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1、 Factors related to grinding wheel
1. Mainly the grain size, hardness and dressing of grinding wheel. The finer the grain size of the grinding wheel, the more abrasive grains per unit area of the grinding wheel, the finer the grinding surface notch and the smaller the surface roughness value. However, if the particle size is too fine, the grinding wheel is easy to be blocked, which makes the surface roughness value increase, and at the same time, it is easy to produce ripple and burn.
2. The hardness of grinding wheel refers to the degree of difficulty that the abrasive grains fall off the grinding wheel after being subjected to grinding force. If the grinding wheel is too hard, the abrasive grains can not fall off after wear, so that the surface of the workpiece is subject to strong friction and extrusion, which increases plastic deformation, increases the surface roughness value, and at the same time, it is easy to cause burns; if the grinding wheel is too soft, the abrasive grains are easy to fall off, and the grinding effect is weakened, the surface roughness value will also be increased. Therefore, the appropriate hardness of the grinding wheel should be selected.
3. The dressing quality of grinding wheel is closely related to dressing tools and longitudinal feed rate of dressing wheel. The dressing of grinding wheel is to remove the passivated abrasive particles in the outer layer of the grinding wheel with diamond to make the cutting edge of abrasive grains sharp and reduce the surface roughness of grinding surface. In addition, the smaller the longitudinal feed of the dressing wheel is, the more micro cutting edges are on the repaired wheel, and the higher the contour is, the smaller the surface roughness is.
2、 Factors related to workpiece material
1. Including hardness, plasticity and thermal conductivity of materials.
2. The hardness, plasticity and thermal conductivity of workpiece material have significant influence on surface roughness. Aluminum, copper alloy and other soft materials are easy to block the grinding wheel and difficult to grind. The heat-resistant alloy with high plasticity and poor thermal conductivity is easy to cause the sand grains to collapse in the early stage, which leads to the increase of grinding surface roughness.
3、 Factors related to processing conditions
1. Including grinding amount, cooling conditions, accuracy and vibration resistance of process system.
2. Grinding parameters include wheel speed, workpiece speed, grinding depth and longitudinal feed rate. With the increase of grinding wheel speed, the propagation speed of plastic deformation of surface metal can not keep up with the grinding speed, and the material has no time to deform, so that the surface roughness value of grinding surface will be reduced. With the increase of workpiece speed, plastic deformation and surface roughness increase. The greater the grinding depth and longitudinal feed rate, the greater the plastic deformation, thus increasing the surface roughness value. Because of the high temperature of grinding wheel, the role of heat plays an important role, so the role of cutting fluid is very important.
3. The use of cutting fluid can reduce the temperature of grinding area, reduce the burn, and wash away the sand and chips, so as to avoid scratching the workpiece, thus reducing the surface roughness value. But choose the appropriate cooling method and cutting fluid.
4. For cylindrical grinder, internal grinder and surface grinder, the spindle accuracy of grinding wheel, accuracy and stability of feed system, stiffness and vibration resistance of the whole machine tool are closely related to surface roughness.
4、 Dressing technique of grinding wheel
1. Dressing is a process to sharpen the abrasive grains of superhard abrasive wheel. In this process, it is necessary to form a sharp cutting edge in addition to the bond between the abrasive grains and the blunt abrasive grains of the grinding wheel, so that the grinding grains with strong grinding performance protrude from the bond. Dressing also removes tiny materials from the pores on the grinding wheel surface to prevent the increase of grinding force acting on the grinding wheel. The increase of grinding force on the grinding wheel will cause vibration and burn on the surface of parts.
2. Without proper dressing, even a very good grinding wheel can not obtain high quality and dimensional consistency of machined parts. In fact, when you invest in high-quality grinding wheels, it is very important to trim them well in order to achieve high grinding performance.
3. Truing can be said to be a part of the preparatory work of grinding wheel, which is carried out at the same time as ordinary grinding wheel dressing. For superhard abrasive wheel, the two processes are carried out separately. First, the grinding wheel is reshaped. In grinding with superhard abrasive wheel, dressing is carried out with shaping tools or rollers, and dressing is often carried out with a dressing rod of ceramic bond. After finishing the dressing, the grinding wheel is dressed.
4. It is very important to ensure that the spindle bearing is in a certain temperature (such as the normal grinding state) before the grinding wheel including truing and dressing. In this way, the geometric shape of parts and abnormal wear of grinding wheel and dressing tool can be avoided. The tools used for dressing should be handled carefully, because they are generally made of hard, wear-resistant and brittle diamond materials, and are very sensitive to tiny cracks and breakage caused by slight impact and stress.
5. As the diamond shaper itself is a tool, it needs to be kept very sharp. The use of a blunt dressing tool to trim the surface of the wheel will blunt the wheel. In order to maintain a high-quality and sharp diamond dressing tool, it is necessary to rotate a single point or cone-shaped dressing tool in 1 / 8 circles every certain time. The number of rotations can be determined according to the dressing condition, and less once a day according to experience. For chisel heads and shaping tools, it is generally necessary to rotate them 180 ° before they are blunt.
On 2018-08-08 11:45:46
