Controlling Independent Parameters of Vibration-Assisted Drilling of Carbon Fiber Reinforced Polymers for Optimized Hole Quality

Drilling induced defects in Carbon Fiber Reinforced Polymers (CFRPs) represent a major challenge for aerospace manufacturers, especially with the growing use of CFRPs in the aircraft structures. Interlaminar cracking... [ view full abstract ]

Drilling induced defects in Carbon Fiber Reinforced Polymers (CFRPs) represent a major challenge for aerospace manufacturers, especially with the growing use of CFRPs in the aircraft structures. Interlaminar cracking (delamination) and thermal damage (matrix burnout) are the most critical defects, which can be avoided by keeping the drilling forces and temperatures below some threshold levels. Vibration-assisted drilling (VAD) is an emerging process that has exhibited lower cutting forces and temperatures and easier chip removal, higher produced surface quality and longer tool life. This is due to the intermittent cutting nature of the process, which provides gradual application of the drilling forces during the engagement cycles in addition to the tool and workpiece cooling during the disengagement cycles. This research provides insight into the effect of the independent VAD parameters (speed, feed, frequency and amplitude) on the produced hole quality geometry as well as on the drilling forces and temperature. The VAD process is investigated in the low frequency-high amplitude (LFHA) regime (<200 Hz, <0.6 mm). The cutting conditions are investigated in the range of speeds between 6,000rpm and 12,000rpm and axial feeds between 0.05 mm/rev and 0.15 mm/rev. The extensive experimental investigation showed that feed has the most dominant effect on the VAD forces and temperatures. The thermal performance of the VAD process was found to be enhanced by the formation of vortices in the air gap created by the separation between the tool and the machined surface, which is mainly controlled by the feed and the rotational speed of the tool. The optimized VAD conditions could reduce the cutting temperature by 40% and the axial force by 20% and produce delamination-free holes, without affecting productivity.