Common defects in internal grinding are:
The surface roughness is too bad, the surface is burnt, there are spiral marks and the shape error of the inner hole.
The causes and elimination methods are briefly described as follows.
1. The surface roughness is too poor
The main reason that affects the surface roughness is the low circumferential speed of the grinding wheel. In the case of poor rigidity of the grinding wheel connected to the long shaft, the vibration of the grinding wheel increases, causing ripples on the surface. In addition, the easy clogging of the grinding wheel is also the reason for the poor surface roughness. For this reason, we should try to increase the circumferential speed of the grinding wheel, and use smaller axial and radial feeds. When selecting the grinding wheel, choose a grinding wheel with a coarser grain size, looser structure and softer hardness, so that it has better self-sharpening. sex.
2. Surface burn of the workpiece
Due to the long contact arc during internal grinding, the heat generation is large and the heat dissipation conditions are poor, causing burns on the high-temperature surface of the grinding area. For this reason, the feed rate should be appropriately reduced, and sufficient coolant should be provided as much as possible. The dullness and blockage of the grinding wheel will increase the friction between the workpiece and the grinding wheel, and will also increase the surface temperature. For this reason, the grinding wheel with better self-sharpening properties should be selected and the grinding wheel should be trimmed in time.
3. The inner hole of the workpiece is not cylindrical
The non-cylindricity error produced in internal grinding is mainly the bell mouth. The main reason is the poor rigidity of the grinding wheel connected to the long shaft, which produces elastic deformation under the action of the radial grinding force. The way to improve the error of the bell mouth is to increase the diameter of the grinding wheel and shorten its length as much as possible, reduce the grinding depth and increase the number of smooth grinding. In addition, adjusting the overtravel amount of the grinding wheel and appropriately controlling the reversing residence time of the grinding wheel can also eliminate the error of the bell mouth.
4. Out-of-roundness in the inner circle of the workpiece
The common out-of-roundness when grinding holes is mainly ellipse and polygon. The reason for the ovality is that the radial runout of the spindle of the headstock is too large. The workpiece is not firmly clamped or the chuck is loose. The reason for the polygon is that the wear of the spindle bearing of the headstock is too large and the spindle is loosened. In addition, the wear of the spindle bearing of the grinding head can also cause the polygon.
The way to eliminate the out-of-roundness is to repair the machine tool, adjust the bearing clearance, and tighten the chuck and the workpiece.