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Injection Molding: Rib Design

This post is part of our Injection Molding Design Guide series.

Ribs can be instrumental to your part’s structural success. If used correctly, you can avoid the main problems caused by walls being too thick and abrupt changes in wall thickness. In this article, we’ll discuss what ribs are, what they’re used for, and their recommended dimensions.

What is a Rib?

Ribs are thin wall-like structures that add support and rigidity to injection molded parts. They are thinner than primary walls and are used to support these walls, as well as bosses, by running perpendicular to these structures. Ribs are often used to replace thick wall sections to avoid sink marks, warp, and voids. By placing ribs in a load bearing direction, such as long unsupported stretches of your part, instead of making a section thicker, you can retain the support and rigidity you want and eliminate problems caused by thick walls.

Recommended Dimensions

To prevent problems from arising, plastic rib design must adhere to certain proportions. These dimensional ratios are detailed below.