laser_beam_machining

8/7/2019 laser_beam_machining

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EPP 212

Advanced Manufacturing Technology

Group Seminar


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L

B

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AASSEERR

EEAAMM

MACHI IN NGACHININM G


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Laser beam machining process uses highly coherent lightsource.

This beam can be focused by means of a lens on a verysmall spot in the work piece.

The high power radiation of laser gives rise to hightemperature on a small area of work piece. This initiatesthe cutting process in the work material.

The equipment consists of ruby crystal placed inside aflash lamp. The flash lamp is used to produce highintensity light rays.


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The ruby crystal is thus simulated and this produces

highly spatial laser beam. When the rays hit the work

surface it causes partial or complete vaporization ofsurface material.


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Design

Consideration


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Non-reflective workpiece surfaces are

preferable

Sharp corners are difficult to produce; deepcuts produce tapers

Consider the effects of high temperature on

the workpiece material


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Laser Beam Machining (LBM) is thermalprocesses considering the mechanisms ofmaterial removal.

Laser Beam Machining or more broadly lasermaterial processing deals with machining andmaterial processing like heat treatment, alloying,

cladding, sheet metal bending. Laser stands for light amplification by stimulated

emission of radiation.

As laser interacts with the material, the energy ofthe photon is absorbed by the work material

leading to rapid substantial rise in localtemperature. This in turn results in melting andvaporisation of the work material and finallymaterial removal.


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Similarly as can be seen in Fig. 9.6.1, laser beams canbe focused over a spot size of 10 100 m with apower density as high as 1 MW/mm2.

Electrical discharge typically provides even higherpower density with smaller spot size.

EBM and LBM are typically used with higher powerdensity to machine materials. The mechanism ofmaterial removal is primarily by melting and rapid

vaporisation due to intense heating by the electronsand laser beam respectively.


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Laser can be used in wide range of manufacturing

applicationsy Material removal drilling, cutting and tre-panning

y Welding

y Cladding

y Alloying

Drilling micro-sized holes using laser in difficult to

machine materials is the most dominant application in

industry. In laser drilling the laser beam is focused over the

desired spot size. For thin sheets pulse laser can be

used. For thicker ones continuous laser may be used.


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Typical Application

and

Product Made


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4 Typical application

Material removal-CuttingWelding

CladdingSoldering


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Method used in laser cutting

vaporization

melt and blow

melt blow and burn thermal stress cracking

scribing

cold cutting burning stabilized laser cutting


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Laser Beam welding

LBW is a versatile process, capable of

welding carbon steels, HSLA

steels, stainless steel, aluminum,

and titanium The weld quality is high.


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Laser Cladding

A method of depositing material by which a powdered orwire feedstock material is melted and consolidated by useof a laser in order to coat part of a substrate or fabricate anear-net shape part.

It is often used to improve mechanicalproperties or increase corrosion

resistance, repair worn out parts, and

fabricate metal matrix composites.

The powder used in laser cladding isnormally of a metallic nature, and is

injected into the system by either coaxial

or lateral nozzles.


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Laser Soldering

A technique where a laser is used to melt and solder anelectrical connection joint. Diode laser systems based onsemiconductor junctions are used for this purpose.

The beam is delivered via an optical fiber to the

workpiece,with fiber Since the beam out of the end of the fiber

diverges rapidly, lenses are

used to create a suitable spot

size on the workpiece at a

suitable working distance. Awire feeder is used to supply

solder.


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Product made by LBM


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Advantage of Laser Beam

Machining


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Easier workholding

Reduced contamination of workpieceReduced chance of warping the material that

is being cut

High precision (more precise and using less

energy when cutting sheet metal compared toplasma machining)


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Consume electricity (eg. A typical 1500-watt

CO2 laser will have a running cost in the region of10 - 20 per hour.)

High initial capital cost

High maintenance cost

High purity gas (for the laser generating chamber)

Limited thickness of sheet metal can cut outcompared to plasma machining

Presence of Heat Affected Zone specially in gas

assist CO2 laser cutting

Thermal process not suitable for heat sensitive

materials like aluminium glass fibre laminate


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AlternativeMethod


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Press tools (working on the shearing principle) are avery quick and efficient way to produce components from

sheet or strip stock in large quantities, they are however

time consuming to set up and expensive to tool.

Machining and forming process, such as combining oflaser cutting and punching of sheet metal

eg. turret punch presses have been equipped with an

integrated laser head; the machine can punch or laser cut,but it cannot do both simultaneously


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New laser cutters have positioning accuracy of10 micrometers and repeatability of 5micrometers.

This process is capable of holding quite closetolerances, often to within 0.001 inch (0.025mm) Part geometry and the mechanicalsoundness of the machine have much to dowith tolerance capabilities. The typical surface

finish resulting from laser beam cutting mayrange from 125 to 250 micro-inches (0.003mm to 0.006 mm)


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Surface roughness is an effective parameter

representing the quality of machined surface.

surface roughness value reduces onincreasing cutting speed and frequency, and

decreasing the laser power and gas pressure

surface roughness value was found to bereduced on increasing pressure in case of

nitrogen and argon but air gives poor surfacebeyond 6 bar pressure. Also, surface finishwas better at higher speeds.


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The surface roughness is minimum andlaser power has a small effect onsurface roughness but no effect onstriation frequency

Micromachining of 0.5 mm thick NdFeBceramic (magnetic material) usingpulsed Nd:YAG laser gives bettersurface finish in water as compared toair


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LBM economics

Depend on number of parts manufactured onthat machine

One laser produced and used in differentmachine, can reduce investment costs of laser

Reduce time of production of laser, hencereduce steps to setting up machine

By increasing the technological compactness,different machining process can be done inone machine

Since the machining procedure is donecontinuously, the total time to produce isreduced, less time for more production


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LBM economics(cont.)

Hardening process was replaced by laserhardening.

Cost is saved due to integration of process.

Less reworking because less distortionoccurred when hardening in finalprocessing.

It is beneficial if the production can be

taken in integrated process as switchinghalf-finished product to another station forfinishing will waste time.


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Perspectives of applications of micro-machining utilizing water jet-guided laser.

- It is accurate, produce small cutting radius- temperature-controlled which no burns on

work piece

- without producing impurities

3D LDM machining such as turning andmilling- controlling different/ many laser in different

angles

Improving laser quality to cut difficult-to-cutmaterials


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Develop the models with no or very fewassumptions to get the real solution of the LBM

problems quantitatively.- optimization of process variables.- consider about beam spot diameter, thermal

conductivity and reflectivity of work piecematerial

Hybrid or integration of LBM with othermachining methods.

Solve the weakness of laser : thermal process- burns on material hence affect mechanical

properties.- surface is not perfect from aspect ofroughness, parallelism and flatness due toburining.


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COHERENTCOHERENT

Laser BeamLaser BeamMachining CentreMachining Centre

(LMC)(LMC)


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Its ApplicationsIts Applications Architectural modelsArchitectural models

PrecisionPrecision ssheet metalsheet metals

Acoustic guitar fabricationAcoustic guitar fabrication

Trophies and awardsTrophies and awards

Medical part fabricationsMedical part fabrications

Printing and nameplatesPrinting and nameplates

Rapid prototypesRapid prototypes


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Extremely reliable ,inexpensive to run ,

provide over 20,000hours of cuttingbefore requiring

service.

Its Laser TechnologyIts Laser Technology

Sealed COSealed CO22 LaserLaser

Compared

to

Flow-through

Gas Lasersrequire an external gas source to

supply gas flowing through the laser

Use onlyUse only100 to100 to

500 Watt500 Wattsealedsealed

CO2CO2


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CombinationCombination of a beam with a low M2of a beam with a low M2

Allowing smaller focus spot

sizes (highly focused spot

(.004 diameter)

Allow square-wave pulsing

characteristics

Allows a 500W model, which

generates 1500W peak power, to

produce instantaneous intensities

of up to 0.3 MW/mm2 at the

material

reduces the Heat Affected

Zone due to lower thermal

conduction

Pulsing gives accurate and

essential control over how

much and how fast energy

is delivered for material

processing by using

dedicated microprocessor

Control to harness

the power of each

pulse and maximize

material processing

efficiency

Less charring when

cutting materials such as

paper, and less melting

when cutting materials

such as polymers.

faster vaporization

of materials, higher

processing speeds

and deeper cuts.


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FarFar--infraredinfraredlight at alight at a

wavelengtwavelength of 10.6h of 10.6microns.microns.

Produce highProduce high--frequencyfrequency

pulses withpulses withextremely fastextremely fast

riserise--andand--fallfalltimes (opposite).times (opposite).

for cutting orfor cutting ordrilling, ratherdrilling, ratherthan for merelythan for merelyheating theheating thematerial to bematerial to beprocessed.processed.


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SlabSlab--discharge CO2 Laserdischarge CO2 Laser VS Conventional CO2Conventional CO2

LaserLaser

Permanentlyconfines thelasing gasmixturebetween two

rectangularplate

Noreplacementgas and noscheduledmaintenance tothe laser headfor up to25,000 hours(roughly two-and-a-halfyears) of

continuousoperation

lowerelectrical andcooling-waterrequirementsthanconventionallasers thatflowconsumablegases throughthe laser head.

Cost

ProductivityProductivity


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from group D

laser_beam_machining

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