Research On Thermal Property Of Vertical Machining Center Based On Contact Analysis

As an important factor influencing machining accuracy of the machine tool, thermal property of machine tool has received more and more attention of experts and scholars from all walks of life. Establishing the thermodynamic model of machine tool and analyzing its thermal property accurately are precondition to ensure that machine tool work stably and reliably. This subject is funded by National Major Science and Technology Project "Research and Development of Key Technology of Digital Design and Toolkit and Its Typical Application of High-Grade CNC Machine Tool"(NO.2012ZX04010-011). The thermal property of vertical machining center was numerically analyzed using the Finite Element Method and the thermal-structure coupling analysis method. And then experimental investigation was carried out on the thermal property of complete machine. The research results may provide the theoretical reference for improving and refining the vulnerable parts of machine tool.At first, the basic theories of finite element analysis of temperature field research, the thermal-structure coupling analysis method and contact analysis were presented briefly. The mechanical models of moving parts of X/Y/Z coordinate direction of vertical machining center were established and the mechanical loads between joint surfaces were also studied. The equivalent models of rolling guides, ball screws, rolling bearings, and the other joint surfaces of machine tool were stated in the thesis. The thermal boundary condition of complete machine was presented and then finite element model of thermodynamic of machine tool was established.Effect of thermal contact resistance of joint-surface on the temperature field of vertical machining center was discussed. The temperature field distribution of machine tool was also analyzed with or without thermal contact resistance and compared with experimental results. The researches proved that thermal contact resistance has an important influence on analysis of thermal property of machine tool. The thermal deformation of complete machine was researched by thermal-structure coupling analysis method and compared with the investigations of experiment. The results demonstrated that the establishment of thermal property analysis model of vertical machining center is reasonable in this subject. The experiments of thermal property of complete machine were investigated under three different test conditions according to the working environment of vertical machining center. The relative deformation (thermal elongation, thermal excursion and thermal declination) of spindle and stage was detected using non-contact displacement measuring method of seven-points. The experimental results showed that the thermal deformation caused by high-speed rotation of spindle is the dominant factor influencing machining accuracy of vertical machining center.The typical condition positions were determined based on the formation of working space of machine tool. The temperature field distributions and thermal deformations of typical condition positions of complete machine were researched. Linear and angular deviations of Geometric lest Code for Machine Tools of China were cited to assess the thermal deformation law of complete machine in the working space. The results indicated that the thermal deformation of machine tool of Z-coordinate direction was larger than the other two directions. And the structure or parameters of machine tool elements of this direction should be optimized and improved particularly.