Machinery's Handbook, 31st Edition
1150
Machining Power
P c =
=
. kW 169 094 181 130 374 . . × × . . × =
K CQW p
E P
P m = c = = Whenever possible the maximum power available on a machine tool should be used when heavy cuts must be taken. . . 080 374 4677 . kW The cutting conditions for utilizing the maximum power should be selected in the following order: 1) select the maximum depth of cut that can be used; 2) select the maxi- mum feed rate that can be used; and 3) estimate the cutting speed that will utilize the maxi- mum power available on the machine. This sequence is based on obtaining the longest tool life of the cutting tool and at the same time obtaining as much production as possible from the machine. The life of a cutting tool is most affected by cutting speed, then by feed rate, and least of all by depth of cut. The maximum metal removal rate that a given machine is capable of machining from a given material is used as the basis for estimating the cutting speed that will utilize all the power available on the machine. Example: A 160–180 BHN gray iron casting that is 6 inches wide is to have 1 ⁄ 8 inch stock removed on a 10 hp milling machine, using an 8 inch diameter, 10 tooth, indexable insert cemented carbide face milling cutter. The feed rate selected for this cutter is 0.012 in/ tooth, and all the stock (0.125 inch) will be removed in one cut. Estimate the cutting speed that will utilize the maximum power available on the machine.
K p = 0.52 (From Table 1a) C = 1.00 (From Table 2) W = 1.20 (From Table 3) E = 0.80 (From Table 4) . . m = =
E K CQW p
Q K CW P E max
. 052 100 120 10 080 # # # .
3
. 1282
in
/
min
P
c
m
=
=
m
p
Q
. 1282 171
. / in
min
wd = = = = max
f
Q f wd m =
h
^ ^ a
=
. 6 0125 . 0012 10 17 #
m
N f n f max
. 1424
rpm
f
f n N
h
=
=
m t t
# # #
t t
. 12 8 142 2983 =
N D V 12 =
π
π
fpm
V DN 12 =
k
=
π
Calculated cutting speed of 298.3 fpm is correct, but very low for available cutting tools. Today, milling of gray irons is performed, mostly, using cubic boron nitride in- dexable inserts. Typical range of the cutting speed for milling with large engagement (0.8) and 0.004–0.008 inch per tooth chip load is 2700–2000 sfm. Estimating maximum productivity of cutting should be based on the recommended cutting speeds versus work materials. Example: A 3.2 mm deep cut is to be taken on a 200–210 BHN AISI 1050 steel part using a 7.5 kW geared head lathe. The feed rate selected for this job is 0.45 mm/rev. Estimate the cutting speed that will utilize the maximum power available on the lathe.
K p = 2.32 (From Table 1b) C = 0.92 (From Table 2) W = 1.30 (From Table 3) E = 0.80 (From Table 4)
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