Reliability: Interpretation and Control

1. RME-085
Total Quality Management
Topic: Reliability: Interpretation of test results and control
By:
Dr. Vinod Kumar Yadav
Department of Mechanical Engineering
G. L. Bajaj Institute of Technology and Management
Greater Noida
Email: vinod.yadav@glbitm.org

2. Life and Reliability testing plans
• Product needs to be used for Reliability testing
(DT or NDT).
• Testing may affect the cost and economy of the
product.
• Final products are generally tested however, parts
may be tested in case of any problem [1].
• Product testing needs laboratories.
• Modern approach for testing is to simulate the
product under real environment.
Product Life test (Types)
Time
terminated
Failure
terminated
Sequential
Product
Life Test
Failure-Terminated life test. Terminated when a pre-assigned number of failures occurs to the sample. Acceptance
criteria for the lot are based on the accumulated item test times when the test is terminated [1].
Time-Terminated life test. This type of life-test sampling plan is terminated when the sample obtains a predetermined
test time. Acceptance criteria for the lot are based on the number of failures in the sample during the test time [1].
Sequential life test. None of the above two conditions for decision making is fixed in advance. Rather, decisions depend on the
accumulated results of the life test. The expected test time and the expected number of failures required to reach a decision as to lot
acceptability are less than the failure terminated or the time-terminated types [1].
Aim: Mean time
determination

3. • Testing may be conducted with replacement of
a failed unit or without replacement.
• With replacement occurs when a failure is
replaced with another unit. Test time continues
to be accumulated with the new sample unit.
• This situation is possible when there is a
constant failure rate and the replaced unit has
an equal chance of failure.
• The without-replacement situation occurs
when the failure is not replaced.
Product Life test (Types)
Tests are based on one or more of the
following four characteristics:
1. Mean Life the average life of the product.
2. Failure Rate the percentage of failures per
unit time or number of cycles.
3. Hazard Rate the instantaneous failure rate
at a specified time. This varies with age except
in the special case of a constant failure rate,
where the failure rate and hazard rate are the
same. The Weibull distribution is applicable
and the hazard rate increases with age if the
shape parameter b is greater than 1 and
decreases with age if the shape parameter is
less than 1.
4. Reliable Life the life beyond which some
specified portion of the items in the lot will
survive. The Weibull distribution and the
normal distribution as they pertain to the wear-
out phase are applicable.
Note: The contents used in this slide is being used for academic purposes only, and is intended only for students
registered in B.Tech Mechanical Engineering at AKTU Lucknow in VIII semester 2019-20, and is not intended for
wider circulation.

4. • Systems require individual components to be
highly reliable.
• Warranty data provides one of the best sources
for repairable products. However, not all
products are repairable.
• Planned effort required to produce highly
reliable products while design phase. Still there
are chances of failure.
• Demonstrating high statistical confidence in a
reliability measure with tests of reasonable size
and length is difficult.
• To optimize this problem, the time period must
be compressed.
• Accelerated life testing (ALT) provides
statistical assurance that reliability goals can be
met.
Product Life test design
Note: The contents used in this slide is being used for academic purposes only, and is intended only for students registered in B.Tech Mechanical Engineering at AKTU Lucknow in VIII semester
2019-20, and is not intended for wider circulation.
Accelerated life testing (ALT) Types:
1. Use-rate acceleration refers to products that
are not in continuous use; therefore, test units
can be run more frequently than is normal [1].
2. Product aging acceleration refers to
exposing test units to severe temperature,
moisture, air quality, or other environmental
conditions. These test conditions accelerate the
physical or chemical degradation process that
causes certain failure modes [1].
3. Product stress acceleration refers to the
application of increased stress such as
vibration, voltage, pressure, or other types of
stress [1].

5. Zero defect
Note: The contents used in this slide is being used for academic purposes only, and is intended only for students registered in B.Tech Mechanical Engineering at AKTU
Lucknow in VIII semester 2019-20, and is not intended for wider circulation.
ZD: A management tool aimed at the
reduction of defects through prevention.
ZD: Directed at motivating people to prevent
mistakes by developing a constant, conscious
desire to do their job right the first time [2].
Aim: Zero defect product
ZD: Ideal concept (impractical)
More precisely: Products with near
perfection.
Setting
up
targets
Pledge
Inspection
Motivation
Defect
cause
removal
Cause
identific
ation
Zero
Defect
concept
Steps to ensure zero defect

6. Quality Circle (W. Edwards Deming - 1950)
Note: The contents used in this slide is being used for academic purposes only, and is intended only for students registered in B.Tech Mechanical Engineering at AKTU Lucknow
in VIII semester 2019-20, and is not intended for wider circulation.
- A group of workers who do the same or similar work, who meet
regularly to identify, analyze and solve work-related problems.
- It consists of minimum 3 and maximum 12 members [3]
- Small size is preferred.
- Circle is led by a supervisor or manager and presents its solutions
to management.
- Workers also implement the rectifications so as to improve the
performance of the organization.
- Popular in 1980, but later adopted by many organizations.
- The first circles started at the Nippon Wireless and Telegraph
Company; the idea then spread to more than 35 other companies
in the first year.
- By 1978 , there were more than 1 million quality circles.
- By 2015: More than 20 million quality circles in China ( As per
President: Chinese Quality Circles Society at the ICSQCC
Conference in Beijing 30 August 1997).
Quality Circle[4]

7. References:
[1] Dale H. Besterfiled. A Text book on Quality Improvement. 9th Edition. Pearson (ISBN 10: 0-13-262441-9) pp: 169-184.
[2] Halpin, James F. (1966). Zero Defects: A New Dimension in Quality Assurance. New York City: McGraw-Hill.
[3] https://en.wikipedia.org/wiki/Quality_circle#cite_note-1 (Accessed on 11.04.2020).
[4] https://www.sketchbubble.com/en/presentation-quality-circle.html (Accessed on 11.04.2020).

8. Thank you