Investigação do rosqueamento interno da liga de alumínio AA6063-T6 com ferramentas de aço rápido revestidas com DLC

Abstract

The AA 6063-T6 aluminium alloy, widely employed in the automotive, naval, and aerospace sectors, exhibits poor machinability in drilling and internal threading operations due to its high ductility and the formation of long chips, which can lead to tool wear and surface deformation of the machined component. This study aimed to investigate the influence of pressurised cutting fluid application and to evaluate the impact of process variables on the performance of high-speed steel internal threading tools coated with Diamond-Like Carbon (DLC). M8 × 1.25 mm taps with a central channel for internal lubrication were used, and four independent variables were tested at two levels: cutting speed (40 and 60 m/min), cutting fluid pressure (15 and 35 kgf/cm²), helix angle (15° and 45°), and two models of axial compensation holders from different manufacturers. During the tests, torque and axial force were monitored, and the tools were analysed by scanning electron microscopy (SEM), in addition to tensile testing and Vickers microhardness measurements on the threaded specimens. The 15° helix angle was identified as the most influential factor, according to the Pareto chart, resulting in an axial feed force approximately 6.5 times higher than that of the 45° angle in the initial trials, and 11.5 times higher after 600 threading cycles. The results indicated a significant increase in adhesion on the clearance face and on the width of the tool’s flank after 300 threadings, particularly when using the 15° helix angle. Loss of the DLC coating was observed and confirmed by energy-dispersive X-ray spectroscopy (EDS), attributed to attrition wear. After 600 threading operations, micro-chipping of the cutting edge was detected, especially under the condition of 40 m/min cutting speed, 15 kgf/cm² fluid pressure, and 15° helix angle, specifically on the third thread of the third pass. Cutting fluid pressure demonstrated a significant influence on the removal of sheared chips. The condition of 35 kgf/cm², combined with the DLC coating, contributed to reduced tool wear, lower axial force, and decreased torque peaks during tool reversal, thereby enhancing the service life of the cutting tap.