Injection molding process and principle

Injection molding is a complex manufacturing process that involves converting a thermoplastic from its solid 

state to a liquid state (melting), which is then injected into a mold, cooled and cured, and finally removed from 

the molded plastic part. The basic process of injection molding process roughly includes the following steps:

Material preparation: Select the appropriate thermoplastic particles (commonly called resins) and ensure that 

they are dry, pure and free of debris.

Plasticizing: Plastic particles are poured into the hopper of the injection molding machine. The particles are 

heated and molded into a viscous molten state by heating the cylinder and the screw.

Injection: A screw or plunger is used to inject molten plastic into a closed mold cavity at high pressure. This 

process requires controlled injection speed, pressure and timing.

Pressure retention: After the injection is completed, the plastic needs to maintain a certain pressure in the mold 

to compensate for the shrinkage of the material when cooling to ensure the quality of the part.

Cooling: The molten plastic is cooled and solidified in the mold. The design of the mold should consider a 

reasonable cooling system to ensure that the plastic parts are cooled quickly and evenly.

Demoulding: Once the plastic part has cooled and cured, the mold opens and the cured part is usually ejected 

from the mold using an ejection system.

Post-treatment: The produced plastic parts can be deburring, grinding, assembly, painting and other subsequent 

processing processes according to the need.

The principle of injection molding mainly involves the flow, heat transfer, pressure retention and curing process 

of molten plastics. Throughout the injection molding process, precise control of material temperature, mold 

temperature, injection pressure and speed, pressure retention and cooling time is essential for the production 

of high-quality plastic products. The injection molding process enables mass production with stable product 

quality and is suitable for the manufacture of parts with complex shapes and fine dimensions.

Hongren plastic mold in more than ten years of injection molding production has accumulated a wealth of 

injection molding process experience and technical precipitation, can provide customers with high-quality plastic parts.