Machine tools are required to realize high precision and high efficiency machining by various industry sectors. A machine tool has some driving systems to position cutting tools and workpieces, and hence driving units are required high speed and precision positioning. However, high speed feed motion causes thermal deformation due to generated heat at friction surfaces such as guideway, feed screw, and bearings, it deteriorates positioning accuracy of driving units. Thermal deformation of a ball screw is one of large error factors of lower positioning accuracy, and a cooling system for reducing thermal deformation is installed into machine tools. Since the cooling system needs additional cost and space in machining systems, a new method for minimizing thermal deformation is required. In this study, a new structure of ball screw is proposed in order to meet these requirements. A new ball screw which has a core pipe made of CFRP was developed. CFRP is one of composite materials which have light weight and low thermal expansion. This paper presents analysis results of a simplified FEM model of the ball screw and the basic experimental results of the developed ball screw. These results confirmed that the proposed ball screw was applied to high performance positioning system in machine tools.

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