32810934-laser-welding.docx

LASER WELDING USING Nd:YAG LASERS Laser is widely used as a thermal source for industrial applications. This is because of the local treatment, precise operation, and short processing time. One of the important industrial applications of laser processing is the laser welding, which offers considerable advantages over the conventional welding methods. High intensity laser beam melts and partially evaporates the welded material during the process. Attainment of high temperature gradient during the heating and cooling periods results in the development of high thermal stresses in the welding zone. Once the cooling period ends, the residual stress in the welding zone is resulted. This, in turn, influences the mechanical performances of the resulting welds. The laser used for laser welding here in this study is Nd

.

:YAG laser which is a solid state gain media laser Nd:YAG laser with its capability of operating in both high power CW and pulsed-modes and its flexible beam delivery through fibre optics. As for the pulsedmode Nd:YAG laser, its inherently complicated pulsed laser parameters permits a wide range of experimental conditions to be applied. The laser also has the ability of pulse shaping at pulse repetition rates of up to several kilohertz and with

a duration varying from 0.5 to 20 ms. This flexibility gives control of the thermal input with a precision not previously available. PROCESS PARAMETERS GOVERNING Nd:YAG LASER WELDING : The laser parameters are :

1. PP is the average peak power (kW) 2. 3. 4. 5. 6.

EP the pulse energy (J) TP the pulse duration (ms) PD the average peak power density(kW/m2) A the laser spot area (m2) PM the mean laser power (kW)

7. PRR the pulse repetition rate 8. TF the pulse-to-pulse time (ms) 9. CD the duty cycle 10. Welding frequency/pulse frequency(in Hz).

Here is a detailed tabulation on the range of process parameters involved in the fabrication of different materials. TABULATION: Author

Year Experime nt

Optimum Process Parameters Metals

S.P.Gadag

M.N. Srinivasan 1994

Result/ Conclusion

Pulse Characteris Frequencyation of 1-1000 Hz dissimilar Tool Steel Power of the joints in laser-400 W laser Pulse welding of and Durationtool steel 0.2-20 ms and Pulse Energyaluminium with pulsed Aluminiu 0-40 W m Rate of Nd:yag weldinglaser. 0.35m/min

Due to locally restricted energy input and high power density, laser welding permits a controlled heat distribution and a minimised interaction of the joining materials. Thus, the formation of brittle intermetallic phases could be avoided.

B.L. Mordike Chengwu Yao

Interface microstruct

Max. output Power of the

A complete metallurgical bond

ure and mechanical properties of laser welding copper– steel dissimilar joint

Binshi Xu

2001

Jun Fu

Copper and Low Carbon Steel

laser-15kW Beam Diameter- 0.7 mm FIRST SPECIMEN: Thickness-7.0 mm Power-8.0kW Penetration3.0mm Offset-0.5mm Acute angle at steel interface-84 degrees SECOND SPECIMEN: Thickness10.0mm Power11.0kW Penetration4.0mm Offset-1.0mm Acute angle at steel interface-85 degrees

was obtained at the interface between the copper plate and the steel plate in the present study. The joint was a slope butt joint and was obtained by focusing the laser beam on the steel side. A copper–steel dissimilar joint free of defects and excellent tensile properties was obtained.

Kovar (Cu-FeNi alloy)

T.A. Mai 2004

A.C. Spowage

Chen Liyun

2003

Teh Kim Ming

M.J. Torkamany

Pulse FrequencyCharacteris 20 Hz ation of Power of the dissimilar and laser-290 W joints in Pulse laser Duration- 8 welding of steel–kovar Tool Steel ms Rate of welding0.3 m/min Pulse FrequencyCharacteris 15 Hz ation of Copper Power of the dissimilar laser-275 W joints in Pulse laser And Duration-8 welding of ms Copper with Rate of aluminium Aluminiu weldingm 150 mm/s Pulse was shaped. Carbon Steel

Power of the laser- 143 W Pulse Energy-

Sound welds of Kovar and tool steel were produced by laser welding with a pulsed Nd:YAG laser. It was concluded that controlling the melting ratio of metals is an important factor for defect-free welding of dissimilar metals.

Sound welds of Copper and Aluminium were produced by laser welding with a pulsed Nd:YAG laser.

Increasing peak power in constant pulse energy caused distractive effect such as

2009 S. Tahamtan

Jose´ Roberto Berretta

Wagner de Rossi

10J Pulse Frequency20Hz Dissimilar And Rate of welding of Weldingcarbon steel 11.5 mm/s to 5754 Work aluminum Distancealloy by 1.5 mm Nd:YAG Peak powerpulsed laser Aluminiu 1.43 kW m Pulse Duration5 ms

Pulsed Nd:YAG laser welding of AISI 304 to AISI 420 stainless steels.

AISI 304 stainless steel (Fe86.2% Ni0.13% Cr13.5%)

to

Pulse energy of up to 10 J, repetition rate of up to 500Hz, average power of 100W, peak power of 3 kW and pulse duration from 0.2 up to 10ms. energy (E)=6.0 J, average power (Pm) =84 W, pulse duration (tp) =7ms and pulse frequency (f) = 14 Hz. The

spattering, high PIC and crack propagation inside the weld metal as well as weld/aluminum interface. Increasing pulse duration caused more heat input per unit length and consequently high values of PIC while decreasing pulse duration restricted enough melt production for joining.

AISI 420 steel, for any incident laser beam position had the highest microhardness value. The position of the laser beam with respect to the joint influenced the wt% of the main chemical elements (Cr, Ni,

Maurı´cio David

2006

Martins das Neves

AISI 420 stainless Steel (Fe-71% Ni-9% Cr-19%)

weld fillets were prepared at a welding speed (v) = 300mm/min and pulse overlaps of approximately 30%. Argon gas was used at a flow rate of 10 l/min.

Fe) in the weld zone but did not interfere with the homogeneity of the elements in the weld zone.

Ivan Alves de Almeida

Zhang Li

1996

G. Fontana

AISI304L nonAutogenous magnetic laser stainless welding of steel stainless steel to free-cutting steel for and the manufactur e of hydraulic valves. AISI12L13 free-

Butt joint of AISI304L and AISI12L13 can be Power of the made using a laserwelding technique. laserThe offset and the 760 W impingement angle Speed of of the laser beam welding-61.26 are two key mm/s parameters for Focus controlling the positionmelt ratio of the 0.2 mm dissimilar Offsetmaterials in order 0.12 mm to to avoid AISI304L i.e. solidification austenitic cracking in the stainless steel fusion zone and

cutting steel tubular parts, which make up the main valve cylinder.

Mild Steel (C0.18%)

TakashiUeda

EisukeSentok u

YoshihiroWaki mur

AkiraHosokaw a

2007

Pulsed Nd:YAG laser welding of Mild Steel to AISI340 stainless steel.

And

Stainless steel

micro-fissuring in the Heat Affected Zone.

Power of the The strength of the laser- 2000 W laser welds is higher than both the yield Welding Speed Range- strength of 1000 mm/min AISI340L mild steel and the rupture strength of Pulse Stainless steel frequencyunder the test 1500 Hz conditions adopted in this Focus setting- study. The greater 127 mm mechanical properties Nozzle gapof the laser welds 1.5 mm demonstrate the beneficial effect of rapid Nozzle solidification in the Diameterfusion zone and of 1.5mm a small HAZ.

CONCLUSION

:

Joining of dissimilar materials is one of the challenging tasks facing modern manufacturers. Dissimilar joining technologies find applications in many sectors including microelectronics , medical , optoelectronics and microsystems. The tiny geometry of the joints and the different optical and thermal properties of the materials makes laser welding one of the most suitable production methods.The details about each and every process parameter and the range of process parameters for welding different metals using Nd:YAG laser has ben studied in detail and a brief summary has been drawn regarding the papers in which rhe results were published and the optimum process parameters for different metal fabrication has been tabulated.