Introduction to molding process

Molding is a molding process in which the required material is placed in an open, heated mold cavity. The mold is then closed and pressure is applied to the mold with a large hydraulic press to make the material contact all areas of the mold. Presses are divided into mechanical and hydraulic types, currently hydraulic type is the main type.

Compression molding is the most common manufacturing process for thermoset and thermoplastic polymer composites. Usually used to produce high-volume composite parts, such as automotive parts. There are two types of compression molding process, namely cold pressing and hot pressing.

For thermosetting polymers, intermediate semi-cured composite materials called molding compounds are used. Bulk molding compound (BMC) and sheet molding compound (SMC) are two widely used thermosetting-based molding compounds.

For thermoplastic polymers, glass mat thermoplastic (GMT) is usually used as the raw material. During compression molding, the composite materials are evenly mixed and distributed in the internal mixer and twin-screw extruder.

For these two types of compression molding processes, cold pressing technology only needs to apply pressure, while in hot pressing technology, both pressure and temperature are required. Cold pressing technology requires room temperature for curing, while hot pressing technology transfers heat to the composite material and starts the curing process by heating the mold.

The advantage of compression molding is that it is widely applicable to various compounds. Since devices can be made for certain polymers at room temperature, the problem of mutual reactions between polymers can be alleviated. The compression molding process can help keep the overall project cost to a minimum. Although compared with other technologies, the cost of a single part may be higher. When choosing the most suitable production solution, all aspects of the product, performance and life cycle must be considered. The right solution may not require expensive injection molds, so even if the cost of the parts is higher, overall, the compression molding solution is still as important as ever