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Injection-molding the "Illuminati Pyramid"

The Illuminati Pyramid

Every year, Northwestern reaches out to local elementary school students to dream up new and unusual ideas of toys to injection-mold.

Of the three drawings my team received, we selected the “Aluminautie” design. Over 12 weeks we designed models, programmed and milled molds, and produced a run of 100 parts.

My Role

On our team of four mechanical engineering students, I developed the early CAD models of our parts. I also was responsible for the CAM programming and CNC milling of one of our four mold blocks.

Making it all Fit Together

Pyramids, as it turns out, are a difficult shape to assemble. My team and I first tried splitting the pyramid in half and molding it in two identical shells that fit together like puzzle pieces. While the parts themselves met best-practice design guidelines for a thin-walled part with no undercuts, the molds couldn’t be manufactured with standard tooling.

We then revised our design: After briefly considering a flat, foldable pyramid with living hinges, we selected an assembly of 5 flat panels that snapped together with a series of open-ended tabs and pockets

The first design concept

The first revised design

The final parts, fit together

Lessons Learned

  • 3D Printing: Using my own desktop 3D printer, I printed sample parts from the very beginning stage of the design process. These models were used at every stage of the process to communicate and iterate on our design.

  • Mold Design: CAD and 3D-printed models helped us visualize how tools could (or could not) physically cut molds for the parts in different orientations. Mold design quickly became a central concern for the team; this early emphasis paid off with molds that were easier to cut, modify, and use.

  • Kids: Since when do they know so much about the Illuminati?


Of the 17 injection molding design projects, the Illuminati Pyramid was awarded first place by a team of academic and professional experts in injection molding.

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