A Study On Q Chart For Short Runs
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Date
2009-05
Authors
Moslim, Nor Hafizah
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Abstract
An important tool in quality control is the Shewhart control chart. The disadvantage
of a Shewhart control chart is that it is only used for high volume manufacturing.
However, in recent years, there exist a trend among manufacturers to produce
smaller lot sizes or low volume manufacturing. This trend is due to just-in-time
techniques (JIT), synchronous productions, job-shop settings and the reduction of inprocess
inventories and costs. This situation contradicts with high volume
production where the lot size is large and initializing a control charting process is
not a problem as the data is readily available. Therefore, a Shewhart control chart is
not suitable for use in low volume production. The term used to describe such a low
volume production is "Short Runs Production" or more commonly, "Short Runs". In
this situation, the sample size is less than 50 and frequent changes from process to
process exists. Thus, a major problem faced is the need to chart a large number of
different processes and the consequent large number of charts required. This
situation will make the work of a quality control inspector more difficult. Therefore,
a lot of research have been made to modify the current control charts so that they
can be applied in a short runs environment. To date, several short runs control charts
that have been suggested are the Q charts, Zed charts, difference charts and
deviation from nominal charts. The objectives of this dissertation are to review the
various types of short runs control charts that are available as well as to conduct a
simulation study to evaluate the average run length (ARL) perfonnance of the Q
chart for the process mean based on individual measurements. All the simulation
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studies in this dissertation are made using the "Statistical Analysis System (SAS)"
program.
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Mathematics