Tungsten Copper Electrode and Other Materials Comparison — Part II

Some researchers put graphite electrode into molten metal (such as Cu or Al) in order to improve the properties of graphite electrode in EDM. At the same time, pressing the liquid metal and make Cu or Al fill in the pore of graphite electrode for improving the strength and thermal conductivity of the electrode.

Except graphite, Cu, Cu-based and Cu composite material is also widely used as electrode in EDM, ECM or other machining.

2. Cu, Cu-based and Cu Composite Material

Copper (commonly known as red copper), which is a kind of electrode material, especially in machining non-ferrous metal. Cu has low melting point so that its wastage is high, the lifespan is short and the cost too much, which requires that other material with high melt point to improve its properties.

Tungsten copper (Cu-W) not only has high melt point, low coefficient of expansion and spark resistance, but also has good conductivity so that it is a new kind of high-performance electrode material. Tungsten copper electrode is widely used in die steel and WC work-pieces, the common ratio of Cu/W is 25:75. However, the higher price than graphite or copper, tungsten copper spreading has been blocked to some extent.

Some researchers use copper, tungsten copper, brass and aluminum as electrode for hardened steel machining. The result shows that Cu and Al have higher speed and better precision, Cu and tungsten copper (W-Cu) has the lowest electrode wastage and brass electrode wastage is the largest. Therefore, Cu is a kind of ideal electrode for hardened steel machining, which has low wastage of electrode and high MRR (Material Removal Rate).

In another experiment, researchers use copper (Cu), tungsten (W) and tungsten copper (Cu-W) as electrode for tungsten carbide machining. The result shows that tungsten copper (Cu-W) can remarkably improve the machining efficiency. What’s more, the wastage of electrode is lower under the low voltage so that Cu-W is the most ideal material for tungsten carbide machining. In addition, the researchers also use different content of Cu and ZrB2 or TiSi as electrode for EDM by PM (Powder Metallurgy). Compared with graphite, copper and tungsten copper, TiSi/Cu has higher wastage of electrode, the machining surface is rough and the efficiency is not so well so that it is not suitable used as electrode. While ZrB2/Cu can be used as electrode, but the combining power between Cu-base and ZrB2 is weak, and the content of ZrB2 will has an effect on EDM properties.

Besides graphite, copper, and Cu-based alloy, Cu-based composite material is also a kind of common materials of electrode.

3. Cu-based Composite Material

Cu-based composite electrode has good conductivity and thermo-plasticity and use air and water as medium, which usually for EDM or polishing. It is composed of 60%-65% solid carbon material (such as graphite powder, graphite slices or carbon nano-tubes and other mixture) distributes thermoplastic matrix and soften over and over again for molding. Compared with graphite and tungsten copper electrode, it has many advantages, like low cost, available for complicated shape and better efficiency, etc.

However, due to its density is much lower than tungsten copper, the electrical resistivity is higher and the wastage of electrode is increasing. This composite material is under development, which requires that low electrical resistivity, low coefficient of expansion, thermal cycling resistance, excellent conductivity and good dimensional stability in liquid.

Besides graphite, copper, and Cu-based alloy, Cu-based composite material, diamond is also a common kind of material of electrode. However, due to the cost of diamond is much higher than graphite and the size is limited, there are some scientists do researches about that.

4. Diamond

CVD (Chemical Vapor Deposition) diamond, which mixed by carbon-containing gas and oxygen was excitation-decomposition under the low standard atmospheric pressure, and come into active diamond carbon atoms. They deposit at the matrix and grow up to polycrystalline diamond (or monocrystalline diamond, mono like diamond).

In order to make it have the same properties of tungsten copper (such as conductivity, electrical resistance), researchers add boron (B) during CVD, which has excellent adsorption to oil medium in electrical discharge machining (EDM). CVD diamond has high MRR (Material Removal Rate) and low wastage of electrode, especially it can work in high current density under certain condition, which Cu, graphite and tungsten copper is unavailable. In addition, there is another kind of PCD (polycrystalline diamond), which has similarities with CVD diamond and its cost is lower than CVD diamond so that it is a kind of ideal material for electrode.

In Micro- EDM, the electrode will increase the energy of spark in unit area, which increase the wastage and decrease the precision of machining. If we change the parameters to reduce the discharge energy unit area, the processing will be longer and efficiency will decrease. Therefore, the choice of electrode materials is also important for Micro-EDM, the common electrode materials are tungsten (W), tungsten carbide (WC) and tungsten copper (W-Cu), etc. Drilling and milling in Micro-EDM often uses tungsten (W) or tungsten carbide (WC) rod or tube as the electrode of tools.

In conclusion, we should choose different materials of electrode according to different process parameters or different work-pieces. Therefore, learn some methods, materials, shape, customer requirements and cost performance before we choose electrode is significant to the quality of products. In addition, tungsten copper and other new materials will promote the development of EDM (Electrical discharge machining).

If you have any interest in our tungsten copper alloy products, please do not hesitated to contact us by Email:sales@chinatungsten.com or by telephone:86 592 5129696, we are at your service.

Tungsten Copper Electrode and Other Materials Comparison — Part I

The using of electrode material has a huge effect on electrical discharge machining (EDM), such as the wastage of tool, MRR (Material Removal Rate), the surface quality of work-piece and so on. Therefore, the choice of electrode material should not be ignored in EDM and it depends on the situation.

First of all, the electrode should have high melting point, good conductivity, low coefficient of expansion and some excellent mechanical properties so that it can be thermal resistance, not easy to deformation and has low wastage in EDM. Theoretically, the micro crystal structure of electrode is beneficial for decreasing the wastage of electrode and properly reduce the size of grain will be better. In addition, the material of electrode should pledge stability, good quality of surface, reasonable price and easily for machining to EDM.

With the development of EDM, the material of electrode and the related manufacture makes a great progress. At present, there are so much electrode materials, such as graphite, tungsten (W), copper (Cu) and some other metal or non-metal elementary substances. In addition, steel, cast steel, Cu-based and W-based composite materials or diamond can be also used as EDM electrode.

1. Graphite

As for the aspect of chemical, graphite is an allotrope of carbon element, which covalently bound covalent molecular bonds. Its has high boiling point and melting point, the melting point up to 3652 ℃, the boiling point of 4827 ℃, insoluble in water. And it also has excellent electrical and thermal conductivity, chemical stability and workability so that it is widely used as EDM electrodes. In addition, graphite also has different kinds, which can be specifically divided by graphite particle density, the size and mechanical and electrical properties.

Fine graphite has small grain, porosity and good mechanical strength, which has low wastage of electrode in EDM. But its MRR (Material Removal Rate) is undesirable. At present, the most of graphite grain size is below 10μm, which depends on the conditions electrode works (finishing, semi-finished or roughing) and its shape when we make a choice. In addition, the roughness of work-piece surface is related with the size of graphite grains, the average particle size below 1 μm is specialized for finishing.

Compared with other materials of electrode, graphite can be used in EDM with large discharge current, which remarkably increasing the efficiency. Although graphite has low proportion and price, it is too fragile to machining into the shape of thin. Therefore, it is limited in EDM and researchers find that high speed milling can be improved to some extent.

Some researchers put graphite electrode into molten metal (such as Cu or Al) in order to improve the properties of graphite electrode in EDM. At the same time, pressing the liquid metal and make Cu or Al fill in the pore of graphite electrode for improving the strength and thermal conductivity of the electrode.

If you have any interest in our tungsten copper alloy products, please do not hesitated to contact us by Email:sales@chinatungsten.com or by telephone:86 592 5129696, we are at your service.

Effect of TiC in Copper-tungsten Electrodes

Due to the high thermal conductivity of Cu, and the better spark erosion resistance, low thermal expansion coefficient and high melting temperature of W, copper-tungsten electrodes have been widely used for machining die steel and tungsten carbide work-piece. The materials normally used in EDM electrodes are various types of copper, graphite, tungsten, brass and silver. But copper-tungsten has better properties. The low melting point of Cu reduces the resistance to electrode wear.

At high tungsten content, there is porosity in the liquid phase sintered electrode due to the insolubility between the Cu and W. This greatly impedes densification during the solution-reprecipitation stage of liquid phase sintering. Hence, this makes it necessary to introduce another material with high melting point. Materials having good electrical and thermal conductivity with a high melting point are used preferably in copper-based electrodes to resist electrode shape-loss.

Titanium carbide (TiC) is an extremely hard refractory material with high melting temperature, and high thermal shock and abrasion resistance. It is used mainly for powder metallurgical parts including cutting tool tips, dies, wear parts and resistant coating. In industry, the manufacturing of Cu-W composites is usually done through infiltration of Cu into a porous, pre-sintered tungsten compact, or through the liquid phase sintering of compacts pressed from mixed powder.

In some researches, Cu-W/TiC was investigated and fabricated through liquid phase sintering. In is reported that the additive metals (iron, cobalt and nickel) can enhance densification in the liquid phase sintering of Cu-W. In order to increase the densification of the Cu-W matrix, nickel (Ni) was introduced. In addition, the densification of Cu-W/TiC sintered electrodes can be improved by the addition of Ni. However, due to the insolubility of Cu, W and Tic, and the amount of Cu apparently reduced by the cold welding in ball milling, porosity cannot be avoided. Nevertheless, with increasing TiC, the distribution of the particle size becomes narrow.

If you have any interest in our tungsten copper alloy products, please do not hesitated to contact us by Email:sales@chinatungsten.com or by telephone:86 592 5129696, we are at your service.

LED Tungsten Copper Heat Base for Heat Dissipation

With the world's attention of environmental awareness, energy saving has been an irresistible trend of the moment. The LED industry is one of the fastest growing industries; LED products not only have a great advantage in terms of energy saving, but also have high efficiency, fast response time, long life cycle and do not contain toxic substances, which is outstanding in similar products. In general, the input power of LED high power products has about 15% of electrical energy into light energy, and another 85% of the electrical energy is dissipated into heat. So if the LED light emitting heat generated not been able to export, it will make the temperature of the LED screen is too high, thus affecting its luminous efficiency, stability and product life cycle. In order to improve the luminous efficiency, thermal dispersion management and design LED system become an important research topic.

The ways of heat dissipation mainly includes: air heat dissipation, heat the substrate to export, export gold wire cooling, through-hole heat dissipation and so on. Here we introduce the substrate cooling. In LED products typically requires multiple LED assembled on a circuit board. In addition to the circuit board is responsible for carrying LED module structure, on the other hand it also needs to play the role in heat dissipation. LED heat dissipation substrate mainly takes advantages of the excellent heat conductivity of its thermal substrate material to derived from the LED grain. Thus according to the ways of LED heat dissipation, can be divided into two types, LED grain board and the system circuit board. These two are multiplied by different heat dissipation board carrying the LED chip LED grain and the LED grain emits light generated by the circuit board to the system, and then absorbed by the atmosphere via the heat dissipating board LED die, to achieve the dissipation of the heat effect. Tungsten copper material has high strength, low coefficient of thermal expansion, excellent plasticity and thermal and electrical conductivity, which is the perfect choice for LED board. Compared with single metal, such as Al substance, it can avoid the thermal mismatch and have better stability and heat dissipation.

If you have any interest in our tungsten copper alloy products, please do not hesitated to contact us by Email:sales@chinatungsten.comor by telephone:86 592 5129696, we are at your service.

Tungsten Copper Throat Insert

Solid rocket motor spray tube by controlling the expansion of the combustion chamber exhaust gas generated energy is efficiently converted to kinetic energy, so as to provide the required power for the aircraft. Throat insert located in the larynx of the spray tube, which plays an important role in restricting the throat area expansion by ablations and the decreases of the thrust. Throat insert usually need to be heated from room temperature to more than 2000℃  and produces a great temperature gradient and thermal stress when the engine working, which is also the main reason for the cracks and failure of throat insert materials. Furthermore, such high-performance engine for rocket often uses metal powders (such as Al) as propellants combustion at high temperature of about 3000 ℃ high burning rate entrained flow of solid particles or liquid droplets (Al2O3) and scoured the throat insert intensely. It is difficult to ensure a stable aerodynamic shape even the fragmentation occurred if the throat insert has severe ablation, so it will has an bad effect on the thrust and efficiency of the engine.

With the application of throat insert becoming wider and wider, such as rocket boosters, long-range missiles, solid rocket engine and so on, and the more and more types of the metal additives, the materials properties for throat insert has been confronted with the higher requirements, which is also a key to the solid rocket technology developments. In general, throat insert materials used for solid rocket engine include refractory metal, graphite, carbon and carbon-based composite material, reinforced plastics and ceramic-based composite materials, etc. Among them, tungsten copper is one of the very suitable materials for throat insert fabricating. In addition, throat insert heat conduction can be divided into three steps: 1.Engine ignition instant impact heating; 2. Ablation when working steady; 3. The cooling process of flameout; wherein the thermal shock of throat insert often occurs at the moment of the ignition.

Tungsten copper throat insert fabricated by the infiltration process, which not only has high hardness, high density, high strength, high melting point, low coefficient of thermal expansion and excellent wear and corrosion resistance of W, but also has excellent ductility, thermal and electrical conductivity of Cu. What’s more, since there is a great difference in the melting point between W and Cu, at high temperature higher than the melting point of Cu, Cu will evaporate and take away the most of heat and the hard phase W left. So it ensures the stability of throat insert works, and tungsten copper is also known as sweating heat sink material.

Through related experiments the researchers found that coarse grain has better performance in thermal shock resistance and poor in ablation resistance, conversely. Rocket spray tube entrained within particles or liquid phase stream high burning rate will continue to scour throat insert, and this two-phase flow weakly oxidizing, such throat insert constantly ablated, which is a complex physical and chemical process covered by heat conduction, mass conduction, transmission capacity and chemical reactions. According to different ablation principles, it can be specifically divided into thermal ablation, melted ablation and mechanical erosion. When the surface temperature of tungsten copper throat insert is higher, melted copper was deposited on the inner surface, which will cause thermal effect and prevent heat transfer to the inside of the material.

In addition, when the gas temperature below the melting point of tungsten, tungsten skeleton does not melt, ablation occurs at this time of the melting of copper and tungsten substrate by gas particles (such as Al2O3) erosion produced by mechanical erosion. Currently, copper tungsten throat insert prepared have been able to successfully applied to 3600 ℃, 6.88MPa under thermal environment at this temperature above the melting point of W, tungsten skeleton is also possible to melt ablation. From the view point of throat insert structure, improving the roughness and prolonging the length of the straight section can remarkably improve the ablation resistance of throat insert.

If you have any interest in our tungsten copper alloy products, please do not hesitated to contact us by Email:sales@chinatungsten.comor by telephone:86 592 5129696, we are at your service.

Nano Tungsten Copper Composite Material

Nano tungsten copper composite material is also known as ultra-fine tungsten copper composite material, which compared with common grain tungsten copper, has better mechanical and chemical properties, such as high density, high hardness, high strength, excellent wear and corrosion resistance and perfect thermal and electrical conductivity, etc. Its granularity usually between 1nm -100nm and the nano grain has several characteristics is given as follow:

1. Small size effect: When the coherence length or penetration depth dimension and the wavelength of light particles, de Broglie wavelength and other physical characteristics of the superconducting state of a considerable size or less, crystal periodic boundary conditions will be destroyed, the density of atoms near the surface of the particle layer of amorphous nano-particles reduced, resulting in characteristic sound, light, electricity, magnetic, thermal, mechanical and other changes in the new physical properties;

2. Surface effect: With the decreasing grain size, the ratio of surface atoms and total atoms of nano tungsten copper grains is dramatically increasing and the binding energy of grain is correspondly increasing, which changes the properties of nano grains;

3. Quantum size effect: When copper tungsten particle size down to a certain size, the electron energy levels near the Fermi level from continuous to discrete energy and transformation. During the existence of discrete energy level occupied molecular orbital, at the same time there are also contrary to occupy the lowest molecular orbital, and the spacing between the high and low rail level with the smaller diameter of the nano particles increased;

4. Macroscopic quantum tunneling effect: Electrons have wave-particle duality and the ability to penetrate the barrier, known as the tunnel effect. Macroscopic quantum tunneling effect will be the basis for future microelectronics, optoelectronics, or it further establishes the limits of miniaturization existing microelectronic device;

5. Coulomb blockade and quantum tunneling: In nano scale dimensions, the charging and discharging process is not continuous, filled with an electron energy required is called the Coulomb energy blockage. In such a small system of single-electron transport behavior is known as Coulomb blockage effect, if the two quantum dots connected by a junction, a single quantum dot electrons through the energy barrier to another quantum dot is the quantum tunneling.

Nano tungsten copper composite material has better performance in thermal properties, magnetic properties, optical properties, the super-conducting properties, catalytic properties and so on. From the thermal properties, at extremely low temperatures, the thermal resistance of tungsten copper nano particle is almost zero; from magnetic properties, nano grain will enter super-paramagnetic state when it exceeds a certain threshold and shows high coercivity; from optical properties, nano particle quantum size effect is more significant, in the optical performance of the wideband receiver, the dispersion obtain some special optical properties; and the super-conducting transition temperature of nano tungsten copper grain increases as the decreasing granularity. In addition, from catalysis nature, as the particle size decreases the reactivity significantly increased under appropriate conditions capable of catalyzing the breakage H-H, C-H, C-C, C-O chemical bond and so on.

If you have any interest in our tungsten copper alloy products, please do not hesitated to contact us by Email:sales@chinatungsten.comor by telephone:86 592 5129696, we are at your service.