This article describes the cavity and core, its processing method, and its arrangement into the mold.

Cavity and core

Core and cavity can be classified into 2 methods, integrated and nested method. You can choose which method will define your cavity and core.

Integrated: When the molded part is formed directly by the die.

Nested: When the molded part is formed by the die components.

Nested Cavity and Core

Benefits:

• There is no restriction to the geometry of the molded part. Processing efficiency can be done when components are separated.
• Mold materials can selected for better wear resistance and temperature control.
• Damaged components can be replaces easily and cost effectively.

The basic structure of a molding die is determined by the geometry of the product, its production volume, molding material, and consideration of other technical and production constraints such as positioning of gate.

2-Plate Mold Configuration

The mold is divided by parting-line (PL) into two parts, the movable and fixed side.

Features:

• The structure is simpler compared to 3-plate and runnerless mold.
• Tooling cost is normally lower.
• Side gate, submarine gate, and direct gate system are typical. More about gate system.

Drawbacks:

• Side gate and direct gate are not suited to save labor cost through automation.

3-Plate Mold Configuration

The mold is divided by 2 PL into three separate parts. The 1st PL is on the runner separating the runner stripper plate and the fixed side plate. The pin-gate is automatically cut off from the product on 1st PL. The 2nd PL is on the product separating the movable and fixed sides.

Features:

• Suitable for full automation.

Drawbacks:

• Mold structure is more complex than 2-plate structure.
• Tooling cost is higher.

Runnerless Mold Configuration

2-plate and 3-plate molds produce product plus runner. Runnerless molds can be achieved by introducing hot runners.

Features:

• Runners will not be discarded at all so cost of material is less.
• Sprue and runner is always in the heater maintaining its fluid state for good filling of molten plastics to cavities.
• There are several advantages for high volume production.
• Suitable for full automation.

Drawbacks:

• Complex structure.
• Much higher price.
• It takes time to replace the material.

This post will be updated will illustrations later.

Fixed Clamping Plate

Locating Ring
It is used to locate the center of the injection machine so that the sprue bushing and the nozzle are aligned. Commonly fitted into the counterbore in the fixed clamping plate.

Fixed Cavity Plate
Used to hold the fixed cavity block, leader pin/bushing, and sprue bushing.

Movable Cavity Plate
Used to hold the movable cavity block, leader pin/bushing.

Movable Clamping Plate
Holds The movable side of the mold to the movale platen of the injection machine.

Spacer Block
Mounted between the movable clamping plate and the movable cavity plate to give space and allow the ejector plate to move when ejecting the
part.

Ejector Retainer Plate
Holds the ejector pins and the return pins in place.

Ejector Plate
Pushes the ejector pins and return pins at the same time. Mounted to the ejector retainer plate to form the ejector unit.

Support Pillars
Bars placed between the spacer blocks to give additional support to the movable cavity plate.

Sprue Bushing
Has a tapered hole through which the material is forced into the runner. It is butted up against the nozzle of the injection machine.

Return Pins
Same as ejector return pins. Make sure that the ejector unit is back in its original position when the mold closes.

Leader Pins and Bushings
Precisely align the two halves of the mold base (fixed and movable).