Dynamics of a machine tool cross-slide

Master thesis (2020)

Authors

M.P. Vermeulen Mechanical Engineering

Contributors

G.J. Verbiest Dynamics of Micro and Nano Systems - Mechanical, Maritime and Materials Engineering (supervisor 1)
P.G. Steeneken Dynamics of Micro and Nano Systems - Mechanical, Maritime and Materials Engineering (supervisor 1)
Faculty
Mechanical Engineering
Copyright: © 2020 M.P. Vermeulen
Hard turning Ball-screw drive dynamics Machine tool cross-slide Closed loop position control Optimla design
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Published Date

29-07-2020

Language

English

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Faculty

Mechanical Engineering

Abstract

Within a great variety in high tech industry there is an increasing demand for complex shaped turning workpieces with diameters up to a meter and accuracy within microns. Examples are bearings in offshore wind energy and high precision applications. For the production of these parts CNC controlled turning machines are used. A motorized spindle rotates a clamped workpiece that gets shaped by a
machine tool. The cutting tool is placed on top of two stacked ball-screw drives. The ball-screw drives allow for two translational degrees of freedom of the machine tool. This thesis is focused on the dynamics of the stacked ball-screw drives, the so called cross-slides. First, the relevant eigenfrequencies are measured and simulated. Based on the eigenfrequencies, plant transfer functions are determined. When implementing the control elements, the closed loop behaviour has been simulated and compared with experimental data. The influence of disturbances, for example non-stationary cutting forces, has been studied. Also, discrepancy of movement of the slides with respect to movement of the machine tool has been characterized with frequency dependence. It has been measured experimentally with multiple accelerometers at different positions. It has also been simulated using dynamic substructering, modelling the ball-screw drive partly with analytical expressions and partly with a dynamic finite element model. With all the gained knowledge a design cycle of optimal (stacked) ball-screw drives design has been proposed. The design cycle allows for both geometrical changes as well as for the selection of varies control strategies. Using the cycle several designs have been created, with the goal to find a design with maximised closed loop position control usable frequency bandwidth. In the x direction an increase from 40 to 110 Hz was realized, in the z-direction an increase from 50 to 90 Hz was realized. Also, the influence of design changes on the disturbance response and the costs have been indicated. When selecting specific requirements the proposed design cycle could be used for optimal design.