Development Of Test Rig And Experimental Study On Performance Of Ceramic Ball Bearing In High-speed Electric Spindle

Electric spindle is the core functional component of numerical control machine, and has many advantages shuch as compact structure, light weight, small inertia, small vibrationd and rapid response, etc. Bearing is the key component of achieving high speed and precision of electric spindle. The performance of bearing affects directly the revolving speed, rigidity, vibration and working temperature of electric spindle, and then impacts the machining accuracy and stability of machine tool. Ceramic ball bearing has some characteristics such as high revolving speed, low temperature rise, no conductivity, no permeability, and so on. Application of ceramic ball bearing in high-speed electric spindle could enhance significantly the revolving speed, stiffness and life of electric spindle.Based on the actual working conditions and operating characteristics of ceramic ball bearing in electric spindle, the test rig of high-speed electric spindle bearing has been developed in this dissertation. The test rig integrated of mechanical, electronic and computer is mainly composed of main body, drive system, loading system, measurement and control system, cooling system and lubrication system. Different shafting components can be changed according to the tpye of testing bearings. Applying control technology of frequency control of motor speed, mechanical-electrical integration technology as well as computer control technology, the lubrication conditions, heat-dissipating conditions of spindle bearing as well as the radial and axial cutting force applied bearing under high-speed machining can be simulated. The main parameters of revolving speed, load, temperature, vibration and other can be monitored, displayed, handled and stored in real time way. The test rig can monitor and control the operation of components, and has functions of automatic alarm and shutdown.The experimental study on performances of high-speed electric spindle bearing was carried out using the developed test rig of high-speed electric spindle bearing in this dissertation. The high-speed performances of grease-lubricated ceramic ball bearings, grease-lubricated steel ball bearings and oil-mist lubricated ceramic ball bearings were analyzed comparatively with different speed and load under circulating water cooling conditions. The failures of test bearing were also analyzed. The research results indicate that the working temperature of grease-lubricated ceramic ball bearing is slightly higher than that of grease-lubricated steel ball bearing and oil mist-lubricated ceramic ball bearing at lower speed. Meanwhile, the rate of temperature growth of grease-lubricated ceramic ball bearing is lower than that of grease-lubricated steel ball bearing. While the D_mN value is 1.8×10~6mm·r/min, grease-lubricated ceramic ball bearing can reach quickly thermal equilibrium state. The working temperature of grease-lubricated ceramic ball bearing is lower than that of grease-lubricated steel ball bearing and close to that of oil-mist lubricated ceramic ball bearing. And the vibration of grease-lubricated ceramic ball bearing is lower than that of oil-mist lubricated ceramic ball bearing. It is suggested that grease-lubricated ceramic ball bearing can be applied into high-speed electric spindle.Using the developed test rig of high-speed electric spindle bearing, the working characteristics of ceramic ball bearing in high-speed electric spindle in a particular condition can be evaluated. It would provide the experimental basis for the design improvement and the application of ceramic ball bearing.