Sustainable machining of carbon fiber and Ti6Al4V stacks with assistence of liquified CO2Rodriguez Bogajo, Iñigo (Avtor) Arazola, Pedro José (Mentor) Pušavec, Franci (Mentor) Cuesta, Mikel (Komentor) sustainable machiningcryogenic machiningdrillingindustrial hygieneaeronautic structuresCarbon Fibre Reinforced Polymers (CFRPs) and Ti6Al4V titanium alloys are widely used for structural applications in aeronautics due to their superior strength-to-weight ratio and corrosion properties. These materials are often combined to create hybrid CFRP/Ti6Al4V stacks. Composite/metal stacks are usually joined with rivets or fasteners regardless of having an adhesive layer between the composite and metal. Thus, drilling is one of the most critical operations in aircraft manufacturing due to the large amount of holes needed to assemble components made of different materials. Good hole quality is crucial to ensure the durability of such assembled structures. A wide range of machinability issues and hole quality defects arise when drilling CFRP/Ti6Al4V stacks. On the one hand, the CFRP creates abrasive wear, rounding the cutting edge, and delamination can occur when the drill fails to shear the plies of the composite. Ti6Al4V on the other hand, can accelerate tool wear due to adhesion. The stacks are usually machined in a single operation (one-shot) from the CFRP to the Ti6Al4V, which creates additional problems like the scratching of the CFRP hole walls by the titanium chips. Coolants and lubricants are employed in many applications to supress machinability and hole quality problems when drilling difficult to cut materials. However, for CFRP/Ti6Al4V stack drilling, conventional water and oil based emulsion coolants cannot be used, as they can degrade the composite phase due to moisture absorption. Moreover, emulsions can create environmental and health hazards. Techniques such as the combination of liquid carbon dioxide (LCO2) and minimum quantity lubrication (MQL) have emerged as sustainable cooling and lubrication alternatives to conventional emulsions. However, their feasibility to drill CFRP/Ti6Al4V stacks and their effect on health and environmental aspects when machining aeronautical components is yet to be proven. In this context, the main objective of the thesis is to define a process window for LCO2+MQL assisted drilling of CFRP/Ti6Al4V stacks and to perform a sustainability evaluation of this technique, considering environmental, economic and social aspects. The machining parameters, drill geometry and cooling lubrication flow rates to achieve superior hole quality and minimal tool wear are experimentally determined. Concerning the sustainability analysis, the effect of employing LCO2+MQL coolants on the airborne emissions at the workplace are characterised, and the environmental advantages of using such coolants in comparison to dry drilling were evaluated through life cycle assessment.[I. Rodriguez Bogajo]20242024-08-08 12:44:45Doktorsko delo/naloga160014UDK: 621.9:678:629.7(043.3)VisID: 263075COBISS_ID: 204076035sl