Milling
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l li
Mi
ng
–
A
sim
ple
e
oic
ch
!
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Experts required?
No – Just follow some basic rules.
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Face milling
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Square shoulder milling
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Disc milling
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Copy milling
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Plunge milling
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High feed milling
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Thread milling
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Solid Carbide milling
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Mini milling cutters
A full range cutters from 0,004” up to
0.080” diameter.
62HRc Phone Mold
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Mill Turning
Face Turnmilling
Peripheral Turnmilling
(helical interpolation ramping)
Cutter off centre-line
External
Cutter on centre-line
Internal
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Machine Capability
Insert application – insert dimensions – cutting conditions
Cutting depth ap inch
Power Turbo
Super Turbo
Micro Turbo
Nano Turbo
Feed fz inch/tooth
(Typical example)
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Nomenclature &
Cutter Geometry
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Milling Cutter Nomenclature
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Cutter Geometry
Milling cutter geometry
• Cutting forces
• Power
• Metal removal rate
Cutting edge geometry
• Tool life
• Cutting forces
Chip breaking geometry
• Chip formation
• Cutting forces
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Cutter Geometry
Cutter positioning
Entry shock
(pressure stress)
Exit shock
(tensile stress)
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The difference between milling and turning
 Varying cutting forces (stress).
 Varying cutting temperatures
(tension in insert).
 Milling has varying chip thickness.
 Turning has a constant chip thickness.
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Varying Edge Temperature
Chipping
Thermal cracks
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Cutter Geometry
γp
κ
γf
Milling cutter geometry = Positioning of the cutting edge
•
Lead angle - κ
•
Axial rake angle - γp
•
Radial rake angle - γf
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Cutter Geometry
Positive – positive
Advantages/disadvantages
+ Smooth cutting.
-
Cutting edge strength.
+ Good chip removal.
-
Unfavorable entry contact.
-
Draws workpiece away from machine
table.
+ Good surface smoothness.
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Cutter Geometry
Negative – negative
Advantages/disadvantages
+ Cutting edge strength.
-
Large cutting forces.
+ Productivity.
-
Chip obstruction.
+ Pushes the workpiece
towards the machine table.
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Cutter Geometry
Negative vs. Positive
Double negative
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Double positive
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Cutter Geometry
Positive – negative
Advantages/disadvantages
+ Good chip removal.
+ Favorable cutting forces.
+ Wide range of applications.
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Insert nomenclature &
cutting edge geometry.
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Milling Insert Nomenclature
OFER070405TN-ME15 T25M
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Edge Condition and Rake Angle
OFER070405TN-ME15 T25M
-E
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-ME
-M
-MD
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Ultra High Positive Rake
20°
24°
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Milling Cutter Application.
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Conventional
Climb
Conventional milling
•
•
Used on older machines / unstable conditions.
Unfavorable milling process.
Climb milling
•
•
Favorable milling process.
Not recommended on older machines / unstable
conditions.
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Cutter positioning
The basic problem in conventional milling is the insert entry.
•
Cutting edge radius, rubbing the edges away – not enough heat!
•
Self-hardening materials – Stainless Steel.
•
Chip jamming/obstruction.
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Cutter positioning
Climb milling can be used for most processes. The machine must have
a stable setup and spindle with no play. (Modern CNC machines)
Advantages of climb milling
 Longer tool life. The chips land behind the cutter on the surface just
milled, and will therefore not be machined again.
 Climb milling causes a downward pressure and therefore does not
lift up the workpiece.
 Better surface finish.
 Easier chip removal.
 Requires less power.
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Cutter positioning
Conventional milling
Central milling
•
Combination of climb and conventional milling.
•
Unfavorable due to varying cutting forces.
•
Unavoidable when slot milling
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Climb milling
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pitch
Arc of tool engagement.
•
Insert spacing.
•
Arc of tool engagement.
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Cutter Engagement
Under-formed chip
Undesirable, sometimes unavoidable.
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Thick chip
Desirable, better tool life.
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Cutter positioning
Entry shock
(pressure stress)
Exit shock
(tensile stress)
If possible position the cutter as shown on the right, if you can.
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Cutter positioning
Interrupted cut milling
•
•
•
Short tool life (cutting edge breakage).
Vibration problems.
This is often unavoidable!
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pitch
Milling cutter pitch
: Impact of each tooth.
: Vibration amplitude.
n
Normal pitch
o
Differential pitch
Differential pitch reduces the risk of vibration.
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Vibrations
F
Fz
Fx
The size and direction of the cutting force for a face milling cutter, 45°
entering angle
(sum of axial and radial forces perpendicular to cutting edge).
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Vibrations
Fz
F
Fx
The size and direction of the cutting force for a square shoulder
milling cutter, 90° entering angle.
(sum of axial and radial forces perpendicular to cutting edge).
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fz = hm ×
D ÷ ae × (1 ÷ sink)
Vibrations
fz = hm ×
•
•
•
D ÷ ae
Change cutter positioning
Minimise tool overhang
Improve stability
(n × π × D)
12
f = ( z or k) × fz
vc × 12
n=
π×D
•
•
•
•
vf = n ×( z or k) × fz
Decrease cutting speed
Increase feed
Decrease depth of cut
Conventional milling
Q = ae × ap × vf
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Vibrations
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Average chip thickness
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Average chip thickness
fz
Chip thickness
= Thickness of the undeformed chip at right angles to cutting edge
.. and is … constantly changing.
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Average chip thickness
fz
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Average chip thickness
fz
hm
Chip thickness
= Thickness of the undeformed chip at right angles to cutting edge
.. and is … constantly changing
THEREFORE average chip thickness is important.
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Average chip thickness
Calculating the average chip thickness, to achieve the correct cutting data
should only be applied when Ae is
LESS THAN 50%
fz
Dc
hm
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Ae = 50%
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Average chip thickness
Relationship between
feed and average chip thickness.
Radial cutting depth - Diameter of the cutter.
Cutter positioning.
Entering angle.
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Average chip thickness
fz
fz
hm
Dc
Dc
ae
hm
ae
Radial cutting depth – Diameter of the cutter
(ae/Dc ratio)
What is happening to the average chip thickness as Ae reduces?
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Average chip thickness
fz
Which will have the higher feed rate?
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Average chip thickness
Formula to calculate fz for square shoulder milling:
f z = hm
D
ae
=.004”
2.5
.118
=.004” 21 = 0.018”
legend
fz = feed per tooth
hm = average chip thickness
D = cutter diameter
ae = radial width of cut
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example
find the fz of a Turbo mill:
hm = 0.004”
D = 2.5”
ae = 0.118”
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Average chip thickness
vf = 21.5”
vf = 25.8”
vf = 48.5”
100%
20%
50%
engagement engagement engagement
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vf = 64.5
10%
engagement
vf = 103.2”
5%
engagement
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Description
ae
Width of
cut
ap
Depth of
cut
( vc )
SFPM
(fz)
FPT
(hm)
Average
Chip
(n)
RPM
(vf )
Feed
Rate IPM
Slotting 100% Engagement
1.00
.1
626
0.003
0.002
2388
21.5
Profiling 50% Engagement
.500
.1
751
0.003
0.002
2869
25.8
Profiling 20% Engagement
.200
.1
813
0.005
0.002
3228
48.5
Profiling 10% Engagement
.100
.1
938
0.006
0.002
3583
64.5
Profiling 5% Engagement
.050
.1
1001
0.009
0.002
3826
103.2
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Average chip thickness
ae
Caution!
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Average chip thickness
Caution!
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Average chip thickness
ae
Caution!
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Average chip thickness
90deg
45deg
h : 100%
h : 70%
fz : 100%
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fz : 100%
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Average chip thickness
h = fz x sin (ҳ )
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Average chip thickness
Formula to calculate fz for face
milling:
f z = hm
D
1
×
0.004” x 2.236 x 1.41 = 0.013”
κ
ae sin
legend
fz = feed per tooth
hm = average chip thickness
D = cutter diameter
ae = radial width of cut
κ = setting angle
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example
find the fz of a Octomill face mill:
hm = 0.004”
D = 4”
ae = 0.8”
κ = 43o
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Average chip thickness
Relationship between
feed and average chip thickness.
Radial cutting depth - Diameter of the cutter.
Small ae/Dc gives larger feeds.
Cutter positioning.
Single sided cutting gives larger feeds.
Entering angle.
Smaller angle of engagement gives larger feeds.
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Average chip thickness
Feed and average chip thickness
Average chip thickness.
If too large Æ broken inserts.
If too small Æ extra wear.
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Average chip thickness
For 90° lead angle cutters only
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Average chip thickness
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Cutting edge geometry
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Cutting edge geometry
.
Difficult
machining
strong edges
SE..
AFTN
-D16
D
SE..
AFTN
-MD15
MD
M
SE..
AFTN
-M14
ME
SE..
AFTN
-ME10
SE..
AFTN
-ME13
SE..
AFTN
-M15
SE..
AFTN
-M16
SE..
AFTN
-ME15
Easy machining
E
sharp edges
SE..
AFN
-E07
SE..
AFN
-E12
10
15
decreasing
chip thickness
increasing
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Cutting edge geometry
– The vertical axis specifies the degree of difficulty in the
machining operation (i.e. E = Easy, M = Medium etc.)
– The horizontal axis denotes the application range. The
numbers indicate the average chip thickness in mm,
10 meaning 0.1mm or 0.004”
13 meaning 0.13mm or 0.005” etc.
XOMX 180608TR-ME13 F40M
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Cutting edge geometry -ME06 example
– ME06 geometry is for medium
easy machining operations
– hm should be kept at 0.06mm
(0.002”) under normal
conditions and for average
material
(Seco material group 3-5)
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Cutting edge geometry -M10 example
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–
M10 geometry is for medium
machining operations
–
hm should be kept at 0.10mm
(0.004”)under normal
conditions and for average
material
(Seco material group 3-5)
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Cutting edge geometry
• To maintain maximum tool life, it is crucial to exceed or
at least equal the edge protection chamfer.
•
Cutting speed can also be increased in side milling operations
thereby optimizing the application.
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Milling methods
1. Peeling Method
2. High speed machining
3. High feed machining
4. Plunge milling
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Peeling method
•Small radial cutting depth
•Deep cutting depth
•High cutting speed
•Spiral Cutter
•Roughing method which normally eliminates semi-finishing
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Peeling method
Ae= .060”
Ap= 0.600”
MM12-12015-B90A30-E05 Rpm=6630 Vf= 70 inch/min
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High speed machining
•Small cutting depth
•Small radial cutting depth
•Small average chip thickness
•High cutting speed
•Sharp cutting edges in hard grades
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High feed milling
•Small cutting depth
•Very high feed per tooth
•High cutting speed
•Good method in hardened steel and difficult material
•Roughing method which normally reduces the cutting
depth for semi-finishing
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High feed milling
Minimaster
high feed insert
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R227.21
high feed cutter
Jabro
high feed cutter
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Plunge Milling
•Method mostly for long overhang or weak machines
•Normal cutting speed
•Good method for difficult material like Inconel
•Roughing method which normally increase productivity
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Plunge Milling
Tool 1
Tool= R220.79-0080-12
V= 524 sft/min
Fz= 0.006” per/tooth
Side step = 3/8”
Tool 2
Tool= L217.79-3250-13
V=524 sft/min
Fz= 0.005” per/tooth
Side step= ½”
Tool 3
Tool= R217.79-2532-09
V= 524 sft/min
Fz= 0.004” per/tooth
Side step= ¼” then .040”
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Trochoidal Milling
The Trochoidal method is a fast and
productive method for slotting
operations.
Dc
Step
over
Width
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Surface Finish
Small radius corner insert
Large radius corner insert
Faceted corner insert
Faceted insert plus
Wiper insert
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Surface Finish
Axial run-out with a non
adjusted cutter.
Cassettes give a better surface finish when correctly adjusted.
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Surface finish & tool life.
Tool tolerances
Tool life
Measured with a
reference insert
Modern
Classic
Run - out influences
• The tool life.
• The surface finish.
• Machining noise level.
Axial/radial run-out
(Typical example )
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Milling insert clamping
Common method uses a screw though the insert.
•
The insert is clamped in the centre, screw head below insert!
•
This system is commonly used for modern milling cutters.
•
This system allows the use of modern chip face geometries.
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Maintenance
• Always clean the insert seating before clamping a new insert in place.
• Always replace damaged anvils or the tool if the insert seating is
damaged. Never use re-built (welded) tools.
• Replace damaged screws and keys. Lubricate moving parts regularly.
• Always use the correct keys (dynamometric keys).
• Always position the insert carefully before clamping it in place. Make
sure the insert fits flush against the supports. If the insert is not
positioned correctly, it will not be clamped properly (insert breakage).
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Milling
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