Design and characteristics of composite structures for high speed machining centers

Abstract

The high speed operation of a machine tool is important for productivity improvement. Although the cutting speed has been increased due to newly developed cutting tool materials such as ceramic, CBN, diamond and so on, productivity is still restricted by the low transfer speed of massive moving bodies which are usually made of steel. Therefore, one of the primary reasons for low productivity is large mass of the moving parts of machine tools, which cannot afford high acceleration and deceleration encountered during operation. Moreover, the vibration of machine-tool-parts is another obstacle to the high speed operation. Modern machine tools are usually equipped with high speed spindle systems rotating up to 50,000 rpm and moving frames operating up to the acceleration and deceleration of $10~30m/s^2$. At these high speed operation, machine tool structures are vulnerable to vibration if the structures were made of conventional metallic materials with inferior damping characteristics. Machine tool structures with high specific stiffness and high damping are required not only to improve the accuracy of a machine tool but also to obtain enhanced productivity. The high specific stiffness and good damping of machine tool structures are contradictory requirements if conventional metallic materials are employed because conventional metals have almost same low specific stiffness(E/ρ) with low damping characteristics. Therefore, the functional requirements can hardly be realized if conventional metallic materials with low specific stiffness and inferior damping characteristics. The requirement of high specific stiffness with high damping for high-speed-machine-tool-moving-parts can be satisfied by employing fiber reinforced polymer composite materials. Moreover, sandwich structures whose face structures are made of fiber reinforced composite materials and whose core materials are made of honeycomb or foam structures maximize their advantages when they are applied to th...