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Basic engineering processes





The processing of metals is considered to be the most indispensable part of fabricating a wide range of products, such as the tiniest parts used in electronics, electrical and radio engineering, watch-making, all kinds of measuring devices, ect., on the one hand, and gigantic parts for turbines, engines, machine-tools and even whole sections of machines to produce machinery, on the other.

Metal processing is known to involve the following major techniques: casting, forming, machining, joining, and heat treatment, each of these manufacturing processes representing a particular branch of the metal-processing industry.

Casting may be briefly described as shaping by means of transforming the metal from liquid to solid state in specially designed moulds, some castings being usable as they come from the mould, others – requiring machining and finishing operations.

There are several casting techniques at the disposal of foundrymen, their selection depending upon the metal or alloy the part is to be made of, the quantities to be produced, the shape and the size desired, the tolerances and the relative cost. The most commonly used casting processes are: sand casting, mould casting, die casting, investment and precision casting, and centrifugal casting, each of them possessing its own peculiarities, advantages and disadvantages, which govern the choice of the methods for the production of the article in question.

Forming, contrary to casting, applies to shaping the metal in the solid state, which is possible due to the peculiar property most metals possess, called “ductility”. Forming is generally assumed to include: rolling, forging, stamping and pressing, that is, the processes involving plastic deformation of the metal being shaped.

Machining is the term applied to a group of processes consisting in removing excess metal from cast, rolled or forged parts in order to obtain a desired shape. To achieve the desired result various kinds of machine-tools are employed, the most important ones being the milling, boring, turning and grinding machines and the lathe, the latter being one of the most widely used production machines.

Joining comprises a variety of methods, such as welding, soldering brazing, and riveting, which are used for attaching one surface to another.

Heat treatment is used to cause the desired property variations by means of controlled temperature changes. Only by heat treatment is it possible to impart the metal the high mechanical properties required for the operation of modern machinery and tools. There are four major groups of heat treatment, namely, hardening, annealing, tempering, and normalizing.

Even the shortest description of fabricating processes, the processing engineer has to deal with, would be incomplete without mentioning finishing operations. Finishing relates to all processes, or rather, operations, which serve to render the product obtained by other processes suitable for use.

The knowledge of all fabricating processes is believed to be necessary for a processing engineer, in order that he may choose the most advantageous and economical techniques.

The ability to see his work as part of the whole process rather than an individual operation may be said to be the major requirement any processing engineer is expected to meet.

 

Note to the text:

1. a wide range of products – разнообразные изделия

2. on the one hand…on the other (hand) – с одной стороны… с другой стороны

3. which govern the choice of the methods for the production of the article in question – которые определяют выбор технологии для производства данного изделия

4. the processes involving plastic deformation of the metal being shaped – процессы, связанные с пластической деформацией обрабатываемого металла

5. rather than – а не

Date: 2015-05-08; view: 1122; Нарушение авторских прав; Помощь в написании работы --> СЮДА...



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