The Mechanism And Active Control Technology For Thermal Tilt Deformation Of The Cryogenic Internal-cooling Spindle

As a new type of green machining technology,the cryogenic machining which use the liquid nitrogen as the cooling medium has been widely concerned because of its advantages in the machining performance for "difficult to machine materials".However,the introduction of cryogenic medium leads to a large temperature gradient in the longitudinal direction of the spindle box of the machine tool,which makes the thermal tilt error of the cryogenic internalcooling spindle larger and affects the accuracy of the machine tool Therefore,how to effectively restrain the thermal tilt of the spindle needs to be solved.In view of the above problems,this paper analyzes the limitations of thermal error compensation and thermal symmetry design method in restraining the thermal tilt angle,and puts forward the thermal deformation control strategy based on the thermal balance to control the thermal deformation,realize the real-time precision self-healing of the machine tool under the combined action of cooling and heating,and improve the machining accuracy of the cryogenic machine tool with internal-cooling spindle.The main work is as follows:Based on the structure of cryogenic machine tool,combined with the theory of heat transfer,thermo-elasticity and multi-physical field coupling numerical simulation method,the temperature field distribution and thermal deformation characteristics of cryogenic machine tool with the effect of liquid nitrogen were analyzed.The mechanism and influencing factors of heat conduction-temperature rise of structural parts thermal tilt deformation of cryogenic internal-cooling spindle is further studied.Finally,the theoretical model of thermal tilt error is established based on the theory of thermo-elasticity.Based on the analysis of the mechanism,the principle of thermal balance for restraining thermal tilt deformation of cryogenic machine tool is studied.Aiming at the influence of labyrinth seal structure performance on thermal tilt deformation,based on the theory of heat transfer and thermo-elasticity,combined with numerical simulation method,the influence of thermal insulation-seal structure parameters on heat and mass transfer characteristics was studied,and then the leakage model of labyrinth seal considering low temperature deformation was established to guide structural optimization to reduce thermal tilt error.In view of the balance in the jet cutting area after liquid nitrogen injection,the influence of liquid nitrogen injection parameters such as temperature and flow rate at the outlet on the heat transfer coefficient of liquid nitrogen is analyzed,the thermodynamic relationship model of liquid nitrogen jet is established,and the control method of jetting is proposed.To solve the problem of thermal tilt caused by temperature gradient of headstock,an active thermal control method based on thermoelectric cooling system is proposed.Based on the analysis of heat transfer theory,the principle of active control method of thermal deformation is explained,and a thermal error testing-bench which can reflect the thermal characteristics of cryogenic internal-cooling spindle is designed;the active control system based on thermoelectric cooling principle is developed,the temperature field and thermal deformation acquisition system are developed,the thermal tilt error model of the test-bench and the heat transfer model of active control system of thermal deformation are established,and then the active thermal control strategy and algorithm are proposed.The results show that the active thermal control method based on thermoelectric cooling system can reduce the thermal tilt error to less than 15% of the original error under various conditions,which verifies the effectiveness of the active thermal control method.The research results of this paper prove that the active control method is effective in solving the thermal tilt of cryogenic internal-cooling spindle and improving the accuracy of cryogenic machine tool.To a certain extent,it provides a new idea for the thermal error suppression of CNC machine tool and makes up for the deficiency of thermal error compensation method and improves the accuracy level of machine tool.