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Dual-Shot Injection Molding

Dual-shot plastic injection molding, sometimes simply referred to as overmolding, is an efficient manufacturing process that allows you to produce your multi-material and/or multi-color part in one mold cycle without extra assembly steps. While it is possible to mold more than two materials/colors this way, this article will focus on using only two materials at a time for simplicity of discussion. 

What is Dual-Shot?

Dual-shot plastic injection molding, also called multi-shot, double-shot, and two-shot, is a type of overmolding where separate nozzles on one machine are used to form a multi-material or multi-colored part during one mold cycle. This allows you to efficiently create single parts with different regional mechanical properties, hardnesses, or colors.

How It Works

Dual-shot is best understood in terms of layers, and each layer is a different material or color that is created by a separate nozzle on the injection molding machine. The first material is injected into the mold to create the first layer, or substrate, that serves as the core for the sequential material to bond around. This initial layer is allowed to solidify and cool before being transferred to the other chamber of the mold. Transfer can be done by hand or robot arm, or, if the mold is on a rotary platen, the mold will open and the half bearing the substrate will rotate 180° to meet the other mold chamber and nozzle. Once the substrate is in place in this new chamber, the second material is injected. This allows the second layer to form a molecular bond with the first and create a strong hold. After this layer cools, the final part is ejected. 

It is important to note that this process may be slowed or sped up by the transfer method used. Hand and robot arm transfer take a few seconds longer than rotary platen movement. While rotary platen molding is more expensive, it may prove to be more efficient if you are producing your part in high volumes. Additionally, your materials and mold design should be carefully evaluated to ensure that the materials will bond to each other correctly and that the mold aligns correctly to prevent