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What are the requirements for the structure of the lathe spindle?

by:JNSN     2021-10-28

 The machine tool spindle refers to the axis that drives the workpiece or tool to rotate on the machine tool. The main shaft is usually composed of main shaft, bearings and transmission parts (gears or pulleys). In the machine, it is mainly used to support transmission parts such as gears and pulleys to transmit motion and torque, such as machine tool spindles; some are used to clamp workpieces, such as spindles.

Lathe spindle

  The index to measure the performance of the spindle component

   The main index to measure the performance of the spindle component is the rotation accuracy , Stiffness and speed adaptability. ① Rotation accuracy: The radial and axial runout in the direction that affects the machining accuracy when the spindle rotates is mainly determined by the manufacturing and assembly quality of the spindle and the bearing. ② Dynamic and static stiffness: mainly determined by the bending stiffness of the main shaft, the stiffness and damping of the bearing. ③Speed u200bu200badaptability: The maximum allowable speed and speed range are mainly determined by the structure and lubrication of the bearing, as well as the heat dissipation conditions.

   Spindle structure of lathe

   With the rapid development of CNC technology, 'composite, high-speed, intelligent, precise and environmentally friendly' It has become the main trend in the technological 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 machining cycle of the workpiece. This requires the machine tool spindle and its related parts to adapt to the needs of high-speed machining. The spindle bearings of CNC machine tools are basically limited to four structural types: angular contact ball bearings, cylindrical roller bearings, bidirectional thrust angular contact ball bearings and tapered roller bearings.

   With the high-speed development of CNC machine tool spindles, ceramic materials (mainly si3n4 engineering ceramics) have low density, high elastic modulus, low thermal expansion coefficient, and wear resistance. , High temperature resistance, corrosion resistance and other excellent properties, thus becoming an ideal material for manufacturing high-speed precision bearings. Ceramic bearings are more and more widely used. In view of the difficult processing of ceramic materials, precision ceramic bearings are mostly hybrid ceramic ball bearings whose rolling elements are ceramic and the inner and outer rings are still made of chromium steel.

  As a precise, efficient and sensitive transmission element, the ball screw pair should be used in addition to high-precision screws, nuts and balls, but also should be selected with high axial rigidity , Bearings with small friction torque and high running precision. In the past, ball screw supports commonly used bidirectional thrust angular contact ball bearings, tapered roller bearings, needle roller and thrust roller combined bearings, deep groove ball bearings and thrust ball bearings. The ball screw support is mostly single-row thrust angular contact ball bearings with a contact angle of 60°, and the accuracy level is mainly p4 and above.

  The rolling bearings installed on general drive shafts for machine tools have the same requirements and selection as ordinary mechanical transmission bearings, only need to meet the requirements of strength and life, and the speed does not exceed the specified The bearing limit speed is sufficient.

 Under normal circumstances, the machine tool bearings we mentioned refer to machine tool spindle bearings and ball screw bearings, while precision machine tool bearings refer to spindle bearings and lead screws with an accuracy of p5 and above. Bearing.

  Rolling bearing requirements

 1. Speed u200bu200band temperature rise: With the development of science and technology, the spindle speed of machine tools is getting more and more High, the transmission range is getting wider and wider, therefore, the requirements for the high-speed running stability of the bearing are also getting higher and higher. The temperature rise of the machine tool spindle bearing is an important factor that limits the bearing speed. Under normal circumstances, the correct selection of bearing type, tolerance level, configuration method, clearance (preload) size, lubricant and lubrication method, etc., can improve the high-speed performance of rolling bearings to a certain extent.

  2. Life and load-carrying capacity: For general machine tools, the life of the spindle assembly mainly refers to the period of use to maintain the accuracy of the spindle. Therefore, the accuracy of the bearing is required to maintain performance Meet the requirements of the life of the spindle assembly. For heavy-duty machine tools or powerful cutting machine tools, the bearing capacity should be considered first.

  3. Rigidity and vibration resistance: In order to ensure the machining quality of the machine tool, the spindle system must be sufficiently rigid, otherwise it will cause a larger replay error or even chatter. . Vibration resistance refers to the ability to resist forced vibration and self-excited vibration. The vibration resistance of the main shaft assembly depends on the rigidity and damping of the main shaft and bearings. The use of preloaded rolling bearings can effectively improve the rigidity of the spindle system.

  4. Noise: In high-speed grinding machines, the noise of grinding head bearings is the main component of the noise of the whole machine, and low-noise rolling bearings should be selected.

   Spindle box design

   The box shape adopts a right-angle connection between the sides to make the box line simple. Lively.

   The spindle box uses the bottom surface of the box body and two guide blocks as the positioning and mounting surface, and is fixed with screws and pressure plates. Simple installation and reliable positioning.

   Lathe spindle maintenance

   To reduce the working temperature of the bearing, lubricating oil is often used. There are two types of lubrication: oil-air lubrication and oil circulation lubrication. Pay attention to the following points when using these two methods: 1. When using oil circulation lubrication, ensure that the oil volume of the spindle constant temperature oil tank is sufficient. 2. The oil-air lubrication method is just the opposite of the oil circulation lubrication, it only needs to fill up to 100% of the bearing space capacity.

The advantage of    cyclic lubrication is that when lubrication is satisfied, friction and heat generation can be reduced, and part of the heat of the spindle assembly can be absorbed.

   There are also two release methods for the lubrication of the spindle: oil mist lubrication and injection lubrication.

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