Concept of Quality Control: Quality control is an overall function designed to ensure that manufactured products meet meaningful specifications. It involves the recognition and removal of identifiable causes or defects and variations from the set standards of quality.
Quality control, in its broadest senses refers to the systematic control of those variables encountered in manufacturing proms which affect the excellence of the end product- Bethel & others.
More comprehensively, quality control may be defined as follows:
an effective system for integrating the quality development, quality maintenance and quality improvement effects of the various groups in an organisation so as to enable production and service at the most economical levels which allow for full customer satisfaction.
It includes all the activities performed to fulfill the quality objectives of the enterprise.
In any manufacturing system, it is physically impossible to produce all the units of a product exactly identical. Despite utmost care, two products are not perfectly identical. Variability in quality is an inevitable feature of industry. Such variability results in rework, scrap and other wastes and losses.
Quality control is entrusted with the task of minimizing this variability. Quality control enters into all phases of the manufacturing process. It begins with designing of product so that it has high customer appeal in terms of appearance, function, life, etc. Then it goes to materials and parts purchased from outside, production methods and techniques, inspection and testing before shipping and finally in the hands of the customer whose satisfaction with the product is the ultimate test of quality.
Steps in Quality Control
The process of quality control consists of the following steps
(i) Determination of quality standards-specification of desired quality level in terms of weight, specific dimension, strength, chemical composition, etc.
(ii) The design of the production system which would be compatible to the achievement of the specified quality.
(iii) Control action to ensure that established quality standards are met.
(iv) Inspection of produced products to see if the overall quality of lots satisfies the specifications.
Thus, quality control involves inspection of raw materials, parts, gauge, tools and finished products. It operates when materials and parts are purchased, during manufacturing process and in case of finished products through performance testing.
Scope of quality control
There are three broad areas where quality control should be applied in manufacturing industry.
1. Supply quality assurance. Supplier quality assurance (SQA) is a contract with the supplier of raw materials and components. Under this agreement, the manufacturer ensures that incoming materials and parts will be of uniform and acceptable quality. It is also called incoming material control wherein the quality of bough-tout components and materials is continuously manicured and maintained.
Unless the materials and parts conform to the establish quality standards, quality of finished products cannot be maintained despite best efforts in manufacturing. Moreover, poor quality materials lead to rejections, idle time, wastage of processing time and labour cost and delay in supplies to customers. Therefore, effective control should be exercised on all incoming materials, components and sub-assemblies.
2. In-process control. During the stage of processing materials, random samples of the product are taken and their quality is measured against predetermined standards of quality. Such tests may reveal certain defects in the production process. Corrective steps are taken to ensure that right quality products are manufactured. In process control helps in building the desired quality into the finished product and prevents production of sub-standard products.
A process is considered satisfactory or under control so long as it continues to produce products of desired quality and specification. In process control techniques involve evaluation of process standards in terms of rework, scrap, dimensions, rejection, etc. In process control consists of all the procedures employed to evaluate, maintain and improve quality standards at different stages of manufacture.
3. Post-mortem inspection. It is taken after the products are manufactured or completed. It is a technique of evaluating the quality of a product and of classifying the units into acceptable and reject-able categories. Inspection controls are often called quality assurance. Design controls after the products leave the plant are known as reliability.