When the product has an undercut, it is removed from the mold using mechanisms such as a sliding core, or a slant projection, or forced projection, etc.
However, in the case of complex undercut shapes, it can also be very difficult to solve the problem using mechanical structures.
In such situations, it may be possible to solve the problem using a traditional method called "insert block structure".

An "insert block structure" is one in which the core is divided at the undercut part, the divided core (insert block) is taken out along with pushing out the molded product, and after that, the insert block is removed by hand.
At the time of the next molding, the insert block is set inside the mold again.
Therefore, in the case of an insert block structure there is the drawback that the molded product becomes a semi-automatically prepared item.
However, since it is possible to provide the desired undercut shape in the integrally molded product, this is a very useful method in special cases when such special structures are required.

In summary, the molded product in which the advantages of the insert block structure are brought out are the following.

1. Molded product in which it is not possible to handle undercuts using the ordinary slide cores, etc.
2. Molded product having undercut shapes, but whose production volume is small.
3. Sample molded product

Since an insert block is installed and removed manually, techniques such as machining or chamfering the escape for guiding the block inserting part, and the mating tolerances will be the know how of the manufacturer.

It is not always necessary that molds must have structures suitable for automatic production, and for designers in the digital age it is very important to know that it is possible to obtain the desired molded product by incorporating manual steps that are more analog than digital.