Staff Site Universitas Negeri Yogyakarta

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Ma nufa c turing is the ind ustria l a c tivity

Ma nufa c turing is the ind ustria l a c tivity tha t c ha ng e s the fo rm o f ra w ma te ria ls to c re a te p ro d uc ts.o c e a e p o d uc s.

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C d t l ti f i

C o mp a re d to p la stic fo rming

te c hno lo g y, ma c hining te c hno lo g y is usua lly a d o p te d whe ne ve r p a rt

usua lly a d o p te d whe ne ve r p a rt

a c c ura c y a nd surfa c e q ua lity a re o f p rime imp o rta nc e .

p p

The te c hno lo g y o f ma te ria l re mo va l in ma c hining is c a rrie d o ut o n ma c hine

i f i

to o ls tha t a re re sp o nsib le fo r g e ne ra ting mo tio ns re q uire d fo r p ro d uc ing a g ive n p a rt g e o me try

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Ma c hine to o ls fo rm a ro und 70% o f

o p e ra ting p ro d uc tio n ma c hine s a nd a re

h i d b h i hi h d i

c ha ra c te rize d b y the ir hig h p ro d uc tio n a c c ura c y c o mp a re d with me ta l fo rming

hi t l

ma c hine to o ls.

Ma c hining a c tivitie s c o nstitute

i t l 20% f th f t i

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The a nc ie nt Eg yp tia ns use d the se ro lle rs fo r tra nsp o rting the re q uire d sto ne s fro m

h b ild i i

a q ua rry to the b uild ing site .

The use o f ro lle rs initia te d the

intro d uc tio n o f the first wo o d e n d rilling ma c hine , whic h d a te s b a c k to 4000 b c .

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Wilkinso n (1775), wa s intro d uc e d b o ring ma c hine , whe n he ma d e the

t f t hi f J

c o mp o ne nt o f ste a m ma c hine o f Ja me s Wa tt.

I 1840 th fi t i l th

In 1840, the first e ng ine la the wa s intro d uc e d

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Ma ud sla y (1771–1831) a d d e d the le a d sc re w, b a c k g e a rs, a nd the to o l p o st to

th i d i

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Pla ne rs a nd sha p e rs ha ve e vo lve d a nd we re mo d ifi e d b y Se lle rs (1824–1905)

we re mo d ifi e d b y Se lle rs (1824 1905).

Fitc h d e sig ne d the first turre t la the in 1845

A c o mp le te ly a uto ma tic turre t la the wa s

A c o mp le te ly a uto ma tic turre t la the wa s inve nte d b y Sp e nc e r in 1896. He wa s a lso c re d ite d with the d e ve lo p me nt o f the

c re d ite d with the d e ve lo p me nt o f the multisp ind le a uto ma tic la the .

In 1818 Whitne y b uilt the first milling

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the c ylind ric a l g rind ing ma c hine wa s b uilt fo r the first time b y Bro wn a nd

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Ma c hining

As the c hip is re mo ve d , a ne w surfa c e is e xp o se d

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Machining

C utting a c tio n invo lve s she a r d e fo rma tio n o f wo rk ma te ria l to fo rm a c hip

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Wa ste ful o f ma te ria l

› C hip s g e ne ra te d in ma c hining a re wa ste d t i l t l t i th it ti

ma te ria l, a t le a st in the unit o p e ra tio n

Time c o nsuming

A hi i ti ll t k

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G e ne ra lly p e rfo rme d a fte r o the r ma nufa c turing p ro c e sse s, suc h a s

i f i d b d i

c a sting , fo rg ing , a nd b a r d ra wing

› O the r p ro c e sse s c re a te the g e ne ra l sha p e o f the sta rting wo rkp a rt

sta rting wo rkp a rt

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Mo st imp o rta nt ma c hining o p e ra tio ns:

› Turning

› Drilling

› Milling

O th hi i ti

O the r ma c hining o p e ra tio ns:

› Sha p ing a nd p la ning Bro a c hing

› Bro a c hing

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Turning

Sing le p o int c utting to o l re mo ve s ma te ria l fro m a ro ta ting wo rkp ie c e to fo rm a c ylind ric a l sha p e

g

a ro ta ting wo rkp ie c e to fo rm a c ylind ric a l sha p e

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Drilling

Use d to c re a te a ro und ho le , usua lly b y me a ns o f a ro ta ting to o l (d rill b it) with two c utting e d g e s

g

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Milling

Ro ta ting multip le -c utting -e d g e to o l is mo ve d a c ro ss wo rk to c ut a p la ne o r stra ig ht surfa c e

g

p g

Two fo rms: p e rip he ra l milling a nd fa c e milling

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1. Sing le -Po int To o ls

› O ne d o mina nt c utting e d g e

› Po int is usua lly ro und e d to fo rm a no se ra d ius

› Turning use s sing le p o int to o ls

M lti l C tti Ed T l

2. Multip le C utting Ed g e To o ls

› Mo re tha n o ne c utting e d g e

Mo tio n re la ti e to o rk a c hie e d b ro ta ting

› Mo tio n re la tive to wo rk a c hie ve d b y ro ta ting

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Cutting Tools

g

Figure 21.4 (a) A single-point tool showing rake face, flank, and tool point; and (b) a helical milling cutter, representative of tools with

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Thre e d ime nsio ns o f a ma c hining p ro c e ss:

p ro c e ss:

› C utting sp e e d v – p rima ry mo tio n

› Fe e d f – se c o nd a ry mo tio n

› De p th o f c ut d – p e ne tra tio n o f to o l b e lo w o rig ina l wo rk surfa c e

Fo r c e rta in o p e ra tio ns ma te ria l

Fo r c e rta in o p e ra tio ns, ma te ria l re mo va l ra te c a n b e c o mp ute d a s

R

₌_{v f d}

whe re v = c utting sp e e d ; f = fe e d ; d = d e p th o f c ut

MR

R

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C utting C o nd itio ns fo r Turning

g

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Ro ug hing - re mo ve s la rg e a mo unts o f g g g ma te ria l fro m sta rting wo rkp a rt

› C lo se to d e sire d g e o me try (not to full depth)

› Fe e d s a nd d e p ths: large

C tti d l

› C utting sp e e d s: slow

Finishing - c o mp le te s p a rt g e o me try › Fina l d ime nsio ns, to le ra nc e s, a nd finish

› Fe e d s a nd d e p ths: p small

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O rtho g o na l C utting Mo d e l – C hip Thic kne ss Ra tio

C hip Thic kne ss Ra tio

o

t r =

c

t r =

whe re r = chip thickness ratio; t_o = thic kne ss o f the c hip

p rio r to c hip fo rma tio n; a nd t_c = c hip thic kne ss a fte r

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C hip thic kne ss a fte r c ut a lwa ys g re a te r tha n b e fo re , so c hip

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Ba se d o n the g e o me tric p a ra me te rs o f

th th l d l th h l

the o rtho g o na l mo d e l, the she a r p la ne a ng le φ c a n b e d e te rmine d a s:

α α φ sin cos tan r r − =

1 s α

h hi ti d k l

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She a r Stra in in C hip Fo rma tio n

ABD a ng le ? 90 - Φ

DBE a ng le ? Φ

E E Stra in: DB AC =

γ = tan(φ - α) + cot φ

BD DC AD + = E DB

whe re γ = she a r stra in, φ = she a r p la ne a ng le , a nd α = ra ke a ng le

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Shear Strain in Chip Formation

Fig ure 21.7 She a r stra in d uring c hip fo rma tio n: (a ) c hip fo rma tio n d e p ic te d a s a se rie s o f p a ra lle l p la te s slid ing re la tive to e a c h o the r, (b ) o ne o f the p la te s iso la te d to sho w she a r stra in, a nd (c ) she a r

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Chip Formation

C p o

a o

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1. Disc o ntinuo us c hip

2. C o ntinuo us c hip

3. C o ntinuo us c hip with Built-up Ed g e (BUE)

S t d hi

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Discontinuous Chip

Brittle wo rk ma te ria ls

Lo w c utting sp e e d s

La rg e fe e d a nd d e p th o f c ut

Hig h to o l-c hip f i ti

fric tio n

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Continuous Chip

Duc tile wo rk ma te ria ls

p

ma te ria ls

Hig h c utting sp e e d s

Sma ll fe e d s a nd d e p ths

Sh tti

Sha rp c utting e d g e

Lo w to o l-c hipo o o c p fric tio n

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Continuous with BUE

Duc tile ma te ria ls

Lo w to me d ium

Lo w-to -me d ium c utting sp e e d s

To o l-c hip fric tio n c a use s p o rtio ns o f c a use s p o rtio ns o f c hip to a d he re to ra ke fa c e

BUE fo rms, the n

b re a ks o ff, c yc lic a lly

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Serrated Chip

Se mic o ntinuo us -sa w-to o th

sa w to o th a p p e a ra nc e

C yc lic a l c hip fo rms ith a lte rna ting

with a lte rna ting hig h she a r stra in the n lo w she a r

t i

stra in

Asso c ia te d with

d iffic ult-to -ma c hine d iffic ult to ma c hine me ta ls a t hig h

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Forces Acting on Chip

Fric tio n fo rc e F a nd No rma l fo rc e to fric tio n N She a r fo rc e F_s a nd No rma l fo rc e to she a r F_n

g

s n

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Ve c to r a d d itio n o f

F

a nd

N

= re sulta nt

R

Ve c to r a d d itio n o f

F

_s a nd

F

_n = re sulta nt

R

'

Fo rc e s a c ting o n the c hip must b e in

Fo rc e s a c ting o n the c hip must b e in b a la nc e :

› RR' must b e e q ua l in ma g nitud e to must b e e q ua l in ma g nitud e to RR

› R’ must b e o p p o site in d ire c tio n to R

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C o e ffic ie nt o f fric tio n b e twe e n to o l a nd c hip :

F

=

μ

N

=

μ

Friction angle related to coefficient of friction as follows:

β

t

β

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She a r stre ss a c ting a lo ng the she a r p la ne : s s A F S = w t A o

where A_s = area of the shear plane

φ

sin

A_s = o

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C o e ffic ie nt o f fric tio n b e twe e n to o l a nd c hip :

F

whe re β is: the friction angle

N F

=

μ = tan β

She a r stre ss a c ting a lo ng the she a r p la ne :

whe re S is: the shear strength

s

A F

S = _g

whe re A_s is: the shear plane area φ

i

w t A_s = o

s

A

x t_o is: cut depth

x w is: cutting edge width

φ

sin s

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Cutting Force and Thrust Force

F, N, F_s, a nd F_n c a nno t b e d ire c tly me a sure d

Fo rc e s a c ting o n the to o l tha t c a n b e

g

g me a sure d :

› C utting fo rc e F_c a nd Thrust fo rc e F_t

Figure 21 10 Forces Figure 21.10 Forces in metal cutting: (b) forces acting on the tool that can be

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Eq ua tio ns c a n b e d e rive d to re la te the fo rc e s tha t c a nno t b e me a sure d to the fo rc e s tha t c a n b e me a sure d :

fo rc e s tha t c a n b e me a sure d :

F = F_c sinα + F_t cosα N = F_c cosα - F_t sinα N F_c cosα F_t sinα F_s = F_c cosφ - F_t sinφ F_n = F_c sinφ + F_t cosφ

Ba se d o n the se c a lc ula te d fo rc e , she a r stre ss a nd c o e ffic ie nt o f fric tio n c a n b e d e te rmine d

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O f a ll the p o ssib le a ng le s a t whic h

she a r d e fo rma tio n c a n o c c ur the wo rk she a r d e fo rma tio n c a n o c c ur, the wo rk ma te ria l will se le c t a she a r p la ne a ng le

φ tha t minimize s e ne rg y, g ive n b y

2 2

45 α β

φ = + −

De rive d b y Eug e ne Me rc ha nt

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45 α β

φ

T i h l l

2 2

45 α β

φ = + −

To inc re a se she a r p la ne a ng le

› Inc re a se the ra ke a ng le R d th f i ti l (

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Effect of Higher Shear Plane Angle

Hig he r she a r p la ne a ng le me a ns sma lle r

she a r p la ne whic h me a ns lo we r she a r fo rc e ,

tti f d t t

ec o

g e S ea

a e

g e

c utting fo rc e s, p o we r, a nd te mp e ra ture

Figure 21.12 Effect of shear plane angle φ : (a) higher φ with a

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A ma c hining o p e ra tio n re q uire s p o we r

The p o we r to p e rfo rm ma c hining c a n b e c o mp ute d fro m:

P

_c_c =

F

_c_c

v

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In U.S. c usto ma ry units, p o we r is

tra d itio na l e xp re sse d a s ho rse p o we r (d ivid ing ft lb / min b y 33 000)

(d ivid ing ft-lb / min b y 33,000)

v F HP_c = c

where HP_c = cutting horsepower, hp 000

33,

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G ro ss p o we r to o p e ra te the

ma c hine to o l

P

_g o r

HP

_g is g ive n b y

P

P c HP HPc

o r

E

P_g = c

E

HP_g = c

where E = mechanical efficiency of machine tool

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Use ful to c o nve rt p o we r into p o we r p e r unit vo lume ra te o f me ta l c ut

p e r unit vo lume ra te o f me ta l c ut

C a lle d unit power, P_u o r unit horsepower, HP_u_u

o r MR c U R P P = MR c u R HP HP =

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Unit p o we r is a lso kno wn a s the

specific energy U specific energy U

w vt v F R P P U o c MR c

u = =

=

Units for specific energy are typically N-m/mm3 _{or J/mm}3

o MR

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Ap p ro xima te ly 98% o f the e ne rg y in ma c hining is c o nve rte d into he a t

This c a n c a use te mp e ra ture s to b e ve ry hig h a t the to o l-c hip

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Hig h c utting te mp e ra ture s

1. Re d uc e to o l life

2. Pro d uc e ho t c hip s tha t p o se sa fe ty

ha za rd s to the ma c hine o p e ra to rp

3. C a n c a use ina c c ura c ie s in p a rt