The Research On Modeling And Compensation For Thermal Error Of CNC Gear Hobbing Machine Tools

In CNC hobbing process, the thermal error accounted for 40% to 70% of the total error, It's the main factor of reducing the machining accuracy. Based on the current research results about thermal error of CNC Gear Hobbing Machine Tools, there are two methods to reduce the thermal error: error prevention and the error compensation. For the former, it can be achieved by temperature controlling and rational design of machine tool structure, but this method is limited by technical and economic factors. The latter method is using a variety of detection ways to measure the thermal error during CNC hobbing directly or indirectly to establish thermal error model and compensate machining. The thermal error compensation of CNC gear hobbing machine can get good results in low cost and relatively simply, so the technology has become the common topic by scholars all over the world. In this paper, the method of error compensation will be used to reduce the effect of thermal error on the precision of gear hobbing machine, the main work is as follows:①The research on modeling and compensation for thermal error of CNC gear hobbing machine tools at home and abroad is analyzed, the significance of this technology for improving the stability of precision of CNC gear hobbing machine tools is described.②The cause of thermal error and the impact of thermal error upon stability of working accuracy are analyzed, the technical route is formed about modeling and compensation for thermal error.③The strategy of the arrangement of temperature sensors in thermal error experiment is proposed, and several key temperature points from multiple layout points of temperature sensors by using use of fuzzy clustering analysis are selected.④The necessary equipments in thermal error experiment such as temperature sensors,temperature data logging devices,displacement sensor and digital display, are selected , a thermal error acquisition software by using C++ builder is developed, using Bluetooth to transfer data to solve the on-site wiring difficulties.⑤The acquisition experiment of thermal error in YKS3120 hobbing machine completed, according to the temperature and displacement data by this experiment to optimize layout of temperature sensors. The method of multiple linear regression is used to establish thermal error model. Because thermal error is mainly reflected in X direction, the transformation law of thermal error on large column and small column in X direction is studied in this paper.⑥Two thermal error compensation methods: namely using a kind of thermal error differential helix compensation scheme and NC system to compensate the thermal error is proposed. The latter is also being used in practice and is more practical, through the PLC of NC system to get the temperature information of the key points, by the R parameter of NC system call the subroutine which was implanted thermal error model and calculate the compensation value. Modify X coordinate real-time while working state to achieve compensating thermal error real-time. The actual results has proved that this method was feasible, simple and had good effect on compensation.