Injection molding — interactive educational simulator
A step-by-step animated cross-section of the six stages of the plastic injection molding cycle, with detailed mold anatomy: barrel, screw, sprue, runner, gate, cavity, core, ejector pins, cooling channels, tie bars, and clamp unit.
Steel mold & machine
Molten polymer (200–300 °C)
Solidified part
Coolant channels
Band heaters
Mold & machine glossary
- Hopper
- Gravity-fed funnel that meters dried polymer pellets into the barrel.
- Barrel
- Heated steel tube housing the screw; melts and homogenises the polymer.
- Reciprocating screw
- Rotates to plasticise pellets, then slides forward as a plunger to inject melt.
- Band heaters
- Resistive heater bands around the barrel; usually 3–5 independent temperature zones.
- Non-return valve
- Ring at the screw tip that prevents melt from flowing backward during injection.
- Nozzle
- Tapered tip that mates with the sprue bushing to deliver melt into the mold.
- Sprue
- The first channel inside the mold; carries melt from the nozzle into the runner system.
- Runner
- Distribution channels (cold or hot) leading from the sprue to each cavity.
- Gate
- Narrow restriction where melt enters the cavity; freezes off to seal the part.
- Cavity (A-side)
- The female half that forms the external (cosmetic) surface of the part.
- Core (B-side)
- The male half on the movable platen; forms internal features and retains the part.
- Parting line
- The seam where the two mold halves meet; visible as a faint line on the molded part.
- Ejector pins
- Push the cooled part off the core after the mold opens.
- Cooling channels
- Drilled or conformal water passages that remove heat from the steel.
- Tie bars
- Four steel columns that take the clamp tonnage in tension during injection.
- Clamp unit
- Hydraulic or toggle mechanism that opens, closes, and locks the mold halves.