When designing components that will be made of plastic, it’s often necessary to add ribs and gussets to improve the stiffness and strength of load bearing features. This reduces material volume and print time for 3D printed parts, compared to the
When designing components that will be made of plastic, it’s often necessary to add ribs and gussets to improve the stiffness and strength of load bearing features. This reduces material volume and print time for 3D printed parts, compared to the time it would take to make these features out of solid structures.
That’s because print time is largely driven by the volume of material for a specific component, so ribs and gussets work to optimize print time, while maintaining structural integrity. Furthermore, adding ribs and gussets will create a plastic part that’s a closer representation of an injection molded part for mass production.
Ribs and gussets are commonly used in injection molding because the parts are very sensitive to thick wall sections and variations in wall thickness. A variety of defects, such as shrinkage and warping, can occur if the features on injection molded parts are too thick.
The image below features ribs on the left bosses and four gussets on the boss on the right:
In this post I'm going to first quantify the structural benefits of adding gussets and ribs to your part designs using FEA studies, and then walk you through the best practices for proper application of these features to plastic prototypes.
Quantifying the Structural Benefits of Gussets and Ribs
Ribs and gussets seem like small features, but the FEA (finite element analysis) studies below demonstrate their importance from a structural standpoint.
The image below depicts a five lbf (pound-force) load on the boss with gussets, to demonstrate total stress and deflection in the current state. All of these simulations use the material properties of ABS, so they’re consistent with common 3D printing materials.
As you can see in the results below, the majority of the part is stressed to the 400 psi range, with the maximum stress reaching just over 1,200 psi (not shown, as it is on the compressive side). The stress flags are all on the tension side, with the high tensile stress in the range of 1,100 psi.
In the following images, we can see the same FEA study conducted without the presence of gussets, and the stresses are now more than double what we saw in the prior study. This indicates that without gussets, the boss is less than half as strong.
It’s immediately apparent that the feature becomes much weaker without the gussets. In fact, this feature is now very near the yield strength of the ABS we have selected (2,900 psi).
In addition to the increase in strength, the parts undergo much less deflection when we add gussets—for applications that require positional alignment or rigidity, this is very important. The side by side images below show just how much more the un-gusseted boss deflects.
We can see that the boss deflects four times as much at the top surface when it has no gussets. This can be a major problem for both function and a