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Generally, cutting tool materials are exposed to high me- chanical stresses and thermal disturbances when machining nickel-based alloys resulting in cutting tool wear and short tool life. The results obtained show that most tools develop chipping wear at the depth-of-cut form while cutting the Hastelloy-276 due to the chip burr occurs during the process. Chip burr hammered the edge ofthe tool along its way with intervals from the cutting zone tacking off parts ofthe edge. Flank wear and BUE were seen at low cutting which along with chipping caused severe damage and tool wear. The wear rate of carbide tools increased dramatically with the increase ofcutting speeds. The inserts were tested by cutting Hastelloy- 276 under a constant feed rate of 0.20 mm/rev, a constant depth-of-cut of 1.5 mm, and different cutting speeds between 100 m/min and 270 m/min. For each experiment, reference flank wear value ofVBB = 0.3 mm was chosen as wear crite- rion according to ISO 3685. A cutting tool was rejected and further machining was stopped based on one or a combination ofthe following rejection criteria in relation to ISO Standard 3685 for tool life testing:

Tool tips CCMT-12 and CNGN-12 were used to machine the nickel-based alloys Hastelloy-276 workpiece material. It was examined by the SEM images ofthe worn cutting edges. It can be seen from these images that wear predominantly occurred in two regions during the tests: at the depth-of-cut line and the nose radius as shown in Figs. 3(a), 3(b), 3(c), and 3(d). The wear at the depth-of-cut line did not have any influ- ence on the machined surface roughness [18]. However, the wear at the nose radius of cutting edge directly influenced the machined surface roughness since the nose edge was in direct contact with the newly machined surface. Fig. 3(a) shows a nose radius wear at a low cutting speed of 100 m/min; when the cutting speed was increased up to 150 m/min flank wear appeared alongside radius wear as shown in Fig. 3(b). This may increase the effect of chatter or vibration which occurrs at this cutting speed, explaining the increase ofthe value of surface roughness with the insert CCMT-12 as shown in Fig. 2. When the SEM images in Fig. 3(c) and 3(d) were closely examined, the highest tool wear was seen on the insert type CNGN-12 as shown in Fig. 3(d) for the cutting speed of 150 m/min compound with the highest surface roughness. How- ever, further increasing in the cutting speed increased the ex- tent oftool wear. In Fig. 3(c), flank wear and edge chipping wear are seen on the edge ofthe cutting tool used at the 100 m/min cutting speed. From Figs. 3 and 4, it can be seen that uncoated type cutting inserts CNGN–12 with entrance type S worn-out more quickly than the coated inserts type CCMT–12 with the same entrance type at low cutting speeds. With an increase in cutting speed, tool wear value decreased. Generally good agreement was observed between these experimental results and the existing literature studies. When the cutting speed was increased from 150 m/min to 200 m/min, a de- crease was observed in roughness except for CNGN as shown in Fig. 2. However, flank wear values of insert CCMT re- mained below the reference case at these cutting speeds. Pre- vious investigations on nickel-based machining confirmed that coated carbide inserts had better performance than uncoated carbide inserts and had good performance for cutting of nickel-based alloys. The results of this study are in good agreement with the existing experimental data in the literature: When the cutting speed was increased up to 200 m/min,CNGN insert worn out to excessively but the other insert re- mained below the reference case. At this cutting speed, the types oftool wear are shown in Figs. 3(a) and 3(b). All inserts were worn out beyond the reference value of 270 m/min cut- ting speed. As a result, the CNGN insert resisted only at low cutting speeds. At high cutting speeds, the CCMT insert showed better performance compared to the other insert. The recommendation for tool inserts for cutting the Hastelloy-276 are coated CCMT at high cutting speed, whereas CNGN insert is not suitable for cutting Hastelloy-276 at high speed range.

Access to the measuring point of contact area was practi- cally limited, with very small area to be measured, and ex- tremely steep gradient of temperature existing in the small area ofthe cutting edge. The tool and the workpiece must be isolated electrically from the machine tool to obtain an accu- rate signal [19]. Finite element analysis was used to measure the temperature ofcutting tool–workpiece contact area. Fig. 9 shows the peak temperature ofthe tool rake face for the six baseline cutting experiments at two tool tips and four cutting speeds; the peak tool temperature is independent ofthe feed which is understandable since the tool cutting edge radius (0.8 mm) was used. The peak tool temperature increased signifi- cantly from about 690°C at 100 m/min, cutting speed to 790°C at 270 m/min cutting speed for the insert tip CNGN- 12, with tool life ending within this range while it increased from about 700°C at 100 m/min cutting speed to 980°C at 270

5iMX.com 我爱模型 玩家论坛 ——专业遥控模型和无人机玩家论坛（玩模型就上我爱模型，创始于2003年）

5iMX.com 我爱模型玩家论坛 ——专业遥控模型和无人机玩家论坛（玩模型就上我爱模型，创始于2003年）