18 Applications in Material Processing

8/14/2019 18 Applications in Material Processing

1/38

Dr. N. Venkatanathan

APPLICATIONS IN

MATERIAL PROCESSING


2/38

LASER WELDING

High-power lasers have foundapplications in welding.Pulsed ruby lasers have also been

used in welding.Laser welding found importantapplication in the fields of electronicsand microelectronics

Requires precise welding of very thinwires (as small as 10 m ) or weldingof two thin films together.


3/38

INTRODUCTION

Laser Beam Welding (LBW) is a modernwelding process.

It is a high energy beam process and has

many advantages like deep weldpenetration and minimizing heat inputs.

Use of laser and computers improved

the product quality through moreaccurate control of welding processes.


4/38

How it works?

The focal spot is targeted on the work piecesurface which will be welded.

At the surface the large concentration of light

energy is converted into thermal energy.The surface of the work piece starts melting and

progresses through it by surface conductance.

For welding, the beam energy is maintainedbelow the vaporization temperature of the workpiece material.


5/38

The penetration of the work piece depends onconducted heat. Therefore the thickness of thematerials to be welded is generally less than 0.80inches.

The role of focusing lenses in this process is itconcentrates the beam energy into a focal spot assmall as 0.005 inches diameters or even less.

Concentrated energy produces melting and joining otwo bodies.

The fatigue strength of the welded joint will beexcellent. So welding is in pure form.


6/38

Laser weld can easily performed between twodissimilar metals.Thus, a thermocouple may easily be welded

to a substrate without much damage toadjacent materials.One can indeed simultaneously form the junction and attach the junction to thesubstrate.This method has been used in attaching

measuring probes to transistors, turbineblades, etc.


7/38

Laser welds not only achieves weldingbetween dissimilar metal but also allowprecise location of the weld.

The Nd-YAG lasers and CO2 lasers are

the two important kinds of lasers that

find-wide ranging applications inwelding.


8/38

In welding, materials are added to join thetwo components.

Thus the laser power must not be too high to

evaporate the material.Removal of material leads, in general, to badweld.

Thus the laser used in welding process musthave a high average power rather than highpeak power.


9/38

Examples for LASER Welding

A weld of inch thick stainless steel can be carried out by CO2 laser having an output power of 3.5 KW. Thematerial was moved at a speed of 2 cm/sec in the focalplane of the lens of focal length of 25 cm.

Pulsed ruby beam having energy of 5 J with pulse lengthof about 5 nanosecond was used in welding 0.18 mmthick stainless steel.

The weld was made using overlapping spots and the laser

was pulsed at the rate of 20 pulses per minutes. Thefocused spots was about 1 mm in diameter and theassociated power density was 6 105 W/cm2


10/38

Laser offers some unique advantages, requiresextremely short time for the laser welding process.

Welding can be done in the region adjacent to theheat-sensitive areas with out affecting theseelements.

Furthermore, welding in otherwise inaccessibleareas can also be done using a laser beam.

In welding of two wires, one may have a effectiveweld even without the removal of insulation.


11/38

Most Popular types of LBW

Nd:YAG (neodymium-yttrium aluminum garnet)Laser: Produces light with a 1.06-micron

wavelength.

Carbon Dioxide Lasers: It produces light with a10.6-micron wavelength.

The Diode Laser: produces several wavelengths.

Industries Served: Aerospace, Defense/military,

Electronics, Research & development, Medical,Sensors & instrumentation, Petrochemicalrefining and Communications & energy.


12/38

ADVANTAGES

Deep and narrow welds can be done.Absence of distortion in welds.

Minimal heat affected zones in welds created.

Excellent metallurgical quality will beestablished in welds.

Ability to weld smaller, thinner components.

Increased travel speeds.


13/38

HOLE DRILLING

Drilling of holes in various substances isanother interesting application of the laser.

Drilling holes less than about 250 m in

diameter by using metal bits becomes verydifficult and is also accompanied by frequentbreakage of drill bits.

With lasers one can easily drill holes as smallas 10 m through the hardest of substances.


14/38

The Swiss watch industry has been using flash-pumped neodymium-YAG lasers to drill ruby stonesused in timepieces.So laser ensures that the absence of problem like drill

breakage.Laser hole drilling has the advantage of precise

location of the hole.A laser pulse having a pulse width of about 1/1000 of

a second and an energy of approximately 0.05J canburn through a 1-mm thick steel plate leaving behinda hole of radius 0.1 mm.


15/38


16/38

The width of the cut should be as small as possibleand it should avoid any re-welding of the cutmaterial.

The efficiency of the laser cutting can be increasedby making use of gas jet coaxial with the laser.

In some cases, one uses a highly reactive gas likeoxygen so that when the laser heats up the material,

it interacts with the gas and gets burnt.The gas jet also helps in expelling the molten

material.


17/38


18/38

Such a method has been used to cut thematerials like stainless steel, low-carbon steel,titanium etc.

For e.g., a 0.13 cm thick stainless steel plate wascut at the rate of 0.8 m per minute using a 190watt CO2 laser using oxygen jet.

In some methods, one uses inert gases in theplace of oxygen.

Such a gas jet helps in expelling the moltenmaterial.


19/38

Such a technique would be very efficient withmaterials which absorb most radiation at thelaser wavelength. Wood, paper, plastic, etc. have been cut using

this method.

A gas jet assisted CO2 laser can be used forobtaining parallel cuts of up to 50 mm depth in

wood products. At the cut edges carbonization occurs, but it is

usually limited to a small depth of the material.


20/38

This causes a discoloration only and can bedecreased by increasing the cutting speed.

Laser cutting of stainless steel, nickel alloys

and other materials finds widespreadapplication in the aircraft and automobileindustry.

It has been recently tested and shown thataluminum sheet metal can be efficiently cutwith high-powered laser beam.


21/38

In fact, it is believed that it could be asmuch as 60% to 70% less expensive than theconventional techniques.

Laser cutting has also been used in thetextile industry for cutting cloth.

It is even claimed that this is the greatest

advance in apparel manufacturing since thesewing machine.


22/38


23/38

Moreover, the laser cut has the capacity of operatingon complex profiles and with very small rays ocurvature.

Unlike water and traditional cutting systems, lightexerts no mechanical pressure on the piece.

Absence of wear in the instrument.

Cutting capability independent of hardness of the

material.Has the capability to cut coated or surface treated

materials.


24/38

Ease of integration with other automatedsystemsVery high trimming capability

Capability of adapting immediately tochanges in production requirements.In many cases, laser cutting can produce

finished pieces that do not require furtherprocessing (polishing, de-burring, finishingetc.).


25/38

Laser Ablation

Laser ablation is the process ofremoving material from a solid (oroccasionally liquid) surface by

irradiating it with a laser beam. At low laser flux, the material is

heated by the absorbed laser energy

and evaporates or sublimates. At high laser flux, the material is

typically converted to a plasma.


26/38

Usually, laser ablation refers to removingmaterial with a pulsed laser.

But it is possible to ablate material with acontinuous wave laser beam if the laser

intensity is high enough.The amount of material removed by a single

pulse is depending on the depth over which thelaser energy is absorbed.

The absorption of laser energy depends on thematerial's optical properties and the laser

wavelength.


27/38

Laser pulses can vary over a very wide range ofduration from milliseconds to femtoseconds.

The laser fluxes can be precisely controlled.

This makes laser ablation very valuable for bothresearch and industrial applications.

The simplest application of laser ablation is toremove material from a solid surface in acontrolled fashion.

Laser drilling is good example.


28/38

Pulsed lasers can drill extremely small,deep holes through very hard materials.Very short laser pulses remove material

so quickly that the surrounding materialabsorbs very little heat.Laser drilling can be done on delicate or

heat-sensitive materials, including toothenamel which called as laser dentistry.


29/38

Laser energy can be selectively absorbed bycoatings, particularly on metal.

So CO2 or Nd:YAG pulsed lasers can be usedto clean surfaces.

Removal of paint or coating, or preparesurfaces for painting without damaging theunderlying surface.

High power lasers clean a large spot with asingle pulse.

Lower power lasers use many small pulseswhich may be scanned across an area.


30/38

ADVANTAGES

No solvents are used, so it is environmentally friendlyand operators are not exposed to chemicals.

It is relatively easy to automate, e.g., by using robots.

The running costs are lower than dry media or CO2

ice

blasting, although the capital investment costs aremuch higher.

The process is gentler than abrasive techniques, e.g.

carbon fibres within a composite material are notdamaged.

Heating of the target is minimal.


31/38

High level Applications

To process the material removed into new forms eithernot possible or difficult to produce by other means.

A recent example is the production of carbon nanotubes.

To create coatings by ablating the coating material froma source and letting it deposit on the surface to becoated, called special type of physical vapor deposition.

Can create coatings from materials that cannot readilybe evaporated any other way.

This process is used to manufacture some types of hightemperature superconductor.


32/38

Remote laser spectroscopy uses laser ablation tocreate a plasma from the surface material.

The composition of the surface can be determined byanalyzing the wavelengths of light emitted by the

plasma.Finally, laser ablation can be used to transfer

momentum to a surface.

The ablated material applies a pulse of high pressureto the surface underneath it as it expands.

The effect is similar to hitting the surface with ahammer.


33/38

This process is used in industry to hardenmetal surfaces.Used as a damage mechanism for a laser

weapon.It is also the basis of pulsed laser

propulsion for spacecraft.

Laser ablation has biological applicationsand can be used to destroy nerves and othertissues.


34/38

Medical Applications

Used to remove part of biological tissue.Surface ablation in the skin (also called

resurfacing, because it induces regeneration)can be carried out by lasers.Its purpose is to remove skin spots, aged skin,wrinkles, thus rejuvenating it.Surface ablation is also employed in the ENT

treatment.For several kinds of surgery, such as for

snoring.


35/38

Ablation therapy using radiofrequency waveson the heart is used to cure a various of cardiac.

It is a process by which the molecular bonds oa material are dissolved by a laser.

For a laser to be able to ablate tissues, thepower density has to be very high.

Otherwise thermo-coagulation will happen, which is just a thermal vaporization of thetissues.


36/38

Roto-ablation is a type of arterial cleansingthat consists of inserting a tiny, diamond-tipped, drill-like device into the affected arterto remove fatty deposits .

The procedure is used in the treatment ocoronary heart disease to restore blood flow.

Bone marrow ablation is a process whereby thehuman bone marrow cells are eliminated inpreparation for a bone marrow transplant.


37/38

Ablation of brain tissue is used for treatingcertain neurological disorders likeParkinsons disease and some time

psychiatric disorders.Recently, some researchers reported

successful results with genetic ablation.

In particular, genetic ablation is potentially amuch more efficient method of removingunwanted cells, such as tumor cells.


38/38

Laser ablation is greatly affected by the nature of thematerial and its ability to absorb energy.Therefore the wavelength of the ablation laser should

have a minimum absorption depth.

Surface ablation of the cornea for several types of eyerefractive surgery is now common, using an excimerlaser system (LASIK and LASEK).Since the cornea does not grow back, laser is used to

remodel the cornea refractive properties, in order tocorrect refraction errors, such as astigmatism, myopiaand hyperopia.

18 Applications in Material Processing

Documents

Transcript of 18 Applications in Material Processing