One is the design of the machine tool. This is the soul of machine precision. Japanese machine tools look nothing special, but they are highly accurate and durable. High-precision machine tools have a good grasp of design details.
The second is machine tool castings. The casting of a machine tool is the bone, which is the key to bear the cutting torque and disperse the vibration force, and is the foundation of the stability of the whole machine. High-precision machine tools, without good castings, even the best spindle screw guides, the accuracy of the whole machine will disappear after one year.
The third is that the system determines the key accuracy of the machine tool. The conventional imported systems include FANUC, Mitsubishi, Siemens, Heidenhain, Rexroth, domestically produced Guangshu and Huazhong CNC, and most of the machines have FANUC. FANUC systems are widely used in gantry, horizontal machining, vertical machining, lathes, sheet metal machine tools, and even robots.
The accuracy of a machine tool refers to the accuracy of the shape, mutual position and relative movement of the main parts of the machine tool, including geometric accuracy, transmission accuracy, movement accuracy, positioning accuracy and accuracy retention. All kinds of machine tools can be divided into ordinary precision level, precision level and high precision level according to their accuracy. The machine tools of the above three accuracy levels have corresponding accuracy standards. If the tolerance is 1, the general ratio is 1: 0.4: 0.25. In the design stage, the accuracy of the machine tool is mainly improved from the aspects of precision distribution, components and material selection of the machine tool.
1) Geometric accuracy
Geometric accuracy refers to the accuracy of the shape, mutual position, and relative movement of the main components when the machine tool is unloaded and does not move (the machine spindle does not rotate or the worktable does not move, etc.) or when the motion speed is low. Such as the straightness of the guide rail, the radial runout and axial movement of the spindle, the parallelism or perpendicularity of the spindle center line to the moving direction of the sliding table, etc. Geometric accuracy directly affects the accuracy of processed workpieces, and is a basic indicator for evaluating the quality of machine tools. It is mainly determined by the structural design, manufacturing and assembly quality.
2) Motion accuracy
Motion accuracy refers to the accuracy when the main parts of the machine tool move at the speed of the working state. Such as the rotation accuracy of the high-speed rotary spindle. For high-speed precision machine tools, motion accuracy is an important index to evaluate the quality of machine tools. Motion accuracy and geometric accuracy are different. It is also affected by the movement speed (rotation speed), the gravity of the moving parts, the transmission force and the friction force. It is related to factors such as structural design and manufacturing.
(3) Transmission accuracy
Transmission accuracy refers to the coordination and accuracy of the relative motion between the end-effectors of the machine tool transmission system. The error in this aspect becomes the transmission error of the transmission chain. For example, when the lathe is turning the thread, the movement of the tool post should be equal to the lead of the dry thread for each revolution of the spindle. But in fact, due to the error in the transmission chain between the spindle and the tool post, the actual displacement of the tool post and the error are the transmission error of the threaded transmission chain of the lathe. The transmission accuracy is determined by the design of the transmission system, the error of the ideal shift distance, the manufacturing and assembly accuracy of the transmission parts, and so on.
