Definitions

Compression molding

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 methods such as transfer molding and injection molding; moreover it wastes relatively little material, giving it an advantage when working with expensive compounds. However, compression molding often provides poor product consistency and difficulty in controlling flashing, and it is not suitable for some types of parts. Compression molding produces fewer knit lines and less fiber-length degradation than injection molding. Compression-molding is also suitable for ultra-large basic shape production in sizes beyond the capacity of extrusion techniques. Materials that are typically manufactured through compression molding include: Polyester fiberglass resin systems (SMC/BMC), Torlon PAI, Vespel PI, Meldin PI, Ryton PPS, and many grades of PEEK.

In compression molding there are four important considerations that an engineer should bear in mind:

  • Determining the proper amount of material
  • Determining the minimum time required to heat the compound, as well as the appropriate heating technique
  • Predicting the required force, to ensure that shot attains the proper shape
  • Designing the mold for rapid cooling after the material has been compressed into the mold

External links

http://www.polyplycomposites.com/molded.htm


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