Basics of End Mills

Contents
1. Cutting and Cutting Tools
2. Processing by End Mills

3. Cutting Action andPhenomena during Cutting

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Contents
1. Cutting and Cutting Tools
2. Processing by End Mills

3. Cutting Action andPhenomena during Cutting

Copyright © UNION TOOL CO. All rights reserved.

What is “Cutting”?
What is “Cutting”?
Making products having desired surface shape by...
•putting and moving a cutting tool on a work piece,•and separating unnecessary parts as chips by breaking with internal stress.

Image drawing

Image drawinga) Cutting work piece by chiselb) Scraping an edge of work piece by cutting tool・Plastic deformation on both sides of the cutting part・Need big force to pushing in・ Plastic deformation occurs only to cutting chips
・Work piece itself does not deform

Material of work piece

Features

Metals, woods, plastics, etc.

Higher accuracy than chip-less processing

Rapid progress and diversification of cutting technology

Systematic understanding to phenomena is important
to use cutting process effectively!
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Tools for Cutting
Milling cutter
Tool bitTool bit
Chip

Shank

Work piece(Cutting image by tool bit)

A cutting tool for lathe, planer, shaper, boringmachine, etc.

ReamerA rotary cutting tool having many
cutting edges on the periphery or
an end face of a cylinder and a
cone.

Drill
A tool for drilling.
Cutting edges are
only on a top.

End mill

A cutting tool for making inside wall of adrilled hole smooth and accurate.

Features of each tool

A multi-functional tool which has cutting edges on
the periphery and an end face.
Side milling, curved surface milling and drilling are
possible only by one tool.

With few cutting edges...Inexpensive production and re-grinding
With many cutting edges...High cutting efficiency

Understanding of features of each tool and also cutting actions areimportant for economical & efficient processing!
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Cutting Related Parts and Names
Cutting tool

Instrument for cutting
Also called simply “Tool”

Rake face

Finished surface

Tool surface in contact
with cutting chipCut surface

Cutting chip

Relief faceRemoved unnecessary part

Opposite side of rake faceCut surface

Surface before cut

Cutting edge
Work pieceIntersection of rake face andrelief face on tool point

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Work Material vs. Tool Material —Comparison of Hardness—
Vickers
hardness

Rockwellhardness4000

ex. TiSiN based coat.

3500
3000

ex. AlCrN based coat.

2500

TiN Coating•Tool materials need more than 3 or 4 times thehardness of work material in Vickers Hardness.

•Cemented carbide tool can process work
materials up to 30HRC. Processing 40HRC is alittle difficult.
High-speed steel tool is not possible to process
hardened steels.

2000

CrN Coating

1600

Coating

～
～

1400
1300
1200
1100
1000
950
900
850
800
750
700
650
600
550
500
450
400
350
300
250

Cemented carbide（WC-Co）

65HRC
60HRC

50HRC
40HRC
30HRC

Highhardness
hardenedmaterials
Mediumhardness
hardenedmaterials

High speed steel(Cover the hardness of tool material)

If coated tools need  x4 harder than work
material...
•40HRC Hardened steels>>> Tool materials need  1600Hv
CrN (Little difficult) TiN (Available)•50HRC Hardened steels>>> Tool materials need  2000Hv
TiN (Actually difficult) AlCrN (Available)•65HRC Hardened steels>>> Tool materials need  3300Hv
TiSiN based coating is available
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Coating —Purpose of Coating—
To improve tool life andcutting ability...

Coating is expected to have...
Hardness

to make cutting edge stand on work piece

Heat resistance

Apply coating technology
Tool obtains new characteristics bycovering tool surface with coating.

not to change in quality underhigh temperature during cutting

Toughnessto stop chipping of cutting edge

Lubricity

to control friction during cutting

Coating methods
PVD method (Physical Vapor Deposition)
Coating method by reacting evaporated metal and reaction gas.
Process temperature is relatively low (500°C).

CVD method (Chemical Vapor Deposition)
Coating method by thermochemical reaction.
Able to deposit on complicated shape, but cannot apply to somematerials because of high treatment temperature (900-1000°C).
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Coating —Actual Use of Coating—Types of coating
Ceramic-base coating
Highly hard and heat resistant. Characteristic can be changed by adding other elements.

Diamond coating
Excellent hardness and anti-welding ability toward non-ferrous metals.
(Coatings constructed by carbon atoms is not suitable for ferrous materials.)

DLC (Diamond-Like Carbon) coating
Carbon based coating which is excellent in smoothness and lubricity, but not as hard as diamond.

Multi-layer coating
High-hardness and high-lubricity layer
High-toughness layer

High adhesion layer

Work piece

Achieved high-performance coating by piling up aplurality of coating which has various characteristics.

Understanding of characteristics & uses of coatings>>>Improvement of tool life and cutting ability
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Summary
What is “Cutting”?

Machining method which puts a hard cutting tool on a part near a edge of awork piece and separates cutting chips by causing plastic deformation.
Advantages of cutting•Application for various work materials•Relatively high machining accuracy
Cutting and tools•Understanding features of each tools and appropriate use are importantfor economical & efficient processing.
•Tools need to be more than 3 times harder than a work material.

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Contents
1. Cutting and Cutting Tools
2. Processing by End Mills

3. Cutting Action andPhenomena during Cutting

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Types of End Mill Processing
Slotting

Side milling

Tapering

Profiling

Contouring

Pocket milling

Ribbing

Spot facing

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Processing Method —Down Cutting vs. Up Cutting—
Basically down cutting is recommended.
Generally down cutting is recommended for the whole range of metal processing
considering direction of deflection and finished surface quality.
For resin materials, up cutting sometimes makes better finished surface.

Down cutting

Up cutting

Remaining: Allowance for rework

Too much cut: Recovery is impossible
Direction of deflection

Target finished surface

Feeding
direction

Feeding
direction

Direction of deflection
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Up Cutting
Impact to contact material……. Small>> Small chipping toward black surface of materialHigh milling temperature because of slip phenomenon>>X Large relief face wearing

Cutting chip
Slip phenomenon

Milling area

Thickness of
cutting chip

Slip phenomenon: a cutting edge does not cut but rub a work piece because of too small cutting depth

Direction of rotation
Feeding direction
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Down Cutting
Low milling temperature because of no slip>> Small rake face wearing
Large impact at a time of biting>>X Large chipping toward materials with black rustCutting chip
ImpactMilling area

Thickness of
cutting chip

Direction of rotation
Feeding direction
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Right/Left Cutting Edge
Direction of rotation differs in direction of cutting edge
Cross-section of end mill
Right cutting edges

Left cutting edges

Direction ofcross-sectional
observation
Direction of rotation

Direction of rotation

Clockwise

Counter-clockwise

A tool rotates clockwise is called “Right cutting edge”.
A tool rotates counter-clockwise is called “Left cutting edge”.
Ordinary end mills are “Right cutting edge” and “Left cutting edge” are very rare.
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Right/Left Twisted Blades
Direction of chip evacuation differs in direction of Helix.
Right cutting edges & right Helix

Direction of
cutting chip flow

Raised upward

Right cutting edges & left Helix

Direction of
cutting chip flow

Lowered downward

Right edges & right Helix: cutting chips are evacuated upward
Right edges & left Helix: cutting chips are evacuated downward
Ordinary end mills are “right edges & right Helix” and “right edges & left
Helix” are very rare.
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Terms Used for Parameters 1
Parameter

Conventional Recommended
expression
expression

Unit

Meaning

Velocity

V

Vc

m/min

Moving distance of an optional point on the circumference per unit
(1min)

Spindle Speed

N

n

min-1

Revolutions per min

Feed RateF

Vf

mm/minMoving distance in direction of feed per unit (1min)

Feed per tooth

Sz

fz

mm/t

Lateral moving distance from one tooth comes to another does

Feed

f

f

mm/rev

Lateral feed rate (moving distance) per one rotation

Number of flutes

Z

Z

-

Number of tool flutes

Axial depth

Ad

ap

mm

Axial cutting amount

Radial depth

Rd

ae

mm

Radial cutting amount

Pick feed

Pf

Pf

mm

Moving distance of tool

Example of side milling

Example of slope milling

Feed Rate Vf

Velocity Vc
Spindle Speed nRadial depth ae

Axial depth ap

Pick feed Pf
Axial depth ap

Work piece
Number of flutes Z

Pick feed Pf

Radial depth ae
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Terms Used for Parameters 2
1. Velocity (peripheral speed) Vc [Unit: m/min]… Moving distance of an optional point on the circumference per unit (1 minute)Related values

Diameter D [mm]Twice of the distance from the rotational center (radius)

The circular constant = 3.14 (Unit: Nil)Spindle Speed n [min-1]

Revolution per minute [Number of revolutions / min.][min-1]=[rpm: revolutions per minute]Circumferential length = Diameter x  = D [mm]Velocity (peripheral speed) Vc: Moving distance per minute = Circumferential length x Spindle rotation speed

Vc = x D [mm] x n [min-1]
1 [min][mm/min]

Unit conversion: 1mm=1/1000 m
D [mm]=D/1000 [m] therefore...

Vc = x D [mm] x n [min-1]
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Terms Used for Parameters 3
2. Feed per tooth fz [Unit: mm/t]
Related Values

Feed Rate Vf [mm/min]Moving distance (of machine axis) in direction of feed per minute

Spindle Speed n [min-1]

Revolutions per minute [Number of revolutions / min.][min-1]=[rpm: revolutions per minute]

Number of flutes z [t]Number of flutes

The amount of feed per rotation f [mm/rev] is as below. (rev=revolution: rotation）

f=

Vf [mm/min]
Vf mm
min
=
[
]×[
]
n [rev/min]
n
min
rev
Vf
=
[mm/rev]n

In case of 2 flutes

The amount of feed per tooth fz [mm/t] is...
calculated by dividing the amount of feed per rotation by
number of tooth (flutes) which contributes for milling.

fz=

f [mm/rev]z=

Vf[mm/t]
n×z

Direction of rotation

Feeding
Direction

f=f/z=f/2 [mm/t]

f=fz×2 [mm/rev]

The other items used for parameters
Radial depth : ae
Axial depth : ap
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Contents
1. Cutting and Cutting Tools
2. Processing by End Mills

3. Cutting Action andPhenomena during Cutting

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Cutting Action
Model diagram of cutting action
Cutting direction

Cutting chip
Share surface

Cut surface

Cutting tool

Finished surface

Procedure of cutting
Cutting edge moves forward
Rake face compresses a part to bechipped off and share occurs

Cutting chips are evacuatedfollowing rake face of cutting edge

(Work piece)
A state of cutting a part close to an edge of a work piece.

•Plastic deformation occurs only on cutting chips and there is almost no
deformation on a work piece.
•Shape of cutting chips changes by cutting conditions.
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Shape of Cutting Chips
Share shape

Tear shape

Crack shape•Deformation of cutting
chips  repeat Sharing•Finished surface is notgood as Flow shape.

•Cutting chips pile up on atool and finally large tear iscaused.
•A finished surface has
scars and remarkably bad.

•Crack occurs during
deformation of cutting
chips and they becomecrack shape.
•Crack makes finishedsurface remarkably worse.

-•Fragile of work piece•Low thermal conductivity•High ductility•Fragile of work piece-•Increase cutting speed•Decrease cutting depth
and increase cutting speed•Increase cutting speed anddecrease feed per toothMeasureReasonCharacteristic

Schematic diagram

Flow shape

Tool

Workpiece•Cutting chips continuously
flow on a rake face.
•Load on cutting edge isconstant and a smooth surface
is obtained.
•Most desirable shape.
Note: Too long cutting chips disturb
cutting instead. need Breaking
cutting chips in certain length (bytool geometry, coolant, etc.).

Shape of cutting chips is information source of cutting situation.
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Shape of Cutting Chips —Heat Generation & Cutting Temperature—
Color of cutting chips

Tool

Conversion

Heat energy（Cutting heat）

Work material

Ex. of chipsby milling

Cutting chips
CuttingchipWork Material

800°C

Frictional heatgenerated between
tool and cutting chip

700°C

Tool

Generation of heat byplastic deformation ona share surface

High

Frictional heat generated
between a tool and afinished surface•Cutting chips change color by cutting temperature.
> By change of chip color, cutting temperature can be estimated.

600°C< Cutting temperature >Powerfor cutting

Low
200°C

Cutting heat is a very important element for tool life!
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Difference of Tool Shape & Cutting Chips
2-flute type

CFB/CFLBWide
 Ideal shape

WideComp. E

Comp. A

Narrow

X Compressive
deformation

X Curled

Narrow
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Setting of Milling Condition
How to increase milling efficiency while reducing tool damage...
Velocity (Spindle Speed)

Axial depth ap

Feed per tooth

Radial depth ae

Velocity (Spindle Speed)

Which should be adjusted?

Feed(Work piece)(Direction ofrotation)

Axial depth ap(Work piece)

Feed per tooth

Radial depth ae

Study caseTool: HMS 6100-2200 (10 x Length of cut: 22)
Work material: SKH51 (63HRC)
Coolant: Air blow Details: Side milling
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Optimization of HMS Milling Condition for SKH51nmin-1

Velocitym/min

VfFeed per tooth
mm/min
mm/t

ap
mm

ae
mm

Efficiency
mm3/min

1

4000

125.6

1350

0.0563

10

0.15

2025

2

3000

94.2

1000

0.0556

10

0.15

1500

3

2000

62.8

675

0.0563

10

0.15

1013

4

2000

62.8

675

0.0563

20

0.2

2700

5

2000

62.8

1000

0.0833

20

0.2

4000

6

2000

62.8

1000

0.0833

20

0.4

8000

Condition Cutting chips

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Optimization of HMS Milling Condition for SKH51
Tools after milling on each condition
Condition

Radial relief
face

Condition１-３: Tools after 9000ｍｍ3 milling
Condition ４-６: Tools after 50000mm3 milling (20min milling with No.5)

Rake face

Cuttingchips

Efficiency[mm3/min]

1

2025

2

1500

3

1013

4

2700

5

4000

6

8000
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Phenomena during Cutting —Build-up Edge—
Various phenomena during cutting become obstacles to processing.
Build-up edge...A phenomenon that a part of cutting chips covers a cutting edge andexhibits cutting function instead of the cutting edge.

Formation cycle of build-up edge
A part of cutting chips adheres to a
tooth part and covers a cuttingedge (formation of build-up edge).

Adhered substances grow graduallywhile exhibiting cutting function
instead of the original cutting edge.
>>Surface roughness becomes worse.

GrowthTool

Tool

Build-up edge
(A flow of work materials
and cutting chips)

Tool

Measures

Build–up edge drops off at a certain size.
>>Tool life decreases.

•Increase cutting speed and raise temperature•Provide high lubricity cutting fluid
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Phenomena during Cutting —Chattering—Various phenomena during cutting become obstacles to process.
Chattering
Phenomenon•On cutting processing, resonance occurs among awork piece, a tool and a machine and stripes appear
on a finished surface.
Influence•Surface roughness becomes worse and tool life
decreases.
•Sometimes difficult to continue because ofchattering.
Measures

Stripes appeared on a work piece bychattering•Adjust clumping of a work piece and a tool
(overhang) and a movement component of a machine.
•Adjust quantity of cutting motion such as cutting
speed, Feed Rate, axial/radial depth, etc..
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Cutting Resistance —Each Component—
Cutting resistance...Reaction force caused when a cutting tool is pushed into a work piece.
It is considered as three force components.
Feed force

Direction of rotation
Feeding direction

Horizontal force
component in a feed
direction.
It determines a magnitude
of feed power for cutting.

Cutting force
Force component acts in a direction
vertical to feed force. It affects heating
value during cutting.
In addition, power requirement during
cutting is calculated by a magnitude of
cutting force.

Work piece

Thrust force
Axial force component.
It becomes force to deform a workpiece and a tool, and decreases
accuracy when it is large.

(ex. In case of round cutting by a lathe)P=

Fxv
60 x 102 x η

P: Cutting power requirement (kW)
F: Cutting force (kgf)
v: Velocity (m/min)
η: Mechanical efficiency

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Cutting Resistance —Magnitude and Changing Factor—•“Cutting force” is especially important among three force components(because it is a factor determining power requirement and heat generation ).

Generally cutting force is sometimes referred to “cutting resistance”.
•Cutting resistance (cutting force) changes according to cutting conditions.
Factors which may change cutting force (general tendency)
Cutting resistance(cutting force)

Small

Large

Note

Work material

Soft

Hard

―

Large rake angle

Small rake angle

Cutting force decreases when rake
angle is up to about 30°.

Large

Sometimes cutting force decreases
by reducing cutting depth andincreasing Feed Rate.

Slow

Cutting force does not change somuch in velocity over certain highspeed.

Tooth part geometry(Rake angle)

Milling area

(Cutting depth x Feed Rate)

Velocity

Small

Fast

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Cutting Fluid —Functions—Cutting fluid is supplied to a cutting area to obtain fine surface and extend
tool life on cutting processing.

3 functions of cutting fluid
Tool
Lubrication•Prevention of friction among
cutting edges, cutting chips
and a finished surface•Prevention of occurrence ofbuild-up edge

Cleaning
Prevention of chipping andscars on a finished surface by
washing away cutting chips

Cutting fluid
Cutting chips
Work piece

Cooling•Extension of tool life by cooling tool
•Prevention of size deviation bytemperature rise of a work piece
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Cutting Fluid —Characteristics—
Requirements to cutting fluid•Be harmless to humans•Do not erode a work piece, a machine and paints

No cutting fluid can satisfy all of there
requirements.

•Has a low risk of ignition and smoking•Be small in putrefaction, degeneration, etc.

Appropriate cutting fluid differs depending on
which is important among “tool life”, “finishedsurface” and “efficiency”.

Types and characteristics of cutting fluid

Cutting fluid

Water-soluble: Fine cooling

Elements determining a capacity of non water-soluble cutting fluid

Viscosity: Low  High cleaning & cooling function
High  High lubrication function

Additive: Contained  Cutting ability improves
Non water-soluble: Fine lubricity(but there is a possibility of corrosion of a work piece or fluid
supplying equipment and outbreak of toxic gas during hightemperature milling)

Fatty oil: Contained Prevention of occurrence of build-up edge
Improvement of lubrication function
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Cutting Fluid —MQL Processing—MQL (Minimum Quantity Lubrication)...Milling method using only very small quantity of cutting fluid.
Problems of using cutting fluid
Cost: Expense for cutting fluid and an electric bill to work a pump
Environmental load: Treatment of used waste liquid,
mass consumption of electrical energy

Wish to decrease
the use amount of
cutting fluid

MQL Processing, which atomizes small quantity (2-10ml/hour) of cutting fluid by high pressure air,attracts attention. (There is a case that reduces energy cost by 25% and cutting fluid cost by 95% by adoption of MQL.)
Function of cutting fluid on MQL Processing
Entering a rake face of a tool and forming lubricant film>>Reduce frictional resistance

Cooling function
by evaporation

Tool

Minimum quantity of cutting fluid is supplied
to a cutting point by vacuum suction>>Continuation of lubrication function

MQL is a effective method using lubrication
function of cutting fluid at the most!
(Cooling might be insufficient on processing with large heating value.)

Work piece
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Tool Wear —Forms of Wear—•A cutting edge wears when continuous milling is performed.
•Tool wear shows various forms according to its factor. Notable examples are as follows.
Mechanical wear

Welding wear
A part of welded work
piece

Tool

Workpiece
Hard particles in a work piece scratch and shave
off a cutting edge.

Diffusional wear

A part of work piece is welded on a rake face, and takes
a part of the tool away when the welded piece peels off.

Chemical wear
Cutting fluid
OxygenMutual diffusion occurs between a work piece
and a tool, and a soft compound is formed.

Compound is made by reaction between a tool and othermaterials (cutting fluid, oxygen in the air, etc.) and removed.
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Tool Wear —Part of Wear—
Wear of an edge part is called as below depending on where it occurs.
Cutting chip

Tool

Work piece

Direction of cutting

EnlargeRake face wear
(Crater)Rake face

Cutting edge

Chipping

Relief face wear
Crater is-concavity that occurs near a cutting edge byrake face wear.
-likely to occur on high-speed milling ofsteels by cemented carbide tools.

When wear occurs and progresses, re-pointing of an edge part or changing
cutting tool is needed.

>>End of tool life

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Tool Life —Standard & Judgment—
Breakage and wearof an edge part

•Increase of cutting resistance•Bad finished surface quality

Re-pointing of the edge
part or changing cutting
tool is needed＝
End of tool life

Standard for judgment•Shiny stripes occur on a finished surface•Change of finished size or roughness of a finished surface reaches a certain value•Thrust force or feed force of cutting resistance increases quickly•Cutting force of cutting resistance increases by a certain value compared to a beginning of milling•Wear of an edge part reaches a certain valueStandard for judgment of cemented carbide tool life
Width of relief face wear w(mm)Max. depth of crater t (mm)Application

0.2

0.03

•Accurate light milling•Finishing of non-ferrous alloys, etc.

0.4

0.05

Milling of alloy steels, etc.

0.7

0.08

General milling of cast iron, steels, etc.

1 - 1.25

0.08

Roughing of gray cast iron, etc.
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Tool Life —Factors Determining Tool Life—
Tool life equation (F. W. Taylor)

Vc・Tm = CT=

From the equation above...
Increase of velocity (Vc)

C
￣
Vc

1
m
￣

Vc: Velocity (m/min)

T: Tool life

m: Constant

C: Constant

Decrease of tool life (T)(because of increase of cutting heat by increase of
speed on a tool end)

•Selection of heat-resistant tool material•Ingenuities to reduce cutting heat (adjustment of milling condition and appropriate use of
cutting fluid) are important!
(Recently, there are almost no tools that are directly applicable to the equation above because ofadvances in coated cemented carbide tools for improving heat resistance.
In addition, intermittent cutting such as processing by end mills shows tendency different from theequation above.)
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Summary
Cutting action

Repeating “moving of a cutting edge”, “plastic deformation” and “chipevacuation” continuously.

Cutting chips

Cutting condition, tool material & heat generation are reflected to chip form.
Information source to know a state of cutting

Phenomenaduring cutting•Build-up edge
•Chattering

Influence on tool life and a finished surface
Measures to prevent occurrence are needed.

Cutting resistanceCutting fluid

Tool life

Changes according to sharpness of a tool, cutting conditions, etc..
(Relationship to a condition of cutting, power and cutting heat)
Need to understand functions of cutting fluid and select suitable one inaccordance with the type of cutting.

Use of a tool

Deterioration of tool
condition by wear, etc.

Deterioration offinished surface quality•Pay attention to determining tool life and making a fine finished surface•Prolong tool life and improve cutting performance by coating technology
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