Structured surfaces for damping enhancements at mechanical interfaces

The development of new high-speed and high-power machine tools has opened the door to a new regime of machining. Many aspects of the machining process remain consistent with traditional methods, but a practical need to predict, reduce, and control regenerative chatter has emerged to the forefront. Previous work done at UNCC on the characterization of the machine tool spindle to toolholder connection showed that decreased drawbar load and worse fit produced a system that was dynamically stiffer and more resistant to regenerative chatter than normal drawbar load and a toolholder with a good fit. It was also found that interface damping is difficult to predict or repeat from tool to tool, and that what would traditionally be considered a "good" fit between the tool holder and spindle might not be "good" for dynamic stiffness (the product of stiffness and damping ratio) or for dynamic repeatability. The explanation for these counter-intuitive results was that dynamic stiffness actually increased with decreased drawbar load; the decrease in stiffness was more than offset by increased damping over a certain drawbar load range. This allowed relative motion (on a microscopic scale) between the two contact surfaces resulting in increased damping without unduly compromising stiffness and tool position accuracy. Presented here is an investigation into the use of engineered surfaces to decrease the sensitivity of dynamic performance to interface tolerances and increase interface damping.