Study On The Rounding Transition Process And Roundness Variation In Hydrostatic Bearing Inner Bore Plunge Grinding

Hydrostatic spindles are often used as core components of high precision and ultra-precision machine tools due to the advantages such as good loading capacity,high rigidity,long life span,and the special characteristic "error equalization effect".Hydrostatic bearings are the supporting parts of hydrostatic spindles,so the bearing inner bore roundness may affect the spindle shaft equilibrium position and rotation precision.Internal grinding is an important process to form the final dimensional accuracy,contour accuracy and surface roughness of the bearing inner bore.Although many scholars have established various models to simulate the internal and external cylindrical grinding process,the existing models cannot provide effective simulations for choosing a reasonable efficient grinding procedure for a given grinding system,furthermore the final roundness prediction of the system and the grinding procedure is also insufficient.To achieve precise prediction for grinding process and bore roundness,urgent research is needed.There are four achievement in this research:(1)According to the structural parameters of the grinding system and the boundary conditions satisfied by the grinding process,the coupling interaction between the grinding wheel-spindle system and the workpiece-spindle system during the inner bore grinding process is further considered,a dual-rotor system dynamic model for inner bore plunge grinding is established with comprehensive consideration of the spindle rotation accuracy and the workpiece initial shape error.(2)Using Newmark-? method to solve the transient response of dynamic model.Based on the iterative algorithm for simulating material removal and roundness change of internal bore plunge grinding process,quantitative simu lation of the internal bore plunge grinding process is realized.By analyzing the inner bore plunge grinding images of the workpiece instantaneous(total)material removal,the grinding wheel instantaneous(total)wear,the spindle vibrational displacement,and the workpiece inner bore roundness error over time,the change of various parameters and the formation mechanism of roundness error during the inner bore plunge grinding transition process are revealed.(3)Based on the structural parameters of the hydrostatic bearing inner bore plunge grinding system and grinding process parameters,the research reveals how the structural parameters of the grinding wheel spindle system,the headstock spindle system structure parameters,the dynamic balance accuracy level and the grinding process parameters affect the workpiece inner bore final roundness error.(4)By calculating the span between the two support bearings when the spindle shaft end displacement reaches the minimum value under load,the spindle structur e parameters are optimized.Based on the theoretical basis of plunge grinding,a method to optimize the grinding quality and efficiency is proposed.Based on the dual-rotor dynamics model and the algorithm for simulating material removal,a software for simulating the inner bore plunge grinding transition process was designed using the GUI platform in MATLAB.(5)A hydrostatic bearing inner bore grinding rest rig was built.The workpiece final roundness error was measured under different wheel speed and wo rkpiece speed.The effectiveness of the model and algorithm is verified through the experiment.The results show that the experimental results are remarkably close to the simulation results under the same system structural parameters and process parameters.The research work in this paper provides a basic model for hydrostatic bearing inner bore grinding transition process,and also provides an engineering reference for inner bore grinding roundness prediction and grinding process optimization.