When designing small features for MIM, there are absolute limits governed by powder particle size, mold strength, and sintering behavior.
Hole design limits:| Hole Feature | Minimum | Recommended | Constraint |
|---|---|---|---|
| Diameter (molded) | 0.2 mm | ≥ 0.5 mm | Core pin strength below 0.3 mm |
| Depth: diameter (blind hole) | 3:1 max | ≤ 2:1 | Core pin deflection during molding |
| Depth: diameter (through hole) | 6:1 max | ≤ 4:1 | Core pin supported at both ends |
| Center-to-center pitch | 2x dia + 0.5 mm | ≥ 3x dia | Mold steel integrity between holes |
| Hole to part edge | 1x diameter | ≥ 1.5x dia | Wall strength |
| Gear Parameter | Minimum | Recommended | Notes |
|---|---|---|---|
| Module (metric) | 0.15 mm | ≥ 0.25 mm | Below 0.15 mm: tooth strength inadequate |
| Tooth thickness at root | 0.2 mm | ≥ 0.3 mm | Risk of tooth fracture during ejection |
| Number of teeth | 6 | ≥ 10 | Below 6: undercut in mold becomes problematic |
| Face width | 0.5 mm | ≥ 1.0 mm | Below 0.5 mm: tooth alignment affected by shrinkage variation |
| Gear outer diameter | 2 mm | ≥ 5 mm | Below 2 mm: handling and inspection become difficult |
| Bore diameter (molded) | 0.3 mm | ≥ 0.6 mm | Must accommodate center core pin |
The absolute minimum molded hole diameter is 0.2 mm, but 0.5 mm is recommended for reliable production. Holes below 0.3 mm require core pins so thin they break during normal molding cycles.
Design tip: For holes smaller than 0.5 mm, consider whether the hole can be eliminated, added as a post-sintering drilling operation, or replaced with a notch or slot that uses a stronger mold feature.