The strength of cemented carbide is one of the key indexes of product toughness and impact resistance. In the field of metal cutting, such as discontinuous cutting and non-uniform cutting (including black leather cutting), tool fracture or breakage is the most important failure mode, so it puts forward very high requirements for the strength of cemented carbide matrix.

In the modern cutting, the introduction of tungsten carbide coatings technology makes the tool high temperature resistance, wear resistance, corrosion resistance and other properties have been greatly improved, to meet the requirements of high-speed processing. However, because the impact resistance of coated tools in high-speed machining is not ideal, most of the rough machining field with bad working conditions in China is still using non-coated tools with very low cutting efficiency. Through analysis and research thinks, coating process of cemented carbide substrate for a long time at 500 degreesto 1100 degrees, to be able to produce adverse effect to the strength of the matrix, the impact resistance performance of coated tools.

Test plan and test results

The test selects 6 kinds of k-series coated cemented carbide matrix brands, matrix WC particle size are 0.4 m, 0.6 m, 0.8 m, 1.5 m, 3.0 m and 4.0 m, the main component is WC+Co, containing trace additives. Select the same batch of raw materials for each brand, and press 30 strength test strips of 5.25mm 6.5mm 20mm respectively, and then sintering them together in the same furnace and vessel at one time. 10 grinding samples were taken for strength testing, and 10 unground blank samples were taken for CVD coating and 10 samples for PVD coating. The strength of cemented carbide matrix was tested by grinding the coated strip and testing the strength of cemented carbide matrix.

The change of strength of substrate with different particle size before and aftertungsten carbidecoatings. Except for the accidental factors such as abrasive sample and human operation in the test, it can be seen from figure 1 that the change trend of strength is obvious. The strength after sintering of the same matrix brand is >PVD coating, >CVD coating.

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1.Has high toughnessDuring the extrusion process, the mold must withstand complicated loads such as excessive pressing force, bending stress and impact. Therefore, the selected materials should have high toughness after heat treatment. Therefore, the mold material should have Good hardenability, so as to ensure the mold can be hardened and evenly organized. Large blocks of carbides and severe defects such as severe deflection, fiber orientation and non-metallic inclusions can reduce the toughness of the mold or cause stress concentration during load, causing early damage to the mold.

2.Good wear resistanceThe mold should have high wear resistance to ensure a normal service life and produce a large number of qualified extrusion parts.In general, the hardness and wear resistance of steel are proportional to certain conditions, so it is required that the mold material not only has sufficient hardenability, but also has high hardenability. However, in addition to the hardness, the wear resistance of the steel is determined by the thickness, composition, excess and tempering precipitation of the tungsten carbide die phase after heat treatment, size, type, dispersion and red hardness. For example, high-speed steel and low-alloy tool steel, although they have the same hardness value after heat treatment, the wear resistance of the former is much higher in actual use, while the hard alloy containing 80% or more of WC has higher wear resistance than steel. Ten times, so in the large-scale extrusion production, in order to obtain the long service life of the mold, high-speed steel and hard alloy with high cost and complicated process are still used as the mold material.

3.Adequate thermal stabilityWhen continuous production, the temperature rise of the tungsten carbide diesometimes reaches or exceeds 200 degrees. This is the mold material with tempering temperature of 160-180 degrees, which will reduce the strength and hardness. Therefore, the mold material with higher temperature rise should be used. Good resistance to tempering.

4.Good processabilityThe cold extrusion die has a long manufacturing cycle, complicated process and high precision. Generally, it must be forged, cut, heat treated, ground or otherwise finished. Therefore, only materials with relatively good processability can meet the needs of production.

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Ultrasonic machining diamond die has long been used in domestic applications, but in the tungsten carbide wire drawing dies processing is currently a small number of, especially the larger aperture wire-drawing die is so. Ultrasonic grinding is a frequency of about 20,000 cycles per second from electrical energy into mechanical energy (20,000 times/second for longitudinal movement); Fast moving processing equipment. In the processing of diamond mold, its copy needle and the link of the spokes are now used in domestic complex softbank welding device, otherwise the processing efficiency will be greatly reduced. Due to the processing speed, if the cemented carbide drawing die processing, according to the requirements of process strictly every processing a wire-drawing die need to replace a needle, the atmosphere day frequently change requires a lot of needle, the needle and complex welding must be conducted, it is seriously hampering the this technology in the application of cemented carbide drawing to touch. In addition, because the processing speed is fast, difficult to master, it is not easy to achieve linear processing, energy and the need for a high degree of concentration and many other factors, therefore, in the promotion and use is also limited.

Wire is machined by passing through small holes in a drawing die to reach a specified diameter. The process is called drawing. Although the principle of wire drawing is very simple, it is rather complicated from the mechanical point of view. Although many theories and speculations have been published to explain the mechanical principles involved in wire drawing, many aspects remain unexplained. Drawing dies are probably the simplest type of tool used in industry to deform metals. The most basic form of a drawing die is a metal block with a tapered hole. People have used this structure of the wire drawing die for more than 500 years, tungsten carbide wire drawing die is still based on the above basic form, but in some aspects made improvements. In 1923,Karl Schroter discovered that a mixture of tungsten carbide powder and drilling, iron or nickel (10% by weight) metals could be pressed and sintered to produce a material with low porosity, high hardness and high strength. He produced die cores that could be used to draw tungsten wires and successfully promoted them to the electric lamp industry. Soon this new material is widely used in the nonferrous metal wire industry. In the mid-1930s, the cemented carbide mould was also widely used in the us steel wire manufacturing industry. Modern cemented carbides are similar to the materials schroter produced in those days.

Thetungsten carbide drawing dieis one of the important tools to produce metal wire, and its quality will directly affect the output and quality of metal wire. There are many factors that affect the service life of the wire drawing die, such as the quality of the material of the wire drawing die itself, the geometry of the wire drawing die, the surface reduction rate of the metal wire, the lubrication effect of the lubricant, the quality of the wire drawing die and the cooling mode of the wire drawing die in the process of use. Due to the wide use of high-speed wire drawing machine, the research on the design of high-speed wire drawing die for high-speed wire drawing machine and extending the service life of the die has been carried out at home and abroad, such as the improvement of the die core material and the research on the pass theory and so on. High-speed wire drawing, because of the speed increase, can bring a series of problems, such as fever, wire drawing die wear such as intensifying make life of drawing die is reduced, the following will only from wire drawing die wire drawing die of calculating and analyzing the power and force of geometric parameters and the relationship between the wear and tear, determine the optimal geometric parameters of drawing die and to reduce wear and prolong the service life of drawing die.

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The tungsten carbide drawing die is one of the important tools to produce metal wire, and its quality will directly affect the output and quality of metal wire. There are many factors that affect the service life of the wire drawing die, such as the quality of the material of the wire drawing die itself, the geometry of the wire drawing die, the surface reduction rate of the metal wire, the lubrication effect of the lubricant, the quality of the wire drawing die and the cooling mode of the wire drawing die in the process of use. Due to the wide use of high-speed wire drawing machine, the research on the design of high-speed wire drawing die for high-speed wire drawing machine and extending the service life of the die has been carried out at home and abroad, such as the improvement of the die core material and the research on the pass theory and so on. High-speed wire drawing, because of the speed increase, can bring a series of problems, such as fever, wire drawing die wear such as intensifying make life of drawing die is reduced, the following will only from wire drawing die wire drawing die of calculating and analyzing the power and force of geometric parameters and the relationship between the wear and tear, determine the optimal geometric parameters of drawing die and to reduce wear and prolong the service life of drawing die.

Wire is machined by passing through small holes in a carbide drawing dieto reach a specified diameter. The process is called drawing. Although the principle of wire drawing is very simple, it is rather complicated from the mechanical point of view. Although many theories and speculations have been published to explain the mechanical principles involved in wire drawing, many aspects remain unexplained. Drawing dies are probably the simplest type of tool used in industry to deform metals. The most basic form of a drawing die is a metal block with a tapered hole. People have used this structure of the wire drawing die for more than 500 years, hard alloy wire drawing die is still based on the above basic form, but in some aspects made improvements. In 1923,Karl Schroter discovered that a mixture of tungsten carbide powder and drilling, iron or nickel (10% by weight) metals could be pressed and sintered to produce a material with low porosity, high hardness and high strength. He produced die cores that could be used to draw tungsten wires and successfully promoted them to the electric lamp industry. Soon this new material is widely used in the nonferrous metal wire industry. In the mid-1930s, the cemented carbide mould was also widely used in the us steel wire manufacturing industry. Modern cemented carbides are similar to the materials schroter produced in those days.

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Wire is machined by passing through small holes intungsten carbide wire drawing diesto reach a specified diameter. The process is called drawing. Although the principle of wire drawing is very simple, it is rather complicated from the mechanical point of view. Although many theories and speculations have been published to explain the mechanical principles involved in wire drawing, many aspects remain unexplained. Drawing dies are probably the simplest type of tool used in industry to deform metals. The most basic form of a drawing die is a metal block with a tapered hole. People have used this structure of the wire drawing die for more than 500 years, hard alloy wire drawing die is still based on the above basic form, but in some aspects made improvements. In 1923,Karl Schroter discovered that a mixture of tungsten carbide powder and drilling, iron or nickel (10% by weight) metals could be pressed and sintered to produce a material with low porosity, high hardness and high strength. He produced die cores that could be used to draw tungsten wires and successfully promoted them to the electric lamp industry. Soon this new material is widely used in the nonferrous metal wire industry. In the mid-1930s, the cemented carbide mould was also widely used in the us steel wire manufacturing industry. Modern cemented carbides are similar to the materials schroter produced in those days.

Production of steel wire and tungsten carbide wire drawing dies using a large number of die hole diameter and advised 3, 10 mm hard alloy drawing die. Die hole grinding BBB 0 0.5~1 mm. The grinding of each part of the hole with the working belt takes the most time. For example, by dk5 mm heavy grinding to 5.5 mm, rough grinding to dozens of minutes, fine grinding at least 3, 5 minutes. Generally, the grinding cone is first mechanically rough ground with boron carbide grinding paste and taper point steel needle, and then fine ground by hand with diamond powder grinding paste and steel or wood grinding needle. The institute of superhard materials, part of the Soviet academy of sciences, worked with a number of factories to develop a new method of electrolytic cathode grinding. Grinding is divided into two steps: first, in the sub-micro cutting conditions, electrolytic method of high efficiency rough grinding; Then mechanical fine grinding (polishing), so that the surface roughness Ra up to 0.08 micron. The same needle (cathode) is used for both steps. During rough grinding, the die hole of the drawing die is concentric with the grinding needle (cathode). Fine grinding, grinding needle up and down and around at the same time. The spindle head frame of the mould grinding machine can ensure that the polycrystal on the grinding needle is always in close contact with the grinding hole surface. The needle (cathode) is a tapered steel needle with a ring of cylindrical polycrystals embedded in the needle. 2-0.3 mm. Polycrystals are made from scrap diamond molds and polished with diamonds.

Due to the wide use of high-speed wire drawing machine, the research on the design of high-speed wire drawing die for high-speed wire drawing machine and extending the service life of the die has been carried out at home and abroad, such as the improvement of the die core material and the research on the pass theory and so on.

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Spraying should be as far as possible on the surface of the coated workpiece polished smooth, smooth, the surface without oxide and micro-pores, if conditions can also be pre-baked, but also effectively reduce the formation of particles.

For the technical personnel ofthermal powder spraying, all understand that if the coating film is too thin, in addition to the appearance of particles, will also produce flow adjustment, orange peel serious, and light color varieties of poor hiding power, at the same time coating film acid, alkali, salt, water resistance and other poor performance. Appropriate increase in coating thickness, can effectively reduce the formation of particles, coating film should not be too thick, generally too thick will affect the size of the coated workpiece, in impact resistance, flexibility, adhesion and other properties decline, general coating thickness control in 40~120um is normal. We can control the film thickness by the following ways: a. the number and arrangement of spray guns in the powder chamber; B. Powder output and air pressure of the spray gun (powder output, atomization and fluidization parameters); C. The running speed of the transmission chain, that is, the chain speed; D. Suspension and arrangement of coated workpieces.

For most enterprises, the recycled powder is generally treated as follows

1. In the automatic powder coating system recovered by the conveyor belt, the escaped powder is automatically recovered and sifted, and then mixed with the new powder coating to continue to be supplied to the powder spraying gun. The quality of such recovered powder is relatively stable and it is not easy to produce particles;

2. In the two-pole recovery system of cyclone separator and bag filter, the powder recovered in the first stage of cyclone separator has little influence on coating and is not easy to produce particles when it is sifted by vibrating screen and circulated with the powder supply system;

3. for the manual spraying coating system to recover the powder, because the dust and impurities in the environment is easy to bring into the recovery of powder, recovery must go through more than 120 mesh vibration screen. For the recycling and reuse of powder, the powder adsorbed on the profile surface only accounts for about 1/3 of the powder output of all the spray guns. There are many powders scattered after thermal powder spraying. The recycled powder must be mixed with the newly added powder in an appropriate proportion to achieve good results.

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