Injection mold for lego brick-like parts

Injection mold for lego brick-like parts

For components like lego bricks, it is critical to get the desired fit tightness, they need to be made to high precision, say, within +/-0.02mm, otherwise, the fit may be too loose or too tight.

similar lego bricks (with sprue attached)

Part specifications

MaterialABS (black)
Weight0.5 grams
Tolerance for the key dimension+/-0.02mm
ProcessesInjection molding

Mold price: $1,200

  • Cavity number: 1+1, family mold
  • Mold material: 718H
  • Lead time: 35 days

These 2 parts we made are quite similar to lego bricks, whether in appearance or function. They need to be pressed into their mating components by hand, with the right amount of pressing force, and should be removed manually without too much difficulty.

Critical quality requirements

Tight tolerance for key dimensions

The dimension on the mating component is 13.90mm, so we define the corresponding dimension on the brick to be 13.90 -0.02/-0.06mm, or 13.86 +/-0.02mm.

pegboard for plastic bricks

cavity for plastic bricks

We made an inspection gauge to check the molded bricks, the key dimensions are all made the same as the matching components.

critical dimensions for inspection gauge

cnc machined inspection gauge for plastic bricks

We check the dimensions with a caliper as well, and the measurements show great consistency.

inspection result for the plastic bricks

Avoid sink marks and weld lines

In order to get an appealing appearance, we need to avoid molding flaws like sink marks and weld lines (or make them as least noticeable as possible).

Here are some close-up views of the plastic bricks:

close up view 2 of plastic bricks close up view 1 of plastic bricks