Thermal error regression modeling of the real-time deformation coefficient of the moving shaft of a gantry milling machine

This paper describes a novel modeling method for determining the thermal deformation coefficient of the moving shaft of a machine tool.Firstly,the relation between the thermal deformation coefficient and the thermal expansion coefficient is expounded,revealing that the coefficient of thermal deformation is an important factor affecting the precision of moving shaft feed systems.Then,thermal errors and current boundary and machining conditions are measured using sensors to obtain the first set of parameters for a thermal prediction model.The dynamic characteristics of the positioning and straightness thermal errors of the moving axis of a machine tool are analyzed under different feed speeds and mounting modes of the moving shaft and bearing.Finally,the theoretical model is derived from experimental data,and the axial and radial thermal deformation coefficients at different time and positions are obtained.The expressions for the axial and radial thermal deformation of the moving shaft are modified according to theoretical considerations,and the thermal positioning and straightness error models are established and experimentally verified.This modeling method can be easily extended to other machine tools to determine thermal deformation coefficients that are robust and self-correcting.

HYDRODYNAMIC AND ELASTOHYDRODYNAMIC STUDIES OF A CYLINDRICAL JOURNAL BEARING

In this article,the effect of the bearing elastic deformation on the performance characteristics of a cylindrical journal bearing is analyzed.The variety of simulation models covers hydrodynamic（HD） and elastohydrodynamic（EHD） lubrication theories.The Reynolds equations governing the flow in the clearance space of the journal bearing are obtained by considering the effect of mass transfer across the fluid film.The finite element method with an iteration scheme was employed to solve both the Reynolds equation and the three-dimensional elasticity equation representing the displacement field in the bearing shell.The converged solutions for the lubricant flow and elastic deformation vector are obtained.Dynamic characteristics of the journal bearing are computed for HD and EHD theories.Numerical simulation results show that the flexibility of bearing liner has a significant influence on the performance of a cylindrical journal bearing.Indeed,the elastic deformations of the bearing liner extend the pressure area in the bearing and increase the minimum film thickness.Although,dynamic coefficient,load capacity and attitude angle decrease.