Systems Engineering – Risk Analysis with FMEA

Special TopicsFishbone ChartFMEA

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Risk/Failure Models

At the ‘project’ level.

At the system or device level. Common methods include Fishbone

analysis or FMEA FMEA – Failure Modes and Effects Analysis

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Fishbone Chart

‘Cause and Effect’ Analysis Create an Ishikawa or Fishbone Chart Head is ‘Problem’ – Skeleton are the ‘Causes’ Typical categories, 5M’s + E

Man Machine Material Method Measurement Environment

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Industrial Monitoring Sensor

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Create a Fishbone Chart for ‘Sensor Not

Working’

Analysis Tool – FMEA

Failure Mode and Effects Analysis

FMEA is an ‘enhanced’ Cause and Effect Analysis. (the 5M’s plus E) Do Fishbone Chart for Industrial Sensor.

Apply FMEA to a Design or Processes at many levels.

Systems often have many SPFs – single points of failure.

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Design Tool – FMEAThe Concept of FMEA:

People Make Mistakes Products and Processes Fail

Anticipate these errors and eliminate them with design or process changes !!

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FMEA Example

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How many ways can a

floppy disk be inserted ??

What design features make this possible??

FMEA Steps-The traditional approach

1. Team activity2. Select component, system, process step, etc.3. Identify possible failure modes.4. Identify causes of failure modes.5. Identify effects of failures.6. Estimate (1-10 ranking):

1. Occurrence – how often (1=not, 10=often)2. Severity – how bad (1=not, 10=severe)3. Detection – how easy (1=easy, 10=difficult)

7. Calculate RPN – ‘risk priority number’

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FMEA RPN example

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Occ Sev Det RPN Comments 1 1 1 1 No Problem 1 10 1 10 No action, easy to detect. 1 1 10 10 No action, not often or severe. 1 10 10 100 Action 10 1 1 10 Chronic problem, fix ? 10 10 1 100 Chronic and severe, fix 10 1 10 100 Chronic and customer issues, fix 10 10 10 1000 Bad, Bad, Bad – top priority

Rules for OSD ValuesThreshold for Action – VariesThresholds 55-100 (?)

10From National Instruments

11From National Instruments

12Detection in Design or Manufacturing

POTENTIAL FAILURE MODE AND EFFECTS ANALYSIS

Page FMEA Number

 Part Number Design or Process Responsibility Prepared by Telephone #

     Original FMEA Date FMEA Revision Date

     Core Team

Design Item or Process Function Requirements

Potential Failure Mode Potential Effect(s) of FailureSev

Class

Potential Cause(s) / Mechanism(s) of Failure

Occ

Current Design or ProcessControls

Det

RPN

Recommended ActionsResponsibility & Target

Completion DateActions Taken

Sev

Occ

Det

RPN

         

System Subsystem Component

Design FMEA Process FMEA Internal Use Only

.

13Many versions of this chart…

Occurrence and Severity

O and S are often the two critical factors and some analysis just looks at these two.

14From Dieter

Industrial Monitoring Sensor

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FMEA Summary

Combines ideas of ‘Cause and Effect’ chart, mistake proofing, and risk.

Useful to identify and prioritize possible failure modes and fixes.

Possible Fixes : High reliability components, De-rate components, Redundancy, Change the design.

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FMEA- A Requirements Approach

FMEA often starts with: Identify possible failure modes. How? – guess, experience, brainstorm, etc.

Consider – Requirements are what the system is supposed to do. Counter-requirements (not being met) are failure modes. Use counter-requirements to populate the FMEA table.

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Design FMEA Example

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Design FMEA

Coyote Hoist

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Class Discussion – Process FMEA You are responsible for developing a process to stuff

several hundred envelopes for a charity group.

Each envelope is to contain three separate flyers and a cover sheet with the recipients name on it. After folding, the name must show in the cutout in the envelope. The final step is to seal and place stamps on the envelope for mailing.

Develop a PFMEA* for this process.

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*Process FMEA