In November of last year, “Father of RepRap” Dr. Adrian Bowyer demonstrated how hollow tubes could make 3D prints stronger. His custom script and analysis software worked just well enough to prove the concept but could not be easily duplicated by less experienced users. Stefan Hermann over at CNC Kitchen on YouTube was excited about the discovery and, like all of us, wanted a way to implement the findings. So he created and documented a workflow for doing just that.
His method relies on Autodesk’s free (to students, makers, and small businesses) Fusion360 cloud-based modeling software and Slic3r PE (Prusa Edition), which is also free. By using the topology optimization simulation tool in Fusion360, the greatest stress points of an object under a specified load are revealed. Those stress points can be converted into a mesh, which can then be used as a mesh modifier in Slic3r PE. The mesh modifier feature allows two different print settings to be used on a single part, so the high-stress mesh can be printed with 100% infill while the rest of the part can be 3D printed with a regular infill of 10%.
Of course, Stefan is a scientist so he used a DIY tensile testing machine to create some lovely data for us all. The normal way to increase the tensile strength of a 3D printed object is to increase the number of perimeters (the thickness of the outer shell) and/or increase the infill percentage (solidity). So he 3D printed a baseline hook with two perimeters and 10% infill as well as two control hooks: one printed with two perimeters and 42% infill and one with five perimeters and 10% infill, both of which weighed the same. Finally, he 3D printed four different versions of the hook with different types of SmartInfill generated by his process, all of which weighed the same as the two control hooks for accurate comparisons.
The results are fascinating. Of course, one of the SmartInfill variants was the strongest, breaking under 97 kilograms of weight. Not bad for a $0.20 piece of plastic! But there’s another data point that stands out, which is the strength difference between the two control hooks: the hook with more perimeters was nearly 22% stronger than the hook with more infill. That clears up a lot of confusion for makers out there trying to determine what print parameters will yield the strongest result: more perimeters! But the SmartInfill 3D print is 33% stronger than even the strongest control hook, so if you want the strongest part, follow Stefan’s workflow.
Eventually, this workflow will be reduced to a tool that requires only a couple of mouse clicks, either in Fusion360 or premium slicing programs. But until then, Stefan has delivered an elegant solution. Thanks, Stefan!