PSI - Issue 53
12
A. Teixeira et al. / Procedia Structural Integrity 53 (2024) 352–366 Author name / Structural Integrity Procedia 00 (2019) 000–000
363
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Fig. 16. R a evolution at: (a) f=0.1 mm/rev; (b) f=0.2 mm/rev.
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Fig. 17. R z evolution at: (a) f=0.1 mm/rev; (b) f=0.2 mm/rev.
The worst surface finish was observed when machining at v c =50 m/min and f=0.2 mm/rev. As explained before, this cutting tool has experienced crater wear and pronounced notching at the tool tip, which impacted the final values of surface roughness. On the other hand, cutting speeds of v c =150 m/min have produced the lowest values of surface roughness, which is consistent with the lower cutting forces registered and less tool wear observed in comparison with the other cutting speeds. It is also possible to observe that the values of surface roughness tend to decrease with the machining time. Arrazola et al. (Arrazola et al., 2014) observed that roughness parameters increased as tool wear progressed until, the tool flank wear reached the value of 0.15 mm. Afterwards the trend is not so clear and even a decrease on the measured values was observed when tool flank wear was between 0.15 and 0.40 mm. Aspinwall et al. (Aspinwall et al., 2007) observed that the worn flank face of cutting tools plays a similar role of “wiper” and can lower the machined surface roughness. However, surface defects were detected, because of high plastic deformation on the machined surface caused by higher cutting temperatures and higher cutting forces with worn tools. This phenomenon, of decreasing surface roughness over machining time, can also be attributed to high amounts of chatter, felt during the initial stages of turning. This is, sharp and “newer” tools are more susceptible to chatter, which cause an increase in surface roughness values. Thus, work tools are more resistant to chatter, as such, a reduction in chatter during machining indicates a more stable process, causing a lower surface roughness (Schmitz & Smith, 2019). 3.4. Simulation results As mentioned, simulation of the cutting process was performed, to obtain results regarding the cutting forces and sustained wear, for a later comparison with the experimentally obtained results. The results obtained for the cutting force values are represented in Fig 18. As anticipated and confirmed in the experimental runs, an increase in feed rate causes an increase in cutting forces. Additionally, a trend that also occurred in the experimental tests is that cutting force tends to decrease as cutting speed increases.
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