Finite Element Model to Predict Residual Stresses in Mig Welding

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International Journal of Mechanical Engineering and Technology (IJMET), ISSN 0976 6340(Print), ISSN 0976 6359(Online) Volume 3, Issue 3, Sep- Dec (2012) IAEME

FINITE ELEMENT MODEL TO PREDICT RESIDUAL STRESSESIN MIG WELDING

1Mr. Harshal K. Chavan 2Mr. Gunwant D. Shelake 3Dr. M. S. KadamM.E. (Manufacturing) M.E. (Manufacturing) HOD (Mechanical Department)JNEC Aurangabad (M.S.) JNEC Aurangabad (M.S.) JNEC Aurangabad (M.S.)

[email protected] [email protected] [email protected]

ABSTRACTThe objective of this research is to simulate the complex arc welding process by usingthe finite element method (ANSYS)[ ] . After the model is built and verified, the mainobjective of the research is to study the effects of varying the welding processparameters on the thermo-mechanical responses. In addition to that, the aim of thisresearch is also to find a relationship between welding parameters and thermo-elasto-plastic responses.

In this research paper, the responses of single pass corner-joint of arc welding areevaluated through the finite element software (ANSYS). The study of this researchpaper covers only the effects of varying heat input, welding speed on the thermomechanical responses of the weldment after cooling down to room temperature.Keywords:- Heat, Weld speed, Distortion, Elastic strain, Stress, FEA

INTRODUCTION

The problem of welding distortion during large steel fabrications causes to thedimensional inaccuracies and misalignments of structural members, which can result incorrective tasks or rework when tolerance limits are exceeded. This in turn, increases

the production cost and leads to delays. In fabrication and design industries, expensesfor rework such as straightening could cost lacks of Rupees. Therefore, the problems of distortion and residual stresses are always of great concern in welding industry. In orderto deal with this problem, it is necessary to define prediction of the amount of distortionresulting from the welding operations. One way to predict the distortion and shrinkageof steel welding is through numerical analysis such as finite element analysis (FEA).

INTERNATIONAL JOURNAL OF MECHANICAL ENGINEERINGAND TECHNOLOGY (IJMET )

ISSN 0976 6340 (Print) ISSN 0976 6359 (Online)Volume 3, Issue 3, September - December (2012), pp. 350-361 IAEME: www.iaeme.com/ijmet.asp

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Once the techniques of prediction of the distortion and shrinkage are identified, then theproblems can be controlled accordingly.

Within the welding procedures, there are many factors such as welding process type,welding process parameters, welding sequence, preheat patterns, level of constraintand joint details that contribute to the distortion of the welded structure. Knowingwhich parameters have a major effect on the quality of the weld and which parametersgive the most significant effects on the weld quality are the main issues in weldingindustry. The research activity in welding simulation started decades ago. Rosenthal(1941,1946) [37,39,41] was among the first researchers to develop an analytical solution of heat flow during welding based on conduction heat transfer for predicting the shape of the weld pool for two and three-dimensional welds. Understanding of the theory of heat flow is essential in order to study the welding process analytically, numerically orexperimentally since the pioneering work of Rosenthal (1946), considerable interest inthe thermal aspects of welding was expressed by many researchers such as. Chen et al.

(2003) [10] Andrea Capriccioli, (2009) [12] , and Heinze et al. (2012) [13].

PROCEDURE FOR FINITE ELEMENT MODEL

Present work requires that finite element model be created to study the effect of processparameter on, deformation, residual stress & strain. We must setup a transient thermalanalysis to determine thermal state in the weld and surrounding components. Followingthis we are required to import the thermal loading to setup structural analysis whichresults in deformation, residual stress & strain. The weldment material propertiesemployed in this paper were mild steel, which were taken from Andrea Capriccioli et

al. (2009)[12].

To simplify the heat transfer analysis, Dean Deng a,(2007)[2] ,

Bonifaz(2000) [40] , assumptions were made. The heat input from weld electrode is modeled byusing heat flux as input from electrode to weld surface and is depends on the efficiencyof arc and welder setting. The heat flux distribution on the surface of weldment is givenby Goldak et al. (1986) [30]

RESULT

Effect of Heat InputHeat input is one of the most important process parameters in controlling weld

response. It can be referred to as an electrical energy supplied by the welding arc to theweldment. In practice, however, heat input can approximately (i.e., if the arc efficiencyis not taken into consideration) be characterized as the ratio of the arc power suppliedto the electrode to the arc travel speed, as shown in the following equation.

Q=VI60/ .


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Where, I is welding current; V is welding arc voltage; v is the arc welding speed, and Qis the heat input. In this work, the effect of heat input on welding responses wasevaluated using three values (heat input in Watt), characterized as low, medium, andhigh. Table 1 illustrates the values used for the analyses. This evaluation was carried

out by considering the rest of parameters; welding speed was kept constant at low valueand restraint was kept constant at high value.

Table 1 Range of heat input used for FEA [27]

LOW MEDIUM HIGH1278W 1448W 1704W

HEAT FLUX CALCULATION FOR FEA

Voltage and current values for High, medium & low heat flux

1)

For High Heat FluxWelding Voltage 14.2 V

Welding Current 20 A

2) For Medium Heat FluxWelding Voltage 14.2 V


3) For Low Heat FluxWelding Voltage 14.2 V


Electrode Diameter = 25.4/8 = 3.175 mm

Area of electrode = 3.14163.1753.175/4 = 7.9173mm 2 = 0.0000079173 m 2

Q= IV60/

1) HIGHQ=2014.260/10= 1704W

q=Q/a= 1704/0.0000079173= 2.15e8W/m 2

2) MEDIUM

Q=1714.260/10=1448W

q=Q/a= 1448/0.0000079173= 1.82e8W/m 2

3) LOWQ=1514.260/10 = 1278W


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q=Q/a = 1278/0.0000079173= 1.61e8 W/m 2

(Where q is heat input per unit area, a is area and Q is Heat input)

ANALYSIS OF RESULTS

Fig 1 shows that x elastic strain and y elastic strains are sensitive to heat input. As heatinput changes strain changes respectively.

Fig 2 shows that stress value decreases as heat input increases. This is due tofact that we cannot consider cooling time in the solution. As we can see from the graphthat X-stress in the vertical plate is more sensitive to the heat input. Also we can seethat Y-stress in horizontal plate is more sensitive to heat input as compare to otherdirectional stresses.

As heat input increases stresses decreases, this is due to the fact material propertiessuch as youngs modulus decreases as temperature in the material increases. As the heatinput increases temperature generates in the plate increases and thus the stressgenerated decreases.


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International Journal of Mec6340(Print), ISSN 0976 6359

Horizontal Plate

Figure 1 Graphs IllustrateElastic Strain

anical Engineering and Technology (IJMET), I(Online) Volume 3, Issue 3, Sep- Dec (2012) IA

Vertical Plate

the Effects of Varying Heat input on

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Figure 2 Graphs IllustratStress


e the Effects of Varying Heat input on

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EFFECT OF VARIABLWelding speed represents theof time. The heat input is invthe heat input is larger, the w

In this research, low,considering the rest of paramat high value.

Table 2 Range of We

LOW

2mmps

ANALYSIS OF

As the speed of welding increwelding speed increase time f the welding speed is made, thinduced decreases. The graphnot shows significant effect iand after that it becomes zero

Horizontal Plate


SPEEDdistance of the torch traveled along the weld lirsely proportional to the welding speed. Therelding speed is slower for a constant heat input r

edium, and high welding speeds were investiters such as heat input is kept at low value an

lding Speed for FEA

MEDIUM HIGH

3mmps 4mmps

ESULTS

ases the stresses induced in the plate decreasesor welding decreases and thus It is noted that th

less heat is absorbed by the base metal and thalso shows the same trend. Effect of welding splastic strain. Plastic strain is maximum in the

.

Vertical Plate

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ne per unitore, when

ate.

ated whilerestraints

ecause asfaster

s stresseseed doweld zone


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Figure 3 Graph Illustrate E

Horizontal Plate


ffect of Varing Speed On Elastic Strain

Vertical Plate

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CONCLUSIONAfter completion of this worabove. Based on the simulapredict the distortion, shrinka

because experimental proceconclude that heat input, welwhich are as follows

Figure1 shows thatinput. As heat inpu

Figure 2 shows thato fact that we canfrom the graph thatinput. Also we canheat input as comp

As heat input incrproperties such asincreases. As theincreases and thus t

As the speed of webecause as weldin

Figure 4 Graph illustrate ef


k, several conclusions are made from the restion results i.e. results shown above in figurges of weldment numerically. This is cost savi

sses are costly. From the simulation resultding speed has significant impacts on the wel

x elastic strain and y elastic strains are sensitchanges strain changes respectively

stress value decreases as heat input increases.not consider cooling time in the solution. AsX-stress in the vertical plate is more sensitivesee that Y-stress in horizontal plate is more sre to other directional stresses.

eases stresses decreases, this is due to the faoungs modulus decreases as temperature in t

heat input increases temperature generates inhe stress generated decreases.lding increases the stresses induced in the platspeed increase time for welding decreases an

ect of varying welding speed on Stress

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lts showns we can

ng process

we alsoresponse

ive to heat

his is duee can see

to the heatensitive to

t materiale materialthe plate

decreasesthus It is


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noted that the faster the welding speed is made, the less heat is absorbed bythe base metal and thus stresses induced decreases.

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Finite Element Model to Predict Residual Stresses in Mig Welding

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