Fraesen_e

TUNGSTEN CARBIDE TOOLS

Training Manual for Milling

2

Milling

Introduction

Definition - Milling

1. Technological Principles

2. Terms and Designations

3. Chip Formation

4. Tool life

5. Performance Criteria for Milling

6. Initial Contact of the Tool Cutting Edge

7. Milling Techniques

8. Milling Application Suggestions

9. Operating Methods

10. Machine Tools

11. Tool Maintenance and Care

3

Introduction

Definition - Milling


1.1 Definitions on the Tool: Cutting Edges - Surfaces - Angles

2. Terms and designations

2.1 Cutting speed vc [m/min)

2.2 Feed per teeth fz (mm/Z)

2.3 Feed Rate vf (mm/min)

2.4 Thickness of cut h

2.5 Chip thickness

2.6 Approach Angle

2.7 Axial and radial depths of cut (ap and ae)

2.8 Conditions for engagement ae/Dc<30 %

2.9 Conditions for engagement ae/Dc>30 %

2.10 Cutting arc angle

ϕ

s

2.10.1 Central position of the milling cutter

2.10.2 Offset position of the milling cutter

2.11 Positioning of the milling cutter

4

3. Chip Formation

3.1 Process for the chip formation

3.2 Types of chips

3.3 Chip shapes

3.4 Influencing factors on chip formation

4. Tool life

4.1 Permissible land of wear VBadm.

4.2 Causes of wear

4.3 Types of wear

4.4 Temperature on the tool cutting edge

4.5 Wear Characteristics

4.6 Troubleshooting

5. Performance criteria for milling

5.1 Chip production volume Q

5.2 Specific chip production volume Qp

5.3 Theoretical l power requirement PMuse.

5.4 Power and torque

6. Initial contact of the tool cutting edge

5

7. Milling techniques

7.1 Indexable insert geometries

7.2 Tool geometries

7.3 ISO code milling inserts / Designation code Walter geometries

7.4 WALTER SELECT for indexable milling inserts

7.5 Surface Finish in Milling / Quality of surface

7.6 Finish milling with surface milling cutter

7.7 Setting of milling tools, examples F2010 and F2140

7.8 Setting of milling tools, examples F2010 and F2140

8. Milling tools - Application suggestions

8.1 Tool Adaption

8.1.1 Modular attachment, NC-Tool system

8.2 Tooth spacing / Cutting edge spacing

8.2.1 Vibration and remedial measures

8.3 Milling diameter / Position of the milling cutter

8.4 Up milling - Down milling

8.5 Selecting the correct milling tool

8.6 Recommendations for an efficient operation

6

9. Operating methods

9.1 Surface milling

9.2 Shell end milling and slot milling

9.3 Shoulder milling

9.4 Copying

9.5 Milling with shank-type cutters

9.5.1 Solid carbide cutters

10. Machine-tools

10.1 Inclination of the spindle

11. Tool maintenance and care

11.1 Indexable insert

11.2 Clamping of the indexable insert

11.3 Contact surfaces

11.4 Tool maintenance

7

8

Introduction

Machining by means of chip removal involves the use of a tool, with wedge shaped cutting edge, to produce an accurate size and shape workpiece. The workpiece will be to a defined size, tolerance and quality of surface finish.

Many factors other than workpiece and cutting material, influence the profitability and efficiency of the machining process.

This metal removal training document is intended to give you a better understanding of the terminology and philisophy in the milling process.

9

10

Definition of milling

Milling is a metal removal method using a tool with a defined cutting geometry. The tool rotates and generally the workpiece feeds linearly against it. The cutting edge is continuously subjected to interrupted cuts, and varying chip thickness through the cut, producing "C" shaped chips.

The milling cutter can have either one or multiple cutting edges (teeth) with each edge removing and amount of material. Each cutting edge produces at least one chip, with a continuously varying thickness, with each rotation. Practically all the shearing work is performed by the major cutting edge. It is responsible for the quality of surface on all cut surfaces. This means on all milling surfaces which are not perpendicular to the main axis. In contrast, the secondary cutting edges determine the quality of surface on the rake surfaces. These are the surfaces which are almost perpendicular to the main axis.

11

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�

Majorcutting edge

Nosechamfer

Cornerfacet

Tool orthogonal rake

Radial angle

Approach angle

Inclination angle

Axial angle

Clearance angle

Clearance angle on the corner facet

γ

0

γ

r

χ

λγ

p

αα

1

12


Geometric relations on the tool cutting edge:

1.1 Definitions on the tool: cutting edges - surfaces - angles

Cutting edge:

The part of the tool where the chip is formed due to the relative movement between the tool and the workpiece is the cutting wedge. The cutting edge is the cutting line of the surface of the wedge.

Cutting nose

Angle at which a primary cutting edge and a secondary cutting edge, with a common rake face meet. The cutting nose can be rounded or chamfered.

Major cutting edge

Cutting edge whose cutting wedge points toward the direction of the feed if it is considered in the working level.

Secondary cutting edge

Cutting edge whose cutting wedge do not point toward the direction of the feed it they are considered in the working level.

Surfaces:

Rake face

Face on whose cutting wedge the chip flows.

Clearance surface

Surfaces on the cutting wedge which are adjacent to the cutting surfaces produced on the workpiece - primary and secondary clearance surfaces.

13

γ

o


γ

r

Radial angle

γ

p

Axial angle

χ

Approach angle

λ

Inclination angle

V

B

= Flank wear

α

1

= small clearance angle

α

2

= large clearance angle

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Angles:

Clearance angle

The clearance angle is normally between

6° and 15°

. Larger clearance angles cause slower wear on the clearance surface, smaller clearance angles increase the resultant cutting force. Clearance angles can be easily defined on ground tools (solid carbide, brazed heli or porcupine cutters) for indexable insert tools they depend upon the insert shape, and insert pocket in the cutter body.

Large clearance angles

are advantageous for milling

soft materials

such as aluminium. For

harder workpiece materials, smaller clearance angles are preferred

.

Nose angle

The angle between the clearance surface and the rake face.

It is advisable to select the largest possible nose angle. It helps the strength and

stability of the

cutting wedge.

It can be

further enhanced by additional chamfers on the rake faces and clearance surfaces

.


The angle between the rake surface and the reference plane.

The tool orthogonal rake can be either positive or negative.

Positive tool orthogonal rakes assist chip clearance and reduce the cutting force

. They enable a

more efficient use of the driving power

on the milling machine.

Negative tool orthogonal rakes

are usually used for milling short-chipping materials. The

cutting wedge is thus more stable

, the

cutting force

is however greater.

For the clearance angles, the tool orthogonal rakes and the nose angles, the rule is always: total of the angles = 90°

15

V

sp.

= Chip flow speed

V

sch.

= Shearing speed

V

c

= Cutting speed

ϕ

= Shear angle

γ

= Tool orthogonal rake

α

= Clearance angle

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2. Terms and designations

2.1 Cutting speed v

c

[m/min]

The cutting speed is the linear speed at a specific point on the cutting edge.

The

cutting speed

is an important

tool-related parameter

. It represents the most important cutting condition and it is essentially determined by the type of

workpiece material and of the cutting grade

which is used.

Experience shows that an incorrect cutting speed clearly reduces the tool life. Aiming at identical batch sizes it is thus appropriate to reduce the cutting speed in favour of the feed per tooth.

Example:

Tool diameter D

c

= 125 mm

rpm n = 500 rpm

v

c

= 196 m/min

Formula: vc

Dc π× n×1000

------------------------------ [m/min]=

vc125 π× 500×

1000---------------------------------------=

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18

2.2 Feed per tooth f

z

[mm/Z]

The feed per tooth f

z

is the feed distance between two cut surfaces which are produced consecutively, ie the feed for each tooth or each cut.

This is a measure of the load on the cutting edge

. In fact, this key-parameter

determines

the total

milling efficiency

. Although a milling tool has multiple cutting edges, the efficiency limits are defined by the output of each individual tooth.

Aiming at a maximum chip removal volume Q, it is necessary to select the largest possible feed.

In order to avoid a scraping cut which would reduce the tool life, it is necessary to exceed a certain minimum value.

An indication of the average thickness of cut for an indexable insert is used as a starting point.

The unit of the feed per tooth is: [mm/Z]

Formula: fz

vfZ n×-------------- [mm/Z]=

19

f

z

= Feed per tooth

h

m

= Average thickness of cut (chip thickness)

ϕ

m

= Cutting arc angle

v

f

= Feed rate

ϕ

s

= Average angle between tool entry and exit

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2.3 Rate of feed v

f

[mm/min]

Feed rate v

f

is the travelling speed of the tool in the feed direction. Feed rate is also called table feed and it is a

machine-related parameter

.

Conventional milling machines -> scope of feeds conditional on the machine

Machining centres -> any feed rate can be applied

Many chip removal problems, encountered when milling with indexable inserts can be avoided by increasing the feed. In practice the opposite occurs and the feed is wrongly reduced.

For milling tools with several rows i e porcupine cutters for slot milling the effective number of teeth must be taken into account. On half effective tooth cutters, 2 teeth are required to make one effective tooth for the purpose of calculating feed rate v

f

.

Formula: v

f

= f

z

x Z x n

[mm/min]

Example:

Feed / tooth f

z

= 0,15 [mm/Z]

Number of theeth Z = 6

rpm n = 900 [U/min]

v

f

= 0,15 x 6 x 900

v

f

= 810 [mm/min]

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Shapes of cutting sections

Thicknesses of cut h

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2.4 Thickness of cut h

The thickness of cut h is the thickness of the chip to be removed and it is measured perpendicular to the cutting edge.

For tools with straight cutting edge, the formula is as follows:

With small approach angles

χ

, i.e. 45°, the thickness of cut h is reduced by approx. 30 % as compared to

χ

= 90°.

As almost every carbide indexable insert is chamfered, ground or rounded, too small a feed per tooth can lead to unwanted friction, which increases the cutting force. Therefore, the feed for

χ

= 45° must be increased by approx. 40% to take into account the degree of bluntness of the cutting edge.

The smaller the setting angle of a milling tool, the more the feed per tooth must be increased in order to ensure a sufficient thickness of cut.

Formula: h = f

z

x sinc

χ

= (Kappa)

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Milling cutter

Workpiece

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2.5 Average chip thickness h

m

As the chip thickness h continuously changes during the action of the cutting edge in the workpiece material, it is appropriate to select the

average chip thickness h

m

. It is used to judge the load on the cutting edge and to

determine

the power requirements for a given milling operation

In order to determine this average chip thickness h

m

, it is necessary to consider the entrance and exit angle of the cut in relation to the length of the arc.

The average chip thickness of h

m

is calculated with the equation:

Formula:

ϕ

s

= angle of cutting arc [degrees]

hm

114 7, fz× χsin× ae Dc⁄×

ϕs-----------------------------------------------------------------------------=

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Shapes of cutting sections

Thicknesses of cut h

26

2.6 Approach angle

The operating angle -

approach angle

χ

- influences the chip section, and load on the cutting edge. Changing the approach angle, changes the thickness of cut h and the length of cut b. The setting angle is often determined by the type of machining, i.e. for shoulder milling, the setting angle is 90°. The most common angles are between 45° and 90°.

The approach angle is the angle measured between the main cutting edge and the workpiece contour. With small setting angles, the

axial force F

A

increases. This is beneficial to the machine, as the load on the milling spindle is more critical in the radial direction. The tool life is improved by the possibility of increasing the F

Z

value, and the risk of breakout on the workpiece is reduced. Higher radial forces F

R

in the direction of feed puts a bending load on the spindle (approach angle 90 degrees).

The advantage of

setting angles of 90°

lies in the machining of

unstable workpieces sensitive

to axial forces

, because the

vibration in the workpiece is reduces to a minimum due to the relatively small axial force F

A

. Little pressure is applied onto the surface to be machined.

With 45 degree approach angle it is possible to increase the table feed, as compared to 90 degrees, without overloading the insert, by increasing the feed / tooth to maintain an acceptable chip thickness. The increased feed rate can then be used to off set the reduced depth of cut.

Milling tools with indexable round inserts

have, depending upon the depth of cut, all angles from 0°- 90°. This gives an extremely stable cutting edge allowing a higher table feed thanks to the thinner chips which are generated. Modern indexable insert geometries greatly increased the range of application of milling cutters, they ensure a smooth cut and require less power and stability from the machine-tool than previously expected.

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Plain milling cutter Shank-type cutter End mill

Side and facemilling cutter End mill

Peripheral surface milling End and peripheral surface milling

Peripheral and end surface milling

Slot milling

End millingSlot milling

Shell end mill

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2.7 Axial and radial depths of cut (a

p

and a

e

)

To determine the feed per tooth, an indication of the axial and radial depths of cut is very important.

The axial depth of cut a

p

is governed by the indexable insert and the approach angle

χ

.

For full side and face milling cutters, when slotting, the axial depth of cut is identical to the tool width B.

The radial depth of cut a

e

describes the radial width of engagement of the milling tool. i.e. for mil-ling slots with side and face milling cutters, the radial depth of cut a

e

equals the depth of the slot to be milled.

a

e

is also a value with a direct influence upon the feed per tooth.

For surface milling, the dimension- and position-related relationship between milling tool and workpiece, has a critical influence It is thus necessary to take into account the width of the workpiece or the milling diameter D

c

when selecting the tool.

A

tool diameter D

c

about 30 % larger than the workpiece width

is considered as

ideal

. The tool must however be appropriate for the driving power and the stability of the machine.

(to remember easily: a

p

=

p

arallel to the rotation axis)

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30

2.8 Condition for engagement a

e

/ D

c

< 30%

Besides the

average thickness of cut h

m

and

the approach angle

χ

, it is also necessary to determine the

condition for the engagement a

e

in relation to D

c

.

Example:

1. Surface milling with a shell end cutter F3038.B.063.Z04.56

radial depth of cut a

e

= 14 mm

tool diameter D

c

= 63 mm

2. Slot-milling with a side and face milling cutter F2253.B.160.Z06.16

radial depth of cut a

e

= 8 mm

tool diameter D

c

= 160 mm

aeDc-------

1463------ 0 22 22%=,= =

aeDc-------

8160---------- 0 05 5%=,= =

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32

Engagement conditions ae/Dc < 30% have the greatest influence upon the feed calculation, as the smaller this ratio, the more the feed per tooth must be increased.

With engagement conditions ae/Dc < 30 %, the following simplified formula is valid:

Typical values for hm:

hm = 0,15 - 0,25 (steel, cast steel, grey cast iron, nodular graphite cast iron)

hm = 0,08 - 0,15 (CrNi steels, titanium alloys)

hm = 0,05 - 0,08 (non-ferrous alloys)

Formula: fz hm

Dcae-------

1χsin

--------------× [mm/Z]=

33

Plain milling cutter

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Calculation of the feed per tooth (approximate version)

Different profiling operations are performed with a shoulder milling cutter F3038.B.063.Z04.56 Dc = 80 mm (χ= 90°). The average chip thickness is given by hm = .1 mm. The radial depth of cut ae = 16 mm for the 1st pass and ae = 4 mm for the 2nd pass

1. 1st pass

Find: fz =?

given: Dc = 80 mm, ae = 16 mm, hm = 0,1 mm, χ = 90˚.

fz = 0,22

aeDc-------

1680------ 20%==

Formula: fz hm

Dcae-------

1χsin

--------------× [mm/Z]=

35

Plain Milling Cutter

36

2. 2nd milling pass

find: fz =?

given: Dc = 80 mm, ae = 4 mm, hm = 0,1 mm, χ = 90˚.

The same tool has been used for both milling operations but the feed per tooth must be increased, as calculated, due to the smaller engagement conditions. If we do not take this fact into account, the average chip thickness hm diminishes and becomes too small for a roughing operation with indexable inserts.

The consequences of a too small feed per tooth (average chip thickness hm) can appear in the form of vibration on the workpiece and tool: of a reduced tool life: poor quality of surface finish and higher specific cutting force.

≈ 0,45 (to be determined with a calculator)

aeDc-------

480------ 5%==

Formula: fz hm

Dcae-------

1χsin

--------------× [mm/Z]=

37

(mm/Z)

fz hm

Dcae-------=

38

The following tools are mainly used with engagement conditions ae/Dc < 30 %

- side and face milling cutters

- shell end cutters

- copying milling cutters

The above listed tools all have a setting angle χ = 90°. The feed-per-tooth formula can thus be further simplified:

for sin 90˚ = 1.

Note - this formula is valid only for ae/Dc < 30%%!!!

Formula: fz hm

Dcae------- [mm/Z]=

39

40

2.9 Condition for engagement ae/Dc > 30%

For surface milling, engagement conditions of 60 to 70 % would be the ideal solution for efficient chip removal. For slot-milling with porcupine cutters and shoulder milling cutters, 100 % engagement is achieved (ae = Dc ; slot-milling from solid with porcupine cutters etc.).

To calculate the exact feed per tooth for engagement conditions ae / Dc > 30 %, it is necessary to use the following formula:

ϕs = angle of the cutting arc (angle between entrance and exit of cut)

By approximation: fz ≈ hm

Formula: fz

hm Dc ϕs× π××

360 ae× χsin×---------------------------------------------------- [mm/Z]=

41

42

2.10 Cutting arc angle ϕs

2.10.1 Central position of the milling cutter

2.10.2 Offset position of the milling cutter

Formula: ϕs 2 arcaeDc-------

sin×=

Formula: ϕs 90 arcae Dc 2⁄( )–

Dc 2⁄( )----------------------------------sin+=

43

F-053

Dc0,75

Dc0,05

Cutter position for surface milling

44

2.11 Positioning of the milling cutter

The positioning of the milling tool relative to the workpiece influences both the tool life of the indexable insert and the operational smoothness.

In an ideal case, with a milling cutter sufficiently larger than the workpiece width, the milling cutter should be positioned slightly offset. This is advantageous because the entry and exit of cut are preferred from an insert load and chip formation point of view.

A centrally positioned milling cutter can be detrimental to the operation. Radial forces from the entry and exit of cut can lead to vibration in the milling spindle, damaged cutting edges and poor surface finish.

Offset positioning of the milling cutter leads to constant direction of the cutting forces.Relation Dc / ae = 4 / 3.

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theoretical thickness of cut

shear plane

shearing angle

effective chip thickness

46

3. Chip formation

3.1 Process of the chip formation

The entry of the wedge into the workpiece under shear force causes a compression of the workpiece material in front of the cutting face and it then slides as a chip on the cutting face of the tool. The chip formation is often schematically shown as a parallel displacement of thin chip lamellas, assuming an entirely homogeneous workpiece material and the formation of a flowing chip

3.2 Types of chips

We make a distinction between three types of chip regarding their formations:

- Flowing chip

- Shearing chip

- Tearing chip

The formation of the chip depends upon the ductility of the workpiece material, the cutting speed (v

c

), the thickness of cut (h, h

m

), and the microgeometry and the macrogeometry of the cutting edge as well as the chip removal temperature.

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Ribbonchips

Snarl chips

Flat helical chips

Oblique helical chips

Long cyl. helical chips

short cyl. helical chips

Spiral helical chips

Spiral chips

Helica chip Disconti-nuous chips

GOOD CHIP SHAPES

UNFAVOURABLE CHIP SHAPES ACCEPTABLE CHIP SHAPES

48

Flowing chip

The chipping process, for a flowing chip, is a uniform and uninterrupted separation process. The deviation takes place in one plane . Flowing chips occur in workpiece materials which deform and have a homogeneous structure. High cutting speed and large tool orthogonal rake helps the formation of flowing chips.

Shearing chips

Shearing chips are formed when the deformation in the shearing level exceeds the ability to de-formation of the workpiece material. They are made of entirely detached chip elements which are welded again at the root of the respective chip. Shearing chips are caused when rough machi-ning with an high thickness of cut and a low cutting speed; when machining brittle materials if the deformation in the shearing level causes a brittleness in the structrure, i.e. at the grain bounda-ries of austenitic steels.

Tearing chip

Tearing chips are formed when brittle materials showing a low ability to deformation, i..e cast iron, brass etc., are used for chip removal operations. The chips are not detached anymore but torn off from the surface. The separation area is irregular and the surface of the workpiece is often damaged by small breaking-offs.

49

Ribbonchips

Snarl chips

Flat helical chips

Oblique helical chips

Long cyl. helical chips

short cyl. helical chips

Spiral helical chips

Spiral chips

Helica chip Disconti-nuous chips

GOOD CHIP SHAPES

UNFAVOURABLE CHIP SHAPES ACCEPTABLE CHIP SHAPES

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3.3 Chip shapes

Chip shape is the shape of the chip as it leaves the cutting face of the tool at the end of cut.We make a distinction between the following chip shapes::

Ribbon chip and Nested chip

Are a risk to the security of the machining operation. They can cause damage to the workpiece surface and tool, and can take up a lot of space. They are difficult to transport and can be a cause of accident

Helical chip type A

They flow as long, uninterrupted, flat, upward-orientated helixes. Helical chips type A are wanted.

Broken chips

Are required to enable the lubricant or coolant to carry away the chips. ie CNC lathes or for deep hole drilling.

When the feed increases, the chip bends more and breaks. If the cutting speed increases, it breaks with more difficulties, tends to become a snarl and ribbon chip.Negative tool orthogonal rakes aggravate a good chip formation.

Ribbon chip Nested chip

Helical chip type A Spiral chip

Helical chip Needle chip

Fragmental and discontinuous chip

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αγ

h

h

1

ϕθ

clearance angle

tool orthogonal rake

thickness of cut

chip thickness

shearing angle

shear plane

Schematic representation of the chip formation

52

3.4 Influencing factors on chip formation

All parameters in the chip removal process have an influence upon the chip formation:

- Property of the workpiece material

- Cutting parameters (v

c

, f

z

, v

f

, a

e

, a

p

, etc.)

- Tool angles (setting angle, clearance angle, tool orthogonal rake)

- Cutting grade

- Chip removal temperature

The interaction of these influencing factors create the different types and shapes of chips.

53

Production costs - Production output

Cutting speed and feed

M = machine costsT = tool costsF = fixed costsQ = piece / hourP = production costs

Pro

duct

ion

cost

s/pi

ece

Pro

duct

ion

outp

ut

54

4. Tool life

The working life of an indexable insert is limited by the wear of the cutting edges. As soon as the cutting edge wear has reached a certain dimension, this is a sign that the tool life has reached a predetermind limit.Perfect performance of the cutting edge is expected for an application within the scope of the tool life.

For this purpose, the tool life is measured according to the number of workpieces produced, or in metre's of distance machined.If the tool life is too short, the production process is interrupted for the replacement of the tool, to the detriment of the machining time. If the tool life is too long, the productivity, has been compromised and as a result we obtain a poor utilisation ratio of the available production time.

The selection of the correct tool is, together with its correct application, a critical factor to determine the economic balance for the machining operation.

The tool wear is the damage on the cutting edge by different wear mechanisms.

Their result can be seen (magnifying glass) on the tool cutting edge.

All tools wear during the chip removal process.

The formation of the chip takes place with a continuous material removal under high pressures and temperatures at the cutting face and at the clearance surface of the cutting edge.

The cutting area brings thus ideal conditions for a series of reaction between the workpiece and the cutting material.

55

Cle

aran

ce s

urfa

ce w

ear

in m

m

Tool life Engagement time in min

56

4.1 Permissible land wear V

Badm

The wear of the clearance surface increases with the engagement duration. After a short engagement duration t, the curve rises in an above-average manner. The cause of this above-average rising curve lies in the growing increase of the wear. It is necessary to determine empirical values defining to which extent the wear can increase before the indexable insert is turned over or replaced..

Generally acceptable values for wear of the clearance surfaces

are from

V

Badm.

.2 - .8 mm.

The criterion for the tool life must be determined according to the machining operation (roughing, finishing).

The wear of the clearance surfaces is generally a reliable value to determine the economic tool life.

Reliable lands of wear as limiting factors for the tool life T:

finishing V

Badm.

= 0,2 - 0,3 [mm]

roughing V

Badm.

= 0,4 - 0,8 [mm]

57

Abrasion

Diffusion and chemical reactions

58

4.2 Causes of wear

There are five main wear causes:

Abrasive wear

This is the most common wear in the field of metal machining.

It is a form of wear which appears between two surfaces rubbing against each other.

Hard metal particles cause a grinding type process. Most workpiece material have a certain quantity of hard carbides in their structure and for this reason set highest requirements to the cutting edge with regards to hardness and a resistance to wear.The harder the cutting grade, the higher the resistance against abrasive wear.

Wear by diffusion

This is mainly a chemical reaction between the workpiece and the cutting grade taking place due to simultaneous high temperature and high pressure.

The dimension of the wear by diffusion is essentially course by chemical reaction and the hardness does not play any part in this case. The ability of the cutting material to resist this reaction with the workpiece determinds the wear. The wear appears as a crater on the cutting face due to the chip rubbing over the face.

59

Oxidation

Adhesion

Stresses due to temperature changesFormation of cracks

60

Oxidation wear

It comes as a consequence of strong pressure and high temperature,

but, as apposed to diffusion, it

needs oxygen.

The wear appears on the cutting edge at the same level as the depth of cut and causes deep indentations in this area - also called blasting wear.

Formation of cracks

Appear in a cutting material with low resistance against the high temperatures changes in the cutting area.

The temperature and the load changes on the cutting edge can lead to breakage. This type of wear can be accelerated by inconsistent use of cooling lubricant.

This type of wear occurs mainly in milling operations where the cutting edge is subjected to extreme temperature change. The edge becomes hot during cut and cool out of cut and lead inevitably to comb shaped cracks.

Wear by adhesion

It generally occurs at low machining temperatures.

This type of wear mostly appears with too low cutting speeds. The cutting material and the workpiece material stick to each other or are welded together

instead of sliding on the cutting face at high temperatures. During the machining operation, particles of the chip build up on the cutting edge changing the cutting edge geometry and creating additional friction and leading to poor chip removal. Some workpiece materials, i.e. low-alloyed carbon steels, stainless steel or aluminium, are particularly susceptible to built-up edge. This risk can in most cases be reduced or even totally avioded if the cutting parameters are increased.

61

Wear of the clearance surfaces Crater wear

62

4.3 Types of wear

The main types of wear can be classified as follows:

Wear of clearance surfaces (flank wear)

This type of wear (V

B

, V

Bmax

), is

the most common and it occurs, as its name indicates on the

clearance surface of the cutting edge.

The principal reason is the abrasive action of hard work piece particles which cause an abrasion in contact with the indexable insert. A balanced wear of the clearance surfaces is often considered as the ideal form of wear for the indexable insert. An unusually high wear of the clearance surfaces causes poor results for finishing operations, due to friction and therefore a higher temperature as the original clearance angle has been artificially reduced. For roughing operations, this often leads to vibration, a greater power requirement and to breakage of the indexable insert. If the wear of the clearance surfaces develops too rapidly, it is necessary to check the cutting speed to make sure that the cutting parameters are not too high for the selected cutting grade. Extreme hardness of the workpiece or a superficial hardening during the machining operation can also be the cause. The best remedy here is a cutting grade with a higher resistance against wear in the upper field of the respective ISO category.

Crater wear

This type of wear,

very similar to the wear of the clearance surfaces,

takes place on the cutting face

where the chip rubs on the cutting edge. Due to the chip contact, cutting material is continuously removed by the workpiece material, at high temperatures and high pressures, in the area of the crater (cutting face). Crater wear can be considered as a normal wear type as long as it remains within acceptable limits. Excessive crater wear modifies the geometry of the cutting edge and leads to a weakening of the cutting edge. If crater wear develops too rapidly, the cause is usually a too high cutting speed. A more wear resistant cutting grade can bring a solution. A more positive cutting edge geometry can also reduce tendancy to crater wear.

63

Plastic deformation Formation of a built-up edge

64

Plastic deformation

High temperature and high pressure can lead in some cases to a weakening and a deforming of the cutting material of the indexable insert.

This causes either a lowering of the cutting edge in the direction of the machining, or the deformation of the clearance surface.

Here, the cutting material must have high temperature hardness, sufficient to resist the plastic deformation. The flattening of the cutting edge leads to increased frictional heat, to larger geometric deviations and to insufficient chip control; this can very rapidly create a critical phase in the machining process. To avoid plastic deformation, a more wear resistant cutting grade better suited to resist this condition thanks to its hardness, should be selected. The reduction of the cutting speed and of the feed can also brings a remedy to this type of wear.

Formation of a built-up edge

The formation of pressure welded workpiece particles on the cutting edge is often the result of too low temperatures in the cutting area, caused by too low cutting speed.

Built-up edge changes the geometry of the cutting edge,

reduces the angles of the positive indexable inserts and reduces the clearance angle. Small particles leaving the built-up edge often tear parts of the cutting edge with them and lead to breakage on the cutting edge. Measures against the formation of built-up edges are to increase the cutting speed, to use a more positive geometry and a cutting material with a low affinity to the workpiece material. Special coating methods can also reduce the friction coefficient. This has a positive effect against the formation of built-up edge.

65

Formation of comb-shaped cracks Chipping

66

Formation of comb-shaped cracks

This is a form of fatigue wear which is due to the stress caused by temperature changes (thermal shock). The risk of the formation of comb-shaped cracks exists particularly for milling (short contact duration between the cutting edge and the workpiece, long cooling down phase). The cracks appear normally perpendicularly, sometimes also parallel to the cutting edge.

The cutting edge is strongly impaired causing particles of the cutting material to break off between the cracks -

this leads ultimately to the breakage of the indexable insert. Big variations in the thickness of the chip can also lead to comb-shaped fissures. A wrong coolant supply or the use of cooling lubricant as a principle are often the case of the formation of comb-shaped cracks. Often, a tougher grade in the lower field of the respective ISO category can be recommended to prevent comb-shaped cracks.

Chipping

When small particles leave the cutting edge, it is decisively impaired.

The cutting edge is not stable enough

(larger chamfer = less positive tool orthogonal rake)

to withstand the mechanical stresses of the respective chip removal operation.

A tougher grade can bring a solution but the golden rule should be applied, always provide the largest possible stability for the chip removal process.

67

Rotation of the milling spindle (0,5 sec)

Cut First cutCooling down of the cutting edge

Feed out

Depth of cut: a

p

= 2mmFeed: f

z

= 0,1mm / ZahnCutting speed: v

c

= 110m/minDistance thermoelement-cutting edge 2mm

Measure of the temperature field with built-in thermo-element for milling with a single-tooth tool

nach H.Opitz und H.Axer

All indications in [˚C]

Tool

Workpiece

Chip

Tem

pera

tur

68

4.4 Temperature on the tool cutting edge

Due to the transformation of the shearing energy in heat, high temperatures appear in the chip, at the tool cutting edge and on the workpiece. The generated heat must be received and dissipated.

The main part of the heat is dissipated through the chip,

further parts are dissipated by the tool and the workpiece, and by the cooling lubricant. The heat proportion dissipated by the chip increases with higher cutting speeds. More important than the heat itself, is the temperature generated at the tool cutting edge. It influences the formation of the chip, the machining property of the workpiece as well as the tool wear, and thus, the toollife.

The highest temperature in the chip removal process appears on the cutting face of the tool, behind the cutting edge.

69

Workpiece material:

16 Mn Cr 5

ϕ

s

= 90˚a

p

x f

z

= 3

*

0,25 mm

2

Removed volume / tooth Q (cm

3

)

Land wear depending on Q and V

Land

wea

r V

B

(m

m)

70

4.5 Wear characteristics

A regular inspection of the wear characteristics is an excellent basis from which to optimise machining parameters.

1. Determine the wear of the clearance surface in relation to the effective engagement time of the cutting edge (V

B

and V

Bmax

).2. Increased power consumption indicates changing cutting conditions. This can be a sign

that the wear of the cutting edge has increased and that the indexable insert must be turned over.

3. During a finishing operation a deterioration of surface finish can indicate an excessive wear on the insert.

4. A heavy burr, particularly in stainless steel, is a sure sign that the cutting edge is worn.5. Glowing of the cutting is also a typical sign that wear is weakening the cutting edge.

A worn cutting edge causes more friction and develops more heat.6. Chipping of the edge can be seen with the naked eye. In this case, the whole chip removal

process or cutting parameters must be redefined. The basis for this redefinition is the stability of the system.

7. Visible marks on the chips or a bad formation of the chips are signs of worn cutting edges. The wear-caused geometric deviations of the insert accelerate the aggravation of the chip formation process.

8. Noises are a sure sign of defects within the chip removal process. They are often causedby vibration due to wear-caused geometric changes on the tool.

71

Remedial measures for milling problems

Chi

ppin

g of

the

cutti

ng e

dge

Hig

h w

ear

of th

e cl

eara

nce

surf

aces

Exc

essi

ve c

rate

r w

ear

For

mat

ion

of a

bui

lt-up

edg

e

Def

orm

atio

n of

the

cutti

ng e

dge

Bre

akag

e of

the

inse

rt

Poo

r su

rfac

e fin

ish

Cha

tterin

g, v

ibra

tion

Chi

p fo

rmat

ion,

chi

p ja

m

Frit

terin

g of

edg

es

on th

e w

orkp

iece

Mac

hine

ove

rload

Problem

Remedy / measure

+ – – + – + ~ –

Cutting speed

– + – + – – – ~ – –

Feed per tooth

+ +

Carbide toughness

+ ++~

Carbide wear resistance

~ – ~ – –

Setting angle

~ ~ ~ + ~


+ + – – ~ ~ –

Chamfer of the cutting edge

+

rise, increase

–

reduce, diminish

~

check, optimise

72

4.6 Troubleshooting

Chipping of the cutting edge under thermal stress

- Use a tougher cemented carbide- Increase the feed per tooth f

z

- Reduce the cutting speed v

c

- Select positive cutting angles

Chipping of the cutting edge under mechanical stress

- Use a tougher cemented carbide- Select negative cutting angles (stabilisation chamfer)- Verify the stability of the machine, of the workpiece and the workpiece clamping- Reduce the feed per tooth f

z

- Modify the angle for the first cut (initial contact of the cutting edge)

Breakage of the indexable insert

- Ensure a free chip clearance- Use a tougher cemented carbide grade- Check the cutting parameters- Modify the angle of the first cut (initial contact of the cutting edge)- Check the stability conditions

73

+ + + +

Stability

– + + ~

Axial and radial accuracy

~ ~ ~ ~ ~ ~

Cutting edge wear

~ ~

Positionin gof cutter (e

E

; e

A

)

~ + + ~ + ~

Coolant, chip clearance

Indexable insert, clamping of cartridges

~ – ~ ~ ~ – –

Cutting depth

~ ~

Checking of cutting material

– – +

Cutting speed

Chi

ppin

g of

the

cutti

ng e

dge

Hig

h w

ear

of th

e cl

eara

nce

surf

aces

Exc

essi

ve c

rate

r w

ear

For

mat

ion

of a

bui

lt-up

edg

e

Def

orm

atio

n of

the

cutti

ng e

dge

Bre

akag

e of

the

inse

rt

Poo

r su

rfac

e fin

ish

Cha

tterin

g, v

ibra

tion

Chi

p fo

rmat

ion,

chi

p ja

m

Frit

terin

g of

edg

es

on th

e w

orkp

iece

Mac

hine

ove

rload

Problem

Remedy / measure

+

rise, increase

–

reduce, diminish

~

check, optimise

74

Crater wear

- Reduce the cutting speed- Use a tougher cemented carbide

Wear of the clearance surfaces

- Increase the feed per tooth f

z

- Use a tougher cemented carbide

Formation of a built-up edge

- Increase the cutting speed and/or the feed- Check the affinity cutting material - workpiece material- Use a ground (polished) positive indexable insert- Check the possibility for the special coating

Vibration (chattering)

- Check the clamping stability- Select another cutting edge geometry- Use a milling cutter with irregular pitch- Check the position of the milling cutter with regards to the workpiece

Poor quality urface finish on the workpiece

- Use indexable inserts with a corner facet- Use a wiper insert- Reduce the feed per tooth fz- Check the stability- Check the run-out accuracy- Possibly too low cutting speed (no formation of flowing chips)

75

No.

Workpiece material

Designation

Tough-ness or

hardness[N/mm

2

]

Real tool orthogo-nal rake

γ

o

/

γ

of

degree

Cutting force

exponent1-m

c

Specific cutting

force k

c1.1

[N/mm

2

]

Specific cutting force k

c

[N/mm

2

]for thickness of cut h

m

[mm] =

0,025 0,04 0,063 0,1 0,16 0,25 0,4 0,63 1

1 St 50.11 520 8/ - 7 0,81 1390 2780 2570 2330 2150 1970 1800 1650 1510 1390

2 St 60.11 620 8/ - 7 0,87 1440 2300 2160 2050 1940 1820 1720 1620 1520 1440

3 St 70.11 720 8/ - 7 0,79 1500 3240 2960 2690 2430 2200 1970 1820 1650 1500

4 CK 45 670 8/ - 7 0,88 1470 2230 2130 2030 1940 1820 1730 1640 1550 1470

5 CK 60 770 8/ - 7 0,86 1430 2400 2250 2110 1970 1840 1740 1620 1520 1430

6 16 Mn Cr 5 770 8/ - 7 0,81 1440 2880 2660 2420 2230 2040 1870 1710 1570 1440

7 18 Cr Ni 6 630 8/ - 7 0,74 1450 3770 3330 2990 2640 2330 2080 1840 1630 1450

8 42 Cr Mo 4 730 8/ - 7 0,80 1550 3220 2940 2680 2450 2230 2040 1860 1700 1550

9 34 Cr Mo 4 600 8/ - 7 0,84 1480 2660 2440 2300 2140 1970 1840 1710 1590 1480

10 50 Cr V 4 600 8/ - 7 0,80 1470 3050 2790 2540 2320 2120 1930 1760 1610 1470

1155 Ni Cr Mo V 6 (G)

940 8/ - 7 0,82 1290 2470 2290 2100 1940 1790 1650 1520 1400 1290

12 GG 26 200 HB 8 0,66 760 2640 2260 1940 1660 1410 1210 1030 880 760

13 Brass Ms 58 500 8 0,66 500 1740 1480 1270 1090 930 800 680 580 500

14 G-AlMg 160 20 0,66 250 870 740 630 540 460 400 340 290 250

15 G-Al Si 200 20 0,66 300 1040 890 760 660 560 480 410 350 300

76

5. Performance criteria for milling

5.1 Chip production volume Q

The chip production volume Q calculates the volume of material removed per minute in relation to the thickness of cut and of the rate of feed.

The dimension of the chip removal rate is included on the performance calculation.

Example:

Find: chip production volume Q

Given: ae = 80mm, ap = 6mm, vf = 600mm/min, shoulder milling cutter Dc = 80mm

Q = 288 cm

3

/min

Formula: Qae ap× vf×

1000---------------------------------- [cm

3/min]=

Qae ap× vf×

1000----------------------------------

80 6× 600×1000

---------------------------------- [cm3

/min]= =

77

No.

Workpiece material

Designation

Tough-ness or

hardness[N/mm

2

]

Real tool orthogo-nal rake

γ

o

/

γ

of

degree

Cutting force

exponent1-m

c

Specific cutting

force k

c1.1

[N/mm

2

]

Specific cutting force k

c

[N/mm

2

]for thickness of cut h

m

[mm] =

0,025 0,04 0,063 0,1 0,16 0,25 0,4 0,63 1

1 St 50.11 520 8/ - 7 0,81 1390 2780 2570 2330 2150 1970 1800 1650 1510 1390

2 St 60.11 620 8/ - 7 0,87 1440 2300 2160 2050 1940 1820 1720 1620 1520 1440

3 St 70.11 720 8/ - 7 0,79 1500 3240 2960 2690 2430 2200 1970 1820 1650 1500

4 CK 45 670 8/ - 7 0,88 1470 2230 2130 2030 1940 1820 1730 1640 1550 1470

5 CK 60 770 8/ - 7 0,86 1430 2400 2250 2110 1970 1840 1740 1620 1520 1430

6 16 Mn Cr 5 770 8/ - 7 0,81 1440 2880 2660 2420 2230 2040 1870 1710 1570 1440

7 18 Cr Ni 6 630 8/ - 7 0,74 1450 3770 3330 2990 2640 2330 2080 1840 1630 1450

8 42 Cr Mo 4 730 8/ - 7 0,80 1550 3220 2940 2680 2450 2230 2040 1860 1700 1550

9 34 Cr Mo 4 600 8/ - 7 0,84 1480 2660 2440 2300 2140 1970 1840 1710 1590 1480

10 50 Cr V 4 600 8/ - 7 0,80 1470 3050 2790 2540 2320 2120 1930 1760 1610 1470

1155 Ni Cr Mo V 6 (G)

940 8/ - 7 0,82 1290 2470 2290 2100 1940 1790 1650 1520 1400 1290

12 GG 26 200 HB 8 0,66 760 2640 2260 1940 1660 1410 1210 1030 880 760

13 Brass Ms 58 500 8 0,66 500 1740 1480 1270 1090 930 800 680 580 500

14 G-AlMg 160 20 0,66 250 870 740 630 540 460 400 340 290 250

15 G-Al Si 200 20 0,66 300 1040 890 760 660 560 480 410 350 300

78

5.2 Specific chip production volume Q

p

The specific chip production volume uses the specific cutting force K

c1.1

of the workpiece material and the relative thickness of cut h or f

z

.

Example:

Find: specific chip volume, Q

p

K

c

- Values

Given: K

c1.1

= 2245 [N/mm

2

] for C45

ISO P = 1700 - 2500

with f

z

= 0,15 [mm]

ISO M = 2000 - 3200

ISO K = 1000 - 1500

Q

p

= 61200 / 2245 [cm

3

/kWmin]

Q

p

= 27 [cm

3

/kWmin]

Formula: Qp61200kc1.1---------------- [cm

3/kWmin]=

79

PMutzQ

Qp-------- [kW]=MreqP

PMzu

ap ae× vf× kc×

6 107 η××

------------------------------------------------=MsuppP

80

5.3 Theoretical power requirement P

Mutil

In order to determine the operating parameters, it is necessary to check the necessary power

P

Mreq.

It is the power which must be available on the spindle. The power PMsupp. supplied to the driving motor must be superior to the effective machine efficiency

η

- usual values 0.75 to 0.9

Example:

Find: P

Msupp.,

P

Mreq.

Given: Q = 228 [cm

3

/min],

η

= 0,85

Q

p

= 27 [cm

3

/kWmin].

P

Mreq

= 228 / 27 [kW]

P

Mreq

= 8,4 kW

P

Msupp

= 8,4 / 0,85 = 10 kW P

Msupp

= 12,6 kW

For this case of application, the machine-tool should have a driving power of approx. 14 kW because the wear of the indexable insert increases the demand for power.

Formula: Exact formula:

PMreqQ

Qp--------[kW]= PMsupp

6 80× 600× 2245×6 10

70 85,××

-------------------------------------------------------=

81

100

200

100 1000 600020 200 376 2000 10000 20000 100000

2000

1000

200

100

20

10

10

20

10

2

60 KW

30 KW

1500 Nm

900 Nm

40 % ED

100 % ED

40 % ED

100 % ED

Number of revolutions n [min

-1

]

Torque M [Nm] Power P [kW]


82

5.4 Power and torque

It is very important to know the relationship between power and torque. The nominal power is available only from a machine-specific number of revolutions. A verification of the torque must be performed in any case. Otherwise the torque diminishes when the number of revolutions increases when it reaches the max. power. It can happen that larger tool diameters get enough motor power at high number of revolutions but that the machine torque with such a number of revolutions is not sufficient to build the torque for the tool (the machine stands still!).

The torque can be calculated with the following formula:

Formula: M 9559=PMnutz

n------------------× [Nm]

83

Power consumption for slot milling

Tool

D

c

= 32 mm

Z = 2

f

z

= 0,2 mm

a

e

= D

c

Workpiecematerial:

3.4364 T

(AIZnMgCu1,5)

84

Torque calculation:

Find: Torque M [Nm]Given: required power P

Mmulti

= 8,4 [kW], f

z

= 0,15 [mm/Z], v

c

= 180 [m/min], v

f

= 600 [mm/min], D

c = 80 [mm], Z = 5, ae = 80 [mm], ap = 6 [mm]

1st step: Calculation of the number of revolutions

n = 1000 x 180 / 80 x π

n = 717 [rpm]

2nd step: Calculation of the torque

M = 9559 x 8,4 / 717

M = 112 [Nm]]

Formula: n1000 vc×

Dc π×---------------------------= [min

1–]

Formula: M 9559=PMreq

n-------------------× [Nm]

85

100

200

100 1000 600020 200 376 2000 10000 20000 100000

2000

1000

200

100

20

10

10

20

10

2

60 KW

30 KW

1500 Nm

900 Nm

40 % ED

100 % ED

40 % ED

100 % ED

Number of revolutions n [min-1]

Torque M[Nm] Power P [kW]


86

If instead of a milling cutter with Dc = 80 mm we use a milling cutter with Dc = 160 mm, we obtain the following torque.

We suppose that the required power is the same, meaning 8.4 kW. The number of revolutions n is less due to the larger tool diameter Dc = 160 mm and due to the same cutting speed, and it is n = 358 min -1.

The required torque doubles!

M = 9559 x 8,4 / 358 = 224 [Nm]

It is now important to check if for a number of revolutions n = 717 [r.p.m.], the machine generates a torque M = 112 [Nm]. We can see on the power/torque - number of revolutions diagram for the machine-tool used, that the condition for the torque will be fulfilled.

Thus, it can be very important to estimate chip removal processes using the torque and also with regards to the achievable power for a given number of revolutions. An overload of the machine can be avoided at a preliminary stage for this can identify a lack of power.

87

F-031

0°

0°

+

+

-

- -

+

T

V

S

U

T

V

S

U

contactS-T-U-V S contact U contact V contact

88

6. Initial contact of the tool cutting edge

The impact point is very important for the stress applied onto the cutting edge of the cutter. The perspective representation of the thickness of cut and of the possible

impact points S, T, U,

V gives the alternatives given below, taking into account that as a simplification we suppose that the cutter axis and the edge of the workpiece are overlapping.

Axial and radial angles 0° surface contact S-T-U-V

Positive axial angle, radial angle 0° inear contact S-V

Negative axial angle, radial angle 0° linear contact T-U

Axial angle 0

∞

, positive radial angle linear contact S-T

These types of contacts S-T-U-V are unfavourable because a large part of the thickness of cut is carried out at the first contact and because they cause an high shock stress on the cutting ed-ges.

If the

radial angle

is negative and the

axial angle positive,

we obtain a

V contact. This is advantageous

because the chip is well directed (helical chip geometry type A) and the tool nose is protected.

If

both angles are positive,

we obtain a

S contact.

This means that the tool nose makes the first contact which increases the risk of breakage and therefore, it is not recommended for tougher workpiece materials. For soft workpiece materials which tend to stick, this cutting edge geometry, which has the lowest power requirement, can be advantageous.

89

F-031

0°

0°

+

+

-

- -

+

T

V

S

U

T

V

S

U

contactS-T-U-V S contact U contact V contact

90

If both angles are negative,

we obtain a

U contact.

This type of contact guarantees the best cutting edge protection against breakage but it has also the highest power requirement and gives unfavourable chip removal. This geometry is thus only used for short-chipping workpieces (i.e. grey cast iron).

The influence of the

exit of the cutting edge

on the tool life is as important as the entry. At the exit of the cutting edges with approximately maximum thicknesses of cut, combined with unfavourable contact, a premature failure of the tool may happen at a point on the cutting edge which is very exposed.

91

92

7. Milling techniques

The modern

trend in the milling technique

clearly leads towards softer

cutting tools.

The advantage of such tools is that they

require less driving power

and that they are "kinder" to the machine-tool, ensuring longer life particularly of the spindle. Large clearance angles on the cutting edges, precision-sintered or ground chipbreakers and thus small wedge angles at the cutting edge can only be achieved with durable cemented carbide grades.

Our development with regards to indexable inserts as well as coating technology is a continuous process. This process enables us to introduce successfully on the market new tools which met our customers (you) requirements.

The first steps for the application of finest-grained grades and of PVD coatings have already been carried out.

93

Comprehensive workpiece material coverage with gemomatry variants

94

7.1 Indexable insert geometry

The following factors are decisive in the selection of the most economic and most secure indexable insert:

- Workpiece material- Required quality of surface finish- Surface condition of the workpiece- Workpiece clamping- Machining operation (milling of pockets, copying, etc.)- Tool overhang length- Power, torque, number of revolutions characteristic of the machine-tool

The

microgeometry

of an indexable insert which gives the

sharpness

or the

bluntness

, can go from a rounded to a strongly chamfered cutting edge. The configuration of the respective cutting edge requires a minimum thickness of cut (h

m

). Good chip formation and thus economic tool life and quality of surface finish are only achievable by taking into account the machining in the area of the minimum chip thickness

!

If you work below the required thickness of cut, there is an inefficient cutting action with a compression process which dramatically reduces the tool life of the cutting edge

95

96

7.2 Tool geometries

A stable cutting edge is obtained with

double negative geometry -ie

when the

radial and axial angles are negative. This design is useful particularly

for oxide ceramic cutting materials due to the low tenacity of the cutting grade. The cutting edge is particularly strong.

The draw back of double negative geometries

is that

the chip is directed towards the workpiece

and there is a

risk of the chips being drawn under the tool

causing bad finish. Furthermore,

negative tool systems generate high cutting forces

which require rigid machine conditions and high driving power. Breaking-out can occur on the workpiece edges (cast iron). The machining of unstable workpieces is not recommended due to the strong axial cutting forces.

Positive milling tools utilise

positive indexable inserts throughout. This type of milling tool has a smoother cutting action and more advantageous chip forming properties. The drawback of such a geometry is the weakened cutting edge nose. Larger radii, corner facets and protection chamfers on the indexable inserts prevent cutting edge breakage.

The tool geometry

most frequently used in insert-type tools today, is the combination of

a radial negative angle and an axial positive angle.

The smooth cutting action and the chip formation are especially suited to machines with low driving power and poor stability.

The golden rule is that

for each 1° of positive tool orthogonal rake the required cutting power is reduces by 1 %.

97

Plattenform

1

Shape of inserts

ISO designation code for indexable inserts

A

B

C

D

E

H

K

L

85�

82�

80°

55�

75�

55�

M

O

P

R

S

T

V

W

86¡

35�

80�

Clearance angle

0=other clearance angles

3°�

5°�

7°�

15°�

20°�

25°�

30°�

0°�

11°

Tolerances

Admissible deviation in mm for

d m s

A ± 0,025 ± 0,005 ± 0,025

C ± 0,025 ± 0,013 ± 0,025

E ± 0,025 ± 0,025 ± 0,025

G ± 0,025 ± 0,025 ± 0,05–0,13

H ± 0,013 ± 0,013 ± 0,025

J

1

± 0,05–0,15

2

± 0,005 ± 0,025

K

1

± 0,05–0,15

2

± 0,013 ± 0,025

L

1

± 0,05–0,15

2

± 0,013 ± 0,025

M ± 0,05–0,15

2

± 0,08–0,20

2

± 0,013

N ± 0,05–0,15

2

± 0,08–0,20

2

± 0,025

U ± 0,05–0,25

2

± 0,13–0,38

2

± 0,05–0,13

1

Insert with ground secondary cutting edge

2

According to size(see ISO standards 1832)

d

m

d

m��

m

��d

s

A H

β

= 70-90˚

R

B

β

= 70-90˚

J

β

= 70-90˚

T

β

= 40-60˚

C

β

= 70-90˚

M U

β

=40-60˚

F N W

β

= 40-60˚

G Q

β

= 40-60˚

X Special configuration (drawing or descripton necessary).

�

� � �

� �

�

�

Special cutting and fastening features

2 3 41

A P H W 20 04 60 T – A 27R

1 32 54 10

7

6 8 9

Example for milling indexable inserts:

98


A P H W

20 04 60 T – A 27R

1 32

5

4

1076 8 9

99

Length of cutting edge

A P H W 20 04 60 T – A 27R

1 32 54 1076 8 9

Example for milling inserts:

Thicknessof insert

02 s = 2,3803 s = 3,18T3 s = 3,9704 s = 4,7605 s = 5,5606 s = 6,3507 s = 7,9409 s = 9,52

s

s

s

s

Type of cutting edge

�

�

�

Cutting direction

�

�

l

l

l

l

l

l

l

d

Corner radius

020408121624

r = 0,2r = 0,4r = 0,8r = 1,2r = 1,6r = 2,4

00 for inch diameter converted into mm. M= for metric diamer

Setting angle

χ

r

A = 45˚D = 60˚E = 75˚F = 85˚P = 90˚Z = other setting angle

Clearance angle of secondary cutting edge

A = 3˚B = 5˚C = 7˚D = 15˚E = 20˚F = 25˚G = 30˚N = 0˚P = 11˚Z = other clearance angle

r

�r

Manufacturer‘s detail

The ISO code comprises 9 symbols. The signg 8 and/or 9 should be only applied, if necessary. The maker can add other signs to be combined with the ISO code by means of a hyphen.(e.g. with reference to the shape of chip breaker)

Turning Milling Precision boring

G1G2M1M2M3

M 20NF 5NM 4NM 5NM 6NM 7

NR 5NR 7NS 5NS 6NS 7PF 5PM 2PM 5PS 5

A 27A 51A 57D 51D 55D 57F 55K 88

X 5X 15X 25

56 7 8 9 10


100


A P H W

20 04 60 T – A 27R

1 32

5

4

1076 8 9

101

A 2 7

larg

ersm

alle

r

shar

p

hea

vily

ch

amfe

red

Chip breaker groove Chutting edge Manufacturer‘s specification

The first letter

describes the chip breaker angle in ascending alphabetical order

The second figure

describes the cutting edge condition, from heavily chamfered = 1 to sharp = 8

the third figure

comprises the manufacturer‘s specification, e.g. clearance.

A

= 0˚

D

= 10˚

F

= 16˚

K

= 25˚

base

2

5

8

base

1

vibration absorption, among other details

5

clearance

7

8

Current geometry combinations of the WALTER programme:• A 27 / A 51 / A 57 • D 51 / D 55 / D 57• F 55 • K 88 / G 88

Designation for ISO indexable inserts for

Milling:

Example: ISO-Code + WALTER Geometry: LPGT 150412 R -

A27

ISO Code indexable inserts / WALTER geometry Designation code

102

7.3 ISO Code indexable inserts / WALTER geometry Designation code

Designation for ISO indexable inserts for

Milling:

Example: ISO Code + WALTER Geometry: LPGT 150412 R -

A27

Current geometry combinations of the WALTER programme:• A 27 / A 51 / A 57 • D 51 / D 55 / D 57• F 55 • K 88 / G 88

A 2 7

larg

er

smal

ller

shar

p

Chip breaker groove Cutting edge Manufacturer‘s specification

The first letterdescribes the chip breaker angle in ascending alphabetical order.

The second figure describes the cutting edge condition, from heavily chamfered = 1 to sharp = 8.

The third figure comprises the manufacturer‘s specification, e.g. clearance.

A = 0˚

D = 10˚

F = 16˚

K = 25˚

basis

2

5

8

basis

1 vibration absorption, among other details

5 clearance

7

8

103

WALTER SELECT for Milling inserts

With WALTER SELECT the easily understood selection system helps you find the right indexable inserts for your individual machining application.

Three faces stand for the different machining conditions:

Taking into account all other criteria required for your machining operation you are systematically led to the optimal insert.

It is very simple: ”Follow the way to the right WALTER indexable insert step by step.“

goodmachining conditions

moderatemachining conditions

unfavourablemachining conditions

WALTER SELECT –the fast road to the best insert

104

7.4 WALTER SELECT for Milling inserts








105

➤

1st step

define ethe code of the

workpiece material group.

Group of materials to be machined Code

Steel:

Unalloyed and alloyed steelhigh-alloy steelstainless steel, ferritic, martensitic

P

Stainless steel and Cast Steel:

austeniticferritic-austenitic

M

Cast iron:

Malleable cast iron, grey cast iron sheroidal graphite cast iron

K

NF Metals:

Aluminium and other non-ferrous metalsnon-metallic materials

N

Difficult cutting Materials

Heat-resistand special alloys with a nickel or cobalt basis,titanium and titanium alloys,high-alloy steels with poor cutting qualities

S

Hard Materials:

Hardened steel, hardened cast iron materials and gravity die cast metals, manganese steel

H

WALTER SELECT for Milling Inserts

106

7.4 WALTER SELECT for Milling inserts








107

Machine stability,clamping system,

Projection workpieceof tool

verygood good mode-

rate

short

extended

Workpiecematerial group

P

F 55 A 57 / D 55 A 27 / D 51

M F 55 / K 88 D 55 / F 55 A 57

K F 55 A 57 / D 55 A 27 / D 51

N K 88 F 55

S A 57 / F 55 A 57 A 57

H A 57 A 27

➤ 3rd stepDefine the recommended geometry by means of the workpiece material code and the face symbol which stands for the existion machining parameters.

➤ 2nd stepSelect the face sybol to suit the existing machining conditions.


108

7.4 WALTER SELECT for Milling Inserts








109

➤ 4th stepThe correct cutting material is chosen by means of the parameters defined in terms of workpiece material group, machining conditions and geometry.

WALTER SELECT–Selection System

Under this name we offer a comprehensive selection system based on the following symbols

good machining coonditions

moderate machining coonditions

unfavourable machining coonditions

● ● Main application● Further application

Workpiecematerial group Geometry

P

A 27 / A 57 WAP 25 WAP 35 WPM

D 55 / D 57 WAP 25 WAP 35 WPM

D 51 WAP 35 WAP 35 WTP 35

F 55 WAP 35 WTP 35 WP 40

K 88 WTP 35 WTP 35

M

A 57 WAP 25 WAP 35

D 55 / D 57 WAP 25 WTP 35

F 55 WTP 35 WTP 35 WP 40

K 88 WTP 35 WTP 35

K

A 57 WAK 15 WAP 35 WKM

D 55 / D 57 WAK 15 WAP 35 WAP 35

D 51 WAP 25 WAP 35 WTP 35

F 55 WAK 15 WAP 35 WKM

K 88 WK 10 WTP 35

N

A 57 WAK 10 WKM WKM

D 57 WTP 35 WTP 35 WTP 35

F 55 WAK 15 WKM WTP 35

K 88 WK 10 WTP 35 WTP 35

SA 57 WAK 15 WAP 35

F 55 WAK 15 WAP 25 WTP 35

K 88 WK 10 WTP 35 WTP 35

HA27 / A 57 WAK 15 WAP 25

D 55 / D 57 WAK 15 WAP 25

D 51 WAP 25


110

7.4 WALTER SELECT for Milling Inserts








111

2nd class: waviness

1st class: form error

3st class:

4st class:

Examples of form errorsForm error(represented as excessive profile cut)

Examples of the type of er-ror

Possible reason for the error

Asperity

Out-of-roundness

Waves

Striations

Striae

Flakes

Summits

Error in the slides of the machine-tool, flexion of the machine or of the tool, wrong clamping of the tool, distortion on hardening, wear

Eccentric clamping or form error on a milling cutter, vibrations of the machine or of the tool

Shape of the tool cutting edge, feed or infeed of the tool

Chip formation process (torn chip, shearing chip, built-up edge), deformation of the workpiece material, formation of buds during the galvanic treatment

112

7.5 Surface finish in milling

A high quality of surface finish is often required on the milled surface. To evaluate qualities of surface finish, we generally determine the peak-to-valley height in mm as a measuring unit. For milling operations, additional to the surface roughness (Rmax) a certain waviness appears on the machined surface.

In order to improve the surface finish, inserts with corner facets can be used. These corner facets are extended secondary cutting edges which remove the feed lines.

The qualities of surface finish achievable with finishing (wiper) inserts or with corner facet widths greater than the feed per revolution, are in the range Rmax = 10 microns. This means that such surface finishes are largely steam-tight.

113

fU is selected to obtain an overlap for each revolution.

fU is too high. There is no overlapping.

The achievable quality of surface finish is in the range Ra < 1,5 µm.

i.e. cprmer facet radius R = 600 mm

Profile of a finishing insert (wiper)

Quality of surface finish

fu = 1 [mm/rev.]

fu = 3 [mm/rev.]

114

7.5.1 Finish milling with surface milling cutter

For surface milling, different height positions of the cutting edges can cause a wavy profile on the surface of the workpiece.

This can be due to the following reasons:

- Rough tolerance range of the indexable insert- Insert seat tolerance (axial run-out) not precise enough- Distorted insert seats i.e. after a collision- Dirty insert seats- Too small corner facet on the indexable insert- Too high spindle inclination For finishing operations, the selected feed per revolution should be less than the corner facet.

The following rule is valid:

Corner facet = 1.6 mm, feed per rev. = 1.2 mm/rev.

In this case, only the most prominent axial corner facet produces the surface because there is an "overlapping". The following rule is valid:

The feed per revolution fU = fz x Z [mm/rev.] should be less than the corner facet by about 10%

fu < width of the corner facet - 10% [mm/rev.]

fz < (width of the corner facet / Z) - 10%

115

Radius insert B < f/u B >f/u

Radius insert Finishing insert (Wiper)

116

Example:

Corner facet width = 1,6 mm, Z = 6

fz < (1,6 / 6) - 10% = 0,24 use: fz = 0,2 [mm/tooth]

fu = fz x Z = 0,2 x 6 fu = 1,2 [mm/rev.]

For tool diameters greater than 100 mm, and in particular for close pitch milling cutters, as this is often the case for machining cast iron, the limits of the overlap are exceeded with only moderate feeds of about 0.2 mm/tooth.

Example:

Corner facet width 1,6 mm, fz = 0,2 mm/tooth, Z = 12, Dc = 200 mm

fu = fz x Z fu = 0,2 x 12 = 2,4 fu = 2,4 [mm/rev.]

Under such conditions we obtain a feed per revolution of 2.4 mm/rev.

An overlap is no longer achieved.

We can however suggest the following method to obtain a high quality surface finish.

117

2nd class: waviness

1st class: form error

3st class:

4st class:

Examples of form errorsForm error(represented as excessive profile cut)

Examples for the type of error

Examples for the reason at the origin of the error

Asperity

Out-of-roundness

Waves

Striations

Striae

Flakes

Summits

Error in the slides of the machine-tool, flexion of the machine or of the tool, wrong clamping of the tool, distortion on hardening, wear

Eccentric clamping or form error on a milling cutter, vibrations of the machine or of the tool

Shape of the tool cutting edge, feed of infeed of the tool

Chip formation process (torn chip, shearing chip, built-up edge), deformation of the workpiece material, formation of buds during the galvanic treatment

118

Utilisation of a finishing insert (wiper)

- Higher feeds per rev. possible- Adjustable tool necessary- Cutting pressure on workpiece surface increases- A low surface roughness Ra is achieved but the visual aspect of the cut surface may not be adequate

Utilisation of a tool with a roughing-finishing insert (corner facet width - 4 mm)

- Medium to high feeds per rev. possible Adjustable tool necessary (not necessary)- Simplified stock-keeping (roughing and finishing with one single type of indexable insert)- Even surface- Reduction of the maximum depth of cut thanks to corner facet

- ∇∇∇ with Microplan adjustment with small width of the secondary cutting edge under unstable machining conditions - machining centre -

119

1

2

4

3

1 - cartridge

2 - adjusting screw

3 - clamping screw

4 - annular grove

1. Before mounting the cartridge -1- tightenthe adjusting screw -2- so that the taperrises above the bottom of slot by about0.3 - 0.5 mm

2. Then fit the cartridge and fighten the screw -3-. Take care to ensure that thecartridge bears against the fixed stop,i.e. the rear annular groovet -4-. The adjustingscrew should not be stressed.

3. By tightening the adjusting screw -2- in in clockwise direction, the cartridge -1-can be adjusted according to the requiredplane position.

After the micro-adjustment, the adjusting screw shold be free from pre-tension. Forthis purpose, rotate the adjusting screw incounterclockwise direction and re-tightenwithout pretension.The adjusting length is about 0.2 mm.

4.When resetting, the adjusting screw -2- should be broughtback to its original position.After untightening the clamping screw -3-, the cartridge -1- returns to the axial starting position.

The Micro Face Milling Cutters F 2010 are available in thediameters from 80 - 315 mmaccording to the applicationon machining centres.

Axial Fine Adjustment of Micro Face Milling Cutter

Setting of milling tools, examples NOVEX® F 2010 and F 2140

120

7.6 Setting of Milling Tools, examples F 2010 and F 2140

Milling Cutter NOVEX

F2010

1. Before mounting the cartridge -1- tighten the adjusting screw -2- so that the taper rises above the bottom of slot by about 0.3 - 0.5 mm.

2. Then fit the cartridge and fighten the screw -3-. Take care to ensure that the cartridge bearsagainst the fixed stop,i.e. the rear annular groovet -4-. The adjustingscrew should not be stressed.

3. By tightening the adjusting screw -2- in in clockwise direction, the cartridge -1- can be adjusted according to the required plane position. After the micro-adjustment, the adjustingscrew sholdbe free from pre-tension. For this purpose, rotate the adjusting screw in counterclockwise direction and re-tighten without pretension. The adjusting length is about 0.2 mm

4. When resetting, the adjusting screw -2- should be brought back to its original position.After untightening the clamping screw -3-, the cartridge -1- returns to the axial starting position.

The Micro Face Milling Cutters F 2010 are available in the diameters from 80 - 315 mmaccording to the application on machining centres.

121

adjusting screw(left-hand thread)for insert

iindexable insert

clamping screw for insert

dial gauge

3

1

2

4

1.Fit the insert -1- tighten the clamping screw -2-.

2. Unscrew the adjusting screw -3- by turningin clockwise direction until the insert -1- isfree from location.

3.-Slightly tighten the screw -2-.

4.Move the insert by 0.2 - 0.25 mm towardsthe dial gauge -4- by turning the adjustingscrew in anti-clockwise direction. The pre-tension is built up.

5.Then adjust the overall height concentricityby rotating the adjusting screw furter in anti-clockwise direction.

6.After addjusting the axial concentricity tighten the clamping screw -2- with a tightening torque of 5 Nm.

7. Check all cutting edges for concentricity. Fine adjustment by means of the adjusting screw -3, if necessary.

Procedure for setting the axial concentricity of cutter:

Setting Instructions for the axial concentricity of NOVEX Cutters F2140

122

7.7 Setting Instructions for the axial concentricity of NOVEX® Cutters F 2140

NOVEX

Cutter F2140

1. Fit the insert -1- tighten the clamping screw -2-.

2. Unscrew the adjusting screw -3- by turning in clockwise direction until the insert -1- is free from location.

3. Slightly tighten the screw -2-.

4. Move the insert by 0.2 - 0.25 mm towards the dial gauge -4- by turning the adjustingscrew in anti-clockwise direction. The pre-tension is built up.

5. Then adjust the overall height concentricity by rotating the adjusting screw furter in anti-clockwise direction.

6. After addjusting the axial concentricity tighten the clamping screw -2- with a tightening torque of 5 Nm.

7. Check all cutting edges for concentricity. Fine adjustment by means of the adjusting screw -3, if necessary.

123

b c d ea

Shank-type milling cutter attachments Mounting of cutters

a: taper mounting(short or Morse taper)

b: cylindrical attachment

c: Clarkson

d: Weldon

e: Whistle notch

124

8. Milling tools - Application Suggestions

For the connection between tools and machine spindles, many adaptors are available.

8.1 8.1 Tool Adaption

The reliable attachment of the milling tools into the machine tool is very important when machining operation, particularly with regards to surface finish and safety The Morse taper or short taper adaption allow quick tool changing but it is not suitable for larger diameters (D

c

> 160 mm).

Usual Adaption:

- Morse taper and short taper (MK, SK...)

The usual sizes for Morse and short tapers are MT3, MT4, MT5, SK30. SK40. SK50. The short taper adaptors can also differ depending on the machine tool and the groove configuration for the gripper for the automatic tool changing. The most common gripper standards for automatic tool changing are DIN69871A for European machining centres and MAS BT 403 for Japanese ones..

- Cutter spindle

The cutter arbor is ejected from the machine spindle by mechanical, pneumatic or hydraulic action or using an automatic gripper system. Centering is achieved by means of a centering arbor, of a cotter or with a centering ring.

- Cylindrical attachment (Weldon, Whistle notch)

One of the most common cylindrical attachments is the Weldon attachment for shank-type milling cutters. Whistle notch is becoming rarer is being replaced by Weldon or cylindrical attachments.

125

A100M...RA AK100M AK100M...RAA100M A100M.7...HSK

A101M

A102M A101M...RA

A102M...RA

A103M

A120M

A130M A155M

AK155M

A170M

A171M

A200M

A201M

A300M

A310M

A120...HSK

A150HSK

A155HSKA155HSK

A170HSK

A171HSKA180HKS

A300HSK

A500 A510 A520

A550 A560 A570

A150M

A175 A305

one-piece HSK

Attachments forshrunk-in front pieces

Attachments for screwed front pieces

Modular NOVEX NC-Tools

126

8. Milling tools - Application Suggestions

For the connection between tools and machine spindles, many adaptors are available.

8.1 8.1 Tool Adaption

The reliable attachment of the milling tools into the machine tool is very important when machining operation, particularly with regards to surface finish and safety The Morse taper or short taper adaption allow quick tool changing but it is not suitable for larger diameters (D

c

> 160 mm).

Usual Adaption:

- Morse taper and short taper (MK, SK...)

The usual sizes for Morse and short tapers are MT3, MT4, MT5, SK30. SK40. SK50. The short taper adaptors can also differ depending on the machine tool and the groove configuration for the gripper for the automatic tool changing. The most common gripper standards for automatic tool changing are DIN69871A for European machining centres and MAS BT 403 for Japanese ones..

- Cutter spindle

The cutter arbor is ejected from the machine spindle by mechanical, pneumatic or hydraulic action or using an automatic gripper system. Centering is achieved by means of a centering arbor, of a cotter or with a centering ring.

- Cylindrical attachment (Weldon, Whistle notch)

One of the most common cylindrical attachments is the Weldon attachment for shank-type milling cutters. Whistle notch is becoming rarer is being replaced by Weldon or cylindrical attachments.

127

Comparison short taper - HSK (hollow shank/taper)

low positioningaccuracy

Draw boltfor clamping

Inconsistent contact pattern

Spindle head with short taper Opening of the spindle mouth

no facecontact

Large mounting dimensions Face contact Clamping taper

Clamping forceClamping force

spindle head

Inclined

faceclamping

128

Hollow shank/taper (HSK...)

The hollow shank/taper attachment widely extended for metal removal operations. For new high-quality machining centres it has a prominent position thanks to its accuracy, rigidity and suitability for high speeds. The pending ISO standard will also increase the international recognition. Due to the specific design features, more knowledge and more caution are required regarding the stress limits for the application of this modern attachment, in order to ensure a safe application without any problem.

Comparison short taper - SK

• Short taper DIN 69871

• Relatively low rigidity

• Poor axial accuracy

• Limited radial accuracy

• Not suitable for high revolutions

• Large dimensions and stroke lengths

• Widely used

Hollow shank/taper DIN 69893

• High static and dynamic stability

• High axial and radial accuracy

• Extremely suitable for high revolutions due to inner clamping

• Small dimensions and stroke lengths

129

130

8.1.1 8.1.1 Modular attachment NC-Tool system

A modular tool system must enable a tool assembly from standard components for different applications. The rigidity of such a system must be comparable to that one-piece tools. An internal cooling lubricant supply to the cutting edge and an easy, reliable assembly and disassembly must be given.

WALTER have developed with NC-Tool a system which is well-proven through many years in the field.

As a building kit for modular tools, the NOVEX NC-Tool system enables complete machining operations on machine-tools. The different standard modules can be classified into sub-groups of components having the same function.

• Master and basic attachment

• Extension and reduction

• Cutting components

• Clamping components and chucks

131

Attachment of the modular tool system WALTER NOVEX

®

NC-Tools

Conical centering and high concentric accuracy

Face contact

Maximum clamping force

Internal coolant supply

Reliable torque transmission

132

A decisive advantage of the NC-Tool system

is its simplicity and the speed for assembling and disassembling the components.Apart from the clamping systems, the attachment components are identical:

• Patented short taper

• Face contact

• Driving pins

The compatibility of all components is ensured.

Characteristics of the WALTER NOVEX system

• Quick solution for new tools

• Assembly of modules on stock to obtain new x

s

dimensions

• Limited stock inventory due to modular versitility

• High rigidity thanks to a positive and non-positive clamping

• Axial and radial connection possibility

133

Ring-shapedstopRadial support

Male taperRetaining ringClamping bolt Female taper

Pull Stud

Clamping jaws

Contact surfaces

Axial

Section

Almost symmetrically acting driving forces and large contact surfaces between pull stud and clamping jaws.

Radial AttachmentAxial Attachment

134

Axial attachment:

Turning the axial clamping screw with the predefined torque, the axial tightening force causes the elastic deformation of the short taper at the 1st contact area. The system is centered and supported with face contact. Coolant can be supplied from the middle or laterally.

Radial attachment:

Small tightening torques bring high axial forces and thus a high clamping reliability. The coolant is supplied though a bore in the tightening bolt. The driving forces have an almost symmetric action onto the contact surfaces between tightening bolt and clamping jaws. The components can be changed individually.

135

Load test WALTER-NCT attachment

modular attachment

F2038M 63 x

s

= 160mm

Z = 2 compl..

P27275-3, WTL71

P28495-1, WTL71

Ck 67, Rm=750 N/mm

2

x

s

= 160 mm

v

c

= 143 m/min

f

z

= 0,28 mm/tooth

v

f

= 400 mm/min

a

e

= 63 mm

a

p

= 65 mm

V

t

= 1638 cm

3

/min

P

c

= 80 kW (actual)

136

Example

Load test -WALTER NCT attachment

Z = 2 compl.

P27275-3, WTL71

P28495-1, WTL71

Ck 67, Rm = 750 N/mm

2

x

s

= 160 mm

v

c

= 143 m/min

f

z

= 0,28 mm/tooth

v

f

= 400 mm/min

a

e

= 63 mm

a

p

= 65 mm

V

t

= 1638 cm

3

/min

P

c

= 80 kW (actual)

137

A close pitch milling tool enables higher feed rates for the same cutting speed and the same F

z

.

Evenly spaced Unevenly spaced

Formula: T DcπZ----×=

138

8.2 Tooth spacing / Cutting edge spacing

The tooth spacing of a milling cutter gives the distance from one tooth to the next.

For the cutting edge spacing on an insert-type tool, irregular spacing is preferred (differential division) as the changing frequency of the teeth penetration reduces vibration. Close pitch insert-type-tools should be used only for short-chipping workpiece materials (cast iron) or for finishing. They allow high feed rates per minute despite a small feed per tooth.

The

close pitch version

of a milling cutter gives a multiple-use tools for a medium chip removal volume (mass production - automotive production = high rate of feed).

The

coarse pitch version

with few indexable inserts is appropriate for machining operations with low stability and under difficult conditions, with long overhangs and for unstable machine-tools with a low driving power. This milling cutter type is well proven although it reduces the chip removal volume with a limited table feed due to the smaller number of teeth. This type of cutters has larger flutes, allows high feeds and is specially appropriate for machining long-chipping materials

- For milling aluminium, use a coarse pitch tool to cope with the high chip volume

- A tool with a narrow spacing is appropriate for short-chipping materials, i.e. cast iron (check the driving power!)

139

140

8.2.1 Vibration and remedial measures

Even spacing on the milling cutter can cause vibration. It can be due to the constant penetration frequency of the cutting edge

Uneven spacing was developed from the design principle of the reamer. With an uneven spacing the penetration frequency of the cutting edge is continuously changing and a constant penetration frequency of the cutting edge is avoided.

The disadvantage of this solution is the fluctuation of the cutting forces.

Regenerative effect

Vibration avoidance with an irregular pitch cutter:

Cause: overload of the system

Remedy: indexable insert with a more positive tool orthogonal rake for a smoother cut

The target must be: to use the maximum depth of cut with regards to thehighest profitability!

Two types of vibrations appear:

a)High frequency vibrationReduce the number of revolutions(Warning: f

z

increases!)

b)Low frequency vibrationsIncrease the number of revolutions(Warning: f

z

diminishes!)

141

F-053

Dc0,75

Dc0,05

Position of the milling cutter for surface milling

min.

142

8.3 Milling diameter / Position of the milling cutter

Large milling cutters do not bring any decisive advantage for the chip removal operation. They are very expensive tools and their use is only pertinent if large workpieces are to be machined.

We can say that for surface milling narrow workpieces the milling tool must be selected about 30 % larger than the workpiece.

Example:

Width of the workpiece to be machined: 120 [mm]

D

c

= 1,3 x 120 [mm] = 156 [mm]

We select a milling cutter with diameter 160 [mm]

If several cycles

are necessary, the

relationship of cutter diameter D

c

and milling width a

e

must be about 4 to 3

in order to prevent the application of the whole cutter diameter at each pass. This is important for a good chip formation and a balanced load on the cutting edge.

143

Down milling (Climb)

Forces on the toolForces on the tool

Area of

Area of up milling

Feed

Penetration area

Exit area

down milling

Up milling (conventional)

144

8.4 Up milling / Down milling

With the combination of the rotary motion and of the feed direction, we have the choice between two basic possibilities which have a particularly strong influence upon the chip thickness at the entry and exit areas.

1. Up milling (conventional)

The

rotation direction of the cutter

in the cutting area is

opposed to the feed direction

of the workpiece. Here, the cutting edge creates the chip itself after an initial sliding and compression. The chip develops from the

penetration of the cutting edge

with the

chip thickness zero

up

to the maximum chip thickness when the cutting edge exits.

2. Down milling (climb)

The rotation direction of the milling cutter in the cutting area is the same as the one of the workpiece feed. The chip thickness is

maximum at the penetration of the cutting edge

and goes towards

chip thickness zero at the exit of the cutting edge.

Different cutting force directions appear particularly for machining with side and face cutters or for surface milling when the centre of the milling cutter is outside of the workpiece.

For Down milling, the workpiece is pressed against the machine table

whereas for

Up milling, it is lifted from the table.

Down milling is usually preferred. Exceptions:

- Older machine with a clearance in the table feed. Here, Up milling stabilises the feed.- Machining of high shoulders. In this case Up milling enhances chip clearance.- For flame cut, forged and cast workpieces. In this case we cut under the harder skin

and reduce the load on the cutting edge.

145

Important Considerations - Checklist

✔

Machining type (i.e. shoulder machining)

✔

Workpiece material, hardness, quality (i.e. annealed etc.)

✔

Machining conditions (stability)

✔

Type of cut (i.e. interrupted)

✔

Machining reliability (i.e. very high in the aviation industry)

✔

Machine-tool (power-torque, mounting system)

✔

Cutter type (setting angle, diameter, spacing))

✔

Indexable insert (cutting grade, geometry)

✔

Cooling lubricant

146

8.5 Selecting the correct milling tool

Among the most common milling operations we have plane surfaces, shoulders, corners, grooves, slots, pockets, chamfers and profiles.

The selection between the different tools is not always very easy as many fields of application of the tools overlap. It is always necessary to compile a checklist with the workpiece quality, the production conditions and the machining reliability.

You always need to ask the following question:

What do I expect from my milling operation?

Three factors must be taken into account for the selection of the appropriate milling tool. The workpiece, the chip removal operation to be performed (i.e. shoulder milling) and the available machine-tool. Taking into account these three factors, we obtain a defined cutter type. A series of additional definitions is necessary for a further optimisation.

Important influencing factors:

- Dimension, form and machining scope- Stability of workpiece and clamping- Overhang of the tool to be used- Type, hardness and condition of the workpiece material (i.e. annealed etc.)- Verification of the efficiency of the machine-tool (torque-power-number of rotations diagram)

147

Recommendations for an efficient operation

✔ Check the characteristic line power-torque-number of rotations of your machine-tool

✔ Check the stability of your machine tool.

✔ As small tool overhang as possible (xs)

✔ Select the correct type of milling cutter (setting angle, spacing, diameter)

✔ Select appropriate indexable inserts (cutting grade, geometry)

✔ Select the appropriate cutting parameters (cutting speed, feed/tooth)

✔ Select the correct machining type (down or up milling)

✔ Position the milling cutter correctly

✔ Use a cooling lubricant only if necessary. Generally it is better to mill without cooling lubricant

✔ Check regularly the tool wear

✔ Take care of the tools and of the machine in accordance with the maintenance recommendations

148

8.6 Recommendations for an efficient operation

• Check the characteristic line power-torque-number of rotations of your machine-tool

• Check the stability of your machine tool

• As small tool overhang as possible (xs)

• Select the correct type of milling cutter (setting angle, spacing, diameter)

• Select appropriate indexable inserts (cutting grade, geometry)

• Select the appropriate cutting parameters (cutting speed, feed/tooth)

• Select the correct machining type (cut-down or cut-up milling)

• Position the milling cutter correctly

• Use a cooling lubricant only if necessary. Generally is better to mill without cooling lubricant

• Check regularly the tool wear

• Take care of the tools and of the machine in accordance with the maintenance recommendations

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F2044

F2033 F2147

F2035 F2233 F2148

F2232

F2140F2010

χ

= 45˚

χ

= 45˚

χ

= 45

°

-90˚

χ

= 45

°

χ

= 42˚

χ

= 75˚

χ

= 75˚

χ

= 88˚

χ

= 90˚

Surface milling

150

9. Operating methods

9.1 Surface milling

For general surface milling operations, a 45° milling cutter is usually the best solution. With NOVEX 3000 with setting angles of 42° to 90°, it is here possible to achieve optimum machining with high feeds and close manufacturing tolerances.

The

setting angle 75°

allows economic roughing and finishing operations and leads to advantageous power requirements.

For

high-performance milling, a setting angle of 45°

gives a better stability for the cutting edge. Here, the axial cutting force component equals the radial cutting force component, which is an advantage on radially weak spindles (meaning with large spindle bearing-outs, overhangs).

We recommend a maximum depth of cut a

p

of about 3/4 of the effective cutting edge length L

c

.

For milling grey cast iron, with a tendency to edge breaking out, we recommend a 45° surface milling cutter.

For milling operations on high-performance modern machining centres, it is advantageous to select milling tools with small diameters and to machine the surface in several cuts. High-perfor-mance machining centres operate at high revolutions at which the driving power is more efficient, see also power-torque-number of revolutions diagram.

For large milling cutter diameters an insufficient force transmission (torque) by the machine-tool often leads to small feeds per tooth and to a small depth of cut. Here also vibration can occur due to the unfavourable relation between spindle bearing and cutter diameter.

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Slot milling

F2036 F2038 F2053 F3038

F2252 F2238 F2243

χ

= 90˚

χ

= 90˚

χ

= 90˚

χ

= 90˚

χ

= 90˚

χ

= 90˚

χ

= 90˚

χ

= 90˚

Solid carbidemilling cutter

152

9.2 Shell end milling and slot milling

Shell end mills, also called

porcupine cutters,

enable the machining of shoulders with large depths of cut, ie the simultaneous machining of bottom faces and side walls in large-sized recesses. These tools are also suited to profiling operations (peripheral milling). Longer cutting edges are usually shaped for better chip clearance.

The advantage of such a tool lies in the long cutting length which allows the machining of high shoulders on the workpieces.

Slot milling from solid, D

c

= a

e

, is rather an exception as this machining type needs a relatively high power consumption. Slot milling from solid is therefore only advised on powerful machines. With a smaller driving power an side and face cutter with the correct width is the more profitable solution for slot milling from the solid.

For slot milling, the chip clearance is as important as the chip removal process itself.

Long deep grooves are preferably produced with side and face milling cutters

where the indexable inserts in this type of milling cutter can be arranged radially and axially. Note that with side and face cutters, a high chip removal is possible even for relatively small slot sections. For limited

engagement conditions (a

e

/D

c

< 30%)

, caused by large tool diameters and small radial slot milling depths,

it is necessary to operate with increased feed per tooth.

153

F2238CE F2238CP F2238CR F2038C...L F2038C...R2 F2038...R6 F2038C...S

F2238CK.N F2038MC F2038MZ F2038ZF2238CK.S

FS1030FS243

FS1030 FS1030FS243FS243

Slot milling

Possible combinations

Basic body

Clamping screw forinserts

frontpieces

154

Short square grooves

are preferably machined with

porcupine cutters.

For roughing-only slot machining, half effective porcupine cutters should be preferred because the full-tooth porcupine cutter requires a double feed for the same stress onto the teeth.

The tool range extends from one-piece tools (mounting shank and insert seats are manufactured from one piece) to exchangeable front pieces. Here, Walter uses the philosophy that the combined porcupine cutters with modular structure enables many possible combinations.

The front piece is usually the hardest working part and is potentially submitted to insert or tool breakage. Replacement of the front piece is possible without need to replace the whole tool. Front pieces also offer alternative geometries from the range (i.e. radius milling).

155

Shoulder milling

χ

= 89

°

45'

χ

= 90

°

χ

= 90

°

χ

= 90

°

χ

= 90

°

F2241 Solidcarbidecutter

F3042

F2042 Brazedporcupinecutter

F2140

brazedHeli milling

F2242

cutter

χ

= 90

°

156

9.3 Shoulder milling

For machining of shoulders an approach angle of 90° is necessary. For surface milling of unstable workpieces the 90° approach angle reduces the axial cutting force components F

A

and the vibration to a minimum.

Some topics to take into account when using shoulder milling cutters:

✔

The depth of cut must be max. 3/4 of the cutting edge length when utilising full diameter.

✔

For shoulder milling the cutter should have the smallest possible diameter.

✔

The diameter must be about 50 % larger than the selected depth of cut a

p

The selection of too large a milling cutter can cause vibration in the spindle. A further inconvenience the longer engagement of cut.

Carbide brazed milling cutters as shank-type versions are best suitable for producing good surfaces with cylindrical milling. The brazed Heli cutters with continuous helix are used only as finishing milling cutters.

157

F2237 F2231 F2139

F2039 F2234 F2239

Solidcarbidemilling

Copying

cutter

158

9.4 Copying

Tools particularly suited to mould and die production and mainly used for machining contours ie to produce surfaces, shoulders and pockets.

With regards to machining security extreme stability is essential.

159

160

9.5 Milling with shank-type cutters

Shank-type cutters are tools which can be used in many ways, whether as solid carbide versions or as insert-type tools. Shank-type tools are clamped with clamping chucks or with modular system attachments and they remove material with a relatively long overhang, but consideration must be given to vibration possibilities.

Shank-type cutters can be used for slot machining and also for shell end milling. Due to the slenderness ratio of these milling cutters, the achievable depth of slot is limited to 1-2 x D

c

.

Small insert-type tools have a diameter D

c

= 16 mm. High revolutions resulting from high cutting speeds v

c

and small diameters lead to considerable feed rates which when compared to HSS cutters, guarantee shorter machining times.

On some shank-type cutters the cutting edges are arranged in order to overlap for boring in the axial direction.

161

Milling tools - Solid carbide cutters

162

9.5.1 Solid carbide cutters

Solid carbide cutters are produced as shank-type cutters mainly in the range of small diameters up to approx 20 mm. They can have straight or helical flutes, be equipped with corner facet, front radius or centre cut. They have various applications for machining grey cast iron, non-ferrous metals, steel, cast steel, plastics and are used extensively the aircraft and mould and die indu-stries.

Their application means low costs per piece and short machining times, high qualities of surface and dimensional accuracy.

Solid carbide cutter with brazed carbide cutting edges

This particular type is mainly used for tool diameters up to approx 100 mm. The cemented carbide cutting edges are firmly secured to the basic body by brazing.

The wedge geometry can be adapted to the material to be machined in an optimum way. A grinding operation ensures a high run-out and concentricity accuracy which leads to high qualities of surface finish.

Porcupine cutter:

the cutting inserts are arranged along an helix with a gap between each insert. This means it takes two flutes or teeth to give one full tooth, where the inserts overlap(important for the feed calculation)

Roughing tool for high chip removal volume.

Heli milling cutter:

continuous helical cutting edges.

Finishing tool for high requirements with regards to the quality of surface

163

164

10. Machine-tools

Milling is a type of machining in which vibration can occur. The individual teeth of the milling cutter are not permanently engaged and the generated cutting forces have no constant dimension. For this reason a

machine-tool

with

maximum stability

is desirable. The

workpiece stability

and

the clamping of the workpiece as well as of the milling cutter

are also important. These factors mutually influence each other. Variety, flexibility and an appropriate ratio of dimensions between workpiece, tool and machine-tool are also factors influencing the selection of the machine-tool for a specific operation. Small machine-tools are normally more appropriate for small milling cutters as they usually have a larger range of number of revolutions and subsequent cutting speeds.

The driving power of a milling machine normally corresponds to its size. If the correct cutting parameters are used, the tendency to vibrate is reduced which improves the tool life of the cutting edge and the quality of milled surface, and lowers the noise level. It is not always easy to select the perfect alternative among suitable and non-suitable, new and older machine tools. Factors which can be modified are the cutting parameters, meaning the combination of depth of cut, feed per tooth and cutting speed.. Sometimes a change of the feed direction or of the cutter position relative to the workpiece can solve existing problems.

Important criteria for a machine-tool are:

Power characteristics, number of revolutions of the spindle, rate of feed, number of axes, control, stability and rigidity, spindle inclination, clamping tools and attachments.

165

Section

166

10.1 Spindle inclination

If the spindle of a vertical milling machine is exactly perpendicular to the feed direction, the cutting edges of the cutter still remove material at the rear circular arc of the already machined surface and generate in this way a cross cut. (back cutting)

To prevent this phenomenon the milling spindle should have an inclination of 1/3' to 1'.

A greater inclination must be avoided because the milled surface would be concave instead of flat.

167

168

11. Tool maintenance and care

Modern metal removal tools are largely free of maintenance . Apart from of turning over and replacing the indexable inserts, modern milling tools can be reliably used over a long period. It is generally not possible to eliminate presetting of the tool. Thanks to the modular design of modern milling tools the tool changing and standstill of the machine-tool can be reduced to a minimum.

169

LubricatingPositioning

Surface contacts

170

11.1 Indexable insert

The most important criterion is to monitor the wear or to prevent subsequent damage. The cutting edge is the focal point as this is the place where tool and workpiece meet.

"The profit depends on the cutting edge".

Wear is the most important indicator that we are working with the correct cutting parameters.

If you can gain a wide experience in wear analysis, you can organise your production more effectively.

11.2 Clamping of the indexable insert

The prerequisite for reliable clamping is the cleanness of the intermediate supports and of the inserts seats. Dirt particles and remaining chips must be removed from the seat. The insert must be pressed against the insert seat once it is clamped. We must ensure that the insert is not laterally tilted but that it has a correct contact with the seat. Screw-type clamping devices must always be clamped with the suitable clamping force. Excessive clamping force leads to stretching of the screw and damage to the thread which causes premature loosening of the screw. Mounting screws should always be treated with the lubricating agent Molykote before being clamped, in order to prevent any seizure of the screw. Screws should be regularly replaced to avoid endangering of the machining reliability and safety.

11.3 Contact surfaces

Check regularly all contact surfaces. The contact surfaces should be smooth and undamaged so that the tool, the attachment and the spindle form a secure unit. Burr's and other irregularities must be carefully removed.

171

172

11.4 Tool maintenance

The key, the screwdriver and the spare parts appropriate to the tools should always be readily available. The keys enclosed with the tools have been specially developed for their defined application and the designs of the different levers automatically limit the pressure upon the tool.

A well-arranged, clean, organised and well-documented tool stock is a cost-saving factor in each production workshop. With a comprehensive view to the variety and frequency of use, you can soon have only the most necessary tools on stock.

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