When comparing MIM and investment casting for a given part, the defect rate difference is a meaningful factor in total cost — especially for high-volume programs where scrap compounds.
Typical defect rates by process:| Process | Typical Yield | Common Defects | Scrap Cost Impact |
|---|---|---|---|
| MIM (standard, qualified process) | 95-98% | Dimensional drift, surface pitting, black lines | 2-5% over per-part cost |
| MIM (automotive/medical, SPC-controlled) | 97-99% | Same but lower frequency | 1-3% |
| MIM (titanium) | 85-92% | Oxygen pickup, porosity | 8-15% |
| Investment casting (standard) | 90-95% | Shell inclusions, porosity, misrun | 5-10% |
| Investment casting (premium, X-ray inspected) | 87-93% | Internal porosity, shrinkage, surface defects | 7-13% |
| Investment casting (large parts, >5 kg) | 85-92% | Shrinkage, shell cracking, inclusions | 8-15% |
| Defect Type | MIM Frequency | Investment Casting Frequency | Why the Difference |
|---|---|---|---|
| Dimensional variation | 1-3% (±0.3% typical) | 3-7% (±0.5-1.0% typical) | MIM molds are more repeatable than ceramic shell/wax pattern systems |
| Surface defects | 1-3% | 3-8% | Investment casting shell inclusions leave surface defects |
| Internal porosity | 1-4% (uniform micro-porosity) | 3-10% (localized macro-porosity) | MIM porosity is fine and uniform; casting porosity is localized |
| Material defects | 0.5-2% | 1-4% | Casting has more oxide/slag inclusion risk |
| Process scrap (setup) | 2-5% | 3-8% | MIM has faster process stabilization |
For parts under 50 grams, MIM typically has a lower defect rate (2-5% vs 3-10%) because the injection molding process is more repeatable than shell-based casting. For larger parts (>50 g), investment casting is the only option, so the comparison is moot.
The lower scrap rate of MIM is one of the hidden cost advantages — not only are fewer parts rejected, but the inspection burden is lower, and production planning is more predictable.