After reading this article you will learn about:- 1. Definition and Concept of Inspection 2. Purposes or Objectives of Inspection 3. Kinds.
Definition and Concept of Inspection:
An item or component or product which is manufactured is required to perform certain functions. The act of checking whether a component actually does so or not is called Inspection. In other words, Inspection means checking the acceptability of the manufactured product.
Inspection measures the qualities of a product or service in terms of pre-decided standards. Product quality may be specified by its strength, hardness, shape, surface finish, chemical composition, dimensions, etc.
Purposes or Objectives of Inspection:
(i) Inspection separates defective components from non-defective ones and thus ensures the adequate quality of products.
(ii) Inspection locates defects in raw materials and flaws in processes which otherwise cause problems at the final stage. For example, detecting the parts not having proper tolerances during processing itself, will minimize the troubles arising at the time of assembly.
(iii) Inspection prevents further work being done on semi-finished products already detected as spoiled.
(iv) Inspection makes sure that the product works and it works without hurting anybody, i.e., its operation is safe.
(v) Inspection detects sources of weakness and trouble in the finished products and thus checks the work of designers.
(vi) Inspection builds up the reputation of the concern as it helps reducing the number of complaints from the customers.
Kinds of Inspection:
(a) Roving, process, patrolling or floor inspection,
(b) Fixed inspection,
(c) Key-point inspection, and
(d) Final inspection.
(a) Roving Inspection:
The inspector walks round on the shop floor from machine to machine and checks samples of the work of various machine operators or workers.
(i) Helps catching errors during process itself, i.e., before the final production is ready; and
(ii) It is more effective and desirable because the work need not be transported to a centralized (inspection) place.
Incoming raw materials are inspected in order to:
(i) Eliminate those materials which do not meet specifications and are likely to cause trouble during processing; and to
(ii) Evaluate vendor’s quality and ability to supply acceptable materials.
Raw materials involving high transportation charges are checked by the buyer at vendor’s end whereas others are inspected as soon as received at purchaser’s plant. Inspection of raw materials may involve a visual check up only, a dimensional check, a test of physical properties and chemical composition, etc.
Raw materials depending upon their characteristics and use may require a Sampling Inspection or 100% Inspection (as in purchased aircraft component parts). After inspection, the right quality parts are sent either to stock room or assembly lines.
(b) Fixed Inspection:
The work is brought at intervals for inspectors to check. Fixed inspection discovers defects after the job has been completed. Fixed inspection is used when inspection equipments and tools cannot be brought on the shop floor. It is a sort of centralized inspection, the worker and the inspector do not come in contact with each other; thus it eliminates any chances of passing a doubtful product.
(c) Key-Point Inspection:
Every product (more or less) has a key point in its process of manufacture. A key point is a stage beyond which either the product requires an expensive operation or it may not be capable of rework. Inspection at a key point segregates and thus avoids unnecessary further expenditure on poor and substandard parts, which are likely to be rejected finally.
In process Inspection:
An effective in process inspection eliminates:
(i) Defects so that the subsequent operation is not badly affected;
(ii) A defect which may be concealed in the final product (e.g., after painting, etc.);
(iii) Extra work from being performed on reject able materials.
In-process inspection is carried out by:
(a) Workers doing the job.
(b) Inspectors from the inspection department.
In process inspection may check:
(a) A first few parts of the new machine set up, or a new operation.
(b) A part before it moves for the next operation.
(c) A part before it goes for an expensive operation.
(d) A part after a series of manufacturing operations.
(e) Parts before sub-assembly or final assembly.
(f) A part before it is being sent for plating or painting.
(g) A part before it moves to the next department.
For in process inspection, the inspectors are stationed at specific stages in the manufacturing process.
Automatic sizing and gauging equipments which can check a large number of dimensions simultaneously are sometimes built in the processing machinery. A feedback system automatically resets the machine to correct for the error measured by the automatic gauging equipments.
(d) Final Inspection:
The final inspection of the product may check its appearance and performance. Many destructive and non-destructive inspection and test methods such as tensile, fatigue, impact testing, etc., and ultrasonic inspection, X-ray radiography, etc., respectively, are available for final inspection of the products manufactured. Final inspection is a centralized inspection and it makes use of special equipments.
Inspection of Finished Goods:
An unthorough inspection of finished and final goods may permit faulty products to be dispatched to the customers, because it is the last chance of detecting imperfections in the products manufactured.
The finished goods inspection is:
(a) Visual to ascertain appearance and dimensions; and
(b) Functional to ensure that the product will work to specification.