High speed grinding technology with high efficiency grinding fluid

High speed grinding technology with high efficiency grinding fluid

(1) Ultra high speed grinding wheel technology

High speed and ultra-high speed grinding wheel should have good wear resistance, high dynamic balance accuracy, crack resistance, good damping characteristics, high stiffness and good thermal conductivity, and its mechanical strength must be able to withstand the cutting force during high-speed and ultra-high-speed grinding, Therefore, it is necessary to use the grinding wheel with high mechanical strength of matrix and high bonding strength between matrix and abrasive

In the middle of the ultra-high speed grinding wheel is a high-strength material matrix disk. Most of the practical superabrasive grinding wheels are aluminum or steel. Only a thin layer of abrasive is bonded around the substrate. There are three kinds of binders used for bonding abrasives, including resin, metal and electroplating, and the single-layer electroplating is the most used. This is because of its high bonding strength, easy to make complex shapes, and does not need to be trimmed in use, In recent years, Norton company has developed grinding wheel by copper welding instead of electroplating, and the tensile strength of bond is more than 1533n / mm2, and the bond strength is more than 1533n / mm2

Corundum, silicon carbide, CBN and diamond abrasives can be used for high-speed and ultra-high speed grinding wheel. Ceramic, resin or metal bond can be used as bond. The speed of resin bonded corundum, silicon carbide and Cubic Boron Nitride Abrasives can reach 125m / s. The speed of single layer electroplated CBN grinding wheel can reach 250m / S, The grinding speed of ceramic bonded wheel can reach 200m / s. compared with other types of grinding wheel, ceramic bonded wheel is easy to repair. Compared with high-density resin and metal bonded wheel, ceramic bonded wheel can obtain a wide range of porosity by changing the production process. The special structure has 40% porosity, It makes the chip holding space large and the trimming is simple. Even in many applications, it can not be sharpened

In high-speed grinding, a new type of microcrystalline alumina abrasive, namely SG (seeded gel) abrasive, has attracted people's attention. SG abrasive has not only high hardness but also good toughness, and its processing ability is between corundum and CBN abrasive particles. Since the auxiliary cutting edge of SG abrasive can self sharpen in grinding process, the grinding force and heat generated in grinding zone are obviously reduced, At the same time, it also reduces the wear of grinding wheel, so as to improve the material removal rate and dressing interval time of grinding wheel. Compared with CBN abrasive particle, SG abrasive has lower cost and has no special requirements for grinding machine tool. The dressing method of grinding wheel is the same as that of traditional abrasive wheel. In the test of grinding tempered steel with wheel speed of 125m / s, the specific material removal rate has reached 100 mm / (mm · s)

In addition, the reliability of the connection between the grinding wheel and the spindle should be fully considered. It is necessary to develop a connection mode between the grinding wheel and the spindle with high precision, high stiffness and good dynamic balance performance. In order to keep the grinding wheel sharp throughout its service life, the structure of the grinding wheel should be conducive to the separation of the abrasive grains and optimize the spatial distribution of the abrasive grains, In addition, it is necessary to have high grinding quality

(2) Spindle and bearing technology of ultra high speed grinder

The performance of the spindle unit for ultra-high speed grinding largely determines the grinding speed limit that the ultra-high speed grinding machine can reach. Therefore, in order to realize high-speed and ultra-high-speed grinding, the grinding 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 and long service life, The manufacturing and dynamic balance of the spindle, the support (bearing) of the spindle, the lubrication and cooling of the spindle system, and the rigidity of the system are very important. In order to reduce the dynamic force caused by the increase of grinding speed, the grinding wheel spindle and the spindle motor system are required to operate accurately with minimal vibration

The spindle speed of ultra-high speed grinding wheel is generally more than 10000 R / min, and the grinding power is usually tens of kilowatts. Therefore, the characteristic value of spindle bearing speed is very high, and it must have high rotation accuracy and stiffness, so as to ensure that the abrasive particles on the circumference of the grinding wheel can participate in the cutting evenly, and can resist the vibration caused by unbalanced mass during ultra-high speed rotation

The ceramic ball bearing has the advantages of light weight, small coefficient of thermal expansion, high hardness, high temperature resistance, dimensional stability at high temperature, corrosion resistance, high service life and high modulus of elasticity. Its disadvantages are difficult to manufacture, high cost and low cost, It is sensitive to tensile stress and notch stress. The surface velocity of Maglev bearing can reach 200m / s, which may become a choice of ultra-high speed spindle bearing in the future. At present, the main problems of Maglev bearing are low stiffness and load capacity, and the size of magnet used is too large compared with rotary body, which is expensive. Aerostatic bearing has high rotary accuracy, no vibration, low friction resistance and durability, It can rotate at high speed. It can be used in high speed, light load and ultra precision occasions. The hydrodynamic bearing is mainly used for low-speed and heavy-duty spindle because of its large power loss without load

Another characteristic of high speed and ultra-high speed grinding is that the reactive power loss of the spindle increases nonlinearly with the increase of the speed. For example, when the grinding speed is increased from 80 m / s to 180 m / s, the reactive power of the spindle will increase from less than 20% to more than 90%. In the high speed range, the motor works in constant power mode, and the output torque decreases when the spindle speed increases, and the increase of reactive power will lead to the reduction of grinding torque