The main body of CNC machine tools has the following features: 1) Due to the use of high-performance continuously variable spindles and servo transmission systems, the limit transmission structure of CNC machine tools is greatly simplified, and the transmission chain is greatly shortened; 2) To adapt to continuous automatic processing And to increase processing productivity, the mechanical structure of CNC machine tools has high static and dynamic stiffness and damping accuracy, as well as high wear resistance, and small thermal distortion; 3) To reduce friction, eliminate transmission gaps and obtain higher processing Accuracy, more efficient transmission components are used, such as ball screws and rolling guides, anti-backlash gear transmission, etc.; 4) In order to improve working conditions, reduce auxiliary time, improve operability, and improve labor productivity, tool automatics are used. Clamping devices, tool magazines, automatic tool changers and automatic chip removal devices. According to the applicable occasions and institutional characteristics of CNC machine tools, the following requirements are imposed on the structure of CNC machine tools:
1, higher static and dynamic stiffness of the machine tool
CNC machine tools are automatically processed according to the instructions provided by numerically controlled programming or manually entered data. Due to the geometrical accuracy and deformation of the mechanical structure (such as machine tool bed, guide rails, table, tool holder, spindle box, etc.), the positioning error cannot be adjusted and compensated during the machining process. Therefore, the mechanical structural parts must be placed everywhere. The resulting elastic deformation is controlled to a minimum to ensure the required machining accuracy and surface quality. The
2, reduce the thermal deformation of the machine tool
Under the influence of internal and external heat sources, various parts of the machine tool will undergo thermal deformation of different degrees, causing the relative motion relationship between the workpiece and the tool to be broken, and the machine tool also declines quarterly. For CNC machine tools, the effect of thermal deformation is even more severe because all the machining processes are controlled by calculation instructions. In order to reduce thermal distortion, the following measures are usually used in the structure of CNC machine tools. (1) Reduce heat generation; (2) Control temperature rise; (3) Improve machine tool organization.
3, reduce the friction between sports and eliminate drive gap
If the displacement of the CNC machine tool table (or carriage) is equal to the minimum unit in the 11-pulse, it is usually required to move at the speed of the base. In order to enable the workbench to respond accurately to the instructions of the numerical control device, corresponding measures must be taken. At present, there are obvious differences in the frictional damping characteristics between the commonly used slide rails, rolling rails, and static pressure rails. The same effect can be obtained by replacing the sliding screw with a ball screw in the feed system. At present, CNC machine tools almost exclusively use ball screw drives. The machining accuracy of CNC machine tools (especially open-loop CNC machines) depends to a large extent on the accuracy of the feed chain. In addition to reducing the machining error of the transmission gear and ball screw, another important measure is the use of a gearless transmission pair. For the cumulative error of ball screw pitch, pulse compensation device is usually used for pitch compensation. The
4, improve the life of the machine tool and precision retention
In order to improve the life of the machine tool and maintain the accuracy, the wear resistance of the CNC airport parts should be fully considered in the design, especially the wear resistance of the main parts that affect the progress, such as the machine tool guide rail and the feed servo spindle component. During use, it should be ensured that the components of the CNC machine tool are well lubricated.
5, reduce the auxiliary time and improve operating performance
In the single-piece machining of CNC machine tools, the auxiliary time (non-chip time) occupies a large proportion. To further increase the productivity of the machine tool, it must be taken to maximise the compression of the auxiliary time. At present, many CNC machine tools have used multi-spindles, multi-turrets, and automatic tool changer with tool magazines to reduce tool change time. For CNC machine tools with increased chip usage, the bed mechanism must be conducive to chip removal.