Statistical quality control
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Transcript of Statistical quality control
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What is SQC ?
Statistical quality control (SQC) is the term used to describe the set of statistical tools used by quality professionals.
The application of statistical techniques to measure and evaluate the quality of a product, service, or process.
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History
SQC was pioneered by Walter A. Shewhart at Bell Laboratories in the early 1920s.
Shewhart developed the control chart in 1924 and the concept of a state of statistical control.
Shewhart consulted with Colonel Leslie E. Simon in the application of control charts to munitions manufacture at the Army in 1934.
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History
W. Edwards Deming invited Shewhart to speak at the Graduate School of the U.S. Department of Agriculture, and served as the editor of Shewhart's book Statistical Method from the Viewpoint of Quality Control (1939) which was the result of that lecture.
Deming was an important architect of the quality control short courses
that trained American industry in the new techniques during WWII.
Deming traveled to Japan during the Allied Occupation and met
with the Union of Japanese Scientists and Engineers(JUSE)in an
effort to introduce SQC methods to Japanese industry
5Characteristics of SQC
It is designed to control the quality standard of goods produced for marketing.
It is exercise by the producers during the production process
It is carried out with the help of certain statistical tools.
It is designed to determine the variations in quality of the goods .
It aims to ascertain whether the production process is in control or not, and whether the products are of specified quality.
It is an economical measure of assessing the quality standard of goods through statistical experiments without checking every product in detail.
6Advantages of SQC
It provides a means of detecting error at inspection.
It revels whether the production process is in control or not.
It leads to more uniform quality of production.
It improves the relationship with the customer, reduced customer complaints
Reduction of Scrap.
It reduces the number of rejects and saves the cost of material.
It reduces inspection costs.
It leads to more uniform quality of product
7Limitations of SQC
It cannot be applies indiscriminately as a solution to all the quality evils
It leads to a false sense of security in the absence of general quality awareness.
It provides only an information service, and it can not reduce the managers responsibility,
It cannot be applied mechanically to all production process without studying their peculiar environments.
It involves mathematical and statistical problems in the process of analysis.
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Descriptive Statistics
Descriptive statistics are used to describe quality characteristics and relationships.
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Descriptive Statistics
The Mean- measure of central tendency
The Range- difference between largest/smallest observations in a set of data
Standard Deviation measures the amount of data dispersion around mean
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Statistical Process Control
Statistical process control (SPC) involves inspecting a random sample of the output from a process and deciding whether the process is producing products with characteristics that fall within a predetermined range. SPC answers the question of whether the process is functioning properly or not
Extend the use of descriptive statistics to monitor the quality of the product and process
Statistical process control help to determine the amount of variation
To make sure the process is in a state of control
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Acceptance sampling
Acceptance sampling is an important field of statistical
quality control that was popularized by Dodge and Romig
and originally applied by the U.S. military to the testing of
bullets during World War II.
Acceptance sampling is the process of randomly inspecting
a sample of goods and deciding whether to accept the
entire lot based on the results. Acceptance sampling
determines whether a batch of goods should be accepted
or rejected
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Variation in Quality
No two items are exactly alike.
Some sort of variations in the two items is bound to be there. In fact it is an integral part of any manufacturing process.
This difference in characteristics known as variation.
This variation may be due to substandard quality of raw material, carelessness on the part of operator, fault in machinery system etc..
Variation due to chance causes/common causes
Variation occurred due to chance.
This variation is NOT due to defect in machine, Raw material or any other factors.
Behave in “random manner”.
Negligible but Inevitable
The process is said to be under the state of statistical control.
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Variation due to assignable causes
Non – random causes like: Difference in quality of raw material
Difference in machines
Difference in operators
Difference of time
It should be identified and corrected.
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