Study On Thermal Characteristics Of Multi-parameter Affected Of High-speed Motorized Spindle

With the continuous development of science and technology,high-speed machining technology has made breakthroughs,and the premise of developing and applying high-speed machining technology is to have a set of high-speed CNC machine tools with excellent performance.As an important part of CNC machine tool,the friction heating of bearing and the electromagnetic loss heating of built-in motor will cause the thermal deformation of spindle when it runs at high speed,which will affect the dynamic and static performance and processing accuracy of spindle system.Therefore,thermodynamics analysis of motorized spindle unit in detail is of great significance.In this thesis,the thermal characteristics of the motorized spindle are studied.Considering the effects of preload,contact thermal resistance and viscous-temperature effect,the distribution of temperature field and displacement field of the motorized spindle are analyzed.The main contents of this thesis include the following points:(1)A formula for calculating the internal thermal deformation of motorized spindle bearings is proposed.In this thesis,Considering the centrifugal expansion,thermal expansion of bearing parts,effective fit interference,and bearing structure,the calculation model of thermal deformation in bearing is established,which provides theoretical basis for subsequent analysis of bearing deformation.(2)A theoretical model of bearing heat generation considering preload and viscous-temperature effect is established.On the basis of heat transfer theory and considering the influence of preload and viscosity-temperature effect,the dynamic heat generation calculation model of bearing is built by adopting thermodynamics,tribology and Harris raceway contact theory,and the heat generation rate of bearing is obtained.The results show that with the increase of lubricant temperature,the lubricant viscosity decreases gradually,which leads to the decrease of friction moment and the decrease of bearing heat generation.With the increase of preload,the heat production of bearings increases continuously.(3)A thermal contact resistance model and a three-dimensional rough surface model are established.On the basis of heat transfer theory and fractal contact theory,combining the improved W-M function fractal contact model and considering three deformation forms of elastic,plastic and elastic-plastic deformation,the thermal contact resistance model and three-dimensional rough surface model are built.and theinfluence of fractal parameters on the thermal contact resistance is analyzed.The results show that with the increase of fractal dimension,the roughness amplitude of the joint surface decreases,the contact chance between the two contact surfaces increases,the dimensionless contact area increases,the thickness of the void space decreases,and the thermal contact resistance decreases.With the increase of scale coefficient,the roughness amplitude of the joint surface increases,the contact chance between the two contact surfaces reduces,the dimensionless contact area reduces,the space thickness of the void increases,and the thermal contact resistance increases.(4)Considering the influence of the above multi-parameter,the finite element analysis model of high-speed motorized spindle is established.The contact thermal conductivity,convective heat transfer coefficient and heat generation rate of heat source were loaded to study the distribution of temperature field and displacement field of motorized spindle.The analysis results show that the contact thermal resistance not only increases the temperature gradient of the spindle system as a whole,but also increases the deformation of the spindle system,especially at the joint surface between the bearing inner ring and the spindle,and the joint surface between the outer ring and the bearing seat.The axial thermal deformation of the spindle seriously affects the machining accuracy of the motorized spindle,while the radial thermal deformation has little effect.