resistance welding of austenitic stainless steels (aisi ... · pdf fileresistance welding of...

6
5 th International & 26 th All India Manufacturing Technology, Design and Research Conference (AIMTDR 2014) December 12 th -14 th , 2014, IIT Guwahati, Assam, India 302-1 Resistance Welding of Austenitic Stainless Steels (AISI 304 with AISI 316) A.B.Verma 1 *, S.U.Ghunage 2 , B.B.Ahuja 3 1* Shree Ramchandra College of Engineering, Pune,412207,[email protected] 2 College Of Engineering,Pune,411005,[email protected] 3 College Of Engineering,Pune,411005,[email protected] Abstract Resistance spot welding (RSW) has a very important role as a joining process in the automotive industry and a typical vehicle contains more than 3000 spot welds. The quality and strength of the spot welds are very important to the durability and safety design of the vehicles. The development of the new materials results constantly in the resistance spot welding tasks with new materials or combinations of them. The lack of experience with the new materials or combinations of them often results in the use of the welding parameters which are not optimal. A few common guideline values and weldability diagrams for spot welding of steels exist and most of the guidelines are for non stainless steels each spot welding is not performed on the same condition because of the alignment of sheets and electrodes as well as the surface condition. For that reason, a spot welding process needs the optimum process condition that can afford allowance in parametric values for good quality of welding. In this paper ASS 304 and ASS 316 is used and its tensile strength and hardness is studied by using Taguchi approach and ANOVA while microstructure is studied by Schaeffer diagram. Keywords: ANOVA, Austenitic stainless steel, Taguchi method. 1 Introduction Resistance spot welding (RSW) is widely used in sheet metal fabrication as an important joining process. It is a simple process that uses two copper electrodes to press the work sheets together and force high current to pass through it. In electric resistance spot welding, the overlapping work is positioned between the water- cooled electrodes and then the heat is obtained by passing a large electrical current for a short period of time. Resistance spot welding is a widely used joining process for fabricating sheet metal assemblies such as automobiles, truck cabins, rail vehicles and home applications due to its advantages in welding efficiency and suitability for automation. For example, a modern auto-body assembly needs 7000 to 12,000 spots of welding according to the size of a car, so the spot welding is an important process in auto-body assembly. Over the last few years, the weight of automobiles has increased considerably due to the addition of safety related items, such as impact resistance bumpers and door impact beams, emission control equipment and convenience items, such as air conditioning. At the same time fuel consumption has increased significantly primarily due to emission control equipment. Dissimilar metal welds are common in welded construction and their performance is often crucial to the function of the whole structure. Dissimilar metal welding involves the joining of two or more different metals or alloys. There are several types of dissimilar metal welds and the most common type is the joining of stainless steel to non stainless steel. In arc welding filler metal is typically used. However, in resistance spot welding, the use of filler metal is very rare. In resistance spot welding, the parameters which control the weld strength are the amount and duration of electric current, electrode force, the shape and material properties of electrode, the surface condition and alignment of sheets. Thus, the quality of weld strength in resistance spot welding process greatly affects overall quality of the entire welding structure. Vural et al. investigated the effect of nugget diameter on the fatigue strength of resistance spot welded joints of galvanized steel and austenitic stainless steel (AISI304) welded as lap joints. Bouyousfi et al. have studied the effect of spot welding process parameters (weld current, welding duration and applied load) on the mechanical properties and characteristics of the spot joints between two stainless steel sheets (304ASS) having the same thickness. Micro hardness and tensile test results have shown that the weld resistance is important and highly correlated to the value of the process parameters especially the applied load. The applied load is control factor of the mechanical characteristics of weld joint compared to the welding duration and the current intensity of welding. Esme has studied optimization of RSW process parameters for SAE 1010 steel using Taguchi method. Esme investigated that increasing welding current and electrode force are prime factors controlling the weld strength. He concluded that Taguchi method can be

Upload: vothuy

Post on 04-Feb-2018

215 views

Category:

Documents


0 download

TRANSCRIPT

Page 1: Resistance Welding of Austenitic Stainless Steels (AISI ... · PDF fileResistance Welding of Austenitic Stainless Steels (AISI 304 with AISI 316) 302-2 effectively used for optimization

5th International & 26th All India Manufacturing Technology, Design and Research Conference (AIMTDR 2014) December 12 th -14th, 2014,

IIT Guwahati, Assam, India

302-1

Resistance Welding of Austenitic Stainless Steels (AISI 304 with

AISI 316)

A.B.Verma1*, S.U.Ghunage2, B.B.Ahuja3

1*Shree Ramchandra College of Engineering, Pune,412207,[email protected] 2College Of Engineering,Pune,411005,[email protected] 3College Of Engineering,Pune,411005,[email protected]

Abstract

Resistance spot welding (RSW) has a very important role as a joining process in the automotive industry and a

typical vehicle contains more than 3000 spot welds. The quality and strength of the spot welds are very

important to the durability and safety design of the vehicles. The development of the new materials results

constantly in the resistance spot welding tasks with new materials or combinations of them. The lack of

experience with the new materials or combinations of them often results in the use of the welding parameters

which are not optimal. A few common guideline values and weldability diagrams for spot welding of steels exist

and most of the guidelines are for non stainless steels each spot welding is not performed on the same condition

because of the alignment of sheets and electrodes as well as the surface condition. For that reason, a spot

welding process needs the optimum process condition that can afford allowance in parametric values for good

quality of welding. In this paper ASS 304 and ASS 316 is used and its tensile strength and hardness is studied

by using Taguchi approach and ANOVA while microstructure is studied by Schaeffer diagram.

Keywords: ANOVA, Austenitic stainless steel, Taguchi method.

1 Introduction

Resistance spot welding (RSW) is widely used in

sheet metal fabrication as an important joining process.

It is a simple process that uses two copper electrodes to

press the work sheets together and force high current to

pass through it. In electric resistance spot welding, the

overlapping work is positioned between the water-

cooled electrodes and then the heat is obtained by

passing a large electrical current for a short period of

time. Resistance spot welding is a widely used joining

process for fabricating sheet metal assemblies such as

automobiles, truck cabins, rail vehicles and home

applications due to its advantages in welding efficiency

and suitability for automation. For example, a modern

auto-body assembly needs 7000 to 12,000 spots of

welding according to the size of a car, so the spot

welding is an important process in auto-body

assembly. Over the last few years, the weight of

automobiles has increased considerably due to the

addition of safety related items, such as impact

resistance bumpers and door impact beams, emission

control equipment and convenience items, such as air

conditioning. At the same time fuel consumption has

increased significantly primarily due to emission

control equipment.

Dissimilar metal welds are common in welded

construction and their performance is often crucial to

the function of the whole structure. Dissimilar metal

welding involves the joining of two or more different

metals or alloys. There are several types of dissimilar

metal welds and the most common type is the joining

of stainless steel to non stainless steel. In arc welding

filler metal is typically used. However, in resistance

spot welding, the use of filler metal is very rare. In

resistance spot welding, the parameters which

control the weld strength are the amount and duration

of electric current, electrode force, the shape and

material properties of electrode, the surface condition

and alignment of sheets. Thus, the quality of weld

strength in resistance spot welding process greatly

affects overall quality of the entire welding structure.

Vural et al. investigated the effect of nugget diameter

on the fatigue strength of resistance spot welded

joints of galvanized steel and austenitic stainless

steel (AISI304) welded as lap joints. Bouyousfi et al.

have studied the effect of spot welding process

parameters (weld current, welding duration and

applied load) on the mechanical properties and

characteristics of the spot joints between two

stainless steel sheets (304ASS) having the same

thickness. Micro hardness and tensile test results

have shown that the weld resistance is important and

highly correlated to the value of the process

parameters especially the applied load. The applied

load is control factor of the mechanical

characteristics of weld joint compared to the welding

duration and the current intensity of welding. Esme

has studied optimization of RSW process parameters

for SAE 1010 steel using Taguchi method. Esme

investigated that increasing welding current and

electrode force are prime factors controlling the weld

strength. He concluded that Taguchi method can be

Page 2: Resistance Welding of Austenitic Stainless Steels (AISI ... · PDF fileResistance Welding of Austenitic Stainless Steels (AISI 304 with AISI 316) 302-2 effectively used for optimization

Resistance Welding of Austenitic Stainless Steels (AISI 304 with AISI 316)

302-2

effectively used for optimization of spot welding

parameters. The development of the new materials

results constantly in the resistance spot welding tasks

with new materials or combinations of them. The level

of importance of the welding parameters on the tensile

shear strength is determined by using ANOVA. Based

on the ANOVA method, the highly effective

parameters on tensile shear strength were found as

welding current and electrode force, whereas electrode

diameter and welding time were less effective factors.

The results showed that welding current was about two

times more important than the second ranking factor

(electrode force) for controlling the tensile shear

strength. The lack of experience with the new materials

or combinations of them often results in the use of the

welding parameters, which are not optimal. A few

common guideline values and weldability diagrams for

spot welding of steels exist and most of the guidelines

are for non stainless steels. In general, an unlimited

number of weld metal compositions can be obtained in

the dissimilar metal welding, depending on the

combination of the base and filler metals and the

welding process. Dissimilar resistance spot welding is

of complex nature due to different thermal cycles

experienced with each metal.

2 Experimental procedure

In this study, different grades of austenitic

stainless steel sheets (AISI 304 and AISI 316) of 0.6

mm thickness were spot welded by KEJE spot welding

machine (TSP 30). Nominal chemical composition and

mechanical properties of the sheets are given in Table

1. The sheets were cut parallel to the rolling direction.

The dimension of sheet are 140 mm length (L), 40 mm

width (w) and 0.6 mm thick (t) (Figure 1). Overlap is

equal to width of the sheet as per AWS standard. Sheet

surfaces were chemically cleaned by acetone before

resistance spot welding to eliminate surface

contamination. The tests were carried out using a

current and time controlled electric resistance spot

welding machine. The electrodes material was

Chromium alloy with end diameter 5 mm. This

machine was equipped with a pneumatic pressure

system. Welding, squeezing and holding cycles were

manually selected.

Figure 1 Dimension of specimen

Three process parameters viz. Current, Electrode

Force and Weld cycles were selected as given in Table

2. The parameters which kept constant are electrode

Table 1 Chemical Composition

Wt % C Mn Si Ni Cr Mo

AISI

304 0.07 0.54 0.3 9.4 18.4 0

AISI

316 0.07 0.55 0.31 9.56 16.5 2.25

diameter and electrode material. Experiments were

conducted according to the test conditions specified

by the Taguchi L9 Orthogonal Array (OA). The

parameters used in the resistance spot welding of the

sheets are given in table 2.

Table 2 Taguchi orthogonal array

Tensile shear tests were carried out on a

electronic Tensometer (Model TM-ER3) having

20KN capacity with the tension speed of 20 mm/min.

For Micro-hardness measurement, Vickers

hardness measurement machine (Future-Tech FM-

700) was used under the 500g load acting over a

period of 10 sec. Microhardness measurements

across the weld nugget were performed on each

sample. The individual indents were made

horizontally along the weld line through HAZ and

the weld nugget. The distance between the indents in

the weld metal was 25 μm.

For metallographic examinations, the

specimens were cut mechanically using wire EDM

machine in the direction parallel to thickness and hot

mounted in bakelite. Grinding was carried bu using

rough and fine emery followed by polishing

operation. These specimens were etched in a

chemical solution of 15 ml HCl, 5 ml HF and 80 ml

water. Microstructures of the specimens were

examined using a Nikon Epiphot 200 type optical

microscope.

3 Results and Analysis

3.1 Tensile shear strength

Spot weld failure mode is a qualitative measure

of the weld quality. In the resistance spot weld

(RSW) failure occurs in two modes: interfacial and

Run

No.

Current

(KA)

Time

(Cycle)

Pressure

(kg/cm2)

1 5 5 2

2 5 6 2.2

3 5 7 2.5

4 6 5 2.2

5 6 6 2.5

6 6 7 2

7 7 5 2.5

8 7 6 2

9 7 7 2.2

Page 3: Resistance Welding of Austenitic Stainless Steels (AISI ... · PDF fileResistance Welding of Austenitic Stainless Steels (AISI 304 with AISI 316) 302-2 effectively used for optimization

5th International & 26th All India Manufacturing Technology, Design and Research Conference (AIMTDR 2014) December 12 th -14th, 2014,

IIT Guwahati, Assam, India

302-3

pullout. In the interfacial failure (IF) mode, failure

occurs via crack propagation through fusion zone. In

the pullout failure (PF) mode, failure occurs via nugget

withdrawal from one sheet. Pull out mode of failure of

the welded specimen was observed as shown in figure

2.

Figure 2 Pull out failure of welded specimen

The tensile-shear test is the most widely used test

for evaluating the spot weld mechanical behaviors in

static condition. Peak load, obtained from the tensile-

shear load displacement curve, describes mechanical

behavior of spot welds. The experimental results of

tensile shear strength are shown in the table 3.

Table 3 Tensile shear strength results

Run 304-304

(N)

316-316

(N)

304-316

(N)

1 4207.2 4050.29 4030.68

2 4060.13 3667.82 3373.61

3 3805.12 3559.94 3824.73

4 3932.61 4011.06 3618.78

5 3765.89 3579.56 3510.91

6 4011.06 3677.63 3942.41

7 4462.19 4197.4 4187.59

8 4276.01 4452.38 4305.27

9 4364.12 4540.82 4557.26

The experimental process involves the test

conditions to compartivley assess the mecahncial

behaviour of spot welded sheets of AISI304-AISI304,

AISI304-AISI316 and AISI304-AISI316. To analyse

the given results, Taguchi methodology and ANOVA

technique have been used. Taguchi recommends the

use of the Signal to Noise (S/N) ratio to measure the

quality characterstics deviating from the desired

values. The main principle of measuring quality is to

minimize the variability inthe products performance in

response to Noise factors while maximize the

variability in response to Signal factors. Noise

321

73.2

72.9

72.6

72.3

72.0

321

321

73.2

72.9

72.6

72.3

72.0

Current

Me

an

of S

N r

atio

s

Time

Pressure

Main Effects Plot for SN ratiosData Means

Signal-to-noise: Larger is better

Figure 3 S/N Ratio of AISI304- AISI304

321

13.0

12.5

12.0

11.5

321

321

13.0

12.5

12.0

11.5

A

Me

an

of S

N r

atio

s

B

C

Main Effects Plot for SN ratiosData Means

Signal-to-noise: Larger is better

Figure 4 S/N Ratio of AISI316- AISI316

321

72.8

72.4

72.0

71.6

71.2

321

321

72.8

72.4

72.0

71.6

71.2

Current

Me

an

of S

N r

atio

s

Time

Pressure

Main Effects Plot for SN ratiosData Means

Signal-to-noise: Larger is better

Figure 5 S/N Ratio of AISI304-AISI316

Page 4: Resistance Welding of Austenitic Stainless Steels (AISI ... · PDF fileResistance Welding of Austenitic Stainless Steels (AISI 304 with AISI 316) 302-2 effectively used for optimization

Resistance Welding of Austenitic Stainless Steels (AISI 304 with AISI 316)

302-4

factors are those that are not under control of the

operator of a product and the Signal factors are those

that are set or controlled by the operator of the product

to make use of its intended functions. Therefore, the

goal of quality imporovement effort can be given as to

maximize the Signal to Noise (S/N) ratio for the

product.

The results are converted into S/N ratios for

Taguchi analysis. The higher the better criterion has

been used to obtain the S/N ratios of the tensile

strength. The main effects of process parameters for

raw data and S/N data are plotted. The response curves

(main effects) are used for examining the parametric

effects on the response characteristics. The analysis of

variance (ANOVA) of raw data and S/N data is

performed to identify the significant parameters and to

quantify their effect on the response characteristics.

The most favorable conditions (optimal setting) of

process parameters in terms of mean response

characteristic are established by analyzing response

curves. The tensile strength result is as shown in table

3.

The summery of ANOVA results for AISI304-

AISI304, AISI316-AISI316 and AISI304- AISI 316

are as shown in table 4.

Table 4 Summary of ANOVA results

Parameters 304-304

(N)

316-316

(N)

304-316

(N)

R2 0.9912 0.9339 0.9501

F(current) 86.46 11.07 13.41

F(time) 5.08 0.79 3.6

F(pressure) 20.49 2.26 2.02

P(current) 0.011 0.083 0.069

P(time) 0.165 0.559 0.217

P(pressure) 0.047 0.307 0.331

As shown in above table, value of R2 is greater

than 0.8, therefore the model established by ANOVA

is acceptable. Also, F-estimated is greater than 3.44

(Ref: statistical tables). Therefore model is validated

and it concludes that all factors have significant effect

on Tensile strength.

3.1.1 Optimsation

The optimum conditions from Taguchi analysis

for spot welding of similar material AISI 304-AISI 304

and AISI 316- AISI 316 are is found to be current at

level 3 (7 KA), time at level at 1(5 cycles) and pressure

at level 1(2.2 Kg/cm2). However, for dissimilar grades

of austenitic stainless steels, AISI304 to AISI316, the

optimum conditions are found to be current at level 3

(7 KA), time at level at 3 (7 cycles) and pressure at

level 1(2.2 Kg/cm2).

From Table 5, 6 and 7, percentage contribution

(% C) of various parameters affecting the tensile shear

strength is clearly indicated. For welding of similar

Table 5 Results of ANOVA for Tensile Shear

Strength AISI304

Table 6 Results of ANOVA for Tensile Shear

Strength AISI316

Table 7 Results of ANOVA for Tensile Shear

Strength of AISI304 to AISI316

sheets (AISI304 to AISI304 and AISI316 to

AISI316), amongst the three factors chosen for the

study that governs tensile shear strength, current is

ranked first, pressure applied electrodes is ranked

second factor and weld time is ranked third factor.

However for the welding of dissimilar sheets of

austenitic stainless steels (AISI304 to AISI316),

current is most influencing factor having highest

contribution of 66.94 %, followed by weld time and

pressure applied having contributions 17.97 % and

10.10 % respectively. This may due to the reason

that more heat is required to cause sufficient solid-

molten pool of weld at the interface of AISI304 with

AISI316 and electrical resistivity of AISI316 is

comparatively more than AISI304. Therefore, more

amount of heat needs to be generated, which is

accomplished by passing current for more amount of

time. This results into more heat generation and

value of contact resistance decreases with increasing

values of temperatures. As AISI 316 has higher

hardness value than AISI304, it has higher contact

resistance at the constant welding force. It is also

observed that for a factor with a high percentage

contribution, a small variation may greatly influence

the output characteristics.

Source DF SS MS F P % C

Current 2 672748 336374 86.46 0.011 76.50

Time 2 39521 19760 5.08 0.165 4.49

Pressure 2 159411 79706 20.49 0.047 18.13

Error 2 7781 3891 - - 0.88

Total 8 879461 - - - 100

S = 62.3749 R-Sq = 99.12% R-Sq(adj) = 96.46%

Source DF SS MS F P % C

Current 2 833692 416846 11.07 0.083 73.24

Time 2 59393 29696 0.79 0.559 5.22

Pressure 2 169869 84935 2.26 0.307 14.92

Error 2 75295 37647 - - 6.61

Total 8 1138249 - - - 100

S = 194.029 R-Sq = 93.39% R-Sq(Adj) = 73.54 %

Source DF SS MS F P % C

Current 2 808489 404245 13.41 0.069 66.94

Time 2 217061 108530 3.6 0.217 17.97

Pressure 2 121971 60986 2.02 0.331 10.10

Error 2 60295 30148 - - 4.99

Total 8 1207817 - - - 100

S = 173.631 R-Sq = 95.01% R-Sq(adj) = 80.03%

Page 5: Resistance Welding of Austenitic Stainless Steels (AISI ... · PDF fileResistance Welding of Austenitic Stainless Steels (AISI 304 with AISI 316) 302-2 effectively used for optimization

5th International & 26th All India Manufacturing Technology, Design and Research Conference (AIMTDR 2014) December 12 th -14th, 2014,

IIT Guwahati, Assam, India

302-5

3.2 Micro-structure of dissimilar SS304/316 RSW

In any welding process, the properties and

performance of the weld are characterized by careful

examination of the microstructure. This in turn is

determined by the thermal cycle of the welding process

which can normally be varied by changing the welding

parameters. Therefore, selection of welding parameters

is crucial that gives best possible microstructure and

that allows welds to be made free from defects and

other undesirable features.

Microgrpah of a dissimilar resistance spot weld

between AISI304 and AISI316 is shown in fig. 6.

Three distinct structural zones are observed in the joint

region:

i) Fusion Zone (FZ) or weld nugget,

ii) Heat Affected Zone (HAZ), and

iii) Base Metal (BM).

Figure 6 Micrograph of AISI304- AISI316

From the micrograph, it is observed that the

welded joint is asymmetrical. The fusion zone size on

the AISI316 side is larger than the fusion zone on the

AISI304 side. On the basis of macrostructure analysis,

it can be stated that the higher the welding current for

the welding, the larger is the fusion zone.

According to Schaeffler diagram, a martensitic

structure is expected to form in the FZ, as confirmed

by the higher hardness of the FZ relative to the BMs.

An ellipse nugget was formed between two sheets, and

HAZ was found around the nugget. Microstructure of

fusion zone (FZ) was found fully austenitic. The

change in microstructure from FZ to BM depends on

the highest temperature reached at each region. The

final solidification structure consists of dendrite

morphology with directional solidification onward the

center. The changes during the solidification mode is

from planar to cellular, cellular to columnar dendrite,

and final equiaxed dendrite. Due to extreme high heat

inputs, some grain coarsening could be observed at

HAZ. The grain size in HAZ is clearly larger than that

of the BM. Since, the HAZ was heated to temperature

approaching the solidus temperature of the alloy; many

of the alloys that were present in the BM may dissolve

at this high temperature. This can led to a super

saturation of the austenite matrix during cooling.

3.2 Hardness Variation of dissimilar RSW sheets

As can be seen, the micro hardness of the FZ is

higher than the micro hardness of both BMs. In AISI

304, the increase in hardness in FZ was from a value

of 178 HV, measured in the base metal, to hardness

of 220 HV (measured in the weld metal). The

hardness measured in AISI 316 steel increased from

a value of 218 HV to a value of 220 HV. Weld FZ

microstructure of dissimilar ASS RSWs can be

predicted by constitution diagrams e.g., Schaeffler

diagram. It should be noted that the application of

this diagram might be inaccurate due to the very high

cooling rates of RSW process. The FZ microstructure

of dissimilar ASS RSWs depends on the chemical

composition of the BMs and the dilution (defined as

the carbon steel to the weld nugget volume ratio).

Dilution is controlled by welding parameters. In the

applied welding conditions the dilution was

measured as 40%.

Figure 7 Hardness variation of welded specimen

Conclusion:

In this study, the properties of resistance spot

welds of dissimilar steels have been studied.

Attempts were made to link a weld’s quality to its

attributes under tensile-shear testing. The influence

of the welding parameters on the weld metal size has

been evaluated. The use of Taguchi method provides

a systematic and effective means to deal with the

multivariable nature of characterizing a spot weld.

The findings can be summarized as follows:

1) Tensile shear strength for different grades of

Austenitic Stainless Steels (AISI304 to

AISI316) was found to be comparatively

more than compared with similar sheets

(AISI304 to AISI304 and AISI316 to

AISI316).

2) Weld current is major governing factor

affecting the tensile shear strength of the

resistance spot welded specimens. As the

weld current increases, size of weld nugget

also increases. This results into increased

values of tensile-shearing strength.

3) For dissimilar RSW between austenitic

stainless steels, asymmetric fusion zone was

obtained due to their different electrical

resistivity and coefficient of thermal

expansion.

Page 6: Resistance Welding of Austenitic Stainless Steels (AISI ... · PDF fileResistance Welding of Austenitic Stainless Steels (AISI 304 with AISI 316) 302-2 effectively used for optimization

Resistance Welding of Austenitic Stainless Steels (AISI 304 with AISI 316)

302-6

4) Hardness of the welded zone is greater than

the hardness of the unwelded zone for AISI

304 and AISI 316 joints, but for dissimilar

joint, there was marginal increase in hardness.

5) For the welding of dissimilar sheets of

austenitic stainless steels (AISI304 to

AISI316), current is most influencing factor

having highest contribution of 66.94 %,

followed by weld time and pressure applied

having contributions 17.97 % and 10.10 %

respectively.

References

Alenius, P. Pohjanne, M.Somervuori, and H. Hänninen

(2007), Exploring the Mechanical Properties of Spot

Welded Dissimilar Joints for Stainless and Galvanized

Steels, Welding Research Journal, pp.305–313.

Bouyousfi B. Sahraoui t., Guessasma S. and Chaouch

K.T. (2003), Effect of process parameter on physical

characteristic of spot weld joints, Materials and

Design, Vol. 28, pp. 414–419.

Hou et al. (2007), Finite element analysis for the

mechanical features of resistance spot welding process.

J Mater Process Technology, Vol. 185, pp. 160–165.

Huh H, Kang WJ. (1997), Electrothermal analysis of

electric resistance spot welding processes by a 3-D

finite element method, J Mater Process Technology,

Vol 63, pp. 672–677.

Mehdi Mansouri Hasan Abadi, Majid Pouranvari.

(2010), Correlation between macro/micro structure and

mechanical properties of dissimilar resistance spot

welds of AISI 304 austenitic stainless steel and AISI

1008 low carbon steel

Montgomery Douglas C. (2007), Design of

Experiments, 5th edition, Wiley, India.

Pouranvari M., P. Marashi, M. Goodarzi, (2008)

Failure mode of dissimilar resistance spot welds

between austenitic stainless and low carbon steels., J

Science and Technology Of Welding & Joining, Vol

15(7), pp. 625-631.

Esme (2009), Application of Taguchi method for the

optimization of resistance spot welding process. The

Arabian Journal for Science and Engineering. Vol.

34(28), pp. 519-528.

Vural M., Akkus A and Eryurek B. (2002), “Effect of

weld nugget diameter on the fatigue strength of the

resistance welds joints of different steel sheets”,

Journal of Materials Processing Technology, 176,

pp.127-132.