effect of welding current on welding … & 100 ampere by using mmaw process in 1g position. the...

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International Journal of Mechanical Engineering and Technology (IJMET) Volume 7, Issue 5, September–October 2016, pp.156–176, Article ID: IJMET_07_05_018

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ISSN Print: 0976-6340 and ISSN Online: 0976-6359

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EFFECT OF WELDING CURRENT ON WELDING

SPEED AND ULTIMATE TENSILE STRENGTH (UTS)

OF MILD STEEL

Syambabu Nutalapati

Research Scholar, M.E (Machine Design), (Ph.D), JNTUK, India.

Dr. D. Azad

Professor, Aitam Tekali, Srikakulam District, India.

Dr. G. Swami Naidu

Professor and Vice-Principal (Administration), Department of Metallurgical Engineering,

JNTUK-UCEV, India.

ABSTRACT

Welding is a fabrication or sculptural process that joins materials, usually metals or

thermoplastics, by causing fusion, which is distinct from lower temperature metal-joining techniques

such as brazing and soldering, which do not melt the base metal. In the heavy as well as small

industries, welding is widely used by metal workers in the fabrication, maintenance and repair of

parts and structures. Welding current is the most influencing parameter in welding process which

controls the depth of fusion; the electrode feed rate and depth of penetration. The amount of heat

developed during welding depends upon the current used for a given size of electrode and filler wires.

It is therefore essential that a correct current is used to produce good quality of weld and reduce the

distortion problems on the job.

The effect of welding current on welding speed and ultimate tensile strength of mild steel material

is investigated in this paper. Mild steel weldment was welded under varying welding current i.e. 90,

95 & 100 ampere by using MMAW process in 1G position. The edge preparation, electrode diameter

and electrode type, CCV, welding technique, polarity and welder remained constant during the test.

It was observed that with increase in welding current melting rate of electrode was increased hence

welding time was reduced.

Key words: MMAW, welding current, welding speed, ultimate tensile strength (UTS).

Cite this Article: Syambabu Nutalapati, Dr. D. Azad and Dr. G. Swami Naidu, Effect of Welding

Current on Welding Speed and Ultimate Tensile Strength (UTS) of Mild Steel. International Journal

of Mechanical Engineering and Technology, 7(5), 2016, pp. 156–176.

http://www.iaeme.com/ijmet/issues.asp?JType=IJMET&VType=7&IType=5

Effect of Welding Current on Welding Speed and Ultimate Tensile Strength (UTS) of Mild Steel


1. INTRODUCTION

1.1. Mild Steel

Steel is any alloy of iron, consisting of 0.2% to 2.1% of carbon, as a hardening agent. Besides carbon, many

other metals are a part of it. They include chromium, manganese, tungsten and vanadium. Other than a

maximum limit of 2% carbon in the manufacture of carbon steel, the proportions of manganese (1.65%),

copper (0.6%) and silicon (0.6%) are fixed, while the proportions of cobalt, chromium, niobium,

molybdenum, titanium, nickel, tungsten, vanadium and zirconium are not. What is known as mildest grade

of carbon steel or mild steel is typically the variety which has a comparatively low amount of carbon (0.05%

- 0.26%). Mild steel is a very popular metal and one of the cheapest types of steel available. It’s found in

almost every metal product. This type of steel contains less than 2 percent carbon, which makes it magnetize

well. Since it’s relatively inexpensive

Properties of metals can be classified mainly into:

• Chemical properties

• Physical properties

1.1.1. Chemical Properties

• Corrosion will spoil the metal surface due to the effect of various elements in the atmosphere and water.

• Oxidation is the formation of metal oxides which occur when oxygen combines with metals.

• Reduction refers to the removal of oxygen from the surrounding molten puddle to reduce the effect of

atmospheric contamination.

1.1.2. Physical Properties

Physical properties are those, which affect metals when they are subjected to heat generated by welding such

as: • Melting point

• Thermal expansion

• Thermal conductivity

• Grain growth

Melting point is the degree of temperature, when a solid metal changes into liquid. Melting points of

some metals are given below:

• Mild steel 1500 to 1530°C

• Cast iron 1150°C

Material c Mn si s p

Mild steel 0.14 0.76 0.28 0.013 0.010

Table 1.1 composition of mild steel

1.2. Joint Types

The American Welding Society defines a joint as “the manner in which materials fit together. There are five

basic types of weld joints but butt welding is used in this operation

1.2.1. Butt Joint (Single V)

Butt joints are used where high strength is required. They are reliable and can withstand stress better than

any other type of weld joint. To achieve full stress value, the weld must have 100 percent penetration through

Syambabu Nutalapati, Dr. D. Azad and Dr. G. Swami Naidu


the joint. This can be done by welding completely through from one side. The alternative is working from

both sides, with the welds joining in the centre.

Figure 1.1 single V butt joint

2. EXPERIMENTAL PROCEDURE

MMA/TIG Welding Machine with a 400A capacity. In this investigation Mild steel alloy plate of dimension

90mm × 25mm × 6mm (figure 1) were taken for SMAW welding technique. These plates are cleaned of dirt,

grease and other foreign materials and were cut into the required dimensions by power hacksaw. Edge

preparation is carried out where single V edge is prepared for a bevel angle of 30, 45, 60 and square butt

joint plates were prepared by smoothing their faces. In all the cases the root gap of 1 mm and root of 1mm

was maintained. The mild steel plates are placed on welding table and in order avoid the undesired distortion

to the minimal the right size of stiffeners was provided at critical locations where the welding process is

carried out.

There are 6 numbers of specimens were prepared from SMAW process viz., single V butt joint. The 6

specimens of single V joint design at six different values of welding current (specimen code 1V at 90 amps

and with angle 30, 2V at 100 amps with angle 45, 3V at 110 amps with angle 60,)

In this process all the various welding parameters such as the arc voltage, number of passes, welding speed, wire

feed rate, arc time and welding current were recorded during the welding of each specimen only welding current was

varied during the welding of specimens, to study the effect of welding current on the tensile strength, yield strength

and elongation of the weldment. Having finished the welding of the joints in order to measure the tensile strength,

welded plates were cut using hacksaw and then machined to the required dimensions to make the tensile test pieces

with the help of the workshop technology. The dimensions of a tensile test specimen shown

At the same time the different angles of specimens are tested by universal testing machine for finding

the strength and also the ansys tutorial and CATIA V5 software are used in this operation with applying of

different load. At last getting the result which is the best strength or capability comparing to other specimen

and the specimens are 30 single V butt joint specimens, 45 single V butt joint specimen, 60 single V butt

joint specimen



2.1. Geometrical Properties

Figure 2.1 Sketched diagram of 300 V-grooved specimen





In this investigation Mild steel plate of dimension 90mm × 25mm × 6mm

• SMAW

• Mild steel electrode

• Single v groove butt joint

• Inclination angle 60

• Curve of 12mm radius

These plates are cleaned of dirt, grease and other foreign materials and were cut into the required

dimensions by manual hacksaw blade. Edge preparation is carried out where single V edge is prepared for a

bevel angle of 60 and square butt joint plates were prepared by smoothing their faces.

2.2. Tensile Test on a Metal

2.2.1. Required Apparatus

• Universal Testing Machine (UTM)

• Mild steel specimens

• Graph paper

• Scale

• Vernier Caliper

2.2.2. After Testing

• Limit of proportionality

• Elastic limit

• Yield strength

• Ultimate strength

• Young’s modulus of elasticity

• Percentage elongation

• Percentage reduction in area.

2.2.3. Procedure

• Measure the original length and diameter of the specimen. The length may either be length of gauge section

which is marked on the specimen with a pre-set punch or the total length of the specimen.

• Insert the specimen into grips of the test machine and attach strain-measuring device to it.

• Begin the load application and record load versus elongation data.

• Take readings more frequently as yield point is approached.

• Measure elongation values with the help of dividers and a ruler.

• Continue the test till Fracture occurs.

• By joining the two broken halves of the specimen together, measure the final length and diameter of specimen.

2.2.4. Observation

After testing the dimensions of the specimen are

A) Original dimensions: Mild steel plate of dimension 90mm × 25mm × 5.5mm

Length = 90

Thickness = 5.5

Area: 90×25=2250mm2



B) Final Dimensions: 92mm × 25mm × 6mm

Length = 92

Thickness =6

Area: 92×25 = 2300

2.3. Observation Table

Specimen Angle Load(N) Original Extension Peak load Strain

A1 30 313 38 39 1.15 1.02

B1 30 475.7 39 40 1.68 1.02

A2 60 487 38 39 1.72 1.02

A3 45 453 38 40 1.72 1.05

B3 45 300 38 39 1.60 1.02

Table 2.1 observation table

2.4. Specimen Code A1

• Percentage reduction in area= Original area-area at fracture / Original area

(1712-1698)/1706= 15.97%

• Percentage elongation= (Final length (at fracture) – original length) / Original length

(92-90) / 90 = 2.63%

• Cross head travel at break: 7.10 mm

Tensile strength: 31.94 N/mm2

2.4.1. Graph between Stress Strain Curve

Figure2.4 graph between stress vs strain curve-A1



2.4.2. Graph between Load and Cross Head Travel Curve

Figure 2.5 Graph between load and cross head travel curve-A1

2.4.3. Graph between Stress and Cross Head Travel Curve (Elongation)

Figure 2.6 Graph between stress and cross head travel curve (elongation) -A1

2.5. Specimen Code B1


(1706-1698)/1706= 19%


(92-90) / 90 =2.56%




• Tensile strength: 46.67 N/mm2


Figure 2.7 Graph between stress strain curves-B1


Figure 2.8 Graph between load and cross head travel curve-B1




Figure 2.9 Graph between stress and cross head travel curve (elongation) -B1



15.97%


2.63%


• Tensile strength: 47.78 N/mm


Figure 2.10 Graph between stress strain curves-A2





8.33%


(92-90) / 90 = 5.26%




Figure 2.13 Graph between stress strain curves-A3







2.8. Specimen Code B3


15.97%


(92-90) / 90 = 2.63%




Figure 2.15 Graph between stress strain curves-B3




Figure 2.16 Graph between load and cross head travel curve-B3


Figure 2.17 Graph between stress and cross head travel curve (elongation) -B3



2.9. Testing Specimen

Figure 2.18 Testing specimen

2.10. Precaution

• If the strain measuring device is an extensometer it should be removed before necking begins.

• Measure deflection on scale accurately & carefully

3. RESULT

Single V joint design of butt joint at 30 inclination angle have depict high

Maximum tensile strength value

• Cross head travel at break = 6.40mm

• Ultimate tensile strength = 47.78 N/mm2

• Percentage of elongation = 2.63

• Percentage reduction in area = 15.97

• Peak load = 1.72KN

4. DESIGN AND ANALYSIS

4.1. CATIA Model

Figure 3.1 3d model of 300 V-grooved specimen.



Figure 3.2 3d model of 450 V-grooved specimen

Figure 3.3 Sketched diagram of 600 V-grooved specimen.

4.2. Introduction to FEA

Structural analysis consists of linear and non-linear models. Linear models use simple parameters and

assume that the material is not plastically deformed. Non-linear models consist of stressing the material past

its elastic capabilities. The stresses in the material then vary with the amount of deformation as in.

Vibrational analysis is used to test a material against random vibrations, shock, and impact. Each of

these incidences may act on the natural vibrational frequency of the material which, in turn, may cause

resonance and subsequent failure.

Fatigue analysis helps designers to predict the life of a material or structure by showing the effects of

cyclic loading on the specimen. Such analysis can show the areas where crack propagation is most likely to

occur. Failure due to fatigue may also show the damage tolerance of the material.

Heat Transfer analysis models the conductivity or thermal fluid dynamics of the material or structure.

This may consist of a steady-state or transient transfer. Steady-state transfer refers to constant thermo

properties in the material that yield linear heat diffusion.



Material Properties

A part’s response is determined by the material properties assigned to the part.

• Depending on the application, material properties can be linear or nonlinear, as well as temperature-dependent.

• Linear material properties can be constant or temperature-dependent, and isotropic or orthotropic.

• Nonlinear material properties are usually tabular data, such as plasticity data (stress-strain curves for different

hardening laws), hyper elastic material data.

• To define temperature-dependent material properties, you must input data to define a property-versus-

temperature graph.

• Although you can define material properties separately for each analysis, you have the option of adding your

materials to a material library by using the Engineering Data application. This allows quick access to and re-

use of material data in multiple analyses.

In the present work, a typical Finite Element (FE) model of a wind turbine blade was developed and

modal were carried out using ANSYS. To simulate the behavior of the blade of FE model summary is given

below.

Number of elements = 34999

Number of nodes = 37522

ELEMENT TYPE =MESH 200

Figure 3.4 Geometry model imported into ansys 16.0 and after meshing

Figure 3.5 Total deformation of 30 0 grooved specimen with welding



Figure 3.6 Stresses of 30 0 grooved specimen with welding

Figure 3.7 Strain of 30 0 grooved specimen with welding





5. RESULTS AND DISCUSSION

The tensile strength of the joints was evaluated. The specimens were tested and the

Results were presented below

5.1. Tensile Strength of the Joint at Welding Time

Specimen

code

Inclination

Angle Joint design

Current

(amps)

Arc

Time(sec)

Welding speed

(mm/min)

A1 30 Single v 90 45 142.66

B1 30 Single v 110 40 152.26

A2 60 Single v 90 36 179.35

A3 45 Single v 90 30 193.56

B3 45 Single v 110 28 199.76

Table 4.1 Tensile strength of the joint at welding time

5.2. Effect of Welding Current on Ultimate Tensile Strength

Specimen

code

Inclination

Angle

Cross head

travel brake

(m)

Ultimate Tensile

Strength(N/mm2)

Percentage

Elongation

Percentage

reduction in

area

A1 30 7.10 31.94 2.63 15.97

B1 30 8.40 34.72 2.56 19.00

A2 60 6.40 47.78 2.63 15.97

A3 45 10.90 44.44 5.26 8.33

B3 45 7.40 29.44 2.63 15.97

Table 4.2 Effect of welding current on tensile strength



5.3. Effect of Welding Current and Joint Design on Ultimate Tensile Strength

From the values of UTS (ultimate tensile strength) obtained for joint design single V at 90amp, 100amp,

110amp etc. it is observed that 110amp weldment depicted maximum ultimate tensile strength when compare

to weldment of 90amp, 100amp and 120amp.Compartively the single V joint design depict maximum value

of ultimate tensile strength 47.78N/mm2.at 90 amp with 60 angle than. From the above analysis it was

observed that the single V joint has maximum tensile strength in comparison to other joint design of angles.

It was also observed that the tensile strength increases with increase in current up to 110 amp which was

optimum value to obtain maximum ultimate tensile strength in case of single V joint, it means that the rate

at which the welding electrode is melted, the amount of base metal melted, dilution, depth of fusion, the

deposition rates, the depth of penetration was good at this value and optimum weldability can be achieved

at joint design of single V current 110 amp, arc time 36sec, welding speed 149.35 mm/min.

5.4. Effect of Welding Current on Arc Time

It can be clearly seen from the table that the arc time is maximum in case of other angle V joint in comparison

to single V at 60. In single V joint most of the welding was done on one side of the weldment, only back

gouging is done after grinding at the back of the joint to completely fuse the edges.

5.6. Effect of Welding Current on Welding Speed

The welding speed is maximum in case of double V joint because welding speed depends upon the current

and the thickness of the material. From the above graph it can be observed that there is an increase in welding

speed with an increase in welding:

Graph 4.1 Current vs. weld speed

0

50

100

150

200

250

A1 B1 A2 A3 B3

Inclination

current

weld speed



Graph 4.2 Inclination vs. UTS

Graph 4.3 Current vs. UTS

6. CONCLUSION

• At the welding current of 90amp the tensile strength was maximum for single V joint design in comparison

with weld carried out of 100amp and 110amp. And also in comparison to other types of joint design, i.e.

double V and square butt joint, the ultimate tensile strength of single V joint design was maximum.

• With the increase in welding current which was taken as a variable parameter the ultimate tensile strength

47.78N/mm2, yield strength 340.23MPa and percentage elongation of 2.63 was recorded. Maximum/optimum

value of tensile strength of single V joint design was obtained when welding speed was 179.35mm/min.

• Hence it can be concluded that the ultimate tensile strength in case of the single V joint was maximum as a

result of correct fusion between weld metal and base metal, right joint design and edge preparation for this

type of material thickness.

• Also, it may be concluded that with the increase in welding current the UTS will increase until an optimum

value. The ansys value and experimental values are approximately same i.e. the single V joint design at 30

0

10

20

30

40

50

60

70

A1 B1 A2 A3 B3

inclination

% of area reduction

ultimate tensile strength

0

20

40

60

80

100

120

A1 B1 A2 A3 B3

current

% of area reduction

ultimate tensile strength



with 90 amp current, the max tensile strength is 47.78N/mm2 comparing to other angles and the code of

specimen is A2

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effect of welding current on welding … & 100 ampere by using mmaw process in 1g position. the...

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