Formation mechanism of outlet damage in interlaminar drilling of CFRP

Interlaminar drilling of CFRP is a specialized drilling technique that is used to maintain the structural integrity of the composite material in specific applications where high performance and durability are critical. The outlet damage has important effects on the connection reliability and service life of components. In this work, the experiments for interlaminar drilling of CFRP were designed, the thrust force during drilling process and the damage morphologies of drilling outlet were extracted, the comprehensive damage factor was proposed, and the formation mechanism of outlet damage was analyzed. In addition, the effects of machining parameters on thrust force and outlet damage were further revealed. The results show that the time-varying curve of thrust force in interlaminar drilling has the same trend as the conventional drilling, but the thrust force in conventional drilling is lower than that in interlaminar drilling. The outlet damage in interlaminar drilling is related to the fiber cutting angles (FCAs). The tear damage at the FCA of 90 degrees is the most obvious. The burrs damage mainly occurs in the fiber layers perpendicular to the feed direction and is concentrated in the areas of FCA of 15 similar to 105 degrees and 195 similar to 285 degrees. The comprehensive damage factor decreases with the increase of feed rate. Increasing the spindle speed can significantly reduce the outlet damage when the feed rate is higher than 0.17 mm/r.