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. The mold is closed with a top force or plug member, pressure is applied to force the material into contact with all mold areas, and 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. Compression molding is a high-volume, high-pressure method 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 advantage of compression molding is its ability to mold large, fairly intricate parts. Also, it is one of the lowest cost molding methods compared with other molding like transfer molding and injection molding, moreover it gives little waste on material provides advantage on expensive compounds. Yet, compression molding often provides least product consistency, difficult to control flash and it is not suitable for some types of parts. Compression molding produces fewer knit lines and less fiber-length degradation than injection molding.

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In compression molding there are 4 important considerations that have to bear in an engineer mind^{[citation needed]}:

• Selection of proper amount of the materials
• Determination of minimum time required to heat the compound as well as the appropriate heating techniques
• The prediction of required force to make sure that every volume of the melt has the desired shape
• Temperature of the molds should decrease rapidly during the cooling process.

References

http://www.molders.com/compression_molding.html