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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=$1ote2
For 3 42 1umber of teeth n = 5.
For 3 62
'aterial of wor!piece2 &ast iron, medium hardness, d = DO =0!214"
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: for Chapter 24: for Chapter 24
8roblems:/ #page ;A=$
(&alculate the table speed fm
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: for Chapter 24: for Chapter 24
8roblems: #page ;A=$
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