In the grinding process, due to the wear of the cutting disc itself, the state of the working surface of the cutting disc is constantly changed. With the extension of the grinding time, the cutting ability of the cutting disc decreases, and various grinding defects continue to appear, making the grinding process unable to continue. At this time, the cutting disc must be trimmed to restore the normal grinding state. The actual grinding time of the cutting disc between two dressings is called the life of the cutting disc. The life of the cutting disc is an important factor that affects the grinding effect, especially for profile grinding.
Determine the life of the cutting wheel:
Generally, it is carried out through observation and testing based on various phenomena generated after the working surface of the cutting wheel is worn. The main grinding phenomena after the cutting wheel are worn are: self-excited vibration during the grinding process and regenerated vibration marks on the surface of the workpiece; Increase of grinding noise; grinding burn on the surface of the workpiece; sharp increase or decrease of grinding force; decrease of grinding precision; increase of grinding surface roughness.
The wear of the cutting disc and its dressing, that is, the influence of the effective contour of the cutting disc’s circumferential surface on the processing, is a systematic error, especially in precision grinding, the cutting disc should be finely trimmed, and a special dressing program should be set so that the cutting disc can be longer Maintain precise contours within time.
Reasons for cutting wheel wear:
A, wear and tear
When the abrasive grains are severely worn, the surface of the cutting wheel is flat after an obvious wear plane appears on the top surface of the abrasive grains. At this time, the total wear area of the cutting edge increases, the friction increases, and it is difficult for the cutting edge to cut into the surface of the workpiece. However, the hardness of the cutting wheel is too high, so that the abrasive particles cannot be broken and fall off in time. If you continue to use it, the grinding force and grinding heat will be significantly increased, and obvious vibration and noise will appear, and the material cannot be effectively removed. At this time, the cutting wheel must be trimmed. This kind of wear generally occurs when the hardness of the abrasive grains is low, the hardness of the cutting wheel is high, the grain size of the abrasive grains is too fine, and the tensile strength of the workpiece material is high. This is the most common reason for the end of the life of the cutting wheel when processing general steel under ordinary grinding conditions.
B, Oxidative wear
Common abrasives are oxides, carbides and nitrides. Oxide abrasives are stable in the air, and the surface of other abrasives will be oxidized at high temperatures, which is gradually consumed.
C, Diffusion wear.
It refers to the wear caused by the mutual diffusion of the elements of the diamond cutting wheel when the abrasive grains and the material to be ground are in contact with each other at high temperatures. The inter-diffusion of elements between the two materials is closely related to the chemical composition of the material. Because the carbon element in the diamond abrasive has a greater ability to diffuse and dissolve in iron than in the boron nitride abrasive, the diamond wheel is not suitable for grinding steel.
D, Thermal stress damage.
During the grinding process, the working surface of the abrasive particles rises to high temperature instantly, and the cutting wheel is rapidly cooled under the action of the grinding fluid. The frequency of the cold and heat cycle is the same as the rotation speed of the cutting wheel, thus forming a great alternation on the surface of the abrasive particles. Thermal stress cracks and breaks the surface of abrasive particles. Thermal stress damage mainly depends on the thermal conductivity of the abrasive, the coefficient of linear expansion and the performance of the grinding fluid. The smaller the thermal conductivity, the lower the linear expansion coefficient. The greater the linear expansion coefficient, the better the cooling performance of the grinding fluid, and the greater the thermal stress, the easier it is for the abrasive particles to be cracked and broken by thermal shock. The order of thermal conductivity of various abrasives is diamond, cubic boron nitride, silicon carbide, corundum.
E, Plastic wear.
Under the action of high temperature in grinding, abrasive grains will wear out due to plastic deformation. Plastic wear mainly depends on the thermal hardness of the workpiece material. During grinding, if the hot hardness of the cutting chips of the cutting disc on the rake surface of the abrasive particles is greater than the hot hardness of the abrasive particle contact area, the abrasive particles will undergo plastic wear.
The above several causes of cutting disc wear. According to the different abrasives, workpiece materials and grinding conditions, the main causes of cutting disc wear are also different. Therefore, the reasonable selection of the cutting disc and the dressing accuracy of the cutting disc will greatly affect the contour accuracy of the workpiece. Therefore, it is necessary to dress the cutting disc in time during grinding. In addition, the cutting disc needs to be dressed after the initial installation. The essence of cutting disc dressing is to shape and sharpen the cutting disc. Shaping is the micro-cutting of the cutting disc, so that the cutting disc meets the required geometric shape requirements, and the abrasive tip is finely broken to form a sharp sharp edge. Sharpening is to remove the bonding agent between the abrasive particles, so that there is a certain chip space between the abrasive particles, and make the abrasive edge protrude out of the bonding agent to form a cutting edge. According to the different abrasives and bonding agents of the cutting disc, the dressing is adopted The method is also different.