fmea class add on
TRANSCRIPT
Prof G.R.C.Nair
FMEA
Prof GRC Nair
What is FMEA?
Prof G.R.C.Nair
• Failure • Modes• Effects• Analysis
Prof G.R.C.Nair
Reasons to do FMEA• Define and guide a logical design
process • Identify, quantify, and reduce design
risk • Provide a traceable document for
design and development • Justify design activities • Provide a means for continuous
product improvement
Prof G.R.C.Nair
Scope of FMEA• The FMEA is a team function
• All team members must participate• Multi-disciplinary expertise and input is beneficial • Input from all engineering fields is desirable
• Representatives from all areas (not just technical disciplines) are generally included as team members • The DFMEA will be refined and evolve with the
product • Numerous revisions are required to obtain the full
benefit of the DFMEA• The DFMEA should include all systems, sub-systems,
and components in the product design
Availability
• Measure of Availability
MTRMTBFMTBFA
MTBF = mean time between failures
MTR = mean time to repair
MTTF = mean time to fail
MTBF or MTTF= (T1+T2+--+--+TN)/NMTR = (t1+t2+t3+---+---+tN)/ N
Prof G.R.C.Nair
Availability is also called UTRUTR = Up time ratioDTR = down time ratioUTR + DTR = 1
System availability can be increased by • Increasing MTBF• Decreasing MTR• Or any favourable combination
Prof G.R.C.Nair
Reliability• Generally defined as the ability of a product to perform as expected, over a period of time
• Formally defined as the probability that a product, piece of equipment, or system performs its intended function adequately for a stated period of time, under specified operating conditions.
Prof G.R.C.Nair
Types of Reliability
• Inherent reliability – predicted by product design.
• Achieved reliability – observed during use.
Prof G.R.C.Nair
Cumulative Failure Curve
Prof G.R.C.Nair
Average Failure Rate
Prof G.R.C.Nair
Bath Tub Curve
“Infant mortality period”/ Debug period
Prof G.R.C.Nair
To take care of ‘Infant Mortality phase’, consider debugging team, Warrantee,free service, free replacement, pre testing for that period before release to market etc
Prof G.R.C.Nair
Reliability Measurement • Failure rate () – number of
failures of break downs per unit time.
• Alternative measures•Mean time to fail (MTTF)•Mean time between failures(MTBF)MTBF orMTTF
Prof G.R.C.Nair
Reliability Function
1
R(t)
R(t)
Time t
Prof G.R.C.Nair
Reliability Function
• Reliability for a period of ‘t’ r(t) = e-t
• Probability of failure within time ‘t’
f(t) = 1 – e-t Prof G.R.C.Nair
Exercises• MTBF = 500 hrs • Find Also find r (50, 400, 800,
1000,2000)
Prof G.R.C.Nair
System Reliability
Depends on ,• Component Reliability• Number of Components• The Configuration
Prof G.R.C.Nair
Series Configuration
R = r1 * r2 * r3 *... rn
1 2 n
Prof G.R.C.Nair
Parallel Configuration
R = 1 – [(1 - r1) (1 - r2)…… (1 – rn)]
1
2
n
Prof G.R.C.Nair
Optimum Reliability
Reliability
costProf G.R.C.Nair
Prof G.R.C.Nair
Frequency Ranking
Severity Rankings
Prof G.R.C.Nair
• RPN (Risk Priority Number) 1 to 1000• Higher the number higher the risk• RPN= SxOxD each 1 to 10 increasing• S= Severity of failure - 1 to 10• O= Prob of Occurrence- 1 to 10• D= Difficulty in identifying 1 to 10
Prof G.R.C.Nair
Prof G.R.C.Nair
Classification of “Risk”
PossibilityOf Occurrence
Severity of Outcome
High Risk
Moderate Risk
Low Risk