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Lesson 2 - Practical Injection Molding Study Guide

Notes Inside the MoldLesson 2

I. Most Common Types of Molds

• Two-plate mold• Three-plate mold• Runnerless mold

A. Two-plate Molds

Two-plate Mold

In the two-plate mold, the runner system and the parts are made on thesame surface. The runner and the molded parts are attached whenejected, except on submarine gated parts.

Runner System

molded part

runner

gate

spruepuller

sprue

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Lesson 2 - Practical Injection Molding Study Guide

Notes B. Three-plate Molds

Three-plate Mold

In a three-plate mold, the runner system and the parts eject fromdifferent mold plates. Three-plate molds always separate the runnersystem from the part.

C. Runnerless Molds

Runnerless Mold

In the runnerless mold, the plastic runner system stays hot inside the moldso no runner is ejected with the part.

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Lesson 2 - Practical Injection Molding Study Guide

Notes II. Parts of the Mold

Parts of the Mold

A. Sprue Bushing - The part of the mold between the machine nozzle andrunner system.

1. Make sure the radius on the sprue bushing matches the radius on themachine nozzle.

a. A mismatch could allow plastic leakage or damage to the metalseating.

2. The opening of the sprue bushing must always be equal to or largerthan the opening in the nozzle.

a. If the opening was smaller than the nozzle, the plastic spruewould break off in the nozzle and block the next shot.

B. Locating Ring - Aligns the mold in the correct position on the platen surface.

1. When the mold is installed, the locating ring must be sized to exactly fitthe opening of the stationary machine platen.

locatingring

clampplate

cavityplate core

platesupportplate

ejectorpin

clampplate

ejectorhousing

supportpillars

ejectorplateejectorretainer plate

spruepullerpin

ejectorpinguide pin

coolantpassages

spruebushing

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Lesson 2 - Practical Injection Molding Study Guide

Notes C. Cavity Plate - The mold plate that contains the cavity halves.

1. Usually in the stationary half of the mold.

D. Core Plate - The mold plate that contains the core halves.

1. Molded parts shrink onto the core half of the mold.2. The ejection system usually works off the core half of the mold.

E. Support Plate - A heavy, stiff plate located behind the core and cavityplates.

1. Purpose is to reduce deflection of the core and cavity plates.

F. Support Pillars - Columns between the core half support plate and theclamp plate.

1. Placed behind the support plate to add more rigidity to the core plate.2. Further reduce deflection in the mold caused by clamp force and

plastic pressure.

G. Guide Pins - Pins projecting from the core or cavity plates.

1. Aligns the two halves of the mold.

H. Clamp Plate - The outside plate on each mold half.

1. Used to attach the mold to the machine platens.

I. Sprue Puller Pin - A pin under the mold sprue.

1. Designed to pull the plastic sprue out of the sprue bushing when themold opens.

J. Ejector Pins - Long pins attached to the ejector plate and flush with thecavity surface.

1. When the mold is opened, the pins are pushed forward to eject therunner and plastic parts out of the mold.

K. Ejector Housing - The outside of the mold that encloses the ejector system.

1. The ejector plates and pins operate between the ejector housing plates.

L. Ejector Plate and Ejector Retainer Plate - Plates which bolted together tohold the heads of the ejector pins and sprue puller pin.