Before going into the details of methods to control quality it will be good if we familiarize ourselves with the basic issues of conducting inspection. The sole purpose of inspection is to provide informational concerning the degree to which items conform to a standard. Some important issues pertaining to inspection are as follows :
(1) The inspection may range from no or zero inspection to rigorous inspection inspecting each item many times as is the case with space vehicles, rockets, etc. But most of the industrial situations lie in between these two extremes. i.e, zero inspection and 100% intensive inspection.
No doubt, most of situations require some inspection but neither it is possible nor economically feasible to critically examine each and every part or activity.
The amount of inspection needed is governed by costs of inspection and expected costs of passing defective items.
From the graph given in Figure, it is very much obvious ,that the goal of course is to minimise the sum of two costs.
(2) Where to inspect - The right answer for this question varies from industry to industry as it depends on type of products, types of processes used, machines used, and the level of human involvement.
Still in practice the following are typical inspection points :
(3) Control procedures will differ depending on the characteristic of a product or service that is to be controlled, i.e., attribute data or variable one. For example, actual weight of cement bag can be measured whereas number of broken bottles in a shipments can be counted.
- How much to inspect ?
- At what points the process inspection should be carried out ?
- Whether to inspect attributes or variables ?
(1) The inspection may range from no or zero inspection to rigorous inspection inspecting each item many times as is the case with space vehicles, rockets, etc. But most of the industrial situations lie in between these two extremes. i.e, zero inspection and 100% intensive inspection.
No doubt, most of situations require some inspection but neither it is possible nor economically feasible to critically examine each and every part or activity.
The amount of inspection needed is governed by costs of inspection and expected costs of passing defective items.
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| Cost vs Amount of Inspection Graph |
From the graph given in Figure, it is very much obvious ,that the goal of course is to minimise the sum of two costs.
(2) Where to inspect - The right answer for this question varies from industry to industry as it depends on type of products, types of processes used, machines used, and the level of human involvement.
Still in practice the following are typical inspection points :
- Raw materials and purchased parts.
- Finished products.
- Before a costly operation is carried out.
- Before an irreversible process.
- Before a covering process, viz. painting, heat treatment, assembly that may hide defects.
(3) Control procedures will differ depending on the characteristic of a product or service that is to be controlled, i.e., attribute data or variable one. For example, actual weight of cement bag can be measured whereas number of broken bottles in a shipments can be counted.
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