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Injection molding is an efficient, cost-effective process for mass manufacturing plastic parts, but first you have to create a mold. That process is plagued with myths and misunderstandings, just like injection molding.

April 9, 2021

4 Min Read
injection mold with computer
Image: Mike/Adobe Stock

Peter Jacobs

Keeping up with the latest production best practices is a smart — and crucial — decision, regardless of whether it pertains to CNC machining, 3D printing, or, as in this case, injection molding.

Injection molding is the most efficient, cost-effective process to mass-manufacture plastic parts — millions of parts can be produced to exacting tolerances in a remarkably short amount of time. But first you have to create a mold, and that part of the process is plagued with a number of myths and misconceptions, just like the injection molding process itself. Here are five of the most common myths.

1. Any shape is moldable

Just as in mechanical engineering, a part design has to be manufacturable. It’s not possible to mold any and every shape. The plastic part should be moldable to a great degree. If there’s an error, or if moldability is poor, you will find yourself running into all kinds of production problems and quality issues during the mold-making process.

The misconception that plastics of any geometry can be perfectly molded is incorrect and misleading. Most designs need to be modified if they are not moldable to at least 90% of the original idea. Perfection depends on the balance of the melt flow and the channels through which heat is exchanged. It’s only logical that if the plastic does not freeze uniformly, the mold will be useless for all intents and purposes.

2. Plastic injection molding is not ideal for prototyping

For various reasons, plastic injection molding has a reputation for not being suited for prototyping. More often than not, it is assumed to be a resource-intensive technique, in the sense that it is “not cost effective” and “takes too much time.” Generally, other techniques are used for prototyping, but the major issue with that is the lack of resemblance with the final product.

In fact, injection molding methods provide the most cost-effective solution for creating samples that resemble the finished product. It can create high-quality prototypes at a much faster rate than any other option at your disposal and more accurately represent the end product. This will enable you to get a feel for the finished product, so that you can make necessary changes without affecting the cost.

3. The production cycle of molds is short

The durability of your molds and their production cycles largely boil down to your requirements. For instance, steel molds are built and developed for long-run productions. On the other hand, molds developed using other materials are engaged in prototyping and other short-run productions. Having said that, regardless of the material used, the molds are quite durable and can function without fault consistently over hundreds of thousands of cycles. That, in turn, will produce thousands of parts for you.

4. Mold making produces a lot of scrap

We all know that using a CNC machine requires trained professionals, but this job is sometimes handed off to engineers with minimal training. An experienced CNC operator usually takes care of many tasks, including workplace loading, unloading, cycle activation and monitoring, workpiece measurement, evaluation, adjustments, and so forth. Hence, it only makes sense to employ highly experienced CNC operators who can minimize scrap and arm them with the best machines in the business.

Moreover, injection molding and mold making produce the least amount of scrap compared with other traditional manufacturing processes. Older, less-advanced processes often can eat away a significant chunk of the original plastic sheet or block.

Four key areas of the machine are responsible for low amounts of waste plastic — the gate locations, runners, sprue, and the cavity, where extra material may leak out.

5. Only injection molding parameters can solve quality problems

This is false. Injection molding parameters are not the only way to rectify the molding process. Constraints like dimensional inaccuracies, warpage, sink marks, and shrinkage can be taken care of partly with the help of mold design.

A job that has run perfectly before may not necessarily run perfectly forever. It is just as important that you use the most effective mold and part designs as you set the injection molding parameters. So, it’s safe to say that the quality of your end product can be greatly determined before production even begins.

Final thoughts

Now that you are aware of the most common mold-making myths, you know what not to do. Bring the right people on board to do the job, find competent programmers who know the process, and use reliable machinery from reputable companies. If you follow that simple advice, optimizing your manufacturing process will be a cakewalk.


About the author


Peter Jacobs is the Senior Director of Marketing at CNC Masters. He is actively involved in manufacturing processes and regularly contributes his insights for various blogs on CNC machining, 3D printing, rapid tooling, injection molding, metal casting, and manufacturing in general.

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