the mold. Examples of items made by compression molding include switches, circuit breakers, gears, coils, and connectors.

1. Compression molding
By Sunil Mor

2. Principle
• A plastic material is placed directly into a heated metal mold
then is softened by the heat and therefore forced to conform
to the shape of the mold.

3. Working
• The thermosetting plastic material is subjected to heat and
pressure in a single stroke.
• This is done by using a hydraulic press with heated platen.
• The actual temperature and pressure depends on the
properties of the thermosetting plastic material to be molded.
• The thermosetting plastic material in compound form is
placed in the cavity of the mold so as to fully filled the
impression of the mold.
• As the mold closes down under pressure, the material is
squeezed between the two halves of the mold and compact
to the shape of the impression.

4. Working
• The excess material flows out of the mold as a thin film
known as flash which is trimmed off.
• Under the influence of heat, the compacted mass gets cured
and hardened to the shape.
• The mold can be opened while still hot to release the molded
article.
• https://youtu.be/pOGpXZ-UMfo

5. Working

6. Example
• Switches, MCB, gears, coil, connector,
automotive parts etc.

7. References
• Plastic engineering handbook by Joel Frados.
• Polymer extrusion by hanser publication.
• Polymer processing by DH Morton Jones.
• Hand book of plastic technology by W.S. Allen/ P.N. Baker.
• SPI Plastics Engineering Handbook by Michael L. Berins.
• SBP Handbook of Plastics.