13-3- Modelling of Fsw

7/28/2019 13-3- Modelling of Fsw

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Author & year Title Source

C. Chen & R.

Kovacevic

(2004)

Thermomechanical modelling and force

analysis of friction stir welding by the finite

element method

J. Mechanical

Engineering Science,

218 : pp 509-519


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AIM

A 3D finite element method is proposed to study the thermal

history and stress distribution in the weld and subsequently, to

compute mechanical forces in the longitudinal, lateral and vertical

directions.


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Model Description

Tool Material -AISI A2 steel

Shoulder diameter -24 mm

Pin Diameter -6 mm Base material - Al 6061-T6

Workpiece dimensions

200 mm 50 mm 6.4 mm


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Material properties of tool and

workpiece material


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Heat transfer model

The rate of heat generation derived from the friction for a

single element at the interface is

dq= 2 (T) p(T) dr

is the rotational speed of the tool

(T) is the coefficient of friction between the tool and the materialp(T) is the pressure on the shoulder of the tool

The rate of heat generation over the entire interface

of the contact will be

q=2/3 ( (T) p(T) (Ro3-ro3))

Where Ro and ro outer radii of the tool and the probe respectively


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Mechanical model

Displacement is given by

U= [D] where [D] is the displacement function matrix

In the displacement formulation, the essential

boundary conditions are specified as

Uy =0

The stressstrain equation is described as

S= [M]


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Meshed model


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Experimental setup


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Three axis force measurement device


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Results and Discussion


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Study of thermal history

A comparison of the calculated and the measured temperature histories at the

location 10mm to the weld centre-line and 1.6mm below the top surface of the plate

V =140mm/min and = 500 r/min)


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A comparison of predicted temperature distribution and measurement along the

lateral direction for nodes 1.6mm below the top surface of the plate (V = 140 mm/min,

= 500 r/min and t =34 s)


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Analysis of stress distribution

Predicted principal stress

distributions in the welded plate

and the tool in three directions at a

time of 34 s (step 20) after the start

of welding: (a) x direction; (b) y

direction; (c) z direction


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Parametric study of three axis force component

Analysis of effects of rotational speed on force components


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Predicted mechanical force histories in three directions at various rotational

speeds of the tool: (a) 344 r/min; (b) 500 r/min; (c) 757 r/min (under constant V

=140 mm/min)


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Analysis of effect of traverse speed on force

components

Predicted mechanical forces in three directions at various traverse

speeds of the tool =500 r/min


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Comparison of predicted and measured mechanical force histories in threedirections

CONCLUSIONS


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CONCLUSIONS

The stress data are subsequently used to predict the three axial force

component.

Parametric studies have been carried out to determine the effect of the

rotational speed, the traverse speed on the stress distribution, and the

mechanical force.

The prediction shows that the longitudinal force is strongly influenced by the

welding parameters.

It decreases with increase in the tool rotational speed and increases with

increasing traverse speed. A strong fluctuation in force occurs in thelongitudinal direction.

The vertical force decreases with increase in the rotational speed and

increases slightly with increase in the traverse speed


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Conclusion Contd..

The lateral force has a weak link with the

rotational speed and increases slightly with

increase in the traverse speed


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Discussion


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Author & year Title Source

Nandan et al.,

(2007)

Improving reliability of heat transfer and

materials flow calculations during friction stir

welding of dissimilar aluminum alloys

Welding journal, 86 :

pp 313-322


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AIM

Friction, slip between the tool and the workpiece, heat

transfer at the bottom surface, and internal heat generation

were studied for their effects on model reliability

Optimization of uncertain parameters

Prediction of temperature fields and magnesium

concentration profiles were examined


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Process Parameters

h l d l


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Mathematical model

The plastic flow in three-dimensional coordinate system is represented

by the momentum conservation equation

is the density

is the non-Newtonian viscosity

U1 is the welding velocity

p is the pressure

Viscosity can be determined from flow stress and effective

strain rate


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The momentum conservation equations with reference to a coordinate system

attached to the heat source in index form

where , Cp is the specific heat

k is the thermal conductivity of the workpiece/tool.

Sin interfacial heat generation rate per unit volume

Sb is the heat generation rate due to plastic deformation


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Optimization of Uncertain FSW Parameters

Where, i different rotational speeds

Experiment s (locations 13 mm from weld center) done at 710, 1000, and 1400

rev/min were used to calculate the objective function, i.e., six different thermal

cycles were used.

Differential Evolution technique was used to optimize the uncertain

parameters.


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Results and Discussion


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Comparison between experimental and calculated time-temperature

profile at a point 13 mm away from the centerline on the advancing

side. The welding velocity was 1.05 mm/s, and the rotational speed was

(A)710 and (B) 1400 rev/min


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Stream-lines in a horizontal plane (A) 3.66 mm and (B) 7 mm below

the top surface, showing plastic flow during FSW. Material flows along the retreating

side around the pin, and a stagnant zone forms in the advancing side.

The welding velocity was 1.05 mm/s and the rotational speed was 710rev/min.


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Concentration profile at depths of 1, 3, and 5 mm from the top surface, across

the weld centerline for AA 6061 (advancing) and AA 1200 (retreating

side) weld at 710 rev/min and a weld velocity of 1.05 mm/s. A Computed; B

measured


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Concentration profile at depths of 1, 3, and 5 mm from the top surface,

across the weld centerline for AA 1200 (advancing) and AA 6061 (retreating

side) weld at 710 rev/min and a weld velocity of 1.05 mm/s. A Computed;

B measured.


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Summary and Conclusion


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Summary and Conclusion The sensitivity of four important parameters on the computed temperature

fields and torque on the tool was examined.

These uncertain parameters were optimized using as small volume of

experimental data, shows good agreement with the experimental data.

The close agreement between the experimentally measured and the

calculated thermal cycles and torque values indicates that the computed shearstress at the tool-workpiece interface is accurate and the optimization of

uncertain parameters provide reliable computed results.

13-3- Modelling of Fsw

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