机械专业英语论文3000字

中国是世界上机械发展最早的国家之一。中国的机械工程技术不但历史悠久，而且成就十分辉煌，不仅对中国的物质文化和社会经济的发展起到了重要的促进作用，而且对世界技术文明的进步做出了重大贡献.传统机械方面，我国在很长一段时期内都领先于世界。到了近代由于特别是从18世纪初到19世纪40年代，由于经济社会等诸多原因，我国的机械行业发展停滞不前，在这100多年的时间里正是西方资产阶级政治革命和产业革命时期，机械科学技术飞速发展，远远超过了中国的水平。这样，中国机械的发展水平与西方的差距急剧拉大，到十九世纪中期已经落后西方一百多年。新中国建立后特别是近三十年来，我国的机械科学技术发展速度很快。向机械产品大型化，精密化、自动化和成套化的趋势发展。在有些方面已经达到或超过了世界先进水平。总的来说，就目前而言中国机械科学技术的成就是巨大的，发展速度之快，水平之高也是前所未有的。这一时期还没有结束，我国的机械科学技术还将向更高的水平发展。只要我们能够采取正确的方针、政策、用好科技发展规律并勇于创新，我国的机械工业和机械科技一定能够振兴，重新引领世界机械工业发展潮流。就小型夯实机械而言：上世纪60年代以前，我国小型夯实机械非常缺乏，很多小型场地的夯实基本上采用人工夯实。上世纪60年代初期，长沙建设机械研究所与北京建筑工程学院等单位合作，在群众性技术革新成果的基础上总结发明了具有中国特色的蛙式夯实机，1962年获国家科技发明奖。蛙式夯实机结构简单，维修、使用方便，很快成为我国60年代夯实机械的主导产品。据不完全统计蛙式夯实机累计产量达到50000多台，在我国经济建设中发挥了重要作用。70年代以后，蛙式夯实机逐渐被性能更先进的振动冲击夯和振动平板夯所替代，目前蛙式夯实机已经很少，基本被淘汰。1964年，长沙建设机械研究所开发了HB120型内燃式夯实机，开始由上海工程机械厂生产，后来主要由津市洞庭工程机械厂生产，年产量200台左右。80年代，内燃式夯实机产品质量有较大提高，曾出口东南亚和非洲地区。90年代以后，内燃式夯实机产销售量也在逐渐减少，目前只有少数小型民营企业生产。1977年，长沙建设机械研究所和柳州市建筑机械厂开发了我国第一台HZR250型和HZR70型振动平板夯，这两种产品分别于1979 年和1982年通过了由建设部组织的鉴定。随后义乌建筑机械厂、四平建筑机械厂、安阳振动器厂、津市洞庭工程机械厂等多家企业都开始生产振动平板夯。1986年长沙建设机械研究所又开发了较大的HZR450型振动平板夯。上世纪90年代以后，振动平板夯在我国有了较快的发展，产品品种、规格和生产企业增多，国外的振动平板夯陆续进入中国市场。1983年，长沙建设机械研究所和湖北振动器厂联合开发了我国第一台HZR70型振动冲击夯，1984年通过了由建设部组织的鉴定，1985年获建设部科技进步三等奖。由于振动冲击夯具有压实效果好、生产率高、体积和重量小、轻便灵活等突出特点，深受用户欢迎，得到了迅速的推广使用，并很快发展到资江机器厂、新乡第三机床厂和津市洞庭工程机械厂等几十家企业生产。振动冲击夯虽然比振动平板夯开发晚，但发展速度、产销量和使用广泛性比振动平板夯大得多，目前已成为我国夯实机械中产销量最大的主导产品。上世纪90年代以后，国外的振动平板夯陆续进入中国市场。振动冲击夯和振动平板夯在我国的成功开发，不仅为我国建设施工部门提供了性能先进的夯实机械，取得了良好的经济效益和社会效益，而且使我国夯实机械技术向前跨进了一大步，缩短了与世界先进水平的差距，促进了我国压实机械的发展。就机械加工而言：热加工 铸造 据考古发现，在北京平谷、昌平、房山等处曾出土了公元前16世纪(商代)的青铜礼器。 明永乐年间(1403～1424年)，北京制造出享誉世界的明永乐大铜钟(吨)和钟楼大铜钟(63吨)及铁钟(25吨)，采用分炉熔化、地坑造型和陶范法铸造。 20世纪50年代以前，北京在铸造上采用粘土砂手工造型。1955年，北京第一机床厂开始采用漏模造型、双面模型型板及铁型板和标准砂箱造型。1965年，开始采用塑料模型。 1980 年，北京市机电研究院与北京玛钢厂研制成功工频无芯塞杆底注式保温浇注电炉。1982年，该院与北京机床铸造二厂研究成功冲天炉风口吹氧技术。 1985～1988年，北京机床研究所试验成功浮动端面密封环的压力铸造工艺。 锻压 1959年，北京第二通用机械厂(后改名北京重型机器厂)建成2500吨水压机。1971年，该厂制造出6000吨水压机，这是当时北京最大的锻压设备。 1968～1979年，北京起重机器厂先后采用300吨油压机和2000吨油压机制造出起重机吊臂和大型覆盖件。 80年代，北京市机电研究院和北京市模具中心研制出一系列高精度多工位冲裁模具，接近或达到进口模具水平，改变了北京精密冲裁模具依赖进口的局面。 热处理 1949年前，北京已采用电炉、盐溶炉、热电偶等手段进行零件退火、回火、淬火、正火、调质、渗碳等热处理。 1956年，北京第一机床厂开始采用高频感应淬火。1961年，北京第二机床厂开始采用气体氮化淬火。1969年，北京量具刃具厂开始采用光亮淬火。 1978年，北京机床研究所研究完成机床导轨表面接触淬火工艺及设备、淬火质量检查技术条件的研究。1979年，铁道科学研究院和中国科学院力学研究所等合作完成大功率柴油机缸套表面的激光改性处理的研究。 1979年，北京市机电研究院研制成功千瓦级二氧化碳激光器，并于80年代初分别应用于汽缸套和邮票印刷设备的激光热处理。其中，清华大学、北京市机电研究院、北京邮票厂共同完成邮票厂七色机打孔器表面激光强化研究。 1984～1990年，北京市热处理研究所研究成功真空热处理、气体渗碳微机控制技术(与北京航空航天大学合作)、稀土软氮化、粉末冶金制品表面强化、煤油加甲醇小滴量法微机可控渗碳、固体渗硼、渗碳过程微机辅助工艺设计及跟踪控制系统等热处理新技术，并应用于生产。 焊接与切割 1949年，北京已有气焊、电弧焊及氧乙炔火焰切割等手工作业。 1963年，北京金属结构厂与一机部机械科学研究院合作开发出钨极氩弧焊，并实现了氮气等离子切割不锈钢。1964年，用直流钨极氩弧焊及焊丝合金化技术解决了核工业用倾斜式电解糟纯镍焊接。 1966年，北京金属结构厂开发出了使被焊球体旋转的埋弧自动焊。1968年，该厂开始以液化石油气代替乙炔切割。 80年代初，清华大学发明了新型MIG焊接电弧控制法，在控制电弧技术上取得突破。 80年代初，北京城建设计院等完成液化石油气移动式气压焊轨技术的研究和应用。 1990年，北京金属结构厂开始采用数控精密切割和具有光电跟踪及数控寻踪读入自动编程的大功率等离子切割技术。可见，我国机械发展在近代发展其迅速。China is the world's first national machinery development. Chinese mechanical engineering technology not only has a long history and splendid achievements in Chinese is not only the material culture and social economic development plays an important role in the world, and to promote the progress of civilization, technology has made great contribution to Chinese traditional machine. And in a long period ahead in the world. In modern times, especially from the early 18th century, due to the nineteen forties, due to the economic and social reasons, such as the China machinery industry, stagnation, in the 100 years is western bourgeois political revolution and industrial revolution, mechanical science and technology is developing rapidly, and far more than the level of China. So, China mechanical development level and the western gap widens, sharply to the 19th century middle behind western one hundred the founding of new China, especially in the past 30 years, our country's mechanical science and technology development speed. To the mechanical product large-scale, precision, automation and discusses the trend of development. In some aspects has reached or exceeded the world advanced level. Generally speaking, currently China mechanical science and technology achievement is huge, developing fast, high level of unprecedented. In this period, China has no end of mechanical science and technology will develop to a higher level. As long as we can adopt the correct policy, with good technology development and innovation, our machinery industry and mechanical technology can revitalize, leading to the development trend of mechanical small ramming machinery:In the 1960s, China mechanical very small tamp lack, many small venues ramming basically USES artificial 1960s, changsha construction machinery institute and Beijing architectural engineering institute, etc., the technical innovation achievements in mass on the basis of summing up Chinese characteristic invented the breaststroke ramming machine, 1962 exceeded national science and technology. The breaststroke ramming machine structure is simple, easy to use and maintenance in 1960s, soon became the dominant products to consolidate machinery. According to not complete count breaststroke tamp cumulative yield reached more than 50,000 machine, in the economic development of our country has played an important role. Since 1970's, the breaststroke ramming machine was gradually more advanced performance of vibration shock ram and vibrating plate ram, now replaced by laying machine has rarely breaststroke, basically be 1964, changsha construction machinery institute HB120 developed movable type, type of Shanghai began laying machine, engineering machine production mainly by tianjin municipal later, annual production engineering machinery dongting about 200. In the 1980s, movable type ramming machine product quality has increased greatly, have exported to southeast Asia and Africa. Since 1990s, internal-combustion type ramming machine production sales, and gradually decreased in only a few small private enterprise 1977, changsha construction machinery factory buildings and developed in liuzhou HZR250 type and the HZR70 type vibrating plate ram, these two kinds of products in 1979 and 1982 passed by the ministry of construction of the organization. Then yiwu building construction machinery factory, siping, anyang vibrators factory, tianjin municipal engineering machinery dongting and other enterprises have started producing vibrating plate ram. In 1986, changsha construction machinery research and develop a larger HZR450 type of vibrating plate ram. Since 1990s, vibrating plate ram in our country has developed very quickly, varieties of products, specifications and increase production enterprises, foreign vibrating plate ram gradually to enter the Chinese 1983, changsha construction machinery institute and the joint development of hubei vibration in the first HZR70 type vibration shock ramming, 1984, passed by the ministry of construction, organization construction technology progress in 1985 won prizes. Due to the vibration impact compaction result has good ramming, productivity, high volume and weight of small, lightweight flexible outstanding characteristics, deeply user etc, obtained a rapid promotion, and soon ZiJiang development to the factory, xinxiang municipal engineering machine tool plant and tianjin dozens of dongting production factory etc. Vibration shock ramming although than vibrating plate ram, but later development speed of development, production and use of extensive than vibrating plate ram, has become the largest in China in the ramming machinery products. Since 1990s, foreign vibrating plate ram gradually to enter the Chinese shock ramming and vibrating plate ram the successful development in our country, not only for our construction department provides advanced performance of mechanical, laying have achieved good economic benefit and social benefit, and make our ramming mechanical technology into a big step forward, shorten the gap with the advanced world level, promoting the development of compaction mechanical processing:According to the archaeological discovery, hot-working casting in Beijing pinggu, changping and so have proved that the 16th century BC shang dynasty (bronze objects. Ming yongle (1403-1424 years), Beijing produce world-renowned Ming yongle great 3-ton bell made ( tons) and tower (63 tons of great 3-ton bell made of iron clock (25) and the furnace of melting, pit TaoFan model and method of casting. In the 1950s, Beijing based on clay sand castings in manual. In 1955, Beijing first machine tool plant began using leakage mould modelling, double-sided model and iron plate type plate and standard sand box modelling. In 1965, start using plastic model. In 1980, the institute and Beijing municipal electrical factory has successfully developed line frequency coreless bathroom plug stem bottom note type electric insulation casting. In 1982, hospital and Beijing the casting machine research cupola tuyere oxygen blowing technology. 1985-1988, Beijing institute of machine of floating end face seal ring by die successful test pressure casting 1959, Beijing second metalforming machinery general factory changed (Beijing) built 2500 ton heavy-duty hydraulic press. In 1971, the factory produced 6,000 tons, which is then Beijing hydrtesting biggest metalforming equipment. 1968-1979, Beijing hoisting machine factory has 300 tons of using hydraulic press 2000 tons and create crane and large panel. In the 1980s, Beijing institute of electrical and developed a series of Beijing mould centre high-precision cutting die, the multistage close to or to import mould level, changed Beijing precision punching moulds dependence on 1949, Beijing has heat treatment furnace, salt dissolved by thermocouples means furnace, quenching and tempering, parts of annealing, normalizing, quenching and tempering, carburizing and etc. In 1956, Beijing first began using high-frequency quenching machine tool plant. In 1961, the Beijing second machine tool plant began using gas nitriding quenching. In 1969, the following enterprise by Beijing gage start light quenching. In 1978, the complete machine tool research institute of Beijing guide surface contact quenching process and equipment, quenching condition of quality inspection. In 1979, scientific research institute of China academy of railway and mechanical institute of high-power diesel engine cylinder collaboration of surface modification of laser. In 1979, Beijing institute of electrical carbon dioxide laser is developed, and the kilowatt in early 1980s respectively applied in cylinder and stamp printing equipments of laser treatment. Among them, tsinghua university, Beijing, Beijing institute of electrical YouPiaoChang jointly completed YouPiaoChang seven color machine DaKongQi laser surface strengthening research. From 1984 to 1990, Beijing institute of vacuum heat treatment research, gas carburizing microcomputer control technology (Beijing university of aeronautics &astronautics and cooperation), rare earth soft nitriding, powder metallurgy products surface strengthening, kerosene and methanol small drops of microcomputer control method of carburizing, solid boriding and carburizing process computer aided process planning and tracking control system, and the application of new technology heat in production. Welding and cutting in 1949, Beijing has geo-drilling, electric welding and cutting etc oxyacetylene flame manual operation. In 1963, Beijing metal structure and YiJiBu mechanical science research cooperation to develop tungsten argon arc welding, and realize the nitrogen plasma cutting stainless steel. In 1964, the use of dc argon arc welding and tungsten wire alloying technology solved by tilting electrolysis industry worse pure nickel welding. In 1966, Beijing metal structure factory developed by rotating sphere of the submerged arc welding automatic welding. In 1968, the plant began to liquefied petroleum gas (LPG) instead of acetylene cutting. In the early 1980s, tsinghua university invented new MIG welding arc arc technology in control, control a breakthrough. In the early 1980s, the Beijing urban construction design completed liquefied petroleum gas (LPG) mobile pneumatic rail welding technology research and application. In 1990, Beijing metal structure factory to adopt CNC precision cutting and with photo-electricity tracking and CNC pursuit of high input automatic programming technology plasma , China mechanical development in modern development of its rapid.

英文部分 Rotary pumps These are built in many different designs and are extremely popular in modern fluid-power system. The most common rotary-pump designs used today are spur-gear, generated-rotary , sliding-vane ,and screw pump ,each type has advantages that make it the most suitable for a given application .Spur-gear pumps. these pumps have two mating gears are turned in a closely fitted casing. Rotation of one gear ,the driver causes the second ,or follower gear, to turn . the driving shaft is usually connected to the upper gear of the pump .When the pump is first started ,rotation of gears forces air out the casing and into the discharge pipe. this removal of air from the pump casing produces a partial vacuum on the pump inlet ,here the fluid is trapped between the teeth of the upper and lower gears and the pump casing .continued rotation of the gears forces the fluid out of the pump discharge .Pressure rise in a spur-gear pump is produced by the squeezing action on the fluid ad it is expelled from between the meshing gear teeth and casing ,.a vacuum is formed in the cavity between the teeth ad unmesh, causing more fluid to be drawn into the pump ,a spur-gear pump is a constant-displacement unit ,its discharge is constant at a given shaft speed. the only way the quantity of fluid discharge by a spur-gear pump of type in figure can be regulated is by varying the shaft speed .modern gear pumps used in fluid-power systems develop pressures up to about shows the typical characteristic curves of a spur-gear rotary pump. These curves show the capacity and power input for a spur-gear pump at various speeds. At any given speed the capacity characteristic is nearly a flat line the slight decrease in capacity with rise in discharge pressure is caused by increased leakage across the gears from the discharge to the suction side of the pump. leakage in gear pumps is sometimes termed slip. Slip also increase with arise pump discharge pressure .the curve showing the relation between pump discharge pressure and pump capacity is often termed the head-capacity or HQ curve .the relation between power input and pump capacity is the power-capacity or PQ curve .Power input to a squr-gear pump increases with both the operating speed and discharge pressure .as the speed of a gear pump is increased. Its discharge rate in gallons per minute also rise . thus the horsepower input at a discharge pressure of 120psi is 5hp at 200rpm and about 13hp at corresponding capacities at these speed and pressure are 40 and 95gpm respectively, read on the 120psi ordinate where it crosses the 200-and 600-rpm HQ curves .Figure is based on spur-gear handing a fluid of constant viscosity , as the viscosity of the fluid handle increases (. ,the fluid becomes thicker and has more resistance to flow ),the capacity of a gear pump decreases , thick ,viscous fluids may limit pump capacity t higher speeds because the fluid cannot into the casing rapidly enough fill it completely .figure shows the effect lf increased fluid biscosity on the performance of rotary pump in fluid-power system .at 80-psi discharge pressure the pp has a capacity lf 220gpm when handling fluid of 100SSU viscosity lf 500SSU . the power input to the pump also rises ,as shown by the power lf rotary pump is often expressed in gallons per revolution of the gear or other internal element .if the outlet of a positive-displacement rotary pump is completely closed, the discharge pressure will increase to the point where the pump driving motor stalls or some part of the pump casing or discharge pipe ruptures .because this danger of rupture exists systems are filled with a pressure –relief valve. This relief valve may be built as of the pump or it may be mounted in the discharge PumpsThese pumps have a number of vanes which are free to slide into or out of slots in the pup rotor . when the rotor is turned by the pump driver , centrifugal force , springs , or pressurized fluid causes the vanes to move outward in their slots and bear against the inner bore of the pump casing or against a cam ring . as the rotor revolves , fluid flows in between the vanes when they pass the suction port. This fluid is carried around the pump casing until the discharge port is reached. Here the fluid is forced out of the casing and into the discharge the sliding-vane pump in Figure the vanes in an oval-shaped bore. Centrifugal force starts the vanes out of their slots when the rotor begins turning. The vanes are held out by pressure which is bled into the cavities behind the vanes from a distributing ring at the end of the vane slots. Suction is through two ports A and AI, placed diametrically opposite each other. Two discharge ports are similarly placed. This arrangement of ports keeps the rotor in hydraulic balance, reliving the bearing of heavy loads. When the rotor turns counterclockwise, fluid from the suction pipe comes into ports A and AI is trapped between the vanes, and is carried around and discharged through ports B and BI. Pumps of this design are built for pressures up to 2500 psi. earlier models required staging to attain pressures approximating those currently available in one stage. Valving , uses to equalize flow and pressure loads as rotor sets are operated in series to attain high pressures. Speed of rotation is usually limited to less than 2500rpm because of centrifugal forces and subsequent wear at the contact point of vanes against the cam-ring surface.. Two vanes may be used in each slot to control the force against the interior of the casing or the cam ring. Dual vanes also provide a tighter seal , reducing the leakage from the discharge side to the suction side of the pump . the opposed inlet and discharge port in this design provide hydraulic balance in the same way as the pump, both these pumps are constant-displacement delivery or capacity of a vane-type pump in gallons per minute cannot be changed without changing the speed of rotation unless a special design is used. Figure shows a variable-capacity sliding-vane pump. It dose not use dual suction and discharge ports. The rotor rums in the pressure-chamber ring, which can be adjusted so that it is off-center to the rotor. As the degree of off-center or eccentricity is changed, a variable volume of fluid is discharged. Figure shows that the vanes create a vacuum so that oil enters through 180 of shaft rotation. Discharge also takes place through 180 of rotation. There is a slight overlapping of the beginning of the fluid intake function and the beginning of the fluid shows how maximum flow is available at minimum working pressure. As the pressure rises, flow diminishes in a predetermined pattern. As the flow decreases to a minimum valve, the pressure increases to the maximum. The pump delivers only that fluid needed to replace clearance floes resulting from the usual slide fit in circuit relief valve is not essential with a variable-displacement-type pump of this design to protect pumping mechanism. Other conditions within the circuit may dictate the use of a safety or relief valve to prevent localized pressure buildup beyond the usual working automatic control of the discharge , an adjustable spring-loaded governor is used . this governor is arranged so that the pump discharge acts on a piston or inner surface of the ring whose movement is opposed by the spring . if the pump discharge pressure rises above that for which the by governor spring is set , the spring is compressed. This allows the pressure-chamber ring to move and take a position that is less off center with respect to the rotor. The pump theb delivers less fluid, and the pressure is established at the desired level. The discharge pressure for units of this design varies between 100 and characteristics of a variable-displacement-pump compensator are shown in figure. Horsepower input values also shown so that the power input requirements can be accurately computed. Variable-volume vane pumps are capacity of multiple-pressure levels in a predetermined pattern. Two-pressure pump controls can provide an efficient method of unloading a circuit and still hold sufficient pressure available for pilot black area of the graph of figure shows a variable-volume pump maintaining a pressure of 100psi against a closed circuit. Wasted power is the result of pumping oil at 100psi through an unloading or relief valve to maintain a source of positive pilot pressure. Two-pressure –type controls include hydraulic, pilot-operated types and solenoid-controlled, pilot-operated types. The pilot oil obtained from the pump discharge cannot assist the governor spring. Minimum pressure will result. The plus figure shows the solenoid energized so that pilot oil assists compensator spring. The amount of assistance is determined by the small ball and spring, acting as a simple relief valve. This provides the predetermined maximum operating type of two-pressure system employs what is termed a differential unloading governor. It is applied in a high-low or two-pump circuit. The governor automatically, Through pressure sensing, unloads the large volume pump to a minimum deadhead pressure setting. Deadhead pressure refers to a specific pressure level established as resulting action of the variable-displacement-pump control mechanism. The pumping action and the resulting flow at deadhead condition are equal to the leakage in the system and pilot-control flow requirements. No major power movement occurs at this time, even though the hydraulic system may be providing a clamping or holding action while the pump is in deadhead position The governor is basically a hydraulically operated, two-pressure control with a differential piston that allows complete unloading when sufficient external pilot pressure is applied to pilot unload minimum deadhead pressure setting is controlled by the main governor spring A. the maximum pressure is controlled by the relief-valve adjustment B. the operating pressure for the governor is generated by the large-volume pump and enters through orifice C. To use this device let us assume that the circuit require a maximum pressure of 1000psi, which will be supplied by a 5-gpm pump. It also needs a large flow (40gpm) at pressure up to 500psi; it continues to 1000pso at the reduced flow rate. A two-pump system with an unloading governor on the 40-gpm pump at 500psi to a minimum pressure setting of 200psi (or another desired value) , which the 5-gpm pump takes the circuit up to1000psi or in figure that two sources of pilot pressure are required. One ,the 40-gpm pump, provides pressure within the housing so that maximum pressure setting can be obtained. The setting of the spring, plus the pressure within the governor housing, determines the maximum pressure capacity of the 40-gpm pump. The second pilot source is the circuit proper, which will go to 1000psi. this pilot line enters the governor through orifice D and acts on the unloading piston E . the area of piston E is 15 percent greater than the effective area of the relief poppet F. the governor will unload at 500psi and be activated at 15percent below 500psi, or 425psi. By unloading, we mean zero flow output of the 40-gpm pressure in the circuit increases from zero to 500psi, the pressure within the governor housing also increases until the relief-valve setting is reached, at which time the relief valve cracks open, allowing flow to the pressure drop in the hosing is a maximum additive value, allowing the pump to deadhead. Meanwhile, the system pressure continues to rise above 700psi, resulting in a greater force on the bottom of piston E than on the top. The piston then completely unseats poppet F, which results in a further pressure drop within the governor horsing to zero pressure because of the full-open position of the relief poppet F. flow entering the housing through orifice is directed to the tank pass the relief poppet without increasing the pressure in housing. The deadhead pressure of the 40-gpm pump then decreases to the lower set value. Thus , at the flow rate to the unloading governor ,the 40gpm pump goes to deadhead. The flow rate to the circuit decreases to 5gpm as the pressure to 1000psi, the 5-gpm pump is also at its deadhead setting, thus only holding system 4-gpm pump unloads its volume at 500psi. It requires a system pressure of 600psi to unload the 40-gpm pump to its minimum pressure of 200psi. the 600-psi pilot supply enters through orifice D and acts on the differential piston E. The pumps volume is reduced to zero circuit-flow output at 500psi. The additional 100-psi pilot pressure is required to open poppet F completely and allow the pressure within the housing to decrease to circuit pressure decreases ,both pumps come back into service in a similar pattern.

IntroductionMachining aims to generate the shape of work-piece form a solid body,or to improve the tolerances and surface finish of a previously formed work-piece,by removing excess materials in the form of chips. Machining is capable of creating geometric configurations,tolerances, and surface finishes often unobtainable by any other , machining removes materials, which has already been paid for, in the form of relatively small particles that are more difficult to recycle and are in greater danger of becoming mixed. Therefore,developments often aim at reducing or-if at all possible-eliminating machining, especially in mass these reasons, machining has lost some important markets, yet, at the same time, it has also been developing and especially having captured new markets with the application of numerical feel for the important of machining may be gained from the observation that in 1983 there were about 2 million metal-cutting machine tools in the unite states ( of which some 5% were numerically controlled ) and that labor and overhead costs amounted to $125 billion, or 3% of the GNP.