Influence of machining parameters and tool structure on cutting force and hole wall damage in drilling CFRP with stepped drills

Carbon fiber-reinforced plastics (CFRPs) have many excellent properties, such as lightless, high specific strength, and high corrosion resistance, and they have been extensively used in the aeronautics and astronautics. It is a challenge for studies on the defect-free drilling technology and the causes of drilling defects to the CFRP materials. The purpose of this study is to research the machining parameters and the stepped drill geometry effect on cutting force and hole wall damage with the test methods. Both a twist drill and three stepped drills were employed in drilling CFRP plates under the experimental conditions. The effects of both the processing parameters and the stepped drill structure (the ratio of the pilot section diameter to the sizing diameter section diameter (D (1)/D)) on thrust force and hole wall damage were investigated, and the damage mechanism of hole walls was revealed by analyzing the cross-section features of the hole wall. The results show that the maximum thrust force of T3 (D (1)/D = 0.5) is minimal, so T3 should be selected to reduce the risk of delamination. D (1)/D, feed rate, and spindle speed are the main factors that affect the size of the hole wall damage. In addition, a special cutting force F (spec) is defined to explain the influence of tool structure and feed rate on hole wall damage.