FMEA - Method of Determining the Occurrence Ranking

[John Bero]

FMEA

I have been developing PFMEA’s for at least 10 years and for the first time one of my work associates insisted that our method of determining the occurrence ranking was incorrect. My method of determining the occurrence ranking is based on the failure rate through statistical analysis (not assumptions) on the process being performed (the output). My associate believes that the occurrence ranking is based on what the process receives from the previous process or incoming component variations. My focus is on the occurrence of process failures in relation to product/process specifications of the process being evaluated,.

What is your take on this?
Is the occurrence ranking based on variation goining into the process or is it based on the process out-put?

 

[Al Dyer]

I have always been taught and believe that occurrence is the projected failure rate of failure mode which is the output of the process.

ASD...

 

[Marc]

Same here, Al. Occurance is the probability (ah, hemmm - rated from 1 to 10 in the case of automotive) that the process under evaluation will output the defect.

 

[Kevin Mader]

I third the motion on the floor.

Regards,

Kevin

 

[Rick Goodson]

How about some source material to support your case.

AIAG Potential Failure Mode and Effects Analysis (FMEA) Page 37 (Process FMEA). "Occurence is how frequently the specific failure cause/mechanism is projected to occur (listed in the previous column)." The previous column is the Potential Cause(s)/Mechanisms of Failure. "Potential Cause of Failure is defined as how the failure could occur, described in terms of something that can be corrected or can be controlled" It goes on to list examples all of which relate to the assembly, manufacturing, etc. process such as torquing, inadequate lubrication, etc. There is no reference to reliability of the incoming parts.

You can find the same information in Stamatis' book "Failure Mode and Effect Analysis, FMEA from Theory to Execution"(ISBN 0-87389-300-X) but it is not as clearly stated.