CONCLUSION
Acceptance sampling is an important field of statistical quality control to
accept or reject products under sampling inspection. It is done on the basis of random
sample taken from a lot. This sampling scheme is used to test the item one by one. In
this situation, the minimum number of groups is required for a given lot size and the
acceptance number is determined when the consumer and producer are satisfied.
Based on this, numerous sampling procedures have been evolved and they are widely
used in practice. Acceptance sampling plan is a middle path between hundred percent
inspections and no inspection.
The work presented in this thesis is mainly relates to a new procedure for
construction and selection of tables for sampling inspection plans / schemes / systems
indexed through Incoming and Outgoing quality levels. It is proposed that an attribute
sampling plan which can be used to test multiple items at the same time. When a
consumer designates some specific value for AQL, the supplier or producer is notified
with the consumer acceptance sampling plan which will accept most of the produced
lots submitted by the supplier, provided the process average of these lots is not greater
than the designated value of AQL. The Operating Characteristic curve and AOQ
curve are well explained in this thesis and these curves clearly shows how the
sampling plan is economical owing to less inspection cost. Fewer inspections can
reduce the cost and the time of the experiment than the ordinary acceptance sampling
plans, it makes both consumer and producer satisfied with specific quality levels.
The incoming quality is good, then a large proportion of the lots will be
accepted by the sampling plan and only a smaller fraction will be screened and hence
the outgoing quality will be small (good). Similarly, when the incoming quality is not
good, a large proportion of the lots will go for screening inspection and in this case
also, the outgoing quality will be good, since defective items will be either replaced or
rectified. Only for intermediate quality levels, lot acceptance will be at a moderate
rate and hence the AOQ will rise. The maximum ordinate of the AOQ curve
represents the worst possible average for the outgoing quality and is generally known
as Average Outgoing Quality Limit (AOQL). In other words, the AOQL is defined as
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the maximum of AOQ over all possible levels of the incoming quality for a known
acceptance sampling plan. The relative slopes shows the steepest decent of OC curve
at AQL and LQL. Through the relative slopes, one can find the point of inflection
through which the Incoming and Outgoing quality levels are decided.
In this thesis, the work mainly relates to the construction and selection of the
Quick Switching System with Repetitive Group Sampling System, Conditional
Repetitive Group Sampling System, Multiple Repetitive Group Sampling System and
Two-stage Conditional Repetitive Group Sampling System as reference plan which
are studied through incoming and outgoing quality levels and their relative slopes.
Some comparisons were made between the various sampling scheme and various OC
curves. The efficiency of the design clearly explains that this plan requires lesser
sample size than the ordinary sampling schemes which were already in existence.
For practical utility of the plan, Poisson unity values have been tabulated for a
wider range of plan parameters. The present development would be a valuable
addition to the literature and useful device to the quality control practitioners. The
concept of this investigation may be assistance to the quality control engineers and
plan designers towards the development of further new plans towards maintaining
standard relating to Total Quality Management (TQM).
FUTURE RESEARCH
•
The study can also be extended to develop MAPD, MAAOQ, Minimum Angle
method and Minimum sum of risk for the newly proposed plan.
•
It is interesting to study simultaneously the normal and tightened case of two
situation of sample size that may be useful for future research.
•
A further study is needed to propose more efficient or economic sampling plan
in terms lesser sample size.
•
The present work emphasis on attribute sampling plans which may be
extended to variable sampling plans and sampling plan through Bayesian
approach.
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