Evaluation and multi-criteria optimization of surface roughness, deviation from dimensional accuracy and roundness error in drilling CFRP/Ti6Al4 stacks

In this study, machinability tests were carried out to investigate the effects of control factors (cutting tool geometry, cutting speed, and feed rate) on the surface roughness (Ra), deviation from dimensional accuracy (Da_dev), roundness error (Re) in drilling CFRP/Ti6Al4V mixed metallic stack and to determine the optimum levels of drilling parameters. The effects of each control factor and their interactions on three quality characteristics were analyzed, and their levels were single-objectively optimized for each component material by the Taguchi method. The material has components (CFRP and Ti6Al4V) with essentially different properties (mechanical, physical, machinability). Single-objective optimization has limited usability as the drilling must be performed in one through both layers. Therefore, in an additional step, the optimum levels of the control factors were determined by optimizing multi-objective with the Additive Ratio Assessment (ARAS) method. Higher Ra, Da_dev, and Re values were obtained on the CFRP component compared to the Ti6Al4V component. The CFRP/Ti6Al4V stack should be drilled with a nano fire coated carbide drill (T3) at medium cutting speed and high feed rate to achieve minimum Ra, Da_dev, and Re values in one go.