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#129 Special Injection Molding Methods (Insert Method)

Category : Molding Technology
June29, 2012

Insert molding is a method of injection molding in which an insert (a metallic part or other inserted item) is installed inside the cavity while the mold is still open, and the mold is then closed and the injection molding is carried out.
This method is used for the injection molding of housings in which brass screws or shafts are insert molded, or for electronic components in which metal terminals or contacts are insert molded.

The simplest method of placing the inserts inside the cavity is to affix to the cavity by hand or by robots the inserts which are machined separately as individual parts (Fig. 1).

[Fig. 1] Example of insert molded items

In order to manufacture a large quantity of a part efficiently, there has also been proposed a method of progressive molding in which the molding is done successively after automatically feeding into the cavity a metal hoop in which the required shapes have been formed previously by a progressive press forming die (Fig. 2).

[Fig. 2] Hoop feeding type insert molding method

Since the insert molding method is a method for manufacturing a molded item by a combination of a metal formed part and plastic, it is necessary to accumulate know-how by making trial and error in order to combine material with different properties such as thermal expansion coefficient, heat transfer coefficient, strength, etc.
Good injection mold design will be difficult if the accuracies and capacities of press forming are also not understood.

Insert molding is a method of molding that offers a high value addition in addition to making it possible to manufacture at a low cost various precision electronic components or excellent quality molded items for automobile parts. On the contrary, without a high level of technical ability, it is not possible to manufacture large quantities in a stable manner.
The precision insert molding technology and mold preparation technology of Japan can be said to be of the top level in the world.

In order to realize insert molding practically, the excellence in the press forming die design and fabrication technology, for example, the technology of positioning or the technology of mold part machining, etc., need to be incorporated into the plastic mold design technology in a flexible manner.

[Fig. 3] Example of insert molded item

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