sojom laser welding simulation

8/3/2019 SOJOM Laser Welding Simulation

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National Institute of Technology, Trichy

N. Siva Shanmugam, Department of Mechanical Engineering

FINITE ELEMENT SIMULATION OF

THE TEMPERATURE AND BEAD

PROFILES OF T-JOINT LASER WELDS

16.11.2011 1

N. Siva Shanmugam1*, G. Buvanashekaran2 and K. Sankaranarayanasamy1

1Department of Mechanical Engineering, National Institute of Technology,

Tiruchirappalli – 620 015, Tamil Nadu, India.2Welding Research Institute, Bharat Heavy Electricals Limited,

Tiruchirappalli – 620 014, Tamil Nadu, India.





16.11.2011 2

The laser welding is a keyhole welding process havingconcentrated heat input. To obtain the required weld profile and

quality of weld, correct process parameters have to be selected.

Laser beam

Keyhole

Base material

Plasma

Melt pool

Input Parameters

Output ParametersBeam power

Welding speed

Beam Angle

Spot Diameter

Exposure time

Bead width

Depth of

penetration

Schematic representation of key hole welding

Laser Beam Welding





16.11.2011 3

• The Heat developed during welding process intermittently

interacts with the work piece over very short time intervals,resulting in very rapid heating and cooling cycles.

• The weld bead is the product of a number of overlapping spot

welds, and every point in the weld area experiences a complex

series of thermal cycles during the passage of the welding heat

source.

• This complexity implies that analytical modeling techniques are

almost impossible.

• The Finite Element Modeling, therefore, is the preferred

option, although the analysis requires a very large number of

small time steps.

WHY FEM ?





16.11.2011 4

Laser head

Cross jet

Work table

Shielding gas

Exhaust

Fibre Optic

Cable

Cross slide

CCTV

2kW Nd:YAG laser welding system at WRI

Power Source

Computer Numerical Controlled

welding system





Material for Experimentation – SS304

The alloy 304 is a general-purpose austenitic stainless steel

The melting point of stainless steel ranges from 1400 to 1455oC.

Chemical Composition of AISI 304 Stainless Steel

16.11.2011 5

Component C Cr Fe Mn Ni P S Si

Wt. % 0.055 18.28 66.34 1.00 8.48 0.029 0.005 0.6





16.11.2011 6

Flow Diagram –

Laser Welding

Simulation


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where(x,y,z) = coordinate system attached to the heat sourceqv = power generation per unit volume in the domain D (W m–3)kx, ky, kz = thermal conductivity in the x, y and z directions (W m–1 K–1)Cp = specific heat capacity (J kg–1 K–1)ρ= density (kg m–3)t = time (s)

vw = velocity of workpiece (m s–1)

z y xq z

T k

z y

T k

y x

T k

x y

T v

t

T C vw p ,,)(

Mathematical Description of the Model

16.11.2011 7




2

0

2

0

3exp

r

r QQr

21

22 )( y x r ) /()(*)(0 ieeiee z z z zr r r r

,

Qr is the source intensity,

Q0 is the maximum source intensity,

r e is the (x,y) parameter of Gaussian curve in the upper plane at z=ze,

r i is the (x,y) parameter of Gaussian curve in the lower plane at z=zi .

3D Conical Gaussian heat source model

16.11.2011 8




Heat Input Calculation

where Qkeyhole is the absorbed laser beam power (75%), r0 is theaverage keyhole radius, H is the plate thickness, r is the currentradius, i.e. the distance from the cone axis and z is the currentdepth.

Where q is the maximum heat flux per unit area and R is theheat source effective radius (R = 2r0, ro is the averagekeyhole radius, about 0.3mm).

Surface

Volume

2

22

0

)(3

exp),( R

y x

q y xq

20

3

R

Qq

top

topQ is a power of the plane heat source (25%)

h

ze

hr

Q zq

r r

keyhole1

2)(

2

01

2

0

vq is a Volumetric heat source

h

16.11.2011 9

H. Du, L. Hu, J. Liu and X. Hu, “A study on the metal flow in full penetration laser beam welding for

titanium alloy”, Journal of Computational Materials Science, 29, 2004, pp. 419-427.




The initial condition is

The essential boundary condition is

Boundary Conditions

z y xT t z xT ,,,,0, 0

z y xT z y xT ,,0,,, 0

on the boundary S1. This condition prescribes

nodal temperatures at the inlet surface S1.

16.11.2011 10





04

0

4

0

T T T T hq

n

T k n

Boundary Conditions

The natural boundary conditions can be defined by

nk

q

h

0T

where

is thermal conductivity normal to the surface (W/m K)

is prescribed heat flux (W/m2)

(varies with beam power, welding speed and beam incident angle)

is heat transfer coefficient for convection (W/m2 K)

is Stefan-Boltzmann constant for radiation (5.67 x 10 -8 W/m2 K4)

is emissivity

is ambient temperature (K)

on the boundary S2.

16.11.2011 11





Heat Input to FEM A three Dimensional Conical Gaussian Heat

Source Model

T - Joint

16.11.2011 12

S S D





Thermal material properties namely conductivity, specific heat, density are

temperature dependent

The latent heat of fusion is considered by the enthalpy of material for the

calculation of phase change The physical phenomena like viscous fore, buoyancy force, convective melt

flow and Marangoni effects are neglected

It is also assumed that, the absorbed laser energy is considered as 69.3% of

the laser power as proposed by Xie and Kar.

The assumptions made in this investigation are:

16.11.2011 13Ref: Xie J, Kar A. Laser Welding of Thin Sheet Steel with Surface Oxidation. Welding ResearchSupplement 1999; 78:343s – 348s

N Si Sh D f M h i l E i i





16.11.2011 14

Sl.No.

BeamPower

(BP), Watts

Weldingspeed(WS),

mm/min

BeamAngle

(BA), deg.Focal Length

(F), mm

1 1000 500 30

1602 1250 600 45

3 1500 700 60

Laser Welding Parameters

Three input laser parameters namely laser beam power, welding speed and

beam incident angle varied at three levels resulting in 33 = 27 welding trials.

The experimental trials are conducted based on full factorial design.

N Si Sh D t t f M h i l E i i





16.11.2011 15

Schematic representation of laser welding process for T-joint specimen

N Si Sh D t t f M h i l E i i





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T-joint laser weld

Beam power -1250 W, welding speed 500 mm/min, beam angle 30o

N Si a Shanm gam Department of Mechanical Engineering





16.11.2011 17

Experimental Work

Cross sectional views of 1.6 mm thick T joint specimen welded with (a)

60o, (b) 30o and (c) 45o beam angles on both sides of the stiffener

Beam power 1250 W,

welding speed 500 mm/min

Partial Penetration

Partial Penetration

N Siva Shanmugam Department of Mechanical Engineering





16.11.2011 18

Physical Model of T-joint configuration






Finite Element Model

2D

3D

T Joint

16.11.2011 19






16.11.2011 20

The temperature distribution during laser welding process at various time steps

Beam power -1250 W, welding speed 500 mm/min, beam angle 30o






Weld pool shape between (a) Experimental investigation and

(b) finite element simulation

(a) (b)

Comparison Exp. Vs. FEM

T Joint

16.11.2011 21

Beam power -1250 W,

welding speed 500 mm/min

beam angle 30o






60o 45o

30o

Beam power - 1250 W,

welding speed - 500 mm/min

Bead Shape

BA - 60o BA - 45o

BA - 30o

T Joint

16.11.2011 22






16.11.2011 23

•

Proper fusion of base material (horizontal and vertical sheets) and tiebetween the bead profiles is achieved when the laser system is operatedwith 30o beam incident angle,1250 W beam power and 500 mm/min.welding speed.

• A partial penetration is established in the macro graph, when the

beam angle is maintained at 60o

• For the beam angle of 45o, proper fusion of base material is achievedbetween the horizontal and vertical sheets, but there is no tie betweenthe resulting bead profiles

• A series of experiments have been conducted to verify the finiteelement simulation results.

• Comparison of experimental and simulation results reveals a verygood correlation for depth of penetration and bead width values with astandard error of 2.78% and 1.9%, respectively

Based on the results of this investigation, the following conclusionsare made:

CONCLUSIONS






16.11.2011 24

sojom laser welding simulation

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