电火花加工技术应用在模具制造中电加工的应用（Application of EDM Technology in die manufacturing）.doc

电火花加工技术应用在模具制造中电加工的应用（Application of EDM Technology in die manufacturing）Application of EDM Technology in die manufacturingRelated topics: Die technology, literature time: 2010-08-25 10:02In todays world, with each passing day, all walks of life are developing rapidly. Among them, the development of materials science and the development of the machinery industry are particularly rapid, and the links between the two industries are becoming more and more close. Among them, a very specific performance is with the development of material science, in order to meet the needs of some special circumstances, a large number of high strength, high hardness, high toughness, high brittleness, high temperature and other special properties of die materials have been produced, which has brought many difficulties and problems to the traditional. With the traditional processing methods to meet the requirements. As for the workpiece with complex structures, such as complex cavity die hole model by cutting the traditional methods it is often difficult to achieve, so people in the production of some new methods, and some have been widely used. Among them, EDM is one of them. It is widely used in die and mould manufacturing industry.First, the mechanism and characteristics of EDMElectrical discharge machining (EDM) is a method of machining workpieces in a certain medium by means of electrical erosion between the electrodes of the tool and the discharge of the electrodes between the workpieces. The principle of EDM is shown in the following figure.Automatic feed adjustment device for the 3 hydraulic cylinder and piston to keep discharge between the tool and the workpiece in a small gap, when the pulse voltage applied between the poles, then at that time under the conditions of relative to a minimum gap or the insulation strength of the weakest breakdown medium in the local production of spark discharge, the tool and the instantaneous high temperature the workpiece surface partial melting, vaporization and even electric erosion off a small part of the metal, each form a small pits. The pulse after discharge, through the pulse interval, so that the working fluid recovery after insulation, second pulse voltage and added to the poles, and at the time the distance between the relatively recent or weakest at the breakdown discharge and electrical insulation, corrosion of a small pit. The entire machined surface will consist of numerous small pits. This discharge cycle repeats thousands of times per second to tens of thousands of times, causing the surface of the workpiece to form many, very small pits called electrical erosion. As the tool electrode continues to feed, the outline size of the tool electrode is precisely "copied" on the workpiece to achieve the purpose of forming.Electrical discharge machining (EDM) can process various materials with high melting point, high hardness, high strength, high purity and high toughness, but its machining mechanism is different from that of the cutting method, and has the following characteristics:1, pulse discharge energy density is high, easy to process, with ordinary mechanical processing method difficult to process or unable to process special materials and complex shape workpiece. Not affected by material hardness, not affected by heat treatment condition. 2, the duration of pulse discharge is very short, the heat conduction in discharge is small and the range of heating is small. 3, when machining, tool electrode and workpiece materials do not contact, the smallest of the micro force between the two. Tool electrode materials do not need to be harder than workpiece materials, so tool electrodes are easy to manufacture. 4, we can reform the structure of the workpiece, simplify the processing technology, improve the service life of the workpiece and reduce the labor intensity of the workers.Two, the main factors affecting the quality of die EDMThe processing quality of the die mainly includes machining accuracy and the quality of the etched surface. Because of the EDM process input and output parameters more and more complex, the influence of die machining precision process factors involved in organic bed itself manufacturing precision, workpiece clamping precision, electrode manufacture and clamping precision, electrode loss, discharge gap, machining inclination etc., the electrode loss and discharge gap greater impact.1, the influence of electrode loss on machining accuracyIn the mold EDM process, pulse discharge will make the tool electrode by galvanic corrosion and loss, thus to understand and grasp the law of electrode loss and take various measures, to minimize the loss of tool electrode,To ensure that the mold has higher machining accuracy. EDM, different parts of the tool electrode loss situation is different, the electric field strength usually sharp corners, edges and projections of the high, easy to form the tip discharge, so the loss ratio of flat parts to be fast, uneven loss will inevitably lead to a decline in accuracy. The electrode loss is also affected by the thermal and physical constants of the electrode material. The higher the melting point, boiling point, specific heat capacity, melting and gasification latent heat of electrode materials, the greater the thermal conductivity, the better the corrosion resistance, the better the heat transfer ability, and thus the electrode loss can be reduced.2, the impact of discharge gap on the machining accuracyEDM die, pulse discharge need to maintain a discharge gap between the tool electrode and the workpiece, and the processed workpiece hole size and electrode size compared to the contour along the processing by a discharge gap. The discharge gap mainly determines the machining stability, and the increase of the pulse gap time can improve the machining stability. Increasing peak current will increase productivity, but the electrode loss will increase.When the surface layer is deepened, the roughness will become larger. To make the discharge gap remained stable, must make the electrical parameters of pulse power supply remains stable, moreover also should make the machine precision and rigidity are stable, while paying special attention to the influence of the two products caused by spark erosion on the discharge gap.3, influence on the machined surface roughnessThe roughness parameter Ra of the etched surface increases with the increase of pulse width and current peak. Under certain processing conditions, the increase of pulse width and current peak will increase the energy of single pulse and increase the cross section size of erosion pits, so the surface roughness mainly depends on the size of single pulse energy. To reduce the value of the surface roughness Ra, the energy of a single pulse must be reduced.4. The influence of surface change layer on the surface quality of moldThe surface of the die after EDM will produce a surface change layer including the solidification layer and the heat affected layer. The surface of the workpiece material layer is solidified in high temperature instantaneous pulse discharge under the melting and not thrown, rapid cooling, in pulsed discharge after the metal layer solidification and preserved, the metal layer of very fine grain, strong corrosion resistance.The heat affected layer is located between the solidification layer and the material of the workpiece. Because of the high temperature caused by the discharge point, the microstructure of the material changes. In the process of processing, due to the selected electrical parameters, the cooling conditions and the workpiece material of the original heat treatment conditions are different, change the hardness of the layer will be different. The thickness of the surface change layer is related to the material parameters of the workpiece and the electrical parameters of the pulse power supply. The thickness of the surface change layer is thickened with the increase of the pulse energy, and the hardness of the solidified layer is usually higher. Therefore, the wear resistance of the die surface after EDM is better than that of the conventional machining.Three 、 application of EDM Technology in die manufacturingDue to the rapid development of mold industry, in order to meet the needs of some special circumstances, a large number of high strength, high hardness, high toughness, high brittleness, high temperature and other special properties of die materials have been produced, which has brought many new difficulties and problems to traditional metal cutting, using the traditional processing methods to at this time, to meet the requirements of EDM technology have been widely used and mold processing. With the application of EDM Technology in the die and mould industry, the traditional mold processing technology has been greatly affected, and the processing flow of the die has been changed. Conventional processing methods are milling after annealing, then heat treatment, grinding or EDM. Finally, grinding and polishing by hand, the processing cycle is very long. Dies are often scrapped because of quenching, deformation or cracking. EDM can be processed after quenching of the template, and avoid disadvantages and the structural thermal deformation, which simplified the mold structure, and can improve the strength and life of die. #p# paging Title #e#Electro spark modification technology is widely used in mould surface to improve the quality of mould surface,The working principle of electrical discharge to produce high temperature, with hard alloy YG8 as electrode materials, hard alloy material is infiltrated into working surface of mould and wearing parts, forming a layer of high hardness, high strength, high wear resistance, high temperature resistance, and stripping of hard white alloy strengthening layer, change the physical and chemical properties of the surface, is to mold surface treatment method is very effective. The electric spark strengthening layer is a new alloy layer formed by the alloying of the electrode and the workpiece material in the instant of discharge at high temperature and high pressure. It is not a simple coating and accumulation of the electrode material. The diffusion layer between the alloy layer and the base metal has the nitrogen element and the like, and is firmly bonded with the base body and is extremely resistant to impact. Strengthening treatment, the discharge time is short, the discharge point of the area is small, the effect of thermal discharge occurs only in small regions of the surface of workpiece, and the workpiece is still in the state of normal temperature or low temperature, the workpiece is cold, short time, no deformation or thermal annealing. Electrical discharge modification is carried out in an air or liquid medium. It can act on the local surface of parts, and can also modify the plane or curved surface of general geometric shapes, such as tools, moulds, mechanical parts, etc. The electrode material can be based on the use of free choice in the repair of worn machine parts, using carbon, copper and brass as electrode materials, the material source is wide, and the material consumption is little. The modified layer with different thickness and surface roughness can be obtained by controlling the electrical parameters and modifying the control time. The operation method is easy to control, and the operators with high technical level are not needed. It can use a small amount of material to the whole material expensive, difficult to achieve results, which can improve the hardness, wear resistance and high red hardness and other properties, improve the service life of the product, but also can greatly reduce the consumption of expensive materials, reduce production or maintenance cost.The precision of precision cavity die in EDM is shown in three aspects: dimension accuracy, profiling accuracy and surface quality. The machining precision of the mold cavity. Should be the correct analysis of the various parts size requirements, precision flexible control of different places. We should pay special attention to the size of those parts of high requirements, important dimensional tolerances can reach precise mould in 2 3 microns, the size of the strict requirements of the visible. Profile accuracy requirements are high, the cavity should be clear angle, edges and corners clear. The surface roughness value is even, and achieves the predetermined surface roughness value, generally requires the Ra value is very small, even requests the mirror surface processing, moreover, the electrical discharge machining part surface metamorphic layer thickness must be very small.Four summaryNowadays, with the rapid development of economy, the huge potential of EDM technology has a series of characteristics and production efficiency, has become an important technology in the field of research to Germany and the United States, Japan and other countries, a variety of different specifications of the high speed machine tool business has also been entered into the market, used in aircraft, automobile and die manufacturing and other industries. But the EDM Technology in the mold industry, the EDM process, there are many factors influencing the processing quality, in the specific processing should be according to the machining requirements, the electrode and the workpiece material, reasonable selection of machining parameters of the process indicators and other factors, and through process test and production practice to master the conversion rules in order to improve the machining accuracy, mold processing, productivity and economy. If these problems are solved properly, we believe that in the near future, EDM technology will be more and more widely used in the die industry, and also has a brighter future