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
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
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
Stack molds are not for everyone!
Randy Hough has worked as a plastic injection mold maker since 1978. He
heads a group of industry professionals who have a web site dedicated to
injection mold making. You can learn the latest trends and techniques by
They also have an interactive blog, which is frequently updated.
Learn how to make a plastic injection mold, mold design, about jobs in
the plastic industry and more.
"You know Dad, I've been thinkin', one is a lot more than zero!" my son,
Thomas, age 5.