In plastic injection molding, recycling sprue and runner material is standard practice. In MIM, the same question arises: can you regrind and reuse the molded sprue, runner, and rejected green parts?
The short answer: Yes — but with strict limits on the regrind-to-virgin ratio and only if the material has not been degraded during processing. How regrind affects MIM feedstock properties:| Regrind Content | MFI Shift | Green Strength | Sintered Density Impact | Recommended Use |
|---|---|---|---|---|
| 0% (100% virgin) | Baseline | Excellent | None | Critical parts, tight-tolerance applications |
| 10-20% | Minimal (<3%) | Good | Negligible | Most production parts, stable process |
| 20-30% | Noticeable (3-8%) | Moderate | 0.2-0.5% density reduction possible | Non-critical parts, internal components |
| >30% | Significant (>10%) | Reduced | 1%+ density reduction | Not recommended — risk of property degradation |
- Use only clean regrind (no contaminated, burnt, or degraded material)
- Keep regrind content below 20% for most applications, 10% for critical dimensions
- Grind to consistent particle size matching virgin pellets
- Test MFI after blending with regrind — if MFI shifts more than 5% from virgin baseline, adjust process parameters or reduce regrind ratio
- Never use regrind for medical implant, aerospace, or safety-critical automotive parts unless specifically qualified
Yes, but limit regrind to 10-20% of the total feedstock weight for production parts. Always re-verify MFI and mold a test shot before committing to a production run with regrind blend.
ATMIK maintains strict material control procedures for regrind handling, with batch-level tracking and MFI verification on every regrind blend.