standardization in design

For easy identification of materials, further improvement of machine elements, and easy replacement of worn-out parts and for quick and easy manufacturing, the parameters of machine elements are standardized.

In design, the aim is to use as many standard components as possible for a given mechanism. Standardization is defined as obligatory norms or standards to which various characteristics of a product should conform. The characteristics include materials, dimensions and quality of the product, method of testing and method of marking, packing and storing of the product. Standardization becomes a global activity to cover all economical, technical and material aspects of engineering products. The work of standardization is accomplished by national or international organizations.

The following standards are used in mechanical engineering design:

1. Standards for materials, their chemical compositions, mechanical properties and heat treatment.

2. Shapes and dimensions of commonly used machine elements such as bolts, screws and nuts, rivets, belts and chains, bearings, wire ropes, keys, gears etc..

3. Standards for fits, tolerances and surface finish of components.

4. Standards for testing of products such as pressure vessels, boilers, overhead traveling cranes.

5. Standards for engineering drawing of components.

There are three types of standards used in the design:

v International standards organization (I.S.O)

ü  National standards, such as I.S (Bureau of Indian Standards), D.I.N (Dutch International Number, German), A.I.S.I or S.A.E (American Iron and Steel Institute, USA), B.S (U.K) standards and J.I.S (Japanese Standards).

ü  Company standards for use in a particular company or a group of sister concerns like air-craft and ship-building industries manufacture their products with their own standard without adopting the general standard parts. This type of individual plant standardization is known as Normalization.

The objective of standardization is to make the mass production of components easier. Interchangeability of components is possible due to standards. Repair and maintenance of machines simple because the worn out or damaged parts can be easily replaced by standard ones. It aims at reduction of design, manufacturing, inventory and handling costs as well as the efforts to achieve uniformity, efficiency and a specified quality.

*) write a short note about preferred numbers:-

A) In engineering design many times the designer has to specify the size of the product. The ‘size’ of the product is a general term which includes different parameters like power transmitting capacity, load carrying capacity, speed, dimensions of the component such as height, length, width and weight of the product. These parameters are expressed numerically e.g.: 5 KW, 10 KN, 1000 rpm. Often the product is manufacturing in different sizes or models for instance, a company may be manufacturing different models of electric motors ranging from 0.5 KW to 50 KW to cater to the need of different customers. Preferred numbers are used to specify the ‘sizes’ of the products in these cases. Preferred numbers were first introduced by Charles Renard. These are nothing but a series of numbers in a geometric progression (G.P) specially selected to be used for standardization in preference to any other random numbers.

They are written as integral powers of 10. The first four are called basic series and other are called derived series, (denoted as R5, R10, R20, R40 and R80 series) which increase in steps of 58%, 26%, 12%, 6%, and 3% respectively. Each series has its own series factor. The series factors are as follows:

R5 series 5√10 = 1.58

R10 series 10√10 = 1.26

R20 series 20√10 = 1.12

R40 series 40√10 = 1.06

R80 series 80√10 = 1.03

The resultant numbers are rounded as per international standards and shown in Design Data Hand Book K. Mahadevan Page No: 402, Table 23.1, 23.2

Ex: Hydraulic cylinder capacities are in R5 series

Hoisting capacities (in tones) of cranes are in R10 series

Wire diameters of helical spring are in R40series

Hydraulic cylinder diameters are in R20 series

USES:-

Preferred numbers are an important tool, which minimize unnecessary variation in sizes. They assist the designer in avoiding selection of sizes in an arbitrary manner. The complete range is covered by minimum number of sizes which is advantageous to producer and consumer. They are unlimited towards the lower as well as higher numbers

*) Enumerate the various manufacturing methods of machine parts which a designer should know.

A) The knowledge of manufacturing processes is of great importance for a design engineer. The following are the various manufacturing processes used in Mechanical Engineering.

1. Primary shaping processes. The processes used for the preliminary shaping of the machine component are known as primary shaping processes. The common operations used for this process are casting, forging, extruding, rolling, drawing, bending, shearing, spinning, powder metal forming, squeezing, etc.

2. Machining processes. The processes used for giving final shape to the machine component, according to planned dimensions are known as machining processes. The common operations used for this process are turning, planning, shaping, drilling, boring, reaming, sawing, broaching, milling, grinding, hobbing, etc.

3. Surface finishing processes. The processes used to provide a good surface finish for the machine component are known as surface finishing processes. The common operations used for this process are polishing, buffing, honing, lapping, abrasive belt grinding, barrel tumbling, electroplating, superfinishing, sheradizing, etc.

4. Joining processes. The processes used for joining machine components are known as joining processes. The common operations used for this process are welding, riveting, soldering, brazing, screw fastening, pressing, sintering, etc.

5. Processes effecting change in properties. These processes are used to impart certain specific properties to the machine components so as to make them suitable for particular operations or uses. Such processes are heat treatment, hot-working, cold-working and shot peening

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