Laser beam welding:Laser beam welding:

High energy density input process Precisely controllable

(close tolerence: ± 0.002 in.)

Low heat input produces low distortion

Does not require a vacuum (welds at atmospheric pressure)

No filler metal required

Why do we need laser for welding?Why do we need laser for welding?Traditional welding:Traditional welding:

Natural limitations to speed and productivity

Thicker sections need multi- pass welds A large heat input Results in large and unpredictable distortions Very difficult to robotize

The term laser is an acronym for Light Amplification by Stimulated Emission of Radiation.

A laser beam is a powerful, narrow, monochromatic and directional beam of electromagnetic radiation.

Often, these beams are within the visible spectrum of light.

A laser device excites the atoms in a lasing medium. The electrons of these atoms move to a higher orbit, then release photons, creating a laser beam.

Laser BasicsLaser Basics Laser ComponentsLaser Components

Lasing Medium:Lasing Medium: Provides appropriate transition and Determines the wavelength (it must be in a metastable state)

Pump:Pump: Provides energy necessary for population inversion

Optical Cavity:Optical Cavity: Provides opportunity for amplification and Produces a directional beam (with defined length and transparency)

Properties of LaserProperties of LaserCoherentCoherent (synchronized phase of light)

Collimated Collimated (parallel nature of the beam)

MonochromaticMonochromatic (single wavelength)

High intensityHigh intensity (~1014W/m2)

LLight ight AAmplification by mplification by SStimulated timulated EEmission of mission of RRadiationadiation

Laser beams are used in industry to cut and weld metal and to survey land and construct buildings.

In scientific research, they're used in laser spectroscopy and chemical analysis.

They are used in medical procedures such as eye, cancer and heart surgery, as well as in cosmetic procedures. Dental applications include cavity treatment, nerve regeneration and reshaping gum tissue.

Laser beams can measure distances with a high degree of accuracy. Laser scanners in grocery stores save time in pricing products and in processing the customer's purchase.

In industry, laser cutting and welding are faster and more precise than other methods. In medical and dental procedures, lasers do less damage than scalpels and drills. Scientific research using lasers has led to real-world advances, such as the use of fiber optics in telephone communications and computer networking.

When overlaying with a laser an optical arrangement is used to focus the laser beam on the work piece and heat it. Simultaneously hardfacing material in the form of powder is introduced into the laser beam and melted. Due to the narrow heat affected zone and the fast cooling rate the heat input is low, thereby producing an almost stress free overlay.

The beam is focused towards the joint which causes the materials to change from solid to liquid state. Upon cooling it returns to a solid state.

Low heat inputFast coolingAlmost stress free overlaysHigh hardnessFine microstructure

lasers used for weldinglasers used for welding

COCO22 Laser

NdNd3+3+:YAG:YAG Lasers

Lamp-Lamp-pumped

LD-LD-pumped

Disk Disk Laser DiodeDiode Laser FiberFiber Laser

CO2 laser The carbon dioxide laser (CO2 laser) was one of the 

earliest gas lasers to be developed  in 1964[, and is still one of the most useful.

 Carbon dioxide lasers are the highest-power continuous wave lasers that are currently available. They are also quite efficient: the ratio of output power to pump power can be as large as 20%.

 The CO2 laser produces a beam of infrared light with the principal wavelength bands centering around 9.4 and 10.6 micrometers

CO2 Laser: Characteristics

Wavelength 10.6 µm; far-infrared ray

Laser Media CO2–N2–He mixed gas (gas)

AveragePower (CW)

45 kW (maximum)(Normal) 500 W – 10 kW

Merits Easier high power (efficiency: 10–20%)

Lamp-pumped YAG Laser: Characteristics

Wavelength 1.06 µm; near-infrared ray

Laser Media Nd3+: Y3Al5O12 garnet (solid)

AveragePower [CW]

10 kW (cascade type & fiber-coupling)

(Normal) 50 W–4 kW

Merits Fiber-delivery, and easier handling (efficiency: 1–4%)

LD-pumped YAG Laser: Characteristics

Wavelength about 1 µm; near-infrared ray

Laser Media Nd3+ : Y3Al5O12 garnet (solid)

AveragePower

[CW] : 13.5 kW (fiber-coupling max.)

[PW] : 6 kW (slab type max.)

Merits Fiber-delivery, high brightness, and high efficiency (10–20%)

YAG Laser Application: Automobile Automobile IndustriesIndustries

Lamp-pumped

3 to 4.5 kW class; SI fiber delivered (Mori, 2003)(Mori, 2003)

LD-pumped 2.5 to 6 kW

New Development

(Bachmann (Bachmann 2004)2004)

Rod-type:Rod-type: 8 and 10 kW; Laboratory Prototype

Slab-type:Slab-type: 6 kW; Developed by Precision Laser Machining Consortium, PLM

YAG Laser

Disk Laser: Characteristics

Wavelength 1.03 µm; near-infrared ray

Laser Media Yb3+ : YAG or YVO4 (solid)

AveragePower [CW]

6 kW (cascade type max.)

Merits Fiber-delivery, high brightness, high efficiency(10–15%)

Disk LaserDisk Laser

A thin disc is used as lasing medium… it is often called active mirror as 

it is used as mirror with laser gain. Within resonator, it acts as end 

mirror… 

Fiber Laser: Characteristics

Wavelength 1.07 µm; near-infrared ray

Laser Media

Yb3+ : SiO2 (solid), etc.

AveragePower [CW]

20 kW (fiber-coupling max.)

Merits Fiber-delivery, high brightness, high efficiency(10–25%)

Recent DevelopmentRecent Development (Thomy et.al. 2004; and Ueda 2001): FiberFiber lasers of 10kW10kW or moremore are commerciallycommercially available Fiber lasers of 100kW100kW and moremore are scheduledscheduled FiberFiber laser at 6.9kW6.9kW is able to provide deeply penetrateddeeply penetrated weld at high high speed FiberFiber laser is able to replacereplace high quality (slab) COCO22 laser laser for remoteremote or scanningscanning welding

Fiber LaserFiber Laser

Fiber laser is meant to be lasers with optical fiber as gain medium….Fiber doped with

rare earth ions e.g. erbium, neodymium or ytterbium is used as gain medium and fiber

brag gratings made either directly in doped fiber or in an undopped fiber which is

spliced to an active fiber are commonly used as optical resonator

Types of LBWTypes of LBWConduction WeldingConduction Welding

DescriptionDescription Heating the workpiece above the melting temperature without vaporizing Heat is transferred into the material by thermal conduction.

CharacteristicsCharacteristics Low welding depth Small aspect ratio (depth to width ratio is around unity) Low coupling efficiency Very smooth, highly aesthetic weld bead

ApplicationsApplicationsLaser welding of thin work pieces like foils, wires, thin tubes, enclosures, etc.

Types of LBWTypes of LBW

Keyhole WeldingKeyhole Welding

DescriptionDescription Heating of the workpiece above the vaporization temperature and forming of a keyhole Laser beam energy is transferred deep into the material via a cavity filled with metal vapor Hole becomes stable due to the pressure from vapor

generated

CharacteristicsCharacteristics High welding depth High aspect ratio (depth to width

ratio can be 10:1) High coupling efficiency

LaserLaser

Beam Delivery UnitBeam Delivery Unit

Workpiece Positioning UnitWorkpiece Positioning Unit

Processing Processing OpticsOptics

Schematic Schematic DiagramDiagram

Beam Beam Delivery Delivery unitunit

Lasers Beam WeldingLasers Beam Welding

Low possibility of HAZ in the joint No need for filler metal Reduce Latency No tool wear LBW is not influenced by magnetic fields

Joints must be accurately positioned Maximum weld penetration is limited (19-21mm) High reflectivity and high thermal conductivity of

materials like Aluminum effect the weldability of the joint