In CNC turning and milling products, the spindle bearing configuration directly determines the equipment's machining accuracy, maximum speed, and rigidity. Balancing high-speed operation with rigidity requirements is a core challenge in spindle design. A reasonable bearing configuration and optimization strategy ensure that the equipment achieves both efficiency and precision in complex machining scenarios.
The spindle bearing configuration should be tailored to the machining requirements. Common bearing types used in CNC turning and milling equipment include angular contact ball bearings, cylindrical roller bearings, and tapered roller bearings. In high-speed applications, angular contact ball bearings are the mainstream due to their lightweight rolling elements and high maximum speed. They are often configured in a back-to-back or tandem configuration. A back-to-back configuration (with the narrow sides of the outer rings facing each other) can withstand bidirectional axial forces and offers enhanced rigidity, making it suitable for high-speed milling. A tandem configuration (with the wide sides of the outer rings facing each other) focuses on unidirectional axial force resistance and is often used for high-speed turning. In scenarios requiring heavy loads and rigidity, a combination of cylindrical roller bearings and angular contact ball bearings is more common. The cylindrical roller bearings carry radial forces and provide high rigidity, while the angular contact ball bearings handle axial forces, creating a dual "radial and axial" support system.
Balancing high-speed operation and rigidity requires optimization from multiple dimensions. Preload control is a key measure: bearing clearance can be adjusted through spring preload, hydraulic preload, or nut preload. Excessive interference fit increases frictional heat, limiting high-speed performance; insufficient interference fit reduces rigidity and can easily cause vibration. CNC turning and milling products typically utilize a "graded preload" design: increasing preload at low speeds and heavy loads to improve rigidity, while reducing preload at high speeds and light loads to reduce power consumption. Some high-end equipment is equipped with automatic preload adjustment systems that can adapt to machining conditions in real time.
Lubrication and cooling technologies significantly impact the high-speed rigidity balance. High-speed operation causes bearing temperature rise, leading to thermal deformation and loss of rigidity and stability. Therefore, targeted lubrication methods are required. Spindle speeds below 15,000 rpm are typically greased, using low-viscosity, high-temperature grease to reduce friction. Spindle speeds exceeding 20,000 rpm utilize oil mist lubrication. Compressed air carries the oil mist, continuously cooling the bearing and forming an air film to reduce frictional losses. Some equipment also incorporates a water-cooling jacket around the bearing outer ring to control temperature through circulating coolant, preventing rigidity loss due to thermal expansion.
Innovation in bearing materials and structures is crucial for achieving balanced performance. Traditional steel bearings are prone to deformation at high speeds due to excessive centrifugal forces. High-end CNC turning and milling products utilize ceramic hybrid bearings (steel inner ring + ceramic rolling elements). Ceramic material has a density only 40% that of steel, reducing centrifugal forces. Its high-temperature resistance allows for higher speeds. Furthermore, ceramic has a higher elastic modulus than steel, improving bearing rigidity. Structurally, the "integrated bearing seat" design reduces clearance between connections. Finite element analysis optimizes the bearing arrangement angle for more even load distribution, maintaining stable rigidity at high speeds.
In practical applications, dynamic adaptation is required based on the processing type. For high-speed milling of aerospace light alloys, the preferred configuration is "tandem angular contact ball bearings + oil mist lubrication," enabling efficient machining at speeds of up to 30,000 rpm. For heavy-duty turning of mold steel, a "back-to-back" configuration of cylindrical roller bearings + angular contact ball bearings is employed. High preload improves radial rigidity, ensuring vibration-free cutting even with forces up to 5,000 N. Some intelligent machine models monitor the spindle load and speed in real time through the CNC system, automatically adjusting preload and lubrication parameters to achieve a dynamic balance between high speed and rigidity.
In short, through scientific bearing selection, preload control, lubrication optimization, and material innovation, the CNC turning and milling series products successfully address the conflict between high-speed operation and rigidity requirements, providing precisely adapted spindle solutions for diverse processing scenarios.
