The geometric accuracy, stiffness, thermal deformation, motion stability, and vibration resistance of the grinding machine will have a direct impact on the machining accuracy of the workpiece.
1. Geometric accuracy of the grinding machine
It refers to the precision of movement and the mutual position of each component without load.
It is impossible to manufacture machine tools with absolute precision, and there is always an unavoidable error in a different extent.
This error will be reflected in the workpiece processing to varying extents to the workpiece, while affecting the machining accuracy of the workpiece.
In general, these errors include radial runout and axial drifting of the spindle, straightness of the movement of the worktable and other moving parts, mutual position errors of the working parts and transmission errors etc.
If the motion error of radial runout and axial drifting of the grinding wheel spindle and the grinding machine headstock is large, it not only can affect the surface roughness of the workpiece after grinding, but also make the workpiece produce roundness and end-face run out, resulting in uneven sparks during the grinding process.
The table moves in the vertical plane when it is not vertical, which affects the straightness of the workpiece bus on the internal and external cylindrical grinder and causes large errors in the flatness of the workpiece when grinding the plane on the surface grinder.
When the centerlines of the wheel spindle axis of the external grinding machine and the internal grinding machine are not equal in height to the centerline of the workpiece headstock axis, the workpiece bus is a hyperbola when grinding the internal and external cone.
If the centerline of the grinding wheel spindle axis is not parallel to the direction of table movement, it will affect the straightness of the workpiece end face after grinding.
The transmission error of the grinding machine has a great influence on the machining accuracy of thread grinding and gear grinding.
2. Rigidity of the grinding machine
It refers to the ability of a grinding machine to resist the deformation of its components when subjected to external forces (grinding force).
In other words, the smaller the deformation of the part, the greater the rigidity of the part, when given the same grinding force.
By contrast, large deformation of a part indicates less rigidity of the part.
The size of these deformations destroys the static original geometric accuracy of the grinder, which changes the size of the machining error of the workpiece.
This is the reason why a good rigidity of the machine, the high precision of the workpiece.
3. Thermal deformation
The heat source inside the grinding machine is not evenly distributed, and the amount of heat generated during movement varies from part to part, resulting in different effects of the external heat source on each part of the machine.
Therefore, precision grinding machines are best installed in a constant temperature room to prevent temperature changes from affecting the accuracy of the machine and the workpiece.
4. Crawling of moving parts on the grinding machine
When the moving parts such as the grinding carriage etc. of the grinding machine worktable are fed in a microcycle or continuously move at a low speed, the phenomenon of uneven movement occurs, which is generally called crawling.
When this phenomenon occurs in the grinder, the feed during grinding is uneven, which affects the surface roughness of the workpiece.
5. Vibration of the grinding machine
The grinding machine generates vibration during the grinding process, which causes periodic changes in the relative positions of the grinding carriage and the workpiece, resulting in vibration patterns on the workpiece surface and seriously affecting machining quality and precision.
In order to improve the precision of the workpiece after grinding, in addition to eliminating the influence of the above factors, it is necessary to pay attention to the reasonable selection of the positioning reference, the clamping method, the selection and correct repair of the grinding carriage, and the reasonable selection of the amount of grinding and the technological method during the workpiece processing.