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Process Failure Mode and Effect Analysis _PFMEA

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					         Design / Process Failure Mode
         and Effect Analysis (D/PFMEA)




Presented by: Andy Peters on Behalf of
Smiths Aerospace
Aim of this session
   To show how to do an FMEA
   To show current best practice
   To show how to gain benefit from the
    tool
Why do an FMEA
   You can DESIGN out the failures before
    they happen
   You can control the process and thus
    process out failures
   Reduce rejects – minimise the risk of
    occurrence
   Take this case in particular
FMEA Case study DC10 Cargo
Door
Reproduced from a paper issued by NASA March 21 2005




     In 1969 per FAA requirements, Douglas,
      manufacturer of the DC-10 asked Convair to
      perform a FMEA of the DC-10 cargo door
      system
     The FMEA discovered 9 sequences that could
      potentially threaten life. 4 involved sudden
      depressurisation in flight
     1 of the 4 was failure of the locking pin
      system causing the door lock not to latch, the
      door could fly open in flight causing sudden
      depressurisation and possible structural
      failure of the floor and damage to the tail
Smoke and mirrors
   The draft FMEA was MODIFIED by Douglas to
    minimize the design deficiency
   A ground test failure in May 1970 was blamed
    on human error. In retrospect, poor design
    was downplayed as a root cause
   During November 1970 memos between
    Convair and Douglas discussed proposed fixes
    to the cargo door problem but NONE were
    implemented
   The FAA certified the DC-10 on July 29, 1971
    with an unsolved design deficiency
From bad to worse and the
smoke thickens
   June 12, 1972 the cargo door of an American
    airlines DC-10 in flight from Los Angeles to New
    York burst open at 11,500 feet due to the locking
    pin failing. This resulted in a sudden
    depressurization. No fatalities at this point
   NTSB investigation resulted in a draft FAA order
    to ground all DC-10s until the design mod was in
    place
   In an infamous “Midnight Gentlemen’s
    Agreement” the President of Douglas convinced
    the FAA Administrator not to ground the DC-10
The Accident
   March 3 1974 a Turkish Airline DC-10 crashed
    in France killing all 346 people aboard. The
    cause was faulty latches on the cargo door.
    Which at 11,500 feet the pressure difference
    forced the door to swing open to the outside
    where it was ripped off by the air stream.
   After this accident, the entire DC-10 fleet was
    finally grounded and the cargo door locking
    system was redesigned and the problem
    eliminated
    Lessons learned
   A safety analysis is no better than the system we
    have in place to deal with it
   A test failure that does not go to root cause is a
    missed opportunity to prevent future mishaps
   A close call should be treated as an opportunity
    to prevent a mishap
   Risk management is about mitigating risks while
    their probability of occurrence is still less than 1

“Destination Disaster” a book by Paul Eddy, details the events of this
major accident
What is an FMEA
   Analytical tool for risk mitigation
   Risk prioritisation method
   Method of linking multiple causes and effects
    to one failure mode
   Structured
   Widely used in both automotive and other
    major engineering industries
   Widely poorly used
   A live document
                        Process Failure Mode Analysis

                                                                    Failure Mode and Effect Analysis
                                                                             (Process FMEA)

 Custome                                                                                                    FMEA
       r:                                                                                                   Team:

 Part No:                       Drawing No:
     Part
                                Issue Date:
  Name:
    Eng.                        Control Item
  Level:                        (Y/N):

                                               =[Alt]+0209
          Process                                                                                           Recomm
          Descripti                                                                                          ended
 Operatio   on/       Failure      Effect of                                                                Correctiv   Action   Action
  n No.   Purpose      Mode        Failure      Cause of Failure     Current Controls     Current Status   e Action     By      Taken                Revised Status
                                                                                          O S D RPN                                           O        S         D     RPN

                                 What are the
                                                                             How bad is it ?                        What can be done?
                                 effects ?
What are the
                                                                                                                    •Design changes
 functions
                                                                                         How often                  •Process changes
                                                       What are the
                                                                                         does it                    •Special controls
                                                       cause(s)
                                                                                         happen
            What can go wrong?                                                                                      •Change to standards,
            •No function                                                                                            procedures or guides
            •Partial function
                                                                                                                                          How good is this
            •Intermittent function                                                   How can this be found?
                                                                                                                                          method of finding it
            •Unintended function
What does it all mean
   Function / Item
        What is it and what does it do?
   Potential Failure Mode
        What could go wrong
   Effect
        What is the knock of impact of the failure
   Cause
        What could of made this happen
   Severity
        How bad is this failure to both the customer and the production process
   Occurrence
        How often could this happen
   Detection
        What is the odds that the current control will find it
   Current control
        How do you look for this at the moment, if at all. Both prevention and detection.
                Prevention – Poka Yoke, fool proofing,
                Detection – Gauging, measurement, spc etc
    Severity
Effect                       Sev erity of effect                                        Rank
                             May endanger machine or assembly operator.
                             Very high sev   erity ranking when a potential failure
Hazardous - with out warning mode affects safe product operation and / or                10
                             involves noncompliance with gov      ernment
                             regualtion. Failure will occur without warning
                             May endanger machine or assembly operator.
                             Very high sev   erity ranking when a potential failure
Hazardous - with warning     mode affects safe product operation and / or                9
                             involves noncompliance with gov      ernment
                             regualtion. Failure will occur with warning
                             Major disruption to production line. 100% of
                             product may hav     e to be scrapped. Vehicle / item
Very high                                                                                8
                             inoperable, loss of primary function. Customer
                             very dissatisfied
                             Minor disruption to production line. Product may
                             hav e to be sorted and a portion less than 100%
High                                                                                     7
                             scrapped. Vehicle operable, but at a reduced lev      el
                             of performance. Customer dissatisfied
                             Minor disruption to production line. Product may
                             hav e to be sorted and a portion less than 100%
Moderate                     may hav   e to be scrapped after sorting. Vehicle           6
                             operable, but some comfort/conv       eniance items
                             inoperable. Customer experiances discomfort
                             Minor disruption to production line. 100% of
                             product may hav     e to be reworked. Vehicle/item
Low                          operable, but some comfort/conv       eniance item(s)       5
                             operable at reduced lev    el of performance.
                             Customer experiances some disatisfaction
                               Minor disruption to production line.The product
                               may hav eto be sorted and a portion (less than
Very low                                                                                 4
                               100%) reworked. Fit & finsh/squeak item does not
                               conform. Defect noticed by av erage customer
                               Minor disruption to production line. A portion (less
                               than 100%) of the product   may hav  e to be
Minor                          reworkedon-line but out-of-station. Fit/finsh /           3
                               squeak & rattle item does not conform. Defect
                               noticed by an av erage customer
                               Minor disruption to the production line. A portion
                               (less than 100%) of the product may hav    e to be
Very minor                     reworked on-line but in-staion. Fit & Finish /            2
                               Squeak & Rattle item does not conform. Defect
                               noticed by discriminating customers
None                           No effect                                                 1
Occurrence
Rank        CPK       Propability of failure                   Possible failure rates
       10   <0.33
        9   >=0.33        Very high: Failure is inevitable           >= 1 in 2
        8   >= 0.51      High: generally associated with               1 in 8
        7   >= 0.67   process similar to previous processes           1 in 20
                                                                      1 in 80
       6 >=0.83        Moderate: generaly associated with
                      processes similar to previous process          1 in 400
       5 >=1.00         withc have experiances occasional
                       failures but not in major proportions        1 in 2,000
       4 >= 1.17
                      Low: isolated failures associated with
       3 >=1.33       similar processes                             1 in 15,000
                      Very low: Only isolated failures
                      associated with almost identical
       2 >=1.5        processes                                    1 in 150,000
                      ??? Failire is unlikely. ???? Failuers
                      ????? Associated with almost
       1 >=1.67       identical processes                          <= 1,500,000
        Detection
       Detection                 Criteria               Inspection Types Suggested Range of Detection Methods        Ranking
                                                          A    B     C
       Almost
                                                                    X   Can not detect or is not checked
       Impossible Absolute certantiy of non-detection                                                                  10
       Very                                                             Control is achieved with indirect or
                                                                    X
       Remote     Controls will probably not detect                     random checks only                             9
                  Controls have poor chance of                          Control is achieved with visual inspection
                                                                    X
       Remote     detection                                             only                                           8
                  Controls have poor chance of                          Control is achieved with double visual
                                                                    X
       Very Low   detection                                             inspection only                                7
                                                                        Control is achieved with SPC or similar
                                                              X     X   charting mthods (Statistical Process
       Low         Controls may detect                                  Control)                                       6
                                                                        Control is based on variable gauging after
                                                                        parts have left the station, or Go/NoGo
                                                              X
                                                                        gauging performed on 100% of the parts
       Moderate    Controls may detect                                  have left the station                          5
                                                                        Error detection in subsequent operations,
       Moderatly   Controls have a good chance of        X    X         OR gauging performed on setup and 1st
       High        detection                                            part check                                     4
                                                                        Error detection in-station, or error
                                                                        detection in subsequent operations by
                                                         X    X         multiple layers of acceptance, supply,
                   Controls have a good chance of                       select, install, verify, can not accept
       High        detection                                            discrepant part                                3
                                                                        Error detection in-station (automatic
                                                         X    X         gauging with automatic stop feature) Can
       Very High   Controls almost certain to detect                    not pass descrepant part                       2
                                                                        Discrepant parts cannot be made
                                                         X              because item has been error proofed by
       Very High   Controls almost certain to detect                    process/product design                         1


Inspection types:
A: Error Proofed – B: Gauging – C: Manual / Visual Inspection
Special Characteristics
   Significant and critical characteristics
    can be identified from this
   These are as shown.
Critical Characteristics
   Critical Characteristics are those product
    requirements that affect compliance with government
    regulation or safe product operation and which
    require special actions / controls.
   Product or process requirements can include
    dimension, specification, tests, processes, assembly
    sequences, tooling, joints, torques, welds,
    attachments, component usage etc.
    Special actions / controls can include manufacturing,
    assembly, supplier, shipping, monitoring and or
    inspection actions / controls
Significant Characteristics
   These are those product, and / or test
    requirements which are important for
    customer satisfaction and for which
    quality planning actions must be
    summarised in the control plan
So How Do We Know Which is
Which?
   Design
       Critical
            Severity of 9 or 10 = PFMEA mandated
       Significant
            Severity of 5 to 8 and Occurrence of 4 to 10 = PFMEA
             mandated
   Process
       Critical
            Severity of 9 or 10. Control is mandated / look at design
             in the long term
       Significant
            Severity of 5 to 8 and Occurrence of 4 to 10 = Control is
             mandated
Severity * Occurrence Vs RPN
   One of the common misconceptions is
    that the RPN (S*O*D) being greater
    than a set number is the way to sort
    the corrective actions out is wrong. (so
    current best practice tells us)

   The trick is to sort initially by S*O
    (criticality) then S*O*D
Corrective Action
   If the severity is > = 9 then corrective
    action is mandatory
   If Severity is >=5 and <9 and Occ is
    >=4 then corrective action is
    mandatory
   There is no trigger level for an RPN
    number – that is up to you.
Responsibility & Target date
   Who is responsible to make sure the
    actions have been done
   When is it due to be finished

This shows that just saying that you are
 going to do something is not good
 enough. This is a live document and
 needs to be followed up.
Assumptions
   DFMEA
       The item is manufactured / assembled within
        engineering specifications
       That the design may include a deficiency that may
        cause unacceptable variation (i.e. miss builds,
        errors) in the manufacturing assembly
   PFMEA
       The design is right
       The parts are supplied correctly
       That all staff are trained
       That no one is wilfully doing it wrong – you can’t
        control for Muppets!

				
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posted:4/14/2012
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