Page 209 - DMGT524_TOTAL_QUALITY_MANAGEMENT

Total Quality Management

Notes
Figure 14.3: A Process that is not Capable: Natural Variation exceeds Spec Range

Process Control on the other hand refers to maintaining the performance of a process at its
current capability level. Process control involves a range or activities such as sampling the
process product, charting its performance, determining causes of any excessive variation and
taking corrective action.

Knowing process capability allows manufacturing and quality managers to predict,
quantitatively, how well a process will meet specs and to specify equipment requirements and
the level of control necessary to maintain the firms’ capability. For example, if a design space
require a length of metal tubing to be cut within one-tenth of an inch, a process consisting of a
worker using a ruler and hacksaw will probably result in a large percentage of non-conforming
products in that case the process, due to its high inherent or natural variability, is not capable of
meeting the design specs. Management would face here three possible choices:
Measure each piece of the non-conforming tubing,
Develop a better process by investing in new technology,
Change the specifications.

Figure 14.4: A Capable Process: Output is Wholly within Spec Limits

Process capability has three important components: (1) the design specifications, (2) the centering
of the natural variation, and (3) the range, or spread, of variation. Figures 14.4 to 14.5 illustrate

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