数控电火花成型机床设计【含PDF图纸+CAD制图+文档】
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Electrical-Discharge Machining1. Electrical-discharge Machining Electrical-discharge machining (EDM),or spark machining, as it is also called, removes material with repetitive spark discharges from a pulsating DC power supply, with a dielectric flowing between the work piece and the tool. The principle of the EDM process is illustrated by the simplified diagram. The tool is mounted on the chuck attached to the machine spindle whose motion is controlled by a servo-controlled feed drive. The workpiece is placed in a tank filled with a dielectric fluid; a depth of at least 50mm over the work surface is maintained to eliminate the risk of fire. The tool and workpiece are connected to a pulsating DC power supply. Dielectric fluid is circulated under pressure by a pump, usually through a hole or holes in the tool electrode. A spark gap of about 0.025 to 0.05mm is maintained by the servomotor.In power supplies for EDM the input power is first converted into continuous DC power by conventional solid-state rectifiers. The flow of this DC power is then controlled by a bank of power transistors which are switched by a digital multivibrator oscillator circuit. The high-power pluses output is then applied to the tools and work piece to produce the sparks responsible for material removal.Each spark generates a localized high temperature on the order of 12000 in its immediate vicinity. This heat caused 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 piece 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 toward the work piece by a servo-controlled feed mechanism.Each pulse in the EDM cycle lasts for only a few microseconds. Repeated pulses, at rates up to 100000 per second, result in uniform erosion of material from the work piece and from the electrode. As the process progressed, the electrode is advanced by the servo drive toward the work piece to maintain a constant gap distance until the final cavity is produced. Application Electrical-discharge machining can be used for all electrically conducting materials regardless of hardness. The process is most suited to the sinking of irregularly shaped holes, slots, and cavities. Fragile work pieces can be machined without breakage. Holes can be of various shapes and can be produced at shallow angles in curved surfaces without problems of tool wander.The EDM process finds greatest application at present in toolmarking, particularly in the manufacture of press tools, extrusion dies, forging dies, and molds. Graphite electrodes produced by copy milling from patterns are often used.A great advantage of EDM is that the tool or die can be machined after it is hardened and hence great accuracy can be achieved. Tools of cemented carbide can be machined after final sintering, which eliminates the need for an intermediate partial sintering stage, thus eliminating the inaccuracies resulting from final sintering after holes, slots, and so on, are machined.Electrical-discharge machining can be used effectively to drill small high-aspect-ratio holes. Diameters as small as 0.3mm in material 20mm or more in thickness can be readily achieved. With efficient flushing, holes with aspect ratios as high as 100:1 have been produced. The process has been used successfully to produce very-small-diameter holes in hardened fuel-injector nozzles. Varying numbers of holes in a precise patten can be drilled around the injector tip.2Numerical Control Numerical control (NC) is a method of controlling the movements of machine components by directly inserting coded instructions in the form of numerical data (numbers and data) into the system. The system automatically interprets these data and converts it to output signals. These signals, in turn control various machine components, such as turning spindles on and off, changing tools, moving the workpiece or the tools along specific paths, and turning cutting fluids on and off. In order to appreciate the importance of numerical control of machines, lets briefly review how a process such as machining has been carried out traditionally. After studying the working drawing of a part, the operator sets up the appropriate process parameters(such as cutting speed, feed, depth of cut, cutting fluid, and so on), determines the sequence of operations to be performed, clamps the workpiece in a workholding device such as a chuck or collet, and proceeds to make the part. Depending on part shape and the dimensional accuracy specified, this approach usually requires skilled operators. Furthermore, the machining procedure followed may depend on the particular operator, and because of the possibilities of human error, the parts produced by the same operator may not all be identical. Part quality may thus depend on the particular operator or even the same operator on different days or different hours of the day. Because of our increased concern with product quality and reducing manufacturing costs, such variability and its effects on product quality are no longer acceptable. This situation can be eliminated by numerical control of the machining operation.We can illustrate the importance of numerical control by the following example. Assume that holes have to be drilled on a part in the positions shown in the picture. In the traditional manual method of machining this part, the operator positions the drill with respect to the workpiece, using as reference points any of the three method shown. The operator then proceeds to drill these holes. Lets assume that 100 parts, having exactly the same shape and dimensional accuracy, have to be drilled. Obviously, this operation is going to be tedious because the operator has to go through the same motions again and again. Moreover, the probability is high that, for various reasons, some of the paths machined will be different from others. Lets further assume that during this production run, the order for these paths is changed, so that 10 of the paths now require holes in different positions. The machinist now has to reset the machine, which will be time consuming and subject to error. Such operations can be performed easily by numerical control machines that are capable of producing parts repeatedly and accurately and of handling different parts by simply loading different part programs.In numerical control, data concerning all aspects of the machining operation, such as locations, speeds, feeds, and cutting fluid, are stored on magnetic tape ,cassetts, floppy or hard disks, or paper or plastic (Mylar, which is a thermoplastic polyester) tape. Data are stored on punched 25mm wide paper or plastic tape, as originally developed and still used. The concept of NC control is that holes in the tape represent specific information in the form of alphanumeric codes. The presence (on) or absence (off) of these holes is read by sensing devices in the control panel, which then actuate relays and other devices (called hard-wired controls). These devices control various mechanical and electrical systems in the machine. This method eliminated manual setting of machine positions and tool paths or the use of templates and other mechanical guides and devices. Complex operations, such as turning a part having various contours and die sinking in a milling machine, can be carried out.Numerical control has had a major impact on all aspects of manufacturing operations. It is a widely applied technology, particularly in the following areas:a) Machining centers.b) Milling, turning, boring, drilling, and grinding.c) Electrical-discharge, laser-beam, and electron-beam machining.d) Water-jet cutting.e) Punching and nibbling.f) Pipe bending and metal spinning.g) Spot welding and other welding and cutting operation.h) Assembly operations.Numerical control machines are now used extensively in small-and-medium-quantity (typically 500 parts or less) of a wide variety of parts in small shops and large manufacture facilities. Older machines can be retrofitted with numerical control. Advantages and Limitations Numerical control has the following advantages over conventional method of machine control:1. Flexibility of operation and ability to produce complex shapes with good dimensional accuracy, repeatability, reduced scrap loss, and high production rates, productivity, and product quality.2. Tooling costs are reduced, since templates and other fixtures are not required.3. Machine adjustments are easy to make with minicomputer and digital readout.4. More operations can be performed with each setup, and less lead time for setup and machining is required compared to conventional methods. Design changes are facilitated, and inventory is reduced.5. Programs can be prepared rapidly and can be recalled at any time utilizing microprocessors. Less paperwork is involved.5. Faster prototype production is possible6. Required operator skill is less, and the operator has more time to attend to other tasks in the work area. The major limitations of NC are the relatively high cost of the equipment and the need for programming and special maintenance, requiring trained personal. Because NC machines are complex systems, breakdowns can be very costly, so preventive maintenance is essential. However, these limitations are often easily outweighed by the overall economic advantages of NC. 3Scope of CAD/CAMComputer-aided design is the use of computer systems to facilitate the creation, modification, analysis, and optimization of a design. In this context the term computer system means a combination of hardware and software. Computer-aided manufacturing is the use of a computer system to plan, manage, and control the operation of a manufacturing plant. An appreciation of the scope of CAD/CAM can be obtained by considering the stages that must be completed in the design and manufacture of a product, as illustrate by the product cycle shown. The inner loop of this figure includes the various steps in the product cycle and outer loop show some of the functions of CAD/CAM superimposed the product cycle. Based on market and customer requirements, a product is conceived, which may well be a modification of previous products. This product is then designed in detail, including any required design analysis, and drawings and parts lists are prepared. Subsequently, the various components and assemblies are planned for production, which involves the selection of sequences of processes and machine tools and the estimation of cycle times, together with the determination of process parameters, such as feeds and speeds. When the product is in production, scheduling and control of manufacture take place, and the order and timing of each manufacturing step for each component and assembly is determined to meet an overall manufacturing schedule. The actual manufacturing and control of product quality then takes place according to the schedule and the final products are delivered to the customers.Computer-based procedures have been or are being developed to facilitate each of these stages in the product cycle. Computer-aided design and drafting techniques have been developed. These allow a geometric model of the product and its components to be created in the computer. This model can then be analyzed using specialized software packages, such as those for finite element stress analysis, mechanisms design, and so on. Subsequently, drawings and parts lists can be produced with computer-aided drafting software and plotters. Computer-aided process-planning systems, including the preparation of NC programs, are available that produce work plans, estimates, and manufacturing instruction automatically from geometric descriptions of the components and assemblies.For scheduling and production control, large amounts of data and numerous relatively simple calculations must be carried out. One example is the determination of order quantities by subtracting stock levels from forecasts of the number of items required during a particular manufacturing period. Many commercial software packages are available for scheduling, inventory control, and shop floor control, including materials requirements planning (MRP) system. At the shop floor levels computers are used extensively for the control and monitoring of individual machines.There is a difference in the time scale required for processing data and the issuing of instruction for these various applications of computers in the product cycle. For example, design and process-planning functions are carried out once for each new product and the time scale required is on the order of weeks to years for the completion of the whole task. Scheduling and production controls tasks will be repeated once every production period (usually one week) throughout the year. A t the machine-control level instructions must be issued continually with a time scale of micro-or nanoseconds in many cases.One of the major objectives of CAM is the integration of the various activities in the product cycle into one unified system, in which data is transferred from one function to another automatically. This leads to the concept of computer-integrated manufacture (CIM), with the final objective being the “paperless” factory. Several developments have taken place, but no totally integrated CIM systems have yet been achieved. Since the design and process-planning function are carried out once in the product cycle, these are the most suitable functions for integration. This integration is particular desirable because the geometric data generated during the design process is one of the basic inputs used by process planning when determining appropriate manufacturing sequences and work plans. Consequently, various activities in design and process planning can share a common design and manufacturing data base. With such a system ,geometric models of the products and components are created during the design process. This data is then accessed by various downstream activities, including NC programming, process planning, and robot programming. The programs and work plans generated by these activities are also added to the data base. Production control and inventory control programs can then access the work plans, time estimate, and parts lists (bill of material file), in preparing the manufacturing schedules, for example. 电火花加工技术1电火花加工电火花加工（EDM），顾名思义，它是通过脉冲直流电源不断产生火花放电来去除工件材料的，且在工件与工具之间有绝缘液体介质。电火花加工的工作原理如简图所示。工具夹在卡盘上，卡盘与由伺服进给系统控制的主轴相连。工件放在充满绝缘液体介质的工作槽中。在工作表面至少要维持50mm的距离，是为了消除火灾的隐患。工具和工件与脉冲电源的两输出端相连。绝缘液体介质通过工具电极的小孔，经油泵加压，强迫循环的。伺服系统控制电火花间隙为0.025-0.05mm。电火花加工的电源首先是将输入的电源通过晶体整流管转化为直流电源，直流电源又受到通过数字多谐振荡电路转换来的晶体管的控制。输出的高频脉冲作用到工具和工件上，产生电火花来去除工件材料。每个电火花瞬间产生高达12000的局部高温，这些热量使部分绝缘液体介质蒸发，也使工件表面蚀除一小部分金属，在工件表面形成一个小凹坑。由于在极间距离相对最近击穿放电，工件表面逐渐被蚀除掉，工具的形状复制到工件上了。在此过程中形成的一些浓缩的金属小屑被流动的绝缘液体介质排除出去。随着金属被蚀除掉，工具电极通过饲服进给系统控制向工件进给。电火花加工中每个脉冲延续的时间只有几个微秒，经过不断的重复放电，工件和工具电极有一样的腐蚀形状。随着电火花加工的进行，工具电极不断向工件进给，直到加工完成，一直保持一定的放电间隙。应用 电火花加工能加工任何硬度的导电材料，且大部分用于加工不规则的孔，槽和型腔。那些刚度低的工件也可以加工。电火花加工还可加工出各种形状的孔以及曲面上角度很小的孔，且不存在工具漂移的问题。目前，电火花加工极广泛地用于模具制造，特别是压力机模具，挤压模，锻模和铸模等。通过模型复制制造出来的石墨电极也经常使用。电火花加工的优点就是工具在硬化处理后仍能加工出来，因此能达到很高的精度。硬质合金的工具在烧结后也能加工出来。电火花加工能有效的加工出又小又深的孔。已经在直径只有0.3mm的材料上钻出深20mm甚至更深的孔。经过有效的吹氮脱气，可以加工出宽径比为100：1的孔。电火花加工已成功地用于已淬硬喷油嘴的极小孔的加工，能在喷油嘴周围精确的钻出大量的孔。2数字控制数控是一种用数字控制机床各部件运动的方法，通过直接向系统输入指令代码（数字和字母）来完成的。系统自动将这些指令代码转化成信号输出。这些信号依次控制机床各种部件的运动，比如主轴的启动和停止，刀具的转换，沿指定路径移动刀具和工件，控制切削液的通断等等。为了说明数控机床的重要性，我们来简单回顾一下传统机床的加工过程。操作者研究零件工作图后，调整合适的加工参数（如切削速度，进给量，切削深度，切削液等等），安排加工顺序，然后将工件夹紧在夹具（如卡盘或夹头）上，再开始加工。根据所规定的工件形状和尺寸精度，这种加工通常需要熟练的操作工。而且，其后续加工是由各个操作者完成的。由于存在不可避免的人为误差，即便由同一个人加工出来的零件也不可能完全相同。因此，零件的质量就可能取决于操作者的操作水平，甚至取决于该工人在不同时期或不同时间的状态。由于我们越来越关注加工质量和降低加工成本，所以我们不再允许存在零件偏差和产品的质量影响，而通过数控加工就可以消除以上这些情况。我们可以通过以下的例子来说明数控加工的重要性。假如要在图示位置的零件上钻这几个孔，当传统的手工操作机床加工此零件时，操作者可选图示三种方法中的任一种，使钻头与工件上的点相对应着，然后钻这些孔。假如要加工100个同样形状，同样尺寸，同样精度的零件，很明显，操作者会觉得很枯燥，因为操作者要一遍又一遍重复同样的动作，而且，由于各种原因。有些零件加工出来的不一样的可能性是很高的。我们进一步假设，在操作过程中，零件的加工要求要改变，现在要在不同的位置加工出10个孔，机械师必须马上调整机床，这样既浪费时间又增加了加工误差。而数控机床能够重复而准确地加工工件，而且可通过简单地输入不同程序来加工不同的零件。因此，使用数控机床就可以轻而易举地完成此类加工。在数控系统中，与加工过程各种相关的数据如工件的定位，切削速度，进给量和切削液，储存在磁盘，盒式录音带，软盘，硬盘，纸带或塑料纸（热塑性树脂）上。将数据存储在25mm宽的穿孔纸带或塑脂带上，这种数据存储方法使用最早并沿用至今。数控的概念就是纸带上的孔表示以字母代码表达的特定信息。这些孔的打开和关闭由控制面板的感应元件控制，然后驱动继电器和其他机械导向装置。一些复
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