Selection of a proper material for the machine component is one of
the most important steps in the process of machine design. The best material is
one which will serve the designed objective at minimum cost .Selection of
material by trial and error method. While selecting the material to follow the
factors
(1) Availability (2) Cost (3). Mechanical properties (4) Manufacturing
considerations.
Availability: The material should be readily available in
the market, in large enough quantities to meet the requirement.
Cost: For every application, there is a limiting cost beyond which the
designer cannot go. When this limit is exceeded the designee has to consider
other alternative materials. In cost analysis there are two factors, namely
cost of material and the cost of processing the material into finished goods.
It is likely that the cost of material might be low, but the processing may
involve costly machining operations.
Mechanical properties: These properties govern the selection of
materials. Depending upon the service conditions and the functional
requirement, different mechanical properties are considered and a suitable
material is selected.
Ex: connecting rod of I .C-Withstand fluctuating stresses due to
combination of fuel- Endurance strength criterion of design.
Piston rings resist wear- Surface hardness criterion of design.
Bearing material – have low coefficient of friction.
Clutch or brake lining -has high coefficient of friction.
Manufacturing considerations: The manufacturing processes
such as casting, rolling, forging, extrusion, welding and machining govern the
selection of the material.
Machine ability of material is an important consideration in
selection. Sometimes, an expensive material is more economical than a low
priced one. Which is difficult to machine. Where the product is of a complex
shape, casting properties are important.
Past experience is a good guide for the selection of material.
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