Cutting Speed Feed for milling machine

7/28/2019 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

Cutting Speed Feed for milling machine

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