Thermal Error Control And Compensation Of Motorized Spindle System Of Turning Center

Thermal errors, mainly result from the thermal deformation of the spindle system, make up 40%-75% of the total machining errors in machine tools. Therefore, control and compensation of thermal errors is the key technology to improve the working accuracy of high-speed machine tools.A kind of high speed turning center was chosen to be the research object in this paper. A finite element (FE) model considering the contacting thermal resistance was established based on the deep analysis of heat generating and transferring principles of the motorized spindle system and simulated analysis was conducted with this FE. Moreover, an experimental platform of temperature field in machine tools was set up and several measurements were carried out. A method to control thermal errors of high speed turning center was proposed and the compensation system of thermal deformation was designed on the base of the simulated analysis and experimental measurements.Firstly, the main heat source and its generating principle of the motorized spindle system in the high speed turning center were analyzed according to its real working conditions. The heat transmission and dissipation involved in this system and conditions were also studied. Then, a FE model was established based on theoretical analysis and physical model. An grid assembling method was proposed and used during the mesh generation of the spindle system, which greatly reduced the difficulties in meshing large assemblies. The consideration of the contact thermal resistance in the FE model made the simulation results more accurate. A dynamic temperature measurement system was constructed to measure the temperature distribution of the motorized spindle system. The correspondence between simulated and experimental results proved that the FE model was reliable.Both of the simulated and experimental results showed that the heating value of the motorized spindle system in the high speed turning center increased rapidly under high rotational speed conditions. There was a significant rise of the temperature when the rotational speed was above 3000r/min, which indicated that the high speed machine tools was not a simple upgrading from general machine tools. The method of thermal deformation control and compensation were studied. A constant temperature controlling method of warming up the machine tools was proposed to improve working accuracy, which had short warm-up time and high work efficiency. The main significance in this method was the effective utilization of the cooling water, which was used to heat the machine at the warm-up stage and cool down the machine during the working stage. A kind of thermal deformation actuator, which was drived by piezoelectric ceramics and had a high-frequency responses, was designed to dynamically compensate the thermal error on-line.