LEGO Uses 3D Printing for Complex Pieces, But Injection Molding Still Runs the Factory

A New Brick Joins the Old Lineup

The LEGO Group released its first mass-produced 3D-printed piece inside a holiday train set late last year. The element is not a standard stud brick. It is a complex curved part with internal geometry that would have required a multi-piece assembly if made by traditional injection molding. That is exactly why LEGO turned to additive manufacturing for it.

LEGO's head of additive design and manufacturing put it plainly: 3D printing lets the company make geometries that injection molding cannot produce at all. Bricks with internal mechanisms, undercuts, or lattice structures fall into that category. For those specific parts, the economics of tooling a custom mold do not make sense. Printing the piece on demand is cheaper and faster to iterate.

Why Molding Still Dominates

Despite the breakthrough, injection molding remains the backbone of LEGO production. The process can churn out millions of identical ABS bricks per week with tolerances measured in microns. The precision of injection molding is hard to replicate even on expensive industrial 3D printers. For high-volume, repeatable geometry, the mold wins on cost per part and surface finish.

The practical constraint is scale. LEGO sells billions of bricks annually. Even with large polymer 3D printers from companies like EOS, the throughput of additive manufacturing cannot match an injection molding press for standard elements. The two processes are complementary, not competing.

What the Podcast Covers

A recent Slant 3D podcast episode went deep on the LEGO versus injection molding question. The hosts broke down tooling costs, part geometry constraints, and the specific cases where 3D printing actually replaces a mold. The discussion also touched on AI-assisted design tools that can optimize part geometry for either process before a single prototype is built.

The podcast is worth listening to if you want to understand the real economics behind the LEGO manufacturing story. It is easy to frame 3D printing as the inevitable replacement for molding. The reality is more nuanced: additive manufacturing opens up design space, but molding still delivers the price and consistency that mass consumer products require.

The Bigger Picture

LEGO's approach is a good model for how other manufacturers will integrate 3D printing. Rather than disrupting the existing process entirely, they are using additive manufacturing for the parts that are uneconomical or impossible to tool. That selective integration is where the technology earns its place on the factory floor.