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Material Selection Of Discharge Electrode

Author:Editor ComeFrom:Hongfa Date:2016-08-01 10:50:26 Hits:1352
        Electrode materials used frequently in the discharge machining include: copper, graphite, copper tungsten alloy, silver tungsten alloy and so on.
Copper
      Copper plastic, machinery processing forming, forging, electroforming and wire cutting, forming, can be made into a variety of complex electrode shape; but difficult to grinding. For EDM of copper electrolytic copper must be free of impurities, the purity of the more the better discharge performance.
      Copper processing stability, in the EDM process, stable physical properties; can easier to obtain the stable process, is not easy to generate arc and other undesirable phenomena, in difficult conditions can also processing stability.
       Finishing in the low loss can get a clear outline of the cavity, because of the compact structure, processing surface is bright and clean degree high, with certain technical means and power, the machined surface rough degree can reach ra0.05 micron mirror ultra light processing.
       The low melting point of copper, not large current density, generally not more than 30 ampere current, otherwise they will be damaged, cracked and influence the processing effect; copper thermal expansion coefficient is larger, in the deep processing of narrow rib part, higher current generated by the local high temperature is easy to make the electrode to the deformation of the surface of the electrode.
       Copper electrode is usually used in low loss processing conditions, low loss processing current is small, its productivity is not high, so the workpiece is often pre processed.
        The copper electrode can be suitable for the discharge machining of high precision mold, such as the processing of the small type cavity, pattern design, fine parts, etc. are very suitable.
Graphite
         Graphite mechanical processing performance is good, its cutting resistance is small, easy to grind, it is easy to manufacture forming, without machining burr.
Density is small, only copper 1/5, electrode preparation and preparation of the operation is easy.
         Graphite electrode is made of special graphite CNC high speed machining machine, CNC processing speed is fast;For the super high (50 mm -90 mm), thin (0.2 mm -0.5 mm) of the electrode, the processing is not easy deformation;When making the whole electrode, there are all kinds of hidden corners, because of the characteristics of the graphite easy to repair, so that this problem can be easily solved;On graphite machining, tool is easy to wear; general recommendations with hard alloy or diamond coated cutting tool, in the rough machining tool can be directly on the workpiece under the knife; finishing prone to chipping and fracture phenomenon, often using light knife to go faster processing, cutting depth is less than 0.2 mm; CNC machining graphite electrode is produced when the dust, dust toxicity, machine tool requires a corresponding processing device, the machine seal is better; in the processing of the previous will graphite in kerosene soaked for a period of time but also to prevent the collapse processing angle, reduce dust method.
        With the continuous improvement of the production process of graphite materials, the development of high and new technology, a variety of graphite materials can meet different processing requirements.
         There are many kinds of graphite electrode material selection, but the following four standards directly determine the performance of the material:
Average particle diameter of material
           The average particle diameter affects the discharge status. The more uniform discharge, the more stable the discharge condition, the better the surface quality, the less the loss of the particles.
         For the precision requirements of the mold is not high, can be used for more coarse materials, high precision mold, recommended the use of the average particle in the following 4 mu m.
   Flexural strength of materials
   Flexural strength is a direct reflection of the strength of the material, showing the close degree of the internal structure of the material.
The high strength of the material, the loss of its discharge performance is relatively good, for the high accuracy of the electrode, as far as possible to choose a better strength of the material.
    Shore hardness of materials
    In the special graphite industry, the general hardness test standard is the shore hardness measurement.
     According to hardness tests on graphite than the metal material is even higher, because of its high hardness, during cutting, tool loss than metal cutting larger; at the same time, high hardness of graphite material in the discharge loss control more outstanding.
     Intrinsic resistivity of materials
     According to the characteristics of the material, if the average particle size of the material is the same, the resistivity of the larger discharge rate will be smaller than the resistivity of the slow.
       For the same average particle material, its strength and hardness will be slightly lower than the resistivity of the material. The rate of discharge, the loss will be different.
      So it is very important to select materials according to the practical application.
      Graphite electrode is particularly applicable to corrosion processing in addition to the large amount of cavity, in the processing of large area can realize low loss, high speed roughing; like in large plastic mold, die, die casting mold mold EDM can play its unique advantages in processing.
       Due to the light weight of the electrode, the graphite material is commonly used in the manufacture of large electrodes, and the thermal deformation is small. It is the first choice for the deep narrow strip of high precision.
Copper tungsten alloy / silver tungsten alloy
       High copper tungsten alloy and silver tungsten alloy electrodes strength and hardness, density, melting point nearly 340 DEG C, due to the high content of tungsten, guarantees extremely low electrode wear; under the extremely difficult processing conditions can achieve stable processing to produce high grade surface.
       The electrode made of the electrode is easy to be formed by mechanical processing. The disadvantage is that the price is expensive, the material source is difficult.

      Processing of electronic connector high-precision molds, the subtle shape part requirements very strict, which requires machining electrode loss must be minimal; copper tungsten alloy and silver tungsten carbide material selected to manufacture the tool electrode is a basic requirement of processing technology.

       The silver tungsten electrode is the best of the spark machine electrode, and the electrode can be used to repair the best finish, so that the mold can achieve very high precision.
Comprehensive consideration of electrode selection in EDM
        Choice of electrode materials, we should consider all aspects of the factors, the various electrode materials to make a comparison, a reasonable choice of electrode materials.
         Electrode material must have the characteristics of the electrical discharge machining process, the electrode used to transfer electrical pulse, and the workpiece material.
        Electrode must have good conductive performance, low loss, easy forming, stable processing, high efficiency, rich material source, low price and so on.
Selection principle of electrode materials
         The electrode is easy to form; electrode discharge performance; machining accuracy, surface quality; the cost of the electrode is reasonable; the weight of the electrode.
    Optimization of electrode material selection
      Even if it is the same part of the processing, the accuracy of different parts of the processing requirements are not the same.
       The choice of electrode materials to ensure the accuracy of the premise, should be a substantial increase in the processing efficiency for the purpose of.
      High precision parts can use copper as rough machining electrode, the choice of copper tungsten alloy is refined; high precision machining parts of coarse and fine processing can use copper; general processing available graphite roughing, finishing flotation of copper or graphite can also; accuracy requirement is not high, rough and finish machining are made of graphite; optimization scheme makes full use of the graphite electrode machining speed.