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Exploratory Data Analysis
Approaches to Reliability: Some New Directions
Chris McCollinCornel BuneaMaria Ramalhoto
Chris McCollinThe Nottingham Trent
University• Involved in Reliability since
1976• Worked as a reliability engineer
for 3 major aerospace companies
• Consultancies/Training: Nuclear, Rail, Commercial
• Involved with Q&RE paper for Engineering Council for last 8 years
• RSS representative for BSI• ENBIS Reliability Website
coordinator
Areas of Common SME Problems
• Effect of short-term management outlook on reliability
• Lack of time, manpower for analysis and improvement
• Lack of expertise, resources
• OEM dependency, meeting requirements only
• Lack of knowledge retention
FMEA/FRACAS Comparison
FAILURE FMEA S E V
O C C
D E T
R P N
RECOMMENDED ACTIONS AND
DATE
ACTIONS TAKEN
AND DATE
Excessive Gap between damper Bracket and assembly
Damper out of position. Effect: Reject Assy. Customer has difficulty assembling
4 6 4 96 None (26/09/95)
None
Excessive weld (material)
Failure: Assy not linished. Effect: customer Unable to use. Reject assembly. Failure: Incomplete linishing Effect: customer unable to use. Reject assembly.
…. 4
…. 3
…. 3
…. 36
None (25/09/95)
None
Faulty weld of Nut.
Effect: Premature Failure in service.
3 3 4 36 None (25/09/96)
None
Burn through at filter neck
The FMEA for this Operation does not Consider this failure. But blowholes are considered.
- …. 9
- …. 3
-
…. 3
-
…. 81
-
……………….. monitor alarm performance
31/08/94
-
………. None
08/05/96
Incorrect filter Fitted
YES: Effect: Possible damage
8 4 7 224 Poka-Yoke delivery of Filter,
to link Filter selection with notching.
(12/07/94)
None. Last FMEA
update 08/05/96
Plating on Filter Neck missing.
No FMEA for Operation 92.
- - - - - -
Filter loose FMEA for fitting Filter did not consider this failure mode or effect.
- - - - - -
Notch being Missed
YES: Effect was severe Customer dissatisfaction.
8 2 4 64 None None
Problem Solving Requirements
• Structured approach, easy to use, computer/web based
• Developing hypotheses to answer (inter-related) problems over life cycle of a product(s)
• Using past/present information across diverse databases
• Central storage access on-line
Flowchart of Problem Solving Database
Issues Site: Examples of Hypotheses
Discussion Site: Past Issues: Papers
Past Solutions Database: Case studies, Reports
Methods Site Existing Data Repository
Statistical Flowcharts + Packages
Recommendations Site
Problem Solving Procedure
• 1. Layout of ScenarioProblem: environment,
conditions, flowcharts, etc2. State Null HypothesisConsider Problem effect across
all interfacing levels leading to possible (multiple) causes (flowchart). Address complexity of problem, whether there is more than one. Alternative hypotheses listed. Costing issues addressed.
• 3. Analysis FlowchartFailure records, statistical
flowcharts – alternative research methodologies identified
• 4. RisksPrevious works, arguments, risk
assessments available?• 5. Problem solving tools,
Working modelPhysical assumptions,
background theory – design equations, physics, use of C and E (appropriate method), 5 Whys, brainstorming, Fault tree, FMEA, MORT, Design of Experiments, etc
• 6. Bias, Rejection criteria for null hypothesis
• 7. Hard Collection, analysis
Analysis: Questionnaires, Engineering analysis: e.g. materials test, statistical analysis, etc
• 8.Conclusions Accept/reject hypothesis based on model/assumption/bias or change hypothesis (go to step 2)
• 9. Recommendations for corrective actionChange to schedules, procedures, Poka-Yoke devices, etc. Standardisation.
• 10. Feedback/Feed forward
To next problem, to database for dissemination and comment
Job Description of Facilitator
• Aids the problem solving activity• knowledge and experience of the
problem solving approach, team dynamics
• knowledge of what expertise is required for a particular problem and who can provide it (available from personnel files)
• has the ability to aid incorporation of diverse knowledge
• can mediate in issues arising from differing viewpoints
• suggest methods of solution (qualitative and/or quantitative)
• provide guidance of the holistic view of the company strategic plan.
No Fault Found (NFF)
Reason: not been installed on the aircraft and since the classification ‘Missing’ did not exist in the failure definitions inventory (because ‘Missing’ was not a failure category) the nearest most appropriate category was NFF. In this case, NFF is a misleading classification because it may indicate that a failure did not exist in the first place.
We should stratify the problem by disseminating our data into more appropriate categories and discuss them individually.
No Fault Found
Plenty of Reasons:No classification for what has
been foundReplace everything (saves time)Interdependencies between
systems, e.g. common power supplies
LoadingWorking at limits of operationIntermittent Wiring faultsGround test conditions cannot
reproduce latent defect
Example Hypothesis• Aircraft operating, external
temperatures and vibration affecting systems
• Time lag of thermal shocks 10º a minute in chamber but system takes longer
• Rise in temperature causes expansions – effects on interconnections (transistors –pnp,npn; solder: DC wetting; may create micro-cracks
• (DC wetting is passing of DC current over dry joint creates an increase in heat, resulting in the joint melting back together) – cannot locate fault
Continued
• Possibly surfaces become more elastic, cracks open quicker over time allowing contamination
• Cracks will close again, only long term exposure to adverse conditions may produce identifiable failure
• Road Surface testing, DOE (long term effects), FEA/Thermal effects, compatible materials, HALT, Simulation within CAD of thermal/vibration effects
Step 1.
The environment, the operating conditions and the problem and associated inter-relationships should be outlined in sketch form (e.g. an Affinity diagram) to highlight areas where a possible solution may lie. Flowcharts, diagrams, previous analyses should be made available (preferably on-line).
Step 3. Structure
• Approaches to identifying structure can be split into two separate areas; where extra explanatory information is available and where it is not.
Multivariate Data Analysis Flowchart
Description of physical and functional system
Check for missing or corrupt data
Discriminant analysis
Multivariate analyses for determining structure - PCA, correspondence, cluster, correlation, distance measures, etc
EDA
Modelling time metric data - time series, PHM, PIM, GLIM, regression
Data Analysis
• Hypothesis 1: The stratum of a number of sockets is homogeneous. The alternatives are that times are clustered (non-independence) and/or inhomogeneous
• Hypothesis 2: The processes are independent against clustering (process identified as “colored”)
• Hypothesis 3: The colored process is stationary
• Hypothesis 4: The process is “color blind competing risk”
• Hypothesis 5: The process is stationary competing risk
• Hypothesis 6: The process is renewal competing risk
• Hypothesis 7: The process is Poisson competing risk and under the alternative hypothesis, H1: Renewal process.
Org NUKEM
VTT JRC - ISPRA
INTER-ATOM
ENEA –VEL
EDA M graph
TT Kaplan Meier plot
TT
Trend Test
No trend found
NT No trend found GF
Trend found CF
TD
Serial Correlation
NT NT Log rank WR LR
NT NT
Distribution
EX WE GF
EX WE GF
See EDA above OS GF
EX WE
EX WE
Assumptions
OU CE
OU CE Trend SC
OU CE
OU CE OU
Other Analysis
AV
Step 5
A repository of tools should be kept with examples of how they may be used in conjunction with each other. The repository may contain examples of the 7 quality tools, the 7 new quality tools, brainstorming, Management Oversight and Risk Tree (MORT), Failure Modes and Effects Analysis (FMEA), radar charts, etc.
MACHINE INTERVENTIONS
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• The Pro-Enbis project is supported by funding under the European Commission's Fifth Framework 'Growth' Programme via the Thematic Network "Pro-ENBIS" contract reference: G6RT-CT-2001-05059.
• The authors (i.e., Pro-ENBIS) are solely responsible for the content and it does not represent the opinion of the Community, the Community is not responsible for any use that might be made of data therein