1. Reliability is the ability of a product to perform its intended function for a specified period of time. Achieving high reliability is important for reputation, customer satisfaction, reducing warranty costs, and gaining competitive advantages. 2. Product reliability can be improved through careful product design, testing, and production. Design approaches include overdesign, redundancy, derating parts, and using reliable parts. Testing evaluates parts, environments, and identifies failures. Production focuses on analyzing failures and implementing corrective actions. 3. Assessing and controlling reliability is crucial because customers expect products to work as intended. Unreliable products can destroy a company's reputation and take a long time to recover from. Reliability also significantly impacts economic

1. Product Reliability
Rakesh K M
Assistant Professor
Department of Mechanical Engineering
JSS Academy of Technical Education Noida

2. Reliability
The ability of an item to perform a required function under stated conditions for a stated
period of time. It is usually denoted as probability or as a success .
Fig: Need for Reliability
Product: A product could be a Goods or Service intended to address or satisfy or create
needs of/for customers.
Or
Product is somethings sold by an enterprise to customer for money.
Or
Product is a set of attributes offered to customers in order to solve their problems or fulfil
their needs.

3. Why reliability for a product ?
There are a number of reasons why reliability is an important for a product
1. Reputation: A company's reputation is very closely related to the reliability of its products.
The more reliable a product is, the more likely
the company is to have a favourable reputation.
2. Customer satisfaction: While a reliable product may not dramatically affect customer satisfaction
in a positive manner, an unreliable product will negatively affect customer satisfaction severely. Thus
high reliability is a mandatory requirement for customer satisfaction.
3. Warranty costs: If a product fails to perform its function within the warranty period, not only the
replacement and repair costs will negatively affect profits, there may be an unwanted negative publicity.
Introducing reliability analysis is an important step in taking corrective action, ultimately leading to a
product that is more reliable.

4. 5. Repeat business: A concerted effort towards improved reliability shows existing customers that a
manufacturer is serious about its product and committed to customer satisfaction. This type of attitude
has a positive impact on future business.
4. Cost analysis: Manufacturers may take reliability data and combine it with other cost information to
illustrate the cost-effectiveness of their products. This life cycle cost analysis can prove that although the
initial cost of a product might be higher, the overall lifetime cost is lower than that of a competitor's because
their product requires fewer repairs or less maintenance.
6. Customer requirements: Many customers in today's market demand that their suppliers have an
effective reliability program. These customers are conscious of the benefits of reliability analysis from their
own experiences.
7. Competitive advantage: Many companies will publish their predicted reliability numbers to help gain
an advantage over their competitors who either do not publish their numbers or have lower numbers.

5. How to achieve product reliability?
Stage:1 Product Design
a) Over design : Specifying parts having higher ratings and more safety margins beyond
requirements
Ex: Use of 1HP motor instead of 0.5hp
Over design will increase the weight, volume and cost of the product.
b) Redundancy : Use of more than one part for the same function.
“Backup”- not desirable for products
c) Parts derating : Use of high rated parts for less rating needs is called parts derating.
Ex: Use of 400 V capacitor when actual requirement is only 200V.
d) Parts engineering : Reliable parts which conform to more rigid specification and with proven
performance should be used.
Stage: 2 Product Testing
Stage:1 Product Design
Stage: 3 Production and Usage
Product reliability can be achieved in design and testing methods as follows

6. Stage: 2 Product Testing
a) Parts burn-In : During testing, the various parts are subjected to an extended test for the
purpose of detecting and removing those parts which have some inherent weakness.
This eliminates most of the early part failures.
b) Environmental testing: Product is tested under its working environmental conditions such
as temperature, humidity, shock, vibrations etc.
Stage: 3 Production and Usage
a) Feedback information analysis : Reporting of failures during fabrication and testing and
usage followed by analysis of failure and corrective action for developing reliable products.
b) Failure Mode Effect Analysis : FMEA

7. Why is the assessment and control of product reliability
important?
We depend on, demand, and expect reliable products
Shipping unreliable products can destroy a company's reputation
It takes a long time for a company to build up a reputation for reliability, and only a short time to be branded as
"unreliable" after shipping a flawed product
In today's technological world nearly everyone depends upon the continued functioning of a wide array of
complex machinery and equipment for their everyday health, safety, mobility and economic welfare. We expect our
cars, computers, electrical appliances, lights, televisions, etc. to function whenever we need them - day after day, year
after year.
When they fail the results can be catastrophic: injury, loss of life and/or costly lawsuits can occur. More often,
repeated failure leads to annoyance, inconvenience and a lasting customer dissatisfaction that can play havoc with the
responsible company's marketplace position.
Reliability is a major economic factor in determining a product's success

8. The following sections will define some of the concepts, terms, and models we need to describe, estimate
and predict reliability.
Basic terms and models used for reliability evaluation
Repairable system :
A repairable system is one which can be restored to satisfactory operation by any action, including parts
replacements or changes to adjustable settings. When discussing the rate at which failures occur during system
operation time (and are then repaired) we will define a Rate of Occurrence of Failure (ROCF) or "repair rate".
Non-repairable population
A non-repairable population is one for which individual items that fail are removed permanently from the
population. While the system may be repaired by replacing failed units from either a similar or a different
population, the members of the original population dwindle over time until all have eventually failed.

9. Is defined as
R(t)=S(t)=the probability a unit survives beyond time t
Reliability Function R(t) or Survival Function S(t) :
Since a unit either fails, or survives, and one of these two mutually exclusive alternatives must occur, we have
Failure (or hazard) rate: The failure rate is the rate at which the population survivors at any given instant are
"falling over the cliff"
"Bathtub" curve : A plot of the failure rate over time for most products yields a curve that looks like a
drawing of a bathtub
Repair rate or ROCOF : The Repair Rate (or ROCOF) is the mean rate of failures per unit time

10. 2. https://www.itl.nist.gov/div898/handbook/apr/apr.htm
1. https://shodhganga.inflibnet.ac.in/bitstream/10603/51738/8/08_chapter%201.pdf
References