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10 Fundamental Plastic Injection Molding Terms

Plastic injection molding requires careful planning from material selection to mold design and characteristics.

plastic injection molding terms guidebook

To ensure that the injection molding process runs as smoothly as possible for your next project, it’s beneficial to understand a few basic concepts.

A fundamental understanding of key terms will foster better communication between the manufacturer and injection molder, resulting in quicker turnaround and a higher level of satisfaction with the job.

10 Key Plastic Injection Molding Terms to Learn Now

  • Cavity – The concave space in the mold, which is filled with hot plastic to create the desired part. Sometimes referred to as the “A-side” or “A-part” of the mold.
  • Flash – Leftover plastic that goes outside of the intended part molding.
  • Gate – Where the plastic enters the mold. It can be trimmed manually or automatically once the part is ejected.
  • Line of Draw – The point at which the two molding halves separate to reveal the injection molded part. This allows the part to be ejected without damage from metal obstructions.
  • Runner – A canal for plastic to travel from the injection molding machine, through the sprue to the gate through which the part is filled.
  • Shear – The heat-inducing force created when layers of resin rub together during the injection molding process.
  • Shrink Rate – Ranging from 0.001-0.060 per inch, the rate at which the injected plastic will shrink once it is cooled.
  • Sprue – The canal connecting the runner to the injection molding machine nozzle.
  • Vestige – Excess material protruding from the gate that can be automatically or manually trimmed by a machine operator.
  • Warp – A distortion in the injection molded part, often caused by residual stresses and differential shrinkage during the cooling process.

Want to learn more plastic injection molding terms? For more information about how injection molding works, we invite you to download the K&B Molded Products Injection Molding Glossary today.