111 weld

American Journal of Scientific Research

ISSN 1450-223X Issue 12 (2010), pp.153-165

© EuroJournals Publishing, Inc. 2010

http://www.eurojournals.com/ajsr.htm

Affect of Different Input Parameters on Weldment

Characteristics in Tungsten Inert Gas (TIG) Welding

Mir Sadat Ali

Asst. Professor, Department of Mechanical Engineering

Jagannath Institute for Technology & Management, Paralakhemundi- 761 211

E-mail: [email protected], [email protected]

Tel: 09437619974

P. Vijaya Kumar

Asst. Professor, Department of Mechanical Engineering


C.V.Gopinath

Professor, Department of Mechanical Engineering


Ch.Srinivasa Rao

Professor, Department of Mechanical Engineering, AU College of Engineering

Visakhapatnam 530 045 AP, India

Abstract

Weldment characteristics like penetration, bead geometry, depth of HAZ are

extremely important characteristics for structural integrity in the case of welded joints. TIG

welding process which is used throughout the world for its simplicity and versatility,

induces various defects like blowholes, porosity, undercut and irregular HAZ depending on

the process parameters used. Electrode diameter, current, voltage, arc travel speed, plate

conditions like preheating are influential factors in deciding weldment characteristics. It is

extremely important to model and predict weldment characteristics depending upon the

local operating conditions and to optimize them.

In this present work effect of process parameters like current, voltage, electrode

diameter, arc travel rate on weldment characteristics in case of TIG were studied. A number

of experiments were conducted on a preset feed based TIG machine using all the process

parameters described above. Weldment characteristics like depth of penetration, depth of

HAZ, number of undercuts, area of penetrations were examined for the weld beads

obtained from experiments. The aim of the work is to study the effect of process parameters

on weldment characteristics.

Keywords: Bead geometry, Heat affected zone(HAZ), Depth of penetration

Affect of Different Input Parameters on Weldment Characteristics in Tungsten

Inert Gas (TIG) Welding 154

Introduction The weldment characteristics like bead geometry, penetraion and depth of HAZ are extremely

important characteristics for structural integrity in case of welded joints. Generally, the arc welding

processes are substantially nonlinear, in addition to being highly coupled multivariable systems. All the

variables aeffecting welding quality are not known, also they may not be easily quantified. Examples

include contamination, work piece heat absorption along the weld, various environmental conditions

and different plate conditions like cryo treated and preheated. All the perplexity contribute to the

difficulties of designing reliable welds and equipments used to produce them. The experience and

knowledge of the human welder provides the last steps towards a reliable weld. The approach of neural

networks methodologies presented here proposed to aid the weld designer and the welder in attaining

the required weld specifications with minimal experimentation.

Bead Geometry

The bead height and bead width together constitute the bead geometry. The portion of the parent

material which has been heated and melted, and has the characteristic dendrite structure of a casting is

called weld bead. Bead geometry depends on the weld process parameters and the work piece

temperature. For example for some welding process parameters formation of a bead may be possible in

preheated plates but it may not possible for work pieces, which are in room temperature. Similar

phenomena may be observed in case of cryo treated plates.

Depth of Penetration

It is the depth to which the base metal and filler material have melted and mixed during welding

process. It depends on the weld process parameters used and can vary for different plate conditions.

Depth of HAZ

The portion of the parent material which has been heated above the critical temperature but has not

melted.

Experimental Investigation To investigate the Weldment characteristics beads were deposited on mild steel flat plates using

Tungsten electrodes. A preset feed machine was used to deposit beads on plates. The feed machine has

the capability to vary the table speed (arc travel rate). The table speeds used for experimentation were

2.543 to 9.066 mm/sec. Since the Weldment characteristics also depend upon the electrode diameter.

So to study the affect of this parameter, electrodes of diameter 4.00 mm.

For depositing the beads on base metal plate (10 cm* 1.2 cm* 6.5 cm) were taken. The table

speed or arc travel speed and the electrode feed rate were set. With the set table speed beads were

deposited on the base plate. Beads were made by varying the current for each electrode at the set arc

travel rate.

To study the bead geometry, Sectioned beads were polished with 220, 320, 400, 600 grade

Emery paper and then etched with 2% Nital solution. To measure the bead height and bead width each

of the sample is placed under microscope having least count 0.001mm. The average values of bead

height and bead width of each pair of samples were noted. The samples prepared for measurement of

bead height, bead width, depth of penetration and depth of heat affected zone are as shown below.

155 Mir Sadat Ali, P. Vijaya Kumar, C.V.Gopinath and Ch.Srinivasa Rao

Figure 2: Photograph of specimen taken for experimental investigation.

Experimental Procedure The project entitled “Modeling of weld bead at the different rate of heat input” has a sequence of

experimental procedure. The following Processes are followed to complete the experiment:-

Process 1

Doing the start of this project, we need to control the welding speed in one direction. For automation of

welding, we have chosen lathe machine.

The most important thing to do at the starting is calibration of automatic motion of lathe

machine. For the movement of a particular distance of tool post, we note the time taken and distance

travelled by tool post. We have chosen five different speeds out of eighteen speeds calculated for the

welding purpose.

Process 2

After calibrating lathe machine speed, the second thing to do is preparing the work piece of specified

dimensions. The dimension of the work pieces taken as;

Width=65 mm

Length=100mm

Thickness =12 mm

For the preparation of work piece, we used the “Power Hacksaw Machine” in our workshop.



Process 3

Before doing welding on prepared work piece, we needed to make a work table. This required because

we need to put the job piece at the same height of tool post of the lathe machine. After making table,

we made it horizontal using Sprit level.

Process 4

This includes welding process. Welding has been done at different speed and different current. We

used five constant speeds which are as follows:

2.543 mm/s

4.858 mm/s

5.985 mm/s

7.629 mm/s

9.066 mm/s

Taking each speed constant once, we have taken ten different current for welding.

Taken currents are in amperes: 145, 160, 165, 195, 225, 250, 275, 300, 325, 350, and 375. For

one velocity and ten current we got ten pieces of Weldment. For 5 speeds, we have prepared total 50

pieces of Weldment.

For preparing the Weldment we fixed the TIG welding torch on the tool post of lathe, keeping

table nearby the lathe, we put the work piece on the worktable. We made lathe for automatic feed and

made a single pass on work piece by TIG torch. Then we made 5 set of sample of constant velocity

which had 10 sample welded at 10 different current.

Process 5

Hardness Test

Hardness is defined as the resistance of a material to plastic deformation usually by indentation. It also

refers to stiffness or resistance to scratching. Indentation hardness refers to number related to the area

or depth of the impression made by an indenter of fixed geometry under a known static load. There are

many methods to determine the hardness, among those Brinnel and Rockwell hardness tests are

frequently used.

In our testing procedure, first test was Hardness test. For hardness test, we made different test

specimen. We cut a piece of 10 mm from the length (100mm) of the welded pieces.

Like that we made 50 pieces of Weldment for hardness test.

Before hardness test, we need to make smooth the surface of piece which we got after cutting.

For making it smooths. We used 220, 320 400 and 600 graded emery papers, we got smoothness

required, after getting appropriate smoothness, we have done hardness test for parent material and

welded zone. In hardness test, we found that hardness of material after welding got increased.

Brinnel Hardness Test

It is method of obtaining the hardness of material in which indenting the surface of a sample by a steel

ball of specified diameter under prescribed load conditions by measuring the diameter of the

indentation. Usually the indenter is a steel ball of 10mm. diameter and maximum load is generally

3000 kg-f. For softer materials a lower load of 500 kg-f. Can also be applied. For hard materials the

steel ball may be replaced by a tungsten carbide (WC) indenter.

The Brinnel hardness number is defined as the load applied to the area of indented surface

which is taken as a spherical surface diameter, D.

BHN = P/A

Where A= (Π * D / 2) * (D - (D2

- d2) 1/2

)

D=Diameter of the indenter and


d= Diameter of the indentation.

Procedure

For mild steel specimen the load applied is 3000kgf in which minor load as 250kgf is applied to

overcome the demerits & proper fixing of the specimen.

The time of application of load on the specimen is 30sec. the Diameter of the indentation is

measured using low power microscope.

Process 6

Calculation Of Heat Flow Rate We have taken reading of open circuit voltage and closed circuit voltage of TIG welding machine.

Open circuit voltage is almost constant, only closed circuit voltage varied. Then after calculation of

total heat input is carried out using formula

Q= (I * V )/S J/mm

Where I= current taken in Am.

V=Voltage in V.

S = Speed (mm/s )

Process 7

Calculation Of HAZ, DOP, BW

For calculation of Heat Affected Zone (HAZ), Depth of Penetration (DOP) and Bead Width we applied

chemical (i.e. Nital solution, 98% Ethyle Alcohol and 2% Nitric Acid). For the test we need to make

test specimen surface very smooth using different emery papers. After making the surface smooth, we

washed it very well. After washing we applied nital solution after few seconds we got black spot for

welded zone and light brown spot for heat affected zone. We marked the bead width, heat affected

zone and depth of penetration. Using microscope, we measured HAZ, BW, and DOP.

When the heat created by welding process, applied on the material, it melts the material and

again freezes due to heat dissipation. The depth, up to which material melts, is called depth of

penetration. After melted zone, heat affects the material up to much more depth, but could not make it

melt. This depth after depth of penetration is called heat affected zone. The width which gets melted is

called welded bead width.

Procedure 8

Impact test (charpy test)

It is usually done for impact strength or toughness of a material. In this test, the loads that are suddenly

obtained to a structure are known as impact loads. Impact tests are performed to assess the shock

absorbing capabilities of the materials like rupture energy, modeling of rupture, notch impact strength.

The principle employed in all impact testing procedure is that a material absorbs a certain

amount of energy before it breaks. The quantity of energy thus absorbed is a characteristic of physical

nature of the material. It if is brittle, it breaks more rapidly and for tougher materials, more energy is

required to get fractured.

Used formulas:

Effective corssectional area, Ae=12*10mm2

Effective Volume=

Initial angle , α=1400

Pendulum radius, R=0.83 m

Effective weight of hammer, W=20.996*9.8 N

Observed angle , ß



Rupture energy, U= W*R[cos ß -cos α] J

Modulus of Rupture, Ur= U/Ve, J/mm3

Notch Impect strength, Ig=U/Ae J/mm2

Procedure

• The charpy test machined consist of a hammer which is positioned at appropriate height in

accordance with the test.

• The pointer of the scale is positioned at the maximum energy value.

• The specimen is fixed in the appropriate orientation for the given test.

• The specimen in fixed in the appropriate orientation for the given test.

• The hammer is released from its standard height so that it fractures the specimen and raises a

certain height.

• The free swinging of the hammer is stopped by a pedestal brake.

• Finally we calculated rupture energy of the material.

Process 9

Bending test

In bending test generally we calculate the crushing strength, for bending test, we used universal testing

machine (UTM). Already prepared specimen of dimension 10x12x65 mm3 has been put on machine in

such a way that the load should be apply perpendicular to the (10X65)mm2 surface of specimen, we

have applied load up to crushing of specimen. Noted value is added in the tables.

Result and Analysis The weldment characteristics, which consists of bead geometry, depth of penetration, heat affected

zone and undercuts are affected by the welding parameters like arc length, diameter of electrode,

electrode feed rate, arc travel rate.

The arc travel rate can be changed by changing the table speed. Table speed of the welding

torch can be increased by changing the gears. It is found that with increasing the table speed the heat

flow rate decreases. The change in heat flow rate for different table speed is shown in graph:1.

Graph: 1

Table Speed v/s Heat Flow Rate

0

200

400

600

800

1000

1200

2.5 4.9 6.0 7.6 9.1

Table Speed in mm/sec

Heat

Flo

w R

ate

in

J/m

m

Table Speed v/s Heat

Flow Rate

There are two types of penetrations- “weld penetration” also called ‘fusion’ and “heat

penetration”. In fusion welding the depth of weld penetration or fusion I generally recognized as the

distance below the original surface of the work to which the molten metal progresses [10, 17, 18]. The


HAZ refers to the parent metal metallurgic ally affected by the heat of welding, but not melted [14].

The heat penetration includes the weld penetration as well as HAZ.

The importance of proper penetration has been amply demonstrated by many researchers [10,

17, 18]. It is generally recognized that penetration is influenced by polarity, current, voltage and arc-

travel rate. By increasing the current supplied while doing welding at the same speed shows increase in

heat flow rate. Due to this increase in heat flow rate the depth of penetration increases and reaches a

maximum value (Shown in graph:2) and then start decreasing. This decrease can be attributed to the

spatter caused at higher current values.

Graph: 2

Depth of Penetration v/s Heat Flow rate

0.0

0.5

1.0

1.5

2.0

2.5

3.0

3.5

305 325 416 481 503 620 631 802 1045 1012Heat flow rate in J/mm

De

pth

of

Pe

ne

tra

tio

n i

n m

m

Depth of

Penetration v/s

Heat Flow rate

It is said that the cooling rate [4] of a weld can be predicted from the weld cross sectional area

and the arc travel rate. The bead cross sectional area together with its height and width affects the total

shrinkage, which determines largely the residual stresses and thus the distortion [23]. The effect of

welding parameters at reduced atmospheric pressures on bead geometry was reported by Begeman et

al. [3] who observed that bead width and height were larger with reverse polarity than with straight

polarity and that the bead width increased in direct proportion to the energy supplied.

As found in the literature the bead width increases with heat flow rate. Experimental results

also agree with the literature as shown in graph:3.

Graph: 3

Bead Width v/s Heat Flow Rate

0.00

2.00

4.00

6.00

8.00

10.00

12.00

305 325 416 481 503 620 631 802 1045 1012

Heat Flow Rate in J/mm

Bead

Wid

th i

n m

m

Bead Width

v/s Heat Flow

Rate J/mm

As we can see that as the heat flow rate increases the bead width is increasing. The increase in

bead width can be attributed to two factors namely arc spatter and the change in arc density. Due to

higher current values at slower arc travel speed the surface area into which the arc touches increases so

the bead width also increase. This will have direct affect on the heat affected zone also.



Graph: 4

Heat Affected Zone v/s Heat flow rate

0.0

0.2

0.4

0.6

0.8

1.0

1.2

1.4

1.6

1.8

305 325 416 481 503 620 631 802 1045 1012

Heat Flow Rate in J/mm

De

pth

of

HA

Z i

n m

m

Depth of HAZ

v/s Heat Flow

Rate

There is not much change in hardness of the material observed by increasing the rate of heat

input. Although the amount of the heat input increases the size of the heat affected zone, but the value

of the hardness remains within a certain range. This may be due to the fact that the matensitic

transformation.

Graph: 5

Variation of Hardness For

Increasing Rate of Heat Input

1150

1200

1250

1300

1350

1400

1450

1500

1550

1600

305 325 416 481 503 620 631 802 1045 1012Increasing Rate of Heat Input in J/mm

Ha

rdn

es

s o

f W

eld

ed

Zo

ne i

n N

/mm

^2

The rapture energy of the test specimen in the welded zone was experimentally found. The

range of rapture energy was found to be within a range of 50 to 100. Although the parent material

energy level also comes within this range, but in none of the welded specimen it can be equated to

parent material. Graph: 6

Rapture Energy v/s Heat Flow Rate

0

50

100

150

200

250

300

350

1101 1055 1376 1770 1733 1828 2364 3460 3211 3605Heat flow rate in J/mm

Ru

ptu

re E

ne

rgy

in

J


The X-ray images taken also depict the defects like porosity and slag inclusion. It was found

that whenever the welding was performed with lower current values the defects like porosity are

created. Also in the higher current range the samples show defects like porosity. It was also observed

that the porosity is not directly dependent on the heat flow rate, but it directly depends on the current.

So it was found that the with the increase in current values the bead with increases and also the

porosity. This is shown in the graph:7

Graph: 7

Current v/s Bead Width

0.00

2.00

4.00

6.00

8.00

10.00

165 145 195 225 250 275 300 325 350 375

Current in Ampere

Bead

Wid

th i

n m

m

Current v/s Bead

Width

The higher current values increases arc spread. Also the arc spatter occurs due to which the

bead width increases. Also due to this spatter the porosity level in the welded zone increases. So this

affect is observed at higher current levels. But at the lower current values due to the instability of the

arc & arc extinction the porosity in the welded zone is observed. Thus an optimum value of the current

is required to be maintained to avoid defects like porosity and arc crater.

Graph: 8

Comparison of change in Crushing Load for

Increasing Heat Flow Rate

0.000

500.000

1000.000

1500.000

2000.000

165 195 250 300 350

Current in Ampere

Valu

e o

f C

rush

ing

Lo

ad

& H

eat

Flo

w R

ate

Heat Flow Rate

Crushing Load in kgf

From the graph: 8 it was observed that the heat flow rate increases for increasing current

values. But there is not any substantial change in the crushing load strength occurs. The crushing loads

strength remains almost in the range of 1000 to 1500 kgf. The crushing load strength change indicates

the change in strength as well as brittleness of the material. As the versions of crushing load change is

very much less, so the change in brittleness well also will be with in a certain range. But the brittleness

of material will be concentrated in the depth of penetration zone and the heat affected zone so the

material became susceptible to cracks within this zone. To reduce the heat affected zone we have

preheating but to control the brittleness of welded zone we have to control the rate of heat flow and

cooling rate.



The variation of rupture energy for increasing flow rate is shown in the graph:9. It indicates not

much variation in rupture energy for increasing heat flow rate the rupture energy remain almost

constant for higher heat flow also this accept of characteristic may be attributed to the thickness of the

plate. As comprised to thickness of the plate if the depth of penetration and heat effected zone are very

very less than the rupture energy of the parent material doesn’t vary with the increase of heat flow rate.

But for thinner plates the variation of rupture energy will be observed if the rate of heat flow is

increased.

Graph: 9

Variation of Rupture Energy for Increasing Heat

Flow Rate

0

200

400

600

800

1000

1200

165 145 195 225 250 275 300 325 350 375

Current in Ampere

Heat

Flo

w R

ate

in

J/m

m

Ru

ptu

re E

nerg

y i

n

Jo

ule

s

Heat Flow Rate

Rupture Energy

In the graph:10 the comparison of depth of heat affected zone to variation of hardness is shown.

It is observed that with the increase of energy flow rate the depth of heat affected zone increases upto

certain extent and then it decrease. The decrease is due to the decrease in Arc density which is due to

the Arc spatter. But it was observed that although it there is increase in the depth of heat increase but

the value of hardness doesn’t change much. It maintains its value within a certain range this is due to

the martensitic transformation. And this martensitic transformation is within a short bend of heat

affected zone. So it doesn’t affect the hardness of the entire material to great extent.

Graph: 10

Comparison of Depth of HAZ to Variation of Hardness

0.0

0.2

0.4

0.6

0.8

1.0

1.2

1.4

1.6

1.8

145 165 195 225 250 275 300 325 350 375

Current in Amperes

De

pth

of

HA

Z i

n m

m

1150

1200

1250

1300

1350

1400

1450

1500

1550

1600

Ha

rdn

es

s o

f W

eld

ed

Z

on

e i

n N

/ m

m^

2

Hardness in N/mm^2

Depth Of HAZ in mm

From the graph:11 the comparison of variation of rupture energy and modulus of rigidity for

increasing heat flow rate is observed. Both the parameters vary in the same pattern. As both the

parameters derived for the same basic component so the variation of both the parameters resembles.

With the increase in heat flow rate both the rupture energy and modulus rigidity gradually increases


and attains a maximum value. After attains of maximum value the variation of both the parameters

becomes less for the increasing heat flow rate. If we increase the heat flow rate to much higher extent

than the rupture energy and the modulus of rigidity may increase further but vary high increase in heat

flow rate causes Arc spatter and an instable arc by which the very purpose of welding is impossible to

attain. So the heat flow rate is not increase beyond a particular value.

Graph: 11

Comparison of Variation of Rupture Energy & Modulus

of Rigidity for Increasing Heat Flow Rate

0

50

100

150

200

145 165 195 225 250 275 300 325 350 375

Current in Ampere

Ru

ptu

re E

nerg

y i

n

Jo

ule

s

0

5

10

15

20

25

30

Mo

du

lus o

f

Ru

ptu

re i

n J

/mm

^3

Rupture Energy

Modulus of

Rupture

In the graph:12 the comparison of modulus of rupture and notch impact strength for increasing

heat flow rate is observed with the increasing heat flow rate the modulus of rupture increases and

attains a range with in which the variation of it is not observed after attainment of maximum value.

Similarly the notch impact strength also behaves. The notch impact strength and the modulus of

rupture are derived from the same basic components. So the variation of them also show a similarity.

The notch impact strength also depends upon the positioning of the notch. As both the parameters are

varying in similar manner so we can conclude that the positioning of the notch is appropriate while

doing the experiment.

Graph: 12

Comparison of Modulus of Rupture & Notch

Impact Stregth For Increasing Heat Flow Rate

0

5

10

15

20

25

30

145 165195225250275300325350375

Current in Amperes

Modulu

s o

f

Ruptu

re in J

/MM

^3

0

0.5

1

1.5

2

Notc

h Im

pact

Str

ength

in

J/m

m^2

Modulus of Rupture

Notch Impact

Strength

For different values of heat flow rate the depth of penetration of observed in different plates.

The comparison depth of penetration for different heat flow rate is shown in the graph:13. It indicates

the variation in the same manner for all the heat flow rate the pattern is same for all the heat flow rate

but the values varies towards the higher level for increasing heat flow rate. In other wards when the



amount of energy supplied increases the depth of penetration upto a certain extent. Then it comes down

with the increase in the energy input this accepts can be attributed to the gain in bead width for the

higher energy inputs. But with the increase of heat flow rate the same characteristic is observed. But if

we increase the heat flow rate to much higher extent than depth of penetration decreases substantially.

Graph: 13

Comparison of Depth of Penetration for Different Heat

Flow Rate

0.0

0.5

1.0

1.5

2.0

2.5

3.0

3.5

145

165

195

225

250

275

300

325

350

375

Current In Amperes

Dep

th o

f P

en

etr

ati

on

in m

m

0.0

0.5

1.0

1.5

2.0

2.5

3.0

3.5

4.0

Dep

th o

f P

en

etr

ati

on

In m

m

Depth of Penetration -

9mm/sDepth of Penetration-

7.5 mm/sDepth of penetration -

6mm/s

Conclusions 1. By increasing the current supplied while doing welding at the same speed shows increase in heat

flow rate. Due to this increase in heat flow rate the depth of penetration increases and reaches a

maximum value (Shown in graph:2) and then start decreasing.

2. There is not much change in hardness of the material observed by increasing the rate of heat

input.

3. With the increase in current values the bead width increases and also the porosity.

4. An optimum value of the current is required to be maintained to avoid defects like porosity and

arc crater.

5. With the increase of energy flow rate the depth of heat affected zone increases upto certain extent

and then it decrease. The decrease is due to the decrease in Arc density which is due to the Arc

spatter.

6. With the increase in heat flow rate both the rupture energy and modulus rigidity gradually

increases and attains a maximum value.

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[23] V. TsegelskyWelder, Foreign Language Publishing House, Moscow, 1976.

111 weld

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