重型数控立车工作台静压计算

Hydrostatic Pressure Calculation of Worktable of Heavy Duty CNC Vertical Lathe

采用预载恒流静压导轨的重型数控立车的工作台由于承载大,静压计算时必须考虑结构变形对油膜厚度的影响,因此该计算问题为静压-结构耦合问题,通常采用迭代方法求解。工作台主轴z向自由情况下,用有限元法求解工作台变形时,如何处理工作台主轴孔处的z向约束是静压求解的关键,目前有关文献对此问题的处理方法存在问题。为解决此问题,提出一种计算刚性位移的方法;即认为油腔的油膜厚度为工作台的刚性位移与工作台导轨在该油腔封油边处的z向平均变形的代数和,该刚性位移值可通过包含油腔静压力的z向受力平衡条件求出。对直接采用不动点迭代方法求解此耦合问题的发散特点进行分析,提出新的校正改进法,用于静压迭代计算,无论工作台主轴z向有无约束均可使用,还可考虑包括切削力在内的外载。采用新方法进行3个工况的静压求解迭代计算,均稳定收敛到指定的精度,验证了新方法的有效性和稳定性。

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 gnideway 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.