Test failure Root cause not found

mgoodman08

Starting to get Involved
#1
Hi Everyone,

Dealing with a return of a unit that failed at the customer testing level. They sent it back and we can't figure out what caused the failure. We have a few potential causes but not a clear cause. Right now its just at the engineering level hasn't been risen to the quality level yet. We've delivered 600 of these units in the past 10 years and this is the first occurrence like this. How do I explain to the customer that no root cause was found? Do I list out the potential causes? Just don't want to open a can a worms where they get an idea to send back 100's of units for us to check when we are confident those are fine. Just having a hard time coming up with a sucient statement.

We are an AS9100 facility.
Thanks!
 
Elsmar Forum Sponsor

blackholequasar

Involved In Discussions
#2
Are you unable to replicate the failure? Or was no fault/failure found when you tested the unit?

There isn't really instances of "no root cause" and, from a customer standpoint, that's the last thing they want to hear. There are instances in which failures cannot be replicated and you can provide proof of that. But if there was a true failure and the unit is not working within typical parameters, then something is causing an issue.
 

optomist1

A Sea of Statistics
Super Moderator
#4
even at a purely "engineering level" or stage...correlation is key...replicate exactly the test setup is its electrical, if mechanical/dimensonal an agreed to QAF or Quality Acceptance Fixture is urged. The QAF is generally from or used in the automotive fields, but is key when solving issues.
 

Tagin

Trusted Information Resource
#5
- We've delivered 600 of these units in the past 10 years and this is the first occurrence like this.
- Just don't want to open a can a worms where they get an idea to send back 100's of units for us to check when we are confident those are fine
Is your confidence based on anything besides the prior 600 units? That is, do you have some evidence that would show that this one defective unit could have escaped whereas no other defective units could have escaped? If not, then the customer's concern is valid.
 

Jim Wynne

Staff member
Admin
#6
Dealing with a return of a unit that failed at the customer testing level.
Do you test the units? If so, how does your test method compare to the customer's?

They sent it back and we can't figure out what caused the failure. We have a few potential causes but not a clear cause.
What prevents you from testing for the potential causes?

Right now its just at the engineering level hasn't been risen to the quality level yet.
What does this mean?

We've delivered 600 of these units in the past 10 years and this is the first occurrence like this. How do I explain to the customer that no root cause was found? Do I list out the potential causes?
You're assuming here that no root cause can be found. Is this the case? Have you exhausted all possibilities through testing?
Just don't want to open a can a worms where they get an idea to send back 100's of units for us to check when we are confident those are fine. Just having a hard time coming up with a sucient statement.
You were apparently confident that the failed unit was OK too. I really don't think that "We can't figure it out" is going to instill confidence in the customer.
 

Mike S.

Happy to be Alive
Trusted Information Resource
#7
I have on at least one occasion been unable to determine the root cause of a failure beyond isolating the component in our assembly that failed. It was not for lack of effort, and we had the customer participating so they knew we were not just blowing smoke or trying to take the easy way out.

We (the customer, the component supplier, and my company) exhausted everything we could think of trying to determine how/why the component failed but couldn't. I think it was about a 1% failure rate IIRC. Because of the application, we ended up developing a rigorous screening test that would detect the rare failures, but never were able to identify and prevent the root cause.
 

John Predmore

Trusted Information Resource
#8
One possibility is that the customer's test is different from yours. Or maybe something has changed so their test and yours are no longer equivalent. Annual calibration, by itself, is no guarantee that things can't change in the weeks and months after the calibration was done. You could suggest a round-robin test where the same sample(s) are tested by both your measurement and the customer's, and results compared.

What prevents you from testing for the potential causes?
Another possibility is what I call a disappearing problem. We had one hard-to-solve problem with leaking assemblies. We suspected a pinched o-ring in the joint. When the leakers were disassembled, the o-ring snapped back into position and it was not possible to recreate the leak by assembling the same parts which previously leaked. There was no visible damage to the o-ring. There were only 4 leakers discovered out of 40000 assemblies shipped, so what sample size would you test to solve a 100 ppm problem?

We hand-made assemblies with intentionally pinched o-rings until we could pass end-of-line leak-test, and the leak became manifest later in the sequence, which proved the validity of this black swan. Then our investigation figured out how the pinched o-ring was occurring in the manufacturing process, and fixed that. No more occurrence of leaks.
 

Mike S.

Happy to be Alive
Trusted Information Resource
#9
John, your o-ring leak story caused the temporary recurrence of a tic I developed over a similar problem once. If I never see another hydrogen leak tester again, it'll be too soon.....
 

John Predmore

Trusted Information Resource
#10
@Mike S., there was more to the story. The supplier was quite proud of their Helium leak tester, they told me it could measure a leak as small as 10cc/40 years. That was their assurance that they weren't shipping leakers. Their smugness disappeared when I showed them their $500K machine would pass parts with the o-ring completely missing from the joint if you put enough oil on the threads. I thought I would have to pick them up off the floor. I was able to document the pinched o-ring in the disappearing problem investigation by freezing the joint in liquid nitrogen, and then I could unscrew the joint and photograph the pinched o-ring before the rubber thawed. Total time on the problem, 4 days.
 
Thread starter Similar threads Forum Replies Date
JoCam Failure to test Class I medical device to IEC 60601-1-11 IEC 60601 - Medical Electrical Equipment Safety Standards Series 2
K Spot weld - Peel test failure Manufacturing and Related Processes 3
R Will multi-time flashovers constitute a failure of Hi-Pot test? IEC 60601 - Medical Electrical Equipment Safety Standards Series 9
B IPCD Sterility test failure during MPQ (EO sterilization validation) ISO 13485:2016 - Medical Device Quality Management Systems 2
T Weibull analysis of life time test of 8 electric motors until failure Reliability Analysis - Predictions, Testing and Standards 9
C Difference between "Pass/Fail Testing" "Test To Failure" "Degradation Test" FMEA and Control Plans 1
R 5% to 95% Non-Condensing Humidity Storage Test Conditions and Failure Modes APQP and PPAP 2
J FDA 510K - Justifying Fatigue Test results - 3rd Party Component Failure US Food and Drug Administration (FDA) 7
Q Semiconductor Inductor Failure - Will HAAS/HALT or any other test detect it? Manufacturing and Related Processes 4
R Steel Casting defects - Again - Pressure Test Failure Manufacturing and Related Processes 10
R Sample Failure/Qualification Test Failure? - A few units were tested many years ago! AS9100, IAQG, NADCAP and Aerospace related Standards and Requirements 13
J TFRR - What is actually required to be TEST FAILURE RESOLUTION REPORT Various Other Specifications, Standards, and related Requirements 2
J Seeking Excel Spreadsheet to help with cycle test for Weibull failure rates Excel .xls Spreadsheet Templates and Tools 2
G PFMEA failure modes for Process Function of Inspection/test FMEA and Control Plans 10
E Test report to certify compliance with IEC 62304 IEC 62304 - Medical Device Software Life Cycle Processes 3
E Tensile test machine, tinius olsen 602 Manufacturing and Related Processes 1
Moumen H Variations between ASTM A29 Standard for steel bars and Mill test certificates specs Manufacturing and Related Processes 1
D Tip test 10° -> 5° IEC 60601 - Medical Electrical Equipment Safety Standards Series 1
M Sponsor name presented in the test report EU Medical Device Regulations 4
M Packing Validation & Accelerated Aging Test ISO 13485:2016 - Medical Device Quality Management Systems 2
S OEM full range calibrations vs Validation special test points Medical Device and FDA Regulations and Standards News 0
C IEC 60601 - 8.8.3 Dielectric Strength test. 4kv being applied to the ground conductor?! IEC 60601 - Medical Electrical Equipment Safety Standards Series 2
S Shelf Life Test for IFU and Implant Card Other Medical Device Related Standards 1
S Mechanical Test Under FDA Freedom of Information Act Medical Device and FDA Regulations and Standards News 5
S Critical characteristic on manufacturing operations test procedure Inspection, Prints (Drawings), Testing, Sampling and Related Topics 0
R IEC 60601-1 Clause 15.3.2, Push test IEC 60601 - Medical Electrical Equipment Safety Standards Series 0
S Knee Implant (Femoral -Cobalt chrome)-Sub chronic toxicity test (ISO 10993-11)choice of root Medical Device and FDA Regulations and Standards News 2
A Defining a lower ESD test level in IEC 60601 safety test IEC 60601 - Medical Electrical Equipment Safety Standards Series 5
N Is there a need for clinical test of Class IIa products (for MDR)? EU Medical Device Regulations 2
A Is calibration of test weight required General Measurement Device and Calibration Topics 4
S Non parametric test for semi-quantitative data. Statistical Analysis Tools, Techniques and SPC 5
Ed Panek Disaster Recovery Test IT (Information Technology) Service Management 3
A How much does a complete biocompatibility test package cost? Other ISO and International Standards and European Regulations 1
M Is it normal / sufficient to have only the IEC 60601-1-2 test report without indicating IEC 60601-1? IEC 60601 - Medical Electrical Equipment Safety Standards Series 2
Z Is Op Amp Common-Mode Rejection Ratio (CMRR) test applicable to battery operated devices? Other Medical Device Related Standards 0
E When to perform accelerated aging studies and transport test(OQ or PQ) Qualification and Validation (including 21 CFR Part 11) 4
U Does *anyone* know a lab that will test to EN 455-4 Medical Gloves shelf life determination? EU Medical Device Regulations 1
A Test requirements for marketing in US when RATED values are not of US IEC 60601 - Medical Electrical Equipment Safety Standards Series 5
H Secondary Circuits, Voltage Test and Clearance/Creepage IEC 60601 - Medical Electrical Equipment Safety Standards Series 0
S Fogging test as per DIN 75201(50ug/g ) VDA Standards - Germany's Automotive Standards 3
R HV Test of HF Surgical Unit IEC 60601 - Medical Electrical Equipment Safety Standards Series 1
R IEC 60601-1 - 11.1.3 e) Test criteria - Temperature Measurements IEC 60601 - Medical Electrical Equipment Safety Standards Series 2
E 60950-1 resistance to abnormal heat test Various Other Specifications, Standards, and related Requirements 0
S User evaluation for self monitoring blood glucose test systems US Food and Drug Administration (FDA) 4
E MSA for Push and Pull test Gage R&R (GR&R) and MSA (Measurement Systems Analysis) 9
Z IEC 60601-2-25; Frequency response test Medical Device and FDA Regulations and Standards News 1
J Confusing on Harmonic Emissions/Voltage Fluctuations/Flicker test for CISPR 11 Class A Equipment IEC 60601 - Medical Electrical Equipment Safety Standards Series 2
E Routine production tests - dielectric voltage withstand test IEC 60601 - Medical Electrical Equipment Safety Standards Series 4
D Difference between Test Method Validation and Gage R&R Qualification and Validation (including 21 CFR Part 11) 18
Crimpshrine13 Laboratory Scope - Calibration vs. Test Methods - IATF 16949 IATF 16949 - Automotive Quality Systems Standard 3

Similar threads

Top Bottom