This will describe the structure of 2-plate, 3-plate, and runnerless molds.

The basic structure of a molding die is determined by the geometry of the molded part, its production volume, molding material/resin, 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.