General: For quality assurance, first of all quality specifications for the product should be established, so that it can meet the requirements of a customer. Suitable quality standards for raw materials, parts, components, tools and equipment, production process etc are also determined in advance so as to manufacture quality products as per the predetermined standard. This all should be done at the initial (design) stage.
Secondly, proper inspection and testing procedures and methods should be evolved to check the quality specifications of raw materials, parts components, tools, and equipment, production processes and methods and also final product. With the help of inspection and testing, a manufacturer can determine whether they all conform to the predetermined quality standards or design specifications or not.
Lastly, periodical evaluation of methods and procedures of inspection as well as quality control is a must to measure their efficiency and effectiveness. On the basis of such evaluation, if it seems that some changes are necessary in the procedures and methods for quality improvements, changes should be made without unnecessary delay. Under such circumstances delay proves to be dangerous. To evaluate the efficiency and effectiveness of inspection as well as control methods, random checking and testing of the products at various stages of production and also random checking and testing of tools, equipment etc should be done.
As we have seen earlier, quality assurance means assurance of the existence of physical and chemical properties in a product as prescribed in advance, assurance of the fitness of a product for intended use and assurance of the rated performance by a product as claimed. Assurance of all these three is called Quality Control. Even though the products, processes, machines, equipment, tools, parts, components, raw materials, inspection and testing methods and procedures etc are all standardized, the product which comes out may not be of a standard quality, because of various reasons. Therefore, it becomes necessary to exercise control at various stages to assure quality.
A lead the USA, Lost to Japan:
Thirty years ago, the United States, probably lead the world in the theory and application of quality control (QC), during the 50s Japan looked to the USA bring Dr WE Deming to speak on statistical quality control and Dr Joseph Juran to lecture on management QC. The first US Government sponsored quality control study group came to Japan at the end of the 50s.
In 60s, however, Japan began to move ahead. It grew less reliant on borrowed ideas as adaptation became innovative, QC circles emerged almost spontaneously, once quality control concepts were taught to foreman and workers for the firs time. Company wise quality control or total quality control followed soon thereafter. In 1966 Juran observed: The Japanese are headed for world quality leadership and will attain it in next two decades, because no one else is moving there at the same place.
During the late 60s, quality control for vendors, subcontractors and suppliers became common. Standards once set had to be met and so they were. As a result, users were able to start phasing out the inspection of incoming components, reducing inventories in some instances to a few hours’ supply and cutting costs. In many factories suppliers now deliver materials directly to the head of the assembly line.
The QC revolution bean to reach non-manufacturing industries, such as construction, by the mid-70s and became widespread in service organizations too at the end of the decade. Comments Hiorosuke Hiraoka of Komatsu, Our People have developed Deming’s theory, applying is not only to manufacturing but to every type of job, in every type of industry.
Control of Quality: General: Toda, in the modern era of industrialization products are being produced on a large scale to take advantage of mass scale production. Things like tooth brushes, tooth pastes, screws, nuts, bolts, cloth, sugar etc are produced in huge quantities everyday. But one screw is not exactly the same as another in all respects. There are bound to be some variations in the size or composition of a product. For example, if screws of length 1.5 cm are produced, some screws will be slightly longer than 1.5 cm, say 1.59 cm or 1.6 cm etc and some screws will be slightly smaller than 1.5 cm, say 1.49 or 1.4 cm etc. variations within certain limits are tolerable, as they are unavoidable, but if they are too large, the product becomes useless. Maintaining the quality of a product means keeping its size and composition within the tolerance limits (upper and lower). Quality control is the actual checking or completion of various tasks involved in the quality procedures which have been determined within the equality assurance function.
Causes of variation: The factors which cause variations in the size or composition of a product can be classified into two classes:
1) Chance variation and
2) Assignable cause of variation
Chance variation arises due to a large number of factors which are out of everybody’s control. These chance causes of variation can neither be discussed nor removed. Chance causes arise from so many very small sources that even if a few were found and something done about them, the overall effect would be negligible. These types of variations may take place due to a slight variation in the electric current supplied to the machine, or a slight variation in the machine.