Module 4 Maintenance Management Flashcards
Why do products need to be designed with more attention to their reliability, for manufacturers and consumers?
Products need to be designed with more attention to their
reliability
For manufacturers:
- Competition: perceived quality of reliable products
- Customer requirements: customers decide on the desired reliability
levels
- Warranty and post-sales service cost: a significant financial burden
when products are unreliable
For consumers:
- Safety: failures can be dangerous
- Inconvenience: delays at airports, car breakdowns. . .
- Cost: unreliable products costs customers money
What is important to study reliability?
Understand failure patterns and hence improve designs
We need to understand how and why products fail to improve
quality
WTo be able to develop effective maintenance policies
What is failure and reliability?
Failure:
Is any event, or collection of events, that causes a system
to lose its functionality (its ability to perform a specified function
according to the specified requirements under the specified
operating conditions).
Reliability:
Is the ability of an item to maintain the required
function for a specified period of time (e.g. mission time) under
given operating conditions. It is the likelihood that a system will
NOT fail during the stated period.
What is the Weibull distribution?
see docs
Why use reliability measures?
Quantify the effectiveness of a system
Depends on what is expected from the system and what we are
trying to measure
Examples:
- An assembly workstation in a manufacturing process: continuously
available for the coming 20 years
- A F1 race car: completes its mission (i.e. the race)
What is the failure function?
see docs
What is a reliability function?
see docs
Consider an item that survived up to time t. What is the probability that
it will fail within time s from t, i.e., between t and t + s?
see docs
What is the failure rate or hazard rate?
see docs
What is the perfect vs. imperfect repair?
Consider an item that is subject to failure. When a failure occurs,
the item is repaired. We can either perform a perfect repair or an imperfect repair.
Perfect repair:
- After the repair, the repaired system returns to the state
“as-good-as-new”.
- The repair moment is modeled as a renewal process
- However, perfect repairs don’t exist in real-life even in case a
complete overhaul with spare parts is performed (unless the failed
system is replaced by a new one)
Imperfect repair:
- Repairs are in general imperfect
- In this course we will consider the special case of minimal repair
- After minimal repair, the state of the repaired system is
“as-bad-as-old”
What is minimal repair?
see docs
What is maintenance?
Maintenance: The combination of all technical and administration
actions, including supervision actions, intended to retain an item
in, or restore it to, a state in which it can perform a required
function
Objectives:
- Reduce the consequences of failures
- Increase the up time and the safety of a system
- Maintain reliability
- Maintain availability
- Reduce overall maintenance cost and hence minimize life cycle
cost
Maintenance concepts are developed already in the design stage
of an item. It should be clear what the maintenance tasks will be,
the frequencies and time, the skills needed, spare parts and other
resources.
What are the differences between acquisition costs, maintenance costs and downtime costs?
The acquisition costs of a high
tech system are high, but a
considerable cost during the
total product life cycle is derived
from maintenance and
downtime.
Maintenance costs include
spare parts, service engineers,
infrastructure and management.
Downtime costs include
reduced output of a production
process, as well as indirect
costs such as loss of reputation
or loss of future revenues.
What is the failure-based maintenance policy?
Corrective maintenance tasks are performed after failure
For items for which failure doesn’t affect the safety of the user and
with limited economic consequences
Systems have built in redundancy
Advantages:
- Full utilization of the item’s operating life
- Get the maximum value of the item
Disadvantages:
- Failures occurs at inconvenient times
- Maintenance activities cannot be planned
- It demands a lot of resources
What is age-based maintenance policy?
Preventive maintenance is performed at fixed intervals to reduce
the probability of
failure occurrence
Items for which failure has “catastrophic” consequences
The condition of the system cannot be monitored (it is unpractical
or uneconomical)
Advantages:
- Maintenance tasks can be planned and coordinated
- The cost of production lost is reduced
- Safety is improved
Disadvantages:
- Unnecessary tasks will be carried out
- Items will not be utilized for their complete operating life
