Increasing Part Strength with Ribs

It may seem natural to add thicker walls to your product to increase its strength. However, walls that are too thick are prone to sinking, warpage, and other defects. Additionally, thicker walls require more material, which increases your cost. 

One great way to increase your part strength is to incorporate ribs into the design. Ribs, along with other features like fillets, radii, and gussets, add strength to your part without adding too much bulk. Here are some rules of using ribs to increase part strength along with some other common ways to increase the strength of parts.

Using Ribs to Increase Part Strength

The draft, height, thickness, orientation, position, and other aspects of a rib are all critical to its effectiveness. Here are some things to keep in mind when adding ribs to your part design.


Taller isn’t better when it comes to ribs. Rib height should be no more than three times the nominal wall thickness.


Ribs should be 50-60 percent of the nominal wall thickness. Thinner ribs can be hard to fill and don’t provide much structure, while thicker ribs can lead to sink on cosmetic surfaces.


A minimum of 1 degree of draft will ensure that the ribs release from the tool during molding.


For the best stiffness, you want more ribs rather than taller ribs. However, they should be spaced at least two times the nominal wall thickness apart from one another.


To help reduce cosmetic sinks, core thick ribs from behind or below to create thinner rib walls and a blank area.


For increased rib strength, radii at feature intersections should be at least 0.5 – 1.0x nominal wall thickness.

Other Ways to Increase Part Strength

While ribs are one of the best ways to increase part strength, they aren’t the only way. Here are some other ways to increase the strength of your part.


Gussets are another way to provide stability in parts without having to increase wall thickness. They should be no more than 60 percent of nominal wall thickness to prevent sink.

Wall Thickness

While increasing wall thickness isn’t always the best way to increase part strength, sometimes it’s the only option. Just keep in mind that walls that are too thick can sink, warp or result in other defects. They also use more material, which will add to the overall cost.


Fillets are curved faces where ribs meet walls. They can eliminate additional mechanical stress concentrations on a finished part, but you need to find the right thickness. Fillets that are too thick can create sink, while fillets that are too thin won’t provide enough support. When adding a fillet to the inside of a corner, try to add a radius to the outside of the corner.

Durable Thermoplastics

Choosing the right material for your part is a critical aspect of its strength. Each material has different durability, stiffness, and toughness, and every part will go through different types of strain, needing different requirements. Material properties differ from resin to resin, so you’ll want to choose the one that best suits your needs.

Get a Quote from Universal Plastic Mold

Universal Plastic Mold has the experience to help you design strong parts without making too many sacrifices in other areas of the part design. To get a quote or learn more, click here or call 1-888-893-1587.

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