Reliability Training Lesson 1 Basics
- 1. Reliability – Lesson 1 The Basics 1
- 2. RELIABILITY - LESSON ONE Overview: Application of Reliability in different industries Importance of Reliability – Cost Impact Bathtub curve Predictability vs. Failure Mode Avoidance P-Diagram Strategies for Improvement 2
- 3. QUOTES ―A man who lacks reliability is utterly useless.‖ Confucius (551-479) ―Engineering is the science of economy, of conserving the energy, kinetic and potential, provided and stored up by nature for the use of man. It is the business of engineering to utilize this energy to the best advantage, so there may be the least possible waste.‖ Willard A. Smith (1908) 3
- 4. RELIABILITY - DEFINITION Wikipedia - the ability of a system or component to perform its required functions under stated conditions for a specified period of time. ASQ – the probability that an item can perform its intended function for a specified interval under stated conditions 4
- 5. RELIABILITY - APPLICATIONS Products: Design for Reliability Software Equipment: Reliability Centered Maintenance Medical – Survival rate 5
- 6. RELIABILITY - COMPARISON Reliability field Nuclear Aerospace Medical Consumer Products Reliability Criteria # units in field 00 000 00000000 00000000 Quality of field records: Failed units excellent excellent Reasonable>good fair Unfailed units excellent excellent none none Units lost to follow-up no no often yes Noise space simple moderate complicated complicated Competing risks no no yes yes Key Reliability redundancy, redundancy, intervention robustness, Strategy intervention intervention some intervention Key reliability measure probability probability cure rate and side effects distance from failure modes Memo: Design improvement yes yes no yes 6
- 7. WHY IS RELIABILITY IMPORTANT ? Safety Customer Satisfaction Warranty Costs Reputation Repeat Business Cost Analysis Customer Requirements Competitive Advantage 7
- 8. RELIABILITY IMPROVEMENT PROCESS Set goals & requirements (customer driven) Perform an assessment Testing Data collection Failure reporting, analysis and corrective action system (FRACAS) 8
- 9. VOCABULARY Mean Time to Failure (MTTF) Mean Time Between Failures (MTBF) Hard Failures – product function ceases Soft Failures – degraded to unacceptable level Failure rate Hardware Breakdown Structure FMEA – Failure Modes, Effects & Analysis SPC – Statistical Process Control DOE – Design of Experiments 9
- 10. LIFE CYCLE COST ―It’s unwise to pay too much, but it’s foolish to spend too little‖— John Rustin Present Value vs. Future Value of money Acquisition Costs Sustaining Costs Cost Breakeven Include Cradle-to-Grave costs converted to NPV models http://www.barringer1.com/pdf/LifeCycleCostSummary.pdf 1 0
- 11. LIFE CYCLE COST $30,000 $25,000 $20,000 C o $15,000 s Product A t Product B $10,000 $5,000 $0 1 2 3 4 5 6 7 8 9 Years in Service Product B has a lower acquisition cost but needs repaired more often and at greater expense 1 1
- 12. RELIABILITY RELATED COSTS Prevention activities - intended to ensure that processes work without fail, such as failure mode and effects analysis, training and preventive maintenance Appraisal activities - how well processes such as product and process approvals are actually working via activities such as inspection and testing Failure costs - related to failures that do occur and are further classified as internal (failure identified before it reached the customer) or external (detected after reaching the customer). The time and expense of reprocessing failed products or services and investigating failures could fall into either failure category, depending on when the event occurs. Warranty costs are decidedly external failures. 1
- 13. BATHTUB CURVE Number of Infant failures Mortality Time 1 3
- 14. BATHTUB CURVE Number of Infant failures Mortality Useful Life Time 1 4
- 15. BATHTUB CURVE Number of Infant Wearout failures Mortality Useful Life Time 1 5
- 16. RELIABILITY PREDICTABILITY Reliability is the probability that an item can perform its intended function for a specified interval under stated conditions, However: We do not have access to all products in the field, particularly those that have not failed We cannot specify a period of time to measure reliability We cannot specify a set of operating conditions 1 6
- 17. RELIABILITY IS FAILURE MODE AVOIDANCE Reliable products are robust and mistake free Failure modes of our products are primarily that something breaks or performance degrades Avoiding failure modes will decrease the probability of failure Reliability prediction is not easy for many industries We need to reduce variation and the sensitivity to noise (ie. Six Sigma and P-diagram) 1 7
- 18. P-DIAGRAM P-Diagram Noise Factors 1 2 3 Input Signal Ideal Function System Error State Control Factors 1 1 2 2 3 3 4 5 1 8
- 19. P-DIAGRAM DEFINITIONS Ideal Function – primary intended function of the design Input Signal – energy which is put into the system to make it work Error State – undesirable output of the system Control Factors – features that can be controlled by design or process 1 9
- 20. NOISE FACTORS Sources of disturbing influences that can disrupt ideal function, causing error states which lead to quality problems Product variations Changes over time/usage Customer duty cycle External environment System interactions 2 0
- 21. P-DIAGRAM EXAMPLE P-Diagram Self contained jet pack Noise Factors 1. Fuel volatility 2. Wind 3. Temperature Input Signal Ideal Function Throttle position System Lifts person off ground Error State 1. No ignition Control Factors 1. Material properties 2. Flame too large 2. Design 3. Manufacturing process 4. Assembly process 2 1
- 22. FMEA Bring P-Diagram List error states (potential failure modes) Ties together P-Diagram and Testing Living and changing document Discovery, legal document Ultimate failure mode avoidance document 2 2
- 23. TESTING Captures the effects of noise factors over useful life Generates a measurable event Generates a failure of degradation of the ideal function Generates results which are directly correlated with real-world performance Can be accelerated for reliability improvement experiments (HALT, HASS) 2 3
- 24. HIGHLY ACCELERATED LIFE TESTING HALT testing 2 4
- 25. STRATEGIES FOR IMPROVEMENT Change the design concept Make basic current design assumptions insensitive to the noises (beef up design, use Design of Experiments, redundancy) Reduce or remove the noise factor(s) Insert a compensation device Send the error state/noise elsewhere else where it will do less harm (disguise effect) 2 5
- 26. FRACAS Failure Reporting, Analysis and Corrective Action System Prioritizes field failures Root Cause Investigation Teams Needs input from Team members Drives problems to closure Documentation in central location Closed Loop System 2 6
- 27. SUMMARY Application of Reliability in different industries Importance of Reliability – Cost Impact Bathtub Curve Predictability vs. Failure Mode Avoidance P-Diagram Strategies for Improvement 2
- 28. WHERE TO GET MORE INFORMATION Reliasoft - http://www.reliasoft.com/ RIAC - http://src.alionscience.com/src/training.do Hobbs Engineering - http://www.hobbsengr.com/ ASQ Reliability Div. - http://asq.org/reliability/ SRE - http://www.sre.org/ You’ll find many more on the web…. 2 8
- 29. REFERENCES Dr. Tim Davis -“Science, engineering, and statistics”. Applied Stochastic Models in Business and Industry, 2006, Vol. 22, Issue 5- 6, pp. 401-430 Dr. Vasiliy Krivstov Dr. Paul Barringer Reliasoft 2