Cutting forces and chip morphology in LCO2 + MQL assisted robotic drilling of Ti6Al4V

Abstract

Robotic drilling is receiving increasing attention in aerospace industry, where Ti6Al4V is used for multilayer composite/metal stacks. Being a difficult-to-machine material, dry drilling of Ti6Al4V results in excessive tool heating and premature tool wear. Through-tool flood lubrication in robotic drilling is difficult due to open and large working area. In addition, flood lubrication is not recommended for drilling of composite stacks. In this study, through-tool delivery of LCO2 + MQL is used on robotic drilling of Ti6Al4V with carbide tools. The flow rate of both LCO2 and MQL are individually varied to study the effect of coolant and lubricant flow rates on thrust force and torque values in comparison to dry drilling. Chip morphology is studied to observe the influence of LCO2 pressure on chip breakability. The results indicate a strong relation between LCO2 flow rate and thrust force due to material hardening and a strong relation between torque and MQL flow rate due to combined effects of lubrication in cutting zone and chip evacuation process. In dry drilling, strong chip adhesion to tool is observed, while LCO2 + MQL assisted drilling improves chip breakability and reduces the workpiece-material adhesion through combination of lower temperatures and lubrication barrier.