Plastic Molding Method: Compression Molding

Compression molding is a high-volume, high-pressure method that is suitable for molding complex, high-strength fiberglass reinforcements. 

Advanced composite thermoplastics can also be compression molded with unidirectional tapes, woven fabrics, randomly orientated fiber mat or chopped strand. 


The plastic material is usually preheated and placed in an open, heated mold cavity. The mold is closed with a top force or plug member, pressure is applied to fill all mold areas with the material, heat and pressure are maintained until the molding material has cured. Finally, wait for appropriate time and eject plastic article out. 
Volatile such as water(H2O), NH3 are generated during production, so normally there are vent holes set on the mold for exhausting the gas.


1. It can be used to mold large, fairly complex parts.
2. It can be used with any kinds of plastic material.
3. Less equipment cost because there's no runner or gate, there's also barely wasted material during the production. 


1. Cycle time is long.
2. The liquid form of plastic material might spill over easily, thus it might create flash on plastic mold article.

3. High manpower demand because the production is hand work, which is difficult to mechanize.


1. When the material is Thermosetting Plastic: Heating temperature should be controled and maintained strictly.
2. When the material is Thermoplastic: It's necessary to have some cooling time until the plastic ariticle has cured, so obtaining rapid cooling is important for compression molding.
3. For producing those large or complex plastic article,  in order to prevent starved feeding or uneven density, the plastic material should be placed appropriately in mold cavity to fill all mold areas, which is based on the prediction of flow direction.

**The information is for references only, compression molding is not available in Ji-Horng Plastic Co., Ltd., if you are interested in injection molding service, please feel free to contact us, thank you!**