Selection of mold type depends on part geometry, tool design, required quality and production volumes. In this article we will discuss various types of injection molds. They can be classified in different categories based on:
- Feeding system
- Number of parts
- Mold Opening
Injection Mold Classification Based on Feeding System
Based on molten plastic Feeding System injection molds can be classified in two types.
It consist of heated physical channel that is used to direct molten plastic into a injection mold tool cavity after it leaves the nozzle. In this system, runner is part of injection mold. Runner temperature is kept above plastic melting point.
It consist of unheated physical channel that is used to direct molten plastic into injection mold tool cavity after it leaves the nozzle. In this system, runner is cooled and ejected with the part. After the complete cycle runner is removed from injection molded part.
Classification Based on number of Cavities
Injection molds are also classified based on number of parts produced per injection cycle.
Single cavity mould produces single part per cycle. Initial investment is lower but unit part cost will be higher for single cavity tool. It is used for low production rates.
Instead of multi cavity, single cavity tool is used to ensure production is always running even if there is a breakdown in one mold.
Single cavity mold will have flexibility in controlling injection molding process.
Multi cavity injection mould produces more than one part per cycle. Initial investment cost is higher but unit part cost is low for multi cavity injection tool.
Multi cavity mold are used to increase production rate.
Cost of multi cavity injection mold is higher as compared to single cavity mould.
Higher tonnage machine is required to run a multi-cavity mould as compared to single cavity mould.
Family mold produces two or more different parts per injection cycle. Overall tool cost is reduced in family molds. Because different parts can be manufactured in single mold. Injection molded parts in family mold shall be of same material and color.
Classification Based on mold Opening
Injection molds also classified based on how mold is opening. In another words how core separates with cavity. Based on mold opening injection molds are classified in two types. Check in detail about two plate and three plate mold here.
It consist of one parting plane and the mold splits into two halves at parting plane. Runner system must be located on this parting plane.
Two Plate injection molds are used for parts that are typically gated on or around their edge.
It consist of two parting planes and the mold splits into three sections when the part is ejected. In this runner system can be located on one parting plane and the part on the other.
Three plate injection molds has flexibility in gating location. A part can be gated anywhere along its surface.
To sum up, selection of the types of injection molds depends on part geometry, tool design, required quality and production volumes.
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