experimental investigation on mig welded mild...

International Journal of Machine and Construction Engineering ISSN (Online): 2394 – 3025. Volume 2 Issue 1 Mar 2015

Experimental Investigation On MIG Welded Mild Steel

S.Sivakumar1, J.R.Vinod Kumar

2

1PG scholar, Department of Mechanical engineering,Mahendra engineering college,

Namakkal. 2Assistant professor, Department of Mechanical engineering,Mahendra engineering

college, Namkkal. Abstract-Gas Metal Arc Welding (GMAW) process is leading in the development in arc welding

process which is higher productivity and good in quality. In this study, the effects of different parameters on welding penetration, micro structural and hardness measurement in mild steel that having the 6mm thickness of base metal by using gas metal arc welding will be investigated. The variables that choose in this study are arc voltage, welding current and welding speed. The arc voltage and welding current were chosen as 22, 26 and 30 V and 90, 150 and 210 A respectively. The welding speed was chosen as 20,40 and 60 cm/min. The penetration, microstructure and hardness will be measured for each specimen after the welding process and the effect of it was studied. As a result, it obvious that increasing the parameters value of welding current increased the value of depth of penetration. Other than that, arc voltage and welding speed is another factor that influenced the value of depth of penetration.

Keywords: Gas Metal Arc Welding (GMAW), welding penetration, micro structural, hardness measurement

I .INTRODUCTION

A. Introduction 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. Along with the wire electrode, a shielding gas feeds through the welding gun,

which shields the process from contaminants in the air. The process can be semi-automatic or

automatic. A constant voltage, direct current power source is most commonly used with GMAW, but

constant current systems, as well as alternating current, can be used. GMAW is currently one of the

most popular welding methods, especially in industrial environments. It is used extensively by the

sheet metal industry and, by extension, the automobile industry.

B. History of GMAW (MIG Welding)

The principles of gas metal arc welding began to be understood in the early 19th century, after

Humphrey Davy discovered the short pulsed electric arcs in 1800.Vasily Petrov independently

produced the continuous electric arc in 1802 (soon followed by Davy).It was not until the 1880s that

the technology became developed with the aim of industrial usage. At first, carbon electrodes were

used in carbon arc welding. By 1890, metal electrodes had been invented by Nikolay Slavyanov and

C. L. Coffin. In 1920, an early predecessor of GMAW was invented by P. O. Nobel of General

Electric. It used a bare electrode wire and direct current, and used arc voltage to regulate ijmce


the feed rate. It did not use a shielding gas to protect the weld, as developments in welding

atmospheres did not take place until later that decade. In 1948, GMAW was finally developed by the

Battelle Memorial Institute. It used a smaller diameter electrode and a constant voltage power source

developed by H.E. Kennedy. It offered a high deposition rate, but the high cost of inert gases limited

its use to non-ferrous materials and prevented cost savings. In 1953, the use of carbon dioxide as a

welding atmosphere was developed, and it quickly gained popularity in GMAW, since it made

welding steel more economical. In 1958 and 1959, the short-arc variation of GMAW was released,

which increased welding versatility and made the welding of thin materials possible while relying on

smaller electrode wires and more advanced power supplies. It quickly became the most popular

GMAW variation.

B. MIG Welding Overview

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. GMAW is currently one of the most popular welding methods, especially in industrial

environments. It is used extensively by the sheet metal industry and, by extension, the automobile

industry. There, the method is often used for arc spot welding, thereby replacing riveting or resistance

spot welding. It is also popular for automated welding, in which robots handle the work pieces and the

welding gun to speed up the manufacturing process.Generally, it is unsuitable for welding outdoors,

because the movement of the surrounding air can dissipate the shielding gas and thus make welding

more difficult, while also decreasing the quality of the weld. The problem can be alleviated to some

extent by increasing the shielding gas output, but this can be expensive and may also affect the quality

of the weld. In general, processes such as shielded metal arc welding and flux cored arc welding are

preferred for welding outdoors, making the use of GMAW in the construction industry rather limited. Gas metal arc welding is a gas shielded process that can be effectively used in all positions. The

shielding gas can be both inert gas like argon and active gases like argon-oxygen mixture and argon-

carbon-di-oxide which are chemically reactive.. Gas metal arc welding (GMAW) process is shown in

figure1.1. It can be used on nearly all metals including carbon steel, stainless steel, alloy steel and

aluminium. Arc travel speed is typically 30-38 cm/minute and weld metal deposition rate varies from

1.25 kg/hr when welding out of position to 5.5 kg/hr in flat position. MIG welding is a well

established semi-automatic process. Continuous welding with coiled wire helps high metal

depositions rate and high welding speed

Fig 1 Sketch of the Gas Metal Arc Welding process (GMAW)

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The GMAW process has the advantages of

1. No flux required 2. Increased corrosion resistance 3. Easily automated welding 4. Welds all metals including aluminium and stainless steel 5. Low skill factor required to operate MIG 6. Can weld quicker and with more efficiency

The GMAW process has the applications of 1. Automotive sub-assemblies and bodywork, 2. Ship building and ship repair yards. 3. Heavy-duty MIG for lorry chassis and off-highway vehicles 4. Structural steelwork for the construction industry 5. Assembly of white goods and office furniture

Welding Of Mild Steels

Mild steel is the most common form of steel as its price is relatively low while it provides material

properties that are acceptable for many applications. Mild steel has a low carbon content (up to 0.3%)

and is therefore neither extremely brittle nor ductile. It becomes malleable when heated, and so can be

forged. It is also often used where large amounts of steel need to be formed, for example as structural

steel.

Mild steel is usually carbon manganese steel. Traditional mild steel used to contain less than 0.10%

carbon in Iron but it is rare these days. Now carbon manganese steels have taken over and are

commonly called mild steel. They contain more carbon and also Manganese which improves the

strength whilst retaining the ductility / malleability. This mild steel is used in the making of vehicle

frames, panels, boxes, cases and sheet metal for roofs. It is now also used as a replacement for

wrought iron in the making railroad rails.

D. Shielding gases

Shielding gases are necessary for gas metal arc welding to protect the welding area from atmospheric

gases such as nitrogen and oxygen. The choice of a shielding gas depends on several factors, most

importantly the type of material being welded and the process variation being used. Pure inert gases

such as argon and helium are only used for nonferrous welding; with steel they do not provide

adequate weld penetration (argon) or cause an erratic arc and encourage spatter (with helium). Pure

carbon dioxide. On the other hand, allows for deep penetration welds but encourages oxide formation,

which adversely affect the mechanical properties of the weld. lts low cost makes it an attractive

choice, but because of the reactivity of the arc plasma, spatter is unavoidable and welding thin

materials is difficult. As a result, argon and carbon dioxide are frequently mixed in a 75%/25% to

90%/10% mixture. Generally, in short circuit GMAW, higher carbon dioxide content increases the

weld heat and energy when all other weld parameters (volts, current, electrode type and diameter) are

held the same. As the carbon dioxide content increases over 20%, spray transfer GMAW becomes

increasingly problematic, especially with smaller electrode diameters.

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Shielding gas mixtures of three or more gases are also available. Mixtures of argon, carbon dioxide

and oxygen are marketed for welding steels. Other mixtures add a small amount of helium to argon-

oxygen combinations, these mixtures are claimed to allow higher arc voltages and welding speed.

Helium also sometimes serves as the base gas, with small amounts of argon and carbon dioxide added.

However, because it is less dense than air, helium is less effective at shielding the weld than argon

which is denser than air. It also can lead to arc stability and penetration issues, and increased spatter,

due to its much more energetic arc plasma. Helium is also substantially more expensive than other

shielding gases. Other specialized and often proprietary gas mixtures claim even greater benefits for

specific applications. The desirable rate of shielding-gas flow depends primarily on weld geometry, speed, current, the type

of gas, and the metal transfer mode. Welding flat surfaces requires higher flow than welding grooved

materials, since gas disperses more quickly. Faster welding speeds, in general, mean that more gas

must be supplied to provide adequate coverage. Additionally, higher current requires greater flow, and

generally, more helium is required to provide adequate coverage than if argon is used. CO2 Gas

CO2 gas is used as the shielding gas in GMA welding of steel plates. The flow characteristics of CO2

are such that the gas issues in a non-turbulent manner from the MIG gun. With CO2 shielding the

metal transfer will be globular and non-axial at low current densities. MIG/CO2 welding with spray

type arc (current density 350 amps) is best suited for welding relatively thick parts. For thin sheets dip

transfer technique is used with low arc voltage (16 - 22 V) and low current (60 - 180 amps). The low

arc voltage results in a reduced arc length and the molten droplet gets transferred into the weld pool

by direct contact. With pure argon or a mixture of argon + 20% CO2, the metal transfer is globular at

low current density, but changes to spray type when the current density increases. In the spray type

transfer the metal travels across the arc in the form of fine droplets which is induced by the magnetic

force acting on the molten electrode tip. CO2 is widely used for welding of mild steel and it gives

sound weld deposits.

E. Electrode

When choosing an electrode, one must consider arc stability, solidification rate, mechanical

properties, deposition rate, base metal compatibility, and parameter settings. Parameter settings for

GMAW electrodes depend on: 1. Diameter of the Electrode 2. Mode of Transfer 3. Shielding Gas Composition 4. Welding Position

The GMAW process uses a consumable, automatically fed wire electrode and is considered a

semiautomatic welding process when welded by hand. Electrode diameters used in GMAW typically

range from 0.024 inches (0.6 mm) to 0.062 inches (1.6 mm). However, electrode diameters are

manufactured from as small as 0.020 inches (0.5 mm) to as large as 1/8 inch (3 mm). As a rule,

electrode size selection is based on base metal thickness, welding position, and mode of metal

transfer. Larger electrodes can obviously provide higher welding speeds and the higher amperages

desired for spray transfer welding on heavier base metals. The most common types of MIG wire for

welding mild steel are ER70S-3 and ER70S-6. ijmce


ER70S-3 Electrodes of this classification contain a relatively low percentage of deoxidizing elements

(silicon and manganese); however, they are one of the most widely used GMAW wires. They produce

welds of fair quality when used on all types of steels, especially if using Argon-O2 or Argon-CO2 as

a shielding gas. Straight CO2 can be used, but parameters should remain in short-circuit mode. The

use of straight CO2 is not recommended when welding with high voltage and high amperage. When

CO2 shielding gas is used, in the high welding currents (high heat input), welds produced may not

meet the minimum tensile and yield strengths of this specification. High heat input using straight CO2

will burn out the relatively low percentage of deoxidizing elements in this electrode wire. Choose an ER70S-6 wire for welding on plate that has mill scale or surface contaminants, since this

wire incorporates the proper deoxidizer to combat these issues. A deoxidizer absorbs oxygen so that it

vaporizes into the arc or forms as scale oxides. ER70S-6 is also better for creating a smooth transition

from the weld to the base metal, also known as wash-in or tie-in. Better wash-in may be a requirement

in applications subject to fatigue. ER70S-6 wire can provide better wetting at the weld toe when

compared to an ER70S-3 wire. ER70S-6 Electrodes in this classification contain the highest

combination deoxidizers in the form of silicon and manganese. This allows them to be used for

welding all types of carbon steel, even rimmed steels, by using CO2 shielding gas.

II . LITERATURE REVIEW

IzzatulAini Ibrahim et al (2012) studied the effects of different parameters on welding penetration,

micro structural and hardness measurement in mild steel that having the 6mm thickness of base metal

by using the robotic gas metal arc welding are investigated. The variables that choose in this study are

arc voltage, welding current and welding speed. The arc voltage and welding current were chosen as

22, 26 and 30 V and 90, 150 and 210 A respectively. The welding speed was chosen as 20, 40 and 60

cm/min. The penetration, microstructure and hardness were measured for each specimen after the

welding process and the effect of it was studied. As a result, it obvious that increasing the parameters

value of welding current increased the value of depth of penetration. Other than that, arc voltage and

welding speed is another factor that influenced the value of depth of penetration. The micro structure

shown the different grain boundaries of each parameters that affected of the welding parameters.

Kamal pal et al (2010) studied the influence of pulse parameters at various torch angles on the tensile

properties of low carbon steel butt weld in pulsed metal inert gas welding. The interface of weld zone

and heat affected zone was found to be the weakest area due to significant variation of weld

microstructure. The weld bead characteristics strongly influenced the joint strength. An infrared

pyrometer and sound sensor have also been used along with arc sensors to monitor the weld quality.

The arc power and arc sound kurtosis were found to be strongly correlated with weld quality.

Ming Gao et al (2008) studied the laser arc hybrid welding, the weld shape and microstructure

characteristics of laser metal inert gas hybrid welded mild steel were analyzed. The results showed

typical hybrid weld could be classified as two parts: the wide upper zone and the narrow zone, which

were defined as arc zone and laser zone, respectively. In the hybrid weld, the microstructure, alloy

element distribution and micro hardness all have evident difference between laser zone and arc zone.

The microstructure of arc zone consists of coarse columnar dendrite and fine acicular dendrite

between the columnar dendrites, but that of laser zone is composed of fine equiaxed dendrite in weld

center and columnar dendrite around the equiaxed dendrite. Compared to arc zone, laser zone has

finer grain size, higher micro hardness, smaller alloy element content in the fusion zone and narrower

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heat affected zone. The discussions demonstrated that the observed difference was caused by the

difference of temperature gradient, crystallizing and the effects of arc pressure on the molten pool

between laser zone and arc zone.

Giovanni Tani et al (2007) studied the Hybrid LASER GMAW welding technique has been recently

studied and developed in order to meet the needs of modern welding industries. The two sources

involved in this process play, in fact, a complementary role: fast welding speed, deep bead penetration

and high energy concentration can be achieved through the LASER beam, while gap bridge ability

and cost-effectiveness are typical of the GMAW process. Particularly interesting, in this context, is

the CO2 LASER MIG welding which differs from the Nd’YAG LASER–MIG technique for the high

powers that can be exploited and for the good power/cost ratio of the process. This paper is a part of a

wide study on the hybrid CO2 LASER MIG welding and investigates the influence of the shielding

gas both on the stability of the process and on the dimensional characteristics of the weld bead. Two

different parameters have been taken into consideration in order to develop this analysis: the shielding

gas composition and the shielding gas flow. The results have been analyzed through a statistical

approach in order to determine the real influence of each parameter on the overall process.

Zielinskaet al (2009) studied the percentage of carbon dioxide in argon induces the increase of the

transition current value from the globular to spray metal transfer mode. This work shows that these

effects are linked to the chemical and micro structural modifications of the anode tip during the gas

metal arc welding process. The microstructure of the anode is investigated for various experimental

conditions. Transition between the two transfer modes is linked to the existence and disappearance of

a rather insulating oxide “gangue” at the wire extremity whose nature depends of the shielding gas. Chemical reactions at high temperature such as oxidation reduction reactions between shielding gas and melted metal govern the transition of the spray-arc to globular transfer mode.

Kimet al (2003) studied the robotic arc welding process involves sophisticated sensing and control

techniques applied to various process variables. One of the major important tasks in the robotic CO2

arc welding process is to understand inter relationship between process variables and bead penetration

and subsequently develop the mathematical models to predict the desired bead penetration. To

achieve the objectives, partial-penetration and single-pass welds were fabricated in 12 mm SS400

plate by using four different process variables. The experimental results were employed to develop

the curvilinear and linear equations, and find the process control algorithms for the CO2 arc welding

process. Mathematical models developed can predict the bead penetration with reasonable accuracy.

The process control algorithms developed will be useful for identifying the various problems that

result from the CO2 arc welding process, and establishing criteria for effective joint design.

Tuseket al (2004) studied the mathematical models for calculation and prediction of melting rate in arc welding with a triple-wire electrode are described. The quantities affecting the melting rate of the filler material were determined by experimental work. Mathematical models with which it is possible

to calculate and predict, with a strong probability, the melting rate in triple-wire arc welding in

different shielding media were elaborated by statistical methods.

UweReisgen et al (2010) studied the effects of shielding gas types and flow rates on CO2 laser

weldability of DP600/TRIP700 steel sheets were studied in this work. The evaluated shielding gases

were helium (He), argon (Ar) and different mixtures of He and Ar. Weld penetration, tensile strength

and formability (Erichsen test) of laser welds were found to be strongly dependent upon the shielding

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gas types. The ability of shielding gas in removing plasma plume and thus increasing weld penetration

is believed to be closely related to ionization potential and atomic weight which determine the period

of plasma formation and disappearance. It was found that the higher helium shielding gas flow rate,

the deeper weld penetration and the lower weld width.

Couleset al (2012) studied the strain field within thin steel plates during gas metal arc welding has

been studied using resistance strain gauges and digital image correlation, allowing the initial

formation of stresses around the weld seam to be observed. Major features of the transient stress field

have been identified, and are explained with reference to the underlying thermal and mechanical

processes. A comparison of stresses occurring during bead-on-plate and butt welding shows they are

very similar. The assumptions and limitations associated with determination of the stress state are

addressed, and the application of such methods to the problem of reducing welding residual stresses is

discussed.

Ganjigatti et al (2007) studied the MIG welding process through regression analyses carried out both

globally as well as cluster-wise. It is important to mention that the second approach makes use of the

entropy based fuzzy clusters. The investigation is based on the data collected through full factorial

design of experiments. Results of the above two approaches are compared and some concluding

remarks are made. The cluster-wise regression analysis is found to perform a slightly better than the

global approach in predicting weld bead-geometric parameters.

Ming Gao et al (2012) studied the mechanical properties of welded joints were evaluated by tensile

test. Under the optimal welding parameters, the stable process and sound joints were obtained. The

tensile strength efficiency of welded joints recovered 84–98% of the substrate. It was found that the

arc was compressed and stabilized by the laser beam during the hybrid welding. The compressed

extent of arc column increased with laser power, and the process stability could be improved by

increasing laser power and arc current or slowing welding speed. The arc stabilized mechanism in

laser–MIG hybrid welding of Mg alloys was summarized in two factors. First, the laser keyhole fixes

the arc root and improves the igniting ability of the arc. Second, the electromagnetic force is

downward and increased by the laser–arc interaction, which prevents the overheating of the droplet

and smoothes droplet transfer from the wire to the weld pool.

RakeshMalviya et al (2011) studied the optimization technique has been used for tuning of neural

networks utilized for carrying out both forward and reverse mappings of metal inert gas (MIG)

welding process. Four approaches have been developed and their performances are compared to solve

the said problems. The first and second approaches deal with tuning of multi-layer feed-forward

neural network and radial basis function neural network, respectively. In the third and fourth

approaches, a back-propagation algorithm has been used along with particle swarm optimization to

tune radial basis function neural network. Moreover, in these two approaches, two different clustering

algorithms have been utilized to decide the structure of the network. The performances of hybrid

approaches (that is, the third and fourth approaches) are found to be better than that of the other two. ijmce


III. METHODOLOGY

A. Selection of material Mild steel

Mild steel is steel in which the main interstitial alloying constituent is carbon in the range of 0.12–

2.0%. The American Iron and Steel Institute (AISI) defines carbon steel as the following: "Steel is

considered to be carbon steel when no minimum content is specified or required for chromium,

cobalt,molybdenum, nickel, niobium, titanium, tungsten, vanadium or zirconium, or any other element

to be added to obtain a desired alloying effect; when the specified minimum for copper does not

exceed 0.40 percent; or when the maximum content specified for any of the following elements does

not exceed the percentages noted: manganese 1.65, silicon 0.60, copper 0.6. Mild steel – A36 material

A36 is the most commonly used mild and hot-rolled steel. It has excellent welding properties and is

suitable for grinding, punching, tapping, drilling and machining processes. Yield strength of ASTM

A36 is less than that of cold roll C1018, thus enabling ASTM A36 to bend more readily than C1018.

The view of Mild steel A36 plate is shown in Figure 1.A36 is produced in a wide variety of forms,

including rectangle bar, square bar, circular rod, steel shapes such as channels, angles, H-beams and I-

beams. ASTM A36 steel is easy to weld using any type of welding methods and the welds and joints

so formed are of excellent quality.

Fig 1 Mild steel A36 plate

The A36 standard was established by the standards organization ASTM International. A36 is readily

welded by nearly all welding processes and the specification of the mild steel A36 plate shown in the

following Table 1.

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International Journal of Machine and Construction Engineering

ISSN (Online): 2394 – 3025. Volume 2 Issue 1 Mar 2015

Table 1 Specification of the Mild steel A36 plate

Length Height Thickness Material No of

specimens

100 50 mm 6 mm Mild steel 12

mm

Therefore the most commonly used for A36 are those which are cheapest and easiest. A36 steel and

their chemical composition shown in following Table 2. It is also commonly used in bolted and

riveted in structural applications and their mechanical properties shown in the following Table 3.

Table 2 Chemical composition of Mild steel A36 plate

Element (%) present

Fe 98.70

C 0.0652

Si 0.158

Mn 0.919

P 0.035

S 0.011

Cr 0.0861

Mo 0.015

Ti 0.0071

V 0.0021

Pb 0.0013

Table 3 Mechanical properties of Mild steel A36

Property Value

Yield Strength 289 Typical Mpa

Tensile Strength 397 Typical Mpa

Brinell Hardness 229 Typical HV

Elongation 33.2 %

Charpy Impact 5.4 joule

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B. Experimental Setup

MIG(metal inert gas) welding also known as MAG (metal active gas) and in the USA as GMAW (gas

metal arc welding) is a welding process that is now widely used for welding a variety of materials,

ferrous and non ferrous. The schematic diagram of MIG welding is shown in the following Figure 2.

Fig 2 Schematic diagram of MIG welding Power source

MIG welding is carried out on DC electrode (welding wire) positive polarity (DCEP). However

DCEN is used for (for higher burn off rate) with certain self-shielding and gas shielded cored wires.

DC output power sources are of transformer-rectifier design, with a flat characteristic (constant

voltage power source). The most common type of power source used for this process is the switched

primary transformer rectifier with constant voltage characteristics from both 3-phase 415v and 1-

phase 240v input supplies. Wire feed unit

The wire-feed unit, or sub-assembly where this is mounted in the power source cabinet (known as a

composite MIG), provides the controlled supply of welding wire to the point to be welded. According

to the welding wire size and Arc voltage provided by the power source, a constant rate of wire speed

is required, in MIG welding the power source provides Arc voltage control and the wire feed unit

provides welding wire speed control, ( in MIG this equates to welding current ). Torch

This provides the method of delivery from the wire feed unit to the point at which welding is required.

The MIG torch can be air cooled or water cooled and most modern air cooled torches have a single

cable in which the welding wire slides through a Liner. Gas flows around the outside of this Liner and

around the tube the Liner sits in is the power braid and trigger wires. The outer insulation provides a

flexible cover. Water cooled MIG torches are similar to the above, but gas hose, liner tube, power lead

(including water return pipe), water flow pipe and trigger wires are allseparate in an outer sleeve.Most

industrial MIG equipment uses a standard European MIG torch connector for easy connectionof torch,

some low cost smaller units use individual manufacturers fittings.The important areas of maintenance

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are: Liners are in good condition and correct type and size; Contact tips are lightly fitted, of correct size and good condition.

Shielding Gas

This is a complicated area with many various mixtures available, but the primary purpose of

the shielding gas in the MIG process is to protect the molten weld metal and heat affected zone from

oxidation and other contamination by the atmosphere.The shielding gas should also have a

pronounced effect on the following aspects of the welding operation and the resultant weld.

C. Tests Conducted

By varying the process parameters the metal inert gas weldedA36 material to the following test under mechanical properties.

1. Mechanical properties 1. Tensile test 2. Brinell hardness test 3. Impact test

Mechanical properties

Mechanical testing plays an important role in evaluating fundamental properties of engineering

materials as well as in developing new materials and in controlling the quality of materials for use in

design and construction. If a material is to be used as part of an engineering structure that will be

subjected to a load, it is important to know that the material is strong enough and rigid enough to

withstand the loads that it will experience in service. As a result engineers have developed a number

of experimental techniques for mechanical testing of engineering materials subjected to tension,

compression, bending or torsion loading. a.Tensile test

The most common type of test used to measure the mechanical properties of a material is the tensile

test and the machine is shown in Figure 3. Tensile test is widely used to provide a basic design

information on the strength of materials and is an acceptance test for the specification of materials.

The major parameters that describe the stress-strain curve obtained during the tension test are the

tensile strength (UTS), yield strength or yield point (σy), elastic modulus (E), percent elongation

(ΔL%) and the reduction in area (RA%). Toughness, Resilience, Poisson’s ratio (ν) can also be found

by the use of this testing technique.

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a) Screw driven machine b) a hydraulic testing machine Fig 3 Tensile testing machines

Testing system

The testing system consists of a tensile testing machine, a load cell, a power supply and an x-y recorder. 1. Testing Machine is a load-controlled machine. 2. Load Cell provides an electrical circuit for measuring the instantaneous load along the loading axis. 3. Power Supply is connected to load cell. It feeds the load cell, amplifies the output signal and displays the load. 4. Recorder plots the variation of load against time. 5. Specimen tensile specimens are machined in the desired orientation and according to the standards.

The central portion (gage portion) of the length is usually of smaller cross section than the end

portions. This ensures the failure to occur at a section where the stresses are not affected by the

gripping device. The gage length is marked and elongation is measured between these markings

during the test.

Procedure

1. Before the test 1. Put gage marks on the specimen 2. Measure the initial gage length and diameter 3. Select a load scale to deform and fracture the specimen. Note that that tensile strength of the material type used has to be known approximately.

During the test 1. Record the maximum load 2. Conduct the test until fracture.

After the test 1. Measure the final gage length and diameter. The diameter should be measured from the neck.

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b..Brinell hardness test

Hardness is the property of a material that enables it to resist plastic deformation, usually by

penetration. However, the term hardness may also refer to resistance to bending, scratching, abrasion

or cutting.

The Brinell hardness test method consists of indenting the test material with a 10 mm diameter

hardened steel or carbide ball subjected to a load of 3000 kg and the schematic view of the brinell

hardness test is shown in Figure 4. For softer materials the load can be reduced to 1500 kg or 500 kg

to avoid excessive indentation. The full load is normally applied for 10 to 15 seconds in the case of

iron and steel and for at least 30 seconds in the case of other metals. The diameter of the indentation

left in the test material is measured with a low powered microscope. The Brinell harness number is

calculated by dividing the load applied by the surface area of the indentation.

Fig 4 schematic diagram of the brinell hardness test

The diameter of the impression is the average of two readings at right angles and the use of a Brinell

hardness number table can simplify the determination of the Brinell hardness. A well

structuredBrinell hardness number reveals the test conditions, and looks like this, "75 HB 10/500/30"

which means that a Brinell Hardness of 75 was obtained using a 10mm diameter hardened steel with a

500 kilogram load applied for a period of 30 seconds. On tests of extremely hard metals a tungsten

carbide ball is substituted for the steel ball. Compared to the other hardness test methods, the Brinell

ball makes the deepest and widest indentation, so the test averages the hardness over a wider amount

of material, which will more accurately account for multiple grain structures and any irregularities in

the uniformity of the material. This method is the best for achieving the bulk or macro-hardness of a

material, particularly those materials with heterogeneous structures. c. Charpy impact test

The Charpy impact test, also known as the Charpy V-notch test, is a standardized high strain-rate test

which determines the amount of energy absorbed by a material during fracture and the schematic

diagram of the charpy impact test is shown in Figure 5. This absorbed energy is a measure of a given

material's notch toughness and acts as a tool to study temperature-dependent ductile-brittle transition.

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Fig 5 Schematic diagram of the charpy impact test

The test consists of breaking by one blow from a swinging pendulum, under conditions defined by

standards, a test piece notched in the middle and supported at each end. The energy absorbed is

determined in joules. This absorbed energy is a measure of the impact strength of a material.

The test bar, notched in the centre, is located on two supports. The hammer will fracture the test bar and the absorbed energy (in Joule) is an indication for the resistance of the material to shock loads.

IV .RESULTS AND DISCUSSION

A. Mechanical Properties

By varying the process parameters the metal inert gas welded mild steel A36 material which exhibited

good mechanical properties. The following tests are conducted under mechanical properties which

indicate the success of the process. 1. Tensile test. 2. Brinell hardness test. 3. Charpy impact test. Tensile test

By following the ASTM E8 standard shown in Figure 6 the tensile specimens are prepared from the

welded specimens.The tensile tests are conducted for all the tensile specimen and their results are

indicated in the following Table 4 and values of tensile strength are also shown in Graph no 1.

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Fig 6 ASTM E8 standard

The tensile strength is calculated by the following formula

Tensile strength = Load at break in (N/mm2)

Thickness × Width

Table 4 Tensile test results

Specimen

Current Voltage Area

Load at Tensile

break strength

No

(Amps) (Volts) (thicknes×width)

(Newton) (N/mm2)

1. 110 22 36 14400 400

2. 120 23 36 15555 432

3. 130 24 36 16160 456

4. 140 25 36 17280 488

Base metal 36 14400 397

Graph no 1 Tensile strength graph for all specimens

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Brinell hardness test

The brinell hardness test are conducted for the metal inert gas welded specimens and the hardness are

taken in the welding zone as well as in the base metal of the advancing side and retreating side and

their results are shown in the following Table 5.The brinell hardness test graph for the individual

specimen is shown in the following Graph no 2, 3, 4, 5, 6. The hardness is calculated by the following

formula BHN = F

π D – (D - √D2 - Di)

F = Applied force = 250 kgf D = Indenter Diameter = 5 mm Ball

Di = Indentation Diameter

Table 5 Hardness test result

Adva Retre

ncin

ating

g

side

side

Spe Cur Volt Base Wel

ding Base

cim rent age meta

zone metal

en (Am (Vol l

(WZ (BM)

no ps) ts) (BM)

)

1. 110 22 229 285 229

2. 120 23 229 285 229

3. 130 24 187 229 187

4. 140 25 229 285 229

1. Specimen no 1

Graph no 2 Brinell hardness graph for specimen no 1

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2. Specimen no 2

Graph no 3 Brinell hardness graph for specimen no 2

3. Specimen no 3

Graph no 4 Brinell hardness for graph specimen no 3 4. Specimen no 4

Graph no 5 Brinell hardness graph for specimen no 4 Charpy impact test.

The charpy impact specimens are prepared from the metal inert gas welded specimens. Then the

charpy impact test are conducted for all the specimens and their result are shown in the following

Table 6.

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International Journal of Machine and Construction Engineering

ISSN (Online): 2394 – 3025. Volume 2 Issue 1 Mar 2015

Table 6 Charpy impact test results

Specimen no

Current (Amps) Voltage (Volts)

Energy absorbed

(joules)

1. 110 22 7

2. 120 23 7.8

3. 130 24 9

4. 140 25 12

Base metal 5.4

Graph no 6 Charpy impact graph for all specimens

V .CONCLUSION

1. The tensile strength for all the metal inert gas welded specimens are ranged from 400 to 488

N/mm2. When compared to base metal the welded specimens exhibit high tensile strength. Therefore

all the metal inert gas welded specimen exhibit good tensile strength. 2. The brinell hardness number are increased for all the metal inert gas welded specimen when compared to the base metal. 3. The charpy impact where all the metal inert gas welded specimen which absorbed more energy when compared to the base metal.

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VI REFERENCES

1. IzzatulAini Ibrahim., SyarulAsrafMohamat.,AmalinaAmir.andAbdulGhalib. (2012) “The Effect

of Gas Metal Arc Welding (GMAW) processes on different welding parameters”,Procedia

Engineering, Vol.41, pp.1502 – 1506. 2. Kamal Pal. andSurjya K. Pal. (2010) “Study of weld joint strength using sensor signals for

various torch angles in pulsed MIG welding”, Journal of Manufacturing Science and

Technology, Vol.3, pp. 55–65. 3. Ming Gao., Xiaoyan Zeng., Jun Yan. andQianwu Hu. (2008) “Microstructure characteristics of

laser–MIG hybrid welded mild steel”,Applied Surface Science, Vol.254, pp. 5715–5721. 4. Giovanni Tani., GiampaoloCampana., Alessandro Fortunato. andAlessandroAscari. (2007) “The

influence of shielding gas in hybrid LASER–MIG welding”,Applied Surface Science, Vol.253,

pp. 8050-8053. 5. Zielinska S., Valensi F., Pellerin N., Pellerin S.,Musioł K. andBriand F. (2009) “Microstructural

analysis of the anode in gas metal arc welding (GMAW)”,journal of materials processing

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electrode”,Journal of Materials Processing Technology, Vol.146, pp. 415-423. 8. UweReisgen., Markus Schleser., Oleg Mokrov. andEssam Ahmed. (2010) “Shielding gas

influences on laser weldability of tailored blanks of advanced automotive steels”,Applied Surface Science, Vol.257, pp. 1401-1406.

9. Coules H.E., Colegrove P., Cozzolino L.D. andWen S.W. (2012) “Experimental measurement of

biaxial thermal stress fields caused by arc welding”,Journal of Materials Processing Technology,

Vol.212, pp. 962-968. 10. Ganjigatti J.P., Dilip Kumar Pratihar. andRoy ChoudhuryA.(2007) “Global versus cluster-wise

regression analyses for prediction of bead geometry in MIG welding process”,Journal of

Materials Processing Technology, Vol.189, pp. 352-366. 11. Ming Gao., Shuwen Mei., Zemin Wang., Xiangyou Li. and Xiaoyan Zeng.(2012) “Process and

joint characterizations of laser–MIG hybrid welding of AZ31magnesium alloy”, Journal of Materials Processing Technology, Vol.212, pp. 1338-1346.

12. RakeshMalviya. andDilip Kumar Pratihar.(2011) “Tuning of neural networks using particle

swarm optimization to model MIG welding process”, Swarm and Evolutionary Computation,

Vol.1, pp. 223-235.

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