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A system is a collection of inter-related processes. According to Deming, the four core processes of a quality-based production system are - market surveys, design, manufacturing, sales (see here).

Deming circle

TQM = continuous process improvement

Process improvement requires that processes be stable, or under statistical control

Statistical control - a state of random variation; it is stable since the limits of variation are predictable

Once the process has been stabilized, special causes (causes of variation that are not part of the system) of variation can be dealt with

Once special causes of variation have been removed, process improvement can begin

Processes are improved by addressing common causes (causes of variation that are an integral part of the system)

To be able to distinguish between special and common causes of variation, we must let the system run for a long time and measure continuously its output

Tampering with a process - ascribing a variation, or a mistake, to a special cause when in fact the cause belongs to the system. This overadjustment adds variation to the process.

Ascribing a variation, or a mistake, to the process when in fact the cause is special leads to doing nothing.

Acceptable Defects: Rather than waste efforts on zero-defect goals, Dr. Deming stressed the importance of establishing a level of variation, or anomalies, acceptable to the recipient (or customer) in the next phase of a process. Oftentimes, some defects are quite acceptable, and efforts to remove all defects would be an excessive waste of time and money.

 

 

TAMPERING VS. IMPROVEMENT

Tampering means making harmful changes in reaction to chance events (i.e., common causes of variation).  Instead of optimizing the process, one reacts to "the issues of the day;" to something that catches one's attention at a particular point in time.

Tampering means adding additional variation by unnecessary adjustments made in an attempt to compensate for common cause variation.

Tampering is not improvement.

Improvement of a stable process may require fundamental change in the process

Improvement means reducing a process's variation and establishing an acceptable performance average and UCL and LCL

A process that is ready for improvement

    - Is stable                                        ----------------------|                           

    - Is predictable                                                             | THE SYSTEM IS UNDER

    - Produces all its variation                                             | STATISTICAL CONTROL

    - All of its variation is due to chance  ----------------------|










 


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