EIN 3390 Chap 24 Milling Spring_2012.ppt

7/25/2019 EIN 3390 Chap 24 Milling Spring_2012.ppt

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Chapter 24Chapter 24

MillingMilling

EIN 3390 Manufacturing ProcessesEIN 3390 Manufacturing ProcessesSpring, 2012Spring, 2012


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24.1 Introuction24.1 Introuction

Milling is the basic process of progressi!e chipre"o!alto produce a surface.

Mill cutters have single or "ultipleteeth thatrotate about an axis, removing material.

Often the desired surface in obtained in a singlepass of cutter or workpiece with !er# goosurface finish.

Milling is particularly well suited and widely usedfor mass production.

More flat surfaces are produced by milling thanby any other machining processes.


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24.2 $una"entals of Milling24.2 $una"entals of Milling

ProcessesProcessesMilling is classified in t%o categories:

Peripheral "illing &also called Sla' "illing( -the surface is generated by teeth located on theperiphery of the cutter body. he surfaceis

parallelwith the a)is of rotation of thecutter.

En "illing: also called facing "illing, thesurfacegenerated is at a right angle to thecutter axis. Material is removed by theperipheral teeth and the face portion providingfinishing action.


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Peripheral MillsPeripheral Mills

FIGURE 24-1 Peripheral

milling can be performed

on a horizontal-spindle

milling machine. The

cutter rotates at rpm Ns ,removing metal at cutting

speed V. The allowance

for starting and finishing

the cut depends on the

cutter diameter and depth

of cut, d. The feed per

tooth, ft and cutting speed

are selected by the

operator or processplanner.


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Peripheral MillingPeripheral Millinghe milling variables, such as cutting spee * and

fee per tooth depend upon the %or+ "aterial,the tool "aterial, and the specific process.he rpm of the spindle is determined from the surface

cutting speed !, the cutter diameter " #in inch$ asbelow:

Ns &12*(-& (

he feed of table fm, in inch per minute, is calculated:

f" ftNsn%here ft, feed per tooth, and n is the number of teeth

in the cutter.he cutting time is:m& #' ( ')$*fm


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Peripheral MillingPeripheral Millinghe length of approach is:

/0 S2-4 5 &-267C(2 8 S&&6((

he M++ is:

M *olu"e-" &/(-" f" in3-"in

where % is width of the cut in inch, d is the depth ofcut in inch.

f ignoring '), the values for ftare given in able -/,along with recommended cutting speeds in feet per

minute.


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Suggeste Starting $ees an Spees using :SS anSuggeste Starting $ees an Spees using :SS an

Car'ie CuttersCar'ie Cutters


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$ace Mills$ace Mills

FIGURE 24-2 Face

milling is often

performed on a

spindle milling

machine using a

multiple-tooth cutter(n = 6 teeth

rotating Ns at rpm

to produce cutting

speed V. The

wor!piece feeds at

rate fm in inches

per minute pastthe tool. The

allowance depends

on the tool diameter

and the width of

cut.


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$ace Milling$ace Millinghe rpm of the spindle is determined from the surface

cutting speed !, the cutter diameter " #in inch$ asbelow:Ns &12*(-& (

he feed of table fm, in inch per minute, is calculated:f" ftNsn

%here ft, feed per tooth, and n is the number of teeth in

the cutter.he cutting time is:

m & #' ( ')( '0$*fmhe M++ is:

M *olu"e-" &/(-" f" in3-"in1or a setup where the tool doesn2t completely pass over

the workpiece,/0 / S&& 5 (( for ; -2/0 / -2 for


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$ace Milling E)a"ple$ace Milling E)a"ple1or a 3 diameter, six-tooth end mill, using

carbide inserts #1ig -4$, the workmaterial is low-alloy steel, annealed #567& 00$. 8lease determine rpm at thespindle and the feed rate of the table.


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$ace Milling E)a"ple$ace Milling E)a"ple

9sing cutting data recommendations, select ! & 00 sfpmwith a ft & 0.003*tooth.

7s& #/!$*#"$ & #/ x 00$* #4./ x $ & 392 rp"

he feed rate of table is:

fm& ft7sn & 0.00 x ; x 4


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*ertical an :ori>ontal Cutters*ertical an :ori>ontal Cutters

FIGURE 24-3 Face millingviewed from above with vertical

spindle-machine.

FIGURE 24-4 "lab or sidemilling being done as a up

milling process with horizontal

spindle-machine.


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En MillingEn Milling

FIGURE 24-5 #nd milling a step feature in a bloc! using a flat-bottomed, end mill cutter in a vertical

spindle-milling machine. $n left, photo. %n middle, end view, table moving the bloc! into the cutter. $n

right, side view, wor!piece feeding right to left into tool.


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En Milling E)a"pleEn Milling E)a"ple

n 1ig -=, an end mill with ?teeth on a 2= ia"eter#carbide cutter$ is used to cut a step in 401stainless. 0.3@A= and the epth of i""ersionis 1.2A=. he vertical milling machine tool has a A6hp "otorwith an B0 efficienc#. he specific

horsepo%er for 401 stainless#567 & 400$ is1.3hp-in3-"in. >an the step be cut in one pass orin multiple passes?


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En Milling E)a"pleEn Milling E)a"ple

he maximum amount of material that can be removed perpass is usually limited by the a!aila'le po%er.

6p& 68sx M++ & 68@x fm"O>max& 68sfmx 7Ix "O>max

1rom able -/, select ft

& 0.00= ipt, ! & =0 fpm.

7s& #/ x =0$*#4./ x $ & AA rpm

fm& ftx n x 7s& 0.00= x ; x AA & /.4/3*min

he actual table feed rates for selected machine are //3*min. or/;3*min. @elect fm& //3*min.


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En Milling E)a"pleEn Milling E)a"ple "O>max& #0.hp$*#68sfm"O$

& #0.x =$*#/.4 x // x /.= $ & 0.22A=

@o t%o cutting passes are needed because 0.4A=*0.= &/.;.

he first pass: "O>/& 0.=3 rough cuthe second pass: "O>

& 0./=3

1or "O>& 0./=3 the ftwould be only slightly increased to0.00=Aipt

1t& #0.hp$*#68sn 7s"O> "O$& #0. x =$*#/.4 x ; x AA x 0./= x /.=$& 0.00=Aipt


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Dp *ersus o%n MillingDp *ersus o%n Milling

Dp "illing orCon!entional "illing he cutter rotates against the irection of fee

of the workpeice. he >hip is !er# thin at the 'eginning and

increase along its length.

he cutter tends to push the %or+ along an liftit up%ars fro" the ta'le. he action tends toloosen the %or+piece fro" the fi)ture.

n the up milling, chips can be carried into thenewly machined surface, causing the surface

finish to 'e poorer than in o%n "illing.


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Dp *ersus o%n MillingDp *ersus o%n Millingo%n "illing orCli"' "illing

the cutterrotates in the sa"e irection asthe irection of fee !antage he %or+ piece is pulle into the cutter, eli"inating

an# effects fro" looseness of the %or+ ta'le feescre%.

here is less tenenc# for the "achine surface tosho% tooth"ar+s, an the cutting process iss"oother, %ith less chatter.

he cutting force tens to hol the %or+pieceagainst the "achine ta'le, per"itting lo%ercla"ping force.

isa!antage he "a)i"u" chip thic+ness is at the point of toothcontact %ith the %or+ piece. ullingthe teeth "oreFuic+l#, especially for workpiece with a hard surface.


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Cli"'ing !ersus Con!entional MillsCli"'ing !ersus Con!entional Mills

FIGURE 24-6 &limb

cut or

down milling versus

conventional cut or up

millingfor slab or face or end

milling.


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Milling Surface $inishMilling Surface $inishMilling is an interrupted cutting process .

I"pact loaing C#clic heating C#cle cutting forces

)s show in 1ig. -A, the cutting force, 1c, buildsrapidly as the tool enters the work at ) and

progresses to 5, peaks as the blade crosses thedirection of feed at >, decreases to ", and then dropsto Bero abruptly upon exit.

he interrupted-cut phenomenon explain in large partwhy milling cutter teeth are designed to have s"all

positi!e or negati!e ra+e angles, particularlywhen the tool material is car'ie or cera"ic.>utters made from :SSare with positi!e ra+es, inthe main, but must be run at lo%er spees.


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$acing Mill$acing Mill

FIGURE 24-7 &onventional face milling (left with cutting force diagram for Fc (right showing the

interrupted nature of the process. (From 'etal &utting Principles, 2nd ed., Ingersoll Cutting Tool

Company.)


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24.3 Milling ools an Cutters24.3 Milling ools an Cutters

here are a variety of mills used, the mostcommon being face mills and end mills Cnd mills are either :SSor have ine)a'leinserts#1igure -$

Cnd Mills come in a variety of geometries 8lain Cnd Mills

@hell Cnd Mills

6ollow Cnd Mills


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7ther Mill Cutter #pes7ther Mill Cutter #pes

1ace mills have indexable inserts alongthe periphery1ace Mills come in a variety of geometry

#1igure -enter hole for arbor mounting @ide mill #1igure -/0$ @taggered-tooth @traddle milling nterlocking slot cutters

@litting cutters


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#pical Cutter Pro'le"s#pical Cutter Pro'le"s


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En Mill Geo"etr#En Mill Geo"etr#

FIGURE 24-8 "olid end mills are often coated. %nsert

tooling end mills come in a variety of sizes and are

mounted on taper shan!s.


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$acing Mill Geo"etr#$acing Mill Geo"etr#

FIGURE 24-9

Face mills come

in many

different designs

using

many different

insertgeometries

and different

mounting

arbors.


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Sie MillingSie Milling

FIGURE 24-10 The

side-milling cutter

can cut on sides

and ends of the

teeth, so it ma!es

slots or grooves.

owever, only a few

teeth are engagedat any one point in

time, causing heavy

torsional vibrations.

The average chip

thic!ness, hi, will be

less than the feed

per tooth, ft . The

actual

feed per tooth fa will

be less than feed

per tooth selected,

Ft .


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r'or Millingr'or Milling

FIGURE 24-11)rbor (two views used on a horizontal-spindle milling machine on left. $n right, a gangmilling

setup showing three side-milling cutters mounted on an

arbor () with an outboard flywheel (*.


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:elical Mills:elical Mills

FIGURE 24-12 The chips are

formed progressively by the

teeth of a plain helical-tooth

milling cutter during up milling.


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Shape CuttersShape Cutters$or" elie!e Cuttersare used when

intricate shapes are needed.6slot cutters are used to produce slots

in material. )n end mill is use first toproduce the initial groove

) woodruff keyseat cutter is used toproduce a slot in a shaft and come instandard siBes

1ly cutters are single toothed face millcutters, with adDustable radii.


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elie!e Cutterelie!e Cutter

FIGURE 24-13 "olid

form

relieved milling cutter,

would be

mounted on an arbor

in ahorizontal milling

machine..


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24.4 Machines for Milling24.4 Machines for Milling

he four most common types of manuallycontrolled milling machines are listedbelow in order of increasing power #andtherefore metal removal capability$: 1. a"6t#pe "illing "achines

2. Colu"n6an6+nee6t#pe "illing"achines a. 6oriBontal spindle b. !ertical spindle

3. $i)e6'e6t#pe "illing "achines 4. Planer6t#pe "illing "achines


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Hasic Mill ConstructionHasic Mill ConstructionMost mills consist of colu"n6an6+nee esigns

he colu"n is "ounte on a 'ase and the spinle"ounte on a +nee e)tening from the column.

he +nee has !ertical "o!e"ent

he material in mounted on a table with longituinal"o!e"ent, and the ta'le is "ounte on a sale

%ith trans!erse "o!e"entMost common of this type mill is the a" "ill

which has a motor and pulley system mounted onthe top of the column.


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Maor Co"ponents of a Plain Colu"n6an6Maor Co"ponents of a Plain Colu"n6an6

Jnee6#pe Milling MachineJnee6#pe Milling Machine

FIGURE 24-14 'a+or components of a plain column-and-!nee-type milling machine, which can

have horizontal spindle shown on the left, or a turret type machine with a vertical spindle, shown

on the right. The wor!piece and wor!holder on the table can be translated in, !, and "

directions with respect to the tool.


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a"6t#pe Jnee6an Colu"na"6t#pe Jnee6an Colu"n

MachineMachine

FIGURE 24-15

The ram-type

!nee-and-

column milling

machine is one

of the mostversatile and

popular milling

machine tools

ever designed.


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He #pe Milling MachineHe #pe Milling Machine

Made for eep cuts an hea!# "aterialre"o!al, the bed only had hori>ontal"o!e"ent

Once the bed is set up, the spindle height

is not changed during operation.hese machines are very common due to

their ease of use.


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He #pe MillHe #pe Mill

FIGURE 24-16

*ed-type

vertical-spindle

heavy-duty

production

machine tools formilling usually

have three aes

of motion.


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Planer #pe MillPlaner #pe Mill8laner type mills can have se!eral heas

to re"o!e large a"ounts of "aterialwhile the material is fed slowly into themachine.

@ystems are setup typically for singlepass operations.

hese are a!antageous for large%or+ piecesreEuiring hea!# "aterial

re"o!al.


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/arge Planer6t#pe Milling Machine/arge Planer6t#pe Milling Machine

FIGURE 24-17 arge

planertype millingmachine. %nset shows /0

head being used.

(Courtesy of Cosa

Corporation.)


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Milling Machine SelectionMilling Machine Selection%hen purchasing or using a milling

machine, consider the following issues: 1. Spinle orientation an rp"

2. Machine capa'ilit# #accuracy andprecision$

3. Machine capacit# #siBe of workpieces$ 4. :orsepo%er a!aila'le at spinle #usuallyA0F of machine horsepower$

A. uto"atic tool changing


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: for Chapter 24: for Chapter 24

+eview Guestions:, and < #pages ;A$

8roblems:/, , ;. #page ;A=$1ote2

For 3 42 1umber of teeth n = 5.

For 3 62

'aterial of wor!piece2 &ast iron, medium hardness, d = DO =0!214"


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8roblems:/ #page ;A=$

(&alculate the table speed fm


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8roblems: #page ;A=$

Documents

EIN 3390 Chap 24 Milling Spring_2012.ppt