Stack molds are some of the most amazing production tools to be found anywhere. The engineering and craftsmanship that goes into a stack mold is truly a marvel.
For the layman, who has never built a plastic injection mold, it might look like a big, fancy piece of machinery that produces plastic widgets. Yet, from the perspective of an plastics mold maker, stack molds represent a very high level of expertise.
What is a stack mold?
There are numerous variations on the theme of stack molds, but some common features are:
Built for very high production runs
Have a one cavity and multiple cores
Use indexable cores to injection mold multi-materials
Have the ability to do multiple operations in the molding cycle
Basically, a stack mold has a stationary "A" half, and at least two "B", or moveable halves. They are similar to the rotary molds that have been in use for many years, but are vertical rather than horizontal.
This means that the moveable cores rotate about a vertical axis, rather than a horizontal. Also, the stack mold is very compact and has a much smaller footprint.
Are stack molds expensive?
Yes, stack molds are quite expensive. That is why a high volume is required to justify their expense. However, especially in medical or cosmetic molding, the ROI is quickly realized.
Considering the tremendous amount of engineering and mold making involved, the expense is understandable. Designing and building a stack mold is not for beginners, or mold makers who cut corners! Plastic injection molding is not easy, and stack molding is on an entirely new level.
What are the applications for stack molds?
Because they are for high production products, the common applications are for cosmetics and consumables, such as deodorant or toothpaste containers. Automotive and medical products are also frequently produced using stack molds.
More and more products are being designed to use soft overmolding, such as toothbrushes or hairbrushes. These are perfect applications for stack molding.Because the part is injection molded, ovemolded, cooled and ejected in sequential cycles, production costs can be minimized.