Analysis of drilling bit geometry based on time varying curve of drilling thrust force for CFRP composite laminates

In order to investigate the drilling bitgeometry of carbon fiber reinforced composite (CFRP) laminates which achieves low defect, T800 CFRP laminates were studied by drilling experiments adopting four kinds of different geometry for drill bits. The effect of drill bit geometry on thrust force of drilling was analyzed. The relationship between thrust force of drilling and delamination damage was discussed. The results show that dropping speed of thrust force and outlet delamination factor have a good positive correlation. Dropping speed of thrust force can characterize the applicability of drill bit geometry to CFRP laminates drilling. In addition, the experiments show that cutting areas of drill bits which have multi-step geometric characters would cause thrust force returning to zero slowly in multi stages during drilling through the exit of the workpiece, and generating lower delamination factor at exit.