The development trend of electric spindle
2020-8-9
The development trend of electric spindle technology is mainly reflected in the following aspects:
one. High speed, high stiffness
Due to the needs of high-speed cutting and practical applications, with the development of related technologies such as spindle bearings and their lubrication technology, precision machining technology, precision dynamic balancing technology, high-speed tools and their interface technology, high-speed spindles for CNC machine tools have become the current development. For example, the motorized spindle for drilling and milling, the speed of HF42 of Swiss IBAG reaches 140000r/min, and the motorized spindle D1733 of PCB drilling of British WestWind company reaches 250000r/min; the motorized spindle of machining center is the highest in Switzerland FISCHER The speed reaches 42000r/min, and the Italian CAMFIOR reaches 75000r/min. In terms of the system rigidity of the electric spindle, due to the development of bearings and their lubrication technology, the system rigidity of the electric spindle is getting larger and larger, which meets the needs of the development of high-speed, high-efficiency and precision machining of CNC machine tools.
2. High speed and high power. High torque at low speed
According to the needs of actual use, most CNC machine tools need to be able to meet the requirements of heavy cutting during low-speed roughing and finishing during high-speed cutting. Therefore, the machine tool electric spindle should have the performance of low speed, high torque, and high speed and high power. For example, the electric spindles for machining centers produced by Italian CAMFIOR, Swiss Step-Tec, German GMN and other manufacturers, it is not difficult to output torque above 200Nm in the low-speed section, and the maximum torque of the German CYTEC CNC milling machine and lathe electric spindle is even more. It reaches 630N m; in terms of high power in the high-speed section, it is generally 10-50kW; the maximum output power of the CYTEC motorized spindle is 50kW; the maximum power of the Swiss Step-Tec motorized spindle reaches 65kW (S1), which is used in aircraft manufacturing. And mold processing; there are reports that the power of the electric spindle reaches 80kW.
3. Further development towards high precision, high reliability and extended working life
Users have put forward higher and higher requirements for the accuracy and reliability of CNC machine tools. As one of the core functional components of CNC machine tools, the electric spindle requires its own accuracy and reliability to be higher and higher. For example, the radial runout of the main shaft is within 0.001mm, and the axial positioning accuracy is less than 0.0005mm. At the same time, due to the use of special precision spindle bearings, advanced lubrication methods and special preload application methods, the life of the electric spindle has been extended accordingly, and its reliability has become higher and higher. Step-Tec's electric spindle is also equipped with an acceleration sensor to reduce the vibration acceleration level of the bearing. In order to monitor and limit the vibration on the bearing, a vibration monitoring module is installed to prolong the working life of the electric spindle.
4. The performance and form of the built-in motor of the electric spindle are diversified
In order to meet the needs of practical applications, the performance of the electric spindle motor has been improved. For example, the ratio of the constant torque and high speed output by the Swiss FISCHER spindle motor to the constant power and high speed (that is, the constant power speed regulation range) has reached 1:14. In addition, permanent magnet synchronous motor electric spindles have appeared. Compared with asynchronous motor electric spindles of the same power, the external dimensions of synchronous motor electric spindles are small, which is conducive to improving power density and realizing small size and high power.
5. Development towards quick start and stop
In order to shorten the auxiliary time and improve the efficiency, the start and stop time of the electric spindle of the CNC machine tool is required to be as short as possible, so a high start and stop acceleration (deceleration) speed is required. At present, the start and stop acceleration of the electric spindle of foreign machine tools can reach more than lg, and the start and stop time at full speed is within 1s.
6. Bearings and their preload application methods and lubrication methods are diversified
In addition to conventional steel rolling bearings, ceramic ball hybrid bearings have become more and more widely used in recent years. The lubrication methods include grease, oil mist, oil and gas, etc., especially the oil-air lubrication method (also known as oil-air). , The characteristics of environmental protection and energy saving have been widely promoted and applied; in addition to rigid preload (also known as positioning preload) and elastic preload (also known as constant pressure preload), the preload application method of rolling bearings has also developed An intelligent preload method is developed, that is, the hydraulic cylinder is used to apply preload to the bearing, and the size of the preload can be controlled according to the specific working conditions such as the spindle speed and load, so that the bearing support performance is better. In terms of electric spindles supported by non-contact bearings, such as magnetic bearing, air bearing electric spindle (Swiss IBAG, etc.), liquid bearing electric spindle (Ingersoll in the United States, etc.), a series of products have been supplied to the market.
Seven, tool interface gradually tends to HSK, Capto tool handle technology
After the high speed of the machine tool spindle, due to the centrifugal force, the traditional CAT (7:24) tool holder structure can no longer meet the requirements of use. It is necessary to use HSK (1:10) and other tool holder interface forms that meet the high speed requirements. HSK tool holder has outstanding static and dynamic connection rigidity, large transmission torque capacity, high tool repeatability positioning accuracy and connection reliability, and is especially suitable for high-speed and high-precision use. Therefore, the HSK tool holder interface has been widely used for high-speed motorized spindles (such as IBAG in Switzerland, CYTEC in Germany, CAMFIOR in Italy, etc.). In recent years, the Capto tool interface proposed by SANDVIK company has also begun to be applied in the machine tool industry. Its basic principle is similar to that of the HSK interface, but the ability to transmit torque is slightly larger. The disadvantage is that the machining of the inner hole of the spindle end is difficult and the process is more complicated .
Eight, multi-function, intelligent
In terms of multi-function, there are angular stop precise positioning (exact stop), C-axis transmission, hollow air blowing for tool change, hollow coolant, shaft end gas seal, low-speed torque amplification, precise compensation of axial positioning, automatic tool change Dynamic balancing technology, etc. In terms of intelligence, it is mainly reflected in various safety protection and fault monitoring and diagnosis measures, such as tool change interlock protection, bearing temperature monitoring, motor overload and overheat protection, bearing unloading protection when the tool is released, spindle vibration signal monitoring and fault abnormality Diagnosis, automatic compensation of axial position change, signal monitoring and automatic control of grinding wheel dressing process, tool wear and damage signal monitoring, etc. For example, Step-Tec motorized spindle is equipped with a diagnostic module, and maintenance personnel can read data through infrared interface to identify overload, Statistics of the working life of the electric spindle.
