3. The three components of turning forces (Fx, Fy and Fz)
are noticed to be higher using uncoated carbide insert in
finish hard turning compared to multilayer TiN and ZrCN
coated carbide inserts. Thrust force (Fy) is found to be
the larger component of turning forces. Chipping and catastrophic
failure of uncoated carbide insert is primarily due
to such higher thrust force (950 N) and found unsuitable in
hard turning within the parameter investigated. It is also
evident that turning forces for ZrCN coated carbide insert
are slightly lower than TiN coated carbide insert during
machining. This reason may be attributed due to the higher
growth of wear during initial period of machining using
TiN coated carbide insert.
4. The surface roughness is within the recommended
range of hard turning, i.e. within 1.6 lm for both multilayer
coated carbide inserts. From the study, it is evident
that, the multilayer coated carbide inserts have performed
well at a combination of cutting speeds (150 m/min), feed
(0.15 m/min) and depth of cut (0.4 mm). However multilayer
TiN coated carbide insert performed well compared
to ZrCN coated carbide insert due to steady wear growth
and higher tool life.
5. From 1st and 2nd order regression model, 2nd order
model explains about 98.3% and 86.3% of the variability
of responses in predicting new observations compared to
1st order model and indicates the better fitting of the
model with the data. Also, the predicted value and the
actual values for both flank wear and surface roughness
are very close to each other showing the significance of
second order model developed for multilayer TiN coated
carbide insert in hard turning.
6. For multilayer ZrCN coated carbide insert, 2nd order
flank wear model fits well and found to be statistically significant
compared to 2nd order surface roughness model.
7. The savings in machining costs using multilayer TiN
coated inserts is 93.4% compared to uncoated carbide and
40% to ZrCN coated carbide respectively in finish hard
machining taking flank wear limit of 0.3 mm.
8. A cost analysis, based on a single cutting edge, shows
that the multilayer TiN coated carbide tools are capable
of reducing machining costs, and therefore, will be an
important complement to uncoated and ZrCN coated tools
for finish hard turning applications.