Development and application of the hottest ultra h

2022-10-18
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Development and application of ultra-high speed grinding technology

ultra high speed grinding can not only greatly improve grinding efficiency, but also effectively improve machining quality. It is one of the most important development directions of grinding technology today

ultra high speed grinding and high-efficiency deep grinding

high speed grinding is a high-speed grinding with the advantages of high machining accuracy compared with the previous ordinary grinding, where the linear speed of the grinding wheel vs> 45m/s. As early as the 1960s, vs had been increased to 60m/s, and then to 80m/s in the 1970s. However, in the following ten years, due to the restriction of the rotation and fracture speed of the grinding wheel at that time and the problem of workpiece burn, the linear speed of the grinding wheel did not increase significantly. Until the late 1980s, with the wider application of cubic boron nitride (CBN) grinding wheel and a more in-depth study of the grinding mechanism, it was found that under the condition of high grinding rate, with the increase of the linear speed of the grinding wheel vs, the grinding force decreased sharply in a certain range around vs=100m/s. This trend will continue with the further increase of the grinding rate, and the surface temperature of the workpiece will also fall. That is to say, after crossing the grinding consumption area where thermal damage occurs, the further increase of grinding consumption will not aggravate the thermal damage, but will make the thermal damage no longer occur, thus laying a theoretical foundation for the development of ultra-high speed grinding and high-efficiency deep grinding

although there is no strict limit for ultra-high speed grinding, the grinding with the linear speed of the grinding wheel vs> 150m/s is usually called ultra-high speed grinding. Generally speaking, ultra-high speed grinding has the following advantages:

high grinding efficiency and small wheel loss

the higher the grinding speed, the more abrasive particles involved in cutting per unit time, the more abrasive debris removed, and the workpiece feed speed should be proportional to the 1.13 power of the linear speed of the wheel, so ultra-high speed grinding will greatly improve the grinding efficiency. Accordingly, the grinding force borne by a single abrasive grain during ultra-high speed grinding is greatly reduced, thereby reducing the wear of the grinding wheel. Many experiments show that when the grinding force is constant, the linear speed vs of the grinding wheel is increased from 80m/s to 200m/s, the grinding efficiency is increased by 2.5 times, and the service life of CBN grinding wheel is also extended by 1 time

small grinding force and high machining accuracy

due to the thinning of debris thickness during ultra-high speed grinding, under the condition of constant grinding efficiency, the normal grinding force will significantly decrease with the increase of vs (the normal grinding force when vs is 200m/s is only 46% of 80m/s), so as to reduce the deformation of the process system. In addition, the excitation frequency of ultra-high speed grinding is much higher than the natural frequency of the process system, which will not cause resonance. The common result is to improve the grinding accuracy

good surface quality of the workpiece

the experimental table shows that the dimensional tolerance of plastic forming parts should be larger due to the large range of shrinkage or poor stability of shrinkage. When other conditions are certain, when the linear speed of the grinding wheel increases from 33m/s to 200m/s, the grinding surface roughness decreases from ra2.0 acid to ra1.1 acid. Because a large amount of grinding heat will be taken away by debris in the process of ultra-high speed grinding, the proportion of grinding heat transferred into the workpiece is very small, which not only is not easy to cause surface burns, but also the depth of the surface residual stress layer becomes smaller

in addition, ultra-high speed grinding can also realize the ductile domain grinding of hard and brittle materials, and also has a good grinding effect on hard grinding materials such as high plasticity. Therefore, industrial developed countries are competing for development, especially Germany, Japan and the United States. It is reported that the German Aachen University of technology has completed the experiment of grinding wheel linear speed vs=400m/s, and is now carrying out the experiment with the target of 500m/s. German companies such as gruhringautomation, schandt and Kapp have successively launched ultra-high speed grinding machines. Japan has been fruitful in practical grinding, and the ultra-high speed grinding machine with vs=200m/s produced by Toyota machinery and other companies has been put into industrial practical application. The ultra-high speed grinding machine using single-layer CBN grinding wheel produced by edgetekmachine company in the United States is also famous. At CIMT2001, Hunan University of China exhibited CNC high-speed cam grinder cnc8312, whose CBN grinding wheel linear speed can reach 120m/s

the ultra-high speed numerical control cylindrical grinder gz32p launched by Toyota machine tools in Japan a few years ago has a maximum linear speed of 200m/s. When it uses the ceramic bonded CBN grinding wheel to grind the reducer parts (made of hardened steel of hrc58) as shown in Figure 2 at the linear speed of the grinding wheel with the motion mode of 16 0m/s, the workpiece speed is 1000r/min, and the machining allowance is △ =0.125mm. The processing results obtained are: processing time 72s, workpiece roundness 1.2 acid, surface roughness rz1.9 acid. Compared with the cutting in grinding with ordinary grinding wheel, the machining time and workpiece roundness error are reduced by more than half

creep feed grinding is characterized by large cutting depth and low working feed rate. The so-called highefficiencydeepgrinding is the application of high-speed CBN grinding wheel to creep feed grinding with high cutting rate, resulting in an efficient deep grinding technology that integrates high wheel speed (vs=80~250m/s), fast working feed speed (0.5~10m/min) and large cutting depth (0.1~30mm). Its grinding rate is very high, especially suitable for full depth single stroke grinding of grooved parts. Figure 3 shows the profimatmt series of plane and forming CNC grinding machines exhibited by German bloom company on cimt2003. Its overall layout is a column with good rigidity and a middle waist moving type. The workbench moves longitudinally with a feed speed of 0.03~25m/min. The three linear movements adopt AC servo machine, ball screw and rolling guide rail. The maximum power of the grinding wheel spindle is 60kW and the maximum linear speed of the grinding wheel is 170m/s. This kind of grinder can be used for high-efficiency deep grinding

some key technologies of ultra-high speed grinding

the process system of grinding is "grinder workpiece Grinder". Naturally, the key technologies of ultra-high speed grinding are also inseparable from grinder, grinding wheel, grinding process and grinding fluid

Research on the mechanism and process of ultra-high speed grinding

the research on the mechanism of ultra-high speed grinding at home and abroad is not comprehensive, and the essence of various grinding processes and grinding phenomena need to be further revealed. At the same time, the optimization of process parameters for different workpiece materials and grinding conditions should be carried out, and the ultra-high speed grinding database should be established accordingly to accelerate its application. The simulation of grinding process with computer is helpful to the above research. Virtual grinding machine can establish a realistic grinding environment

superhard abrasive wheels and their dressing

superhigh speed grinding wheels are one or more layers of superhard abrasive consolidated on the substrate, so they are further divided into two categories: multi-layer dressing and single-layer abrasive wheels. CBN is used for all the superhard Abrasives except that the hard and brittle grinding material is diamond. The matrix of ultra-high speed grinding wheel should not only have enough strength to bear huge centrifugal force, but also have high modulus of elasticity/density ratio and low coefficient of thermal expansion. At present, the commonly used material is high-strength alloy steel. Materials with better properties such as high-strength aluminum alloy and beryllium are being sought as the matrix. A carbon fiber composite CFRP has been used as the matrix of ultra-high speed grinding wheel in Japan. In addition, the shape design of ultra-high speed grinding wheel matrix is also very important

the multi-layer dressing superhard grinding wheel has three kinds of binders: resin, metal and ceramic. Among them, the ceramic bonded grinding wheel is porous, and the bond is brittle. It can be trimmed with diamond rollers. Generally, shaping and sharpening can be completed at one time. There is also a new type of porous ceramic bonded CBN grinding wheel, which can enhance the natural porosity through artificially induced pores. This kind of grinding wheel will introduce more grinding fluid and facilitate chip removal, so that it can grind both high hardness and medium hardness ferrous materials. Therefore, in ultra-high speed grinding, ceramic bonded superhard abrasive wheels are used more

the dressing of resin bonded or metal bonded superhard abrasive wheels is difficult, and the shaping and dressing should be carried out separately. The dressing of superhard abrasive wheels, especially dressing, is still a research hotspot so far. The electrolytic dressing (ELID) method suitable for metal bonded superhard abrasive wheels developed by the Japanese more than a decade ago has played a certain role in the development of ultra precision mirror grinding. At present, the laser dressing method being studied is not only convenient for dressing resin or metal bonded superhard abrasive wheels, but also has small heat affected zone, small grinding wheel dressing loss, easy to realize automation, and high dressing efficiency, which has great development prospects

there are two kinds of single-layer superhard abrasive wheels without dressing, including electroplated wheels and (high temperature) welding wheels. Due to the excellent performance of superhard abrasives, even single-layer Abrasives still have a long life. Among them, the manufacturing process of electroplated grinding wheel is relatively simple (after the abrasive is blunt, it can be electroplated for many times). The coated metal can be closely embedded around the abrasive, and can withstand the grinding speed of 250~300m/s at most. It has been widely used in ultra-high speed precision grinding and form grinding. The bonding strength between the abrasive of the welding wheel and the matrix is particularly high, and the exposed height of the abrasive particles reaches 60~70%. Therefore, the chip holding space is large and the abrasive particles can obtain a sharper shape. It is reported that the linear speed of the foreign welding wheel can reach 500m/s

spindle system and feed system of ultra-high speed grinder

the overall structure and foundation large parts of ultra-high speed grinder should have high dynamic and static stiffness, which is usually analyzed and optimized by finite element method. The safety protection of machine tool is also very important, but the most critical is the spindle system and feed system

spindle system

increasing the linear speed of the grinding wheel is mainly to increase the speed of the grinding wheel. The maximum speed of the spindle of the ultra-high speed grinder is more than 10000r/min, and the transmitted grinding power is often dozens of kW. Therefore, the spindle system is required to have good rigidity, high rotation accuracy, small temperature rise and low power consumption. In recent years, ultra-high speed grinding machines increasingly use motorized spindles that integrate motors and spindles. The bearings they use are mainly oil-gas lubricated ceramic ball angular contact ball bearings and hydrodynamic hydrostatic bearings, which are mostly used in cylindrical ultra-high speed grinding machines. Although the magnetic bearing has good high-speed performance and high precision, it is expensive and has the problems of heating and magnetic leakage, which is rarely used at present. The vibration caused by the dynamic imbalance of the high-speed rotating grinding wheel shaft and the grinding wheel will seriously affect the grinding quality. In addition to the strict dynamic balance of the grinding wheel and spindle system in advance, continuous automatic balance should also be implemented in the grinding process of the machine tool. In addition, we should pay full attention to the reliability of the connection between the grinding wheel and the spindle of ultra-high speed grinder

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