01英语翻译资料03.15.doc

郑州大学 机械工程学院 机械工程及其自动化专业 2000级9班 常志军 2000013905 2004-03-15 Research and a few and new improvement measures of the electricity spark processing technology（EDM） Electrical-Discharge Machining (EDM), or spark machining, as it is also called, is based on the eroding, effect of an electric spark on both the electrodes used to produce it. It has been found from observation that if both electrodes are made of the same material, greater erosion occurs on the positive electrode. Hence, to obtain maximum metal removal with minimum wear on the tool electrode, the work is made the positive and the tool the negative electrode.The electricity spark processes the principle of the craftThe essential condition that electricity spark process(1) the work piece is to conducts electricity. (2) the tool electrode were processed with the work piece the surface keeps certain cleft.Turn on electricity the cleft roughly 0.01 mms.Cleft over big broke through to lie the quality do not produce to turn on electricity, cleft over small result in the short circuit to also does not produce to turn on electricity. (3) the spark turns on electricity to want to proceed in had certainly liquid of insulating the function lay quality. (4) the spark turns on electricity to turn on electricity for the pulse spark of the moment, close together pulse contain a partition, can make insulate to lie the quality 消 electricity leave.Turn on electricity even to take to give or get an electric shock a son in the passage compound for neutral a son, in order to wait for a pulse turns on electricity, also can avoid the calories proliferation results in to suffer burns.The principle of the electrical-discharge-machining process is illustrated by the simplified diagram in Fig.1. the tool is mounted on the chuck attached to the machine spindle whose vertical feed is controlled by the servomotor through a reduction gearbox. The workpiece is placed in a tank filled with a dielectric fluid; a depth of at least 50 mm (2 in.) over the work surface is maintained to eliminate the risk of fire. The tool and workpiece are connected to a dc relaxation circuit fed from a dc generator. Dielectric fluid is circulated under pressure by a pump, usually though a hole (or holes) in the tool electrode. A spark gap of about 0.025 to 0.05 mm (0.001 to 0.002 in.) is maintained by the servomotor.When the power supply is switched on, the condenser voltsge Vc begins to increase exponentially toward the supply voltage Vs (Fig.2).During this initial period the spark gap behaves as an open circuit, and no current flows. As the voltage Vs builds, it reaches the gap breakdown voltage Vc(determined by the gap width and the dielectric fluid),a spark is produced across the gap, the dielectric fluid ionizes, and the condenser is discharged. The surrounding dielectric then deionizes so that it again becomes effective insulator, and the cycle is repeated. In this way a rapid succession of spark is obtained, the interval between successive sparks being on the order of 100us. Fig.1 Electrical-discharge machining Fig.2 Voltage and current in electrical-discharge machiningEach spark generates a localized high temperature on the order of 12000in its immediate vicinity. This heat causes part of the surrounding dielectric fluid to evaporate; it also melts and vaporizes the metal to form a small crater on the work surface. Since the spark always occurs between the points of the tool and work that are closest together, the high spots of the work are gradually eroded, and the form of the tool is reproduced on the work. The condensed metal globules, formed during the process, are carried away by the flowing dielectric fluid. As the metal is eroded, the tool is fed in by a servocontrolled feed mechanism. Servocontrol system with affect the important factor that give or get an electric shock the spark processThe servomechanism, shown in its simplest form in Fig.2, consists mainly of a reversible servomotor connected between one terminal of the condenser (D) and the slider of a variable resistance (B) .A and C are at the same potential; if the mean value of the voltage Vc(Fig.2) is equal to the preset voltage between A and B, the potentials at B and D are equal, and the servomotor remains stationary. If however, the mean value of the voltage Vc changes because of changes in gap width, the potential at D will change, and the servomotor will rotate until the require gap is again obtained. In this way the servo system maintains the mean sparkgap voltage(and hence the gap width) at a constant value. The motor must be reversible because if the servomechanism overshoots or short circuits as a result of the accumulation of swarf in the gap, the tool must be withdrawn. A constant gap of about 0.025 to 0.05 mm(0.001 to 0.002 in.) is usually maintained, the exact gap value may be varied by changing the setting of the variable resistance.Other types of control used in practice usually operate by sensing either the gap voltage or the gap capacitance.The high rate of tool wear is one of the major difficulties in EDM. The wear ratio, defined as the volume of metal removed from the tool divided by the volume of metal removed from the work, varies with the tool and work materials used. For example, with a brass tool and a brass workpiece theratio is approximately 0.5, while for a brass tool and a hardened-carbon-steel workpiece it is approximately unity and for a brass tool and a tungsten carbide workpiece the ratio may be as high as 3. With suitably chosen materials wear ratios as 0.1 can be achieved. High tool-wear rates result in inaccurate machining and add considerably to the expense since the tool electrode itself must usually be accurately machined. For these reasons, the search for suitable tool materials has received much attention in the past. For common purposes brass or copper is often used, but where electrode wastage must be minimized, copper graphite and tungsten carbide are used to advantage. Tungsten wire is often employed for drilling deep holes of small diameter because it can better withstand the tendency to buckle as a result of shock waves produced by the spark discharge or physical contact with the workpiece in the case of overshoot.The higher the melting point of the tool material, the lower the melting point of the tool material like copper graphite are used, it is found that while the copper matrix quickly erodes at the tip of the tool, the graphite (which has a high melting point) prevents further rapid erosion. (The copper in the ramainder of the tool is thus protected and helps keep the electrical resistance of the tool low.)The metal-removal rate depends mainly on the electrical parameters, and these parameters are discussed in this chapter. However, it is important to note that a lower removal rate results in an improved surface finish so that a compromise must be achieved depending on whether rough or finish machining is intended. This compromise is similar to that in conventional processes where a good surface finish requires low feeds, which, in conjunction with the practical limitation on cutting speeds, means low metal-removal rates.With improved types of pulse generators a removal rate of 0.09cm/s (0.33 in./min) has been obtained under roughing conditions.The removal rate is affected by the duration of the individual sparks for a given quantity of electrical energy. It has been found that for a given power an optimum discharge time exists giving maximum metal removal per discharge. However, if the discharge time is too small, the wear on the tool becomes excessive, and this excessive tool wear reduces the accuracy of the process.General applications The electricity spark processes of used for the type bore that process the molding tool that have the complicated shape with the type antrum primarily with the spare parts; Process every kind of hard, frailty material, wait with the quenching fire steel such as the hard quality metal alloy; Process the deep thin bore, abnormal shape bore, deep slot, narrow sew with incise thin slice etc; Process every kind of take shape the knife have, the sample product have with thread wreath rules etc. tool with the deal.A great advantage of the spark-machining process is that the tool or die can be spark-machined after it is hardened, and hence great accuracy can be achieved. Tool cemented carbide can be machined after final sintering, which eliminates the need for an intermediate partial sintering stage and hence eliminates the inaccuracies resulting from final sintering after holes, etc., are machined.The oil-retention property of the surface produced makes the process suitable for finishing plain bearings and the bores of internal combustion engine cylinders. Moreover, the absence of directional patterns and microcracks in the surface reduces the possibility of fatigue failures. The process has also been successfully used to drill very-small-diameter holes in such hardened parts as nozzles for diesel engine fuel injectors.A few and new improvement of the electricity spark processing technology1. Have the very high bearing the development of the corrosive electrode material It be experimented by science proof, draw in the brass electrode surface a the layer is thicker and high to melt to order the material, for example W, ZRB2, TIB2 can than goodly exaltation electrode service life. According to this principle, from TEXAS A& the university of M is new to develop a heat for in the tool, work an electrode a creation term next, bear the really fine electrode in function in corrosion material. This kind of is new- researched to manufacture to make to bear corrosive electrode material as the ZRB2/ CU in order to, belonging to the metals porcelain and ceramics. It has the high melting point, transmit heat the characteristics that sex like. Therefore, it can compare the brass electrode to turn with the tungstate and the service life of the copper electrode increases 3 5 times, but lower than graphite electrode in price. Increases to process the spare parts surface quantity at the same time. New electrode material ZRB2/ CU from below the step makes into: For making its can process in laser that choose the type burning knot machine bed( SLS), draw the pure the powder of ZRB2 first a the layer comes together; it Will put into through the powder of ZRB2 that draw to glue to connect to model in the SLS machine molding tool in the bed the juniors line burn the knot; The laser burns the coming together of knot empress ZRB2 powder inside draws the thing to under the heat vaporize; Will burn the density that knot like to 35 s 70% ZRB2s place in the vacuum furnace, make into after seeping into the CU. In addition to making the electrode, the ZRB2/ CU can still used for the other aspect, for example, create to give or get an electric shock the electric welding can also be used as the micro-electronics a surface draws with wait the ion the jet draws the material.2Replace to process the liquid with the air From the TOKYO agriculture university a research for proceeding detection: The high pressure air can pass on the electrode oil bore enters the tool, work an electrode contact area; A very high pressure air can rise the commonness processes the liquid can not rises of insulate the result; High pressure air can the clearance be processed by electrode the miscellaneous quality in etc. in broken bits of a creation, combine to have the good cooling function. As a result can used for small scaled three-dimensional sophisticate the electricity spark of the spare parts processes, replacing best the commonness process the liquid, can lower the production cost.3. Increase to conduct electricity the powder in process liquid It be processed by electricity spark to experiment the enunciation, increase the powder of silicon in process liquid, ameliorable after processing superficial and rough degree in spare parts. This is because of the affiliation of the powder of silicon , enlarged the tool, work an electrode a long-lost electric capacity for of resistance, repressing pulse turning on electricity inside. Along with the decrease of the long-lost electric capacity, make rough degree in a surface for of electric capacity letting up, each time turning on electricity pulse number of times reducing, as a result improving processing spare parts in an electrode in tool, work. According to same principle with process the fulfillment proof, the usage contents suspend other conduct electricity the powder process the liquid, also can improve rough degree in surface that after processing spare parts. This process with the molding tool to precise aviations spare part particularly important, it can the province go to the work preface to process after throwing the light before, increase production efficiency, lower the production cost.4. To conduct electricity not the material proceed to process The usually so-called electricity spark processes, it must be to conduct electricity the material. Japan most in the last few years threw in a flood of material resources, manpower, to insulate goodly the porcelain and ceramics material proceeded the electricity spark processes to experiment the research. They adopt the good metals in electrical conductivity material, drawing or electroplating to process at the porcelain and ceramics spare parts that wants superficial, make experiment to achieve success in common electricity spark processing machine bed. Can see from experiment, turn on electricity to process to the surface at the same time at the electrode metals layer that draw, the heat, thermal energy of the mighty electricity spark creation can melt, decay the porcelain and ceramics spare parts at the same time. Current, have caned insulate with the other to every kind of porcelain and ceramics material the material proceed to process. This a technical improvement, not only extend to process the scope biggest, but also the adoption draws the material that electrical conductivity like in the common metals the method on the material, also can increase the electricity spark process the speed with process the accuracy.5. Revolve the electrode to proceed to give or get an electric shock to a c