The geometric precision, rigidity, thermal distortion, motion stability, and vibration tolerance of the grinding machine directly affect the precision of the workpiece machining.
1. Geometric accuracy of the grinding machine
Geometric accuracy refers to the precision of movement and the relative positions of each component without any external force. Although it is not possible to manufacture machine tools with perfect precision, there will always be an unavoidable error to some extent. This error will affect the machining accuracy of the workpiece to varying degrees.
These errors can include radial runout and axial drift of the spindle, straightness of the movement of the worktable and other moving parts, mutual position errors of working parts, and transmission errors, among others.
Large radial runout and axial drift errors of the grinding wheel spindle and headstock can not only impact the surface roughness of the workpiece after grinding, but also cause roundness and end-face runout, leading to uneven sparks during the grinding process.
When the worktable is not vertical, it moves in the vertical plane, affecting the straightness of the workpiece axis on internal and external cylindrical grinders and causing significant errors in the flatness of the workpiece when grinding a plane on a surface grinder.
If the centerlines of the wheel spindle axis on an external grinding machine and an internal grinding machine are not at the same height as the centerline of the workpiece headstock axis, the workpiece axis will form a hyperbola when grinding internal and external cones.
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 significant impact on the machining accuracy of thread grinding and gear grinding.
2. Rigidity of the grinding machine
Stiffness refers to the ability of a grinding machine to resist deformation of its components when subjected to external forces, such as grinding force. In other words, the lower the deformation of a component under a given grinding force, the higher its stiffness. Conversely, a large deformation of a component indicates a low level of stiffness.
These deformations alter the original geometric accuracy of the grinder and impact the size of the machining error of the workpiece. Therefore, a machine with high stiffness leads to higher precision in the workpiece.
3. Thermal deformation
The heat generated within the grinding machine is not evenly distributed, causing different levels of heat production among its components. This results in varying effects of external heat sources on different parts of the machine.
To prevent temperature changes from impacting the accuracy of the machine and workpiece, it is ideal to install precision grinding machines in a room with consistent temperature.
4. Crawling of moving parts on the grinding machine
When the moving parts of the grinding machine worktable, such as the grinding carriage, move in small increments or continuously at a low speed, they may experience uneven movement, known as “crawling.”
If this phenomenon occurs in the grinder, it results in uneven feed during grinding and impacts 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.