Chapter 19 Summary What is failure Why failures happen How do we measure failures Detection and analysis of failures How operations can improve their reliability How should the operations should recover from the failures ID: 477628
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Slide1
Failure Prevention and recovery
Chapter -19 Slide2Slide3
Summary
What is failure?
Why failures happen?
How do we measure failures?
Detection and analysis of failures.
How operations can improve their reliability?
How should the operations should recover from the failures? Slide4
Failure Slide5
Failure Slide6
Failure Slide7
Failure Slide8
What is failure?
At its simplest ‘failure’ is when something does not work as it should do. If the shop assistant who sells you an item of clothing ‘fails’ to inform you of the fact that it should be dry cleaned, it is technically a failure. Yet usually in operation management, we use the term failure to denote a more dramatic event. Usually we mean something stopping to do what it should do. So a piece of material fails, or a process fails.Slide9
Why do operations fail?
There are various reasons for the operations failures:
Design failures
Facilities failures
Supplier failures
Customer failures
Environmental failures Slide10
Design failures
A design may look fine on paper, but in real circumstances the limitations will become clearer.
Design failures happen due to two different situations:
Because miscalculating or overlooking a characteristic of demand – process fail to adjust with demand. For example a company process is designed to manufacture 3 televisions per hour, but the demand is to manufacture 7 televisions per hour. Slide11
Unexpected circumstances – product size on the design becomes different from demanded size. Slide12
Why systems fail
Design failures
Facilities failures
Staff failures
Failures inside the operation
Supply failures
Customer failuresSlide13
B. Facilities failure
Failures with machines, equipments, buildings, and fittings.
c. People failure
People failures come in two types:
Errors and Violations
Errors – are mistakes in judgments (run motorbike on reserve petrol)
Violations – are doing the things contrarily to the operating procedure. (driver avoiding changing the engine oil, causing major problems to engine)Slide14
D. Supplier failure
Failure in the delivery or quality of goods and services. (a music band of the hotel fails to turn – in)
E. Customer failure
Misuse of products and services from the production.
F. Environmental disruption-related failure
All the causes outside the
opration
. Example hurricanes, floods, lightning, temperature, fire, crime, theft, terrorism. Slide15
Measure failures
Failures are usual happening as human failure.
For example :
A machine failure may happen due to the poor design or maintenance .
A delivery failure by someone's errors to manage supply schedule.
Customers mistake, because no one to instruct the customer Slide16
So, failures can be controlled to an extent, again an organization learn from failures. Thereby we call failures as opportunities.
There are three main ways of measuring failure:
Failure rates – checking how often failure occurs.
Reliability - checking the chances of an occurrence of failure.
Availability – checking the amount of available useful operating time. Slide17
FR (Failure Rate) measuring
The number of failures occurring over a period of time. The failure of an airport security system can be measured by measuring the failure of security breaches.
FR=
number of failures
× 100
total numbers of products testedSlide18
Failure over-time – the ‘bath tub’ curve
Failure is a function of time. Different stages the probability for failing will be different.
The curve that describes failure probability is called ‘bath-tub’ curve. According to this curve the failure probability is high at beginning and end of the life cycleSlide19
There are three distinct stages.
The ‘infant-mortality’ or ‘early-life’ stage where early failures occurred by defective parts or improper use.
The ‘normal-life’ stage when the failure rate is usually low and constant.
The wear-out stage – when the failure rate increases as it reaching the end of its working life. Slide20
How
failure is measured
Time
Failure rate
‘Infant-mortality’ stage
Normal-life stage
Wear-out stageSlide21
Reliability measuring
It measures the ability of a system, product or service to perform as expected over time.
Rs = R1
×R2 ×R3 ×
Rn
…..
Rs = reliability of system
Here we consider that a single failure in a component of process causing failure to the whole components.
So the more the components in a system, the lesser will be the reliability. Slide22
MTBF (MEAN TIME BETWEEN FAILURES)
MTBF =
OPERAITNG HOURS
NUMBER OF FAILURES
Availability
The degree to which the operation is ready to work. An operation is not available if it has either failed or is being repaired followed by a failure. Slide23
Failure prevention and recovery
There are three sets of activities which relate to failure:
1. The first – understanding what failures are occurring in the operation and why they are occurring.
2.Second – examine or find the ways to reduce chances for failure and minimize consequences of failures.
3. Third – make plans and procedures to help the organization from recovering when they occur. Slide24
The three tasks of failure prevention and recovery
Failure detection and analysis
Finding out what is going wrong and why
Improving system reliability
Stopping things going wrong
Recovery
Coping when things do go wrongSlide25
Mechanisms to detect failure
There are six techniques to find out the failure:
In-process checks – employees check that the service is acceptable during the process itself (restaurants )
Machine diagnostic checks – a machine is tested by putting it through many activities. ( computer service)
Point of – departure – interviews - the staff may formally or informally check that the services has been satisfactory.
Phone surveys – used to solicit opinions about products or services.
Focus groups - group of customers are brought together to discover problems or finding out attitude towards products or services . Slide26
Complaint feed back cards and questionnaires
Many organizations using them for collecting views about products or services.
Failure Analysis
Understand why its has occurred.
Accident investigation – specifically trained staff analyze the cases of accident.( airplane, road accident)
Failure traceability - making sure an operation can trace (
fing
proof or evidence)
Complaint analysis – analyze the complaints.
Slide27
CIT or critical incident analysis
Finding out the satisfying and non – satisfying factors from customers. Slide28
How failure is detected and analyzed
–
in-process checks
–
accident investigation
–
failure mode-and-effect analysis
–
fault-tree analysis
Failure detection mechanisms include:
Failure analysis procedures include:
–
point-of-departure interview
–
machine-diagnostic checksSlide29
Failure mode and effect analysis
Identify the product or service or process that are important in determining the effect of failures. Or identifying failures before they happen by providing checklist procedures.
It has three steps
What is likelihood that failure will occur?
What would the consequence of failures be?
How likely a failure to be detected before affecting customers?. Slide30
Based on the above questions, we use the RPN or Risk Priority number and find out the cause of failure.
There are seven steps involved in this
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Failure
Severity of consequence
Effect on customer
Normal operation
Probability of failure
Degree of severity
Likelihood of detection
Risk priority number
Failure modes effects analysisSlide32
Fault-tree analysis
It is a logical procedure starting from a failure or potential failure and works back- wards to indentifying all possible causes and origins. Slide33
Fault-tree analysis for below-temperature food
being served to customers
Food served to customer is below temperature
Key
AND node
OR node
Cold plate used
Plate taken too early from warmer
Plate warmer malfunction
Oven malfunction
Timing error by chef
Ingredients not defrosted
Plate is cold
Food is coldSlide34
Improving process reliability
The responsibility of this step of operational managers is to prevent failures, we can do it by following 4 steps.
Design out fail points.
Build redundancy
Fail-
safeing
Maintenance Slide35
a. Design out fail points
We can do it by proper product/service designing, by quality planning and control, by process controlling.
b. Redundancy
Building redundancy to an operation means, having a back-up system. (airplane, kidney, two red lights in cars) Slide36
c.fail-safeing
Coming from Japanese methods of operations improvement. It is known as
Poka
-yoke in Japan, which means prevent. So the
Poka
-Yoke are devices used against failures. Slide37
3.5 inch diskette cannot be inserted unless it is orientated correctly. This is as far as a disk can be inserted upside-down. This feature, along with the fact that the diskette is not square, prohibits incorrect orientation. It is a control method.
Warning lights and chimes alert the driver of potential problems. These devices employ a control method
and
a warning method.
Poka-yoke (fail-safing)Slide38
Filing cabinets can fall over if too many drawers are pulled out. For some filing cabinets, opening one drawer locks all the rest, reducing the chance of the filing cabinet tipping. It is a control method.
The window in the envelope is not only a labour saving device. It prevents the contents of an envelope intended for one person being inserted in an envelope address to another. It is a control method.
Poka-yoke (fail-safing)Slide39
Examples for Poke-yoke techniques
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Maintenance
Maintenance is how organizations try to avoid failure by taking care of their physical facilities.
Benefits of maintenance
1. it enhances safety
2.It enhances reliability
3. It enhances quality
4. Low operation cost
5. Longer life
6. Higher end value ( can be sued as second hand)Slide40
Three basic approaches for maintenance
Run to breakdown ( RTB) - operate till something fails and do maintenance.
Preventive Maintenance – eliminate or reduce chances of failure by servicing the facilities.
Condition-based maintenance – perform maintenance only when facilities required. It is
appliccable
for expensive facilities. Slide41
Mix of maintenance approaches Slide42
A mixture of maintenance approaches is often used –
in a motor car, for example
Use condition-based monitoring maintenance
Use run-to-breakdown maintenance
Use preventive maintenanceSlide43
Total productive maintenance
Means the productive maintenance carried out by all employees through small group activities. So TPM means maintenance management.
Five goals of TPM
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Reliability-centered maintenance
It is another method of maintenance where different types of maintenance for different parts of a process. Slide45
One part in one process can have several different failure modes, each of which requires a different approach
Cutters
Shredding process
Failures
Time
Cutter ‘wear out’ failure pattern
Solution
Preventive maintenance before end of useful lifeSlide46
One part in one process can have several different failure modes, each of which requires a different approach
Cutters
Shredding process
Failures
Time
Cutter ‘shake loose’ failure pattern
Solution
Ensure correct fitting through trainingSlide47
Recovery
The activities designed to adjust with the failures are known as recovery.
Failure planning
The procedures which allow the operation to recover from failure is called failure planning Slide48
What’s happened
What consequences
Inform
Contain
Follow up
Find root cause
Engineer out
Analyze failure
Plan recovery
The stages in failure planning
Discover
Act
Learn
PlanSlide49
Procedures of business continuity
Avoid or recover from failures and keep business going.
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