WATCH: Talkin’ Cosmetic Defect Blues

The next short video in our Fundamentals of Molding series takes a trip down the Mississippi River to explore different cosmetic flaws like sink, warp and blush, which can find their way into injection-molded parts.


For a lengthier examination on avoiding cosmetic defects when designing for injection molding, read our free white paper.

Thirsty for more quick tips? Here’s our previous video on draft considerations:


TIPS WITH TONY: Watch Out for Warp, Sink and Voids!

In my years of working closely with product designers, I’ve seen some really great designs, but on occasion, I’ve encountered part designs by both novice and experienced designers and engineers that have needed some work to improve moldability and reduce cosmetic defects. Let’s look at some common design mistakes that could result in parts with sink, warp and voids.

Wall Thickness
Why is uniform wall thickness important? Thermoplastics simply don’t like transitioning from thin to thick sections due to the ununiformed cooling. All thermoplastics shrink as they cool but when thin areas cool before thick areas, stress is created. The results may vary depending on material selection and part design, but if you’re not following the proper material guidelines for wall thickness and mold design, you may end up with unsightly voids, sink and possibly even warp within your parts.

How can you reduce the risk of these molding concerns? Provide proper wall thickness through appropriate coring, rib and boss design, which in turn, helps you avoid excessive thick or thin wall sections.

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