Interpretation of the grinding wheel in the clogging
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Grinding is a long history, widely used method of metal cutting. In the country, the main tool used in the traditional cutting of hard materials is difficult and the precision, surface quality requirements of parts processing. With the emergence of a large number of new materials and applications, and scientific and technological development brought about by the precision of parts, the quality of the new requirements, the growth rate of grinding applications than any other conventional processing methods. Overseas, the grinding process has been widely used directly in the rough processing, in many ways replaced the traditional methods of cutting, grinding machine of the total number has reached around 60%. Grinding, not only particle size, shape and distribution of processing plays an important role, often in the processing of ductile metal, the rapid emergence wheel passive congestion, leading to premature termination of wheel life, to avoid passivation and wheel jam The resulting adverse effects of the blocking mechanism of grinding wheel, the process is necessary. First, the formation of debris Grinding process is a complex multi-factor, multi-variable process of interaction, and its purpose is to remove the workpiece material is given a certain amount of high surface quality and precision. Is an abrasive grinding wheel, bonded by the compact, dry, porous sintered body, which is a tiny single abrasive cutting edge, a very large negative rake angle and the blade edge radius. High speed through the sliding abrasive brush, plow cut into the workpiece after. Cutting layer material along the shear plane was formed after the short slip and thin chips, debris in the grinding area which is heated to very high temperatures (such as the carbon steel up to 1200K and above), then oxidized and melting, and then solidified into spherical particles, the surface of the sphere there is some cross sticks, this spherical wear debris is a major form of wear debris. Stainless steel grinding, through the scanning electron microscope and found that a large number of spherical wear debris, of course, accompanied by band, festival-like wear debris and ash, some of these debris will fill many holes in the wheel, attached around the abrasive , causing the wheel jam, resulting in precision grinding down, burn the workpiece, reducing wheel life. Since the control of vitrified better, well over the abrasive layer and the subgrade adhesion, vitrified diamond wheel in the case of wet debris clogging the probability is very small. In today's machining ceramic bond diamond play an important role. Kingmax super-hard materials recommend that you use vitrified grinding wheel diamond blade, diamond grinding of ceramic diamond grinding wheel and the use of PDC coarse vitrified diamond wheel. Second, the type and mechanism of wheel block The type of grinding wheel embedded block, attachment type, adhesive type, mixed type. Embedded block is embedded in the grinding wheel wear debris at the work surface pores blocked state. By attaching a temporary plug is the power of abrasive grain cutting edge attached to the surface of a block after the knife situation. Adhesion-type plug is melted adhering abrasive grinding cutting edge protruding around or on the binder. Hybrid is more than three types of jam in a small part of the collection or layer set. Embedded plug-and mechanism of attaching Embedded and dependent-type plug is filled with debris mechanically generated in the wheel gap clogging. Fill power from two aspects, one is outside, one is internal, involving physics, electricity, heat and other factors. External factors: the grinding process has a very important feature of radial grinding contribute more than tangential component Fy Fz, Fy / Fz ≥ 2 ~ 10, the workpiece material more rigid, plastic smaller, Fy / Fz ratio of more large, so the wear debris in the grinding zone is strong under pressure, the surface was mechanically squeezed into the gap in the wheel. From the microscopic analysis of debris slide along the front of abrasive, abrasive front of the local area with several layers of debris piled in the back of grain, due to the role of high-speed rotating wheel to form an air vortex area, vortex area air pressure was significantly decreased under negative pressure, so that part of the abrasive wear debris attached to the back of the formation of the dependence of particle plug flank, attached to most of the ashes and particulate matter. The role of electrostatic field: grinding wheel and workpiece relative velocity is much larger than the V V sand workers, general grinding machine V s = 3 ~ 50m / s, the speed of high speed mature Grinding value is 50 ~ 80 / s, the foreign trials speed of 200m / s ~ 250m / s, workpiece speed 1.5m / s or less. Relative movement of the grinding wheel and work in the grinding zone, the grinding wheel and workpiece surface will occur due to the reasons for electronic escape arranged according to certain rules of charge. Meanwhile, the grinding area of the gas will cause it to be stimulated by high temperature discharge, the neutral gas is ionized into ions and electrons. Some small area in the grinding zone formed by the grinding wheel and workpiece composed of a small electric field in the electric field, there are neutral atoms, positive ions, electrons, impurities, dust, not only the process of neutral atom is ionized, there is ion and electron recombination process. The role of the electric field, some debris will show the polarity of the opposite sex attraction under the principle of opposite polarity with the grinding wheel wear debris to be attracted to the grinding wheel working surface. As the electric field strength is small, so the adsorption force is weak, debris in the wheel surface is not solid, but by means of the grinding wheel and workpiece to high mechanical pressure, so that the surface has been adsorbed on the wheel stable debris embedded in wheel between the surface of the gap. The mechanism of adhesion-type plug Most of the grinding process the input power into the grinding heat, so that the grinding point temperature up to 1200K or more, in such a high temperature, the grinding of the first case of air rapid oxidation, the formation of low melting point metal oxide, and then the metal oxide was heated to high temperatures in the grinding zone melting state, covering the surface of the wheel when the wheel once again participated in this part of the surface grinding, grinding force in the role of, and some pushed open, and some strengthening, an increase of affinity and adhesion with the wheel, there's been squeezed adhere to the surface uplift of the trench surface. Through multiple random grinding, abrasive wear debris surrounding many of the adhesion, so that the grinding force increases, temperature increases, thus forming a vicious cycle, increasing congestion, until the grains break or fall off, which is the melting of the bonding . Chemical affinity between the different elements is blocked adhesion another important reason. Abrasive and grinding materials are exposed at high temperature, the temperature factor to enhance their activity, increased affinity, as have certain conditions, to cause chemical reactions, so abrasive and debris on the surface of the grinding wheel cutting ability of a loss of crystal. Class of the grinding wheel, such as alumina titanium, the wear debris on quickly adhere to the abrasive, and spread and grow up to around the trend, clear debris, there are still a number of adhesive residue around the particle, They are oxygen, titanium, aluminum complex compound, a process that occurred in a chemical reaction equation for the 3Ti +2 Al2O3 = 3TiO2 +4 Al, resultant in TiO2-based, some free of aluminum molecules, such as the use of silicon carbide grinding wheel, plug will be reduced, by grinding the workpiece surface quality also improved, because the affinity of titanium and silicon carbide small, the particle surface is not only scattered some adhesive properties, adhesive properties of these re-entry into the grinding zone, most In the friction loss under compression. Third, the wheel of their own on the block Abrasive Abrasive and workpiece material of different chemical affinity for different temperature, different grinding, grinding force of different levels in order to reduce congestion, different workpiece materials, should be used in different types of abrasives. Abrasive grinding of corundum class of iron-carbon alloy, carbon and oxygen in the air generates a thin oxide film, can effectively prevent the workpiece and the abrasive effect between the chemical affinity, but the grinding of titanium alloy, is a serious multi-plug the. The thermal stability of the abrasive block also has a significant impact, thermal stability, thermal stability, good abrasive worse than the multi-block light. Such as titanium alloys with CBN abrasive grinding, the grinding efficiency ratio improved by Bai Yugang grinding wheels a few times. Abrasive grains Under the same premise in the organization, the more fine abrasive, abrasive wheel size the number of units within the perimeter more, the more uniform, the number of stomata are more, but the less the volume of individual pores in the same grinding parameters, the fine easy to plug the wheel. In the semi-fine grinding and fine grinding, the cut more times, cut into small amount of low temperature, blocking light, often choose the small wheel. In the coarse grinding, the cut capacity, high grinding temperature, plug in the pore of the wear debris, fusing material and more coarse grinding wheel should be selected. Binder with the hardness Hardness refers to the abrasive wheel off the degree of difficulty, be guaranteed by the strength of the binder, they blocked a greater impact on the grinding wheel. The higher adhesive strength, hardness grinding wheel larger amount of grain to the more blunt, abrasive workpiece off scratch before, squeezing even more serious, more likely a mechanical debris fill the pores to the wheel, the wheel gap in the debris intensified the friction wheel on the workpiece material, extrusion, and debris to be strengthened in the process, this process also produces more friction with heat, friction heat to melt adhesion complexes provide plug. Therefore, the higher the hardness grinding wheel, the more serious blockage. So difficult to machine the workpiece in the grinding material, should be chosen softer wheel. Wheel organization Organization reflects the abrasive wheel, binder, pore proportional relationship between the organization more closely, the less porosity ratio, the smaller the distance interval between the cutting edge, the wheel is more prone to clogging. Containing 53% of the abrasive wheel abrasive than the average with 49.2% higher amount of blocked twice with 45% of the abrasive wheel abrasive than the average with 49.2% less than half the amount of blockage. Difficult to process materials in the grinding should be chosen No. 7-8 Organization of the wheel. Fourth, the impact of grinding conditions Wheel speed Wheel speed is comparatively complex, when the wheel from 28.8m / s up to 33.6m / s when the speed is only increased by 16%, while blocking increased threefold. Because the increase in wheel speed to the maximum grain depth of cut decreases, chip cross-sectional area decreases, while the number of cutting and grinding heat increases, so increase congestion. But when the high speed wheel to a certain extent (for example, to 50m / s and above), but the amount of wheel block declined significantly. Therefore, grinding wheel speed is best to avoid the selection of 20m / s to 50m / s this speed. Workpiece speed Experimental results show that the work rate of doubling, tripling the amount of wheel block. Because of the higher speed of the workpiece, the larger the particle load, the more shallow depth of abrasive cut, chip cross-sectional area smaller, when the grinding thickness increases, increased glazing, increasing the grinding wheel layer of extruded parts equivalent wheel features hardened, and thus will aggravate the wheel jam. Grinding mode In the grinding way, any increase of grinding wheel and workpiece contact area of the grinding wheel will increase congestion. This is because the grinding wheel and workpiece contact area, and abrasive cutting edge will be worn on many occasions in the same scratch the workpiece on the grinding layer is increased, the coolant into the grinding zone and difficult, grinding more calories, high temperatures , to create conditions for the plug, easy to produce chemical adhesion and embedding of plug plug. End mill grinding as easy to plug than the week, more than longitudinal cross cut grinding grinding plug serious. Cut into the amount of radial Radial cut into the amount of the impact of congestion on the wheel was hump trend. When the radial cut into the amount of small, (ap <0.01mm) produced jams, with the cut into the amount of the increase, the average block also increased, when the cut volume to a certain extent (ap = 0.03mm), the block volume is presented decreased and then continue to increase as the cut into the amount of (up to ap = 0.04mm), the block volume is rising sharply. Grinding Fluid Different effects of grinding fluid on grinding a great influence on the present emulsion contains a lot of common mineral oils and oil additives, oil in water was diluted milky white liquid, its heat capacity and thermal conductivity, in the severe friction process is easy cause the adhesion between wheel and workpiece wear and diffusion wear, wheel block, grinding force increases, ultimately resulting in premature breakage and shedding abrasive, so that the grinding ratio decreased. Therefore, the use excellent grinding performance of grinding fluid to improve an important role. In short, the wheel size, hardness, structure, wheel speed, workpiece speed and grinding methods, such as cutting depth and grinding fluid phenomena is the process of grinding and grinding results of important parameters. Therefore, the influence of various factors such as wheel block analysis, the amount of grinding parameters such as single-factor, multi-factor test to establish optimal grinding parameters and a reasonable summary of the law, is an effective method to guide the production, but also Grinding Technology in one of the study should focus on.