Minimum center-to-center distance for adjacent holes: 2× the hole diameter + 0.5 mm. For 2 mm diameter holes: minimum pitch = 4.5 mm. For 0.5 mm diameter holes: minimum pitch = 1.5 mm. The distance from a hole edge to the part edge: minimum 1× the hole diameter.
Hole spacing design rules:
| Hole Diameter | Min Center-to-Center | Min Edge Distance | Core Pin Diameter | Core Pin Life (shots) |
|---|---|---|---|---|
| 0.3 mm | 1.1 mm | 0.3 mm | 0.3 mm | 50k-100k (fragile) |
| 0.5 mm | 1.5 mm | 0.5 mm | 0.5 mm | 100k-200k |
| 1.0 mm | 2.5 mm | 1.0 mm | 1.0 mm | 200k-500k |
| 2.0 mm | 4.5 mm | 2.0 mm | 2.0 mm | 500k-1M |
| 3.0 mm | 6.5 mm | 3.0 mm | 3.0 mm | 1M+ |
Core pins are the most fragile components in a MIM mold. A 0.3 mm core pin will bend or break under normal injection pressure after 50k-100k shots. Design strategies for closely-spaced holes:
- Group small holes into a single slot or oblong opening where possible
- Use stepped core pins (larger diameter near the base, smaller at the tip) for holes deeper than 3× diameter
- Consider post-sintering drilling for holes under 0.5 mm diameter — the drill may be more reliable than an ultra-thin core pin
- For grid patterns (e.g., cooling holes, mesh), a single wire-EDMed slot may be more moldable than individual holes