Other material selection principle of mechanical parts - Economic requirements
(1) The processing cost of materials accounts for a large proportion of the total cost of the parts when the quality of the parts is small and the processing quantity is very large. Although cast iron is cheaper than steel plate, for some single or small batch box parts, the cost of using cast iron is higher than that of steel plate welding, because the latter can save the manufacturing cost of die.
(2) In many cases, the local quality principle has different requirements for materials in different parts. It is actually impossible to choose a material to meet different requirements, even if it is possible, the price is very expensive. At this time, according to the principle of local quality, different materials or different heat treatment processes can be used in different parts, so that the local requirements can be met separately. For example, the gear teeth of worm gear must have excellent wear resistance and high gluing resistance, and the other parts only need to have general strength, so bronze gear ring should be used in cast iron wheel core coat to meet these requirements. It's also like a sliding bearing. Friction reduction is required at the surface of its contact with the journal, so only the bearing is made of antifriction material, not the whole bearing is made of antifriction material.
Local quality can also be obtained by carburizing, surface quenching, surface spray plating, surface rolling and so on.