Becoming a better plastic part designer

Learning new things to enhance old skills…

I’ve been designing injection molded parts for over two decades. None of my college courses covered it, and I was never formally trained. Instead, I simply started designing parts with the help of awesome mentors, online design guides, and by acquiring knowledge though examining existing plastic parts.

The fundamental rules (uniform wall thickness, adding draft & radii, etc.) are relatively easy to grasp. Over time, I learned how to design more complicated parts, using techniques such as side-actions, bypass shutoffs, and lifters. I designed overmolded and insert-molded components. I also learned ways in which you could break the basic rules to create even more complex and feature-rich parts, reducing part counts and simplifying assembly.

Now, I consider plastic part design one of the primary areas of expertise I bring to ANGLE.

However, until recently, I still understood only the basics of mold design and how the press operated. It’s generally not covered in any depth in the materials you find about part design. You can definitely learn how to design parts, even with complicated features, without needing to really understand runner systems or ejector options or the challenges of cooling. You can get by without knowing the difference between a stripper plate and an ejection plate, or what a sprue-puller does.

In one of my recent projects, I was working closely with suppliers in China, including tooling reviews where they shared the CAD of the mold designs. Exploring those CAD models was both informative and a bit overwhelming. I was fortunate enough to be collaborating on this project with a retired engineer with deep tooling knowledge, who taught me a lot about those tools in particular, but I was still unclear about some things.

I realized that in order to become a better part designer, I should learn more about tool design. So I got a textbook and read it cover-to-cover (something I don’t think I’d ever even done while in college).

I chose “Injection Mold Design Engineering” by UMass Lowell professor David O. Kazmer. Reading it confirmed a lot of what I had gleaned over the years and corrected a few of my misconceptions.

At the basest level, it helped me get the nomenclature right, understanding the pieces and systems that make up most molds. But the explanations of layout design, feed systems, gating and venting designs, and cooling and ejections systems gave me insights into how tool design impacts part quality. And beyond tool design, the information about the stages of the molding cycle (plastication, filling, packing, cooling, and ejection) all have implications regarding the performance and appearance of final molded parts.

I wish the book went a little deeper into actions, shutoffs, and lifters (and other techniques for creating even more complicated features), but that just drives me to continue delving into this subject.

I have no intention of ever getting into actual tool design. But I always implore my students to continue building their skills and tool sets. For me, learning more about tool design will help me to design better parts and to be more knowledgeable when collaborating / negotiating with suppliers and mold-makers to ensure the highest quality parts for my clients.