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Laser CuttingLaser Cutting

University of Texas at AustinUniversity of Texas at AustinME392QME392Q Manufacturing Processes: Unit ProcessManufacturing Processes: Unit Process

ByBy

Riko TantraRiko Tantra

Date: April 22, 2003Date: April 22, 2003


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Presentation OverviewPresentation Overview

Laser & Laser Cutting FundamentalsLaser & Laser Cutting FundamentalsMaterial Removal TypesMaterial Removal TypesEquipmentEquipment

Different Type of Lasers for Laser CuttingDifferent Type of Lasers for Laser CuttingLaser Parameters for different materialsLaser Parameters for different materialsCutting Speed & Depth of CutCutting Speed & Depth of CutComparison of Laser cutting to other methodComparison of Laser cutting to other method

CostsCostsAdvantages & Disadvantage of Laser CuttingAdvantages & Disadvantage of Laser CuttingReferencesReferences


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Laser FundamentalsLaser Fundamentals

Acronym ofAcronym of LLightight AAmplificationmplificationSStimulatedtimulated EEmission ofmission of

RRadiationadiation

Basic:Basic:

1.1. Atoms initially at theAtoms initially at the GroundGroundStateState

2.2. The atoms go toThe atoms go to ExcitedExcitedState when a high energy isState when a high energy isapplied (called pumping)applied (called pumping)

3.3. When atoms moves back toWhen atoms moves back tothe ground state, photonsthe ground state, photons(particle of light) are released(particle of light) are released

Laser Beam Characteristics:Laser Beam Characteristics:

a.a. MonochromaticityMonochromaticity

b.b. CoherenceCoherence

c.c. Very Limited DiffractionVery Limited Diffraction

d.d. Extremely high RadianceExtremely high Radiance


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Laser Beam Formation Example (Ruby Laser)1. Laser in OFF state

2. Flash Tube excite atoms in

the Ruby Rod

3. Some Atoms emit Photons

4. Photons runs parallel tothe rod direction & reflect back

and forth and stimulateemission on more atoms

5. Laser light passes throughpartially-reflective mirror


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Laser MachiningLaser Machining

Laser CuttingLaser Cutting


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Material Removal Types of Laser CuttingMaterial Removal Types of Laser Cutting1.1. VaporizationVaporization: low vaporization: low vaporization

temperature materialstemperature materials2.2. FusionFusion: Material is melted &: Material is melted &ejected (by an inert gas jet)ejected (by an inert gas jet)

3.3. Reactive Fusion:Reactive Fusion: dross is nodross is nolonger a metal, but an oxidelonger a metal, but an oxide

4.4. Thermal stress cracking orThermal stress cracking or

controlled fracturingcontrolled fracturing: for brittle: for brittlematerialsmaterials

5.5. ScribingScribing: Mechanical snapping: Mechanical snappingalong scribed linealong scribed line

6.6. AblationAblation (Excimer laser):(Excimer laser):breaking organic materialbreaking organic materialbondsbonds

7.7. Burning in reactive gasBurning in reactive gas


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EquipmentEquipment1.1. LaserLaser--beam generatorbeam generator

2.2. Beam delivery: Circular polarizers,Beam delivery: Circular polarizers,mirrors, beam splitters, focusingmirrors, beam splitters, focusinglenses and fiber optic couplingslenses and fiber optic couplings

3.3. Workpiece positioningWorkpiece positioning

4.4. Auxiliary devices: Laser head,Auxiliary devices: Laser head,

safety equipment, etc.safety equipment, etc.In addition, assist gases also requiredIn addition, assist gases also required


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Smart Laser Cutting SystemSmart Laser Cutting System

Picture from[2]


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Different Type of Laser for Laser CuttingDifferent Type of Laser for Laser Cutting

1.1. COCO22 laserlaser (most(mostcommonly used forcommonly used forlaser cutting):laser cutting):

a. Have the highesta. Have the highestContinuous WaveContinuous Wave

(CW) power(CW) powerb. Capable to extractb. Capable to extractas much as 10kW/mas much as 10kW/mof discharge tube (withof discharge tube (withtraverse flow laser)traverse flow laser)

c. Have a high energyc. Have a high energyefficiency (up to 10%)efficiency (up to 10%)

d. Capable of bothd. Capable of bothCW and PulsedCW and Pulsedoperation (5kHz)operation (5kHz)

CO2 Laser Schematic [8]


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2.2. Nd:YAGNd:YAG::a. has the highest peak power for pulseda. has the highest peak power for pulsed

operationoperationb. May be operated in either CW or pulsedb. May be operated in either CW or pulsed(200Hz) temporal modes(200Hz) temporal modes

3.3. Nd: GlassNd: Glass: more economical but has lower: more economical but has lowerthermal conductivity. Used for low pulsethermal conductivity. Used for low pulserepetition rates (1Hz; due to its poor thermalrepetition rates (1Hz; due to its poor thermalproperties) & high pulse energies. Ideal forproperties) & high pulse energies. Ideal fordrilling.drilling.

4.4. Nd: RubyNd: Ruby: low energy efficiency & power,: low energy efficiency & power,Limited to pulsed laser operationLimited to pulsed laser operation


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5.5. ExcimerExcimer::a. High power (Average power over 100W) pulseda. High power (Average power over 100W) pulsedbeams (1kHz)beams (1kHz)

b. Laser length limited to 2b. Laser length limited to 2--3 m due to the absorption3 m due to the absorptioncoefficientcoefficient pp Material narrower materials that can beMaterial narrower materials that can beprocessed vs. that of COprocessed vs. that of CO22 laserlaser

c. Used to machine solid polymer pieces, removec. Used to machine solid polymer pieces, removepolymer films, micromachine ceramics, medicalpolymer films, micromachine ceramics, medicalapplicationsapplications

d. Ablation material removal processd. Ablation material removal process

e. Higher precision & less heat affected zone vs. COe. Higher precision & less heat affected zone vs. CO22& Nd:YAG lasers& Nd:YAG lasers

f. Produces large area beamsf. Produces large area beams pp use mask to produceuse mask to produceseries of holes. 5000 holes in a polymide sheet in 3series of holes. 5000 holes in a polymide sheet in 3sec vs 50 sec using CO2 or Nd:YAG lasers.sec vs 50 sec using CO2 or Nd:YAG lasers.


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Laser Beam Temporal ModesLaser Beam Temporal ModesContinuous Wave (CW) commonlyContinuous Wave (CW) commonly

results in the highest cuttingresults in the highest cutting

speed & better surface finish.speed & better surface finish.Roughness is determined byRoughness is determined bythickness, alloy content, etc. [52]thickness, alloy content, etc. [52]

Pulsed beam results in the fewestPulsed beam results in the fewest

thermal effects & least distortionthermal effects & least distortionof workpiece. With drillingof workpiece. With drillingoverlapping holes (see right), itsoverlapping holes (see right), itspossible to cut with smootherpossible to cut with smoothersurface.surface.


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Comparison of MajorMaterial Machining Lasers


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Cutting Considerations for Different MaterialsCutting Considerations for Different Materials

A.A. Ferrous Metals:Ferrous Metals:

i.i. High efficiency due to easyHigh efficiency due to easy--toto--remove oxideremove oxidecreationcreation

ii.ii. One approximate rule:1.5kW laser power willOne approximate rule:1.5kW laser power willcutcut

a. 1mm thick mild steel at approx 10m/mina. 1mm thick mild steel at approx 10m/min

b. 10mm thick mild steel at approx 1m/minb. 10mm thick mild steel at approx 1m/min

B.B. NonNon--Ferrous Metals:Ferrous Metals:

i.i. Mostly less efficient than cutting steel, due toMostly less efficient than cutting steel, due tothe higher reflectivity, thermal conductivity &the higher reflectivity, thermal conductivity &less efficient oxidation reactionless efficient oxidation reaction

ii.ii. Similar edge qualities to SSSimilar edge qualities to SS


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C.C. NonNon--Metal: Most nonMetal: Most non--metallic materials aremetallic materials arehighly absorptive at CO2 laser wavelength.highly absorptive at CO2 laser wavelength.

Cutting process:Cutting process:i. Melt Shearing (mostly for thermoplastic): cuti. Melt Shearing (mostly for thermoplastic): cut

very quickly & high quality edgesvery quickly & high quality edgesii. Vaporization: usually only for acrylicii. Vaporization: usually only for acrylic

iii. Chemical degradation: slow cutting, highiii. Chemical degradation: slow cutting, hightemperature, but flat & smooth resulttemperature, but flat & smooth result


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Cutting Speed on MildSteel

Cutting Speed onStainless Steel


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Cutting Speed on Aluminum Cutting Speed on Acrylic

Max Cutting Speed for Polymer: V=PQt-B

P = Laser Power (W) t = material thickness (mm)

Q = an experimentally derived constant for the polymer

B = an experimentally derived constant for the material


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Power setting for different cuttingPower setting for different cuttingapplications [9]applications [9]

ApplicationApplication

RequirementRequirement

RecommendedRecommended

Laser PowerLaser Power

CuttingCutting

considerationconsideration

Thin materials:Thin materials:NonNon-- metalsmetals

150 Watt Average,150 Watt Average,450 Watt peak450 Watt peak

Up to 0.04 thick canUp to 0.04 thick canbe cut at full speed ofbe cut at full speed of

1200in/min with 1501200in/min with 150wattwatt

Thicker materials:Thicker materials:NonNon--metalsmetals

250 watt to 500 watt250 watt to 500 wattaverageaverage -- up to 1500up to 1500watt peakwatt peak

Up to 1: PowerUp to 1: PowerooppCutting SpeedCutting Speed oo ,,cleaner result & lowercleaner result & lower

HAZHAZMetalsMetals 150 watt to 500 watt150 watt to 500 watt

averageaverage -- up to 1500up to 1500watt peakwatt peak

Al, Brass, SS use 500Al, Brass, SS use 500W due to itsW due to itsreflectivity. Asreflectivity. Asthicknessthickness oo, also, also

power need to bepower need to be oo


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Laser Cutting AnalysisLaser Cutting Analysis

Cutting depth, sCutting depth, ss = 2.a.P/(s = 2.a.P/(TT1/21/2..VV.v.d.(cp.(Ts.v.d.(cp.(Ts--To)+L))To)+L))

a = absorbtivity of the materiala = absorbtivity of the material

P = Beam powerP = Beam powerVV = density= densityv = scanning velocityv = scanning velocityd = spot diameter (=2.R)d = spot diameter (=2.R)

cp = specific heatcp = specific heatTs = surface temperatureTs = surface temperatureTo = ambient temperatureTo = ambient temperatureL = latent heat of fusionL = latent heat of fusion


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Typical COTypical CO22 Laser Cutting ParametersLaser Cutting Parameters


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Characteristics of cuts by Laser CuttingCharacteristics of cuts by Laser Cutting

1.1. Kerf Width: COKerf Width: CO22 laser range from 0.1laser range from 0.1--1mm1mm

2.2. Roughness: 0.8mm materialRoughness: 0.8mm material pp 11 QQmm

10 mm material10 mm material pp 1010 QQmm

3.3. Dross: undesirable; removed by extremelyDross: undesirable; removed by extremelyhigh assist gas or by applying antisplatterhigh assist gas or by applying antisplattercoatings (i.e. graphite)coatings (i.e. graphite)

4.4. Dimensional Accuracy: main problem isDimensional Accuracy: main problem isthermal effect (distortion)thermal effect (distortion)


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Comparison of Laser cutting to other methodsComparison of Laser cutting to other methods


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Cutting Cost exampleCutting Cost exampleCAPITAL COST:CAPITAL COST:a.a. Laser Generation: $ several hundred thousandLaser Generation: $ several hundred thousandb.b. Cooling system, power supply, multiCooling system, power supply, multi--axis robot: exceed cost ofaxis robot: exceed cost of

laserlaserOPERATING COST:OPERATING COST:i.i. CO2 lasers cost $70CO2 lasers cost $70--$100/watt (Nd:YAG costs 10$100/watt (Nd:YAG costs 10--20%more)20%more)ii.ii. Safety devicesSafety devicesiii.iii. Skilled operatorSkilled operator

ExampleExample COCO22 system operating at 1500Wsystem operating at 1500Wa.a. Electricity at 7cent/kWElectricity at 7cent/kW--hrhr $2.10/hr $2.10/hrb.b. Internal laser opticsInternal laser optics $2.06/hr $2.06/hr

(lifetimes per manufacturer)(lifetimes per manufacturer)c.c. Focusing lens (500hr lifetime)Focusing lens (500hr lifetime) $1.10/hr$1.10/hr

d.d. Laser gasLaser gas $1.03/hr $1.03/hre.e. Assist gasAssist gas $3.60/hr $3.60/hr

(based on 10ga. Carbon steel w/ O(based on 10ga. Carbon steel w/ O22 assist)assist)TOTAL:TOTAL: $9.89/hr $9.89/hr


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Advantages of Laser CuttingAdvantages of Laser Cutting

1.1. Laser machining is aLaser machining is a thermal processthermal process::depends on thermal and optical rather than thedepends on thermal and optical rather than themechanical propertiesmechanical properties

2.2. Laser machining is aLaser machining is a nonnon--contactcontactprocess: Noprocess: Nocutting forces generatedcutting forces generated

3.3. Laser machining is aLaser machining is a flexibleflexible processprocess

4.4. Laser machining produces a higher precisionLaser machining produces a higher precisionand smaller kerf widths results (as small asand smaller kerf widths results (as small as0.005mm dia hole)0.005mm dia hole)

(contd)


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Advantages of Laser Cutting (Contd)Advantages of Laser Cutting (Contd)

5.5. For most industrial materials up to 10mm thick,For most industrial materials up to 10mm thick,laser cutting has a significantly higher MRRlaser cutting has a significantly higher MRR

6.6. Laser Cutting has ability to cut from curvedLaser Cutting has ability to cut from curvedworkpiecesworkpieces

7.7. For cutting fibrous material (wood, paper, etc.)For cutting fibrous material (wood, paper, etc.)laser cutting eliminates residue and debrislaser cutting eliminates residue and debris


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Disadvantage of Laser CuttingDisadvantage of Laser Cutting

1.1. Low energy efficiencyLow energy efficiency

2.2. Material damage: Heat affected zone (HAZ)Material damage: Heat affected zone (HAZ)

3.3. Laser cutting effectiveness reduces as theLaser cutting effectiveness reduces as theworkpiece thickness increasesworkpiece thickness increases

4.4. Laser cutting produces a tapered kerf shapeLaser cutting produces a tapered kerf shape(due to divergence)(due to divergence)


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ReferencesReferences1.1. Chryssolouris, G.,Chryssolouris, G., Laser Machining Theory and Practice,Laser Machining Theory and Practice,

SpringerSpringer--Verlag, New York City,NY 1991Verlag, New York City,NY 1991

2.2. Steen, W M.,Steen, W M., Laser Material Processing 2Laser Material Processing 2ndnded.,ed., SpringerSpringer--Verlag,Verlag,London 1998London 1998

3.3. Migliore, L.,Migliore, L., Laser Materials Processing,Laser Materials Processing, Marcel Dekker, Inc, NewMarcel Dekker, Inc, NewYork City, NY 1996York City, NY 1996

4.4. How Laser Works.How Laser Works. Maschler, M. Howstuffworks homepage AprilMaschler, M. Howstuffworks homepage April18. 2003. 18. 2003.

5.5. Wang F.F.Y,Wang F.F.Y, Laser Materials Processing,Laser Materials Processing, NorthNorth--Holland, NewHolland, NewYork City, NY 1983York City, NY 1983

6.6. Benedict, G.F.,Benedict, G.F., Nontraditional Manufacturing Processes,Nontraditional Manufacturing Processes, MarcelMarcelDekker, New York City, NY 1987Dekker, New York City, NY 1987

7.7. Kalpakjian, S.,Kalpakjian, S., Manufacturing Processes for EngineeringManufacturing Processes for EngineeringMaterials,Materials,Addison Wesley Longman, Menlo Park, CA 1997Addison Wesley Longman, Menlo Park, CA 1997

8.8. Fast Axial Flow LasersFast Axial Flow Lasers Theory of Operation.Theory of Operation. April 18. 2003.April 18. 2003.PRC Laser Homepage March 14, 2000PRC Laser Homepage March 14, 2000

9.9. Advance Laser Cutting Technology.Advance Laser Cutting Technology. April 18. 2003. BeamApril 18. 2003. BeamDynamics HomepageDynamics Homepage

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