In addition to meeting the main drive requirements of ordinary machine tools, the main drive system of CNC machine tools also proposes the following requirements:
(1) It has a larger speed regulation range and realizes stepless speed regulation. In order to ensure the cutting performance of the tool and to obtain higher productivity, machining accuracy and surface quality, CNC machine tools must have higher speed and larger speed range in order to ensure reasonable cutting amount during machining. For CNC machine tools with automatic tool change, the process is concentrated, and the workpiece can be clamped at one time, which can complete many processes. Therefore, in order to meet the requirements of various processes and various processing materials, the speed regulation range of the main drive should be further expanded.
(2) It has high precision and rigidity, stable transmission and low noise. The improvement of the machining accuracy of CNC machine tools is closely related to the stiffness of the main drive system. To this end, the manufacturing precision and rigidity of the transmission parts should be improved. The gear tooth surface is subjected to high-frequency induction heating and quenching to increase wear resistance. The last stage uses helical gear transmission to make the transmission stable, using high-precision bearings and reasonable support spans. To increase the rigidity of the spindle assembly.
(3) Good vibration resistance and thermal stability Generally, roughing and finishing are required on the machine. The machining may be due to intermittent cutting, uneven machining allowance, unbalanced moving parts and self-cutting during cutting. The impact force or alternating force caused by vibration or the like causes the main shaft to vibrate, which affects the machining accuracy and surface roughness. In severe cases, it even destroys the tool or the part, making the machining impossible. Therefore, the main components in the main transmission system must have a certain static stiffness, and it is required to have sufficient ability to suppress vibration caused by various interference forces - vibration resistance. Vibration resistance is measured by dynamic stiffness or dynamic compliance. For example, the dynamic stiffness of the spindle assembly depends on the equivalent static stiffness of the spindle, the damping ratio, and the natural frequency. In order to improve the vibration resistance of the spindle assembly, the value of the dynamic stiffness must be made large. Therefore, the values of the damping ratio, the equivalent static stiffness or the natural frequency should be made as high as possible. When designing the main drive system of a CNC machine, pay attention to the reasonable relationship between the above parameters.
The heat generated by the main drive system of the machine tool during the cutting process causes thermal deformation of all the components, which destroys the relative positional accuracy between the components and the machining error caused by the motion accuracy, and the thermal deformation limits the increase of the cutting amount and reduces the transmission efficiency. , affecting productivity. For this reason, the spindle component is required to have high thermal stability, and is achieved by maintaining a proper fitting clearance and performing cyclic lubrication to maintain thermal balance.
