According to the feeding system, plastic injection molds can be divided into two categories, cold runner system molds and hot runner system molds.
Based on the number of steel plates, there are two plate mold and three plate molds.
Three plate mold is is generally composed of three pieces of steel plate as shown below.
THREE-PLATE MOLD is usually structured with a point point gate and it is used for automatic degating and center gating on multi-cavity molds. Three-plate molds are less expensive than hot runner molds and there is also a runner left over. An advantage to gating with a three-plate mold eliminates the need for cutting the gate off the part. Some multi-cavity molds must have a center gate on each part. A three-plate mold is the most economical way to achieve this.
Generally, there are pros and cons of three-plate molds
Pros of three plate molds
Cost less to build than a hot-runner system mold
Less likely to break down than a hot-runner mold
Thermally sensitive materials are less likely to degrade
Gate is easily moved on the part and edge gate mold
Cons of three-plate molds
Longer cycle time due to ejection of the runner system
More material is wasted due to extra feeding plate for runner system
Greater injection pressure is required to fill the mold and larger press is required.