Development and key technology of the hottest ultr

The development and key technology of ultra-high speed grinding (Part 2)

ultra high speed spindle

improving the linear speed of the grinding wheel is mainly because the quality of the house has become a major event for builders to improve the speed of the grinding wheel spindle. Therefore, in order to achieve high-speed cutting, the wheel drive and bearing speed are often required to be very high. The high-speed spindle requires sufficient stiffness, high rotation accuracy, good thermal stability, reliability, low power consumption, long service life, etc. In order to reduce the increased dynamic force due to the increase of cutting speed, the grinding wheel spindle and spindle motor system are required to operate extremely accurately with minimal vibration. At present, a large number of high-speed and ultra-high-speed machine tools produced abroad use motorized spindles

foreign high-speed motorized spindles have developed rapidly. For example, in Japan, at the 19th JIMTOF exhibition in October 1998, the ultra-high-speed spindles on display were basically between r/min. At present, the highest level motorized spindle in the world is the product of Swiss Fisher company (nmax=40000 R/min, n=40kw). Practical high-speed motorized spindles with speeds up to 200000 R/min and 250000 R/min are also under research and development. The ultra-high speed turning milling plastic simply supported beam impact testing machine developed by Shenyang Institute of technology places the sample horizontally on the bed, adopts the motorized spindle speed regulation range of r/min, and the maximum output power is 7.5kW. The GD-2 high-speed motorized spindle with a rated speed of 1500r/min developed by Guangxi University of technology adopts Si3N4 ceramic ball bearings, with a maximum speed of 18000r/min and a main motor rated power of 13.5KW

main shaft bearings can be ceramic rolling bearings, magnetic bearings, aerostatic bearings or hydrodynamic bearings. Ceramic ball bearings have the advantages of light weight, low coefficient of thermal expansion, high hardness, high temperature resistance, dimensional stability at high temperature, corrosion resistance, high service life, and high elastic modulus. Its disadvantage is that it is difficult to manufacture, high cost and sensitive to tensile stress and notch stress_ The maximum surface speed of magnetic bearing can reach 200m/s, which may become a choice of ultra-high speed spindle bearings in the future. At present, the main problems of magnetic bearing are low stiffness and load capacity, and the size of the magnet used is too large compared with that of the rotating body, which is expensive. Aerostatic bearing has the characteristics of high rotation tip, no vibration, low friction resistance, durability, and high-speed rotation. It is used in high-speed, light load and ultra precision occasions. It may also contain a lot of information unrelated to important content (for example, the advertising body dynamic and static pressure bearing has too much power loss when there is no load, and it is mainly used for low-speed and heavy-duty spindles.

ultra high speed grinding wheel

high speed grinding wheel should have good wear resistance, high dynamic balance accuracy, crack resistance, good damping characteristics, high stiffness and good thermal conductivity. It is usually composed of a matrix with high mechanical properties and thin-layer abrasive particles. The matrix of the wheel should avoid residual stress and elongation stress during operation minimum. By calculating the tangential and normal stresses of the grinding wheel, it is found that the maximum stress occurs in the tangent direction of the inner diameter of the grinding wheel base, and this stress should not exceed the strength limit of the grinding wheel base material. Most practical superhard abrasive wheels are made of aluminum or steel. Japan and Europe have also developed other materials, mainly including polyurethane (PU) for earthquake resistance, ballast pads, sleepers and other materials, and CBN grinding wheels for rubber products such as CFRP composites. Although the elastic coefficient of CFRP is low, the ratio of elastic coefficient to specific gravity is high, which can inhibit the extension of grinding wheel in the radial direction. Another advantage of CFRP is its low linear elongation coefficient. At present, CBN grinding wheel with a diameter of 380mm based on CFRP can achieve grinding of 200m/s and a feed speed of 2m/s. In Japan, a 300m/s grinding test has been carried out on a 400m/s ultra-high speed grinder using a 250mm ceramic bonded CBN wheel with CFRP as the substrate

corundum, silicon carbide, CBN and diamond abrasives can be used for ultra-high speed grinding wheels. The bond can be made of ceramic, resin or metal. The use speed of resin bonded corundum, silicon carbide and cubic boron nitride abrasive wheels can reach 125m/s. The service speed of single-layer electroplated CBN grinding wheel can reach 250m/s, and it has reached 340m/s in the test. The grinding speed of ceramic bonded grinding wheel can reach 200m/s. Compared with other types of grinding wheels, ceramic bonded grinding wheels are easy to dry finish. Compared with high-density resin and metal bonded grinding wheels, ceramic bonded grinding wheels can obtain a wide range of porosity by changing the production process. The special structure has 40% porosity. Due to the structural characteristics of ceramic bonded grinding wheel, the chip holding space is large after trimming, and the trimming is simple, even in many applications, it can not be trimmed. Using the sheet sintered ceramic grinding wheel and reliable bonding, the defect that the elastic coefficient of the ceramic bond is too different from the matrix and is easy to crack is solved. Norton company of the United States has developed a method of holding abrasive particles with the help of chemical bonding force, which can make the abrasive particles protrude 80% of the height without falling off, and the tensile strength of its bond exceeds 1553n/mm (n/mm for electroplated nickel based bond). Ahern University of technology has achieved the reliable bonding between the abrasive layer and the substrate by using the solution injection technology on the aluminum base plate of its grinding wheel