Comparison of dynamic stiffness in tombstone materials

The pre-process selection of stable cutting conditions in milling requires knowledge of the structural dynamics. An important metric for describing the dynamic response of a system is the dynamic stiffness, or product of modal stiffness and damping ratio for each vibration mode, for both the cutting tool (as reflected at the tool point) and workholding setup. A common workholding method in horizontal machining centers is a tombstone. Traditionally, these tombstones are cast iron or steel weldments; however, there are potential dynamic stiffness and cost benefits to the use of different materials. In this work, impact testing was used to measure the frequency response functions for cast iron, aluminum, steel, epoxy-mineral, and concrete tombstones. Improved dynamic characteristics were observed in the epoxy-mineral and concrete tombstones when compared to traditional cast iron.