MECHANICAL PROPERTIES AND MACHINABILITY EVALUATION OF ANNEALED TITANIUM GRADE 2

Abstract

The rapid growth in the utilization of titanium has brought many manufacturing challenges. Developing a new sustainable machining strategy is of utmost importance. In this study, the machinability of commercially pure titanium grade 2 (CP-Ti grade 2) was investigated under three different conditions of CP-Ti grade 2 namely, as-received (T1), annealed at 700°C (T2) and 900°C (T3). The response were cutting force, cutting power and surface roughness. The data collected from the tensile test indicate that there was an increase in ductility in T2 compared to T1 and T3 workpieces but T2 demonstrates a decrease in tensile strength. The XRD (X-Ray diffraction) analysis on the developed oxidation layer showed that T2 had a thin oxidation layer of 843 nm whereas T3 had a thicker layer of 20 μm. The formation of the oxide layer on CP Ti grade 2 is beneficial to the biomedical implants for the proper cell attachment. A full factorial design of experiment (DOE) was applied with three factors at two levels and three replicates. The machining parameters used during this study were cutting speed at 110 and 130 m/min, depth-of-cut of 0.1 and 0.3 mm and feed rate of 0.12 and 0.35 mm/tooth. Due to the decrease in hardness of T2, the cutting forces recorded was 30 % lower compared to the T1 and T3. On the other hand, the average cutting power was also found to be lower by 15 % during the milling operation of CP-Ti grade 2. The evaluation of the surface roughness under the minimum quantity lubrication (MQL) with the newly adjustable nozzle system demonstrates that low surface roughness of 0.2 μm can be achieved rather than under dry or flood condition. Finally, this study found that by annealing CP-Ti grade 2 at 700°C for one hour can contribute to a better machinability due to a soften effect that reflected on the hardness value of 180 Hv under an MQL condition. It was also found that the optimum milling parameter was with a cutting speed of 130 mm/min, feed rate 0.12 mm/tooth and depth of cut of 0.1 mm that can achieve the lowest cutting power and cutting force. This valuable data can contribute to the industry so that the machinability of CP Ti grade 2 or similar material with the same range of hardness can be machined without much difficulty.