Grinding processing is the grinding tool as a "tool" for the workpiece precision cutting processing.Compared with other cutting methods, grinding has many unique features, which can be summarized as follows:
(1) during the grinding process, the number of abrasive grains participating in cutting is extremely high
The grinding wheel contains a large number of grinding grains.According to the measurement, there are tens of thousands or even hundreds of thousands of grinding grains per gram of white corundum abrasive.While a piece of white corundum grinding wheel with size of 300×32×75 (mm) weighs about 5kg, excluding 10% of the binder accident, the number of grinding grains per square centimeter of grinding wheel with different particle size and hardness is about 60~1400.But on the surface of the grinding wheel, the distribution of grinding grains is irregular and irregular.The number of grinding grains on the surface of grinding wheel is less than the total number of grinding grains on the surface of grinding wheel.If the working conditions during grinding are taken into account, the number of abrasive grains actually participating in the cutting (that is, the dynamic effective number of abrasive grains) is even smaller.According to the measurement, the number of grinding grains actually involved in grinding on the surface of the grinding wheel accounts for 10%~50% of the total number of grinding grains on the surface of the grinding wheel due to the different characteristics of the grinding tool and grinding conditions.Even so, the number of grains involved in grinding is still high.Therefore, the grinding process is the statistical cutting process of a large number of abrasive particles, while other cutting methods only have one or several cutting edges with certain geometric shapes participating in the cutting process.
(2) the abrasive grains playing a cutting role have special properties
1) as a tool, the abrasive particles have a high hardness, so it can smoothly cut the high hardness of the workpiece materials.Especially for some high hardness and brittleness of the workpiece material with other cutting methods can not be compared to the cutting ability, and can obtain other processing methods impossible to achieve the processing quality.
2) the abrasive particles have good thermal stability and will not lose their cutting ability at high temperature
3) the abrasive particles have a certain degree of brittleness, which can be broken under the action of grinding force to form a new sharp cutting edge.
4) the shape of the abrasive cutting edge is irregular and the abrasive particles are squeezed into the workpiece at a large negative front Angle.Due to the different growth mechanism of abrasive crystals and the different grinding methods in the granulation process, the shapes and sizes of abrasive grains are various, and the arrangement in the grinding wheel is irregular.The total number of abrasive particles is cut into the workpiece at a negative front Angle, which is generally -15°~-60° or larger.The size of abrasive particles with the same size size is also different.
For example, according to GB/T 2481.1~1988, F46 grinding particles are 100% through the mesh size of 600 × m no. 30 screen, and allow 30% of the mass force with no. 40 screen size (its mesh size is 125 × m) of the coarse particles, through the screen size of 60 (mesh basic size is 250 × m) of the fine particle mass is not more than 3%.That is to say, in the F46 grain, the grain size of soybean is between 250 and 600 liters.The edge tip of the abrasive has a certain center Angle and arc radius.At the same time, the surface and cutting edge curves are not smooth, there are small irregularity.
(3) the cutting depth of a single abrasive is very small
During grinding, the number of abrasive particles involved in cutting is large, and the number of cutting edges is even larger.Therefore, even in the case of high grinding efficiency, the workpiece volume under a cutting edge is only 10-4~10-5mm3. In the case of fine grinding, the volume of each grinding chip is even smaller.In milling, the volume of each chip is generally 40mm3, much larger than the grinding volume.
(4) extremely high cutting speed of abrasive grains
During grinding, the speed of the circumferential surface of the grinding wheel is extremely high, and the contact time between the abrasive cutting edge and the processed workpiece is extremely short, generally 10-4~10-5s.In such a short time to complete the cutting, grinding particles and the workpiece produced a strong friction, and produce a sharp plastic deformation, resulting in a large amount of grinding heat, grinding area to produce a very high grinding temperature (400℃~1000℃), and more than 80% of the heat will be transferred to the workpiece.
(5) the mill has a self-sharpening effect
The abrasive particles involved in grinding are constantly rubbing with the workpiece and gradually become dull, and the forces on the abrasive particles increase gradually. When the forces on the abrasive particles exceed the control ability of the binder on the abrasive particles, the abrasive particles will fall off the surface of the abrasive.The new and sharp grinding grains under the grinding grains are exposed to form the self-sharpening of the grinding tools;In addition, the abrasive particles in the process of interference with the workpiece and the grinding tool and the workpiece continue to be squeezed, if the extrusion pressure exceeds the compressive strength of the abrasive particles themselves, then the grinding particles crushing produces a new sharp cutting edge.This self-sharpening ability of the tool is not available to other cutting tools.
(6) larger than grinding energy
Because of the small power in grinding, and each grinding particle cutting edge to remove the chip volume is very small, the degree of grinding material subdivision, so the unit volume of metal removal (than grinding energy) is much larger than the turning.