sqc hb.rtf
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What is statistical quality control (S.Q.C.)?There are various methods of quality control like 100 per cent check system, spot
checking method and statistical quality control system. Under statistical quality control,
observation for a fairly long period is made regarding the quality of the product. Theobservation enables to determine average quality of the product. The distribution of
values is shown on a graph paper. A quality control chart is prepared which gives upper &
lower limits of errors. The method of statistical quality control lower the cost of office•services and ensures greater accuracy. It lowers the cost of inspection and informs
management when things are not going smoothly.
How did Statistical Quality Control Begin?
Historical perspective Quality Control has been with us for a long time. How long? It issafe to say that when manufacturing began and competition accompanied manufacturing,
consumers would compare and choose the most attractive product (barring a monopoly of
course). If manufacturer A discovered that manufacturer B's profits soared, the former
tried to improve his/her offerings, probably by improving the quality of the output, and/or lowering the price. Improvement of quality did not necessarily stop with the product - but
also included the process used for making the product. The process was held in high
esteem, as manifested by the medieval guilds of the Middle Ages. These guilds mandatedlong periods of training for apprentices, and those who were aiming to become master
craftsmen had to demonstrate evidence of their ability. Such procedures were, in general,
aimed at the maintenance and improvement of the quality of the process.In modern times we have professional societies, governmental regulatory bodies such as
the Food and Drug Administration, factory inspection, etc., aimed at assuring the quality
of products sold to consumers. Quality Control has thus had a long history.
Science of statistics is fairly recent On the other hand, statistical quality control is
comparatively new. The science of statistics itself goes back only two to three centuries.
And its greatest developments have taken place during the 20th century. The earlier applications were made in astronomy and physics and in the biological and social
sciences. It was not until the 1920s that statistical theory began to be applied effectively
to quality control as a result of the development of sampling theory. The concept of
quality control in manufacturing was first advanced by Walter Shewhart The first toapply the newly discovered statistical methods to the problem of quality control was
Walter A. Shewhart of the Bell Telephone Laboratories. He issued a memorandum onMay 16, 1924 that featured a sketch of a modern control chart.
Shewhart kept improving and working on this scheme, and in 1931 he published a book
on statistical quality control, "Economic Control of Quality of Manufactured Product ", published by Van Nostrand in New York. This book set the tone for subsequent
applications of statistical methods to process control.
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Contributions of Dodge and Romig to sampling inspection Two other Bell Labs
statisticians, H.F. Dodge and H.G. Romig spearheaded efforts in applying statistical
theory to sampling inspection. The work of these three pioneers constitutes much of whatnowadays comprises the theory of statistical quality and control. There is much more to
say about the history of statistical quality control and the interested reader is invited to
peruse one or more of the references. A very good summary of the historical backgroundof SQC is found in chapter 1 of "Quality Control and Industrial Statistics", by Acheson J.
Duncan. See also Juran (1997).
Material PlanningFor each operation in a maintenance order, you can dispatch the materials required for carryingout the task. Materials can be BOM components of the reference object, or materials that werecreated in the system in Materials Management.
The materials that you plan for the maintenance order are reserved for it in the warehouse,provided they are held in stock. You can define when the reservation should be performed using
the Customizing function. For each order type, you can:
• Automatically create the reservation immediately
In this case, the system enters the indicator "Reservation applicable to MRP" in the header data screen for each maintenance order of this type. This indicator applies to the entire order and cannot be reversed.
• Individually define when the reservation is to be created
In this case, you can define yourself when the indicator "Reservation applicable to MRP" is tobe set. In this way, you can individually define for each maintenance order when thereservation is to be created.
The indicator "Reservation applicable to MRP" is automatically set when you release themaintenance order.
Once the order has been released, the materials can be removed from the warehouse by thepersons carrying out the job. Non-stock materials need to be ordered and delivered for the order.
Using the Customizing function, you can define for each order type whether materialreservation or purchase requisition creation should occur immediately or once the order has been released. You can, however, change this indicator in the order header whenprocessing the order. Note that you cannot reverse this change.
You can basically allocate the material needed to carry out the activity described in an operation
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to every operation of a maintenance order. You can use the following standard material types, or material types you have defined yourself, which have the same properties:
• Stock material
• Non-stock material
•Raw material
• Text
You cannot allocate materials to sub-operations. For information on how to dispatchmaterial using bills of material in order processing, see Contents: Work Scheduling withBills of Material.
For information on how to allocate the individual material types, see the following topics:
• Assigning Stock Material
• Assigning Non-Stock Material
• Assigning Raw Material
• Assigning Text
The following functions are also available:
Deleting the Material Assigned
Displaying Assigned Materials
Checking Material Availability
Usage of SQC
• It provides better quality assurance at lower inspection cost
• It reduce wastage of time and material
• It helps in identification of many production bottlenecks that occurs during the
production process
• It helps in improvement in quality
• It helps in reduction of scrap and rework
• It helps in decreased inspection cost
• It helps in scientific evaluation of quality and production
• It helps in reduction in customer complaints
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example
Major stages of Production process
The way that businesses create products and services is known as the production process.
A production process is said to be in a state of statistical control if it is governed bychance causes alone. There are three main parts to the production process as
Input,Process and Output stage.
A firm must purchase all the necessary inputs and then transform them into the product
(outputs) that it wishes to sell. For example a football shirt manufacturer must buy the
fabric, pay someone for a design, invest in machinery, rent a factory and employ workers
in order for the football shirts to be made and then sold. How well-organized a firm is atundertaking this transformation process will determine its success. This is known as the
productive efficiency of a firm and it will want to be as efficient as possible in
transforming its inputs into outputs (i.e. using the minimum number of inputs as possibleto achieve a set amount of output). This will reduce the cost per unit of production and
allow the firm to sell at a lower price. Hence the objective of the production process is tocreate goods and services that meet the needs and wants of customers.The needs andwants of customers will be met if a business can produce the correct number of products,
in the shortest possible time, to the best quality and all at a competitive price.
Function of Production process
The main objective of any production process is to control and maintain the quality of the
manufactured product so that it conforms to certain specified quality standards. Any
production process consists of two stages they are process control and product control.
Process control- The concept of process control was pioneered by W. A. Shewhart of
Bell telephone laboratories in 1924 by using the concept of theory of probability and
sampling. A typical control chart consists of three horizontal lines. They are
• A central line(CL), indicates the desired standard or the level of the process
• Upper control limit(UCL)
• Lower control limit(LCL)
Product control- The concept of product control was pioneered by Dodge and Romig by
using the concept of sampling inspection plans. It means controlling the quality of the product by critical examination at strategic points. It attempts to ensure that the product
marketed by sale department does not contain a large number of defective items.
Function of Quality Control
In SQC there is a term called quality. It plays vital role in statistical quality control.
Quality control technique is a powerful tool or productive technique for effective
diagnosis of lack of quality in any one of them like material, machine, or managementetc. It is essential that the finished products must possess the optimum quality that the
consumer expects of them. In quality control the term quality depends upon four M's.
They are as follows.
• Quality of material-Good quality of material reducing waste, smooth processing
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and increasing output. It will also provide better finish to end products.
• Quality of manpower-Well qualified and skilled personnel will increased
efficiency of the any production process due to better quality production through
the application of their skills and also reduce the production cost and time.
•
Quality of machine-Good quality of machine will increased the production,reduce breakdown situation and reduce the cost of finished product.
• Quality of management- A good management is imperative for increase in
efficiency, harmony in relations, growth of business and their related markets.
Usage of Quality Control in industry
The following diagram gives a summary of the usage of quality control in industry.
QUALITY CONTROL
APPROACH AND BENEFITS
Planned collection of data, analysis and interpretation
?
Improvement in product quality and design
Reduction in operating costs and losses
Reduction in scrap
Savings in excess use of materials
Removing production bottlenecks
Reduction in inspection
Evaluation of scientific tolerances
Improvement of employee morale
Maintenance of operating efficiency
Quality consciousness
Greater customer satisfaction
?
ENHANCED PRODUCTIVITY
A gradual increase in productivity, savings in costs and improvement in quality of products are attainable in any industry by means of the application of quality control
technique.
Conclusion
Thus Statistical Quality Control plays vital role in any production process by using
various statistical tools. It also plays a vital role in all walks of life starting from the
household to big engineering and service industries. It helps in improving the quality of finished goods and reducing total cost. In other words, the determination of both quality
and quality costs can be achieved by using SQC.