機(jī)械英漢翻譯-機(jī)械設(shè)計(jì)概論(完整版)
【正文】 elements of machines． With all ideas subject to change and improvement， several solutions may be 3 and usually are found， the seemingly best one being chosen． The actual practice of designing is applying a bination of scientific principles and a knowing judgment based on experience． It is seldom that a design problem has only one right answer， a situation that is often annoying to the beginner in machine design． Engineering practice usually requires promises． Competition may require a reluctant decision contrary to one’s best engineering judgment； production difficulties may force a change of design； etc． A good designer needs many attributes， for example： (1)A good background in strength of materials， SO that the stress analyses are sound． The parts of the machine should have adequate strength and rigidity, or other characteristics as needed． (2)A good acquaintance with the properties of materials used in machines． (3)A familiarity with the major characteristics and economics of various manufacturing processes， because the parts that make up the machine must be manufactured at a petitive cost． It happens that a design that is economic for one manufacturing plant may not be so for another. For example， a plant with a welldeveloped welding department but no foundry might t5nd that welding IS the most economic fabricating method in a particular situation； whereas another plant faced with the same problem might decide upon casting because they have a foundry (and may or may not have a welding department)． (4)A specialized knowledge in various circumstances， such as the properties of materials in corrosive atmospheres， at very low (cryogenic) temperatures， or at relatively high temperatures． (5)A preparation for deciding wisely： (a)when to use manufacturers’ catalogs， buying stock or relatively available items， and when custom design is necessary； (b) when empirical design is justified； (C)when the design should be tested in service tests before manufacture starts； (d) when special measures should be taken to control vibration and sound (and others)． (6)Some aesthetic sense， because the product must have ”customer appeal” if it is to sell． (7)A knowledge of economics and parative costs， because the best reason for the existence of engineers is that they save money for those who employ them． Anything that increases the cost should be justified by, for instance， an improvement in performance，
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