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Архитектура Аудит Военная наука Иностранные языки Медицина Металлургия Метрология Образование Политология Производство Психология Стандартизация Технологии |
Basic Engineering Processes
Vocabulary: to subject – подвергать condition – состояние, условие initial – начальный, первоначальный to determine – устанавливать, определять reduction – сокращение to achieve – достигать beyond – выше, свыше to retain – сохранять, удерживать to join – соединять source – источник available – имеющийся в наличии, доступный advantage – преимущество considerably – значительно, гораздо to harden – упрочнять application – применение, использование, употребление Text 1 . METALWORKING Metals are important in industry because they can be easily deformed into useful shapes. A lot of metalworking processes have been developed for certain applications. They can be divided into five broad groups:
During the first four processes metal is subjected to large amounts of strain (deformation). Bit if deformation goes at a high temperature, the metal will recrystallize – that is, new strain-free grains will grow instead of deformed grains. For this reason metals are usually rolled, extruded, drawn, or forged above their recrystallization tempetature. This is called hot working. Under these conditions there is no limit to the compressive plastic strain to which the metal can be subjected. Other processes are performed below the recrystallization tempetature. These are called cold working. Cold working hardens metal and makes the part stronger. However, there is a limit to the strain before a cold part cracks. Rolling Rolling is the most common metalworking process. More than 90 percent of the aluminum, steel and copper produced are rolled at least once in the course of production. The most common rolled product is sheet. Rolling can be done either hot or cold. If the rolling is finished cold, the surface will be smoother and the product stronger. Extrusion
Extrusion is pushing the billet to flow through the orifice of a die. Products may have either a simple or a complex cross section. Aluminum window frames are the example of complex extrusions. Tubes or other hollow parts can also be extruded. The initial piece is a thick-walled tube, and the extruded part is shaped between a die on the outside of the tube and a mandrel held on the inside. In back-extrusion (штамповка выдавливанием) the workpiece is placed in the bottom of a hole and a loosely fitting ram is pushed against it. The ram forces the metal to flow back around it, with the gap between the ram and the die determining the wall thickness. The example of this process is the manufacturing of aluminum beer cans. Additional vocabulary: metalworking – металлообработка shape – форма, штамповать rolling – прокатка extrusion – экструзия, выдавливание drawing – волочение forging – ковка sheet – лист at least – по крайней мере common – общий billet – заготовка, болванка orifice – отверстие cross section – поперечное сечение die – штамп, пуансон, матрица, фильера, волочильная доска window frame – рама окна tube – труба initial piece – заготовка hollow – полный thick-walled – толстостенный mandrel – оправка, сердечник loosely – свободно, с зазором fitting – посадка ram – пуансон, плунжер Answer the questions: 1. Why are metals so important in industry? 2. What are the main metalworking processes? 3. Why are metals worked mostly hot? 4. What properties does cold working give to metals? 5. What is rolling? Where is it used? 6. What is extrusion? What shapes can be obtained after extrusion?
7. What are the types of extrusion? Find the following in the text:
Translate into English: 1. Способность металла перекристаллизовываться при высокой температуре используется при горячей обработке. 2. Перекристаллизация – это рост новых, свободных от деформации зерен 3. Во время горячей обработки металл может подвергаться очень большой пластической деформации сжатия. 4. Холодная обработка делает металл тверже и прочнее, но некоторые металлы имеют предел деформации. 5. Листовой прокат может производиться горячим или холодным. 6. Поверхность холоднокатаного листа более гладкая и он прочнее. 7. Поперечное сечение фильеры для экструзии может быть простым или сложнымю 8. Алюминиевые и медные сплавы являются наилучшими для экструзии из-за их пластичности при деформации. 9. Алюминиевые банки, тюбики для зубной пасты являются примерами использования штамповки выдавливанием. 10. Толщина стенки алюминиевой банки определяется зазором между пуансоном и штампом. Text 2. TECHNOLOGICAL PROCESSES Drawing consists of pulling metal through a die. An example of drawing is wire drawing. The diameter reduction that can be achieved in one die is limited, but several dies in series can be used to get the desired reduction. Sheet metal forming (штамповка листового металла) is widely used when parts of certain shape and size are needed. It includes forging, bending and shearing. One characteristic of sheet metal forming is that the thickness of the sheet changes little in processing. The metal is stretched just beyond its yield point (2 to 4 percent strain) in order to retain the new shape. Bending can be done by pressing between two dies. Shearing is a cutting operation similar to that used for cloth. Each of these processes may be used alone, but often all three are used on one part. For example, to make the roof of an automobile from a flat sheet, the edges are gripped and the piace pulled in tension over a lower die. Next an upper die is pressed over the top, finishing the forming operation (штамповку), and finally the edges are sheared off to give the final dimensions. Forging is the shaping of a piece of metal by pushing with open or closed dies. It is usually done hot in order to reduce the required force and increase the metal’s plasticity. Open-die forming is usually done by hammering a part between two flat faces. It is used to make parts that are too big to be formed in a closed die or in cases where only a few parts are to be made. The earliest forging machines lifted a large hammer that was then dropped on the workpiece, but now air or steam hammers are used, since they allow greater control over the force and the rate of forming. The part is shaped by moving or turning it between blows. Closed-die forming is the shaping of hot metal within the walls of two dies that come together to enclose the workpiece on all sides. The process starts with a rod or bar cut to the length needed to fill the die. Since large, complex shapes and large strains are involved, several dies may be used to go from the initial bar to the final shape. With closed dies, parts can be made to close tolerances so that little finish machining is required. Two closed-die forging operations are given special names. They are upsetting and coining. Coining takes its name from the final stage of forming metal coins, where the desired imprint is formed on a metal disk that is pressed in a closed die. Coining involves small strains and is done cold. Upsetting involves a flow of the metal back upon itself. An example of this process is the pushing of a short length of a rod through a hole, clamping the rod, and then hitting the exposed length with a die to form the head of a nail or bolt.
Additional vocabulary: to pull – тянуть in series – сери, последовательно yield point – точка текучести металла shearing – обрезка, отрезание to grip – схватывать lower die - нижний штамп upper die – верхний штамп forming operation – операция штампования open - die forming – ковка в открытом штампе (подкладном) coining – чеканка imprint – отпечаток to hit – ударять required – необходимый hammering – ковка within – внутри, в пределах to enclose – заключать machining – механическая обработка rod – прут, стержень tolerance – допуск upsetting – высадка, выдавливание blow – удар clamp – зажим, зажимать
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Text 3. WELDING Welding is a process when metal parts are joined together by the application of heat, pressure, or a combination of both. The processes of welding can be divided into two main groups: · pressure welding, when the weld is achieved by pressure and
Heat welding is the most common welding process used today. Nowadays welding is used instead of bolting and riveting in the construction of many types of structures, including bridges, buildings, and ships. It is also a basic process in the manufacture of machinery and in the motor and aircraft industries. It is necessary almost in all productions where metals are used. The welding process depends greatly on the properties of the metals, the purpose of their application and the available equipment. Welding processes are classified according to the sources of heat and resistance welding. Other joining processes are laser welding, and electron- Beam wilding. Gas Welding Gas welding is a non-pressure process using heat from a gas flame. The flame is applied directly to the metal edges to be joined and simultaneously to a filler metal in the form of wire or rot, called the welding rod, which is melted to the joint. Gas welding has the advantage of using equipment that is portable and does not require an electric power source. The surfaces to be welded and the welding rod are coated with flux, a fusible material that shields the material from air, which would result in a defective. Are Welding Arc-welding is the most important welding process for joining steels. It requires a continuous supply of either direct or alternating electrical current. This current is used to create an electric arc, which generates enough heat to melt metal and create a weld. Arc welding has several advantages over other welding methods. Arc welding is faster because the concentration of heat is high. Also, fluxes are not necessary in certain methods of arc welding. The most widely used arc-welding processes are shielded metal arc, gas-tungsten arc, gas-metal arc, and submerged arc. Resistance Welding In resistance welding, heat is obtained from the resistance of metal to the flow of an electric current. Electrodes are clamped on each side of the parts to be welded, the parts are subjected to great pressure, and a heavy current is applied for a short period of time. The point where the two metals touch creates resistance to the flow of current. This resistance causes heat, which melts the metals and creates the weld. Resistance welding is widely employed in many fields of sheet metal or wire manufacturing and is often used for welds machines especially in automobile industry. Additional vocabulary: pressure welding – сварка давлением heat welding – сварка нагреванием instead – вместо, взамен bolting – скрепление болтами riveting – клепка basic – основной to manufacture – изготовлять to depend – зависеть от purpose – цель gas welding – газосварка are welding – электродуговая сварка resistance welding – контактная сварка laser welding – лазерная сварка electron - beam welding – электронно-лучевая сварка flame – пламя edge – край simultaneously – одновременно filler – наполнитель wire – проволока rod – прут, стержень to melt – плавить(ся) joint – соединение, стык coated – покрытый flux – флюс fusible – плавкий touching – касание to shield – заслонять, защищать tip – кончик
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Text 4. TYPES OF WELDING |
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