| At present,most domestic movable cross-rail gantry machining centers have low spindle output torque and the rigidity of moving parts are poor.The cutting efficiency is low and processing cost is high.However,other domestic gantry machining centers have low spindle output torque and low spindle speed,which are unable to complete high-precision machining tasks.In order to meet high efficiency and precision production demand of workpieces,our school cooperates with an enterprise to develop new spindle system with high output torque and movable cross-rail system of gantry machining center.The spindle with high output torque is designed and the mechanical and thermal characteristics of spindle and movable cross-rail system are studied by combining finite element analysis and test,which realize the characteristics of high precision and efficiency.(1)The newly designed structure of spindle system is standard spindle+intermediate carbon fiber coupling+transition shaft and the maximum output torque is 1700N·m.Next,based on finite element method,stiffness and strength of the newly designed spindle are checked and the results meet the design requirements.And then,dynamic balance accuracy of the spindle is improved by the double-face dynamic balance test.After the test,the maximum remaining dynamic unbalance value of adjustment face is 63.7g·mm and the accuracy grade of spindle dynamic balance attains G1 class of ISO 1940-2-1997.(2)The temperature field of the spindle system is studied by combining finite element simulation and test,and the thermal error compensation model is also established.Before finite element thermal analysis,the temperature of measured points versus time under different working conditions are plotted after the test.According to the test results,when spindle speed is increased to 4000rpm and spindle system reaches the thermal equilibrium state,the maximum temperature of the measured point is 43.0?and the time for spindle system to reach thermal equilibrium state is about 75min.Then,through steady-state thermal analysis,when the circulating oil cooling system is applied and the spindle speed is increased to 4000rpm,the temperature of front supporting bearing outer ring drops by 15.1?.Next,the comparison diagram of simulation and test of the temperature of measured points versus time under different working conditions are obtained through transient thermal analysis of spindle system.And the maximum error between calculated and test temperature value of each measurement point is less than 5%.It proves that the results of simulation analysis are reliable.And the thermal deformation of spindle system under different working conditions are obtained by thermal—structure coupling analysis,and the spindle thermal error compensation model is established.(3)By combining finite element analysis and test verification,the tilt error and deformation error of movable cross-rail system under its own gravity are analyzed and compensated.First of all,a movable cross-rail synchronous balance adjustment system is designed to compensating tilt error by subarea method.The compensation data corresponding to each leveling interval on the movable cross-rail is obtained by the test.Then getting the displacement error data of ram and long milling head along the X-axis,Z-axis when ram is at different location of Y-axis of machining center.The error compensation models are obtained by polynomial fitting method.Finally,the compensation results are verified by the test and the results show that movable cross-rail can meet the requirement of high precision production.(4)The natural frequency of movable cross-rail system is solved by energy method.And the first eight order natural frequencies and vibration models of movable cross-rail system are gotten by modal analysis.The results show that the movable cross-rail system will not resonate within the rated rotation speed.Next,the harmonic response characteristics of movable cross-rail guide rails are analyzed.The maximum amplitude of guide rails along the X-axis,Z-axis are 97.5?m and 95.2?m,respectively.And the corresponding frequency values are 140Hz and 160Hz,respectively.Furthermore,the harmonic response characteristics of movable cross-rail system with different damping ratios are analyzed,which provide a theoretical basis for improving the dynamic performance of movable cross-rail.Finally,a tuned mass damper(TMD)is designed to suppress the amplitude and improve the dynamic performance of movable cross-rail system.The study shows that after the installation of TMD,the maximum amplitude of guide rails along the X-axis,Z-axis are reduced 63.9%and 64.0%,respectively.And the corresponding frequency values are 220Hz and 250Hz,respectively.When spindle speed increases to 8000rpm,the resonance will not occur.The results show that the TMD has a good effect on improving the vibration resistance of movable cross-rail system.(5)It is proved that the spindle system meets the requirement of high efficiency cutting by the heavy cutting load test and metal removal rate reaches 1320cm3/min in the test.Next,when the thermal error compensation system is not loaded or loaded,high precision milling of the selected planes of the workpieces are carried out.By comparing their cutting accuracy,it is proved that the thermal compensation system plays a significant role in controlling the thermal error of spindle system.The new spindle system with high output torque is designed and thermal error of spindle system and deformation error of movable cross-rail system are compensated.Moreover,the dynamic performance of the gantry machining center is improved by the TMD.These improve precision and reliability of the machining center and realize high output torque,high efficiency and precision machining of workpieces.The study is of great significance to the research and development of similar domestic machining centers,extending applicable processing range of gantry machining centers and improving the cutting efficiency and precision of workpieces. |
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