The stack molding process is one of the most amazing production methods 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 plastic mold making, stack molds represent a very high level of expertise.
An example of a stack mold is in the video listed below. There are many variations on the stack molding theme, this is just one. This video gives a good, visual overview of what a stack mold does.
Designing and building stack molds requires a high level of skill and expertise. This is the kind of tool where tolerances must be held exactly.
What is the stack molding process?
There are numerous variations 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 movable 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 movable 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!
Stack injection molding is expensive; the entire process is exacting and expensive, yet, in the right market, the ROI can be high.
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.
Advantages 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.
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!