Milling.qxd 17/03/04 9:38 Page 1 MILLING - silmax.it shell and side end mills ... How to achieve...

MILLING

T h i n k e f f i c i e n c y , T h i n k H S S

Milling.qxd 17/03/04 9:38

MILLING

MILLING TOOLS2 Zoom on a milling cutter

3 Which HSS for maximum efficiency?

4 Coatings for the best performance

5 Vocabulary

6 Choose the right design

7 Select an edge profile

8 Special edge profiles

9 The right number of teeth

10 Different helix angles

11 Popular end designs

12 Dimensions and tolerances

13 Clamping end mills with a shank

14 Clamping shell and side end mills

MILLING PROCESS15 The basics of milling

16 Operating modes of end mills

17 Operating modes of other milling cutters

18 Conventional vs. climb milling

19 Typical cutting speeds

20 How to achieve high metal removal rates

21 Cooling and chip removal

22 Problem solving

23 How to monitor wear

24 What chips have to say

25 Useful milling formulae

1

SU

MM

AR

Y

Milling.qxd 17/03/04 9:45

ZOOM ON A MILLING CUTTER2

Coating Cutting edge profiles: N, NR, NRF, …

End types: square, corner chamfer, ballnose, …

Number of teeth:from 1 to 10

Helix angles: 25°, 40°, 50°, etc.

Dimensions

Tool material

Shank types: Weldon,plain, Clarkson, …

Milling.qxd 15/03/04 10:44 Page 1

WHICH HSS FOR MAXIMUM EFFICIENCY?

• Seldom used formilling cutters

• Basic choice • The most populargrade

• For high cuttingspeeds

• For highproductivity

• High performancein roughing

• Long tool life

• Best suited fornickel alloys ortitanium alloys

• Suitable for drymachining

• High performancein finishing, butalso in roughing

• High cuttingspeeds

• Long tool life


TOOL MAKER’S TIP

Attain the highest

performance with HSS-PM

3

HSS HSS-E5% cobalt

HSS-E8% cobalt

HSS-PM(powder metallurgy)

HSS-E-PM(powder metallurgy)


COATINGS FOR THE BEST PERFORMANCE

• Conventional, generalpurpose coating

• Reduces friction

• Good abrasion-wearresistance

• Multi-purpose coating,especially for roughingend mills

• High abrasion-wearresistance

• Available as mono- ormultilayer

• Recommended forcontruction steels(Rm<1000 Mpa)

• High performancecoating for a wide rangeof cutting parameters

• 2x to 6x longer tool lifethan with conventionalcoatings

• Reduced heating of thetool

• Multilayered,nanostructured oralloyed versions offereven better performance


• Reduces friction

• Limited temperatureresistance

• Recommended foraluminium alloys, copperand non metallicmaterials

TOOL MAKER’S TIP

For maximum coating efficiency,prefer a HSS -PM

substrate

4

TiNGold

TiCNGrey-violet

TiAlN or TiAlCN

Black-violet

MoS2, WC-C


VOCABULARY5

A MILLING CUTTERAROUND THE WORLD

French: une fraise

German: ein Fräser

Italian: una fresa

Japanese:…

Spanish: una fresa

Length of cut

Mill

diam

eter

Radial primaryrelief angle

Radial primary relief width

Land width

Overall length

Shank

Hack taper

End cutting edgeconcavity angle

Axial rakeangle

Endteeth

Axial primary relief angle

Axial secondary clearance angle

Radial secondaryclearance angle

Chip room

Cutting face

Radial rake angle

Flute

Axial primaryrelief width

End gash

Helix angle

Sha

nkdi

amet

er


CHOOSE THE RIGHT DESIGN

Solid end mill

For small tool diameters (1 to 32 mm or up to 63 mm)+ For complex geometries

(3D surfaces) : pocket,radius, axial plunging,etc.

+ For modern machiningcenters

+ For both roughing andfinishing operations

End mill with HSSIndexable inserts

For large tool diameters (10 to 160 mm)

+ Sharper edge and morepositive cutting anglethan carbide inserts

+ Suitable when carbideinserts fail, especially instainless steels

+ No resharpening needed(throw-away inserts)

Solid shell end mill

Mounted on an arbor.

For large tool diameters (32 to 100 mm).

+ Very productive inroughing operations

- Fragile body (due to thelarge clamping hole)

- Only for operationwithout center cut

Side and face millingcutters

Mounted on an arbor.

+ Possible to pile upseveral cutters forprecise large slots

+ Good torquetransmission

- Accurate tolerance of theclamping hole necessaryto avoid out-of-true

TOOL MAKER’S TIP

HSS inserts arerecommended when

carbide inserts fail

6


SELECT AN EDGE PROFILE

TOOL MAKER’S TIP

Chip breakers areessential to increasethe depth of cut anddecrease the power

and cutting forces

7

• Rounded chip breakers• Normal pitch• For roughing and deep

slotting• Lower surface quality

Ra > 6.3• For steels, cast iron

• For all materials• Universal profile• Most used profile

• Rounded chip breakers• Fine pitch• For roughing-finishing

• For hard materials• Short chips• Excellent surface quality

Surface of a workpiece after roughing

• For non ferrous• Excellent surface quality

NRNormal round

HR

NNormal

H

W

ROUGHING PROFILES FINISHING PROFILES

WORKPIECECoarse Pitch

Large chip

END MILL

Feed

per

rev

olut

ion


SPECIAL EDGE PROFILES

TOOL MAKER’S TIP

Thanks to theproperties of HSS,tool producers candesign proprietary

cutting edge profilesto solve specific

machining problems

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• For non ferrous

• For roughing-finishing

• Normal pitch

• For roughing-finishing

• Flat chip breakers

• Flat chip breakers

• Normal pitch

• For roughing/finishing

ROUGHING - FINISHING PROFILES

WR

NFNormal flat

HFS


THE RIGHT NUMBER OF TEETH

2 teeth

• Large chip room andsmall web diameter

• Good results in roughingand in slot milling

• Also used for plungingand drilling in aluminiumalloys and materials withlong chips

3 teeth

• The most universalmilling tool

• Excellent choice for slotmilling and “ramping” inferrous materials andheat resistant alloys

4 teeth

• Universal geometry, usedfor side and face millingand peripheral milling

• High tool rigidity due tothe large web diameter

• Lower chip removal ratein slot milling than with a3-tooth endmill

5 teeth and more

• Mainly for finishing -good surface finish

• Allow a high feed rate

• Soft cut because there isalways a tooth in theworkpiece material

• Also for roughing withtool diameters > 20 mm

TOOL MAKER’S TIP

Prefer a 2 teeth cutter for soft

materials. Prefer a 4 teeth cutter for

difficult-to-machinematerials

9


DIFFERENT HELIX ANGLES

For roughing andfinishing in largediameters

+ Used in steel and castiron and for all materialswhen large tooldiameters are required

+ Low axial cutting force(interesting in large tooldiameters)

- Not for deep slot millingdue to radial chipremoval

- Shocks due todiscontinuous contactbetween the tool and theworkpiece

Basic choice forroughing and finishingin all materials

+ Universal use, with agood balance of cuttingforces

- Not always the mostproductive

For roughing andfinishing of nonferrous alloys

+ High depth of cut inferrous alloys whencombined with a smallnumber of teeth.

+ Constant tooth contactwith the workpiece

- Fragile corners

- High axial cutting forcesin roughing operationswith large diameter tools

For finishing ofhardened materials

+ Very good surfacequality and highproductivity, whencombined with a largenumber of teeth

- Fragile corner if nocorner chamfer or cornerradius exists

TOOL MAKER’S TIP

Select the helix angle according to

the workpiecematerial and the

type of operation (roughing / finishing)

10

UNDER 25°

25 TO 35°

40 TO 50°

ABOVE 50°


POPULAR END DESIGNS

Gen. mechanics

• True square angle

• Fragile corner

Gen. mechanics

• Resistant corners

• Good cutting inroughing operations

• Suitable for coatedtools

Aeronautics

• Typical use:roughing 3D parts

• High cornerresistance

• Suitable for coatedtools

Moulds and dies

• Finishing 3D parts

• Zero cutting speedat center: badsurface quality insoft materials

Gen. mechanics

• Used to roundcorners

• Fragile corner

DID YOU KNOW?

The toughness ofHSS prolongs

the tool life of square end mills

11

Long tool life Long tool life

SQUARE CORNER CHAMFER CORNER RADIUS BALL NOSE CORNER ROUNDING


DIMENSIONS AND TOLERANCES

Four typical tool lengths (ISO 1641/1)

The cutting length defines the depth which can bemachined in one pass.

For highest performance, especially in roughing, use theshortest cutters and work as close to the machine headas possible.

Diameter

Tolerances on shank diameter (h6) are very tight (needfor accuracy in milling operations).

Tolerances on cutting diameter depend on the type ofoperation (roughing, finishing, slotting), and oninternational or tool-maker standards.

DID YOU KNOW?

The tolerances ofHSS end mills are

identical to thetolerances of carbide

endmills

12

Extra short

Short (standard)

Long

Extra long


CLAMPING END MILLS WITH A SHANK

Basic choice

+ Choice of one or twoclamping flats

+ Simple clamping,without tuning of thecutting length

+ Good capacity of torquetransmission in roughing

- Large tool holder

- Out-of-balance problemsat high speeds due tothe screw

Good choice for very smalltool diameters

+ Adjustable tool length

+ Suitable for precisionclamping or shrink fitting

+ No unbalance at highrotating speeds (no flat,no screw)

- Low torque transmissionwhen clamped with acollet

- Not for roughing if tooldiameters > 12 mm.

Former basic choice

- Low torsion rigidity

- No possible adjustmentof the overhang length inthe tool holder

Former basic choice

+ Good coaxiality (conicalassembly)

+ Moderately large toolholder allows use indifficult-to-access cases

- Limited torquetransmission

- Tool length too long forroughing

TOOL MAKER’S TIP

For longer tool lifeand improved

tolerances, HSSmilling cutters can be

shrink fitted !

13

Weldon shank Plain shank Clarkson shank Morse taper shank


CLAMPING SHELL AND SIDE END MILLS

With tenon

For both face milling and surfacecutters

+ Good torque transmission

With keyway

For side milling cutters

+ Good torque transmission

+ Permits « piling-up » of severaltools

Plain

The economical choice

+ Adapted to thin tools

+ Careful clamping prevents the toolfrom sliding on the tool holder

14


THE BASICS OF MILLING

Milling is a machining operation with interrupted cut.

The cutting edge moves circularly, producing a chip ofvarying thickness.

At each turn, the tooth goes in and out of theworkpiece material.

Combined with variable chip thickness, this alternatemotion leads to a continuous variation of cutting forcesand produces shocks.

Milling ischaracterized by an

interrupted cut and avariable chip

thickness

15


OPERATING MODES OF END MILLS

Side milling Face milling Side and face milling Slot milling

Plunging Diagonal plunging Pocketing Helical interpolation

16


OPERATING MODES OF OTHER MILLING CUTTERS

T-slot cutter Woodruff cutter Side and face cutters

Angular cutter Angular cutter Corner-rounding cutter

17


CONVENTIONAL VS. CLIMB MILLING

Conventional milling

The width of the chip starts at zero and increases to amaximum at the end of the cut.

+ Used only when the machine tool lacks rigidity or worksloosely (old milling machine, low quality machine, wornmachine)

- Tendency to push workpiece away (Tool edge slidesinstead of cutting, causing high friction between toolflank face and material)

Climb milling

The tooth meets the work at the top of the cut,producing the thickest part of the chip first.

+ Efficient cutting

+ Long and reliable tool life

+ Better surface finish, especially with stainless steels,aluminium or titanium alloys

- Risk of tool breakage, due to sudden machinebacklash when the machine lacks rigidity

TOOL MAKER’S TIP

Thanks to anextremely sharp

edge, HSS millingcutters can mill back

and forwardefficiently.

No unproductive time !

18


TYPICAL CUTTING SPEEDS19


HOW TO ACHIEVE HIGH METAL REMOVAL RATES

TOOL MAKER’S TIP

Always increase the feed before the

speed

• The metal removal rate depends on two parameters, feed (fz) and speed (N): Q = ap x ae x N x zu x fz / 1000

• For high productivity in milling, increase the feed before increasing the speed, especially in roughing operations.

• A minimum feed is also necessary. When the feed is too low, the milling cutter no longer cuts but tears off the material.

20

SUCCESS STORIES High metal removal rates in…

Operation • Roughing with a 4-tooth coated tool Ø 16 mm, ap 24 mm, ae 8 mm

Cutting data • N 1350 tr/min, vc 68 m/min, fz 0.1 mm (100% higher than with acarbide tool)

Metal removal rate • Q 103.7 cm3/min

ConstructionSteel

(Rm 700 N/mm2)

Aluminium

(<6% Si)

Operation • Slot milling with a 3-tooth coated tool Ø 6 mm, ap 6 mm, ae 6 mm

Cutting data • N 15650 tr/min, vc 295 m/min, fz 03 mm

Metal removal rate • Q 50.8 cm3/min (30% higher than with a carbide tool)

Inconel 718

Operation • Roughing with a 6-tooth HSS-PM 8%Co + TiCN tool Ø 32 mm, ap 30 mm, ae 8 mm

Cutting data • vc 5 m/min, fz 0.16 mm (double than with a carbide tool)

Benefits • Q 11.5 cm3/min (same as carbide) and longer tool life: 2.1 m vs. 0.45 m for carbide


COOLING AND CHIP REMOVAL

Cutting fluids in milling

• Usual cutting fluids: soluble oil, or oil. Soluble oils withadditives significantly increase the tool life of HSSmilling cutters

• Cutting fluids are essential when non-coated tools areused, especially in slot milling where the contact timebetween the tool and material is important

The coolant should be carefully oriented :

• When the tool enters the workpiece, for efficientcooling during the milling operation

• When the tool comes out of the workpiece, toevacuate chips and calories properly

DID YOU KNOW?

Thermal shockscaused by cooling

problems? Only HSS resists!

21

NO YES

SUCCESS STORY Dry milling with a HSS cutter !

Operation • Roughing with a HSS-PM 8% Co + Ti2CN tool ap 12 mm, ae 8 mmin tool steel 40CrMnMo7

Cutting data • vc 45 m/min, fz 0.03 mmBenefits Compared with wet machining:

• Reduction of the specific cutting energy (56.8 vs. 46.6 W/cm3/min)• Tool life only slightly modified (7 m vs. 8.1 m)• Potential for an increase in feed and productivity

Tool steel

(Rm 1040 N/mm2)

Dry milling

• HSS milling cutters can also be used either withminimum quantity lubricant or dry

• TiAlN coatings, a real thermal barrier, also allow highproductivity dry milling with HSS milling cutters


PROBLEM SOLVING22


HOW TO MONITOR WEAR

• Normal wearpattern

• If too high, decreasefirst the cuttingspeed (vc) then thewidth of cut (ae)

• Increase thecoolant flow

• Use HSS-PM

• To be limited

• Decrease thecutting speed (vc)

• Use a coated tooland a 8% Co HSSmaterial

• Theck coolant flow

• To be avoided

• Decrease first thefeed (fz) andsecond the depthof cut (ap)

• Use a toughermaterial (HSS-PM)

• To be avoided

• Decrease first thecutting speed (vc),then the feed (fz)and third (ae)

• Use a coated tooland a 8% Co HSSmaterial


• Use a coated tool

• To be limited

• Increase thecutting speed (vc)and/or the feed (fz)

• Increase theeffective cuttingangle


• Use a low frictioncoating

TOOL MAKER’S TIP

In milling, carefulmonitoring of corner

wear prolongs toollife.

23

Flank wear Crater wear Chipping Deformation Built-up edge


WHAT CHIPS HAVE TO SAY

Shape of chips

A milling chip has a spiral shape.

The extremity lying inside the spiral is formed when theedge enters the workpiece.

In conventional milling, this extremity will be the thickest.

Due to the interrupted cut, the chip length is limited tothe length of the arc of the cut in the material.

Chip control

Control the milling operation by measuring and observingthe chip:

• The width depends on the depth of cut: the longestchip is obtained in slot milling operations.

• The length depends on the width of cut and the tooldiameter; the larger the tool diameter, the longer the chip.

• The thickness depends on the milling mode and isproportional to its calculated thickness.

• Milling chips should be regular.

• Milling chips should present an homogeneous color.

• When a coolant is used, there should be no trace ofthermal effects on the chip.

How to avoid problems ?

It is important that chips not remain in the cutting area.

If chips are irregular, if there are needle chips, or if chipshave several colors, this means that the cutting data isnot well chosen, that the cooling is not efficient, that thereare vibrations or that the tool cutting edges are worn.

DID YOU KNOW?

Careful observationof milling chips

provides valuableinformation!

24


USEFUL MILLING FORMULAE25

Symbol Unit Name Formulae

Vc m/min Surface cutting speed

N mm/rev Revolution per minute

Vf mm/min Feed per minute

fZ mm/tooth Feed per tooth

Q cm3/cm Chip volume

hm mm Average chip thickness

hmax mm Maximum chip thickness

V1=NZ fz

Vc= πDN1000

N= 1000V cπD

Q= aaae NZfz1000

√aeD

fz

fz= VfNZ

Symbol Unit Name

D mm Tool diameter

T mm Machining time

Z No. of teeth

ap mm Depth of cut

ae mm Width of cut


Milling.qxd 17/03/04 9:38 Page 1 MILLING - silmax.it shell and side end mills ... How to achieve...

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Transcript of Milling.qxd 17/03/04 9:38 Page 1 MILLING - silmax.it shell and side end mills ... How to achieve...