DEVELOPMENT OF A COMPOSITE BORING BAR

A composite boring bar, whose stability against chattering is superior to not only conventional steel bars but also cemented carbide bars, h as recently been developed. The main material of this composite bar is pitch-based carbon fiber reinforced plastic. Carbon fibers aligned un idirectionally in the longitudinal direction of the bars give high ben ding stiffness. Four types of bar having different shaped steel cores were designed by FEM analysis and produced for actual testing. A bar h aving a cross-shaped steel core shows the best cutting capability and stability amongst all bars designed. This bar can be used when the len gth (L) and diameter (D) ratio L/D is 7 or even at severe conditions w hile a cemented carbide bar cannot control the chatter vibration even if the L/D is less than 6. Emphasis should be placed on the fact that the cross-shaped steel core can increase the bending stiffness of the bar in both tangential and radial directions by constraining the shear deformation of the fiber layers without sacrificing the increase of r esonant frequencies. (C) 1997 Published by Elsevier Science Ltd.