Factors affecting surface roughness of grinding machine and their improvement measures
1. Factors related to grinding wheel
It is mainly about grinding wheel grain size, hardness and dressing of grinding wheel.
The finer the grain size of the grinding wheel, the more grains per unit area of the grinding wheel, the finer the scratches on the grinding surface, and the smaller the surface roughness value.But the grain size is too fine, grinding wheel is easy to block, increase the surface roughness, and also easy to generate ripples and burns.
The hardness of the grinding wheel refers to the degree of difficulty for the grinding grains to fall off the wheel after being subjected to grinding force.If the grinding wheel is too hard, the abrasive particles cannot fall off after being worn out, which makes the surface of the workpiece subject to strong friction and extrusion, increases the plastic deformation, increases the surface roughness, and at the same time, it is easy to cause burns.The grinding wheel is too soft, the grinding grains are easy to fall off, and the grinding effect is weakened, which will also increase the surface roughness value. Therefore, the suitable grinding wheel hardness should be selected.
The dressing quality of grinding wheel is closely related to the dressing tool used and the longitudinal feed of dressing grinding wheel.The dressing of grinding wheel is to remove the passivated abrasive particles in the outer layer of grinding wheel with diamond to make the cutting edge sharp and reduce the surface roughness of grinding surface.In addition, the smaller the longitudinal feed of the dressing grinding wheel, the more cutting micro-edges on the repaired grinding wheel, the better the contour, so as to obtain a smaller surface roughness value.
2. Factors related to the material of the workpiece
Including the hardness of the material, plasticity, thermal conductivity, etc.
The hardness, plasticity and thermal conductivity of the workpiece material have significant influence on the surface roughness.Soft materials such as aluminum and copper alloy are easy to block the grinding wheel and are difficult to grind.The high plasticity and poor thermal conductivity of the heat-resistant alloy can easily lead to sand caving in the early stage and increase the roughness of the grinding surface.
3. Factors related to processing conditions
It includes grinding amount, cooling condition, precision and vibration resistance of process system, etc.
Grinding parameters include grinding wheel speed, workpiece speed, grinding depth and longitudinal feed.If the grinding wheel speed is increased, the propagation speed of surface metal plastic deformation may not keep up with the grinding speed, and the material has no time to deform, thus reducing the surface roughness of the grinding surface.The workpiece velocity increases, the plastic deformation increases, and the surface roughness increases.The greater the grinding depth and longitudinal feed, the greater the plastic deformation, thus increasing the surface roughness.The grinding temperature of the grinding wheel is high, and the role of heat is dominant, so the role of cutting fluid is very important.The use of cutting fluid can reduce the temperature of grinding zone, reduce burns, and wash away the sand and chips, so as not to scratch the workpiece, thus reducing the surface roughness.But the appropriate cooling method and cutting fluid must be chosen.
In addition, for cylindrical grinder, internal grinder and surface grinder, the spindle precision of the grinding wheel of the machine tool, the precision and stability of the feed system, the stiffness and vibration resistance of the whole machine tool are all closely related to the surface roughness.