Project Report (Arc Weldinng)

By: Ayalasomayajula Somashekara Koushik

ABSTRACT

Arc-welding is the most commonly and widely used welding technique for variety of purposes.

Welded joint may not be very reliable unless the weld is of reasonably good quality. Improving

the weld quality is of prime concern. This project work is intended to investigate the effect of

magnetic field on the structure and properties of weld in shielded metal arc welding. The

objective is to study the effect of welding parameters and to use magnetic field advantageously to

improve the weld qualities and properties (such as strength and hardness). However there is lack

of information for optimum parameters, very little work has been reported in this direction. A

magnetic field externally applied to the welding arc, deflects the arc by electromagnetic force in

the plane normal to the field lines. The magnetic field exerts force on the electrons and ions

within the arc, which causes the arc to be deflected away from the normal arc path. The welding

arc can be deflected forward, backward, or sideways with respect to electrode and welding

direction depending upon the direction of an external magnetic field

In this project work various mechanical properties tests as tensile strength, harness, toughness

etc. are conducted to see the effect of external magnetic field on it. A set of weld-pieces (with

magnetic field and without magnetic field) are tested for various mechanical properties and

comparable study is done to know the change in these properties.

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TABLE OF CONTENTS

page

CERTIFICATE ………………………………………………………………………………….ii

DECLERATION …………………………………………………………………………. ……..iii

ACKNOWLEDGEMENT ………………………………………………………………………iv

ABSTRACT ……………………………………………………………………………………..v

Chapter 1: Introduction

1.1 General …………………………………………………………………………………….1

1.2 Shielded metal arc welding (SMAW)……………………………………………………...2

1.3 Gas Tungsten Arc Welding (GTAW)……………………………………………………...3

1.4 Gas Metal Arc Welding (GMAW)………………………………………………………....4

1.5 Gas Welding………………………………………………………………………………..5

Chapter 2: Review of Literature

2.1 Summary of shielded metal arc welding …………………………………………………...6

2.2 AC/DC Power Sources……………………………………………………………………..7

2.3 Electrode used in SMAW…………………………………………………………………...9

2.4 Welding process…………………………………………………………………………...10

2.5 Influence of magnetic field………………………………………………………………...11

2.6 Objective …………………………………………………………………………………..13

Chapter 3: application of magnetic field

3.1 Longitudinal magnetic field……………………………………………………………….14

3.2 Transverse magnetic field…………………………………………………………………15

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Chapter 4: Weld quality and weld geometry

4.1 Defects in weld-pieces…………………………………………………………………….16

4.2 Geometry of weld-pieces………………………………………………………………….19

Chapter 5: Welding set-up on lathe

5.1 Automation to welding process…………………………………………………………...20

5.2 Arrangement for magnetic field…………………………………………………………...21

5.3 Equipments and instruments used……………………………………………...................21

5.4 Line diagram of set-up…………………………………………………………………….23

Chapter 6: Welding with the set-up

6.1 Preparation of specimens………………………………………………………………...24

6.2 Welding with magnetic field(M)…………………………………………………………24

6.3 Welding without magnetic field(WM)…………………………………………………...25

6.4 Grouping and cutting of weld-pieces ……………………………………………………26

Chapter 7: Weld tests

7.1 Hardness test………………………………………………………………….. ………….29

7.2 Tensile strength test………………………………………………………….. …………..31

7.3 Impact test…………………………………………………………………………………36

Chapter 8: Effect of magnetic field

8.1 Visual effects………………………………………………………………. …………….38

8.2 Effect on weld properties………………………………………………………………….40

8.3 Effect on weld geometry…………………………………………………………………..43

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Chapter 9: conclusion and suggestions for further work

9.1 Conclusions………………………………………………………………………………45

9.2 Suggestions for further work……………………………………………………………..46

References………………………………………………………………………………………..47

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INTRODUCTION

1.1 General

Welding is a process in which materials of the same fundamental type or class are brought

together and caused to join (and become one) through the formation of primary chemical

bonds under the combined action of heat and pressure . The definition found in IS0 standard

is “Welding is an operation in which continuity is obtained between parts for assembly, by

various means”. Hence, the welding is the fusion of two or more pieces of metal together by

using the heat produced from an electric arc welding machine. Arc welding dates back to the

late 1800’s, when a man was welding with a bare metal rod on iron, the sparks from the

welding caught a stack of newspapers on fire near him and while welding, he noticed that his

welds started looking a lot better. The reason for this was the smoke took the oxygen out of

its welding environment and decreased porosity. The arc is struck between the electrode and

the metal. It then heats the metal to a melting point. The electrode is then removed, breaking

the arc between the electrode and the metal. This allows the molten metal to “freeze” or

solidify. The arc is like a flame of intense heat that is generated as the electrical current

passes through a highly resistant air gap.

Types of arc Welding processes: -

• SMAW (Shielded Metal Arc Welding)

• GMAW (Gas Metal Arc Welding)

• GTAW (Gas Tungsten Arc Welding)

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• 1.2 SMAW (Shielded metal arc welding):

• SMAW is the most common form of welding. An arc welding machine supplies electric

current to an electrode wire. The electric current travels through the air gap between the end

of the electrode wire and the base metal. As the electric current flows through this air gap, an

electric arc is formed. The electric arc produces heat that heats the base metal to its melting

temperature. The heat from the base metal produces a shielding gas that protects the base

metal, arc, electrode, and weld from the atmosphere during the welding process. As the flux

covering on the electrode wire melts, a shielding gas is created. When the flux cools, it

solidifies and forms a protective slag over the weld bead. As the electrode wire melts, it

becomes the filler metal to the weld.

Fig -1.1 Shielded metal arc

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GTAW (Gas Tungsten Arc Welding):

Gas Tungsten Arc Welding (GTAW), also known as tungsten inert gas (TIG) welding is a

process that produces an electric arc maintained between a non consumable tungsten

electrode and the part to be welded. The heat-affected zone, the molten metal and the

tungsten electrode are all shielded from atmospheric contamination by a blanket of inert gas

fed through the GTAW torch. Inert gas (usually Argon) is inactive or deficient in active

chemicalproperties.

Fig 1.2 -Gas Tungsten Arc Welding

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The shielding gas serves to blanket the weld and exclude the active properties in the

surrounding air. Inert gases such as Argon and Helium do not chemically react or combine

with other gases. They pose no odor and are transparent,

Permitting the welder maximum visibility of the arc. In some instances Hydrogen gas may

be added to enhance travel speeds. The GTAW process can produce temperatures of up to

35,000° F (19,426° C). The torch contributes heat only to the work-piece. If filler metal is

required to make the weld, it may be added manually in the same manner as it is added in the

oxyacetylene welding process. GTAW is used to weld stainless steel, nickel alloys such as

Monel and in conel, titanium, aluminum, magnesium, copper, brass, bronze and gold.

GTAW can also weld dissimilar metals to one another such as copper to brass and stainless

to mild steel.

1.2 GMAW (Gas Metal Arc Welding):

Gas Metal Arc Welding (GMAW) is a welding process which joins metals by heating the

metals to their melting point with an electric arc. The arc is between a continuous,

consumable electrode wire and the metal being welded. The arc is shielded from

contaminants in the atmosphere by a shielding gas.

Fig.1.3- Gas Metal Arc Welding

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CHAPTER 2

REVIEW OF LITERATURE

2.1 Summary of Shielded Metal Arc Welding:

The process produces a protective slag that will need to be removed for cleanliness and to

prevent slag inclusions in multiple pass welds. The process also produces spatter, which is a

visual defect. However, the spatter can be easily removed with a grinder.

There are several advantages to SMAW.

Low Start Up Costs - SMAW welding machines are relativity inexpensive

Portability - SMAW is a very portable process because it does not require any external

shielding gas and equipment due to the ability of the electrode to produce its own shielding

gases.

Outdoor Weld ability - SMAW welding can be done outdoors. The shielding of the weld

puddle from the coating of the electrode is not susceptible to winds and draft, and therefore,

is an excellent choice for outdoor welding.

All Position Welding - SMAW can be done in all welding positions, which eliminates the

need for expensive fixture or manipulation of the part being welded.

Variety of Materials - Many base materials and alloys can be welded with the SMAW

process.

There are certain disadvantages of SMAW:

Low Efficiency - The efficiency of a SMAW electrode can be defined as the percentage of

the electrode that is consumed and becomes part of the weld. SMAW electrodes are 60%-

65% efficient. The primary reason for this low efficiency is stub loss, or the portion of the

electrode that is unused and discarded. .

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Operating Factor - Operating factor can be defined as the amount of arc on time in a shift of

work, labeled as a percentage. SMAW welding has an operating factor of approximately

25% - 30%--workday is spent arc welding.

Restarts - SMAW electrodes are only 9”-18” in length. When the electrode is consumed in

the arc, it needs to be replaced with a new one. This means that welding stops, and time is

taken to replace each electrode.

Operator Skill - SMAW welding requires a high level of operator skill. This process is one

of the hardest arc welding processes to learn.

Slag & Spatter.

2.2 AC/DC power sources:

AC (Alternating Current)-- Current direction alternates, between positive & negative.

DC (Direct Current) -- Current flows in one direction

a. DC Positive (STRAIGHT)

Electrode negative, work positive

b. DC Negative (REVERSE)

Electrode positive, work negative

AC/DC Rectifiers

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Fig.2.1- AC Power source

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Fig.2.2 - DC Power source

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2.3 Electrode used in SMAW:

The American Welding Society or AWS sets guidelines for SMAW electrodes with which

manufacturers have to comply. These guidelines include chemistry and mechanical

properties, and usability tests. Each letter and digit stands for something very specific. The E

stands for electrode. AWS defines an electrode as the current carrying device, not

necessarily the consumable that becomes the weld-ment. In the case of SMAW, the electrode

core is consumed as well as any metallic elements in the coating to become the weld deposit.

70 stand for minimum tensile strength in 10,000 psi. The weld deposit made by this SMAW

electrode must consistently meet a minimum tensile strength requirement of 70,000 pounds

per square inch (psi). The next digit is either a 1 or a 2 and indicates welding position. A

“1” indicates that the electrode is an all position electrode-- (flat, horizontal, vertical up,

vertical down, and overhead). While the 2 stands for welds that can only be made in the

flat/horizontal position. The 3rd and 4th digit combined indicates the type of current the

electrode operates on and the type of coating.

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Fig.2.3- Designation of welding electrode

2.4 Welding process of SMAW :

Shielded metal arc welding (SMAW), also known as manual metal arc (MMA) welding, flux

shielded arc welding or informally as stick welding, is a manual arc welding process that

uses a consumable electrode coated with flux to lay the weld. An electric current, in the form

of either alternating current or direct current from a welding power supply, is used to form an

electric arc between the electrode and the metals to be joined. As the weld is laid, the flux

coating of the electrode disintegrates, giving off vapors that serve as a shielding gas and

providing a layer of slag, both of which protect the weld area from atmospheric

contamination.

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http://en.wikipedia.org/wiki/Shielding_gas

http://en.wikipedia.org/wiki/Welding_joints

http://en.wikipedia.org/wiki/Metal

http://en.wikipedia.org/wiki/Electric_arc

http://en.wikipedia.org/wiki/Welding_power_supply

http://en.wikipedia.org/wiki/Direct_current

http://en.wikipedia.org/wiki/Current_(electricity)

http://en.wikipedia.org/wiki/Flux_(metallurgy)

http://en.wikipedia.org/wiki/Electrode


Fig.2.4- Welding process with end view

2.5 Influence of Magnetic Field:

Application of external magnetic field has been reported in the literature to affect the

characteristics of the welding arc and the weld properties. Magnetic field can be applied to

the welding arc in three different modes. If magnetic field is in the direction of electrode

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travel, it is considered to be a longitudinal magnetic field. if the field is perpendicular to the

direction of electrode travel and electrode axis, it is referred to as a transverse field.

Factors which affect the arc behavior during the application of a magnetic field are as

follows:

1. Distance between the electrodes

2. Magnetic field intensity

3. Arc current

4. Weld material

Fig.2.5- Without magnetic field

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Fig. 2.6- Arc deflection in magnetic field

Fig.2.7-

Fleming’s Left Hand Rule

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2.6 Objective: -

The objective of this project work is to study effect of magnetic field on the weld quality and

geometry when the field is applied longitudinal to the electrode travel i.e. the field lines are

perpendicular to the electrode travel. The material of the weld-piece taken is mild steel and

the welding process is shielded metal arc welding. The weld quality of the pieces will be

checked by conducting different weld test as hardness, tensile strength and impact test. The

tensile test will be conducted on the UTM and hardness test is on hardness tester with steel

ball penetrator. The impact test will be conducted on the impact testing machine. Charpy test

will be conducted to check the toughness of the weld-piece. The weld geometries will be

checked through the visual inspection and penetration depth, reinforcement height and weld

bead width will be considered.

Objective of the project work at a glance :-

To study the effect of magnetic-field on weld-quality and weld geometry when the field

is applied-longitudinal to electrode.

To compare the process of arc-welding with magnetic-field and without magnetic-field.

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CHAPTER 3

APPLICATION OF MAGNETIC FIELD

3.1 Longitudinal magnetic field:

A magnetic force acts on the arc, in this system when the angle between the direction of the

electron stream and magnetic lines of force are not zero. As the arc has a conical shape and

the current carrying electrons also moves along the surface of the arc, their motions can be

resolved in two components, one along the axis of the arc and other perpendicular to it. The

component along the arc does not contribute to the magnetic movement. The component

perpendicular to arc exerts a force on the arc causing the arc to rotate clockwise or

anticlockwise depending upon the direction of the magnetic field and polarity used.

Fig.3.1- Longitudinal magnetic field

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3.2 Transverse magnetic field:-

According to the Flemings left hand rule the arc in the influence of transverse magnetic

field will be deflected forward or backward depending upon the direction of magnetic field

lines force and the polarity of welding system. Work of earlier investigation can be analyzed

keeping this in mind.

Kovalev showed that the transverse magnetic field can be used as automatically regulating

the depth of penetration. Hicken and Jackson found beneficial effects of constant transverse

magnetic field when the arc was deflected forward with respect to the electrode travel speed.

It was possible to increase the welding speed four times and steel obtains the welds free from

undercuts. Weld width was found to reduce with increase in magnetic field. Sheinkin found

the application of transverse magnetic field to increase the productivity of the submerged arc

welding process used for making butt joints between prepared edges.

Fig.3.2 Transverse magnetic field

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CHAPTER- 4

WELD QUALITY AND WELD GEOMETRY

4.1 Weld quality: -

To ensure the satisfactory performance of a welded structure, the quality of the welds must

be as per acceptance standards. The quality of the welds must be determined by adequate

testing procedures. These tests includes measure of various defects occur in a weld. The

acceptance standards are the minimum weld quality which must be achieve for satisfactory

performance of welds.

Defects in weld-pieces-

The defects which occur in the weld-pieces due to the imperfect welding conditions and their

causes are as follows:

1. Undercutting:-

Undercutting is the burning away of the base metal at the toe of the weld.

Causes:

Current adjustment that is too high.

Arc gap that is too long.

Failure to fill up the crater completely with weld metal.

2. Incomplete penetration:- This term is used to describe the failure of the filler and base

metal to fuse together at the root of the joint.

Causes:

The rate of travel is too high.

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The welding current is too low

3. Lack of fusion:-

Lack of fusion is the failure of a welding process to fuse together layers of weld metal or

weld metal and base metal.

Causes:

Failure to raise to the melting point the temperature of the base metal or the previously

deposited weld metal.

Dirty plate surfaces.

Improper electrode size or type.

Wrong current adjustment.

4. Slag inclusion:-

Slag inclusions are elongated or globular pockets of metallic oxides and other solid

compounds. They produce porosity in the weld metal.

Causes: Failure to remove the slag between the layers causes slag inclusions

5. Porosity:

Porosity is the presence of pockets which do not contain any solid material. They differ from

slag inclusions in that the pockets contain gas rather than a solid.

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Gases are derived from:

Gas released by cooling weld

Gases formed by the chemical reactions in the weld.

Fig.4.1- Welding defects

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4.2 Geometry of weld-pieces:-

Weld Bead Geometry –

The mechanical properties of the welded joints greatly depend on weld bead geometry,

which in turn, is influenced by welding parameters like arc current arc voltage, and arc travel

speed. The bead geometry is specified by weld bead width, reinforcement height,

reinforcement area, penetration height, penetration area and the contact angle of weld bead.

Other factors like nugget area, percent dilution, pool shape factor, bead shape factor and

ripple shape factor may also be included in the bead geometry. Fig shows some aspects of

weld bead geometry. The Weld Bead Width is the maximum width of the weld metal

deposited. It increases with arc current, arc voltage, electrode weaving and decreases as arc

travel speed increases.

Penetration:

Depth of penetration or simply penetration is the distance from base plate top surface to the

maximum extent of the weld nugget. Penetration determines the load carrying capacity of a

welded structure. Penetration area is that covered by the fusion line below the base metal

level. Penetration area affects the weld strength.

Reinforcement Height:

Reinforcement height is the maximum distance between the base metal level and the top

point of the deposited metal and Reinforcement Area is one included between the contour

line of the deposited metal above the base metal level.

CHAPTER 5

WELDING SET-UP ON LATHE

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5.1 Automation to welding process:

A lathe machine is used to provide the semi-automation to the welding process. A wooden

block covered by a metallic sheet is fixed on the carriage and the means of magnetic field is

attached with the tailstock. The arrangement is shown in fig.

Fig.5.1- Welding set-up on lathe

The welding electrode with holder is to be operated manually while the weld-piece is moved

through the lead screw of lathe automatically with a fixed speed. A metallic rod is also used

to provide the electric connection within the work-piece. This rod is so connected that there

will be no any gap produce which can fluctuate the electric supply. There is a proper gap

maintained within the magnet and work-piece throughout the welding process.

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5.2 Arrangement for magnetic field :

A bar magnet is used for the production of magnetic field. In the first arrangement we used a

solenoid but a problem occurred with current carrying capacity and the strength of produced

magnetic field. A Gauss-meter is used for measuring the magnetic field.

Fig.5.2- Magnetic field measurement by Gauss-meter

5.3 Current and Voltage measurement:

Current and voltage measuring devices used are clamp-meter and multi-meter respectively.

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Fig.5.3- Clamp-meter & Multi-met

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5.4 Line diagram of set up:

Fig.5.4- Set-up on lathe in Magnetic field

1. Multi-meter, 2. Battery Eliminator, 3. Electric Board, 4. Gauss-Meter,

5. Table, 6. Measuring-Probe, 7. Transformer Welding-Set, 8. Clamp-meter

9. Tail-Stock, 10. Sleeve, 11. Link (Wood), 12. Solenoid, 13. Tool post,

14. Iron sheet, 15. Work-piece, 16. Electrode, 17. Electrode Holder, 18. Metal-Strip

Connected with head stock, 19. Head stock, 20. Connection Wires.

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CHAPTER 6

WELDING WITH THE SET-UP

6.1 Preparation of Specimens:

The mild steel pieces of the dimension 150 mm X 50 mm X 6 mm are used as a work-piece

for the welding. Each metal piece first cleaned for dust and rust. Before the actual welding

process the space between the specimens is fixed with a support. The space between the

specimens for the butt welding is depends upon the thickness of the work-piece. For a 6 mm

thickness there is no requirement of making groove, so a 3 mm gap is maintained during the

whole process of welding. The quality and geometry of weld is much depends on correct and

same gap throughout length of the specimen.

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6.2 Welding In Magnetic Field(M):

The magnetic field is applied as per the set-up and then the arc welding machine and

electrodes are fixed at their respective places. Multi-meter, clamp-meter and gauss-meter are

placed and connected to take the readings. As per the semi-automation to the process feed

rod is connected with the work-piece motion. The weld-pieces obtained after the process is

shown in fig. different readings obtained with the process are tabulated and it is shown in the

table no. 6.1.

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Welding Without Magnetic Field (WM):

The similar setting as with magnetic welding is used in without magnetic field process of

welding. Only change is that the magnetic field arrangement is removed. The range of

current and voltage are remained similar to the magnetic field welding. The weld-pieces

obtained in this process are shown below and the readings are tabulated.

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WORK-PIECE NO.

CURRENT (A)

VOLTAGE (V)

M1, M2, M3

110 - 120 23-26

M4, M5, M6

125-135 18-22

M7, M8, M9

90-100 27-30


TABLE NO. 6.2

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WORKPIECE

NO.

CURRENT(A) VOLTAGE

(V)

WM1, WM2,

WM3

110 - 120 23-26

WM4, WM5,

WM6

125-135 18-22

WM7, WM8,

WM9

90-100 27-30


6.3 Grouping and cutting of weld-pieces:

Each weld-piece (with and without magnetic field) cut into three pieces and grouped

according to the range of current and voltage and provided a specific code. Now, the total no.

of weld-pieces is 9 and their corresponding parametric readings are tabulated as below. Each

weld specimen has a code which shows its specifications. The letter shows the weld-piece is

from the category of magnetic field or without magnetic field. The letter M shows magnetic

field and WM shows without magnetic field. The number provided to the code shows its

range of current and voltage. The number 1, 2, 3 shows the range of current 110-120 Ampere

and voltage 23-26 volts.

Weld-pieces with magnetic field:-

Table No. 6.3

WORK-PIECE

NO.

CURRENT(A) VOLTAGE (V) MAGNETIC-FIELD

INTENSITY

(GAUSS)

WELDING SPEED

(mm/min )

M1. 120 24.5 70 60

M2. 110 23.7 70 60

M3. 115 23 70 60

M4. 135 18.5 70 60

M5. 125 21.5 70 60

M6. 130 19 70 60

M7. 90 27.5 70 60

M8. 95 27.7 70 60

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M9. 100 28.5 70 60

Weld-pieces without magnetic field:-

Table No. 6.4

WORK-PIECE

NO.

CURRENT(A) VOLTAGE (V) WELDING SPEED

(mm/min)

WM1. 115 23 60

WM2. 120 24.7 60

WM3. 110 23 60

WM4. 135 18.6 60

WM5. 125 21.3 60

WM6. 130 23 60

WM7. 95 28.7 60

WM8. 100 31 60

WM9. 90 31.5 60

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CHAPTER 7

WELD TESTS

7.1 Hardness test:

Hardness may be defined as the ability of a substance to resist indentation of localized

displacement. A hardness test is used to determine the hardness of weld metal. In the

Rockwell hardness test, the specimen is mounted on the anvil of the machine and a load is

applied against a hardened steel ball which is in contact with the surface of the specimen

being tested.

The load is allowed to remain 1/2 minute and is then released, and the depth of the

depression made by the ball on the specimen is measured. The resultant Rockwell hardness

number is obtained from the dial.

Rockwell hardness tester:

The principle of the Rockwell tester is essentially the same as the Brinell tester. It differs

from the Brinell tester in that a lesser load is impressed on a smaller ball or cone shaped

diamond. The depth of the indentation is measured and indicated on a dial attached to the

machine. The hardness is expressed in arbitrary figures called "Rockwell numbers." These

are prefixed with a letter notation such as "B" or "C" to indicate the size of the ball used the

impressed load, and the scale used in the test.

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Fig.7.1- Rockwell Hardness Tester

The test result of the hardness test was conducted on both type of weld-pieces (with

magnetic field and without magnetic field) are shown in the table below.

Table No.7.1

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WORK-PIECE NO. PARENT METAL

(RHN)

WELDMETAL

(RHN)

M2. 90 83

M5. 92 80

M8. 89 84


Table No.7.2

-

7.2 Tensile strength test:

This test is used to measure the tensile strength of a welded joint. The tensile strength, which

is defined as stress in kgf per square meter. It is calculated by dividing the breaking load of

the test piece by the original cross section area of the specimen. The test result which is

conducted on universal testing machine ( UTM) is given in the table. The gripping and

rupture points located in the figures. This test is used to measure the strength of a welded

joint. A portion of the welded plate is locate the weld midway between the jaws of the testing

machine. The width thickness of the test specimen are measured before testing, and the area

in square inches is calculated by multiplying these before testing , and the area in square

inches is calculated by multiplying these two figures.

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WORK-PIECE NO. PARENT METAL

(RHN)

WELD METAL

(RHN)

WM2. 93 85

WM5. 95 86

WM8. 92 88


Fig.7.2- Tensile Testing Process

The tensile test specimen is then mounted in a machine that will exert enough pull on the

piece to break the specimen. The testing machining may be either a stationary or a portable

type. A machine of the portable type, operating on the hydraulic principle and capable of

pulling as well as bending test specimens.

The specimen is ruptured under tensile load, and the maximum load in pounds is determined.

The shearing strength of the weld in pounds per linear inch is determined by dividing the

maximum load by the length of fillet weld that ruptured. The shearing strength in pounds per

square inch is obtained by dividing the shearing strength in pounds per linear inch by the

average throat dimension of the weld in inches. The test specimens are made wider than

required and machined down to size.

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Fig.7.3-UTM Used for tensile test

Fig. 7.4 – specimen for tensile test

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Fig.7.5- Gripping of work-piece

Fig 7.6 FRACTURE OF TEST PIECE

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Table for the tensile test of the weld-pieces with magnetic field-

Table No.7.3

WORK-PIECE

NO.

TENSILE LOAD

(IN Kgf)

CROSS-SECTIONAL

AREA (mmXmm)

TENSILE

STRENGTH

(Mpa)

M1. 10480 290 354.51

M4. 10320 287 352.75

M6. 10560 292 354.77

Table for tensile test without magnetic field specimens-

Table No.7.4

WORK-PIECE

NO.

TENSILE LOAD

(IN Kgf)

CROSS-SECTIONAL

AREA (mmXmm)

TENSILE

STRENGTH

(MPa)

WM1. 10160 300 332.23

WM4. 10240 294 333.67

WM6. 10000 304 330.44

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7.3 Impact Test:

The two kinds of specimens used for impact testing are known as Charpy and Izod. Both test

pieces are broken in an impact testing machine. The only difference is in the manner that

they are anchored. The Charpy piece is supported horizontally between two anvils and the

pendulum strikes opposite the notch. The Izod piece is supported as a vertical cantilever

beam and is struck on the free end projecting over the holding vise

A Charpy test measures the welds ability to withstand an Impact force. Low Charpy test

readings indicate brittle weld metal Higher Charpy readings indicate the samples toughness.

Fig.7.7- Weld-pieces for Charpy test

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Table No.7.5 Table No.7.6

The toughness values of the weld-pieces are tabulated above. Weld-pieces are placed at the

impact testing machine as simply supported. The hammer of the heavy weight is then

released and corresponding values of weight provides the toughness values for weld-pieces.

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WORKPIECE NO. TOUGHNESS

(J)

WM3. 59

WM6. 64

WM9. 62


CHAPTER 8

EFFECT OF MAGNETIC FIELD

8.1 Visual effects:

The welding process is semi-automated and this result there is a little improvement in weld

quality. Welding speed is also increasing as the weld width is shaped by itself. The effect of

magnetic field is to deflect the arc as perpendicular to the weld bead. This implies to increase

in weld speed. Some weld defects are also reduced as weld spattering and incomplete

penetration. Complete penetration occurs due to attraction of molten material. Welding

process which is applied here is providing the ease to welder and improves the weld quality.

Some of visual effects are as follows:

Welding speed:

Welding speed is the linear rate at which an arc is moved along the weld joint. With any

combination of welding voltage and welding current, the effect of changing the welding

speed confirms to a general pattern. If the welding speed is increased, power or heat input

per unit length of weld is decreased and less filler metal is applied per unit length of the

weld, resulting in less weld reinforcement. Thus, the weld bead becomes smaller. Weld

penetration is affected more by welding speed than any variable other than current. This is

true except for excessively slow speeds when the molten weld pool is beneath the welding

electrode. Then the penetrating force of the arc is cushioned by the molten pool. Excessive

speed any cause undercutting, porosity, arc blow, uneven bead shape, cracking and higher

slag inclusion in the weld metal.

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Higher welding speed results in less heat affected zone and finer grains. Within limits,

welding speed can be adjusted to control weld size and penetration. Relatively slow welding

speed provides time for gases to escape from the molten metal, thus reducing porosity. An

excessive slow speed produces a convex bead shape which is subject to cracking and

excessive arc exposure which is uncomfortable for the operator. Too low welding speed may

also result in a large molten pool that flows around the arc, resulting in rough bead, slag

inclusions and burn through of the weld plate. Here the application of magnetic field is

significantly increases the welding seed. The semi-automation provided to the welding

process is also helping to increase the welding speed.

Fig.8.1-Speed vs. Depth of Penetration

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Spatter on weld metal:

It has appeared that the welding with magnetic field has less spattering action on the weld

metal than the without magnetic field. fig shows it below.

Fig .8.2

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8.2 Effect on weld properties:

The effect of magnetic field on the weld quality is checked through the various tests for

mechanical properties. The weld properties which we have considered here are hardness,

tensile strength and toughness. The specimens for each welding test are prepared and the

tests are conducted on them. Test results for various mechanical properties are tabulated

above.

Tensile test:

The effect of magnetic field on the tensile strength is to increase it. The weld test conducted

on the pieces shows the increase of tensile strength. The change in the properties is

calculated in terms of percentage and there is an increase of 6.6% on an average. This shows

that a magnetic field applied longitudinal to weld bead, deflected the arc such that the tensile

properties of the weld-pieces increases.

Table No.8.1

PROPERTIES WITHOUT

MAGNETIC

FIELD

MAGNETIC

FIELD

CHANGE

TENSILE

STRENGTH

332.11 354.01 6.6%

INCREASE

HARDNESS 86.33 82.33 INCREASE

TOUGHNESS 61.66 73.66 16.2%

INCREASE

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Hardness test:

The hardness of the material and weld section both are checked and result is found which shows

the decrease in the hardness of weld metal. When we are comparing the weld-pieces which are

welded without magnetic field the hardness is decreases. The hardness value of the materials are

taken in terms of RHN ( Rockwell hardness number ). When the RHN increases it shows the

increase in hardness of the material. All the hardness reading in our work is taken at the B scale

of the Rockwell hardness tester.

Toughness:

Toughness test is used to check the ability of a weld to absorb energy under impact without

fracturing. This is a dynamic test in which a test specimen is broken by a single blow, and the

energy used in breaking the piece is measured in foot-pounds. This test compares the toughness

of the weld metal with the base metal. It is useful in finding if any of the mechanical properties of

the base metal were destroyed by the welding process.

The two kinds of specimens used for impact testing are known as Charpy and Izod. Both test

pieces are broken in an impact testing machine. The only difference is in the manner that they are

anchored. The Charpy test piece is supported horizontally between two anvils and the pendulum

strikes opposite to the notch. The Izod piece is supported as a vertical cantilever beam and is

struck on the free end projecting over the holding vice .the magnetic field applied longitudinal to

work-piece increases the toughness of the material. This effect is obtained as per the impact test

which is conducted on the specimens of Charpy test. Result shows the change in the value of

impact load sustained by both type of specimens.

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8.3 Effect on weld geometry:

Bead width-

The effect of longitudinal magnetic field is to deflect the arc perpendicular to welding

direction. As alternating current changing its direction, direction of electrons changes and

this changes the direction of force on them. Hence arc is deflecting right and left to the line

of weld. This movement increases the bead width. The weld bead width is the maximum

width of the weld metal deposited. It influences the flux consumption rate and chemistry of

the weld metal. Weld bead width is directly proportional to arc current, welding voltage and

electrode diameter and indirectly proportional to the welding speed. The bead width

increases with an increase in electrode diameter. It observed that bead width increased with

an increase in current until it reaches a critical value and then it decreases with an increase in

welding current. The bead width was not affected significantly by the types of power source

(constant voltage or constant current) when an acidic fused flux was used. However, using a

basic fused flux with constant current operation showed somewhat larger bead width than

with welds laid using acidic fused flux.

Penetration:

The penetration depth is increased when magnetic field applied. Weld bead penetration is the

maximum distance between the base plate top surface and depth to which the fusion has

taken place. The more the penetration, the less is the number of welding passes required to

fill the weld joint which consequently results in higher production rate. It is observed that the

penetration is influenced by welding current, polarity, arc travel speed and physical

properties of the flux. It was observed that penetration was directly proportional to welding

current. It was further investigated that the penetration was indirectly proportional to welding

speed and electrode diameter. Penetration decreases with the increase in welding speed

because the time during which the arc force is allowed to penetrate into the material. The

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penetration decreases with the increase in electrode diameter due to decrease in current

density reported that the penetration decreased with the decrease in electrode extension and

included angle of the joint. The effect of magnetic field when applied longitudinally shows

that the depth of penetration is decreases. This is the most significant effect which is found

during the visual inspection. Although the value of this change, not measured in this project

work.

Reinforcement Height-

Reinforcement is decreases as the bead width of the weld increasesReinforcement is the

maximum distance between the base metal level and the top point of the deposited metal.

Reinforcement is the crown height of the weld bead from the base plate. It affects the strength of

the weld joint and welding wire consumption rate. It increases with the increase in welding wire

feed rate irrespective of the welding current and the type of polarity employed .It is indirectly

proportional to welding voltage, welding speed and electrode diameter. Increase of reinforcement

with an increase of welding filler wire feed rate is mainly due to the larger amount of metal

deposited per unit length. The decrease of reinforcement with the increase in voltage is due to

increase in weld bead width. The magnetic field increases the bead width and this leads to the

decreases in the reinforcement height.

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CHAPTER 9

CONCLUSIONS AND SUGGESTIONS

9.1 Conclusions :

On the basis of different experiments, automation of welding process and effect of magnetic

field the following conclusions are derived:

1. The welding set-up on lathe provides automatic motion to the work-piece and welder has

to provide only the feed to electrode. This provides the smoothness in welding process.

2. Effect of magnetic field applied transverse to welding direction affects the bead width of

joint and increases it.

3. Undercuts, spatter etc. welding defects are reduced.

4. The tensile strength of the weld joint is on improvement side due the refinement of grains.

5. Hardness of the weld decreases as compared with the weld-pieces which are welded

without magnetic field.

6. Reinforcement height of weld reduces as the weld bead width is increasing.

7. Toughness of the weld metal increases.

Hence, we can say that the use of external magnetic field transverse to the welding direction

is helping in improvement of weld quality and weld geometry. Here we can say that the

transverse magnetic field can also affect the weld quality .

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9.2 Suggestions For Further Work:

In this project we have constrained our work by testing the effect of magnetic field in

longitudinal direction only. Further this can be study for

Magnetic field in transverse direction of weld bead

Magnetic field applied axial to the electrode

Further the study can be extended by conducting the following mechanical properties test

Bend test

Non destructive tests

In this project work the weld geometry tests are not conducted only the visual inspection is

done and the results based on that are considered. Further the study can be extended by

performing the macro structure study of the weld metal. This can be done on polishing and

grinding machines. This could be result in perfect testing of weld bead width and penetration

depth.

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REFERENCES

1. Serdyuk, d. b., and Kornienko, a. n.1963. The welding arc in an alternating

transverse magnetic field. Automatic welding (10):7–13.

2. A study on the modeling of magnetic arc deflection and dynamic analysis of arc

sensor by Y. H. Kang and s. j. na. Welding journal 13-s.

3. Mallya, U. D., and Srinivas, h. s. 1993. Magnetic steering of arc and bead

characteristics in submerged arc strip cladding. welding journal 72 (11): 517-s to

522s

4. Engineering Principles of Welding- processes, physics, chemistry and metallurgy by

Robert, Wissler 2004, and welding journal.

5. Dennary F., (1966), Electric field distribution in welding arc, physics of welding arc,

sym.IW, Cam UK.

6. Amstead, B.H., P.F. Ostwald, and M.L.begman (1979), manufacturing processes,

john wiley, N. Y.

7. Serdjuk, G.B.,(1966), magnetic forces in arc welding metal transfer, physics of

welding arc, SYM. IW, Cambridge, London.

8. Khan M.I. (1979), a study of Hardfacing under magnetic field, proc. ISME conf.

New Delhi, paper E.P. 4.1 Dec., PP.174.-176.

9. Khan M.I., (1992), study of effect of superimposition of longitudinal magnetic field

onarc characteristics, bead geometry, microstructure and mechanical properties.

Conf. on prod. Engg. Design and control, university of Alexandria, Egypt, dec. 1992.

10. Mandal, N. R. (2004), Welding and Distortion Control, Narosa.

11. Needham, J.C., (1978), (Tech. Dir) Advances in welding process, 4th Int. Conf.

Herrogate, IW Cambridge, London.

12. Nikolaev, G., and N. Olshansky, (1977), advanced welding processes, mir pub.,

Moscow.

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Documents

Project Report (Arc Weldinng)