Abstract: Since worktable of heavy duty CNC vertical lathe equipped with preloaded constant current hydrostatic guideway is to bear heavy loads, the influence of structural deformations on oil film thicknesses should be taken into accounts in their hydrostatic pressure calculations. Hence they are hydrostatic pressure-structure coupling problems usually solved by iterative method. When finite element methods are used to analyze the worktable deformations on condition that the worktable spindle has no constraint in z direction, the key problem is how to deal with the constraint of the spindle part in z direction. In related literature, this problem is not solved properly. To address this issue, a new method for calculating the rigid displacement is proposed under the assumption that the pocket film thickness is the algebraic sum of the worktable rigid displacement and the average deformation of the worktable guideway area that aligns with the pocket margin. The rigid displacement value can be derived from the equilibrium condition in z direction considering the hydrostatic forces. After analyzing the divergence characteristic of the fixed-point iteration method directly used to solve this coupling problem, a novel correctionimprovement method is presented for the iterative hydrostatic pressure calculation. This method can take cutting forces into accounts and is valid no matter whether the worktable spindle is constrained in z direction. The calculation results for three loading cases are given by using the new method. All of their iteration procedures are steadily converged to an assigned accuracy, which verify the effectiveness and stability of the proposed approach.

Key words: CNC vertical lathe, Finite element method, Hydrostatic pressure calculation, Preloaded constant current hydrostatic guideway, Worktable