The term cavity is derived from the Latin cavum (cavity). In mold and die making, cavity refers to the free or hollow space between the lower and upper part of the forming mold into which the liquid or flowable material (melt) flows or is pressed. The cavity is also referred to as a mold cavity. To ensure that dimensionally accurate molded parts can be produced, the material shrinkage factor must be included in the design of the cavity. The cavity dimension must be used when calculating warpage as part of the injection molding simulation.
Number of cavities
The number of cavities in the mold can vary.
- One cavity = 1‑cavity mold
- Two cavities = 2‑cavity mold
- Four cavities = 4‑cavity mold
- Eight cavities = 8‑cavity mold
A distinction must be made as to whether the cavities are always the same or have different shapes.
Positioning of the cavities in the mold
In a 1‑cavity mold, the cavity is usually planned in the center of the mold. The sprue is placed directly on the molded part. Other placements are possible, but result in a larger mold.
From a 2‑cavity mold, it is important when positioning the cavities that the melt has the same path from the sprue to all cavities. Otherwise, the cavities will fill with the melt in an offset manner. This can result in overmolding of the cavities that are filled too early, or the cavities that are filled too late are not completely filled.
Why are more cavities planned in a mold?
The more cavities a mold has, the more individual parts can be produced in one injection molding cycle. This enables a rapid reduction in the cost per molded part. On the other hand, there is the greater effort to design the mold and is also limited by the machine size.
Shrinkage is always
Material shrinkage must be considered and planned for when creating the cavity. In order to insert the plastic into the cavity with an exact fit, it is melted. This allows the melt to fit easily into any mold. As it cools in the target location, the part retracts minimally, making it smaller. This process is called shrinkage and is different for each material.« Zurück zum Glossar Index