Machined Graphite Parts Copper as the electrode material, in the mold factory EDM is widely used. Many people think that only in the production of large electrodes and mold processing requirements are not high or rough processing, the graphite material will become an alternative consideration.
Today, more than 90% of the die materials are made of graphite in manufacturing technology leading Europe. But in China, most of the current mold enterprises or the choice of copper as the main electrode material.
According to the characteristics of graphite materials, the following comprehensive analysis of the advantages and disadvantages of its EDM.
(1) discharge processing speed
Machined Graphite Parts Machined Graphite Parts is a non-metallic material, the 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 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, graphite electrode discharge processing speed than the copper electrode as a whole 1.5 times faster.
(2) electrode loss
The graphite electrode has the characteristic of being able to withstand high current conditions. In addition, under the condition of suitable rough setting, the corrosion of the steel workpiece containing the carbon element in the processing and the carbon in the decomposition product of the working fluid at high temperature 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 electrode in the rough processing of the loss is minimal, or even "zero loss."
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 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 electrode loss of the two considerable situation.
(3) surface quality
Machined Graphite Parts 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.
Machined Graphite Parts It can be seen that if the discharge processing to the pursuit of extremely fine surface, the use of copper material to do more appropriate electrode, which is the main advantage of copper electrodes than graphite electrodes. 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 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 graphite and copper, 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 electrode processing surface particle size is more clear, This grain effect is better than the copper electrode discharge surface effect.
(4) processing accuracy 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 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 electrode will not be the case; for large diameter copper electrode, in the processing settings also need to compensate for a certain degree of thermal expansion Correct the size while the graphite electrode is not needed.
(5) Electrode weight
Machined Graphite Parts material is smaller than the density of copper, the same volume of graphite 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., The use of graphite electrodes in mold processing makes sense.
(6) electrode making difficulty
Machined Graphite Parts materials, mechanical processing performance, cutting resistance is only 1/4 of copper, in the correct processing conditions, the efficiency of milling graphite electrode is 2-3 times the copper electrode. Graphite 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 graphite is dust deposits, milling graphite will produce a lot of dust, so the milling machine must have a sealed and vacuum device. If you need to use EDM wire cutting graphite electrode, the processing performance is not as good as copper material, cutting speed is about 40% slower than copper.
(7) Electrode installation and use
Graphite material can be bonded, and can use conductive adhesive to graphite 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.