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Saturday, 11 April 2015

General Considerations in Machine Design

General Considerations in Machine Design Points : General Considerations in Machine Design Following are the general considerations in designing a machine component:
1. Cost of Construction
2. Frictional Resistance and Lubrication
3. Type of Load and Stresses Caused by Load
4. Use of Standard Parts
5. Motion of the Parts or Kinematics of the Machine
6. Selection of Materials
7. Convenient and Economical Features
8. Safety of Operation
9. Number of Machines to be Manufactured
10. Form and Size of Parts
11. Assembling
12. Workshop Facilities
1. Cost of Construction Cost of creation of an article is mainly important consideration involved in design. In some cases, it is fairly possible that high cost of an article can immediately bar it from extra consideration. If an article has been made-up and tests of hand made example have shown that it has marketable value, it is then possible to excuse costs of a considerable sum of money in design and increase of automatic machines to make article, specially if it can be sold in large numbers. The aim of design engineer under every condition should be to decrease the manufacturing cost to minimum. 2. Frictional Resistance and Lubrication There is constantly a loss of power due to frictional resistance with it must be noted that friction of starting is high than that of operation friction. It is, thus, necessary that a careful concentration must be given to the substance of lubrication of every surfaces which move in contact by others, whether in rotating, sliding, or rolling bearings. 3. Type of Load and Stresses Caused by Load Load, on machine part, can operate in numerous ways due to which internal stresses are set up. 4. Use of Standard Parts Use of standard parts is intimately linked to cost, as the cost of standard or stock parts is just a fraction of cost of same parts prepared to order. The standard or stock parts must be use when possible; parts for which patterns are already in existence for example gears, pulleys and bearings and parts which can be chosen as of regular shop stock for example screws, nuts and pins. Bolts and studs must be as little as possible to shun the delay down to change drills, reamers and taps and too to reduce number of wrenches necessary. 5. Motion of the Parts or Kinematics of the Machine The doing well process of every machine depends mostly upon simplest collection of the parts which will give motion necessary.
The motion of parts can be:
(a) Curvilinear motion which contain rotary, oscillatory and simple harmonic.
(b) Rectilinear motion which contain unidirectional and reciprocating motions.
(c) Constant or changeable acceleration.
(d) Constant velocity.
6. Selection of Materials It is necessary to a designer must have a thorough information of properties of materials and their behaviour under functioning conditions, various of main characteristics of materials are: strength, flexibility, durability, weight, resistance to heat and corrosion, capability to cast, welded or hardened, electrical conductivity, machinability, etc. 7. Convenient and Economical Features In design, operating features of machine must be carefully study. The initial, controlling and stopping levers must be located on basis of suitable handling. Adjustments for wear have to be give employ various takeup devices and arrange them so that position of parts is preserved. If parts are to be changed for unusual products or replace on account of wear or breakage, simple contact must be provided and necessity of remove other parts to achieve this should be avoid if feasible. The inexpensive process of a machine which is to be use for production, or for the processing of material must be studied, in order to study whether it has utmost capacity consistent by the production of fine work. 8. Safety of Operation Various machines are dangerous to function, specially those which are speed up to assure production at a highest rate. Thus, every moving part of a machine which is within zone of a worker is consider an misfortune hazard and can be the reason of an damage. It is, thus, required that a designer must always give safety devices for safety of operator. The safety appliance should in no way hinder by process of the machine. 9. Number of Machines to be Manufactured The amount of articles or machines to be manufactured affects design in a number of ways. The manufacturing and shop costs which are call fix charges or slide expenses are distributed over number of articles to be contrived. If only a little articles are to be made, additional expenses are not justified except machine is large or of some particular design. An order work for small number of product will not permit every undue expense in workshop process, so that the designer must contain his condition to standard parts as much as possible. 10. Form and Size of Parts Form and size are base on judgement. The least workable cross-section can be used, but it can be checked that stresses induce in calculated cross-section are sensibly safe. In arrange to design any machine part for shape and size, it is needed to know forces which part must sustain. It is too important to expect any rapidly applied or impact load which can cause failure. 11. Assembling All machine or formation have to be assemble as a unit before it can purpose. Large units must frequently be assembled in shop, tested and then taken to be transported to their place of service. The last place of every machine is main and the design engineer must expect exact location and local facilities for creation. 12. Workshop Facilities A plan engineer must be common by the limitations of his employer’s workshop, in order to shun need of having work done in various other workshop. It is occasionally necessary to plan and manage the workshop operation and to draft methods for casting, handling and machining special parts.

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