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What You Need to Know About Injection Mold Design



There has never been a more challenging profession than injection injection mold design today. Shrinking markets, global competition, new technologies, and a vanishing skilled workforce all contribute to the challenge.


Those days of having one mold maker do virtually everything are long gone. The jobs are simply too complex and the lead times too short for this antiquated method to be used. Over the past twenty or so years, technological advances have enabled a much more integrated and efficient approach to replacing the old ways.


The following tips are based on my own experiences as well as those of some of my colleagues. There are obviously many other valuable ideas, but these ten tips are based on what mold makers know.

1. Give up the old ways, yield to change

There is nothing wrong with clinging to the familiar. But in a trade like mold making this is a formula for extinction. Here are some examples from real life.


There are some shops who purchase high end electrode holding tooling such as System 3R or Erowa and use it as if it were simply a way to hold graphite or copper electrodes. They don't realize that it has the capability to orient and repeat very accurately.


This type of tool has been abused in embarrassing ways over the years. It is insane to spend thousands of dollars and use 10% of its capabilities. Some shops still use Vee-blocks and angle plates in sinker EDMs! In an exception, this might be okay, but it is absurd in a modern mold facility.


CAD systems are no different. Perhaps because there is a learning curve involved with any CAD system, some people learn a few features and just stay at that level. Why not network the entire shop so everyone has access to the same information? It is totally inefficient to constantly have mold makers contact the designer for information.

2. Communicate clearly between the project manager, mold designer, and mold maker.

When you have a clear understanding of what is required from the beginning of the job, it makes it much easier to work on the various aspects of it.

When several people work on the same problem independently, many hours are wasted. By discussing the procedure together, mistakes can be minimized, and everyone knows what their role is.

3. Do not skimp on the design

There are some shops without an in-house designer, so they must outsource their design work. This is fine and works quite well, except when the boss decides to save money by cutting costs on the design.


When the mold design is faulty or missing details, plastic injection mold making can consume profit margins very quickly. Even with the best mold design, plastic injection mold making is fraught with potential problems. Troubleshooting a simple feature, like radii that interfere with a shut-off area, can take a great deal of time and handwork at the end of the project.


Another rather common omission in mold designs is the fit of precision holes to their components, which is often overlooked until assembly, when mold makers must make new parts or modify existing ones.


If no draft angle is specified, the mold maker might not question the design, resulting in the part failing to eject during molding. Draft angles are obviously much easier to machine before the mold is completed.

4. Focus on your strengths

Do what you do well and leave the rest to the experts. You may really want to learn something like horizontal milling, but does it make sense to sacrifice your limited time and effort for it?

5. Clarify concepts using 3D models or prototypes

As a mold maker, I've never understood why some bosses are so reluctant to let the mold maker spend five minutes familiarizing himself with the molded part he is about to build a mold for. Starting with an end in mind is always much easier. It saves a lot of visualizing and guessing.

6. Standardize components

You can almost always buy high quality components at very competitive prices, so why waste precious mold making time machining standardized components?


The most foolish example of this I've seen is a set of ejector pins that were ground down to a smaller size. It must have taken hours to do this, and they could have bought them off the shelf for a fraction of the cost.

7. Make sure that the mold base is strong and sturdy

By buying a cheap mold base, you might save a lot of money; however, this almost always leads to problems, such as misaligned pockets, out-of-square plates, incorrect plate thickness, and misaligned pins and bushings.


Discount mold bases often require so much re-machining that the initial savings quickly disappear. It is extremely demoralizing to work with junk when you're trying to produce quality products.

8. Clarify from the outset who is responsible

It seems obvious, but many shops are so poor at communication that everyone just assumes they know what's going on.


It would be good to post it on a bulletin board with other pertinent information about the shop happenings at the break-out meeting.

9. Confirm that everything has been ordered correctly and is available

When you discover that nobody ordered this or that, it can send everyone scrambling. Of course, this usually happens at the end of a job, when shipping has run out. Read more:

10. Avoid wasting time on meaningless precision

It is true that injection molds are highly precise tools, but do they really need the ejector pin plate to be ground to .0002 tolerances? Many hours can be wasted on such details that do absolutely nothing to improve the mold at all.

Final thoughts

It's important to take a step back, take a look at your approach, and look at your execution with common sense. With all the talk about lean manufacturing and programs available, the best advice can be found by talking to those who are doing the work! If you can get them to share from their experience, that is.

Creation date: Dec 16, 2022 9:31am     Last modified date: Dec 16, 2022 9:32am   Last visit date: Jul 21, 2024 6:07pm