In addition to polymers, different plastic additives (such as stabilizers, plasticizers, colorants, lubricants, fillers, etc.) are generally added to the raw materials used in the processing of plastic injection parts to improve the molding process and the use performance of the products or to save the cost of the products. Additive and polymer are mixed and evenly dispersed into powder, also known as a dry mixture. Sometimes the powder needs to be plasticized and processed into pellets. This kind of powder and pellets are collectively referred to as batch or molding compounds.

　　Plastic molding is a key link between the processing of plastic injection parts. Different forms of plastics (powder, granule, solution or dispersion) are made into products or blanks with required shapes by more than 30 molding methods. Its choice mainly depends on the type of plastic (thermoplastic or thermosetting), initial shape and the shape and size of the product. The common methods of processing thermoplastics include extrusion, injection molding, calendering, blow molding and thermoforming, etc. The processing of thermosette plastics generally adopts compression molding, transfer molding, and injection molding. The above plastic processing methods can be used for rubber processing.

　　In addition, there are also casting using liquid monomers or polymers as raw materials. Among these methods, extrusion and injection molding are commonly used.