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.
