Statistical Process Control

Introduction:

SPC (Statistical process control) is the group of techniques used for process monitoring so as to remove the special causes and improve the process. Most important technique of SPC is shewart control chart. There are many charts like X bar, R, p, c charts. With the help of these charts out of control points are found out and the causes related to those points are removed.

In addition to control charts SPC gives ways to measure the process capability with the help of capability indices. Most importantly there is lag between the theoretical research and practical application of SPC so there is a need to develop more complex tools than control charts. There is much research needed to reduce the gap between applications and theoretical

There are many experts who think that all the problems should be tackled statistically, but then there are also people who think that no problem should be tackled statistically. Needless to comment on this discussion, both of these attitudes are wrong. The best approach would be to lie between both these statements. The polarization of attitudes is itself a research issue because it leads to lost opportunities. Figure 1: Boundary object trajectory: Boundary object trajectory. The lines represent boundaries between different communities and the boxes represent the computer tools at those boundaries.

Research issues in SPC are the difficulty in using the concepts and methods and then interpreting the result which needs more attention. The issue can be that everyone in the institution cannot understand the procedure because of different background, so the employees may be trained at a common level.

Many times the SPC is used as a process of demonstrating quality standards to the third party. For creating a favorable impression the statistical methods can be manipulated. Also a research issue is the changing technological and business environment. It means that SPC needs to be applied in an ever greater diversity of

With the pre control technique the performance process has no control limits and also importance is not given to specify whether the process is in statistical control or not. The pre control technique is based on the specification limits. The range of these specification limits is divided into four parts of equal length. “Green zone.” describes the middle two parts. The outer two parts within the specification limits comprise the “yellow zones” and the region outside the specification limits is the “red zone.” Various decision and samplings rules are set up such that the process is allowed to operate as long as measurements don’t fall into the red zone or into the yellow zone too