Effect of gate size on the melt filling behavior and residual stress of injection molded parts

• A visualization mold was built up for observing the melt filling behavior in cavity.
• Visual results showed that the gate size significantly affects melt filling behavior.
• Higher melt filling speed or nozzle temperature lead to reduction of residual stress.
• Undersized gate causes many adverse effects on filling process and residual stress.

This paper studies the effects of gate size on the cavity filling pattern and residual stress of injection molded parts. A total of three rectangular gates with different sizes were used. Experiments were carried out by using a dynamic visualization system. A flow visualization mold was specially designed and made for this study. A high-speed video camera was used to record the mold filling phenomena of cavities with different gate size and different processing parameters. In addition, a Stress Viewer was used to characterize the residual stress of molded samples. It was found that the undersized gate has many adverse effects on the filling behavior and residual stress of molded parts. With a larger gate, the cavity will be filled faster and residual stress of parts may be smaller. The result of the study also indicates that nozzle temperature and injection rate can significantly affect the above two aspects.