O tli R i f MilliOutline – Review of Milling• Cutting Tools• Millingg

– Milling Operations– Workpiece Materials– Tool Selection– Machining Tips

• Toolholders• Fixtures

Chapter 4 ME 440 2

Cutting Tools g– HSS tools

• Coated (TiN, Al2O3, TiAlN, ...) versions are available,

• Mostly used for drilling reaming• Mostly used for drilling, reaming, boring.

– Carbide Inserts (WC, TiC)• Mostly coated,• Suitable for general machining

operations. – Solid Carbide Tools

• Some are coated,• Also called “Hard Metal ”• Also called Hard Metal,• Used in high-speed machining.

Chapter 4 ME 440 3

Cutting Tools 1 (Cont’d)g ( )

A th b i t l t hi i t• As the basic tool, most machining centers use HSS- or carbide insert tools.

• Insert endmills cut many times faster than HSS:– HSS endmills usually leave a better surface finish

when side cutting.• Solid Carbide tools combine the desired

features of both HSS- and carbide insert tools. – Unfortunately, they are still quite expensive!

Chapter 4 ME 440 4

Cutting Tools 1 (Cont’d)

Facemills flatten large Ball endmills are used for aFacemills flatten largesurfaces quickly and withan excellent finish.

Ball endmills are used for a variety of profiling operations.

Chapter 4 ME 440 5

Cutting Tools 1 (Cont’d)g ( )• HSS tools are used as drills, taps, , p ,

and reamers.• A spot drill is employed instead of

a center-drill.– spiral point / gun taps are for through

holesholes– spiral flute for blind holes.

• Slitting- and side cutters are usedSlitting and side cutters are usedwhen deep, narrow slots must becut.

Chapter 4 ME 440 6

End Mills 4

Slot Drill

End Mill

This one is unsuitable for drilling!

Ball-Nose End-Mill

g

Chapter 4 Slot DrillME 440

7

End-mills (Cont’d)

• End mills are the tools • Slot drill are the end-that have cutting teeth at one end as well as

mill tools that are specially designed to

on the periphery.– Suitable for peripheral

p y gdrill straight down into the materialmilling and facing.

– Cannot remove material f

the material.– Mostly have two / three

flutes (and rarely four!)axially if no tooth is present at the center of the flat end

flutes (and rarely four!)– Used to create pockets

and keyway slots.the flat-end. and keyway slots.

Chapter 4 ME 440 8

End-mills (Cont’d)( )

• Right-hand (helix)Right-hand Right hand (helix) tools are the most common:common:– Must rotate

l k i t tclockwise to cut.• Left-hand tools are

quite rare:– Must spin counter

Left-hand

– Must spin counter clockwise.

Chapter 4 ME 440 9

Milling Operations 2g p

1: facemilling2: square-shoulder milling

6: turn milling7: thread milling8 tti ff

11: ramping12: helical interpolation

3: profile/contour milling4: cavity milling5: slot milling

8: cutting off9: high-feed milling10: plunge milling

13: circular interpolation14: trochoidal milling

Chapter 4 ME 440 10

Milling Parameters 2g

Some important milling parameters are as follows:ae: Cutting width [mm] (or radial depth of cut),a : Depth of cut [mm] (or axial depth of cut)ap: Depth of cut [mm] (or axial depth of cut),fz: Feed-per-tooth [mm/tooth],fn: Feed-per-revolution [mm/rev],

N b f tti dzn: Number of cutting edges,hex: Maximum chip thickness [mm],hm: Average chip chickness [mm].

Chapter 4 ME 440 11

Milling Types 2

• Modern CNC machines are equipped with ball screws to minimize the effect of backlash

h h i f d di tiwhen changing feed directions:– They allow climb milling instead of

conventional (up) milling as done on most conventional machinesconventional machines.

• Climb milling has many advantages:– Better surface finish for most materials

S f ff

Climb-milling*

• Surface is not affected by revolution marks– Low overall power– Smoother operation

• Better load conditions• Less tendency to chatter

– Longer tool lifeHi h tti d d f d• Higher cutting speeds and feeds

• Climb-milling is generally prefered on a CNC machining center!Up-milling*

Chapter 4 ME 440 12

Kinematics of End-Millingg3 • Consider a four-flute endmill

with straight edges:– Helix angle: 0

M ti f th tti d24

R• Motion of the cutting edges:

– Translation (f×t)Rotation about the center (n×t)

1

– Rotation about the center (n×t)

• Each cutting edge follows a trochoidal path1 trochoidal path.– The difference between two

successive (edge) trajectories i ld th id l hi thi k

R: Radius of cutter [mm]S i dl d [ ] yields the ideal chip thickness. n: Spindle speed [rpm]

zn: No. of cutting edges: 4f: Table feed(rate) [mm/min]

Chapter 4 ME 440 13

Kinematics of Milling (Cont’d)g ( )Conventional Milling:

Coordinates of Edge “k”(k = 1 2 3 4) at instant t:

[ ]2)1(

602sin

60ππ −−+

⋅= kn t

Rtf

Rx

(k = 1,2,3,4) at instant t:

[ ]

[ ]2)1(

602

260

cos1

60ππ −−−= kn t

Ry

RR

Climb Milling:

[ ]2)1(

602sin

60ππ −+−

⋅= kn t

Rtf

Rx

[ ]2)1(

602cos1 ππ −+−= kn t

Ry

Chapter 4 ME 440 14

Kinematics of Milling (Cont’d)g ( )

2

⎟⎞

⎜⎛

Note that the height of tooth-mark(h) is higher in climb-milling:

28

⎟⎟⎟⎟

⎠

⎞

⎜⎜⎜⎜

⎝

⎛

±=

nz

z

zfR

fRhUse (-) for climb-milling;(+) for conventional.

Chapter 4 ME 440 15

2 ⎠⎝ π

Calculation of hm & hex

Chapter 4 ME 440 16

Plan for Manufacturingg• Manufacturing engineers face with a number of difficult

ti i t l ttiquestions in metal cutting:– How to select the cutting tools?

• Tool type (material) and geometry (diameter, length, number of yp ( ) g y ( , g ,cutting edges, helix angle, ...)

– How to determine machining parameters so as to obtain the desired part quality while minimizing the overall cost?p q y g

• Machining plan:– Type of milling, axial- and radial depth of cuts, feedrates, spindle speeds

– How about machining conditions?How about machining conditions?• Wet or dry machining?• If wet, what type of coolant?

Is the CNC machine tool capable of performing the specified– Is the CNC machine tool capable of performing the specified operations?

• Force, power calculations.

Chapter 4 ME 440 17

ISO Workpiece Material Classification

f (• The properties of workpiece material (like yield strength, hardness, ...) play a key role in the selection of machining parameters.selection of machining parameters.

• ISO classifies workpiece materials into six categories:– P (Plain carbon steels)– M (Stainless steels)– K (Cast irons)K (Cast irons)– N (Non-ferrous metals/materials)

• Typically Aluminum alloysS (S ll )– S (Super alloys)

• Heat resistant alloys– H (Hardened steels)

Chapter 4 ME 440 18

( )

P-Class

ISOClass Material Type Examples

Pl i b t l 1000 i 1100 iPlain carbon steel 1000 series, 1100 seriesFree-machining carbon steel 1100 series, 1200 seriesAlloy and tool steels (150-450 HB, 1300, 2000, 3000, 4000,

Poy a d too stee s ( 50 50 ,< 47 HRC)

300, 000, 3000, 000,5000, 6000, 7000, 8000,9000 series

Ferritic martensitic and 400 500 17-4 PH 15-5 PHFerritic, martensitic, andprecipitation hardening (PH)stainless steels

400, 500, 17-4 PH, 15-5 PH

C t t lCast steels

Chapter 4 ME 440 19

M-Class

ISOISO Class Material Type Examples

Austenitic stainless steels 200 series, 300 series,

M (<28 HRC) Duplex, ASTM XM series

Free machining steels 300 series

Alloy cast irons and malleableirons

ASTM A48 class 50-60

Chapter 4 ME 440 20

K-Class

ISO Class Material Type Examples

Gray cast irons ASTM A48 class 20-45, SAE J431 series

L hi i ll bl i

KLong-chipping malleable irons

Nodular / ductile, ferritic / pearlitic,pearlitic / martensitic, ASTM

Short-chipping malleable irons(120-320 HB)

pearlitic / martensitic, ASTM A536 series, SAE J434 series,ASTM A47 series, SAE J148 series

Chapter 4 ME 440 21

N-ClassISO

Cl M t i l T E lClass Material Type ExamplesFree-machining and low siliconaluminum alloys (<12.2% Si)

Alcan, Alcoa 510, Duralumin, A2, AA 2000 series, AA 3000 seriesy ( )

High-silicon aluminum alloys(>12.2% Si)

Duralcan, AA A380 series, AA A390 series, AA A413 series

Zi i

N Non-ferrous metals

Zirconium, manganese, magnesium, tin alloys, metalmatrix composites (MMCs), lead alloys zinc alloys tungstenalloys, zinc alloys, tungsten alloys

O h i lCarbon and graphite composites,

l l i d iOther materials glass, plastics, wood, ceramics, nylon, rubbers, phenolics, and resins

Chapter 4 ME 440 22

S-Class

ISO Class Material Type Examples

C b lt b d h t i t tAiResist, Haynes, Stellite, Jetalloy

I b d h t i t t llCobalt-based heat-resistantAlloys

Iron-based heat-resistant alloys Discaloy, Incoloy 801, N-155, A-286

S Nickel-based heat-resistantalloys

Astroloy, Hastelloy, Inconel, Incoloy 901, Nimonic, Nimocast, Rene, Udimet, Waspaloy, Monel, Refractaloy

Titanium Ti98.8, Ti99.9

Titanium alloys Ti5Al2.5Sn, TiAl6V4, TiAl6V4ELI

Chapter 4 ME 440 23

H-Class

ISOISO Class Material Type Examples

Chilled cast irons

HTool steels and hardenedsteels

D2, D3, L2, L3, 440C, 6150, A2, M3, M42, 52100, Ni-Hard coatings

Hardened cast iron Carburized and nitrided irons highHardened cast iron Carburized and nitrided irons, high chrome white cast iron

Chapter 4 ME 440 24

Tool Selection Procedure 2

• Select the tool material (grade) id iconsidering:

– Workpiece materialMachining job (roughing semi-finishing– Machining job (roughing, semi-finishing, finishing, super-finishing).

• Classify the machining operation and y g pselect proper tool geometry:– Profiling– Milling / Grooving

• Employing the cutting data (cutting speed feedrate) of the manufacturerspeed, feedrate) of the manufacturer, determine the machining parameters.

Chapter 4 ME 440 25[*] Courtesy of Sandvik

Example for Tool Selectionp• Let us consider finishing with

Sandvik CoroMill Plura™ Endmill (Solid Carbide).– Workpiece: AISI 1090 steel

• ISO P-class (carbon steel) • Normalized structural steel• Yield strength: 590 MPa• Hardness: HB < 300• Hardness: HB < 300

– Dry contour milling / profiling• Finishing operationFinishing operation

Chapter 4 ME 440 26

Grade Selection 2Grade Selection

• The grade GC1620 works well for semi finishing to• The grade GC1620 works well for semi-finishing to finishing (wet or dry).– Wear resistance is especially high when dry machining.

• This grade also performs well when machining stainless steels wet.

Chapter 4 ME 440 27

Machining Operations 2g p

Chapter 4 ME 440 28

Tool Geometry 2y

Chapter 4 ME 440 29

Tool Selection 2

Chapter 4 ME 440 30

Cutting Speed 2For this specific finishing operation, let ae = ap = 0.5 mm.

Chapter 4 ME 440 31

Spindle Speed Calculationp p

Since the cutting speed (vc = 410 m/min) is determined c using the corresponding table of tool catalog, the spindle speed (n) [rpm] can be calculated as

110001241010001000

≈⋅⋅

=⋅⋅

=ππ

c

Dvn

12ππ cDIf the machine tool is not capable of reaching such speeds, it can be modified to accommodate the limitations ofit can be modified to accommodate the limitations of the machine.

R ll th t th l i th t bl lRecall that the values in the tables are only recommendations!

Chapter 4 ME 440 32

Feedrate Recommendations 2

Chapter 4 ME 440 33

Feedrate Calculation

Since feed for milling cutters is read as f = 0 139 mm/toothSince feed for milling cutters is read as fz = 0.139 mm/tooth, the feed rates (f) on milling machines become

min]/[12.6110004139.0

mfnzff nz

=⋅⋅==

min]/[12.6 mf

• Note that for solid carbide cutters, the feedrates as well th i dl d hi has the spindle speed are very high.

• In general, slow feedrates give a better finish, but sometimes this actually dulls the cutter faster than asometimes this actually dulls the cutter faster than a higher feedrate.

Chapter 4 ME 440 34

Issues in Feedrates

• Feedrates calculated thru the tool datasheets• Feedrates calculated thru the tool datasheets (catalogs) are oftentimes NOT optimal:

Employ the calculated values as a starting point to– Employ the calculated values as a starting point to optimize the perfomance the actual machining task.

• Data for carbide insert milling cutters should be• Data for carbide insert milling cutters should be obtained from the insert manufacturer.

Unlike lathe cutters (which are fairly standard)– Unlike lathe cutters (which are fairly standard), milling cutters vary widely among manufacturers, so use your manufacturer’s data.use your manufacturer s data.

Chapter 4 ME 440 35

Summary• Properties of the selected

tool are as follows:– Sandvik CoroMill Plura™

ball-nose end mill• R216.44-10030-AK22N

(GC1620)(GC1620)• Diameter: 12 mm• 4-Fluteute

• Machining parameters are– Spindle speed: 11000 rpm– Spindle speed: 11000 rpm– Feedrate: 6 m/min

Chapter 4 ME 440 36

Recommendations for Face Milling3

Cemented carbideFace milling

Cemented carbideRoughing Finishing

Cutting speed: vc (m/min) 170-230 230-270Feed: fz (mm/tooth) 0.2-0.4 0.1-0.2Depth of cut: ap (mm) 2-5 0-2

Suitable grades P20-P40 coated carbide P10-P20 coated carbide

1. Use a milling cutter with a positive-negative or positive-positive geometry.2. Climb milling should generally be used.3. Milling should generally be done without coolant. If a high surface finish is required coolant g g y g q

may be used.4. Cermets can be of use when finishing under stable conditions.

Chapter 4 ME 440 37

Square Shoulder Milling 3q g

Square shoulder milling with cemented carbideSquare shoulder milling with cemented carbide

ae = 0.1×D ae = 0.5×D ae = 1×D

C tting speed (m/min) 160 210 150 200 140 190Cutting speed, vc (m/min) 160-210 150-200 140-190

Feed, fz (mm/tooth) 0.25-0.3 0.15-0.2 0.1-0.15

Suitable grades P15 P40 coated carbideSuitable grades P15-P40 coated carbide

1 Cli b illi h ld ll b d1. Climb milling should generally be used.2. Choose the cutter diameter (D) and the radial depth of cut (ae) so that at least two cutting edges

are engaged simultaneously.3. If the machine tool power is inadequate for the data given reduce the depth of cut, but do not

reduce the feedreduce the feed.

Chapter 4 ME 440 38

Slot-milling 3Slot millingDepth of cut: ap = 1×D

Cutter diameter (mm)3 - 5 5 - 10 10 - 20 20 - 30 30 - 40

Uncoated HSS 1-4

vc (m/min) 30-35

fz (mm/tooth) 0.01-0.03 0.03-0.04 0.04-0,05 0.05-0.06 0.06-0.09

Coated HSS vc (m/min) 50-551-4

c ( )

fz (mm/tooth) 0.02-0.04 0.04-0.05 0.05-0.06 0.06-0.07 0.07-0.10

Solid cemented carbide 5-8

vc (m/min) 110-140

f (mm/tooth) 0 006-0 01 0 01-0 02 0 02-0 04fz (mm/tooth) 0.006-0.01 0.01-0.02 0.02-0.04

Indexable insert (carbide inserts) 6-8

vc (m/min) 130-180

fz (mm/tooth) 0.06-0.08 0.08-0.10 0.10-0.12

S it bl d P15 P40 t d bid

1. Climb milling is generally recommended.2. Use a cutter with chip breaker when side milling with radial depths of cut, ae > 0.3 xD.3 When side milling with small radial depths of cut (a e) the cutting speed can be increased by up to 15%

Suitable grades P15-P40 coated carbide

3. When side milling with small radial depths of cut (a e) the cutting speed can be increased by up to 15%.4. Use liberal amounts of cutting fluid.5. It is recommended to use a TiCN coated cutter when milling with solid cemented carbide tools. The axial depth of cut should not exceed the

cutter diameter when slot milling.6. Climb milling is generally recommended.7. When side milling with small radial depths of cut (a e) the cutting speed can be increased by up to 30%.8 The radial run out at the cutting edges must be small and not exceed 0 03 mm

Chapter 4 ME 440 39

8. The radial run-out, at the cutting edges, must be small and not exceed 0.03 mm.

Side-milling 3

• For side milling the same• For side milling, the same cutting speed as for slot milling can be used:milling can be used:– Feeds must be adjusted to

obtain a suitable averageobtain a suitable average chip thickness:

fz = fz(slot-milling)×Cf

– Axial depth of cut: ap = 1.5×D

Chapter 4 ME 440 40

Drilling 3Drilling Drill diameter (mm)

1 - 5 5 - 10 10 - 20 20 - 30 30 - 40U t d HSS ( / i ) 15 17Uncoated HSS1-2

vc (m/min) 15-17f (mm/rev) 0.05-0.15 0.15-0.25 0.25-0.35 0.35-0.40 0.40-0.45

Coated HSS1 2

vc (m/min) 26-281-2

f (mm/rev) 0.07-0.18 0.18-0.30 0.30-0.40 0.40-0.45 0.45-0.50Cem.Carbideinsert 3-4

vc (m/min) 200-220f (mm/rev) 0 05 0 10 0 10 0 15f (mm/rev) 0.05-0.10 0.10-0.15

Solid cem.carbide 5-7

vc (m/min) 120-150f (mm/rev) 0.08-0.10 0.10-0.20 0.20-0.30 0.30-0.35

Brazed cem.carbide 5-7

vc (m/min 70-90f (mm/rev) 0.15-0.25 0.25-0.35 0.35-0.40

1 Th tti fl id h ld b l d di t d t th t l1. The cutting fluid should be ample and directed at the tool.2. When drilling with short "NC drills" the feed may be increased by up to 20%. For extra long drills the feed must be decreased.3. Use insert grades in the range of ISO P20-P30. Under unstable conditions a tougher carbide grade should be used for the centre position.4. Use a high cutting fluid pressure and flow rate for a good chip removal.5. If machining with solid or brazed cemented carbide drills, a rigid set-up and stable working conditions are required.6. The use of drills with internal cooling channels is recommended.

Chapter 4 ME 440 41

g7. Use a cutting fluid concentration of 15-20%.

Machining Tips 3

Problem Suggested Remedy

ChatterReduce cutting speed. Increase feed rate, sharpen tool,

check rigidity of machine or set up, reduce nose radius of lathe tool, check spindle bearings, etc. reduce tool and

k hwork overhang.Poor surfacefinish

Sharpen tool, increase cutting speed, reduce feed rate, increase nose radius of lathe tool.

Rapid toolwear

Reduce surface speed. Use harder grade of tool material, use cutting fluid.

Reduce depth of cut reduce feed increase cutting speedTool breakage

Reduce depth of cut, reduce feed, increase cutting speed, use more rigid set up, sharpen tool, check alignment of tool.

T t t j i b tt f h l t i tTap breakage

Tap not square, tap jamming on bottom of hole, tapping too far with taper tap, too small a tapping size, swarf jamming tap, use cutting compound.

Chapter 4 ME 440 42

Toolholders 1

• All cutting tools must be held in a holder that fits in the spindleholder that fits in the spindle.

• These include end mill holders, collet holders, face mill adapters, etc., p ,

• The gage length shown in the drawing is entered in the machine control as the tool length. The machine thecompensates for the length.

Chapter 4 ME 440 43

Fixtures

• Fixtures include• Fixtures include anything that holds the work on the machiningwork on the machining center table.

Th i l t fi t i– The simplest fixture is a vise!

Do ble ise ith• Double vise withmachinable jaws are used to hold oddused to hold odd shaped pieces.

Chapter 4 ME 440 44

Fixtures (Cont’d)( )

• Tombstone shown has a vise on two of its facesfor use on a four or five axis machining center.

Chapter 4 ME 440 45

Fixtures (Cont’d)( )

Fi t f d ti• Fixtures for mass-production are often custom designedand manufactured at greatand manufactured at great expense.

• For small runs of odd-• For small runs of odd-shaped parts, manymanufacturers have turnedmanufacturers have turned to modular fixturing:– consists of many precisiony p

ground pieces that fit together to hold all sorts of parts.

Chapter 4 ME 440 46

ReferencesReferences

• Some of the materials used in these notes are adapted from the following references:are adapted from the following references:1. MFET 275: CNC Applications, Purdue

University @ CalumetUniversity @ Calumet.2. Sandvik Coromant 2007 Catalog.3. Cutting Data Recommendations, Grane

Engr., 2005.4. Wikipedia.

Chapter 4 ME 440 47