Compression Molding:
Compression molding uses a preformed slug of rubber which is placed in the cavity area of a mold. When the mold is closed, the rubber material is displaced throughout the cavity area forming the part. This method of molding uses less material than transfer molding, which has a waste pad of material.

The drawback to compression molding is that preformed slugs of material must be made for each cavity of the mold. The loading of these slugs into the mold is time consuming and lengthens the production cycle times.  It has the potential for higher scrap rates than other methods of molding.

Transfer Molding:
In transfer molding, a single piece of rubber material is place in the top of the mold and transfers down through sprue holes into the cavity area below. This forms the part with minimal flash because the cavity area is already closed, unlike compression molding.

Transfer molding can be used to produce a wide variety of parts, including rubber to metal and rubber to plastic bonding.

Transfer molding is much more efficient than compression molding. The production cycle times are shorter because of the reduced amount of time needed to load material into the molds.

Injection Molding:
Injection molding is similar to transfer molding except that cure times are usually shorter. In injection molding, the rubber is preheated in a barrel before it is injected into the mold cavity areas. This lowers the amount of time in the production cycles.

Injection molding is very versatile in terms of mold design. Molding concepts such as automatic ejection, rotating core bars and centerplates can be used.  In this type of molding, parts can be removed from the core bar or the centerplate of the mold while other parts are curing in the injection press. This increases production of parts, lowering the amount of time needed for curing and demolding of parts. This is probably the most efficient type of molding for most designs.