Reducing per-part cost by converting from CNC machining to MIM is one of the most common engineering cost-reduction initiatives. But the conversion requires more than just sending the same drawing to a MIM manufacturer — the design must be re-optimized for the MIM process.
The 5-step conversion process: Step 1 — Geometry screeningNot every CNC part is a candidate. A good MIM conversion candidate has:
- Weight under 50 g (ideally under 20 g)
- Maximum dimension under 50 mm
- Annual volume above 5,000-10,000 parts
- Complex 3D geometry that currently requires multiple machining operations
CNC parts are often over-toleranced for MIM. Review every dimension:
| CNC Tolerance | Suggested MIM Tolerance | Savings Opportunity |
|---|---|---|
| ±0.013 mm | ±0.05 mm (IT9) | Any tight dimension that can be relaxed reduces cost |
| ±0.025 mm | ±0.10 mm (IT10) | Major cost driver — relax if function allows |
| ±0.05 mm on 3+ features | Keep 1-2 critical; relax rest | 30-50% cost reduction |
- If the original material is 316L or 17-4PH: direct replacement, no change needed
- If the original is 303 stainless: switch to 316L (303 is not MIM-compatible)
- If the original is aluminum: cannot MIM directly — consider MIM stainless as a replacement or keep the part as CNC/die cast aluminum
- If the original is titanium: MIM Ti6Al4V is feasible at sufficient volume
- Add draft angles (0.5-1.0° minimum) to vertical surfaces
- Increase internal radii (R ≥ 0.3 mm)
- Add uniform wall thickness or core out thick sections
- Orient holes parallel to mold opening to avoid side actions
| Annual Volume | CNC Cost (10 g, 316L, complex) | MIM Cost (converted) | Savings |
|---|---|---|---|
| 5,000 | $8-18 | $3-6 | 50-65% |
| 20,000 | $7-16 | $1.50-3.00 | 65-80% |
| 50,000 | $6-15 | $0.80-1.80 | 70-85% |
For complex parts under 20 g at volumes above 10,000/year, expect 50-80% cost reduction. The largest savings come from eliminating material waste (MIM uses >95% of input material vs 15-40% for CNC) and consolidating multiple machining operations into a single molding step.
ATMIK provides a free CNC-to-MIM conversion feasibility analysis — send your current CNC part drawing and annual volume for a side-by-side cost comparison.