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.

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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