Handling Nonconforming Parts
Tag, segregate, and contain a bad part, write it up, and follow the disposition process instead of deciding alone.
Table of contents
Finding a bad part is not a failure. It is the system working. The failure comes afterward, when a part gets set back on the good pile, a suspect lot keeps moving, or someone decides on their own that it is "close enough." This is the routine for what you do in the minutes after you find a problem, and what happens to the part after that.
What You Will Be Able to Do
- Say what makes a part nonconforming.
- Tag and segregate a bad part.
- Work out how many other parts are suspect.
- Write a clear nonconformance report.
- Explain each disposition and who can make it.
What Nonconforming Means
A part is nonconforming when it fails to meet any requirement. That includes a size, a finish, a material, a marking, a missing certificate, or a missing inspection. One failed requirement is enough. A part that is out by 0.0005 inch is just as nonconforming as a part that is out by 0.050 inch, even if it would probably work.
The word is about the requirement, not about your opinion of the part. Whether it can still be used is a separate decision, and that decision belongs to the people with the authority and the data to make it.
The First Five Steps
Do these right away, in this order.
- Stop. If the problem might still be happening, stop adding to it. Follow your plan on whether to stop the machine, and get your lead.
- Tag it. Attach a red tag or nonconforming label to the part or its container.
- Segregate it. Move it to the marked nonconforming area, such as a red bin or a locked cage. Keep it away from good parts.
- Contain it. Work out which other parts might have the same problem, and hold them too.
- Report it. Tell your supervisor or quality, and start the report.
A good tag shows the part number, job or lot number, quantity, the problem, the date, and your name. Write enough that someone who was not there can understand it.
Warning: Never put a questionable part back into the flow, and never remove someone else's tag. A hidden defect can reach a customer in a part that carries load, pressure, or current, and that can hurt people.
Containment: How Far Does It Go
One bad part usually means there are more. Containment works back to the last time you know the parts were good.
Worked example: you check a shaft every 25 parts. Part 125 passed. Part 150 fails, and the machine ran on until you stopped it at part 163. The suspect range is everything after the last good check: parts 126 through 163.
163 - 125 = 38 suspect parts
Hold all 38 until they have been checked. Then look further:
- Have any of them moved to the next operation, or to shipping?
- Are other machines using the same tool, program, or material lot?
- Did the problem come from something that would affect earlier lots too, such as a bad gauge?
If parts have already reached a customer, quality decides how to contact them. Tell quality quickly. Do not wait until you have every answer.
Writing the Nonconformance Report
The nonconformance report (NCR) is the record of what is wrong. A good report contains facts, not guesses or blame.
| Field | Example |
|---|---|
| Part, revision, lot | 44871 Rev C, Lot 2093 |
| Requirement | Bore 1.2500 +0.0005 / -0.0000 |
| Actual condition | 1.2512, 1.2510, 1.2513 on three parts |
| Quantity | 38 suspect, 3 confirmed |
| Where found | In-process check, Machine 7 |
| How measured | Bore gauge ID 1187, calibration current |
Weak: "Bore is bad." Strong: "Bore measures 1.2512, over the 1.2505 upper limit by 0.0007."
Leave the cause out if you do not know it. You can note what you saw, such as "tool changed at part 120," without calling it the cause.
Disposition: What Happens to the Part
A disposition is the formal decision on a nonconforming part. Simple cases may go to a quality engineer. Harder cases go to a Material Review Board (MRB), which is a group from quality, engineering, and production, and sometimes the customer.
| Disposition | What it means | What has to happen |
|---|---|---|
| Rework | Fix it so it fully meets the requirement | Follow written steps, re-inspect, release if it meets spec |
| Repair | Make it usable, though it won't fully meet the print | Needs approval, often from the customer |
| Use as is | Accept it unchanged | Engineering shows it still works, customer approval if required |
| Scrap | Destroy it | Mark or deface it so it can't be used by mistake |
| Return to supplier | Send purchased material back | Purchasing handles the return and the supplier response |
Rework and repair are not the same. Reworked parts meet the print afterward. Repaired parts do not, so they need more authority. Examples of rework are re-machining an undersize bore to its limit, chasing a thread, or removing a burr.
Reworked parts are not good just because someone worked on them. They go through inspection again and are released only if they meet the specification.
A customer's written approval to ship something that is not to print goes by names such as a concession, a deviation, or a waiver. Without it, the parts stay.
When the Order Is Late
This is where people get tempted.
Worked example: a batch has one critical dimension out of tolerance by 0.0005 inch. The customer needs the parts tomorrow. Your supervisor is under pressure.
- Do not ship and do not change the record. Being close is not approval.
- Write the NCR with the real numbers.
- Push it through the disposition process quickly. Ask for a same-day review if needed.
- If engineering believes the parts will work, the customer can be asked for a concession.
- Ship only if the formal decision and any needed customer approval are on file.
Urgency changes how fast you move through the process. It does not change the process.
Supplier Problems
Bad material or purchased parts follow the same rule. Quarantine them at receiving, tag them, and notify purchasing. Purchasing then contacts the supplier, and the supplier may be sent a formal corrective action request. Do not use the parts "for now" while you wait.
Stopping It From Coming Back
A correction fixes the parts in front of you. A corrective action finds the root cause and removes it, so the problem stops. Sorting 38 parts is a correction. Learning that the tool life setting was too long, then changing it, is a corrective action.
You help this along by reporting what you saw, even if it seems small. Repeat problems are often the ones nobody wrote down.
Common Mistakes
| Mistake | What it causes |
|---|---|
| Fixing a part quietly without a record | Parts changed outside the process, and no one learns the cause |
| Leaving tagged parts next to good ones | Mix-ups |
| Checking only the one bad part | Suspect parts move on |
| Re-measuring until you get a passing number | False records |
| Scrapping without marking the part | Scrap finds its way back into stock |
| Skipping inspection after rework | A second defect slips through |
Check Your Understanding
1. A dimension is out by 0.0003 inch, and you are sure it would still fit. What do you do?
Tag it, segregate it, and write it up. Whether it can be used is a disposition decision, not yours alone.
2. A check every 50 parts passed at part 200 and failed at part 250. The machine stopped at part 258. How many parts are suspect?
58 parts: 201 through 258.
3. An MRB gives a part the disposition of rework. What has to happen before it can ship?
The defect is corrected by a written method, the part is inspected again, and it is released if it meets specification.
4. What is the difference between rework and use as is?
Rework changes the part so it meets the requirement. Use as is leaves the part unchanged and accepts it because engineering has shown it will work, with customer approval if the contract requires it.
Key Takeaways
- One missed requirement makes a part nonconforming, however small the miss.
- Stop, tag, segregate, contain, and report.
- Contain back to the last known good check.
- Write the NCR with facts and real numbers.
- Disposition belongs to the people with authority, such as an MRB.
- Reworked parts must be inspected again.
- Urgency never replaces formal approval.