Optimization of mig welding parameters using taguchi optimization technique

I
OPTIMIZATION OF MIG WELDING PARAMETERS
USING TAGUCHI OPTIMIZATION TECHNIQUE
A Project report submitted in partial fulfilment of the
requirements for the degree of
Bachelor of Technology
in
Mechanical Engineering
Submitted By
K. VENKAT RAMANA 15311A0370
R. TEJA RAM 15311A03A8
K. VINEETH GOUD 15311A03A9
Under Guidance of
Dr S. Vijaya Bhaskar
Professor in Mechanical Engineering
Department of Mechanical Engineering
SREENIDHI INSTITUTE OF SCIENCE AND TECHNOLOGY
(An autonomous institute under JNTUH)
Yamnampet, Gatkesar (M), Hyderabad – 501301, TS
MAY 2019

II
CERTIFICATE
This is to certify that the project work entitled
“OPTIMIZATION OF MIG WELDING PARAMETERS USING
TAGUCHI OPTIMIZATION TECHNIQUE” being submitted by
the following students
K. Venkat Ramana 15311A0370
R. Teja Ram 15311A03A8
K. Vineeth Goud 15311A03A9
for the partial fulfilment of the requirement for the award of
Bachelor of Technology in Mechanical Engineering to the
Jawaharlal Nehru Technological University Hyderabad (JNUTH),
Kukatpally, Hyderabad, TS is a record of bonafied work carried
out under my guidance and supervision.
Dr S. Vijaya Bhaskar Dr.T.CH.Shiva Reddy
(Professor in Mech.Engg.) (Professor & HOD )
Department of Mech.Engg.
Internal Guide
External Examiner

III
DECLARATION
We hereby declare that the work described in this thesis, entitled
“OPTIMIZATION OF MIG WELDING PARAMETERS USING TAGUCHI
OPTIMIZATION TECHNIQUE” which is being submitted in partial fulfilment
for the award of Bachelor of Technology (B.Tech) in the Department of
Mechanical Engineering to the Sreenidhi institute of science and technology
is the result of investigations carried out by me under the guidance of
Prof. S. Vijaya Bhaskar
The work is original and has not been submitted for any Degree/Diploma of
this or any other university.
K. Venkat Ramana (Roll No: 15311A0370)
R. Teja Ram (Roll No: 15311A03A8)
K. Vineeth Goud (Roll No: 15311A03A9)

IV
ACKNOWLEDGEMENT
We express our grateful thanks to Dr. P.Narasihma Reddy,
Director, Dr.T.Ch.Shiva Reddy, Principal & HOD, Department of
Mechanical Engineering, for their support in completing our
project.
We would like to express our gratitude to our project guide,
Dr.S.Vijaya Bhaskar for this continuous guidance, support and
the motivation throughout our project. We would also like to
thank him for his valuable suggestions and support in successful
completion of the project.
We finally thank our family and friends who directly/indirectly
helped us in completing the project.

V
ABSTRACT
Generally in any welding process, there are numerous
parameters that affects the quality, productivity and cost of
welding. The present research work aims to identify the influence
of each welding parameter on outcome and identify the optimized
parametric combination for better weld strength, weld pool
geometry of low and medium carbon steel materials. Welding
current, welding voltage, Gas flow rate, wire feed rate were
considered as controlled input process parameters. By using
DOE method, the least number of experimental trials were
designed and prepared orthogonal array. The prepared L9
Orthogonal array was employed to investigate the welding
characteristics of Mild Steel material in order to identify the
optimized welding parameters. Finally the results were compared
with ANOVA analysis and it was noticed that ANOVA has
confirmed the results of Taguchi Analysis.

VI
CONTENTS
Acknowledgement
Abstract
Contents
CHAPTER-1: INTRODUCTION 01
1.1 Different ways of GMAW 01
1.2 Working principle of MIG welding 04
1.3 MIG welding equipments and specifications 08
1.4 MIG welding applications 11
1.5 MIG welding effecting parameters 12
CHAPTER-2: REVIEW OF LITERATURE 18
CHAPTER-3: OPTIMIZATION TECHNIQUES 23
3.1 Design of experiments 25
3.2 Advantages of design of experiments 26
3.3 Taguchi method 26
3.4 S/N Ratio 29
CHAPTER-4: EXPERIMENTAL SETUP AND PROCEDURE 34
4.1 Experimental setup 25
4.2 Pre-experimental procedure 27
4.3 Experimental procedure 27
4.4 Tensile testing (universal testing machine) 28
CHAPTER-5: RESULTS AND ANALYSIS 42
CHAPTER-6: CONCLUSION 54
References 56

VII
LIST OF FIGURES
Fig. No Title page no.
1 Working condition of work piece 07
2 Working principles of GMAW 07
3 Mig welding equipment 08
4 Mig welding machine 10
5 Mild steel electrode 11
6 Mild steel 38
7 EN8 38
8 Universal testing machine 39
9 Main effect plots for means for Mild Steel 44
(Elongation)
10 Main effect plots for S/N ratio for Mild Steel 47
(Elongation)
11 Main Effects Plot for SN ratios for Mild Steel 47
(Tensile Strength)
12 Main effect plots for means for Mild Steel 49
(tensile Strength)
13 Main Effects Plot for SN ratios for EN8 50
(Tensile Strength)
14 Main Effects Plot for Means for EN8 52
(Tensile Strength)
15 Main Effects Plot for SN ratios for EN8 53
(Elongation)
16 Main Effects Plot for Means for EN8(Elongation) 53

viii
LIST OF TABLES
Table no. Title page no.
1 Mig welding specifications 09
2 Current range 13
3 Chemical composition of mild steel 33
4 Chemical composition of EN8 33
5 Selection of orthogonal array 36
6 Control parameters 37
7 orthogonal array and control parameters 38
8 Response table for signal to noise for MS(Elongation) 38
9 Analysis of variance for SN ratios MS(Elongation) 43
10 S/N and Mean values for each run for MS(Elongation) 44
11 Response table for signal to noise for MS 45
(Tensile Strength)
12 Analysis of variance for SN ratios for MS(Tensile Strength) 46
13 S/N and Mean values for each run for MS(Tensile Strength) 46
14 Response table for signal to noise for EN8(Tensile Strength) 48
15 Analysis of variance for SN ratios for EN8(Tensile Strength) 49
16 S/N and Mean values for each run for EN8 51
(Tensile Strength)
17 Analysis of variance for SN ratios for EN8(Elongation) 51
18 S/N and Mean values for each run for EN8(Elongation) 52

ix
NOMENCLATURE
MIG Metal inert gas
DOE Design of experiments
GMAW Gas metal arc welding
ANOVA Analysis of variance
UTM Universal testing machine
MS Mild steel

1
CHAPTER - 1
INTRODUCTION
1. Introduction
The welding is a process of joining two or more, similar or dissimilar metals
by heating them to a suitable temperature, with or without the application
of pressure, filler material and flux. The heat may be supplied by electric arc
(In case of arc welding), combustion of gas (in case of gas welding), electrical
resistance (in case of resistance welding) or by black Smith’s fire (in case of
forge welding). The filler material has a similar composition and melting
paint less than that of the base metal. The filler rod is used to supply the
extra material, to fill the gap between joint and to produce a round, oval or
fillet. Also, its function is to make-up the losses during welding process. A
flux is sometimes used to remove the oxides formed during process, in the
form of fusible slag which floats on the molten metal. This also prevents the
re-formation of Oxides by environmental conditions. Welding of similar
metals without filler material is known as autogenesis welding while with
filler material is called homogeneous welding. On the other hand, welding of
dissimilar metals with filler rod is called heterogeneous welding. Welding
phenomenon is comes into existence since 1930. Its growth is very fast in
fabrication industries. It is an alternative method for casting or forging.
Today, the scope of welding technology is wide and extensive. It is
successfully employed in daily use items like automobile vehicles, aircrafts,
ships, household appliances, electronic equipment’s, bridge construction,
building construction, pressure vessels, tanks, Rail and road equipment’s,
Piping’s and pipelines, trucks, trailers, trusses etc.
1.1 Classification of Welding Process
Welding process can be classified on the basic of certain criteria mentioned
below:
(i) On the basis of type of interaction.

2
(ii) On the basis of source of heat.
(iii) On the basis of metallurgical aspect.
(i) On the Basis of Type of Interaction:
This can be divided in following three groups:
(a) Fusion welding (Non-pressure welding).
(b) Forge welding (Pressure or plastic welding).
(c) Solid state welding.
(a) Fusion Welding:
In fusion or non-pressure welding, the edges of the metal pieces to be joined
and the filler material are heated together to a melting temperature, and
then allowed to solidify. This is most widely used welding process.
(b) Forge Welding:
In forge or pressure or plastic welding, the metal pieces to be joined are
heated to a plastic state and then forced together by applying mechanical
pressure, with the help of hammer. No filler material is required in this type
of welding.
(c) Solid –State Welding:
The welding which is done at solid state of metal work piece is called solid
state welding. This again classified into two groups i.e., pressure welding
and electrical resistance welding. Explosive welding, Friction welding,
Ultrasonic welding and Cold-pressure welding are some different types of
solid-state welding.
(ii) On the Basis of Source of Heat:
This can be divided in following different groups:
(a) Electric Arc Welding.
(b) Gas Welding.

3
(c) Resistance Welding.
(d) Thermo-Chemical Reaction Welding (Thermit welding).
(e) Radiant Energy Welding.
(iii) On the Basis of Metallurgical Aspect:
This can be divided in following three groups:
(a) Autogeneous Welding.
(b) Homogeneous Welding.
(c) Heterogeneous Welding.
(a) Autogeneous Welding:
The process of joining similar metals without the addition of filler material is
known as autogenously welding.
(b) Homogeneous Welding:
The process of joining similar metals with the addition of filler material is
known as Homogenous welding.
(c) Heterogeneous Welding:
The process of joining dis-similar metals with the addition of filler material
is known as Heterogeneous welding.
1.3 IMPORTANCE OF WELDING
1. It is a permanent joint that provided adequate strength as per the
requirement.
2. Welding done in a organised way will provide leak-proof joint.
3. Suppose the purpose is to join to plates in butt joint configuration,
at this point riveted joint, bolted joint are of no use, even if you
joined them backing strap is required and still required strength will
not be there, at this stage welding is optimal way for joining.

4
4. Proper welding joint provides strength more than the base material
as in case of submerged arc welding(SAW) and in other processes
too.
5. Nowadays in major of application, you will find the use of welding.
6. Components of thicker dimensions can be joined through welding in
a convenient way.
Apart from above mentioned roles, welding can be used in day to day
applications.
1.4 WORKING PRINCIPLE OF MIG WELDING
Metal Inert Gas (MIG) welding as the name suggests, is a process in which
the source of heat is an arc formed between a consumable metal electrode
and the work piece, and the arc and the molten puddle are protected from
contamination by the atmosphere (i.e. oxygen and nitrogen) with an
externally supplied gaseous shield of inert gas such as argon, helium or an
argon-helium mixture. No external filler metal is necessary, because the
metallic electrode provides the arc as well as the filler metal. It is often
referred to in abbreviated form as MIG welding. MIG is an arc welding
process where in coalescence is obtained by heating the job with an electric
arc produced between work piece and metal electrode feed continuously. A
metal inert gas (MIG) welding process consists of heating, melting and
solidification of parent metals and a filler material in localized fusion zone by
a transient heat source to form a joint between the parent metals. Gas metal
arc welding is a gas shielded process that can be effectively used in all
positions. The MIG welding process is based on the principle that a
consumable metal electrode is used to produce an arc in between the metal
electrode and the workpiece. The arc so produced creates a large amount of
heat and this heat is used to join the two metal pieces together. The whole
process takes place under a shielding gas (argon or helium) to prevent the
weld from atmospheric contamination.
(a) TOOL STYLE
In gas metal arc welding, the most commonly used electrode holders are

5
 Semi-Automatic Air-Cooled Holder: This type of holder uses compressed
air to maintain the temperature at required level. It uses low level currents
to make lap and butt joints.
 Semi-Automatic Water-Cooled: Its working is same us above holder but
the difference is that it uses water for the cooling instead of compressed air.
This uses higher level of currents to weld T or corner joints.
 Water Cooled Automatic Electrode Holder: It is a typical electrode holder
and is used with automated equipment.
(b) POWER SUPPLY
The MIG welding process or GMAW most commonly uses constant voltage,
direct current power source for the welding. It can also use constant current
systems and alternating current.
(c) SHIELDING GAS
The shielding gases are of two types- inert or semi inert. The shielding gases
that are used in MIG welding are
 Argon and helium are inert and most cost effective shielding gas used in the
MIG welding. Pure argon and helium is used to weld non-ferrous materials.
 The semi- inert gases are the mixtures of carbon dioxide, nitrogen, hydrogen
and oxygen in the argon.
WORKING
 In MIG welding process, the electrode wire from wire feed unit and shielding
gas supply is attached with the welding gun. The positive terminal of DC
power source is connected to the welding gun and the negative terminal is
connected to a clamp.
 The clamp is connected to the workpiece to be joined. The welding gun is
bring near the workpiece and as the trigger is pressed, arc is produced at
the tip of the welding gun. The arc produced melts the electrode wire and it
gets deposited in between the two metal piece to be joined and form a slag
free weld.
 A shielding gas also starts to spread as the arc is produced. It protects the
weld from reacting with atmospheric air and prevents weld from
contamination.

6
 The weld formed in Gas Metal Arc Welding is free from slag. It is a clean and
efficient process.
 This is the working of GMAW or MIG welding process.
Advantages and Disadvantages
The various advantages and disadvantages of GMAW of MIG welding process
are as follows
1.5 ADVANTAGES AND DISADVANTAGES OF MIG WELDING
ADVANTAGES
 It is faster welding process.
 It has greater deposition rates.
 It provides better weld pool visibility.
 After the welding process is over, it requires less cleaning.
 A semi-skilled operator can operate MIG welding easily.
 It can be learn easily without much hard work.
 Absence of filler metal. The consumable metal electrode itself works as filler
metal.
 The MIG welding process can be automated easily.
 It is clean and efficient welding process.( no slag to chip off the weld)
DISADVANTAGES
 Its initial setup cost is high.
 High maintenance cost because of more electronic equipment.
 It creates radiation effect which more severe.
 It is not suitable for outdoor welding.
 Thick metals cannot be welded by GMAW or MIG welding process.
 It is not capable to weld in all positions.
Application
The GMAW or MIG welding process are mostly used in automotive industries
and pipe industries, building bridges and in the repair work.

7
FIG:-1 Working condition of Work piece
FIG:-2 Working principles of GMAW

8
1.6 MIG WELDING EQUIPMENTS AND SPECIFICATIONS
Gas metal arc welding (GMAW), sometimes referred to by its subtypes metal
inert gas (MIG) welding or metal active gas (MAG) welding, is a welding
process in which an electric arc forms between a consumable wire electrode
and the work piece metal(s), which heats the work piece metal(s), causing
them to melt and join. Mig welding equipment is shown in the figure:-3
below on which we have performed the experiment. Single IGBT MIG-250F
3-phase its technical specifications are shown in the table:-1
FIG:-3 Mig Welding Equipment

9
TECHNICAL SPECIFICATIONS
Model Single IGBT MIG-250F 3-phase
Power voltage frequency Three phase 380V ±15% 50Hz-60Hz
Input current 14A
Power capacity 9.2KVA
Rate output current 50-250A
Output Voltage 26.5V
Duty cycle 60%
Power factor 0.9
Efficiency 85%
Type of wire feeder Separated
Overall dimension 570×280×495mm
Protection class of case IP21
Feeding speed 2.7-11m/min
Past flow time 1±0.5
Diameter of coil 102mm
Weight 24kg
Diameter of earth cable 2.5m
Table:-1 Mig welding specifications

10
1.3.1 Single IGBT MIG-250F 3-phase NBC Welding Machine
1.IGBT inverter technology with current control, reliable quality, stable
performance.
2.Equip with closed loop feedback, constant voltage output, good at
protest fluctuation of voltage with automatic compensation
function(±15%).
3.Be controlled by electronic reactor, make it possible for stable welding
process, little spark, deep pool, excellent molding.
4.Can observe the current and voltage at the same time.
5.2T/4T switch be selected, suitable for long distance operation.
6.Proper slowly wire feeding when igniting arc, wipe off molten drop after
welding, can ensure success rate of arc-strike.
7.Small volume and light weight, it is utility and economic, very easy to
operate.
1.4 MILD STEEL ELECTRODE (AWS/SFA 5.18: ER 70S-6)
DESCRIPTION: ER70S-6 is a premium mild steel solid wire formulated to
provide high quality welds and trouble-free performance from heavy duty,
FIG:-4 Mig Welding Machine

11
high speed, spray transfer applications all the way to light duty low speed,
short-arc applications. ER70S-6 is designed for use with various gas
mixtures such as 100% CO2 ,75/25 Ar/CO2 or 98/2 Ar/O2. Even in the
most difficult applications ER70S-6 produces a smooth stable arc with low
spatter, producing a weld bead that ties in evenly with the sides and has a
smooth finished appearance shown in figure.
APPLICATIONS: Frame fabrication, automotive structures, farm
implements, construction equipment, pressure vessels, pipe fabrication,
railcar construction and repair, general fabrication. Widely used in high-
speed robotic and automatic welding applications and semi-automatic
applications.
NOMINAL COMPOSITION: Carbon 0.06-0.15 % Copper 0.50 % max.
Manganese 1.40-1.85 % Silicon 0.80-1.15% Sulphur 0.035 % max.
Phosphorus 0.025 % max. Nickel 0.15 % max. Chromium 0.15 % max.
Vanadium 0.03% max. Molybdenum 0.15 % max. Iron-Balance Others Total
0.50 % max.
1.4 GMAW / MIG welding applications
MIG may be operated in semiautomatic, machine, or automatic modes. All
commercially important applicable metals such as carbon steel, high-
strength, low-alloy steel, and stainless steel, aluminum, copper, titanium,
FIG:-5 Mild Steel Electrode

12
and nickel alloys can be welded in all positions with this process by
choosing the appropriate shielding gas, electrode, and welding variables.
1.5 MIG Welding Effecting parameters
Weld quality and weld deposition rate both are influenced very much by the
various welding parameters and joint geometry. Essentially a welded joint
can be produced by various combinations of welding parameters as well as
joint geometries. These parameters are the process variables which control
the weld deposition rate and weld quality. The weld bead geometry, depth of
penetration and overall weld quality depends on the following operating
variables.
• Electrode size, Welding current, Arc voltage
• Arc travel speed, Welding position
• Gas Flow rate, Shielding Gas composition
• Electrode extension (length of stick out)
1.5.1 Electrode Size
The electrode diameter influences the weld bead configuration (such as the
size), the depth of penetration, bead width and has a consequent effect on
the travel speed of welding. As a general rule, for the same welding current
(wire feed speed setting) the arc becomes more penetrating as the electrode
diameter decreases. To get the maximum deposition rate at a given current,
one should have the smallest wire possible that provides the necessary
penetration of the weld. The larger electrode diameters create weld with less
penetration but welder in width. The choice of the wire electrode diameter
depends on the thickness of the work piece to be welded, the required weld
penetration, the desired weld profile and deposition rate, the position of
welding and the cost of electrode wire. Commonly used electrode sizes are
(mm): 0.8, 1.0, 1.2, 1.6 and 2.4. Each size has a usable current range
depending on wire composition and spray- type arc or short- circuiting arc is
used[2].

13
1.5.2 Welding Current
The value of welding current used in MIG has the greatest effect on the
deposition rate, the weld bead size, shape and penetration. In MIG welding,
metals are generally welded with direct current polarity electrode positive
(DCEP, opposite to TIG welding), because it provides the maximum heat
input to the work and therefore a relatively deep penetration can be
obtained. When all the other welding parameters are held constant,
increasing the current will increase the depth and the width of the weld
penetration and the size of the weld bead[3].
1.5.3 Welding Voltage
The arc length (arc voltage) is one of the most important variables in MIG
that must be held under control. When all the variables such as the
electrode composition and sizes, the type of shielding gas and the welding
technique are held constant, the arc length is directly related to the arc
voltage. High and low voltages cause an unstable arc. Excessive voltage
causes the formation of excessive spatter and porosity, in fillet welds it
increases undercut and produces narrower beads with greater convexity,
but an excessive low voltage may cause porosity and overlapping at the
Wire
diameter
(mm)
Dip transfer Spray transfer
Current
(A)
Voltage
(V)
Current
(A)
Voltage
(V)
0.6 30 – 80 15 – 18 120-210 24-32
0.8 45 - 180 16 – 21 150 - 250 25 – 33
1.0 70 - 180 17 – 22 230 - 300 26 – 35
1.2 100 - 200 17 – 22 250 - 400 27 – 35
1.6 120 - 200 18 – 22 250 - 500 30 – 40
Table:-2 current range

14
edges of the weld bead. And with constant voltage power source, the welding
current increase when the electrode feeding rate is increased and decreased
as the electrode speed is decreased, other factors remaining constant. This
is a very important variable in MIG welding, mainly because it determines
the type o metal transfer by influencing the rate of droplet transfer across
the arc. The arc voltage to be used depends on base metal thickness, type of
joint, electrode composition and size, shielding gas composition, welding
position, type of weld and other factors.
1.5.4 Shielding Gas
The primary function of shielding gas is to protect the arc and molten weld,
pool from atmosphere oxygen and nitrogen. If not properly protected it forms
oxides and nitrites and result in weld deficiencies such as porosity, slag
inclusion and weld embrittlement. Thus the shielding gas and its flow rate
have a substantial effect on the following: Arc characteristics, Mode of metal
transfer, penetration and weld bead profile, speed of welding, cleaning of
action, weld metal mechanical properties. Argon, helium and argon-helium
mixtures are used in many applications for welding non-ferrous metals and
alloys. Argon and Carbon dioxide are used in Carbon steel.There are three
primary metal transfer modes
 Spray transfer
 Globular transfer
 Short circuiting transfer
The primary shielding gasses used are:
 Argon
 Argon - 1 to 5% Oxygen
 Argon - 3 to 25% CO2
 Argon/Helium
CO2 is also used in its pure form in some MIG welding processes. However,
in some applications the presence of CO2in the shielding gas may adversely

15
affect the mechanical properties of the weld. Welding current and arc voltage
ranges for selected wire diameters operating with dip and spray metal
transfer.
1.5.5 Arc Travel Speed
The travel speed is the rate at which the arc travels along the workpiece. It
is controlled by the welder in semiautomatic welding and by the machine in
automatic welding. The effects of the travel speed are just about similar to
the effects of the arc voltage. The penetration is maximum at a certain value
and decreases as the arc speed is varied. For a constant given current,
slower travel speeds proportionally provide larger bead and higher heat
input to the base metal because of the longer heating time. The high input
increases the weld penetration and the weld metal deposit per unit length
and consequently results in a wider bead contour. If the travel speed is too
slow, unusual weld build-up occurs, which causes poor fusion, lower
penetration, porosity, slag inclusions and a rough uneven bead. The travel
speed, which is an important variable in MIG, just like the wire speed
(current) and the arc voltage, is chosen by the operator according to the
thickness of the metal being welded, the joint fit-up and welding position[4].
1.5.6 WIRE FEED SYSTEM
The performance of the wire feed system can be crucial to the stability and
reproducibility of MIG welding. As the system must be capable of feeding the
wire smoothly, attention should be paid to the feed rolls and liners. There
are three types of feeding systems:
 pinch rolls
 push-pull
 spool on gun
The conventional wire feeding system normally has a set of rolls where one
is grooved and the other has a flat surface. Roll pressure must not be too
high otherwise the wire will deform and cause poor current pick up in the
contact tip. With copper coated wires, too high a roll pressure or use of
knurled rolls increases the risk of flaking of the coating (resulting in copper

16
build up in the contact tip). For feeding soft wires such as aluminium dual-
drive systems should be used to avoid deforming the soft wire.
Small diameter aluminium wires, 1mm and smaller, are more reliably fed
using a push-pull system. Here, a second set of rolls is located in the
welding gun - this greatly assists in drawing the wire through the conduit.
The disadvantage of this system is increased size of gun. Small wires can
also be fed using a small spool mounted directly on the gun. The
disadvantages with this are increased size, awkwardness of the gun, and
higher wire cost.
1.5.6.1 CONDUIT
The conduit can measure up to 5m in length, and to facilitate feeding,
should be kept as short and straight as possible. For longer lengths of
conduit, an intermediate push-pull system can be insert, it has an internal
liner made either of spirally-wound steel for hard wires (steel, stainless steel,
titanium, nickel) or PTFE for soft wires (aluminium, copper).
In addition to directing the wire to the joint, the welding gun fulfils two
important functions - it transfers the welding current to the wire and
provides the gas for shielding the arc and weld pool.
1.5.6.2 GUNS
There are two types of welding guns: 'air' cooled and water cooled. The 'air'
cooled guns rely on the shielding gas passing through the body to cool the
nozzle and have a limited current-carrying capacity. These are suited to light
duty work. Although 'air' cooled guns are available with current ratings up
to 500A, water cooled guns are preferred for high current levels, especially at
high duty cycles.
Welding current is transferred to the wire through the contact tip whose
bore is slightly greater than the wire diameter. The contact tip bore diameter
for a 1.2mm diameter wire is between 1.4 and 1.5mm. As too large a bore
diameter affects current pick up, tips must be inspected regularly and

17
changed as soon as excessive wear is noted. Copper alloy (chromium and
zirconium additions) contact tips, harder than pure copper, have a longer
life, especially when using spray and pulsed modes.
Gas flow rate is set according to nozzle diameter and gun to workpiece
distance, but is typically between 10 and 30 l/min. The nozzle must be
cleaned regularly to prevent excessive spatter build-up which creates
porosity. Anti-spatter spray can be particularly effective in automatic and
robotic welding to limit the amount of spatter adhering to the nozzle [5].
--**--

18
CHAPTER - 2
REVIEW OF LITERATURE
Dinesh Mohan et al. studied to investigate the optimization process
parameters for Metal Inert Gas welding (MIG). This paper presents the
influence of welding parameters like wire diameter, welding current, arc
voltage welding speed, and gas flow rate optimization based on bead
geometry of welding joint. The objective function have been chosen in
relation to parameters of MIG welding bead geometry tensile strength, Bead
height, Penetration and Heat affected zone (HAZ) for quality target. The most
significant factor also found in this case welding current is having maximum
percentage contribution. So it is most significant factor in this result [1].
Lenin et al. has studied welding as a basic manufacturing process for
making components or assemblies. In this paper, the optimization of the
process parameters for MMA welding of stainless steel and low carbon steel
with greater weld strength has been reported. The higher-the-better quality
characteristics is considered in the weld strength prediction [2].
M.Aghakhani et al. studied that gas metal arc welding is fusion welding
process having wide applications in industry. One of the important welding
output parameters in this process is weld dilution affecting the quality and
productivity of weldment. The wire feed rate has the most significant effect
as such as far as the dilution is concerned[3].
L. Suresh kumar, S.M. Verma, P.Radhakrishna Prasad, P.Kirankumar,
T.Sivasankar has studied that TIG welded specimen can bear higher load
than MIG welded specimen[4].
A.S.Vagh, S.N. Pandya studied that tool design is the main process
parameter that has the highest statistical influence on mechanical
properties[5].

19
S.V, Sapakal selected input parameter are welding current, wire feed and
output are tensile strength and hardness[6].
G. Haragopal, P V R Ravindra Reddy and J V Subrahmanyam presented a
method to design process parameters that optimize the mechanical
properties of weld specimen for aluminium alloy (Al-65032), used for
construction of aerospace wings. The process parameters considered for the
study were gas pressure, current, groove angle and pre-heat temperature.
Process parameters were assigned for each experiment. The experiments
were conducted using the L9 orthogonal array. Optimal process parameter
combination was obtained. Along with this, identification of the parameters
which were influencing the most was also done. This was accomplished
using the S/N analysis, mean response analysis and ANOVA. Mechanical
properties obtained for three samples of each run were obtained. Signal to
noise ratio for each quality (S/N) ratio for each quality characteristic was
calculated, significant parameters were identified and optimum input
parameter for each quality characteristic were predicted from S/N values
and mean response. Analysis of variance (ANOVA) ascertained significant
parameters identified through S/N analysis. A confirmation test was
conducted at optimum conditions to ensure correctness of analysis[7].
A. Narayana and T.Srihari has presented optimizing weld bead geometry by
process variables viz current, speed, wire feed rate, nozzle plate distance. If
some more parameters like inclination of nozzle to the plate, wire diameter,
polarity etc can be used optimize bead geometry more precision[8].
Pawan kumar, Dr.B.K.Roy was worked carried out on plate welds AISI 304
& Low Carbon Steel plates using gas metal arc welding (GMAW) process.
Taguchi method is used to formulate the experimental design. Design of
experiments using orthogonal array is employed to develop the weldments.
The input process variables considered here include welding current,
welding voltage & gas flow rate. A total no of 9 experimental runs were
conducted using an L9 orthogonal array and the ideal combination of
controllable factor levels was determined for the hardness to calculate the

20
signal-to-noise ratio. After collecting the data signal-to-noise (S/N) ratios
were calculated and used in order to obtain optimum levels for every input
parameter. The Nominal-the better quality characteristic is considered in the
hardness prediction. The Taguchi method is adopted to solve this problem.
Subsequently, using analysis of variance the significant coefficients for each
input parameter on tensile strength & Hardness (WZ & HAZ) were
determined and validated[9].
K. Srinivasulu Reddy was investigated on in submerged arc welding (SAW),
weld quality is greatly affected by the weld parameters are closely related to
the geometry of weld bead, a relationship which is thought to be complicated
because of the non-linear characteristics. Beadon-plate welds were carried
out on mild steel plates using semi automatic SAW machine. Input
parameter are used like, weld current, voltage, weld speed, electrode stick
out with output parameter are carried out penetration, weld width, weld
hardness using Taguchi’s DOE. Data were collected as per Taguchi’s Design
of Experiments and L8 orthogonal Array, analysis of variance (ANOVA) was
carried to establish input–output relationships of the process. By this
relationship, an attempt was made to minimize weld bead width and
maximum penetration is one objective and developing artificial neural
network (ANN) models to predict the weld bead properties accurately along
with sensitivity analysis is also the prime objective to determine optimal
weld parameters. The optimized values obtained from these techniques were
compared with experimental results and presented. Modular network model
predicts accurately and corresponding sensitivity analysis revels that bead
width is highly sensitive to welding current, weld reinforcement and bead
hardness are sensitive to electrode stick out and depth of penetration is
sensitive to welding speed[10].
M.Agka Khani et al. studied for the material IS 2062 ES250 Mild steel and
take input parameter as wire feed rate(W),welding voltage(V),nozzle to plate
distance(N),welding speed (s) and gas flow rate (g) and the response was the
relationships between the weld dilution and the five controllable input
welding parameters such as wire feed wire, welding voltage, nozzle-to-plate

21
distance, welding speed, gas flow rate. And it was found that among main
input welding parameters the effect of wire feed rate is significant.
Increasing the wire feed rate and arc voltage increases the weld dilution
where as increasing the nozzle to plate distance the welding speed results in
decreases weld dilution and gas flow rate did not affect the weld dilution[11].
Gautam Kocher et al. studied for the material IS 2062 E250 Mild Steel and
take input parameter as welding speed variable while arc voltage(V),welding
current(A),Wire feed rate(W),Distance between the nozzle and the plates are
fixed and the response was the effect of weld speed on penetration and
reinforcement. This study was undertaken with the objective of determining
the effects of weld speed on the weld profile and dilution analysis of the MIG
butt welds of IS2062 E250 A mild steel plates at constant wire speed rate
and constant arc voltage and welding current[12].
S.R.patil et al. studied for the material AISI 1030 Mild steel and take input
parameter as welding current,voltage,weld speed. The response was the
signal-to-noise(SN) ratio and ANOVA(analysis of Variance) were used for
optimization and It was found that tensile strength depends on welding
speed. And the result show that by increasing the welding speed and
decreasing the current increases the UTS of welded joint while voltage do
not affect the weld strength[13].
Harshal k chavan et al. studied single pass corner joint are evaluated by
FMEA by ANSYS covers varying heat input, welding speed on thermo
mechanical response of weld mint after cooling down to the room
temperature. From Results shows that heat input, welding speed has
significant impacts on the response[14].
Ajit Hooda et al. studied for the material AISI 1040 Medium carbon Steel
and take input parameter as welding voltage,current,wire speed and gas
flow rate and the response was RSM(Response Surface Methodology) for
maximum yield strength of joint. The similar weld joint of AISI 1040 material
was developed effectively with MIG welding with selected range of input

22
variable parameters. The longitudinal yield strength is greater than the
transverse yield strength[15].
J.pasupathy et al. studied for the material AA1050 low carbon steel and
take input parameter as welding current, welding speed, Distance of
electrode from work piece and the response was Signal to
Noise(SN),ANOVA(analysis of Variance) for strength. The experiment value
that is observed from optimal welding parameters, the strength & S/N
ratio[16].
Miss Nihau Bhadauria et al studied for Experiments were conducted based
on central composite face centered cubic design and mathematical models
were developed for GMAW process parameters like voltage(V),welding
speed(s) and gas flow rate(G).Using these models the direct effect of the
process parameters on weld bead penetration were studied. And results
shows that as penetration increases the strength of the weld[17].
H.J.Park et al. studied for Experiment on optimizing the wire,feed,speed
against the welding speed for lap joint fillet weld of 1.6 mm aluminum alloy
which is used for light weight car body and the response was for the same
welding speed has wire feed speed increases the bead becomes wider and
the bead cross sectional area is increases. As wire feed speed increases the
penetration changes from incomplete penetration to excessive melting. The
objective function consist of the sum of the bead width, back bead width
and bead cross section area for the objective function value 3 the weld
quality is ideal[18].
A.R.Rahemanet et al. studied for Experiment on change in hardness, yield
strength and UTS of welded joints produced in st37 grade steel his work
focus on relationship between MIG welding variables and Mechanical
Properties of st37 steel joint. The welding current and welding speed were
fixed on 135 A and 50 cm/min and effect of arc voltage on mechanical
properties of weld metal was investigated[19].

23
CHAPTER - 3
OPTIMIZATION TECHNIQUES
3.1 WELDING – INFLUENCING FACTORS
• Electrode size, Welding current, Arc voltage
• Arc travel speed, Welding position
• Gas Flow rate, Shielding Gas composition
• Electrode extension (length of stick out)
3.1.1 Electrode Size
The electrode diameter influences the weld bead configuration (such as the
size), the depth of penetration, bead width and has a consequent effect on
the travel speed of welding. As a general rule, for the same welding current
(wire feed speed setting) the arc becomes more penetrating as the electrode
diameter decreases. To get the maximum deposition rate at a given current,
one should have the smallest wire possible that provides the necessary
penetration of the weld. The larger electrode diameters create weld with less
penetration but welder in width. The choice of the wire electrode diameter
depends on the thickness of the work piece to be welded, the required weld
penetration, the desired weld profile and deposition rate, the position of
welding and the cost of electrode wire. Commonly used electrode sizes are
(mm): 0.8, 1.0, 1.2, 1.6 and 2.4. Each size has a usable current range
depending on wire composition and spray- type arc or short- circuiting arc is
used.
3.1.2 Welding Current
The value of welding current used in MIG has the greatest effect on the
deposition rate, the weld bead size, shape and penetration. In MIG welding,
metals are generally welded with direct current polarity electrode positive
(DCEP, opposite to TIG welding), because it provides the maximum heat
input to the work and therefore a relatively deep penetration can be
obtained. When all the other welding parameters are held constant,

24
increasing the current will increase the depth and the width of the weld
penetration and the size of the weld bead.
3.1.3 Welding Voltage
The arc length (arc voltage) is one of the most important variables in MIG
that must be held under control. When all the variables such as the
electrode composition and sizes, the type of shielding gas and the welding
technique are held constant, the arc length is directly related to the arc
voltage. High and low voltages cause an unstable arc. Excessive voltage
causes the formation of excessive spatter and porosity, in fillet welds it
increases undercut and produces narrower beads with greater convexity,
but an excessive low voltage may cause porosity and overlapping at the
edges of the weld bead. And with constant voltage power source, the welding
current increase when the electrode feeding rate is increased and decreased
as the electrode speed is decreased, other factors remaining constant. This
is a very important variable in MIG welding, mainly because it determines
the type o metal transfer by influencing the rate of droplet transfer across
the arc. The arc voltage to be used depends on base metal thickness, type of
joint, electrode composition and size, shielding gas composition, welding
position, type of weld and other factors.
3.1.4 Shielding Gas
The primary function of shielding gas is to protect the arc and molten weld,
pool from atmosphere oxygen and nitrogen. If not properly protected it forms
oxides and nitrites and result in weld deficiencies such as porosity, slag
inclusion and weld embrittlement. Thus the shielding gas and its flow rate
have a substantial effect on the following: Arc characteristics, Mode of metal
transfer, penetration and weld bead profile, speed of welding, cleaning of
action, weld metal mechanical properties. Argon, helium and argon-helium
mixtures are used in many applications for welding non-ferrous metals and
alloys. Argon and Carbon dioxide are used in Carbon steel.

25
3.1.5 Arc Travel Speed
The travel speed is the rate at which the arc travels along the workpiece. It
is controlled by the welder in semiautomatic welding and by the machine in
automatic welding. The effects of the travel speed are just about similar to
the effects of the arc voltage. The penetration is maximum at a certain value
and decreases as the arc speed is varied. For a constant given current,
slower travel speeds proportionally provide larger bead and higher heat
input to the base metal because of the longer heating time. The high input
increases the weld penetration and the weld metal deposit per unit length
and consequently results in a wider bead contour. If the travel speed is too
slow, unusual weld build-up occurs, which causes poor fusion, lower
penetration, porosity, slag inclusions and a rough uneven bead. The travel
speed, which is an important variable in MIG, just like the wire speed
(current) and the arc voltage, is chosen by the operator according to the
thickness of the metal being welded, the joint fit-up and welding position.
3.2 DESIGN OF EXPERIMENT [DOE]
Design of Experiments (DOE) is a powerful statistical technique introduced
by R. A. Fisher in England in the 1920's to study the effect of multiple
variables simultaneously. The DOE using Taguchi approach can
economically satisfy the needs of problem solving and product/process
design optimization projects. By learning and applying this technique,
engineers, scientists, and researchers can significantly reduce the time
required for experimental investigations. DOE is a technique of defining and
investing all possible combinations in an experiment involving multiple
factors and to identify the best combination. In this, different factors and
their levels are identified. Design of experiments is also useful to combine
the factors at appropriate levels, each with the respective acceptable range,
to produce the best results and yet exhibit minimum variation around the
optimum results. Therefore, the objective of a carefully planned designed
experiment is to understand which set of variables in a process affects the

26
performance most and then determine the best levels for these variables to
obtain satisfactory output functional performance in products.
3.2 The advantages of design of experiments are as follows:
• Numbers of trials is significantly reduced.
• Important decision variables which control and improve the
performance of the product or the process can be identified.
• Optimal setting of the parameters can be found out.
• Qualitative estimation of parameters can be made.
• Experimental error can be estimated.
• Inference regarding the effect of parameters on the characteristics of
the process can be made.
Thus Design of experiment (DOE) is a method to identify the important
factors in a process, identify and fix the problem in a process, and also
identify the possibility of estimating interactions.
DOE for study of process parameter effects in welding
Following are the DOE techniques used process parameter optimization
work in welding.
1) Full factorial technique
2) Fractional factorial technique
3) Taguchi orthogonal array
4) Response Surface method (Central Composite design)
ANOVA stands for Analysis for Variance and it is the tool used for the
analysis of contribution of each process parameter on
response parameter. Mathematical models are used to establish the
relationship between the input and output parameters in welding
processes.“MINITAB” and “Design Expert” are the softwares used for DOE
techniques and ANOVA.
3.3 Taguchi method
These are statistical methods, or sometimes called robust design methods,
developed by Genichi Taguchi to improve the quality of manufactured goods,

27
and more recently also applied to engineering, biotechnology, marketing and
advertising. Professional statisticians have welcomed the goals and
improvements brought about by Taguchi methods,[editorializing]
particularly by Taguchi's development of designs for studying variation, but
have criticized the inefficiency of some of Taguchi's proposals
Taguchi's work includes three principal contributions to statistics:
 A specific loss function
 The philosophy of off-line quality control and
 Innovations in the design of experiments.
3.3.1 Loss functions in the statistical theory
Traditionally, statistical methods have relied on mean-unbiased
estimators of treatment effects: Under the conditions of the Gauss–Markov
theorem, least squares estimators have minimum variance among all mean-
unbiased estimators. The emphasis on comparisons of means also draws
(limiting) comfort from the law of large numbers, according to which
the samples means converge to the true mean. Fisher's textbook on
the design of experiments emphasized comparisons of treatment means.
However, loss functions were avoided by Ronald A. Fisher
3.3.2 Taguchi's use of loss functions
Taguchi knew statistical theory mainly from the followers of Ronald A.
Fisher, who also avoided loss functions. Reacting to Fisher's methods in
the design of experiments, Taguchi interpreted Fisher's methods as being
adapted for seeking to improve the mean outcome of a process. Indeed,
Fisher's work had been largely motivated by programs to compare
agricultural yields under different treatments and blocks, and such
experiments were done as part of a long-term program to improve harvests.
However, Taguchi realized that in much industrial production, there is a
need to produce an outcome on target, for example, to machine a hole to a
specified diameter, or to manufacture a cell to produce a given voltage. He

28
also realized, as had Walter A. Shewhart and others before him, that
excessive variation lay at the root of poor manufactured quality and that
reacting to individual items inside and outside specification was
counterproductive.
He therefore argued that quality engineering should start with an
understanding of quality costs in various situations. In much
conventional industrial engineering, the quality costs are simply represented
by the number of items outside specification multiplied by the cost of rework
or scrap. However, Taguchi insisted that manufacturers broaden their
horizons to consider cost to society. Though the short-term costs may
simply be those of non-conformance, any item manufactured away from
nominal would result in some loss to the customer or the wider community
through early wear-out; difficulties in interfacing with other parts,
themselves probably wide of nominal; or the need to build in safety margins.
These losses are externalities and are usually ignored by manufacturers,
which are more interested in their private costs than social costs. Such
externalities prevent markets from operating efficiently, according to
analyses of public economics. Taguchi argued that such losses would
inevitably find their way back to the originating corporation (in an effect
similar to the tragedy of the commons), and that by working to minimize
them, manufacturers would enhance brand reputation, win markets and
generate profits.
Such losses are, of course, very small when an item is near to
negligible. Donald J. Wheeler characterized the region within specification
limits as where we deny that losses exist. As we diverge from nominal, losses
grow until the point where losses are too great to deny and the specification
limit is drawn. All these losses are, as W. Edwards Deming would describe
them, unknown and unknowable, but Taguchi wanted to find a useful way
of representing them statistically. Taguchi specified three situations:
1. Larger the better (for example, agricultural yield);
2. Smaller the better (for example, carbon dioxide emissions); and

29
3. On-target, minimum-variation (for example, a mating part in an
assembly).
The first two cases are represented by simple monotonic loss functions. In
the third case, Taguchi adopted a squared-error loss function for several
reasons:
 It is the first "symmetric" term in the Taylor series expansion of real
analytic loss-functions.
 Total loss is measured by the variance. For uncorrelated random
variables, as variance is additive the total loss is an additive
measurement of cost.
 The squared-error loss function is widely used in statistics, following
Gauss's use of the squared-error loss function in justifying the method
of least squares.
3.3.3 Reception of Taguchi's ideas by statisticians
Though many of Taguchi's concerns and conclusions are welcomed by
statisticians and economists, some ideas have been especially criticized. For
example, Taguchi's recommendation that industrial experiments maximize
some signal-to-noise ratio(representing the magnitude of the mean of a
process compared to its variation) has been criticized widely.
3.4 S/N RATIO (Signal-to-noise ratio)
(Abbreviated SNR or S/N) is a measure used in science and engineering
that compares the level of a desired signal to the level of background noise.
SNR is defined as the ratio of signal power to the noise power, often
expressed in decibels. A ratio higher than 1:1 (greater than 0 dB) indicates
more signal than noise.
While SNR is commonly quoted for electrical signals, it can be applied to any
form of signal, for example isotope levels in an ice core, biochemical
signaling between cells, or financial trading signals. Signal-to-noise ratio is
sometimes used metaphorically to refer to the ratio of useful information to

30
false or irrelevant data in a conversation or exchange. For example, in online
discussion forums and other online communities, off-topic posts and spam
are regarded as "noise" The mean is the average response for each
combination of control factor levels in a static Taguchi design. Depending on
the response, your goal is to determine factor levels that either minimize or
maximize the mean.
For example, you want to know how four control factors affect the flight
distance of golf balls. The means for this example provide an estimate of
flight distance at each factor level. Because you are interested in maximizing
flight distance, you want to determine factor levels that result in the largest
means that interferes with the "signal" of appropriate discussion.
The objective of parameter design is to take the innovation which has been
proven to work in System Design and enhance it so that it will consistently
function as intended. Usually by using classical parameter design there are
a large number of experiments to be carried out when the number of the
process parameter increases. To solve this task, Taguchi come out with a
special design of orthogonal arrays to study the entire parameter space with
a small number of experiments only. Taguchi recommends the use of the
loss function to measure the performance characteristics deviating from the
desired value (Glen Stuart, 1999). The value of the loss function is further
transformed into a signal-to-noise ratio. There are three categories of the
performance characteristics in the analysis of the S/N ratio, that is
 The smaller- the- better
 The nominal-the-better
 The larger-the-better
The S/N ratio for each level of process parameters is computed based on
the S/N analysis (Yuin Wu, Alan Wu, 2000). Regardless of the category of
the performance characteristic, the larger S/N ration corresponds to the
better performance characteristics. Therefore, the optimal level of the
process parameters is the level with the highest S/N ratio.

31
3.4.1 THE SMALLER-THE-BETTER: The smaller-the-better
characteristics is one in which the desired goal is to reduce the measured
characteristics to zero. This applies, for instance to theporosity, vibration,
the consumption of an automobile, tool wear, surface roughness, response
time to customer complaints, noise generated from machine or engines, per
cent shrinkage, percent impurity in chemicals, and product deterioration.
N = -10 Log10 [mean of sum of squares of {measured - ideal}]
3.4.2 THE LARGER-THE-BETTER: The opposite of the lower-the-
better is the larger-the-better characteristics. This is one in which the ideal
value is infinity. This type characteristics applies to tensile strength, pull
strength, car mileage per gallon of the, reliability of a device, efficiency of
engines, life of components, corrosion resistance and others.
3.4.3 THE NOMINAL-THE-BETTER: The nominal-the-better
characteristics is one where a target value is specified and the goal is
minimal variability around the target. This type of characteristics is
generally considered when measuring dimensions such as diameter, length,
thickness, width etc. Other examples include pressure, area, volume,
current, voltage, resistance, and viscosity.
N = -10 Log10 [squares of mean variance]
3.4.4 ANAYLSIS USING VARIANCE METHOD: The acronym
ANOVA refers to analysis of variance and is a statistical procedure used to
test the degree to which two or more groups vary or differ in an experiment.
In most experiments, a great deal of variance (or difference) usually
indicates that there was a significant finding from the research. The optimal
combination of the process parameters can be predicted by S/N ratio and
ANOVA analyses. Finally, a confirmation experiment is conducted to verify
the optimal process parameters obtained from the parameter design. The
adequacy of the developed models was tested using the Analysis of Variance

32
(ANOVA) technique. The experimental results are analysed with analysis of
variance (ANOVA), which used for identifying the factors significantly
affecting the performance measures. In this project smaller the better is
adopted for optimization. An ANOVA conducted on a design in which there
is only one factor is called a one-way ANOVA. If an experiment has two
factors, then the ANOVA is called a two-way ANOVA. To perform ANOVA,
there must be a continuous response variable and at least one categorical
factor with two or more levels. ANOVAs require data from approximately
normally distributed populations with equal variances between factor levels.
The name "analysis of variance" is based on the approach in which the
procedure uses variances to determine whether the means are different. The
procedure works by comparing the variance between group means versus
the variance within groups as a way of determining whether the groups are
all part of one larger population or separate populations with different
characteristics.
WORK MATERIALS
 MILD STEEL
 EN8
Material (mild steel): Mild steel (iron containing a small percentage
of carbon, strong and tough but not readily tempered), also known as
plain-carbon steel and low-carbon steel, is now the most common form of
steel because its price is relatively low while it provides material
properties that are acceptable for many applications. Mild steel contains
approximately 0.05–0.25% carbon making it malleable and ductile. Mild
steel has a relatively low tensile strength, but it is cheap and easy to
form; surface hardness can be increased through carburizing.

33
Material (EN8): EN8 is a very popular grade of through-hardening
medium carbon steel, which is readily machinable in any condition. EN8 in
its heat treated forms possesses good homogenous metallurgical structures
giving consistent machining properties. EN8 is suitable for the manufacture
of parts such as general-purpose axles and shafts, gears, bolts and studs.
Element(MS) Composition (wt %)
Carbon 0.16-0.18(maximum 0.25 is allowable)
Silicon Maximum 0.40
Manganese 0.70-0.90
Phosphorus Maximum 0.04
Sulphur Maximum 0.04
Ferrous Balance
Element(EN8) Composition (wt %)
Carbon 0.36-0.44%
Silicon 0.10-0.40%
Manganese 0.60-1.00%
Sulphur 0.050 Max
Phosphorus 0.050 Max
Carbon 0.36-0.44%
Table:-4 Chemical Composition of EN8
Table:-3 Chemical Composition of Mild Steel

34
CHAPTER - 4
EXPERIMENTAL SETUP AND PROCEDURE
There are many researches done on DOE or optimization techniques for
Process parameter for mechanical Properties and weld penetration, weld
bead geometry. But I found that are very few researches done on low and
Medium carbon steels so we want to do research on this material. We like to
use Design of experiment for parametric optimization. Welding current, arc
voltage, welding speed, type of shielding gas, gas flow rate, wire feed rate,
diameter of electrode etc. are the important control parameters of Metal
Inert Gas Welding process. They affect the weld quality in terms of
mechanical properties and weld bead geometry. The value of depth of
penetration increased by increasing the value of welding current and the
grain boundaries of the microstructure are varied when the welding
parameters are changed.
Taguchi Technique shall be used to conduct the experiments: - The Taguchi
method has become a influential tool for improving output during research
and development, so that better quality products can be produced quickly
and at minimum cost. Dr. Taguchi of Nippon Telephones and Telegraph
Company, Japan has established a method based on "ORTHOGONAL
ARRAY" experiments which gives much reduced "variance" for the
experiment with "optimum settings" of control variables. Thus the marriage
of Design of Experiments with optimization of control parameters to find
best results is attained in the Taguchi Method. "Orthogonal Arrays" (OA)
gives a set of well balanced (minimum) experiments and Dr. Taguchi's
Signal-to-Noise ratios (S/N), which are log functions of desired output, serve
as objective functions in optimization, help in data analysis and The
purpose of the analysis of variance (ANOVA) is to examine which design
parameters significantly affect the quality characteristic and estimation of
optimum results. The Factorial Design, Taguchi Method, Response surface
method can be applied as the DOE (Design of Experiment). And we can also
use Optimization techniques like, artificial neural network, Grey relation

35
analysis, Genetic algorithm, S/N ratio etc. Minitab software is a useful aid
for the above purpose.
Mild steel and EN8 medium carbon steel plates, with chemical composition
as shown in tables and the balance Iron, were selected as base metal for the
experiments. T
as weld blanks. The surface of
the plates was grind to remove the dust and other foreign particles. In order
to obtain a strong bonded joint the properties of the base metal and the
welding wire must comply with each other. The type of material of welding
wire total depends upon the material that is required to be welded. So (AWS
/ SFA 5.18: ER 70S-6) mild steel copper-coated wire was selected as welding
wire, whose chemical composition as shown in Table. The diameter of the
welding wire depends upon the base metal thickness. As the thickness of
base metal was 8 mm, welding wire with a diameter of 1.2 mm was selected.
There are totally 9 experiments to be conducted and each experiment is
based on the combination of level values as shown in the table. For example,
the third experiment is conducted by keeping the independent design
variable 1 at level 1, variable 2 at level 3, variable 3 at level 3, and variable 4
at level 3.The orthogonal arrays have the following special properties that
reduce the number of experiments to be conducted.
OBJECTIVE OF THE WORK
In this thesis, materials AISI 1050 Mild Steel and EN8 are welded by varying
process parameters gas flow rate, welding current and welding voltage.
Effect of process current on the tensile strength of weld joint will be
analysed.
4.1 EXPERIMENTAL SETUP
4.1.1 SELECTION OF ORTHOGONAL ARRAY
The present research work is aimed to evaluate the output parameters such
as tensile strength and elongation of a MIG welding Machine using Design of
Experiments technique. In order to conduct experimental analysis with

36
minimum test runs, an orthogonal array was prepared using Taguchi's
Design of Experiments (DoE). To determine the orthogonal array, Minitab
ver.16 was used and the derived L-9 orthogonal array is shown in Table 2.
The steps involved in deriving the L-9 orthogonal array in the Minitab ver.16
software are given below:
 Open Minitab ver.16 software
 Click on Stat → DOE → Taguchi → Create Taguchi Design
 A tab opens indicating Taguchi's design where we need to select the
levels of design and number of factors
 Select 3 level design → Number of factors=3
 Then click on options and select L-9 → OK
 Now a worksheet opens and the orthogonal array L-9 is listed.
In this setup three parameters are taken into consideration and are altered
so as to obtain the optimized result. The three altering parameters are
welding current, arc voltage and welding speed.
EXPERIMENT VARIABLE 1 VARIABLE 2 VARIABLE 3
1 1 1 1
2 1 2 2
3 1 3 3
4 2 1 2
5 2 2 3
6 2 3 1
7 3 1 3
8 3 2 1
9 3 3 2
Table:-5 SELECTION OF ORTHOGONAL ARRAY

37
4.2 PRE-EPERIMENTAL PROCEDURE:
1. Both the works mild steel and EN8 is cut into the required dimension i.e
100x50x6 mm and 80x50x6 mm.
2. Then the edges of the work pieces are cleaned thoroughly so as to obtain
a good weld with high strength when attached through a butt joint.
3. The working of a machine and the welding speed is verified before
beginning the experiment
4. Three values of welding current are chosen: 90, 100 and 120 amps.
Three values of arc voltage are chosen: 20, 22 and 24 volts. Three values
of gas flow rate are chosen: 5, 10 and 15 Mpa.
4.3 EXPERIMENTAL PROCEDURE:
1. Both the work pieces are first adjusted in proper position to begin the
task of welding.
2. The parameters on the machine are adjusted as current being 90amps,
voltage being 20 volts.
3. MIG welding is performed and the welding time is noted down.
4. The above procedure is repeated for the decided nine experimental value
combinations.
5. All the parameters are properly noted down.
Variables Unit Level 1 Level 2 Level 3
Current (I) Amp 90 100 110
Voltage (V) Volt 20 22 24
Gas flow rate Mpa 5 10 15
Table:-6 Influencing parameters with values

38
4.4 UTM (UNIVERSAL TESTING MACHINE)
A universal testing machine (UTM), also known as a universal tester
materials testing machine or materials test frame, is used to test the tensile
strength and compressive strength of materials. The “universal” part of the
name reflects that it can perform many standard tensile and compression
tests on materials, components, and structures.
EXP.NO VOLTAGE CURRENT GAS PRESSURE
1 20 90 5
2 20 100 10
3 20 110 15
4 22 90 10
5 22 100 15
6 22 110 5
7 24 90 15
8 24 100 5
9 24 110 10
Table:-7 Orthogonal Array (L9) and Control Parameters
FIG:-6 Mild Steel FIG:-7 EN8

39
UTM consists of
 Load frame - Usually consisting of two strong supports for the
machine.
 Load cell - A force transducer or other means of measuring the load is
required.
 Cross head - A movable cross head (crosshead) is controlled to move
up or down.
 Means of measuring extension or deformation- Extensometers are
sometimes used.
 Output device - A means of providing the test result is needed.
 Test fixtures, specimen holding jaws, and related sample making
equipment are called for in many test methods.
The specimen is placed in the machine between the grips and the machine
itself can record the displacement between its cross heads on which the
specimen is held. However, this method not only records the change in
length of the specimen but also all other extending / elastic components of
the testing machine and its drive systems including any slipping of the
specimen in the grips. The welded joints go through a destructive testing on
Universal Testing Machine to determine tensile strength.
 The work piece with a total length of 200mm length mild steel 160mm
length EN8 are fit into the jaws of UTM.
 The load is slowly applied until the joint finally breaks.
 The value of tensile strength obtained is noted down. Also, graph is
generated.
FIG:-8 Universal testing machine

40
The steps involved for obtaining the S/N ratios and mean values for
Elongation in the Minitab ver.16 software are given below:
1. Open Minitab ver.16 software.
2. Enter the experimental values of Elongation in one column.
3. Click on Stat → DOE → Taguchi → Analyze Taguchi design.
4. A tab opens indicating Analyze Taguchi design .Click on required
column i.e., Elongation → Select → Options → Smaller is better →
OK→ Storage → tick on Signal to Noise ratio and means → OK
5. The required S/N ratios and mean values of MRR are presented on the
worksheet.
6. To obtain graphs click on Stat → DOE → Taguchi → Analyze Taguchi
design.
column i.e., Elongation → Select → Graphs → tick on signal to noise
ratio and mean → OK →OK.
8. The required graphs of S/N ratios and mean values are obtained.
9. The response table for mean and S/N ratios can be taken from the
sessions tab.
The steps involved for obtaining the S/N ratios and mean values for Tensile
Strength in the Minitab ver.16 software are given below:
1. Open Minitab ver.16 software.
2. Enter the experimental values of Material removal rate in one column.
3. Click on Stat → DOE → Taguchi → Analyze Taguchi design.
column i.e., Tensile Strength → Select → Options → larger is better →
OK→ Storage → tick on Signal to Noise ratio and means → OK
5. The required S/N ratios and mean values of MRR are presented on the
worksheet.
6. To obtain graphs click on Stat → DOE → Taguchi → Analyze Taguchi
design.

41
column i.e., Tensile Strength → Select → Graphs → tick on signal to
noise ratio and mean → OK →OK.
8. The required graphs of S/N ratios and mean values are obtained.
9. The response table for mean and S/N ratios can be taken from the
sessions tab.

42
CHAPTER - 5
RESULTS AND ANALYSIS
In this research work effect of main input welding Parameters on the tensile
strength of welded joint in metal inert gas welding process were
investigated, Results show that among main input welding parameters
the effect of the voltage is significant. Increasing the voltage and
increasing the shielding gas rate increases the ultimate tensile strength of
welded joint. In this research work it was observed that the current did not
contribute as such to weld strength. Regardless of the set of the quality
characteristic, a greater S/N ratio relates to better quality characteristics.
Therefore, the optimal level of the process variables is the level with the
greatest S/N ratio.
MILD STEEL - Elongation:
Using the experimental data, Taguchi analysis was carried out using
Minitab Ver. 18. The calculated S/N ratios presented in Table 8 and
presented in graph form in Fig. 9 and 10. The data in Table 8 reveals that
the MIG welding for MS was achieved at 20 Volts, 100 Amps of Current, 10
Mpa of Shielding gas flow rate when elongation alone considered as output
parameter. The highest angles in Fig 9 is confirming the same.
As shown in Table 9, the delta values indicates that Voltage has most
influence with delta value of 2.92, followed by shielding gas pressure with
value of 2 and least influenced by current with delta value of 1.38. The
results of ANOVA is presented in Table 10 and confirms the same as results
of Taguchi.

43
Voltage
(V)
Current
(Amps)
Shielding
gas pressure
(Mpa)
Elongation
(mm)
S/N
RATIO MEAN
20 90 5 9.9 -19.9127 9.9
20 100 10 9.1 -19.1808 9.1
20 110 15 10.8 -20.6685 10.8
22 90 10 13.3 -22.477 13.3
22 100 15 14.1 -22.9844 14.1
22 110 5 12.1 -21.6557 12.1
24 90 15 17.4 -24.811 17.4
24 100 5 11.1 -20.9065 11.1
24 110 10 13.8 -22.7976 13.8
LEVEL
Voltage
(V)
Current
(Amps)
Shielding gas pressure (Mpa)
1 -19.92 -22.4 -20.82
2 -22.37 -21.02 -21.49
3 -22.84 -21.71 -22.82
Delta 2.92 1.38 2
Rank 1 3 2
Table 8: S/N Ratios for Elongation – Mild Steel
Table:-9 Response Table for Signal to Noise ratio

44
Analysis of Variance for SN ratios
Source DF Seq SS Adj SS Adj MS F P
Voltage (V) 2 14.7408 14.7408 7.3704 25.29 0.038
Current (Amps) 2 2.8416 2.8416 1.4208 4.87 0.17
Shielding gas pressure 2 6.2064 6.2064 3.1032 10.65 0.086
Residual Error 2 0.5829 0.5829 0.2915
Total 8 24.3717
Table:-10 analysis of variance for SN ratios
FIG:-9 Main effect plots for S/N ratio

45
MILD STEEL – Tensile strength:
The calculated S/N ratios presented in Table 11 and presented in graph
form in Fig. 10 and 11. The data in Table 11 reveals that the MIG welding
for MS was achieved at 22 Volts, 100 Amps of Current, 15 Mpa of Shielding
gas pressure when tensile strength alone considered as output parameter.
The highest angles in Fig 10 and 11 are confirming the same.
influence with delta value of 6.26, followed by current with delta value of
1.36 and least influenced by shielding gas pressure with value of 0.91 . The
of Taguchi.
Voltage
(V)
Current
(Amps)
Shielding gas
pressure(Mpa)
Tensile
Strength
(N)
S/N
RATIO MEAN
20 90 5 40120 92.06722 40120
20 100 10 48112 93.64507 48112
20 110 15 53136 94.50778 53136
22 90 10 88135 98.90297 88135
22 100 15 102110 100.1814 102110
22 110 5 99125 99.92366 99125
24 90 15 91265 99.20609 91265
24 100 5 91086 99.18903 91086
24 110 10 98104 99.83373 98104
Table 11: S/N Ratios for Tensile strength – Mild Steel

46
Larger is better
Level
Voltage
(V)
Current
(Amps) Shielding
gas pressure (Mpa)
1 93.41 96.73 97.06
2 99.67 97.67 97.46
3 99.41 98.09 97.97
Delta 6.26 1.36 0.91
Rank 1 2 3
Source DF Seq SS Adj SS Adj MS F P
Voltage (V) 2 75.323
3
75.323
3
37.661
7
871.
4
0.00
1
Current (Amps) 2 2.9269 2.9269 1.4634 33.8
6
0.02
9
Shielding gas
pressure
2 1.2342 1.2342 0.6171 14.2
8
0.06
5
Residual Error 2 0.0864 0.0864 0.0432
Total 8 79.570
9
Table:-12 Response Table for Signal to Noise Ratios
Table:-13 Analysis of Variance for SN ratios

47
FIG:-10 Main Effects Plot for SN ratios
FIG:-11 Main Effects Plot for Means

48
EN8 - Elongation:
gas flow rate when elongation alone considered as output parameter. The
highest angles in Fig 12 and 13 are confirming the same.
The results of ANOVA is presented in Table 15 and confirms the same as
results of Taguchi.
Voltage
(V)
Current
(Amps)
Shielding
Gas pressure
(Mpa)
Tensile
Strength
(N)
Elongation
(mm)
S/N
RATIO
20 90 5 77710 11.7
-
21.3637
20 100 10 90121 13.6
-
22.6708
20 110 15 75234 14
-
22.9226
22 90 10 80316 7.9
-
17.9525
22 100 15 104110 9.3
-
19.3697
22 110 5 91278 10.1
-
20.0864
24 90 15 114365 10.5
-
20.4238
24 100 5 109145 10.7
-
20.5877
24 110 10 83621 9.4
-
19.4626
Table:-14 S/N Ratios for Elongation – EN8

49
Source DF
Seq
SS
Adj
SS
Adj
MS F P
Voltage (V) 2 15.84
4
15.84
4
7.922
2
10.5
9
0.08
6
Current (Amps) 2 1.759 1.759 0.879
3
1.18 0.46
0
Shielding Gas pressure
(Mpa)
2 1.243 1.243 0.621
5
0.83 0.54
6
Residual Error 2 1.496 1.496 0.748
2
Total 8 20.34
2

50
EN8– Tensile strength:
gas pressure when tensile strength alone considered as output parameter.
The highest angles in Fig 14 and 15 are confirming the same.
influence with delta value of 1.98, followed by current with delta value of
1.67 and least influenced by shielding gas pressure with value of 1.14 . The
of Taguchi.

51
Level
Voltage
(V)
Current
(Amps)
Shielding
gas pressure (Mpa)
1 98.14 99.02 99.26
2 99.22 100.07 98.55
3 100.12 98.39 99.68
Delta 1.98 1.67 1.14
Rank 1 2 3
Voltage
(V)
Current
(Amps)
Shielding Gas
pressure(MPa)
Tensile
Strength
(N)
S/N
RATIO
20 90 5 77710 97.80954
20 100 10 90121 99.09652
20 110 15 75234 97.52828
22 90 10 80316 98.09604
22 100 15 104110 100.3498
22 110 5 91278 99.20732
24 90 15 114365 101.1659
24 100 5 109145 100.7601
24 110 10 83621 98.44631
Table:-16 S/N Ratios for Elongation – EN8
Table:-17 Response Table for Signal to Noise
Ratios

52
Source
D
F
Seq
SS
Adj
SS
Adj
MS F P
Voltage (V) 2 5.890 5.890 2.945
2
2.9
8
0.25
1
Current (Amps) 2 4.294 4.294 2.146
9
2.1
7
0.31
5
Shielding Gas pressure
(Mpa)
2 1.975 1.975 0.987
3
1.0
0
0.50
0
Residual Error 2 1.975 1.975 0.987
3
Total 8 14.13
3

53

54
CHAPTER - 6
CONCLUSION
Therefore series of experiments has been conducted on Mild Steel and EN8
using L9 orthogonal array in taguchi. The experiments evaluate the
following results.
For Mild Steel material
By taking Tensile Strength into consideration, the following combination can
be welded to obtain optimized one.
Voltage 22 volts, Current 100 Amps and shielding gas pressure 15Mpa has
high strength.
By taking Elongation into consideration, the following combination can be
welded to obtain optimized one.
Voltage 20 volts, Current 100 Amps and shielding gas pressure 10Mpa has
optimized elongation.
For EN8 material
By taking Tensile Strength into consideration, the following combination can
be welded to obtain optimized one.
Voltage 24 volts, Current 90 Amps and shielding gas pressure 15 Mpa has
high strength.
By taking Elongation into consideration, the following combination can be
welded to obtain optimized one.
Voltage 22 volts, Current 90 Amps and shielding gas pressure 10 Mpa has
optimized elongation.
By comparing tensile Strength for both the materials, EN8 has high strength
i.e. 114365(N) than mild steel material and by comparing
elongation EN8 has lowest elongation 7.9mm than mild steel

55
material. Therefore EN8 can be welded to obtain optimized
strength and elongation.

56
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