Research progress of tool electrode materials for

2022-06-22
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Research progress of tool electrode materials for EDM

1 introduction

in EDM, tool electrode is a very important factor, and the performance of electrode materials will affect the EDM performance of electrodes (material removal rate, tool loss rate, workpiece surface quality, etc.). Therefore, the correct selection of electrode materials is very important for EDM

tool electrode materials for EDM should meet the basic requirements of high melting point, low thermal expansion coefficient, good electrical and thermal conductivity and mechanical properties, so as to have low loss rate and resistance to deformation during use. The micro crystalline structure of the electrode is also beneficial to reduce the electrode loss. It is generally believed that reducing the grain size can reduce the electrode loss rate. In addition, the tool electrode material should make the EDM process stable, with high productivity and good workpiece surface quality, and the electrode material itself should be easy to process, rich in sources and low in price

as the application scope of EDM continues to expand, new requirements are constantly put forward for the corresponding electrode materials (including the corresponding electrode preparation methods). With the development of material science, people continue to explore and innovate the electrode materials for EDM tools. At present, the tool electrode materials used in research and production include graphite, Cu or W and other single metals, Cu or w-based alloys, steel, cast iron, Cu based composites, polymer composites and diamond

2 tool electrode materials for common EDM

(1) graphite

graphite is a tool electrode material widely used in EDM because of its good conductivity, thermal conductivity and machinability

there are different types of graphite, which can be classified according to the size of graphite particles, density of materials, and mechanical and electrical properties. Among them, fine graphite has smaller particles and porosity, higher mechanical strength and higher price. When used in EDM, the electrode loss rate is usually low, but the material removal rate is correspondingly lower. The average particle size of graphite grade available on the market is 20 μ M or less, the selection mainly depends on the working conditions of the electrode (rough machining, semi finishing or finishing) and the geometry of the electrode. The surface roughness of the workpiece is directly related to the size of graphite particles. Generally, the average particle size is 1 μ Graphite grades below m are used exclusively for finishing. S two different grades of graphite electrodes were used to machine deep and narrow grooves on difficult to machine materials, and their material removal rate and electrode loss rate were compared. The results show that the choice of graphite type mainly depends on which aspect of EDM requires higher material removal rate and electrode loss rate

compared with other electrode materials, graphite electrode can use large discharge current for EDM, so the productivity is higher; During rough machining, the electrode loss rate is small, but during finish machining, the electrode loss rate increases and the machined surface roughness is poor. Graphite electrode is light in weight and low in price. Due to the high brittleness of graphite, it is usually difficult to make thin and fine shapes by machining. Therefore, the application of graphite in EDM of fine and complex shapes is limited, and high-speed milling can better solve this problem

in order to improve the EDM performance of the graphite electrode, IRA and others immersed the graphite powder sintered electrode into the molten metal (Cu or Al) and applied high pressure to the liquid metal to make the metal Cu or Al fill the pores of the graphite electrode to improve its strength and thermal conductivity. After metal injection, the density, thermal conductivity and bending strength of the graphite electrode increased, the resistivity decreased significantly, and the surface roughness of the electrode was improved. The experimental results show that the new material electrode has no significant difference in electrode loss rate and material removal rate compared with the conventional graphite electrode, but the machined surface roughness is smaller, especially the graphite electrode injected with Cu can obtain much smaller machined surface roughness

(2) Cu, Cu based alloys and Cu based composites

pure Cu (electrolytic copper, commonly known as red copper) is also a commonly used electrode material, especially when processing non-ferrous metal materials, electrolytic copper is commonly used as tool electrode material

cu has low melting point and high electrode loss rate, so it is necessary to introduce another high melting point material to reduce electrode loss rate. Cu-W alloy has the characteristics of high thermal conductivity of Cu, high melting point of W, low thermal expansion coefficient and strong resistance to electric spark erosion, making it a high-performance tool electrode material. Cu-W electrode is mainly used for processing die steel and WC workpiece, in which the content ratio of Cu and W is generally 25:75. However, because the price of Cu-W electrode is higher than that of common Cu or graphite electrode, it is not widely used in production at present

ngh et al. Used Cu, Cu-W alloy, brass and Al electrode to process a kind of hardened tool steel. The results show that the processing speed and precision of Cu and Al electrode are high, the loss rate of Cu and Cu-W electrode is the smallest, and the loss rate of brass electrode is the largest. In contrast, Cu is a better electrode material, which can obtain higher machining accuracy and better machining surface roughness, and has high material removal rate and low electrode loss rate. The performance of Al is second only to Cu, and it can be selected when the requirements for machined surface roughness are not high. Yong Yaowei et al. [7] used Cu, W and Cu-W alloy as electrode materials to process cemented carbide. The results show that Cu-W alloy electrode can significantly improve the processing speed, and the electrode loss is not large under low processing voltage. Therefore, Cu-W alloy is an ideal electrode material for processing cemented carbide

tic is a new kind of high hardness, fire-resistant and green plastic material, which is widely used in the construction market. It has high melting point, good heat shock resistance and wear resistance. The effect of TiC in sintered cu/tic and cu-w/tic electrodes on the EDM performance of tool electrodes was studied. The results showed that the loss rate of cu/tic electrode containing 5% ~ 45% TIC was lower than that of conventional Cu electrode. Considering the processability, 25% tic is the ideal composition ratio. The cu-w/tic electrode material also shows good properties. The roughness of most of its EDM surfaces is better than that of the Cu-W electrode machined surfaces, so it can be used for precision machining. For cu-w/tic electrode material, the best effect can be obtained by adding 15% tic

zrb2 and TiSi have good electrical and thermal conductivity and high melting point. W et al. Studied the EDM tool electrode made by powder metallurgy with different content of Cu and ZrB2 or TiSi, and compared the EDM performance with graphite, Cu and Cu-W electrode materials. The results show that tisi/cu electrode has serious wear and tear, low machining speed and rough machined surface, so this material is not suitable for EDM electrode. Zrb2/cu can be used as electrode material, but the bonding force between Cu matrix and ZrB2 is poor. The content of ZrB2 and electrode manufacturing process parameters will affect the EDM performance of this electrode

tib2 particles have the characteristics of high melting point, good conductivity and thermal conductivity, and low thermal expansion coefficient. Tib2/cu composites have good conductivity, high temperature resistance and mechanical properties, which meet the basic requirements of electrode materials for EDM tools. Qiu Yan et al. Carried out EDM test with powder metallurgy tib2/cu composite electrode, and analyzed the EDM loss mechanism of the composite. The results show that the EDM characteristics of tib2/cu electrode are similar to those of other Cu based composite electrodes, and the EDM effect of electrode material is better when the volume fraction of TiB2 is 5%

Cu matrix composite electrode is usually used in EDM. U et al. Used cu/sicp composite electrode for EDM grinding. The composite electrode containing a certain amount of SiCp has significantly improved the hardness and wear resistance compared with pure Cu electrode, while the electrical properties remain almost unchanged. It has good thermal conductivity and high thermal shock resistance, showing the characteristics of low electrode wear rate. The EDM grinding effect of cu/sicp composite electrode containing 2%sicp is the best

when the electrode is prepared by electroforming, due to the mature process of electroforming Cu, there are many studies on the outward moving electrode of electroforming Cu (including Cu matrix composites) production base. The Cu or Cu matrix composites obtained by electroforming have compact microstructure and can reach small grain size. The results show that the pits formed on the electrode surface with fine grain and dense structure due to the melting and throwing out of the material during spark discharge are small, which can reduce the electrode loss rate

(3) polymer composites

rodeau and others use a conductive thermoplastic polymer composite as the electrode and air or water as the working medium to perform EDM or polishing on the workpiece surface. The electrode used is made of 60% ~ 65% of solid carbon materials (such as the mixture of fine carbon black powder, graphite powder, graphite sheet and even carbon nanotubes) uniformly distributed in thermoplastic matrix materials (such as polystyrene), which can be repeatedly softened and molded into the required geometric shape. Compared with graphite electrode, this polymer carbon composite electrode has lower cost, can be molded into complex geometry, and its manufacturing speed is much faster than milling; At the same time, its density is low and its resistivity is high, so the electrode loss rate is high. However, the electrode can be repaired by re molding during use

the components of the composite are still in the research and development stage. A good plastic electrode should have low resistivity, high thermal conductivity, low thermal expansion coefficient, good formability and dimensional stability in water, and be able to withstand heat cycling

(4) diamond

zuki et al. Studied EDM with conductive CVD diamond thick film (0.5mm) as electrode material. This kind of CVD diamond is conductive by doping boron in the CVD process. It has low resistance and high thermal conductivity, and has strong adsorption capacity for carbon precipitated from oil working medium during EDM. The EDM test shows that under certain machining conditions, CVD diamond electrode can achieve high material removal rate, and the electrode loss is almost zero. Especially, it can be machined under the high current density of Cu or graphite electrode. However, the conductive CVD diamond has the problems of high cost and limited size, so zuki et al. Used polycrystalline diamond (PCD) as electrode material for EDM. The PCD material used is made of micron diamond particles sintered with CO as binder under the conditions of ultra-high pressure and temperature and the presence of metal catalyst, which is mainly from plastic products processing plants. Its thermal conductivity is close to that of conductive CVD diamond. Different grades of PCD materials can be obtained by using diamond with different particle sizes, and their thermal conductivity is different. The results show that under certain EDM conditions, the electrode loss is very small or zero. With the increase of thermal conductivity, the material removal rate and electrode loss of different grades of PCD material electrodes in EDM decreased. Because PCD material has the same EDM effect as conductive CVD diamond, but its cost is low, it may become an ideal electrode material

3 electrode materials for EDM surface modification

EDM surface modification mostly uses the characteristics of electrode loss during EDM to transfer the electrode materials to the surface of materials to be machined, so as to form a high hardness and high wear-resistant coating. Usually, carbon particles decomposed from kerosene in the working fluid react with the electrode materials falling off due to rapid loss to form carbides on the workpiece surface. To realize this form of EDM surface modification, the tool electrode should be made of materials with low thermal conductivity小孩挑食厌食怎么办
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