Investigation On Thermal Characteristics And Cooling Method For High-speed Motorized Spindle

High-speed motorized spindle directly determines the machining accuracy and performance of high-performance machine tool as a core component of high-speed machining technology.Due to the high integration of high-speed motorized spindle,its internal structure is very compact,which makes it difficult for bearings and motor to dissipate heat and then leads to large thermal deformation that ultimately reduces the machining accuracy of machine tool and life of high-speed motorized spindle.This paper firstly investigates the heat sources of high-speed motorized spindle and the effects of factors on thermal characteristics for grease-lubricated high-speed ball bearings are obtained through theoretical modeling and experiments.The electromagnetic power consumption of high-speed motors is measured by the experimental method through motorized spindle towing test rig.Furthermore,the distributive characteristics of temperature field for motorized spindle,on which effects of factors are obtained by finite element method.Finally,the centrifugal air cooling method of high-speed motorized spindle is proposed to optimize the thermal characteristics of motorized spindle.The main contents of this paper are as follows:Frictional heat generation and heat transfer characteristics of high-speed angular contact ball bearings.Firstly,the friction of highspeed angular contact ball bearing is modeled and analyzed theoretically and the effects of speed and preload on the sliding friction of bearing are obtained and verified experimentally.Then,the thermal characteristics of high-speed bearing are analyzed by thermal resistance network method.Also,the effects of speed and preload on the thermal characteristics of bearings are obtained and the relationship between heat generation and sliding friction is found by correlating with each other.Finally,the temperature of outer ring for high-speed ball bearing is measured by towing test rig for high-speed motorized spindle,and the effects of speed,preload,type and amount of grease on temperature rise of bearing are verified,which are shown that the minimum temperature rise is obtained when the bearing preload,grease type and filling ratio are respectively about 150 N,SKF LGLT,45%.Measurement of electromagnetic power consumption and heat transfer of high-speed motorized spindle.The electromagnetic power consumption and the forced water cooling inside the motorized spindle are analyzed.A method for measuring the electromagnetic power consumption of motorized spindle is proposed and it is implemented by the towing test rig for high-speed motorized spindle.Then,the main heat transfer boundary conditions of high-speed motorized spindle are analyzed and the temperature distribution of high-speed motorized spindle is calculated with finite element method.Next,the effects of bearing,high-speed motor and forced cooling medium on the temperature distribution of high-speed motorized spindle are analyzed.Finally,the effects of rotational speed,preload,cooling water flow and cooling water inlet temperature on the spindle temperature rise are obtained by using a high-speed spindle temperature test rig,which are shown that the minimum temperature rise is obtained when the cooling water flow rate is 3 L/min and the overall temperature of motorized spindle depends on the temperature of inlet cooling water.Centrifugal air cooling and heat transfer of spindle rotor.Due to the heat accumulation caused by limited heat dissipating ways in highspeed motorized spindle rotor,the structure of rotor's auxiliary impeller is designed and the principle of high-speed centrifugal air cooling is analyzed.The air flow in the auxiliary impeller is simulated by finite volume method and the distribution of flow field which includes velocity,pressure and heat transfer coefficient on the wall of central hole are obtained.Then,the effects of the spindle speed,the diameter of centrifugal holes,the number of radial centrifugal holes and the diameter of the rotor's central hole on the heat transfer coefficient of the central hole are studied.The optimization method of the heat transfer characteristics of the rotor's central hole is proposed.Finally,the temperature distribution difference of the high-speed motorized spindle with and without centrifugal air cooling is simulated and compared by finite element method,and also the cooling effect of high-speed centrifugal cooling air is verified by experiments,which is shown that the fall of rotor's maximum temperature rise is nearly 9 ?.The optimization method of temperature field for high-speed motorized spindle is proposed in this paper and it can effectively reduce the overall temperature of motorized spindle and make temperature distribution more uniform.Moreover,it can reduce the stress concentration caused by inconsistent thermal deformation of parts and elongation of spindle to improve the machining accuracy of machine tool and service life of motorized spindle.