1. The formation of wear debris
The grinding wheel is a loose body made of abrasives and binders through compaction, drying and sintering. Each abrasive grain is a micro-cutting edge. In the process of high-speed operation, the abrasive particles cut into the workpiece after slipping, and the cutting layer material has obvious short and thin chips formed after sliding along the shear surface, which are oxidized and melted under the action of grinding heat, and then solidified into Particle band-shaped crumbs. Through the scanning electron microscope, it can be found that a large number of band-shaped abrasive debris and ash are filled in the pores of the grinding wheel, and they are attached to the periphery of the abrasive, causing the blockage of the grinding wheel, resulting in a decrease in grinding accuracy and shortening the life of the grinding wheel.
2. Types and causes of blockage of CBN grinding wheel
The types of wheel blockage include embedded type, attached type, adhesive type, and mixed type. Embedded blockage is the blockage state of the grinding debris embedded in the pores of the working surface of the grinding wheel. Attached blockage is a kind of blockage in which the temporary force of abrasive grains is attached to the flank surface of the abrasive grain cutting edge. Adhesive clogging refers to the adhesion of abrasive particles around the protruding cutting edge or on the adhesive after grinding and melting. Hybrid blockage is a collection or layered collection of the above three types in a small part. 1. Causes of plugging of embedded and dependent types
Embedded and dependent blockages come from two aspects, one is external and the other is internal, involving many factors such as physical reactions.
External factors: The wear debris slides out along the front of the abrasive particles, and there are several layers of wear debris accumulated in the local area in front of the abrasive particles. Due to the high-speed rotation of the grinding wheel, an airflow vortex area is formed, and the air pressure in the vortex area is significantly reduced. , So that part of the abrasive debris is attached to the back of the abrasive grains, forming an attachment blockage on the blade face of the abrasive grains, and most of the attachments are ashes and particles.
The effect of the electrostatic field: When the grinding wheel and the work are moving relative to each other, the electric charge on the surface of the grinding wheel and the workpiece and the gas in the grinding area will cause a physical reaction due to the high temperature to form a small electric field. Under the action of the electric field, according to the principle of opposite sex attraction, the grinding debris with the opposite polarity to the grinding wheel is adsorbed on the working surface of the grinding wheel. With the help of the greater mechanical pressure between the grinding wheel and the workpiece, the grinding debris that has been adsorbed on the surface of the grinding wheel It can be stably embedded between the gaps on the surface of the grinding wheel.
2. Causes of sticky blockage
During the grinding process, the grinding point temperature is as high as 1200K. Under the action of such high temperature, the grinding debris will form a low-melting metal oxide in the air. It will be heated and melted at the high temperature in the grinding zone, covering the surface of the grinding wheel. Under the action, it is squeezed apart, strengthened, and squeezed to adhere to the raised groove surface on the surface of the workpiece. Through multiple random grinding, more abrasive debris will adhere around the abrasive particles, thereby forming a vicious circle, aggravating the blockage, until the abrasive particles are broken or falling off, which is a fusion bond.
3. The influence of CBN grinding wheel itself on blockage
Different abrasives have different chemical affinity with the workpiece material, the grinding temperature is different, and the grinding force is different. In order to reduce the degree of clogging, different types of abrasives should be selected for different workpiece materials.
2. Abrasive particle size
Under the premise of the same organization and grinding wheel size, the finer the abrasive, the more grains, the more uniform the arrangement, the more the number of pores, and the smaller the volume of a single pore. Under the same grinding parameters, the fine grinding wheel is easy to block.
3. Binder and hardness
The hardness of the CBN grinding wheel is guaranteed by the strength of the binder, which has a greater impact on the blockage of the grinding wheel. Adhesive grinding wheel has high hardness. The scratch and squeeze of the workpiece before the blunt abrasive particles fall off are serious. The grinding debris is easy to fill into the pores of the grinding wheel. The grinding process is accompanied by a large amount of frictional heat, which is cohesive. The blockage provides sinter.
4. Grinding wheel organization
The structure of the grinding wheel reflects the proportional relationship between the abrasive, the binder, and the pores. The denser the structure, the smaller the proportion of pores and the smaller the distance between the cutting edges, which makes the grinding wheel easier to block.
Fourth, the influence of grinding conditions
1. Linear speed of grinding wheel
The increase in the linear speed of the grinding wheel will cause the large depth of cut of the abrasive particles to decrease and the cross-sectional area of the chip to decrease. At the same time, the number of cuts and the heat of grinding increase, so that the amount of blockage increases. The speed of the grinding wheel should be selected reasonably during the grinding process.
2. Workpiece speed
Practice has proved that the working speed is doubled and the blockage of the grinding wheel is tripled. Because the higher the workpiece speed, the greater the abrasive load, the shallower the penetration of the abrasive particles, and the smaller the cross-sectional area of the chips. When the thickness of the grinding increases, the passivation of the abrasive particles increases, which increases the extrusion of the grinding layer of the workpiece by the grinding wheel. , Which is equivalent to the hardening of the characteristics of the grinding wheel, which will aggravate the blockage of the grinding wheel.
3. Grinding method
In the grinding method, increasing the contact area between the grinding wheel and the workpiece will aggravate the blockage of the grinding wheel. Due to the large contact area between the grinding wheel and the workpiece, it is difficult for the coolant to enter the grinding area, the grinding heat is high, and the temperature is high, creating conditions for clogging, and it is easy to produce chemical adhesion clogging and embedded clogging. For example, the end grinding is easier to block than the peripheral grinding, and the horizontal cutting grinding is more serious than the longitudinal grinding.
4. Radial cutting amount
The influence of the radial cutting amount on the blockage of the CBN grinding wheel shows a hump trend. When the radial cutting amount ap<0.01mm, clogging occurs. When the cutting amount increases to ap=0.03mm, the blocking amount shows a decreasing trend. When the cutting amount continues to increase ap=0.04mm, the blocking amount rises sharply.
5. Grinding fluid
Choosing an excellent grinding fluid can change the grinding blockage.
The particle size, hardness, structure, wheel speed, workpiece speed, grinding method, cutting degree and grinding fluid of CBN grinding wheel are the factors that affect the blockage of the grinding wheel during the grinding process; establish optimized and reasonable grinding parameters and summarize the rules.
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