According to the characteristics of graphite materials, the following comprehensive analysis of the advantages and disadvantages of its EDM.
(1) discharge processing speed
Graphite material is a non-metallic material, melting point is extremely high, can withstand greater current setting conditions. When the discharge area and the electrode size of the larger amount of scaling, the high efficiency of graphite materials, the more significant advantages of rough processing. The thermal conductivity of graphite material is 1/3 of copper, the heat generated during the discharge process can be more effectively used to remove metal materials, therefore, in the processing, the processing efficiency is higher than the copper electrode. According to the processing experience, under the correct conditions of use, the graphite material electrode discharge processing speed than the copper electrode as a whole 1.5 times faster.
(2) electrode loss
The graphite material electrode has the characteristic of being able to withstand high current conditions. In addition, under the condition of suitable roughing setting, the corrosion of the steel workpiece containing the carbon element in the processing and the decomposition of the working fluid at the high temperature Carbon particles, in the role of the polar effect, part of the corrosion, carbon particles will adhere to the electrode surface to form a protective layer to ensure that the graphite material electrode in the rough processing of the loss is minimal, or even "zero loss" The
EDM processing in the main electrode loss from the rough processing, finishing conditions, although the high rate of wear and tear, but the parts reserved for processing allowance is less processing erosion less, the total loss is less The In general, the graphite material electrode in the large current roughing loss will be less than the copper electrode, in the finishing loss may be slightly larger than the copper electrode, the two electrode loss is quite the case.
(3) surface quality
The particle diameter of the graphite material directly affects the surface roughness of the EDM, and the smaller the diameter, the lower the surface roughness value. A few years ago, the use of graphite particles with a diameter of φ5μm, the best surface of EDM can only reach VDI18 (Ra0.8μm), today, the graphite material particle diameter has been able to achieve within φ3μm, EDM the best surface can be Stable to VDI12 (Ra0.4μm) or finer level.
The resistivity of copper material is low, the structure is dense, EDM is easy to obtain stable processing state, and it can be processed stably under difficult conditions. The surface roughness can be less than Ra0.1μm, which can be used for mirror EDM.
It can be seen that if the discharge process to pursue a very fine surface, the use of copper material to do more appropriate electrode, which is the main advantage of copper electrode electrode than graphite materials. But the copper electrode in the high current setting conditions, the electrode surface is easy to become rough, and even cracks, and graphite materials are no such problems, the surface roughness requirements for the VDI26 (Ra2.0μm) around the cavity processing , The use of a graphite material electrode can be completed from coarse to fine processing, to achieve uniform uniform surface effect, the surface will not be defective.
In addition, due to the different structure of the graphite material and the copper structure, the graphite electrode surface discharge corrosion point than the copper electrode to the rules, therefore, in the processing of VDI20 and above the same surface roughness, the use of graphite material electrode processing surface particle size More clearly, this grain effect is better than the copper electrode discharge surface effect.
(4) processing accuracy
Graphite material thermal expansion coefficient is small, the thermal expansion coefficient of copper material is 4 times the graphite material, therefore, in the discharge processing, the graphite material electrode compared to the copper electrode is not easy to deformation, can be more stable and reliable processing accuracy. Especially in the processing of deep narrow ribs part of the local high temperature easy to make the copper electrode bending deformation, and graphite material electrode will not be the case; for the larger diameter than the copper electrode, the processing set also need to compensate for a certain degree of thermal expansion To correct the size, while the graphite material electrode is not needed.
(5) Electrode weight
Graphite material is smaller than the density of copper, the same volume of graphite material electrode weight is only 1/5 of the copper electrode. It can be seen that the larger electrode is very suitable for the use of graphite materials, greatly reducing the EDM machine tool spindle load, the electrode will not be because of the weight caused by improper clamping, processing displacement caused by displacement, etc., Mold processing using graphite material electrode is very meaningful.
(6) electrode making difficulty
Graphite materials, mechanical processing performance, cutting resistance is only 1/4 of copper, in the correct processing conditions, milling graphite electrode electrode efficiency is 2-3 times the copper electrode. Graphite material electrode is easy to clear angle, can usually be completed by a number of electrodes designed to work as a whole electrode to process.
Graphite material unique particle structure, making the electrode after milling does not produce a burr, for the complex shape is not easy to remove the burr of the situation directly meet the requirements, eliminating the need for artificial polishing of the electrode process, to avoid the polishing caused by the shape change , Size error and so on.
It should be noted that, because the graphite material is dust deposits, milling graphite material will produce a lot of dust, so the milling machine must have a sealed and vacuum device. If you need to use EDM wire processing graphite material electrode, its processing performance is not as good as copper material, the cutting speed is about 40% slower than copper.
(7) Electrode installation and use
Graphite material can be bonded, and can use conductive adhesive to the graphite material and fixture bonding method milling electrode, discharge processing, can save the electrode material in the processing of screw holes in the process, saving working hours.
Graphite material is more brittle, especially small narrow long electrode, in the use of external forces easily broken, but can immediately know the electrode damage occurred. If it is copper electrode will only bend will not break, this situation in the course of the use of very dangerous and difficult to find, it is easy to lead to scrap.
(8) the price
Copper material is non-renewable resources, the price trend will be more expensive, and the price of graphite material tends to be stable. In recent years, copper material prices continue to rise, and the major graphite material manufacturers continue to improve the production of graphite materials to make it more cost-effective advantage.
At present, the world's leading suppliers of graphite materials in different suppliers have a variety of different grades of graphite materials to choose from. Usually according to the average particle diameter of graphite material to classify, particle diameter ≤ φ4μm is defined as fine graphite material, particles in φ5-φ10μm is defined as graphite material, particles in 10μm above the definition of crude graphite material.
The smaller the particle diameter, the more expensive the material is. Can be based on EDM requirements and costs, select the appropriate graphite material.