Efficient Plant Jan./Feb. 2021 - 6

column | implementations

Reliability
And Quality
Are Related
Dr. Klaus M. Blache
Univ. of Tennessee Reliability
and Maintainability Center
(RMC)

Reliability and quality cannot be treated
as separate entities and both are affected
throughout the entire product life cycle.

Based in Knoxville, Klaus M. Blache
is director of the Reliability &
Maintainability Center at the Univ. of
Tennessee, and a research professor in
the College of Engineering. Contact him
at kblache@utk.edu.

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EP2101implementations.indd 6

CCORDING TO THE American Society for Quality (ASQ),
Milwaukee, (asq.org): " Reliability
has sometimes been classified as 'how quality
changes over time.' The difference between
quality and reliability is that quality shows
how well an object performs its proper
function, while reliability shows how well this
object maintains its original level of quality
over time, through various conditions. "
Reliability and quality are interrelated.
For high quality you need high data integrity.
Operations require reliable power. Proper
skill level enables precision maintenance,
which ensures longer machine reliability.
Standardized maintenance improves the
repeatability of best work practices.
Weibull analysis can be used to monitor
reliability growth and identify warranty
times. If you buy a product and it breaks
within the warranty period, you're consoled
that the repair/replacement cost is covered.
Either the manufacturer has not performed
a good warranty break-even calculation, or a
replacement is less expensive than the repair.
After the warranty period, the product may
break more often, and repairs will be at your
expense. Understanding and managing these
relationships supports higher reliability,
quality, and customer satisfaction.
When purchased, an automobile that
is comfortable, easy to drive, gets expected
mileage, and is safe and dependable is considered high quality. Similarly, a new machine
that consistently produces within specification and has no downtime is also considered
high quality. Quality refers to the inherent
capability (how well it conforms to specifications/requirements) at the start of machine or
product use. Reliability is what happens after
that with daily use.
As explained in Practical Reliability Engineering, (Patrick D. T. O'Connor, John Wiley
& Sons Ltd, 2002, Fourth Edition):

" .... times to occurrence can seldom be
forecast accurately. Reliability is therefore an
aspect of engineering uncertainty. Whether
an item will work for a particular period is a
question that can be answered as a probability. This results in the usual engineering
definition of reliability as: The probability
that an item will perform a required function
without failure under stated conditions for a
stated period of time. "
The relationship of reliability and quality
to producing good product is also evident in
the OEE (Overall Equipment Effectiveness)
calculation. OEE of a process/manufacturing
facility is calculated as the product of three
components:
OEE = Availability x Performance x Quality
Availability is the percentage of scheduled
time the machine or operation is available. It
includes downtime losses and uptime. Performance is the speed at which the machine
or operation functions, as a percentage of
its designed speed. Quality is the number of
good units produced as a percentage of the
total units started.
Reliability has a probability component
and comprises various elements such as
availability (as described above), quality over
time, and durability. Reliability and quality
are affected throughout the entire product
life cycle. All persons in these areas need to
understand and be involved, but it needs to
be managed holistically at the systems level.
During these challenging times I've
noticed more quality issues in various
companies, things such as lax processes, poor
follow-up, poor craftsmanship, and insufficient quality control. This is not the time to
let reliability and quality slip. " A company
cannot buy its way into quality-it must be
led into quality by top management. " (W. Edward Deming, Out of Crisis, MIT, 1986). EP

JAN/FEB 2021

1/26/21 12:39 PM

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Efficient Plant Jan./Feb. 2021

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