Experimental study on machinability of pre-hardened Toolox 44 and Nimax mould steels

In this study, the machinability of Nimax and Toolox 44 materials, which are among the mould steels was investigated experimentally. Cutting experiments were carried out with PVD-AlCrN coated carbide end mill using three different cutting speeds (50-70-90 m/min), feed rate (0.04-0.08-0.12 mm/tooth) and constant depth of cut (1.5 mm). As a result of the experiments, it was observed that more cutting force and surface roughness were measured than Nimax when machining Toolox 44 under the same cutting conditions. While the optimum cutting parameters are high cutting speed and low feed rate (V: 90 m/min and f: 0.04 mm/tooth) in machining of Nimax, low cutting speed and feed rate (V: 50 m/min, f: 0.04 mm/tooth) in Toolox 44. It was observed that cutting force increased with the increasing of cutting speed from 50 m/min to 90 m/min at 0.04-0.08 and 0.12 mm/tooth feed rate values in Toolox 44 by 140.139%, 11.286% and 15.179%, respectively while it decreased in Nimax by 3.221%, 2.974%, and 5.062%, respectively. It was determined that surface roughness increased with the increasing of cutting speed from 50 m/min to 90 m/min at 0.04-0.08 and 0.12 mm/tooth feed rate values in Toolox 44 by 78.162%, 34.721% and 8.878%, respectively while it decreased in Nimax by 3.515%, 30.027% and 9.806%, respectively. According to the machined sub-surface images, the cavity is formed with the increase of the feed rate on the machined surface of Nimax, while the deformed and heat affected layer is formed in Toolox 44. In addition, the Toolox 44 has more feed marks on the machined surface than Nimax at constant feed rate which has been found to increase the surface roughness.