Single abrasive process

Abrasive belt grinding is accomplished by a large number of abrasive cutting edges that are vertically aligned on the surface of the belt. Each abrasive grain can be approximated as a micro-tool, so studying the grinding process of these single abrasive particles is the basis for studying the entire abrasive belt grinding.

From the microscopic point of view, the abrasive grains on the surface of the abrasive belt are like a cutting tool whose cutting edge is an arc and whose cutting angle is obtuse or obtuse. The radius of the arc is from a few microns to a few tens of microns, and the size is related to the material and particle size of the abrasive particles. Due to the geometrical characteristics of the abrasive grains, the high performance cutting disc cutting depth is small (thickness of the chip) during grinding, and is generally about 0.005 to 0.05 mm. Therefore, most abrasive cutting edges cut the workpiece under conditions of large negative rake angle. This is the same as the cutting process of the machine tool. The workpiece material is deformed into chips under the action of the extrusion and friction of the abrasive cutting edge to form a machined surface. The elastic contact characteristics of the abrasive belt make the cutting process of the abrasive cutting edge roughly divided into four stages of extrusion, sliding, ploughing and cutting, as shown in the figure. Initially the abrasive particles are squeezed into the workpiece due to the cut

The depth of penetration is smaller than the radius of the sharp edge of the abrasive grain, forming a large negative rake angle, and the surface of the workpiece is only elastically deformed. As the depth of plunging increases, the pressure of the abrasive particles on the surface of the workpiece gradually increases, and the workpiece begins to be pressed into the workpiece, and the surface of the workpiece starts from elastic deformation to plastic deformation. The abrasive grains continue to be squeezed, the friction is intensified, and the thermal stress is sharply increased. The ploughs are ploughed on the surface of the workpiece, and the metal slips on both sides of the groove mark. The plastic deformation of the workpiece material is increasing. As the plunging depth continues to increase, the pushed metal layer slips significantly. After the pressing force exceeds the strength of the workpiece material, the chips are formed to flow out from the rake face and cut away from the surface of the workpiece. The processing materials are not the same, and the proportion of the grinding process in the four stages of the grinding process is different.

The grinding process is the process of cutting the metal by the abrasive cutting edge. Like the cutting of the machine tool, the ground metal is subjected to elastic deformation, plastic deformation, cutting formation, etc., and has a large amount of grinding force and grinding heat generation. .Due to the different shape and distribution of the abrasive grains during the grinding process, the abrasive grains on the surface of the abrasive belt have less effective abrasive grains actually participating in the grinding than the total number of abrasive grains. Therefore, the same effect of the abrasive grains on the metal extrusion, sliding, ploughing and cutting at the same time, the effect obtained is also different. Even the different parts of the same abrasive grain and the same part play different roles in different processing times. It can be seen that the grinding of the abrasive belt is very complicated. In particular, the negative rake cutting process of the abrasive grain cutting edge has poor cutting conditions. The severe extrusion at each stage causes severe plastic deformation of the grinding surface, and a large amount of plastically deformed metal does not become a chip outflow, but remains in the The surface has been machined, so the hardening of the machined surface is severe and the residual stress is large. Due to the high-speed movement of the abrasive particles and the blunt cutting edge of the abrasive grains, large friction and elastic deformation and plastic deformation occur in the grinding zone, and a large amount of heat is generated during the grinding process, resulting in an increase in the surface temperature of the workpiece in the grinding zone. Will cause a change in the surface layer of the workpiece. Especially in the case of abrasive belt abrasive wear, the grinding friction is intensified, a large amount of grinding heat is generated, and the surface temperature of the workpiece rises sharply, resulting in structural changes of the surface metal (such as burns, cracks, thermal stress, etc.). high performance cutting discThis is one of the reasons why abrasive belt grinding sometimes burns the surface of the workpiece. From the perspective of the micro-tool-grinding geometry, the negative rake angle is large and the back angle is small. Especially the elastic grinding of the belt makes the abrasive particles have a strong pressing effect on the workpiece during grinding. Far greater than the stretching effect when the chips are separated. In the vertical direction of the grinding, the metal on both sides of the abrasive grains is strongly pressed, resulting in a large residual compressive stress. In addition, the surface deformation of the workpiece under the combined action of abrasive grain extrusion, sliding rubbing, ploughing, etc., will cause lattice distortion, distortion, metal density reduction, specific volume increase, surface residual compressive stress, and lower layer formation. Pulling stress. Therefore, based on the above analysis, it is known that when the abrasive belt is ground, the grinding force and the plastic deformation factor often cause residual compressive stress on the surface of the workpiece. This is extremely important for machining parts with very high reliability requirements (such as aircraft blades, generator shafts, etc.).

Therefore, in summary, the mechanism of abrasive belt grinding can be summarized as follows: due to the uniform distribution of abrasive grains on the surface of the belt, the contour is good, the sharp edge is exposed, the cutting edge is sharp, and the cutting conditions are better than the abrasive grains of the grinding wheel, so that the abrasive belt is ground. In the process, the plough and cutting effect of the abrasive grains are large, so the material removal rate is large and the efficiency is high.

Due to the elastic contact state of the abrasive belt, the abrasive belt has a large effect on the extrusion and sliding of the surface material of the workpiece, so that the abrasive particles have a strong grinding and polishing effect, and the surface quality of the grinding is good.

Due to the large space of the abrasive belts, the possibility of frictional increase caused by the clogging of the abrasive grains is reduced, and the heat generated thereby is small; since the arc length of the abrasive belt and the workpiece is large, the single abrasive grains are less stressed and uniform; The abrasive belt of the abrasive belt is sharp and sharp, the material deformation is small during grinding, and the heat generated is correspondingly small. In addition, the abrasive belt has a long circumference and good heat dissipation, so the grinding force generated by the abrasive belt during the whole grinding process is generated. The grinding heat is much lower than that of the grinding wheel, and the grinding temperature is low, so it is called cold grinding.