Download - Cutting Speed Feed for milling machine
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Cutting Speed,Feed, and Depth of
CutSession 13
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Efficiency of a MillingOperation
Cutting speed Too slow, time wasted
Too fast, time lost in replacing/regrindingcutters
Feed
Too slow, time wasted and cutter chatter Too fast, cutter teeth can be broken
Depth of cut Several shallow cuts wastes time
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Cutting Speed
Speed, in surface feet per minute sfm ormeters per minute smm at which metalmay be machined efficiently
Work machined in a lathe, speed inspecific number of revolutions per min(r/min) depending on its diameter to
achieve proper cutting speed In milling machine, cutter revolves r/min
depending on diameter for cuttingspeed
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Important Factors inDetermining Cutting
Speed
Type of workpiece material
Cutting tool material
Diameter of cutter
Surface finish required
Depth of cut taken
Rigidity of machine and work setup
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Milling Machine CuttingSpeeds
High-Speed Steel Cutter Carbide CutterMaterial ft/min m/min ft/min m/min
Alloy steel 4070 1220 150250 4575
Aluminum 5001000 150300 10002000 300600Bronze 65120 2035 200400 60120
Cast iron 5080 1525 125200 4060
Free m steel 100150 3045 400600 120180
Mach steel 70100 2130 150250 4575
Stnless steel 3080 1025 100300 3090
Tool steel 6070 1820 125200 4060
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Inch Calculations
For optimum use from cutter, properspeed must be determined
Diameter of cutter affects this speed
D
xCS
x
xCS
xinncecircumfere
ftCSr 4
141633
12
141633
90
...)()(min/
Calculate speed required to revolve a 3-in. diameterhigh-speed steel milling cutter for cutting machine
steel (90 sf/min).
simplify formula
1203
360
3
904
xr min/
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Metric Calculations
Formula for r/min of the milling machine
using metric measurement
)()(
x.D(mm)x)(min/
mmD
xmCS
D
CSxxmCSr 32014163
10001000
simplify formula
Calculate the r/min required for a 75 mm diameter
high-speed steel milling cutter when cutting machine
steel (CS 30 m/min)
12875
9600
75
32030min/
x
r
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Cutting Speed Rulesfor Best Results
1. For longer cutter life, use lower CS inrecommended range
2. Know hardness of material to be machined3. When starting, use lower range of CS and
gradually increase to higher range
4. Reduce feed instead of increase cutter
speed for fine finish5. Use of coolant will generally produce better
finish and lengthen life of cutter
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Milling Machine Feed
Distance in inches (or mm) per minute thatwork moves into cutter Independent of spindle speed
Feed: rate work moves into revolving cutter Measured in in/min or mm/min
Milling feed: determined by multiplying chipsize (chip per tooth) desired, number of teeth in
cutter, and r/min of cutter Chip, or feed, per tooth (CPT or FPT): amount
of material that should be removed by eachtooth of the cutter
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Factors in Feed Rate
1. Depth and width of cut
2. Design or type of cutter
3. Sharpness of cutter
4. Workpiece material
5. Strength and uniformity of workpiece
6. Type of finish and accuracy required
7. Power and rigidity of machine, holdingdevice and tooling setup
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Recommended Feed PerTooth - HSS
Slotting
Face Helical and Side
Mills Mills Mills
Material in. mm in. mm in. mmAlloy steel .006 0.15 .005 0.12 .004 0.1
Aluminum .022 0.55 .018 0.45 .013 0.33
Brass and bronze
(medium) .014 0.35 .011 0.28 .008 0.2
Cast iron
(medium) .013 0.33 .010 0.25 .007 0.18
Sample Table
See Table 60.2 in Text
Table shows feed per tooth for roughing cuts
for finishing cut, the feed per tooth would be
reduced to1/2 or even 1/3 of value shown
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Recommended Feed PerTooth Cemented Carbide
Slotting
Face Helical and Side
Mills Mills Mills
Material in. mm in. mm in. mm
Aluminum .020 0.5 .016 0.40 .012 0.3
Brass and bronze
(medium) .012 0.3 .010 0.25 .007 0.18Cast iron
(medium) .016 0.4 .013 0.33 .010 0.25
Sample Table
See Table 60.3 in Text
Table shows feed per tooth for roughing cuts
for finishing cut, the feed per tooth would be
reduced to1/2 or even 1/3 of value shown
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Ideal Rate of Feed
Work advances into cutter, eachsuccessive tooth advances into workequal amount
Produces chips of equal thickness Feed per tooth
F = no. of cutter teeth x feed/tooth x cutter r/min
Feed (in./min) = N x CPT x r/min
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Feed Calculations
Inch Calculations
Find the feed in inches per minute using a
3.5 in. diameter, 12 tooth helical cutter to
cut machine steel (CS80)
First, calculate proper r/min for cutter:
91
53
8044
.
min/
x
D
CSxr
Feed(in/min) = N x CPT x r/min
=12 x .010 x 91
= 10.9 or 11 in/min
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Feed Calculations
Metric Calculations
Calculate the feed in millimeters per minute
for a 75-mm diameter, six-tooth helical carbide
milling cutter when machining cast-iron (CS 60)
First, calculate proper r/min for cutter:
25675
20019
755
32060320
,min/
x
D
xCSr
Feed(in/min) = N x CPT x r/min
= 6 x .025 x 256
= 384 mm/min
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Direction of Feed:Conventional
Most
common
methodis to feed
work
against
rotationdirection of
cutter
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Direction of Feed:Climbing
When cutter
and workpiece
going in same
direction
Machine
equipped with
backlasheliminator can
increase cutter
life up to 50%
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Advantages of ClimbMilling
Less edge breakout
Thickness of chip tends to get smaller as
nears edge of workpiece, less chance of
breaking
Easier chip removal
Chips fall behind cutter
Lower power requirements Cutter with higher rake angle can be used
so approximately 20% less power required
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Disadvantages of ClimbMilling
Method cannot be used unless machine
has backlash eliminator and table gibs
tightened
Cannot be used for machining castings
or hot-rolled steel
Hard outer scale will damage cutter
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Depth of Cut
Roughing cuts should be deep
Feed heavy as the work and machine will
permit
May be taken with helical cutters having
fewer teeth
Finishing cuts should be light with finer
feed Depth of cut at least .015 inch
Feed should be reduced rather than cutter
speeded up