An Investigation into the Effects of Lubrication, Surface Finish, and Clearance on Machine Tool Slideway Damping and Friction

Ram M. Kuchibhotla | MS | 2002

Abstract:

The role of a machine tool structure is to support the machine tool and the workpiece under the action of various, mainly cutting forces. These forces often result in unacceptable levels of vibration of tool and workpiece. Mechanical joints are the primary source of damping in most passive structures. Therefore, vibration reduction and energy dissipation characteristics of machine tool joints is of great interest. In a large class of machine tools, either the workpiece and/or the tool translates along slide-ways. Design of these joints is critical to the machining performance. Understanding the effect of interface parameters (lubricant viscosity, saddle/slide-way clearance, and slide0way surface finish) is needed to achieve appropriate balance of mechanical performance (friction, energy dissipation), environmental sensitivity (type and amount of fluid) and economic concerns. Experiments were conducted to analyze these parameters. Specifically four lubricant conditions were investigated, dry (no lubricant), and three commercially available lubricants (spanning a broad range of viscosity). Initial investigation showed minor differences between three lubricants (damping is primarily of viscous and of similar level), but significant difference between dry (primarily structural damping). The effect of machined versus ground slideway shows different energy dissipation characteristics. The investigation of clearance showed some effect on the damping behavior.

Impulse response experiments were conducted to evaluate the damping capacity of the slide-ways. It was observed that interface friction is the main governing factor controlling the damping properties. The higher the friction in the bearings, the better the damping and the less chance of generating chatter in the tool. Further, high friction causes heat to be generated in the bearings. Therefore it is of primary importance to understand the behavior of common joints, to properly design a machine tool to have appropriate damping levels. The research work provides insight into the aspect of lubrication in controlling machine tools damping capability.

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