Experimental study on drilling mechanisms and strategies of hybrid CFRP/Ti stacks

Mechanical drilling has been frequently used for hole making of hybrid CFRP/Ti stacks in order to ensure excellent fastening assembly. Owing to their inhomogeneous behavior and poor machinability, drilling CFRP/Ti stacks in one-shot time has brought great challenges to the modern manufacturing community. Compared to the previous studies on drilling CFRP/Ti, this paper aims to highlight the following aspects: (i) the features of tool-work interaction and machinability classification in the bi-material drilling, (ii) the influences of different cutting sequences on CFRP/Ti drilling responses, and (iii) the effects of different tool geometries/materials on CFRP/Ti drilling performance. The experimental results have shown that the drill geometrical features, which ensure the cutting contacts of the stack combination, have a more significant effect on CFRP/Ti drilling output than tool material composition. The Ti → CFRP drilling strategy promotes higher quality of the machined hole surfaces (e.g., more consistent hole diameters and much better surface finish) with lower Ti burr extents, while the CFRP → Ti drilling strategy reduces only the induced delamination. The experiments discussed in this paper allow besides several recommendations for the cutting sequence selection and drill geometrical design when drilling hybrid CFRP/Ti stacks.