Determination of the Dynamic Stiffness of a Hydrostatic Carriage of a High-Speed Milling Machine

Abstract

Comprehensive vibration data were generated for a hydrostatic carriage system that carries workpiece of a High-Speed Milling Machine at the Machine Tool Research Center of the University of Florida. Machine toolaccuracy is critical if final quality of machined parts is of importance. In high speed machining, easy movementof parts is also a desired feature and the use of a hydrostatic bearing and guides provides a way to achieve this.Data was generated using experimental modal analysis; a technique that has found wide use with vibrationanalysts. To obtain various stiffnesses within the broader carriage, a series of measurement was taking across thelength a breadth of the hydrostatic table, the results obtain depicts the dynamic behavior of workpiece tableduring the high speed operations. The data shows good vibration characteristics of the hydrostatic carriage.Analysis of data in across the whole show high dynamic stiffness as expected from design. The k value obtainedfor pitching is 1.3386+009N/m. The stiffness of each bearing is k. Estimated bearing stiffness is 0.6693+009N/m.For the case of rolling, obtained is 1.7859+009N/m. Estimated bearing stiffness is 0.8925+009N/m. Thevariability in stiffness may be due to unequal tolerances in the bearing gaps of individual bearings Modalparameters of the hydrostatic table, which include all important natural frequencies, modal damping ratios andmode shapes, were observable.

Keywords: hydrostatic carriage, experimental modal analysis, dynamic stiffness