Research University

Arizona State University School of Engineering

Design Automation Research Facility

Theory of injection molding

The theory of injection molding can be reduced to four simple individual steps: Plasticizing, Injection, Chilling, and Ejection.  Each of those steps is distinct from the others and correct control of each is essential to the success of the total process.

• Plasticizing - describes the conversion of the polymer material from its normal hard granular form at room temperatures, to the liquid consistency necessary for injection at its correct melt temperature.
• Injection - is the stage during which this melt is introduced into a mold to completely fill a cavity or cavities.
• Chilling - is the action of removing heat from the melt to convert it from a liquid consistency back to its original rigid state.  As the material cools, it also shrinks.
• Ejection - is the removal of the cooled, molded part from the mold cavity and from any cores or inserts.

Repetition of these basic steps in sequence is the process of injection molding.