vdoc

Chapter 19
B. Statistical Process Control
The concept of quality is centuries old. However, the concept of statistical
quality control (SQC) is less than a century old. SQC is merely a set of interrelated
tools such as statistical process control (SPC), design of experiments
(DOE), acceptance sampling plans, and other tools that are used to monitor and
improve quality. SPC is one of the tools comprising SQC. SPC consists of several
tools that are very useful for process monitoring. The quality control chart, which
is the center of our discussion in this chapter, is one of the tools comprising SPC.
Walter A. Shewhart presented the first quality control chart in 1924.
Part IV.B
BASIC CONCEPTS OF QUALITY AND ITS BENEFITS
Different authors have defined the concept of quality in different ways. We define
it as defined by Deming: a product is of good quality if it meets the needs of a
customer and the customer is glad that he or she bought that product. The customer
may be internal or external, may be an individual or a corporation. If
a product meets the needs of the customer, the customer is bound to buy that
product again and again. On the contrary, if a product does not meet the needs of
a customer, then he or she will not buy that product even if he or she is an internal
customer. Consequently, that product will be deemed of bad quality and eventually
the product is bound to go off the market.
Other components of a product’s quality are its reliability, how much maintenance
it demands, and, when the need arises, how easily and how quickly one can
get it serviced. In evaluating the quality of a product, its attractiveness and rate of
depreciation also play an important role.
As described by Deming in his telecast conferences, the benefits of better
quality are numerous. First and foremost is that it enhances the overall image and
reputation of the company by meeting the needs of its customers and thus making
them happy. A happy customer is bound to buy the product again and again.
Also, a happy customer is bound to tell the story of a good experience with the
product to friends, relatives, and neighbors. Therefore, the company gets firsthand
publicity without spending a dime. This obviously results in more sales and
higher profits. Higher profits lead to higher stock prices, which mean higher net
worth of the company. Better quality provides workers satisfaction and pride in
their workmanship. A satisfied worker goes home happy, which makes his/her
family happy. A happy family boosts the morale of the worker, which means more
dedication and more loyalty to the company. Another benefit of better quality is
246