Analysis of high temperature and mixed tool wear effects on UD-CFRP cutting mechanism in stacks drilling

Carbon fiber-reinforced polymer and titanium alloy are widely employed in the aerospace industry. In the integrated drilling of CFRP/Ti stacks, the interface heat accumulation and severe tool wear are more serious than that in single CFRP drilling, which generated significant composite borehole damages. To address these complications, a fundamental study was conducted to explore the cutting mechanism of UD-CFRP using a controlled temperature and edge profile. Combined with the Digital Image Correlation technique, the loading states of carbon fiber and matrix were comprehensively investigated, and their effects on machined damages at four fiber cutting angles were analyzed. Results show that progressive wear of the cutting edge causes the initial fracture point of fiber to move up, leading subsequently to fiber bending or buckling. This further results in the separation induced by the compressive stress under the friction and ploughing functions of flank wear in the cutting process, affected by which the value of cutting force and shear strain increases along the worn edge profile. When the temperature exceeds the glass transition temperature (T-g = 110 C-degrees), the low-rigidity fibers without support tend to overbend and fracture in the subsurface, ultimately resulting in matrix loosening and debonding damages at phi = 90(degrees)similar to 135(degrees) of the CFRP hole-wall at the interface region.