A tilted orbital grinding technique for hole-making of CFRP composite laminates

Carbon fiber reinforced polymer (CFRP) laminates have been widely employed in the manufacturing of airplane. Usually, hole-making is the final machining process to join CFRP laminates with other components. However, CFRP laminates are considered as hard-to-machine materials, which results in some serious failures during hole-making process such as fiber pull-out, fiber break, and matrix delamination. To improve the hole-making quality, a tilted orbital grinding (TOG) method was proposed in this study. In the proposed TOG method, a grinding wheel was used as the machining tool and its axis was set as tilted against the axis of the hole with a small angle. Through replacing the revolving motion of the tool in conventional helical milling with conical pendulum motion of the grinding wheel, a hole could be made by a grinding process. The thrust forces, cutting temperatures, and the quality of the holes in the proposed TOG process were investigated by experimental methods. The results show that the thrust forces and cutting temperatures in TOG process are greatly less than those in the conventional orbital milling process. Scanning electron microscope (SEM) images of the hole that made by TOG method show that there is no crack generated in the entrance side of the hole, and the pull-out delamination in the exit side of the hole is significantly reduced. The experimental results indicate that the proposed TOG method has a potential application in the hole-making of CFRP laminates.