Use the 8D (8 Disciplines) methodology: (1) Contain the problem — quarantine suspect material, sort it, protect the customer. (2) Identify the root cause — was it powder, process, or inspection? (3) Implement corrective action — fix the specific defect cause. (4) Preventive action — update PFMEA, control plan, and SPC. (5) Verify effectiveness over 90 days of production.
Common MIM quality escapes and most likely root causes:
| Escape | Most Likely Root Cause | Immediate Containment | Permanent Corrective Action |
|---|---|---|---|
| Dimensional drift | Sintering temperature shift or powder PSD change | Measure last 3 batches; re-inspect inventory | Add sintering profile SPC alarm; tighten powder PSD acceptance |
| Black lines / carbon contamination | Incomplete debinding | Verify debinding weight loss on last 10 batches | Increase debinding cycle time; add MFI check on feedstock |
| Surface pitting | Coarse powder particles or binder-rich surface | Sort affected lots by visual inspection | Tighten PSD D90 spec; optimize gate location |
| Low density | Sintering temperature below spec | Check furnace profile vs setpoint | Recalibrate furnace; add daily profile verification |
| Cracks in sintered part | Handling damage or thermal gradient | X-ray or dye-penetrant inspect inventory | Improve brown part handling procedure; slow sintering ramp rate |
| D Step | Question | Example Response |
|---|---|---|
| D1 — Team | Who is investigating? | Quality engineer + process engineer + production supervisor |
| D2 — Problem description | What exactly is wrong? | "Hole diameter Ø3.05 ±0.08 measuring Ø3.18 on 12% of parts in Lot 2406-12" |
| D3 — Containment | What protects the customer? | "100% sorted; suspect inventory quarantined" |
| D4 — Root cause | Why did it happen? | "Feedstock batch 2406-08 had MFI 12% above nominal — higher flow = lower green density = more shrinkage" |
| D5 — Corrective action | What fixes this specific cause? | "Reject feedstock with MFI >±8% from target; add MFI check before production release" |
| D6 — Preventive action | What prevents recurrence? | "Update PFMEA: add MFI to incoming inspection. Update Control Plan: MFI check every compounding batch" |
| D7 — Verification | Did it work? | "No recurrence in 90 days of production (8 batches, 24,000 parts)" |
| D8 — Close | Is the problem resolved? | "Yes — process updated. Sharing lessons learned with customer quality team" |