华南理工大学机械工程专业英语翻译
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Unit 1Metal generally have good electrical and thermal conductivity and good mechanical properties, such as high strength, high stiffness, and good ductility.A ceramic an inorganic nonmetallic material with high stiffness and high brittleness.The difference between glass production and ceramic production is that glass production could be manufactured by casting and blowing, while production of ceramics could only be made by sintering and firing.Composites, always with high modulus, are formed from two or more types of materials and properties of composites are superior to any individual component.Fracture toughness can be defined as a material's ability to avoid fracture when a flaw is introduced.Fiber-reinforced composites are used in some of the advanced expensive sports equipment, such as a time-trial racing bicycle frame which consists of carbon fibers in a thermoset polymer matrix.Polymers are used widely because they are lightweight, corrosion resistant, easy to process at low temperatures, and generally inexpensive. It’s mechanical properties are high strength and high stiffness.Unit 2The portions of the iron-carbon diagram near the ferrite region and those above 2% carbon content are deleted.Metallurgy is the physics, chemistry, and engineering related subject, which focus on metals from ore extraction to the final product.Heat treatment can remove internal stresses, reduce grain size, increase toughness, and produce a hard surface on a ductile interior.Temperature and the rate of cooling are the two main controlling factors in heat treatment.Steels having less than the eutectoid amount of carbon (less than 0.77%) are known as hypoeutectoid steels.Hardening is the process of heating a piece of steel to a temperature within or above its critical range and then cooling it rapidly.The primary purpose of annealing is to soften hard steel so that it may be machined or cold worked.Unit 4Forging is the process by which metal is heated and is shaped by plastic deformation by suitably applying compressive force.With proper design, the grain flow can be oriented in the direction of principal stresses encountered in actual use.One valuable feature of forging is that it improves the strength of the metal by refining the grain structure and making it uniform.Forgings are consistent from piece to piece, with any of the porosity, voids, inclusions and other defects.Open die forgings or hand forgings are made with repeated blow in an open die, where the operator manipulates the workpiece in the die.In roll forging, a round bar stock is placed between die rollers which increases the length axially.In the most of forming process, use of undercuts should be avoided, as these will make the removal of the part difficult.Unit 7Rake angle is the angle between the tool rake face and the normal to the machining direction.If taking the friction between the tool rake face and the underside of the chip, the chip gets further deformed, which is termed as secondary deformation.Build up edge is a localized, highly deformed zone of material attached on the tool face.The continuous chip characterized by a general flow of the separated metal along the tool face.The cutting tool should have high abrasion resistance to improve the effective life of the tool.One the function of cutting fluids is to cool the cutting tool and the workpiece.Since a lot of heat is generated at the cutting zone, the tool material should have higher thermal conductivity to dissipate the heat in the shortest time. Otherwise, the tool temperature would become high, reducing its life.Unit 13A drill jig is a device for ensuring that a hole to be drilled, trapped, or reamed in a workpiece will be machined in the proper place.Responsibility for the accuracy of hole location is taken from the operator and given to the jig.When the workpiece is located, as many of freedoms of degree as possible should be eliminated to ensure the operation is performed with required accuracy.One of the advantages of jigs is that unskilled workers could proceed confidently and quickly in the knowledge that the workpiece has been positioned correctly.The clamping system should ensure that the workpiece is held against the cutting forces, while the clamping forces must not be so great as to cause the workpiece distorted or damaged.Fixtures ensure the workpiece is correctly located and clamped, but it is different from jigs that fixtures don't have special devices to guide tools.Unit 14Dimensioning is an involved subject and long experience is required for its mastery.Allowance, which is sometimes confused with tolerance, has an altogether different meaning.Drawings should be checked carefully to ensure the dimensioning is done in a manner that will be most convenient and understandable to the production department.Tolerance is the permissible variations in size, is designed to allow unavoidable imperfection in manufacturing.There are three classes of fits: 1) clearance fits 2) transition fits 3) interference fitsDimensions that affect the function of parts should be specified and not left as the sum or difference of other dimensions.When dimensioning a drawing, the numbers placed in the dimension lines represent dimensions that are only approximate and do not reprensent any degree of accuracy unless so stated by the designer.。
