Compression molding is the process of molding in which a preheated polymer is placed into an open, heated mold cavity. The mold is then closed with a top plug and compressed in order to have the material contact all areas of the mold.
This process is able to produce parts with a wide array of lengths, thicknesses, and complexities. The objects it produces are also high in strength, making it an attractive process for a number of different industries.
Thermoset composites are the most common type of material used in compression molding.
Four Main Steps
There are four main steps to the thermoset composite compression molding process:
- A high strength, two part metallic tool is created that exactly matches the dimensions required to produce the desired part. The tool is then installed in a press and heated.
- The desired composite is pre-formed into the shape of the tool. Pre-forming is a crucial step that helps to improve the performance of the finished part.
- The pre-formed part is inserted into the heated mold. The tool is then compressed under very high pressure, usually ranging from 800psi to 2000psi (depending on the thickness of the part and the type of material used).
- The part is removed from the tool after the pressure is released. Any resin flash around the edges is also removed at this time.
Advantages of Compression Molding
Compression molding is a popular technique for a number of reasons. Part of its popularity stems from its use of advanced composites. These materials tend to be stronger, stiffer, lighter, and more resistant to corrosion than metal parts, resulting in superior objects. Manufacturers accustomed to working with metal parts find that it is very simple to convert an object designed for metal into a compression molding part. Because it is possible to match metal part geometry with this technique, in many circumstances one can simply drop-in and replace the metal part altogether.
Another advantage of compression molding is its ability to create very complex parts. While this technique can not quite reach the production speed of plastic injection molding, it does offer more intricacies in geometry than typical laminated composites. It also allows for longer fibers than plastic injection molding, resulting in stronger and stiffer materials. Therefore, compression molding can be seen as a middle ground between plastic injection molding and laminated compound fabrication.
With its ability to create complex parts with a huge variety of applications while keeping part cost and turnaround time a priority, compression molding is an advantageous process for manufacturers in a wide range of industries.
Compression Molded Plastic Pallets
TranPak’s ProPal 48×40 Pallet is a great example of a pallet made by compression molding.
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