DETERMINATION OF OPTIMUM PARAMETERS BY INVESTIGATING THE SURFACE ROUGHNESS AND HARDNESS OF INCONEL 718 SUPERALLOY AFTER FACE MILLING

In this study, the effect of cutting speed and feed rate on the surface roughness and hardness of Inconel 718 nickel-based superalloy was investigated. Milling operations were carried out at various cutting speeds (30-40-50-60-70 m/min) and feed rates (0,025-0,05-0,1 mm/rev) using a TiSiN coated carbide milling cutter. Surface roughness increased significantly with increasing feed rate at all cutting speeds. However, the effect of cutting speed became less pronounced at lower speeds (60 m/min). With increasing cutting speed (50 m/min), the machinability of the material increased due to the increase in temperature and thus softening of the material surface, and the surface quality improved in parallel with this and the roughness decreased. On the other hand, surface hardness decreased as the feed rate increased at all cutting speeds due to increased surface temperature caused by friction, inversely proportional to the increase in feed rate. The highest hardness values were obtained at a cutting speed of 30 m/min. At higher speeds (30 m/min), the hardness decreased due to thermal effects and became the effective factor for surface hardness. In other words, at cutting speeds greater than 30 m/min, the effects of cutting speed on surface hardness are relatively lower than the effects of feed rate on surface hardness. Consequently, slower feed rates are recommended for better surface quality at low cutting speeds. At higher cutting speeds (50 m/min), the combination of high cutting speed and low feed rate is ideal for low surface roughness values. For higher surface hardness values, lower feed rates can be applied at all cutting speeds. For the highest hardness values, a combination of low cutting speed and low feed rate is preferable, especially at cutting speeds below 40 m/min.