No — internal threads cannot be molded directly. The thread profile cannot eject from the mold. Instead, the core hole is molded to near-net size and threads are tapped after sintering. External threads can be molded to approximately 80-90% of final form and chased with a thread die. Always design MIM parts with cored holes for tapping rather than expecting threads to be molded.
Pre-tap hole diameter recommendations for MIM:
| Thread Size | Standard Tap Drill (mm) | MIM Cored Hole (mm) | After Sintering (mm) | Tap to Final |
|---|---|---|---|---|
| M1.6 × 0.35 | 1.25 | 1.52 | 1.27-1.30 | M1.6 × 0.35 |
| M2.0 × 0.40 | 1.60 | 1.95 | 1.63-1.66 | M2.0 × 0.40 |
| M2.5 × 0.45 | 2.05 | 2.50 | 2.08-2.12 | M2.5 × 0.45 |
| M3.0 × 0.50 | 2.50 | 3.05 | 2.54-2.58 | M3.0 × 0.50 |
| M4.0 × 0.70 | 3.30 | 4.02 | 3.35-3.40 | M4.0 × 0.70 |
| M5.0 × 0.80 | 4.20 | 5.12 | 4.27-4.32 | M5.0 × 0.80 |
| M6.0 × 1.00 | 5.00 | 6.10 | 5.08-5.15 | M6.0 × 1.00 |
- Minimum thread engagement: 2× thread diameter for standard applications; 3× for high-strength
- Distance from thread to edge of part: minimum 1.5× thread diameter
- Cored hole draft angle: 0.5-1.0° (the tap cuts through this taper to produce straight threads)
- Through-holes preferred over blind holes for tapping (easier chip evacuation)