（12） Plastic molding and processing methods Injection Molding Process Defect Handling Manual (65 types)

Plastic products are usually made of polymers or mixtures of polymers and other components, which are molded into a certain shape under certain conditions after being heated
After cooling, shaping, and trimming, this process is the molding and processing of plastic. If the performance of plastic and thermosetting plastics after heating is different, their molding and processing methods are also different. There are dozens of plastic molding methods, the most important of which are extrusion, injection, calendering, blow molding, and molding. The weight of the products they process accounts for about 80% of all plastic products.
Extrusion molding - Extrusion molding, also known as extrusion molding or extrusion molding, is the most important molding method for thermoplastics, and about half of plastic products are extruded. Extrusion can form almost all thermoplastics, and products mainly include continuous production, uniform cross-section pipes, plates, films, wire and cable cladding, and various special-shaped products. Extrusion molding can also be used for plasticizing, granulating, coloring, and blending of thermoplastic materials.
After mixing thermoplastic polymers with various additives evenly, they are subjected to mechanical shear force, friction heat, and external heat in the plastic cylinder of the extruder, making them plasticized and melted. Then, under the push of the screw, they enter the molding mold through a filter plate and are extruded into products.
Injection molding - Injection molding is also known as injection molding or injection molding. This method of molding involves heating and melting plastic (usually granular material) within the barrel of an injection molding machine. When in a flowing state, the molten plastic is compressed and moved forward under the pressure of a plunger or screw, and then injected quickly into a closed mold at a lower temperature through a nozzle at the front end of the barrel. After a certain period of cooling and shaping, the mold is opened to obtain the product.
Injection molding is developed based on the principle of metal die casting. Injection molding is widely used because it can produce products with complex shapes, precise dimensions, or metal inserts in one shot, accounting for more than 20% of the total molding process.
The injection molding process usually consists of five stages: plasticization, mold filling (i.e., injection), pressure maintaining, cooling, and mold release.
Generally, injection molding products have waste materials such as gates and runners that need to be trimmed and removed. This not only consumes labor, but also wastes raw materials.
The development of non gate injection molding in recent years not only overcomes the above drawbacks, but also helps to improve production efficiency.