Ten Top Tips For Plastic Injection Mold Making

Plastic injection mold making is always a challenging profession, and this has never been more true than today. Shrinking markets, global competition, new technologies and a vanishing skilled work have forced the mold making process to dramatically change.

The old days of one mold maker doing virtually everything required are long gone. The jobs are just too complex and the lead times too short to allow for this antiquated method. With all the technical advances in the last twenty or so years, the old ways have been replaced by a more integrated and efficient approach.

Here are some tips gained from my own experience, as well as some of my colleagues. There are obviously many other valuable ideas, and these ten tips are from an injection mold making perspective.

Injection Mold Making
Dr.Kaiser Form Wheel

It is just human nature to cling to the familiar. But in a trade such as injection mold making this is a formula for extinction. Here are a few real life examples to demonstrate.

Injection mold making lives on adaptability

Some shops buy high end electrode holding tooling such as System 3R or Erowa and proceed to use it as if it were simply a way to hold graphite or copper electrodes. Never mind that it has the ability to orient and repeat very accurately.
I have witnessed some embarrassing abuses of this type of tooling over the years. It defies logic to spend thousands of dollars and use 10% of the abilities of the tooling. Some shops actually still use Vee-blocks and angle plates in the sinker EDM! This might be fine for exceptions, but not for 98% of the EDM jobs out there.

Why aren’t injection mold makers using the CAD system?

The same can be said for CAD systems. Maybe because there is a learning curve involved with any CAD system some people learn a few features and just stay at that level.
For example: why not network the entire shop so everyone has access to the same information? It is totally inefficient to have mold makers run to the designer for information all the time. Let the mold makers learn how to use the CAD system and solve their own problems.

Injection Mold Making
Hansterfer’s EDM Dielectric Oil

10 tips for effective injection mold making. Maybe you have some ideas that you could add as a comment at the end of the article?

Make sure the project manager, mold designer and mold maker are all on the same page.
It helps immensely to take some time at the outset of a job to have a meeting where the big picture is discussed. It is always much easier to work on the various aspects of the job when you have a clear idea of what is required.
Many hours are wasted when several people figure out the same problem independently. Mistakes can be minimized by going over the procedure together, plus everyone knows who is responsible for what.
Do not skimp on the design
Some shops do not have an in-house designer and must outsource their design work. This is fine and works quite well- unless the boss decides to save money by cutting costs on the design. This is just asking for trouble.
Even with a high quality mold design, injection mold making is fraught with potential problems. When the design is faulty or missing details it can eat up the profit margins very quickly. For example: simple features, such as the radii that interfere in a shut-off area, can be very time consuming to troubleshoot and handwork at the end of the job.
The fit of precision holes to their components is another rather common omission in mold designs as well. Often this does not show up until assembly, at which time the mold maker must make new components or modify existing ones.
Another overlooked area is the draft angles of molding surfaces. The mold maker might not question the design when no draft is specified, and as a result the part will not eject in molding. Draft angles are obviously much easier to machine before the mold is finished!
Concentrate on what you do best
Every shop has it’s own strengths and weaknesses. Do what you do best and leave the rest is usually good advice. You may really want to learn something like horizontal milling, but does it make sense to sacrifice your limited time and energy?
Use 3D models or prototypes to clarify
As a mold maker, I’ve never understood why some bosses are so reluctant to allow the mold maker five minutes to familiarize himself with the molded part he is about to build a mold for. This would save a lot of visualizing and guessing. It is always much easier to begin with the end in mind.
Use standardized components
Why spend precious mold making time machining standardized components? You can almost always buy high quality components at a very competitive price.
The most foolish example of this, that I have seen, was a series of ejector pins that were ground 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 shop time they used.
Do not skimp on the mold base
It might be tempting to save a lot of money by buying a cheap mold base, but this almost always leads to problems. Some of the problems might include misaligned pockets, out of square plates, incorrect plate thickness, misaligned pins and bushing, etc.
I have worked on discount mold bases that required so much re-machining that the initial savings quickly vanished. Not only that, it is very demoralizing to work with junk when you are trying to produce quality.
Clarify from the outset who is responsible
This would seem to be obvious, but in many shops the communication is so poor that it is just assumed that everyone knows what is going on.
A good way to do this is with the break-out meeting or posting it on a bulletin board along with other pertinent information about the shop goings on.
Make sure everything is correctly ordered and available
Few things can send everyone scrambling like discovering that nobody ordered this or that. Of course, this usually is discovered at the end of the job,when there is no time left for shipping.
Do not waste time on meaningless precision
Sure, an injection mold is a highly precise tool, but is it really necessary for the ejector pin plate to be ground to .0002 tolerances? Many hours can be wasted on such details that do absolutely nothing to make the mold better.
Slow down, take a common sense look at your approach and execution. With all the talk of lean manufacturing and programs available, some of the best advice can be gained by simply communicating with the ones doing the job! That is, if you can get them to open up and share from their experience.

Learn more about plastic injection mold making

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