Evaluation of Noncoated Carbide Drill with Sharp Cutting Edge and Multistage Point Angle for Drilling of Carbon Fiber Reinforced Thermoplastics

This paper presents the application of a noncoated carbide drill having a sharp cutting edge and multistage point angle (drill A) for drilling carbon fiber reinforced thermoplastics (CFRTP). The cutting characteristics were evaluated by comparing the drill A with a diamond-coated carbide drill having a constant point angle (drill B). The influence of the contact state between the cutting edge and carbon fiber on the cutting force was evaluated using a CFRTP with a unidirectional fiber. The drill A exhibited a maximum thrust force at the drill rotation angle where the fiber orientation and cutting edge travel direction matched. It was found that the thrust force of the drill A was lower than that of the drill B at any drill rotation angle. Moreover, the thrust force of the drill A was always lower than that of the drill B during the drilling of the CFRTP with a plain-woven fabric. Additionally, the uncut fiber of the drilled hole obtained by the drill A was more satisfactory than that obtained by the drill B. The temperature of the area near the cutting point during the drilling was lower in the drill A than in the drill B. In the drill A, the thrust force tended to increase with the number of drilled holes. However, no considerable reduction in the drilled hole quality was observed at 200 holes.