CNC machine tool spindle refers to the axis on the machine tool that drives the workpiece or tool to rotate. The main shaft component is usually composed of the main shaft, mate bearing and a transmission member (gear or pulley). In the CNC machine is mainly used to support the transmission parts such as gears, pulleys, transmission of movement and torque, such as machine tool spindle; some used to clamp the workpiece, such as the spindle.
CNC machine tool spindle refers to the axis on the machine tool that drives the workpiece or tool to rotate. The main shaft component is usually composed of the main shaft, a bearing, and a transmission member (gear or pulley). In the machine is mainly used to support the transmission parts such as gears, pulleys, transmission of movement and torque, such as machine tool spindle; some used to clamp the workpiece, such as the spindle. In addition to machine tools such as planer and broaching machine whose main movement is linear movement, most machine tools have spindle components.
CNC machine spindle component movement accuracy and structural rigidity are important factors in determining the machining quality and cutting efficiency.
The indicators for measuring the performance of the main shaft components are mainly rotation accuracy, stiffness and speed adaptability.
- Rotational accuracy: Radial and axial runout (see form-position tolerances) in the direction of the spindle rotation affecting the machining accuracy is mainly determined by the manufacturing and assembly quality of the spindle and the bearing.
- Dynamic and static stiffness: Mainly determined by the bending stiffness of the spindle, the stiffness, and damping of the bearing.
- Speed adaptability: The maximum allowable speed and speed range are mainly determined by the structure and lubrication of the bearing and the heat dissipation conditions.
Four structures of CNC machine tool spindle
With the rapid development of numerical control technology, ‘compounding, high speed, intelligence, precision, and environmental protection‘ have become the main trends in the development of today’s machine tool industry. Among them, high-speed machining can effectively improve the machining efficiency of the machine tool and shorten the processing cycle of the workpiece. This requires the machine tool spindle and its related components to meet the needs of high-speed machining. CNC machine tool spindle bearings are basically limited to four types of angular contact ball bearings, cylindrical roller bearings, two-way thrust angular contact ball bearings and tapered roller bearings.
With the development of high-speed development of the main axis of CNC machine tools, ceramic materials (mainly referred to as si3n4 engineering ceramics) have become high speed due to their low density, high elastic modulus, low coefficient of thermal expansion, wear resistance, high-temperature resistance, and corrosion resistance. The ideal material for precision bearings. Ceramic bearings have become more and more widely used. In view of the difficult workability of ceramic materials, precision ceramic bearings are mostly hybrid ceramic ball bearings in which the rolling elements are ceramics and the inner and outer rings are still made of chrome steel.
As a precision, high-efficiency, and sensitive transmission element, the ball screw pair should not only adopt the high-precision screw, nut, and ball, but also pay attention to the use of bearings with high axial stiffness, small friction torque, and high running accuracy. Ball screw bearings used in the past commonly used two-way thrust angular contact ball bearings, tapered roller bearings, needle roller and thrust roller bearings, deep groove ball bearings and thrust ball bearings. The ball screw support uses a single row angular contact thrust ball bearing with a contact angle of 60°, and the accuracy grade is also based on p4 and above.
Rolling bearings mounted on the general drive shaft of the machine tool have the same requirements and choices as ordinary mechanical transmission bearings. They only need to meet the strength and life requirements, and the rotation speed does not exceed the specified bearing limit speed.
Under normal circumstances, the machine tool bearings we refer to are machine tool spindle bearings and ball screw bearings. Precision machine tool bearings are spindle bearings and screw bearings with an accuracy of p5 and above.
CNC Machine Tool Spindle Bearing Requirements
- Rotation speed and temperature rise: With the development of science and technology, the spindle speed of the machine tool is getting higher and higher, and the transmission range is getting larger and larger. Therefore, the requirements for high-speed operation stability of bearings are also increasing. The temperature rise of the spindle of the machine tool is an important factor limiting the rotational speed of the bearing. Under normal circumstances, the correct choice of bearing type, tolerance level, configuration, clearance (preload) size, lubricant and lubrication methods, can improve the high-speed performance of rolling bearings to a certain extent.
- Lifetime and load carrying capacity: For general machine tools, the life of the main shaft assembly mainly refers to the service life of the main shaft to maintain the accuracy of the main shaft. Therefore, the accuracy of the bearing needs to meet the requirements of the life of the main shaft assembly. For heavy machine tools or powerful cutting machines, the bearing’s load carrying capacity should be considered first.
- Stiffness and vibration resistance: In order to ensure the machining quality of the machine tool, it is necessary to make the spindle system have enough rigidity, otherwise it will produce a large recurrence error or even flutter. Vibration resistance refers to the ability to resist forced vibration and self-excited shock. The vibration resistance of the spindle assembly depends on the stiffness and damping of the spindle and the bearing. The use of preloaded rolling bearings can effectively increase the stiffness of the spindle system.
- Noise: In high-speed grinding machines, the noise of the grinding head bearing is the main component in the noise of the whole machine, so low-noise rolling bearings should be used.
CNC machine tool spindle maintenance
Reducing the operating temperature of the bearing, often used lubricants. Lubrication methods include oil-air lubrication and oil circulating lubrication. When using these two methods, pay attention to the following points:
- When using oil circulation lubrication, ensure that the oil volume of the spindle constant temperature fuel tank is sufficient.
- The oil-air lubrication method is just the opposite of the oil circulation lubrication. It only needs to fill the bearing’s space capacity by a percent.
The advantage of recirculating lubrication is that it can reduce friction and heat generation when lubrication is satisfied, and it can also absorb part of the heat from the main shaft assembly.
There are also two types of release for lubrication of the main shaft: oil mist lubrication and injection lubrication.
About HAISHU Machinery
Taian HAISHU Machinery Co., Ltd (Haishu Machinery) is the high-tech enterprise specialized in CNC machine development, production, sales and service since 2001. We have more than 16 series 80 kinds of CNC machines and related parts had been manufactured to satisfy your requirements. HAISHU Machinery is not only manufacturing best quality CNC machine products but also providing custom product design and after sale services. Welcome, contact us for detailed information.The company also has a lot of CNC equipment, such as CNC lathes, pipe threading lathes, turning and milling complex centers, etc
