Most Common Injection Molding Defects (and How to Avoid Them)

Designing injection molded products is not for the faint of heart. There are many things that can – and sometimes do – go wrong that can negatively affect your production and, ultimately, the quality of your finished parts.

Below, we take a look at some of the more common defects as well as steps you can take to avoid them.


Warping happens when sections of injection-molded plastic cool too quickly. This is often a result of injection molds that were not designed with uniform wall thickness. The thicker the wall, the more likely it is that your part will experience shrinkage during cooling.

What You Can Do

Your best bet is to carefully design your mold with uniform wall thickness in mind, paying close attention to part symmetry throughout your design. You can also work with your manufacturer to test out designs using mold flow analysis to see how your design will operate out in the wild.

Sink Marks

Another unfortunate result of shrinkage is the presence of sink marks or small depressions that can be seen on a part’s surface. Unlike with warping, however, sink marks are caused when the plastic material cools too slowly.

What You Can Do

When it comes to the injection mold design, wall thickness is just as important as its uniformity. For sink marks, you will need to work on designing thinner walls for your injection molded components to help reduce cooling time and the likelihood of those unsightly sink marks.

Short Shots

Short shots happen when an injection molded material stops short of filling the entire cavity or cavities of a mold, and they indicate a major issue with your injection mold design, often the result of injection mold gates that were designed to be too narrow, making it difficult for melted plastic to flow through them evenly. Since these types of defects can have a dramatic effect on the quality and aesthetics of a finished part, these issues must be found and addressed before production to maintain cost-effective manufacturing.

What You Can Do

In this case, redesigning your mold to increase the width of your gates is your best plan for success. Working with an engineering partner can help you evaluate your design to ensure optimal production using software modeling and analysis.

When you’re ready to turn your big idea into reality, talk to the experts at KASO Plastics. Our team has over 50 years of experience designing and manufacturing quality plastic parts.