Determine grinding wheel life:
Generally, it is carried out through observation and testing according to various phenomena caused by wear of grinding wheel working face. The grinding phenomena caused by grinding wheel wear mainly include: self-excited vibration in grinding process and regenerative vibration pattern on workpiece surface; The increase of grinding noise; Grinding burns appear on the surface of the workpiece; The grinding force increases or decreases sharply; The grinding accuracy decreases; The grinding surface roughness increases.
The wear and dressing of grinding wheel, that is, the influence of the effective contour of grinding wheel circumference on machining, is a systematic error. Especially in precision grinding, it is necessary to dress the grinding wheel carefully and set up a special dressing program to maintain the accuracy of the grinding wheel contour for a long time.
Causes of grinding wheel wear:
First, wear and tear
When the abrasive wear is serious, the grinding wheel surface is flat after the obvious wear plane appears on the top surface of the abrasive. At this time, the total wear area of the cutting edge increases and the friction intensifies, making it difficult for the cutting edge to cut into the surface of the workpiece. However, the hardness of the grinding wheel is high, which makes the abrasive particles unable to break off in time. If it continues to be used, the grinding force and grinding heat will increase obviously, and obvious vibration and noise will appear, which can not effectively remove materials. At this time, the grinding wheel must be trimmed. This kind of wear generally occurs when the hardness of abrasive particles is low, the hardness of grinding wheel is high, the particle size of abrasive particles is too fine and the tensile strength of workpiece material is high. This is the most common reason for the end of grinding wheel life when processing ordinary steel under ordinary grinding conditions.
Oxidative wear
Common abrasives are oxides, carbides and nitrides. Oxide abrasives are stable in air, and the surfaces of other abrasives will be oxidized at high temperature and will be gradually consumed.
C, diffusion wear.
It refers to the wear caused by the mutual diffusion of elements of diamond grinding wheel when abrasive particles contact with the ground material at high temperature, which leads to the weakening of the surface layer of abrasive particles. The mutual diffusion of elements between the two materials is closely related to the chemical composition of the materials. Because the diffusion and dissolution ability of carbon in iron in diamond abrasive is greater than that in boron nitride abrasive, diamond grinding wheel is not suitable for grinding steel.
D, thermal stress damage.
In the process of grinding, the working surface of abrasive particles instantly rises to high temperature, and the grinding wheel cools rapidly under the action of grinding fluid, and the frequency of its cold and hot cycle is the same as the rotating speed of the grinding wheel, thus forming great alternating thermal stress on the surface of abrasive particles, which makes the surface of abrasive particles crack and fracture. Thermal stress damage mainly depends on the thermal conductivity, linear expansion coefficient of abrasive and the performance of 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 grinding fluid, and the greater the thermal stress, the easier it is for abrasive particles to crack and fracture due to thermal shock. The order of thermal conductivity of various abrasives is diamond, cubic boron nitride, silicon carbide and corundum.
E. plastic wear.
Under the action of high grinding temperature, abrasive particles will be worn due to plastic deformation. Plastic wear mainly depends on the thermal hardness of the workpiece material. When grinding, if the chip hardness of the grinding wheel on the rake face of abrasive particles is greater than that in the contact area of abrasive particles, plastic wear of abrasive particles will occur.
The above reasons cause grinding wheel wear. According to different abrasives, workpiece materials and grinding conditions, the main causes of grinding wheel wear will be different. Therefore, the reasonable selection of grinding wheel and the dressing accuracy of grinding wheel will greatly affect the contour accuracy of workpiece. Therefore, the grinding wheel should be dressed in time when grinding. In addition, the grinding wheel needs to be dressed after the initial installation, and the essence of grinding wheel dressing is to reshape and sharpen the grinding wheel. Shaping is to micro-cut the grinding wheel to make it meet the required geometric requirements, sharpen its tip finely and form a sharp grinding edge. Dressing is to remove the bonding agent between abrasive particles, so that there is a certain chip space between abrasive particles, and the grinding edge protrudes from the bonding agent to form a cutting edge. Dressing methods are different according to different abrasives and binders of grinding wheels.