Position error refers to the change or deviation degree of the relative position of the actual surface, axis or symmetry plane of the part after CNC machining, relative to its ideal position, such as perpendicularity, position, symmetry, etc.
The position error in CNC machine tool machining usually refers to the dead zone error. The reason for the position error is mainly that in the CNC machining of machine tool parts, the machining error occurs caused by the gap and elastic deformation during transmission. Besides, it is caused because the tool head of the machine tool needs to overcome factors such as friction during processing.
In the open-loop system, the position precision will be greatly affected, while in the closed-loop follow-up system, it mainly depends on the displacement detection.
In CNC machine tool machining, due to the influence of external factors such as external forces and heat generated in CNC machining by tools and fixtures, the geometric precision of the machine tool is affected, and the parts processed on the machine tool are geometrically deformed, resulting in geometric errors.
According to research, the main reasons for the geometric errors of CNC machine tools are nothing more than the following two: internal factors and external factors.
The internal factors of the machine tool's geometric errors refer to the geometric errors caused by the machine's own factors, such as the levelness of the machine table, the levelness and straightness of the machine tool rails, and the geometric precision of the machine tools and fixtures.
External factors mainly refer to geometric errors generated under the influence of factors such as external environment and thermal deformation during CNC machining and manufacturing. For example, during the cutting process of tools or parts, due to thermal expansion and deformation, geometric errors are generated and thus affect the precision of CNC machine tool machining and the precision of CNC machining of parts.
Through long-term data analysis and practical operation of CNC machining of parts and components, it can be seen that machine tool positioning has a greater impact on the precision of CNC machine tool machining.
From the structural point of view, the machining errors of CNC machine tools are mostly caused by positioning precision. Among them, the feed system of the machine tool is the main link that affects the positioning precision.
The feed system of a CNC machine tool usually consists of two parts: a mechanical transmission system and an electrical control system. The positioning precision is related to the mechanical transmission system in the structural design.
In a closed-loop system, CNC machine tools can usually prevent the main components in the feed system from generating position deviations, such as ball screws and other components, through positioning monitoring devices. As for the open-loop system, due to many influencing factors and complicated conditions, positioning monitoring cannot be performed, so it has a greater impact on the CNC machining precision of the CNC machine tool.