Compression molding is one of the original processing methods for manufacturing plastic parts developed at the very beginning of the plastics industry. In fact, it was widely used in the bakery industry for cookie or cake molding before plastic materials existed.
Although it is also applicable to thermoplastics, compression molding is commonly used in manufacturing thermoset plastic parts. The raw materials for pressing moulds are usually in the form of granules, putty-like masses, or preforms. They are first placed in an open, heated mold cavity. The pressing mold is then closed and pressure is applied to force the material to fill up the cavity. A hydraulic ram is often utilized to produce sufficient force during the molding process. The heat and pressure are maintained until the plastic material is cured.
There are two different types of compounds most frequently used in pressing moulds (pressing tools): Bulk Molding Compound (BMC) and Sheet Molding Compound (SMC). SMC molding material costs higher but can be pre-cut to conform to the surface area of the pressing moulds. The more evenly distributed material over the pressing mould surface usually results in less flow orientation during the compression stage and, therefore, higher product consistency.
Compression molding is commonly used for manufacturing electrical parts, flatware, gears, buttons, buckles, knobs, handles, electronic device cases, appliance housing, and large container.
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