Principles of Quality Control | Economic Aspects of Quality Assurance

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Quality Control :

Quality control is the synthetic and regular control of the variable which affect the quality of a product.

The operational techniques and activities that sustain the quality of a product or service in order to satisfy given requirements . It consists of quality planning , data collection, data analysis and implementation and is applicable to all phases of product life cycle ; design, manufacturing, delivery and installation, operation and maintenance.

Principles of Quality Control:

The essential requirements for producing a reliable product has been stated as follows:-

  • A satisfactory design of product, thoroughly proved by adequate development testing in order to establish its reliability under the conditions to which it will be subjected in use. This is the Requisite Quality of the product.
  • A full specification of the requirements of this quality, which must be clearly understood by everyone concerned with the production of the constituent parts and of the complete end product.
  • Confirmation that the manufacturing processes are capable of meeting these requirements.
  • Full acceptance, by all those concerned with production, of the responsibility for meeting the standards set by the specification.
  • Checks on the product at every stage of manufacture to detect any departures from the specification.
  • Record essential information derived from these checks to provide accurate evidence for action.
  • Establishment of lines of communication, – i.e. Feedback to Production, – to ensure that this action is taken to effect the appropriate adjustments to materials, process and operatives to maintain future production within the specification.

An important feature to realise in the establishment of these principles is that, whilst tolerances and quality standards for goods going for despatch may often vary rapidly, depending on the urgency of call off, it is the duty of Quality Control in enacting items 4-7 above, to stabilise the tolerances and quality standards for goods in production, based on the recognized Requisite Quality and this largely established from the continual experience gained from item 9 above. Only by production personnel knowing exactly what is expected can they respond to the requirements of Quality Control.


Quality Assurance:

“The establishment and maintenance of all activities and functions concerned with the attainment of requisite quality”


“The systems required for programming and co-ordinating the efforts of the various groups in an organization to maintain the requisite quality” As such Quality Control is seen as the agent of Quality Assurance or Total Quality Control


Economic Aspects of Quality Assurance:

 The ideal situation is to keep the cost of conforming to the requisite quality as low as possible, whilst at the same time achieving the highest percentage of acceptable production.

To find if a company is approaching the optimum total cost trials need to be made to establish the costs of quality control and the cost of defectives.

As a first approximation and as a guide, this total cost is usually achieved when prevention costs = failure costs + appraisal costs, as illustrated in the above diagram, and in the diagram below:-

In this firm the total quality costs were approximately 10% of turnover (very low). By increasing appraisal and prevention a saving on total costs of 15% was effected. This is 15% on 10% of turnover, improved product, improved delivery times, and improved customer satisfaction.

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