Compression molding is a manufacturing process that uses pressure to mold parts. A heated rubber material is placed in one side of a mold. The other side of the mold is then clamped down, and the rubber material is compressed into the desired shape. The mold must be heated, as the combined compression and heat is what causes the rubber to take its new shape. The mold also has to be designed to meet certain criteria for compression manufacturing. Compression molds need to have overflow grooves to allow excess material to exit the mold. It is difficult to accurately predict the amount of rubber material needed without any overflow. Using a little extra material will ensure the mold is filled completely and the product comes out as intended. The excess material is referred to as flash and must be trimmed after the compression molding has been completed.
Cost is one of the driving factors behind the popularity of compression molding. Compression mold tooling is much cheaper than tooling for a comparable process like injection molding. Compression molds are far less complicated, requiring fewer machine hours to complete. Compression molds do not require the gates and runners needed for injection molding. Compression molded parts can vary in thickness without issue. Parts as thin as 0.5 mm (0.02 in.) or as thick as 25 mm (1 in.) are easy to produce. Designers are able to specify seamless design features with compression molding. There is no need to worry about flow or knit lines that may appear with injection molding.
Cycle time is the main drawback when considering compression molding. One cycle can last several minutes. A technician has to manually place the material into the mold, heat it up, apply pressure, and then wait for the mold to cool off enough to remove the part before starting the process again. Multi-cavitation is a way around this issue. Parts will require some post processing after they are molded. Flash is the excess material that is squeezed out of the mold during compression. The flash will still be attached to the main product in some areas and will need to be manually removed. Compression molding is an ideal choice for simple products but may leave under-filled sections if the design is too complex.
FormexMold by Fathom can help you take your idea from design to marketplace. Use our instant quote system to find out if your design is a good candidate for compression molding. Our experts will review the design and let you know whether or not the part can be created with compression molding. Design review is typically completed in about one business day. We look forward to working with you.
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