the Number of Cavities in a Mold

In plastic injection molding, the number of items that can be molded in one shot using one mold is called the number of cavities.
The number of cavities can be from 1 to a reported maximum of 216.

Since the number of items molded in one shot becomes large as the number of cavities becomes large, it is possible to reduce the cost of production per item.
However, as the number of cavities becomes larger, there is a trend of the quality fluctuations becoming large such as the dimensions, weight, external appearance, etc. of the molded item of the different cavities.
It is necessary to determine whether to make the number of cavities large or small upon studying comprehensively the advantages and disadvantage.

In general, the following trend is seen in the number of cavities depending on the type of mold.

  • Large molded items … Basically one cavity
    Reason – Since the mold is large, it is physically difficult to have two or more cavities.
  • Medium to small molded items of automobiles, home electrical appliances, etc. … About 4 to 8 cavities
    Reason – Considering the relationship between the total production quantity and quality fluctuations, about this number of cavities is found to make the risk low by experience.
  • Electronic components, precision components … 2 or 4 cavities
    Reason – The number of cavities is made small considering the quality fluctuations of the molded item.
  • Food containers, etc. … 24 to 64 cavities, or more (hot runner specifications)
    Reason – Since a production quantity of several million or more can be forecast, the number of cavities is made large thereby reducing the production cost.
  • Molds of new products … 1 cavity
    Reason – Since the sales of a new product in the market cannot be forecast, initially it is produced using a mold having one cavity, and when the sales becomes brisk, a mold with increased number of cavities is prepared to meet the larger demand.

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