Page 205 - DMGT524_TOTAL_QUALITY_MANAGEMENT

Total Quality Management

Notes Objectives

After studying this unit, you will be able to:
Explain Statistical Process Control

Discuss Statistical Quality Control
Describe Process Capability
Explain the Concept of Control Charts
Elaborate the Design of Experiment and Statistical Process Control

Explain the Statistical Fundamentals in SPC
Introduction

The concept of TQM is basically very simple. Each part of the organization has customers some
external and many internal. Identifying what the customer requirements are and setting about
to meet them is the core of a total quality approach. This requires a good management system,
methods including Statistical Quality Control (SQC) and teamwork.
A well-operated, documented management system provides the necessary foundation for the
successful application of SQC. Note, however, that SQC is not just a collection of techniques. It is
a strategy for reducing variability, the root cause of many quality problems. SQC refers to the
use of statistical methods to improve or enhance quality for it customer satisfaction. However,
this task is seldom trivial because real world processes are affected by numerous uncontrolled
factors. For instance, within every factory, conditions fluctuate with time. Variations occur in
the incoming materials, in machine conditions, in the environment and in operator performance.
A steel plant, for example, may purchase good quality ore from a mine, but the physical and
chemical characteristics of ore coming from different locations in the mine may vary. Thus,
everything isn’t always “in control.”

14.1 Statistical Process Control (SPC)

The application of statistical techniques to control a process; often used interchangeably with
the term “statistical quality control.”
Statistical Process Control (SPC) involves using statistical techniques to measure and analyze
the variation in processes. Most often used for manufacturing processes, the intent of SPC is to
monitor product quality and maintain processes to fixed targets. Statistical quality control
refers to using statistical techniques for measuring and improving the quality of processes and
includes SPC in addition to other techniques, such as sampling plans, experimental design,
variation reduction, process capability analysis, and process improvement plans.

SPC is used to monitor the consistency of processes used to manufacture a product as designed.
It aims to get and keep processes under control. No matter how good or bad the design, SPC can
ensure that the product is being manufactured as designed and intended. Thus, SPC will not
improve a poorly designed product’s reliability, but can be used to maintain the consistency of
how the product is made and, therefore, of the manufactured product itself and its as-designed
reliability.
A primary tool used for SPC is the control chart, a graphical representation of certain descriptive
statistics for specific quantitative measurements of the manufacturing process. These descriptive
statistics are displayed in the control chart in comparison to their “in-control” sampling
distributions. The comparison detects any unusual variation in the manufacturing process, which

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