DFM/DFA: Injection-Molded Cube

Photograph of a 3x3 mechanical puzzle cube with the top layer exposed, showing the internal core mechanism.

Fig. 1 — Subject of the analysis, internal mechanism exposed.Photo, own work

The problem

Anyone can say a part "should be injection molded." Fewer people can price out what that actually costs at a given volume, defend a tonnage and mold-cavitation choice, and show where the manufacturing cost is actually coming from. This project was an exercise in doing that rigorously, alone, for a deceptively complex assembly — a 3x3 puzzle cube has more interacting plastic geometry than it looks like from the outside.

Approach

I ran a full Boothroyd-Dewhurst Design-for-Assembly analysis on the cube's internal mechanism to quantify assembly time and part-count efficiency, then moved into manufacturing process economics: modeling injection-molding cycle time from cooling and packing equations, selecting an appropriate clamping tonnage and mold configuration for the part geometry and production volume, and building a per-part cost model that separates material, machine-time, and tooling-amortization cost.

Comparison photo of four injection-molded plastic parts in yellow, blue, and black, showing part geometry and draft details used in the manufacturability analysis.

Fig. 2 — Molded part geometry referenced in the tooling and draft-angle analysis.Comparative part study

Fig. 3 — Video walkthrough of the analysis.Own work

Why this is on the site

Most of my other work is team-based; this one is entirely mine, start to finish, and it's the most quantitatively "manufacturing" piece in the portfolio — directly relevant to any role where a design decision has to be justified in dollars per unit at production volume, not just in CAD.