Dynamic Performance Evaluation of Two-axis Lathes

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Abstract

With the increasing demand for extended service life and increased precision and accuracy of precision mechanics across various industries, machine tool manufacturers face the challenge of increasing the performance of their machines. To achieve this goal, the performance of the machines must be evaluated, points of improvement must be identified and subsequently be acted on.

This thesis is focused on the evaluation of the dynamic performance of a two-axis CNC lathe, subject to vibration modes excited by movement of the machine axes. To this end, two experiment setups are designed to measure displacement at the cutting tool in either axial or lateral directions and compare these displacements against the positions and controller setpoints of the corresponding machine axes. Additionally, a finite element model is created and expanded such that it emulates the machine encoders and additional cutting tool sensors, as well as the third order motion profile that is used to excite the system. Methods for automatically processing the data from these experiments and simulations are developed in parallel, allowing for large sets of data to be processed with little effort.

These experiments show that with a maximum amplitude of approximately 0.3 μm the vibrations that occur at the tool, relative to the axis encoder, are most significant in axial direction. A qualitative comparison with the finite element model indicates a mechanical issue relating to the Z axis drive mechanism, causing additional vibrations in the system. Finally, the experiment setups, corresponding data processing methods and finite element models are reflected on and incorporated into a framework for experimental machine performance evaluation. By implementing this framework, machine tool manufacturers can further evaluate and improve the dynamic performance of their machines.