Experimental Investigation of Vibration and Damping of Machine Tool Slideways
 
 

  Ching Hung | MS | 1998

Machine tool manufacturers are constantly required to improve machine tools performance. The damping capacity of machine tools is one of the performance characteristics that needs to be improved. Vibration in machining processes is highly undesirable because it introduces great inconsistency in the machined products. Therefore, a machine tool must exhibit good damping capacity to dissipate the vibrational energy. Slideways are the oldest and most common components of machine tools. Many studies have suggested that joints like slideways possess great damping capacity. This research further explains the damping mechanism of a machine tool slideway.

To estimate the amount of damping originating from a slideway, a set of experiments were conducted. These experiments investigate the dynamics response of the individual members and the assembled slideway. The effect of different contact geometries was studied by varying the surface finishes of the saddle. The damping ratios were estimated by the DDS modeling method in the time domain and Half-power Bandwidth method in the frequency domain. The results indicated that the damping capacity is much higher in the assembled slideways than the individual members. Some damping ratios obtained for the slideway experiments were about forty times higher than those observed for the individual members. The surface finish of the contact area was also observed to affect the damping property. A milled surface on a ground surface was seen to provide better damping characteristics than a ground surface on a ground surfaces.

In an un-lubricated slideway, friction is the predominant source of energy dissipation (i.e. damping). Because of the importance of damping characteristic to the design of successful machine tools, predictive friction models are developed based on the preload and clearance of the slideway. Factorial experiment design was used to develop the predictive models, and a series of hypothesis tests was applied to check the adequacy. The friction models were then incorporated into the analytical equations for the motion of the slideways.

The predictive friction models and the equation of motion for the slideways were experimentally validated. The average percent error for the friction models is about 3%. The predicted motion of the slideway matches with the experimental results very well.

Using the friction force model, the desired friction force can be adjusted through the preload and clearance. Therefore, the magnitude of damping can be tailored to the specific need of different machine tools.

If you have any comments or suggestions please e-mail jwsuther@mtu.edu.