Principles of Injection Molding Process

Injection molding is a process in which plastic melt is injected into the closed mold cavity at high speed under high pressure, and then plastic injection products with the same shape as the cavity come into being after cooling shaping.

Injection molding must meet two molding requirements:  the plastic must be injected into the injection molding mold cavity in a molten state, and the injected plastic melt must have sufficient pressure and flow speed to fully fill the mold cavity. Therefore, injection molding must have basic functions of plastic plasticization, melt injection and packing injection molding and so on.

Plastic plasticizing: During the plasticization process of injection molding, the solid plastic moves forward along the direction of the screw channel continuously through the transport of rotating screw. Dispersive mixing of screw and thread reacts and heats up with heating and compaction, transformed into viscous plastic melt with uniform density, viscosity, composition and stable and uniform distribution.

Injection molding process: The plasticized plastic melt is stored in the reservoir of the barrel and the screw moves axially during injection. Under the action of the screw injection pressure, plastic melt flows at a certain rate through the nozzle installed in the front of the barrel, the mold casting system and so on, and is injected into the cavity of the mold.

Cooling shaping: plastic melt injected into the cavity overcomes various flow resistance and fills the whole cavity, suffering huge pressure from the mold cavity which has the tendency to drive the plastic melt flow back to the cylinder. Due to the cooling effect of the mold cavity, the plastic melt generates cooling shrinkage.

At this point, the injection screw continues to provide pressure to keep the plastic melt filled cavity without backflow, and replenishes plastic melt to cavity properly, filling up the cavity shrinkage space until the plastic melt is gradually cooling solidified into products.

Details determine success or failure has become the standard pursued by every industry. Nowadays, the precision of injection molding products is getting higher and higher and the quality requirements are becoming more and more strict, which requires the manufacturers of injection molding products to strictly control and supervise every link in the production process.