Stack Molding For Plastic Injection Molding

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.

What are the benefits of stack molding?

Stack molds are available in numerous configurations to meet a variety of molding demands. Stack molding offers an economical and efficient manufacturing solution for the production of multiple plastic parts. Injection molding companies are always looking for more efficient way of molding, and for the right

A few of the benefits of the stack molding process include: Increased output efficiency (productivity)

  • Decreases number of machines required
  • Lower machine size requirement vs.. multi-cavity single face molds
  • Produce twice as many parts without increasing press size or clamp tonnage, which greatly reduces part costs
  • Set-up time and run-time costs are divided by all the parts produced
  • Producing the front and back parts of a key fob at the same time is a good example of an application for stack molding
  • Mold ejection functions are self-contained, no additional labor or steps required

Stack molds are not for everyone!