pulse duration ( durasi gelombang ) the range pulse duration suitable for hole drilling is found to...

8/14/2019 Pulse duration ( Durasi Gelombang ) The range pulse duration suitable for hole drilling is found to be from 0.1 to

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Pulse duration ( Durasi Gelombang )

The range pulse duration suitable for hole drilling is found to be from 0.1 to 2.5 ms .

High pulse energy (20 ) and short pulse duration are found suitable for deep hole drilling in

aerospa!e materials.

"ssist gases (Gas #antuan)

The gas $et is normally dire!ted %ith the laser beam into the intera!tion region to remo&e

the molten material from the ma!hining region and obtain a !lean !ut. "ssist gas also shield the

lens from the e'pelled material by setting up a high presure.

aterial properties and en&ironment

These in!lude the surfa!e !hara!teristi!s su!h as refle!ti&ity an absorption !oeffi!ient of

the bul* material+ additonally+ thermal !ondu!ti&ity and diffusi&ity+ density+ spe!ifi! heat and

latent heat are also !onsidered.

Gagilano et al (1,-,) used a pulsed ruby laser for pier!ing holes in diamond %ire dra%ing dies of

1. mm diameter.

They also found that the depth of holes produ!ed in!reases initially as the diameter %idens+ up to

a limit beyond %hi!h the penetration depth de!reases. They dra% attention to small hole/drilling

appli!ations su!h as fuel filters+ !arburetor noles+ and $et engine blade !ooling holes.

" neodymium doped yttrium aluminum garnet (d/"G) laser+ fitted %ith 33 on fi&eindependent a'es for positioning !omponents %eighing up to 1 *g+ has been used in the air!raft

engine industry by 3orfe (1,4). a!!ordingly+ holes in gas turbine !omponent and noles guide

&ans+ 4 mm long and %ith an aspe!t ratio of 1061+ %ere produ!ed+ thus realiing sa&ings of 20 to

0 7 o&er 8D. 9igure sho%s laser drilled !ooling holes in turbine &ane.


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#oehme (1,4) pointed out that pulsed solid/state lasers produ! hole diameters bet%een 0.1 and

0.5 mm at a rate of 0.1 to 10 holes per se!nd+ the depth to diameter ratio lying in the range 161 to

1061. During laser light as the hole drilling+ opti!al pumping arises from the internal refle!tions

of laser light as the hole be!omes progressi&ely deeper. the ma'imum hole depth a!hie&able is+

therefore+ diminished by the energy lost due to refle!tion+ from the hole %all and also by the

de!rease of the hole aperture. "nother detrimental effe!t to laser ma!hining is the produ!tion of

plume &apor %ihtin the !a&ity that absorbs laser energy: as a result + a shallo%er hole is

produ!ed. ;nder su!h !ir!umstan!es+ repeated pulses are re!ommended by !Geough (1,44) to

o&er!ome su!h pro!ess limitations.

The problem of limited ma'imum hole depth+ non!ylindri!al profile and the presen!e of

e'!essi&e re!ast material are+ normally+ asso!iated %ith !on&entional lasers.


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9iber !omposites are sensiti&e to !on&entional !utting and drilling due to their

inhomogenous and unisottropi! nature. Delaminating + spilintering the presen!e of burrs+ and

short tool life !aused by the abrasi&e nature of the fibers are tyi!al problem. Bn laser !utting of

!omposites+ the effe!t of material anisotropy su!h as the fiber arrangement is of less importan!e.


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"nd modeling be!ome eassential. Bn this regard ilbas (1,,-) studied the brination of strias by

monitoring the high emission + from the uppor surfa!e of the %or*pie!e. During laser !utting

using fiber opti! !able and a fast response photo dete!tor.

Ce!ently ueda et al+ (1,,) and spur et al (1,,) in&estigated the temperature of a

%or*pi!e!e irradiated %ith a 3?2 pulsed laser in order to determine suitable !onditions for

!lea&age !utting of brittle materisis. Bn an attempt to !ontrol the heat !ondu!tion in the %or*pie!e

material during laser groo&ing . !hryasolouris et al (1,,) adepted the use of %ater $et in tandem

%ith the laser beam thus redu!ing the heat affe!ted one by 0 per!ent.

5.2.3.3 Texturing and structuring. Te'tured steel and aluminium strips or sheet are %idely

used parti!ulary among ear manufa!turers te'turing fa!ilitates lubri!ation during metal formingand pre&ents adheren!e of sheet during annealing. The pro!ess is applied to the roll from %hi!h

the steel or aluminium sheet ta*es its surfa!e pattern during the final stages of !old rolling.


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5.2.3.4 Dressing of grinding wheeis.hen these !rater are formed in the bond the grits are

loosened and subse =uently remo&ed due to an insuffi!ient &olume of bond surrouding the grain.

9uther multiple !ra!*s that are indu!ed thermally during %hi!h then e'poses ne% !utting edges.

Bt is also possible to refresh the %heel by e&aporting only the metal !hips !logged on the %heel

by fo!using to laser beam suitably6 ho%e&er+ sele!tion and !ontrol of the %heel by fo!using the

laser beam should be !arefully !onsideed as mentioned by ramesh et al. (1,4,).

5.2.3.5 Milling.or*pie!e tilting depends on the in!ident of the material. Todd and !opley (1,,) de&eloped a

prototype laser pro!essing system for shaping ad&an!ed !erami! materials.

This prototype is a fully automated+ fi&ea'is !losed/loop !ontrolled laser shaping system that

a!!urately and !ost effe!ti&ely produ!es !omple' shapes in the abo&e/mentioned material.

5.2.3.6 Fine cutting and drilling.Tabata et al . (1,,-) reported that 3> 3?2laser are %idely

used for fine !utting of steel plates in the auto applian!es6 ele!tri! and ele!troni! industries:offi!e

e=uipment parts: and !onstru!tion material. Bn fine !utting the thi!*ness of the steel plate &aries

from 0+5 to 1- mm+ allo%ing a !utting speed to &ary from - to1+0 m@min respeti&ely. "s depi!ted


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in fig 5.1+ the a!hie&ed fine they also ad ded that high/po%er d "G laser %ith high beam

=uality !an be used for steel plate !utting in pla!e of 3? 2lasers. The d/"G laser !an be also

ma!hine nonferrous metal su!h as !opper+ brase + and aluminum alloys more effi!iently than 3? 2

laser sin!e d/"G laser is less refle!ti&e to su!h metal. Plates of thi!*ness from 0+2 to 2 mm

are plate has been also also reported. The slit %idth and surfa!e !leanliness are almost similiar to

3?2laser pro!essing.

3ao and huang (1,,5) in&ented a ne% te!hni=ue for mi!rosie (F0+0 mm) laser ma!hining+ %ith

&arying !ur&ed %all surfa!es diamond %ire dra%ing dies using 3> d/"G laser. Cepetition

fre=uen!y+ laser po%er + and feed stop of the laser head along the 2 a'is are the most+ !riti!al

parameters. i!rohole drilling+ in a single pulse using a pulse slab d/"G laser has been

reported by rohde and &erbo&en (1,,5). "!!ordingly+ hole %ith diameter of 5 Am in a steel

plate of 1.2 mm and diameters of - Am in 0+0 mm steel foil ha&e been obtained (fig 5. 2 ).

The re!tangular spot slab laser beam !an also !reate a slit+ using a single pulse. Bndustrial

appli!ations for food industries are sie&es %ith slits of 0+0- mm ' 2 mm in stainless steel 0+5 mm

thi!*ness at a rate of 100 slits per se!ond. Ee&eral pulses are used to !reate a hole in per!ussion

drilling mode. " -0 Am diameter hole has been obtained in 100 n3r mm steel plate of

mm thi!*ness %ith an aspe!t ratio of -561 using four to fi&e pulses. i!ro blind !oles of 0 Am

diameter %ith a ma'imum aspe!t ratio 1261 to 400 Am %ith aspe!t ratio 61 ha&e also been

reported by rohde and &erbo&en (1,,5). Bt is a!!ordingly re!omended to ad$ust the pulses

duration and fre=uen!y to e&a!uate the molten material from the path of the laser beam.

The trepan te!hni=ue drills holes of diameter larger than the laser beam diamtere and


7/14

offers smaller !oni!ity and higher repeatability of the hole diameter. ;sing su!h a method+ hole

in!lined to the surfe!e into fuel/in$e!tion noles ha&e be!ome possible. i!ro!utting of 1 mm

thi!* steel plate lea&ing a*erf of 45 Am at the entran!e side and -0 Am at the e'it side and

lea&ing a taper of 1+25 per!ent ha&e been reported.

5.2.3.7 Maring of co!"uter e#$oard.Ci!!iardi et al (1,,-) de&eloped an e'!imer laser

based te!hni=ue for mar*ing !ompuetr *eybroards %ith high speed and fle'ibility of the

produ!tion line that a&oids the use of to'i! solution in the mar*ing pro!ess.


8/14

or shaped by laser s!ribing. >ith this te!hni=ue+ material is remo&ed by laser along a spe!ifi!

path on the surfa!e of the %or*spie!e. >han the material is suffi!iently stressed+ a fra!ture

a!!urrs along the s!ribed path . sili!on transistor %afers ha&e been sue!essfully s!ribed %ith a

repetiti&ely I/s%ithed d/"G laser of pea!* po%er 00 > + pulsed + at a rate of 00 pulses per

se!ond and of duration 00 ns . The rate of s!ribing reported by !Geough (1,44) is 1+5 m @

min.

5.2.3.'2 Micro!achining.Tonshof et al+(1,,) in&estigated the appli!ation of e'!imer laser

radiation in a multia'is 33 mi!roma!hining unit %ith nodular design . the unit is used to

generate mi!rostrures in !erami! and pelymer surfa!es. ;sing su!h an arrangement+ it %as

possible to produse mi!rome!hani!al parts of these materials in the fiber reinfor!ed plasti!s.

5.2.3.'3 *aser+assisted ,DM."llen and huang (1,,) de&elopment a no&el !ombination of

ma!hining pro!esses to fabri!al small holes. #efore the mi!ro 8D of holes+ !opper &apor laserratiation %as used to obtain an gray of small holes frist. These holes %ere then finished by mi!ro/

8D. Their method sho%ed that the ma!hining speed of mi!ro/8D had been in!reased and

ele!trode tool %ear %as mar*edly redu!ed %hile the surfa!e =uality remained un!hanged.

Bn general+


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-dvantages

J Tool %ear and brea*age are not eneauntered.

J Holes !an be loented a!!uralety by using an opti!al laser system for alignment.

J ery small holos %ith a large aspe!t ratio !an be produ!ed.

J " %ide &ariety of hard and diffiout/to/ma!hine material !an be tne*led.

J a!hining is e'tremely rapid and the sotup times are e!onomi!al.

J Holes !an be drilled at diffi!ult entran!e angles (10 to the surfa!e).

J #e!ause of its fle'ibility. The pro!ess !an be automated ensily su!h as the on/the/fly operation

for thin gauge material + %hi!h re=uires one shot to produ!e a hole.

J Tho operating !ost is lo%.


10/14

Then refo!used by a magneti! or ele!troni! lens system so that the beam is dire!ted under !ontrol

to%ard the %or*pie!e. The ele!trons maintain the &elo!ity (224 ' 10

*m@s ) imparted by thea!!eleration &oltage until they stri*e the %or*pie!e+ o&er a %ell/defined area+ typi!ally 0.25 mm

in diameter.

The *ineti! energy of the ele!trons is then rapidly transmitted into heat+ !ausing a

!orresponding rapid in!rease in the temperature of the %or*pie!e+ to %ell abo&e its boiling point+

thus !ausing material remo&el by e&aporation. >ith po%er densities of 1.55 >@mm 2in&ol&ed

in 8#+ &irtually all engineering materials !an be ma!hined by this ma!hining te!hni=ue.

"!!urate manipulation of the %or*pie!e !oupled %ith the pre!ise !ontrol of the beam is reported

by !Geough (1,44) to yield a ma!hining pro!ess that !an be fully automated.

The %ay in %hi!h the fo!used beam penetrates the %or*pie!!e is not !ompletely understood+

o%ing to the !omple'ity of the me!hanism in&ol&ed. Ho%e&er+ it is belie&ed that the !omple'ity

of the me!hanism in&ol&ed. Ho%e&er+ it is belie&ed that the %or*pie!e surfa!e tension. The

melted li=uid is rapidly e$e!ted an &aporied+ thus !ausing material remo&al rates of about 10

mm@min. " pulsed ele!tron beam at 10H redu!es the temperature of the %or*pie!e outside

the region being ma!hined. "n early attra!tion of 8# %as the !omparati&ely large depth/to/

%idth ratio (10061) %ith appli!ation in fine hole drilling be!oming feasible. The absen!e of

me!hani!al !onta!t and the suitability for automati! !ontrol enhan!e the pro!ess !apabilities+ but

the ne!essity to %or* in a &a!uum lengthens the floor/to/floor !y!le time.

The number of pulses re=uired to remo&e a hole of depth g!an be des!ribed by

The ma!hining time tm!an be gi&en by


11/14

The drilling rate L (mm@min) !an therefore be !al!ulated by

"!!ording to Ka!mare* (1,-)+ the number of pulses ne !an simply be des!ribed as a fun!tion

of the a!!lereaitng &oltage a and the emission !urrent Ieby

Hen!e the drilling rate L (mm@min) and the &olumetri! rate (CC) be!ome

Bn !ase of slotting a depth g and length L+ the slotting time tm is

The slotting rate (mm@min) be!omes

The CC (mm@min) !an be !al!ulated by


12/14

>here geM depth of hole remo&ed per pulse+ mm

gM depth of hole or slot re=uired+ mm

NpM fre=uen!y of pulses + s/1

tpM pulse time+ As

tiM pulse inter&al+ As

dbM beam diameter in !onta!t %ith the %or*pie!e (slot %idth)+ mm

VaM beam a!!lelerating &oltage+ *

IeM beam emission !urrent+ m"

KM !onstant

LM slot length+ mm

of pulses re=uired in!reases hyperboli!ally as the depth of the hole in!reases. Bn pra!ti!al trems+

this !on!lusion means that %hen a !ertain depth has been rea!hed+ any futher 8# to deepen the

hole %ould re=uire a &ery large in!rease in the number of pulses. The ma!hining time + in 8# +

re=uired to drill a hole depends on the number of pulses re=uired to erode a !ertain depth and

pulses fre=uen!y . for slotting by 8# + the ma!hining time is affe!ted by slot length+ beam

diameter pulse re=uired to remo&e a spe!ified depth. The 8# rate is usually e&aluated in trems

of the number of pulses re=uired to e&aporate a parti!ular amount of material. The use of

ele!tron !ounters %hi!h register the number of pulses +enables ready ad$ustment of the

ma!hining time to produ!e a re=uired depth of !ut . %or*pie!e material properties su!h as boiling

point and thermal !ondu!ti&ity play a singnifi!ant role in determining ho% readlily they !an be

ma!hined. ?ther thermal properties su!h ele!tri!al !ondu!ti&ity are !onsidered as additional

fa!tors. 9igure 5. summaries the fa!tors affe!ting the performan!e of 8#.


13/14

9ig. 5.5 sho%s the numberof pulses &ersus the relati&e ma!hinability inde'. Bn this ense+

!admium is !onsidered as the best ma!hinable material sin!e it re=uires the minimum number of

pulses. " further inde' utilies the relati&e po%er re=uired to remo&e an e=ual &olume of &arious

metals in e=ual ma!hining time basen on aluminum is sho%n in fig. 5.-. aterial ha&ing a

lo%er po%er !onsumption utilie a Emaller number of pulses to remo&e the same &olume+ and

hen!e the ma!hinability is impro&ed. The ma!hinability is affe!ted $ointly by the thermal


14/14

propertties of the material as %ell as by the density and ele!tri!al !ondu!ti&ity. Etudies ha&e

sho%n that in!reasing the a!!elerating &oltage abo&e 120 * is =uite ineffe!ti&e. T he number of

pulses+ ta*en as a ma!hniablity inde'+ depends on the hole sin*ing depth. Bnereasing the pulse

duration redu!es the number of pulses re=uired due to the higher energy a&ailable in this !ase.

The diameter of holes or ea&iti!s obtainned as a reult of pulses depends on the material being

ma!hined as %ell as on the pulse energy . the ma'imum groo&e %idth in!reases linearly %ith the

pulse !harge. 9or a gi&en pulse !harge+ "g has the largest groo&e %idth that !onstitutes a large

remo&ed &olume and hen!e the highest ma!hinability.

pulse duration ( durasi gelombang ) the range pulse duration suitable for hole drilling is found to...

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