PFMEA failure modes for Process Function of Inspection/test

G

GBGYMDAD

#1
What is the general consenus on what the failure modes should be if you have a process step where all you are doing is some type of inspection or test. I was told in a training class by a consulting group that the failure modes should always be "Accept a bad part" or "Reject a good part". Any comments?
 
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Ron Rompen

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#2
The failure modes are fairly simple, and I would agree with the two you have listed. Possibly add in one more (Misidentify part).

The more DIFFICULT part of this exercise is to determine the potential failure mechanism, and the prevention and detection controls that are in place.
 
#3
Ron Rompen said:
The more DIFFICULT part of this exercise is to determine the potential failure mechanism, and the prevention and detection controls that are in place.
Having spent years inspecting initial samples, I would agree with that, and can also come up with another failure mode:

Inspection / test not carried out, or incomplete. It's been known to happen... ...for a number of reasons :rolleyes: .

/Claes
 
B

Bill Ryan - 2007

#4
Welcome to the Cove, GBGYMDAD :bigwave:

Just a couple of others to consider might be "gage out of calibration/damaged/broken/etc." and "Poka-Yoke not validated".
 
W

wangxingde

#5
For Visual inspection PFMEA

we have a same situation with your process, and we have some visual inspection, maybe we also should conside operator tiredness? but it difficuld define the Detection, even for other failure modes.
 
B

Bill Ryan - 2007

#6
wangxingde said:
we have a same situation with your process, and we have some visual inspection, maybe we also should conside operator tiredness? but it difficuld define the Detection, even for other failure modes.
I would tend to look at operator "tiredness" as a Potential Cause as opposed to a Potential Failure Mode. One way to address "tiredness" might be rotation of inspectors/operators.

Just as an FYI - Most of my automotive customers won't accept a Detection index of less than 6 when a visual inspection is involved - and then only with three layers of 100% inspection.
 
B

bgwiehle

#7
Inspection and Testing PFMEA

Last year (as a result of the research on the Cove!), we created a number of new PFMEAs, including generic FMEAs for inspection and testing.

The potential failure modes and causes we identified of course would never all be applicable to a particular program or test but during the planning for the cross-functional meeting, I was able to reference examples for most of the scenarios! :bonk:

This PFMEA was intended for internal planning rather than distribution to customers.

B.G. Wiehle
(PFMEA co-ordinator)


Failure modes and causes:
(A) Missed inspection or missed task in list of tasks.
• Wrong frequency or timing, including out-of-sequence.
• Lack of opportunity to do test (can't get parts, access equipment, manpower, communication).
• Operator / inspector error, including wrong assumptions.
• Missing tool/ fixture/ document.
• Changed requirements because of GP-12 or FPSC.
• Test never specified (requirement not documented).

(B) Wrong task completed.
• Wrong frequency
• Similar task substituted.
• Operator / inspector error.
• Missing or wrong criteria.
• Changed requirements because of GP-12 or FPSC added or removed.

(C) Wrong technique.
• Part loaded incorrectly, part test location incorrect.
• Wrong fixturing/ missing fixture.
• Data misinterpreted (gauge scale needs conversion, hard to read)
• Test run incorrectly.
• Wrong sample size.
• Wrong sample selection.
• Wrong sample preparation (cooling, aging, etc.)
• Wrong ambient conditions (temperature, humidity, dust, etc.)
• Test not appropriate for parameter being tested.

(D) Wrong or bad tool used (gauges, measuring equipment, read-outs, etc.).
• Out of calibration / calibrated incorrectly.
• Broken / poorly maintained / dirty.
• Replaced with different model.
• Sensor malfunction (if present)
• Wrong rev level (esp. attribute gauges)
• Reagent shelf-life expired or contaminated (if applicable).
• Low battery (if applicable).

(E) Wrong decision / determination made after inspection / test.
• Criteria too subjective / missing / wrong / still in development.
• Insufficient lighting / lack of contrast surface.
• Decision made by wrong (unauthorized) person (ie. operator or supervisor instead of inspector).
• Inexperienced inspector / operator, including new defects not previously identified.
• Operator / inspector disability (color-blindness, poor vision, illiteracy, innumeracy).
• Determination based on documentation / labeling error.
• Operator / inspector error, including time pressures, lack of commitment to quality, etc.

(F) Test samples / part being inspected not dispositioned properly.
• Defective/ failed parts returned to production.
• Passed parts returned to production downstream of a required operation or test.
• Parts being sorted placed in wrong container (during sorting).
• Parts replaced in wrong container.
• Set-up parts or parts generated during maintenance/ trouble-shooting not segregated as suspect parts.

(G) Test results not acted on (process not adjusted, parts not segregated).
• Operator / supervisor / lead-hand/ facilitator error. Lack of communication.

(H) Test / inspection not documented, or recorded incorrectly (if required).
• Operator / inspector error (including forgot, couldn't find form, didn't know how to fill in form, too long between test & record creation).
• Form missing place to record data due to new or changed requirements (document control issue).
• Record misplaced / sent to wrong location.
 
B

Bill Ryan - 2007

#8
Nice list, BG. Looks like your team really put forth some effort. :applause:

Might I ask how your Detection levels panned out for the eight Failure Modes identified (or did you lean more towards the Prevention control side of things)?
 
P

pthareja

#9
PFMEA's list for inspection and testing.

It is an exhaustive compilation. gr8 work! claps again.

May we add:

( D) Calibration zero error corrections not applied.
ovelap with (G) or (H) can't be ruled out ;-)

Room temperature /environmental situations in say hot & cold junctions or where some chemical reaction or shielding is necessitated are some other FMEA's. More like gage setting correction (like selection of right scale) could be pertinent in deserving cases.

P Thareja
 
B

bgwiehle

#10
Bill Ryan said:
Nice list, BG. Looks like your team really put forth some effort.
Might I ask how your Detection levels panned out for the eight Failure Modes identified (or did you lean more towards the Prevention control side of things)?
Thanks!

Most of our Detection ratings on the Inspection & Testing PFMEA are 8 (visual detection), some 9 (random checks). On the prevention side, we identified qualification testing for personnel, adequate training, document control & updating for work instructions and forms, checklists, MSA studies, gauge control, DVP&R (APQP) planning activities, etc.

More and more of our processes supplement operator inspection with set-up & process poka-yokes. Self-checking sensors are now standard for new assembly machines (program logic ensures sensor must cycle every machine cycle and should fail all parts when sensor fails). Automated data gathering is also used when feasible. Always room for improvement!

B.G. Wiehle
 
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