In the grinding process, internal grinding is also a very common process. Internal grinding can process through holes, through holes, step holes, etc. on machine parts, so it is widely used in mechanical processing. The dimensional accuracy of machining can generally reach the tolerance grade IT6-IT7. If high-precision grinding process is adopted, the dimensional accuracy can be controlled within 0.005mm. So, what are the methods of internal grinding?
1、 Form of internal grinding
Internal grinding can be divided into the following three forms:
1. Center type internal grinding
During grinding, the workpiece rotates around the center line of the spindle of the main axle box. The common internal grinder or the universal external grinder belong to this type, which is suitable for grinding the internal holes of sleeves, gears, flanges and other parts.
2. Planetary internal grinding
When grinding, the workpiece is fixed and does not rotate. In addition to high-speed rotation around its own axis, the grinding wheel also rotates around the center of the grinding hole at a lower speed to achieve circular feed; In addition, the grinding wheel also makes longitudinal feed motion and periodic cross feed. The cross feed of grinding wheel is realized by increasing the turning radius of planetary motion. Planetary internal grinder is mainly used for grinding parts with large volume and inconvenient rotation.
3. Centerless internal grinding
On the centerless internal grinder, the workpiece is supported on the support wheel and the pressing wheel by its finished excircle, and is driven by the guide wheel to rotate. This grinding method is suitable for grinding the inner hole of thin-walled annular parts.
2、 Characteristics of Internal Grinding
Compared with cylindrical grinding, internal grinding has the following characteristics:
1. In internal grinding, the diameter of the grinding wheel used is small, and the rotation speed of the grinding wheel is limited by the rotation speed of the internal grinder, so the grinding speed is generally 20-30m/s. Because of the low grinding speed, the roughness of the workpiece surface is not easy to reduce.
2. During internal grinding, the contact arc between the grinding wheel and the workpiece is larger than that of the external grinding because the grinding wheel is in tangential contact with the workpiece. Therefore, the grinding heat and force are relatively large, the abrasive grains are easy to blunt, and the workpiece is easy to heat or burn.
3. During internal grinding, the cutting fluid is not easy to enter the grinding area; The wear debris is not easy to discharge. When the wear debris accumulates in the inner hole of the workpiece, it is easy to cause the blockage of the grinding wheel and affect the surface quality of the workpiece. Especially when grinding brittle materials such as cast iron, grinding chips and cutting. When liquid is mixed into paste, the grinding wheel is more likely to be blocked, which affects the grinding performance of the grinding wheel.
4. The rigidity of the extension shaft of the grinding wheel is relatively poor, and it is easy to produce bending deformation and vibration, which has a great impact on the machining accuracy and surface roughness, and also limits the improvement of grinding parameters.
3、 Method of internal grinding
The position of the grinding wheel must be adjusted before grinding. When grinding the inner hole on the universal cylindrical grinder, the grinding wheel contacts the front wall of the hole. At this time, the cross feed direction of the grinding wheel is the same as that when grinding the excircle. On the internal grinder, the grinding wheel contacts the back wall of the hole, which is convenient for the operator to observe the working surface with longitudinal grinding method.
Longitudinal method and cut in method are commonly used in internal grinding.
1. Longitudinal grinding method
This grinding method is the same as the cylindrical longitudinal grinding method. When grinding through holes, first select the diameter of the grinding wheel and the extension shaft according to the diameter and length of the workpiece. The rigidity of the extension shaft is better, and the length of the extension shaft only needs to be slightly greater than the length of the hole.
2. Cut in grinding
This grinding method is the same as the cylindrical cut in grinding method. It is suitable for grinding workpieces with shorter inner holes and has higher production efficiency.
When the cutting in method is used for grinding, the rigidity of the extension shaft is better, and the grinding wheel is easy to be blocked and blunt in continuous feeding, so the grinding wheel should be trimmed in time. Low cutting speed shall be adopted for fine grinding.