See discussions, stats, and author profiles for this publication at: https://www.researchgate.net/publication/287195291
A REVIEW ON THE APPLICATION OF RESISTANCE SPOT WELDING OF
AUTOMOTIVE SHEETS
Article · January 2015
CITATIONS
READS
10
3,237
3 authors:
Sunusi Marwana Manladan
Ibrahim Abdullahi
Bayero University, Kano
Bayero University, Kano
43 PUBLICATIONS 554 CITATIONS
1 PUBLICATION 10 CITATIONS
SEE PROFILE
Mukhtar Fatihu Hamza
Bayero University, Kano
73 PUBLICATIONS 461 CITATIONS
SEE PROFILE
Some of the authors of this publication are also working on these related projects:
Laser Beam Welding of Dissimilar Metals View project
Hydrogen Induced Cracking View project
All content following this page was uploaded by Mukhtar Fatihu Hamza on 17 December 2015.
The user has requested enhancement of the downloaded file.
SEE PROFILE
ISSN : 1597-5835
Manladan, S.M et al /(JET) Journal of Engineering and Technology Vol. 10 (2) 2015 ,20-37
A REVIEW ON THE APPLICATION OF RESISTANCE SPOT WELDING OF AUTOMOTIVE
SHEETS
1
S. M. Manladan , I. Abdullahi2, M.F. Hamza3
1,2
Department of Mechanical Engineering, Bayero University, Kano
3
Department of Mechatronics Engineering, Bayero University, Kano
ABSTRACT
The automotive industry is now one of the most important sectors of all developed economies. It provides job
opportunities to many people at various levels of the economy. Resistance spot welding is the dominant welding
process in the automotive industry. The structural integrity of a vehicle depends largely on the quality of resistance
spot welds. The process is fast, effective and also complicated due to complex interactions between electrical,
mechanical, thermal and metallurgical processes. Due to increasing demand for improved fuel efficiency, reduced
CO2 emission and superior crashworthiness, significant effort is continuously being applied to develop lightweight
materials with excellent strength-ductility combination. This paper reviews automotive sheet materials and
mechanical performance of resistance spot welds in terms of weld nugget size, load bearing capacity and failure
mode, under quasi static loading conditions. It also reviews the effect of process parameters such as welding current,
welding time and electrode force on the mechanical performance of spot welds.
Keywords: Automotive sheets; resistance spot welds; weld nugget size; failure mode; mechanical properties.
INTRODUCTION
1.1 Fundamentals of Resistance Spot Welding
Resistance spot welding (RSW) is a welding process in
which two or more similar or dissimilar overlapping
metal sheets are placed between two water-cooled copper
alloy electrodes and large electrical current is passed
through them for a controlled period of time under
controlled pressure. The electrodes compress the base
metals together and the electrical resistance at the metals
interface causes a localized heating. When the flow of
current ceases, the electrode force is maintained while
the weld metal rapidly cools and solidifies. The cooling
.
www.bayerojet.com
20
is achieved by heat conduction via the two water-cooled
electrodes, which serve as efficient heat sinks, and also
radially outwards through the sheets. The weld is
normally formed in a fraction of a second and the
electrodes are retracted after each weld is formed
(Charde et al., 2014; Kocabekir et al., 2008; Liu et al.,
2010).
Figure 1 and Figure 2 show schematic diagrams for
resistance spot welding of two and three sheets
respectively
ISSN : 1597-5835
Manladan, S.M et al /(JET) Journal of Engineering and Technology Vol. 10 (2) 2015 ,20-37
Electrode force
Top electrode
To electric
current source
Top sheet
Bottom sheet
Bottom electrode
Electrode force
Figure 1: Schematic diagram for RSW of two sheets
Electrode force
Top electrode
Top sheet
Middle sheet
To electric power source
Bottom Sheet
Bottom electrode
Electrode force
Figure 2: Schematic diagram for RSW of three sheets
1.1.1 Heat Generation in RSW
current and time increases the heat input.
The heat generation in RSW is due to the resistance of
the parts being welded to the flow of a localised electric As shown in Figure 3, two types of resistances exist in
current, based on Joule’s law which can be expressed as RSW processes, namely, bulk resistance (R2 and R4) and
follows (Pouranvari & Marashi, 2013; Razmpoosh et al., contact resistance, which is found at the electrode-sheet
2015; Wang et al., 2007):
interfaces (R1 and R5) and at the faying interface (R3).
The total electrical resistance is due to these two
2
resistances. Both the contact resistance and bulk
Q = I Rt
--(1)
resistance are usually not constant. The contact resistance
Where: Q (joules) is heat, I (ampere) is welding current, is a strong function of both temperature and pressure.
R (ohms) is electrical resistance, t (seconds) is time of The bulk resistance is sensitive to temperature and
current application. Generally, increasing the welding independent of pressure (Zhang & Senkara, 2011)
www.bayerojet.com
21
ISSN : 1597-5835
Manladan, S.M et al /(JET) Journal of Engineering and Technology Vol. 10 (2) 2015 ,20-37
Figure 3: Illustration of the electrical resistances in a sheet stack-up during RSW(Zhang & Senkara, 2011)
1.1.2 RSW Process Parameters
The quality of the joint in RSW is influenced by the
welding parameters. These parameters mainly include
welding current, welding time, electrode force and
electrode geometry (Hongqiang et al., 2014).
1.2 Significance of RSW in Automotive Industry
RSW is the dominant metal sheet joining process in the
automotive industry because of minimum skill
requirements, inexpensive equipment, ease of control, its
versatility, high operating speeds, repeatability,
suitability for automation or robotization and inclusion in
high-production assembly lines. Moreover, the process
can be used to join most metals provided suitable
welding conditions are applied (Qiu et al., 2011; Vural &
Akkus, 2004).
Typically, there are about 2000–5000 spot welds in a
modern vehicle. The quality, structural performance,
durability, safety design, stiffness, strength and integrity
of a vehicle depend not only on the mechanical
properties of the sheets, but also on the quality of
resistance spot welds (Alizadeh-Sh et al., 2014; Dancette
et
al.,
2011;
Zhang
et
al.,
2014).
2. AUTOMOTIVE SHEET MATERIALS AND RESISTANCE SPOT WELDING
2.1
(Kuziak et al., 2008; Tamarelli, 2011). The main
materials used in automobile are as follows:
Automotive Sheet Materials
Materials selection is a key stage of vehicle design. As
the motivation to reduce the mass of vehicles continues
to grow, more attention is being given to materials
selection in the automotive industry(Pouranvari &
Marashi, 2013). Some of the properties required of
automotive materials are high strength-to-weight ratio,
toughness, formability, weldability, corrosion resistance,
fatigue resistance, crashworthiness and cost effectiveness
www.bayerojet.com
22
2.1.1 Mild Steel
Conventional mild steel has a relatively simple ferritic
microstructure; with low carbon content and minimal
alloying elements. Mild steels are inexpensive and have
relatively low strength with excellent formability. They
have long been used for many applications in vehicles,
including the body structure, closures, and other ancillary
parts
(Tamarelli,
2011)
ISSN : 1597-5835
Manladan, S.M et al /(JET) Journal of Engineering and Technology Vol. 10 (2) 2015 ,20-37
carbon content and no other additional interstitial solutes
2.1.2 Interstitial Free (IF)
IF is essentially a single phase bcc steel, with very low
(Hadzima et al., 2007). IF steels are extensively used for
manufacturing car bodies and other different parts (Dutta
& Ray, 2013).
2.1.3 High-Strength Low-Alloy (HSLA)
High-strength low-alloy (HSLA) steels, also called
micro-alloyed steels, are carbon steels in which microalloying is done with small amounts of elements such as
Nb and V (Zhang et al., 2013). They are designed to
meet specific mechanical properties. They have better
mechanical performance and resistance to atmospheric
corrosion than conventional carbon steels. They possess
high strength and good toughness and are widely used in
automotive industry (Han et al., 2014; Zhang et al.,
2013).
2.1.4 Advanced High Strength Steels (AHSS)
Advanced high strength steels (AHSS) are a new
generation of steel grades developed to meet light weight
requirements without compromising passenger safety.
They possess an excellent combination of strength and
ductility. The high strength enables vehicle
manufacturers to realize weight reduction by using
thinner gages while the increased ductility enhances
crashworthiness and production of components with
more complex geometry. In the future, these steels are
expected to be the dominant structural steels in an
automobile, especially in body-in-white applications (Li
et al., 2015; Rossini et al., 2015). The main reasons for
the increased use of AHSSs include (Pouranvari &
Marashi, 2013) : (i) the reduction in passenger car weight
by the increased use of high strength thinner gauge sheet,
leading to reduced fuel consumption and emissions (ii)
the improvement of the passive safety of vehicles, which
leads to a better passenger safety by an improved
crashworthiness (iii) the strong competition from the
lightweight materials, in particular Al and Mg alloys, and
plastics.
www.bayerojet.com
23
AHSS can be divided into first generation, second
generation and third generation. The microstructure of
first generation AHSS is based on ferrite and they
include: Dual phase (DP), complex phase (CP),
martensitic (MS) and transformation-induced plasticity
(TRIP) steels. The microstructure of second generation
AHSS is based on austenite. Typical example of second
generation AHSS is twinning-induced plasticity (TWIP).
The third generation AHSS possess strength–ductility
combinations significantly better than first and second
generations. They are still being researched and they
have the potential of further reducing the mass of vehicle
and at the same time offer improved crash
worthiness(Pouranvari & Marashi, 2013; Tamarelli,
2011).
Dual phase (DP) steel
The microstructure of DP steel consists of a mixture of
ferrite phase and the martensitic phase. It is an ideal
material for automotive application due to its high tensile
strength (up to 1.2 GPa), ductility (10% or higher) and
toughness (Han et al., 2014; Koyama et al., 2014).
Complex Phase (CP) Steel
The microstructure of CP steels consists of a
ferrite/bainite matrix, containing bits of martensite,
retained austenite and pearlite. They have fine
microstructure and possess high strength, good wear
characteristics, fatigue strength, high energy absorption
and crash worthiness(Tamarelli, 2011).
Martensitic (MS) Steels
In these steels, the microstructure consists of martensitic
matrix with a small amount of very fine ferrite and/or
bainite phases. They have extremely high strength.
Although, they have low ductility, quenching and
tempering can be used to improve their ductility. They
ISSN : 1597-5835
Manladan, S.M et al /(JET) Journal of Engineering and Technology Vol. 10 (2) 2015 ,20-37
are used where high strength is critical, such as door
intrusion beams, rocker panel inners and reinforcements,
side sill and belt line reinforcements, springs and clips.
Transformation-Induced Plasticity (TRIP) Steels
TRIP steels possess a multi-phase microstructure of
retained austenite and finely dispersed bainite in a ferrite
matrix. The retained austenite is the most important
constituent. It is metastable and during deformation, it
undergoes a stress-induced transformation into
martensite, thus improving strength. TRIP steels possess
high strength, good ductility and formability (Khan et
al., 2008; Kuziak et al., 2008).
Figure 4 schematically illustrates the microstructures of
DP, TRIP, CP and MS steels.
Twinning Induced Plasticity (TWIP) Steels
TWIP steel is a new type of AHSS with high manganese
content (usually between 15 to 25 wt%), an austenitic
microstructure at room temperature and low stacking
fault energy (SFE). TWIP steels possess both high
strength and superior plasticity. During plastic
deformation, mechanical twins are formed. These
mechanical twins impede dislocation glide and localized
necking (dynamical Hall-Petch effect). The extraordinary
combination of high strength and ductility is due to high
strain hardening rate associated with the deformation
twinning phenomenon. Tensile strengths greater than
1000 MPa and elongation at fractures above 50% could
be obtained (Kim et al., 2015; Rossini et al., 2015; Spena
et al., 2014). The occurrence of TWIP effect depends
strongly on SFE. Generally, intense twinning occurs
during deformation when the SFE is between 20 to 45
MJ/m2. Automotive sheet components made with TWIP
steels are still under development (Spena et al., 2014) .
The industrial focus is now mainly on TWIP steels of FeMn-C-Al and Fe-Mn-Si-Al alloy systems. Figure 5
compares the strength-ductility combinations of various
automotive sheet materials.
www.bayerojet.com
24
2.1.5 Stainless Steels
Stainless steel has recently been identified as an ideal
candidate for car body structural applications. It offers
weight savings, enhanced crashworthiness, corrosion and
oxidation resistance and excellent manufacturability.
Under impact, it offers excellent energy absorption in
relation to strain rate. The next generation vehicle
programme demonstrated that stainless steels can be used
to reduce weight and to increase safety and sustainability
of the structural automotive systems. The main types of
stainless steels are: Austenitic, ferritic, martensitic and
duplex stainless steels. Stainless steels can be used in
door pillars
including A and B pillar reinforcement parts, bumper
beams, rollover bars, crash boxes, suspension/wheel
housings and sub frames(Alizadeh-Sh et al., 2015;
Pouranvari et al., 2015).
2.1.6 Aluminum Alloys
In recent years, there is a growing interest in the use of
aluminum alloys for automobile body structures, closures
and chassis. Aluminum alloys continue to attract
attention in the automotive industry due to their low
density (approximately one third that of steel), high
strength-to-weight ratio, excellent corrosion resistance,
ease of being recycled, excellent formability and good
crashworthiness. Aluminum alloys are expected to be
extensively used in the future to partially replace steel
that is primary construction material in an automobile
(Cui et al., 2014; Qiu et al., 2011; Zheng et al., 2015).
2.1.7 Magnesium Alloys
Magnesium has been described as a green engineering
material and one of the most promising material
categories in the twenty-first century. It possesses low
density, approximately one-fourth that of steel and twothirds that of aluminum (Palanivel et al., 2015), high
specific strength, high elastic modulus, strong ability to
withstand shock loads and hot formability. Other
remarkable properties which make magnesium an
ISSN : 1597-5835
Manladan, S.M et al /(JET) Journal of Engineering and Technology Vol. 10 (2) 2015 ,20-37
attractive structural material include excellent
electromagnetic interference shielding, high heat
dissipation capability, good castability, damping capacity
and recyclability(Zhao et al., 2015). In the future,
magnesium alloys are expected to replace steel and
aluminum alloys as the primary structural material in the
automotive and aerospace industry(Babu et al., 2012).
According to “Magnesium Vision 2020”, the average
magnesium content in an automobile could increase to as
much as 772kg by the year 2020(Cole, 2007).
Figure
4:
Schematic representation of first generation of AHSSs(Pouranvari & Marashi, 2013)
Figure 5: Relationship between the tensile strength and elongation in various automobile steels(Chen et al., 2013)
2.2 Resistance Spot Welding
2.2.1 Metallurgical Characteristics of Resistance Spot
Welds
The rapid heating and cooling cycles encountered in
www.bayerojet.com
25
RSW lead to the formation of temperature gradient
across the sheets assembly. Upon cooling, three distinct
zones can be identified, as shown in Plate 1: (i) Fusion
Zone (FZ) or weld nugget which experiences melting
and solidification and normally shows a cast structure.
ISSN : 1597-5835
Manladan, S.M et al /(JET) Journal of Engineering and Technology Vol. 10 (2) 2015 ,20-37
The Fusion zone size is controlled by heat input and it
determines bonding area of the joint
(ii) Heat Affected Zone (HAZ) which does not
experience
changes.
(iii)
melting
Base
but
undergoes
microstructural
Metal
(BM).
Plate 1: A typical macrostructure of resistance spot weld in a galvanized low carbon steel (Goodarzi et al., 2009)
Hardness variation could be observed across the sheets
assembly after welding. This variation depends on the
chemical composition, initial microstructure of the BM,
temperatures encountered and cooling rate. Figure 6
shows hardness profile for some resistance spot welded
AHSSs.
Figure 6: Hardness profile for resistance spot welded DP780, DP600 and 590R steels (Khan et al., 2008)
2.2.2. Resistance Spot Welding of Multiple Sheets
Resistance spot welding of multiple (three or more)
sheets is now inevitable in vehicle manufacturing and
other engineering fields. In the present manufacturing of
automobiles, resistance spot welding of three steel sheets
comes up to one third of total welded joints (Lei et al.,
2011; Shen et al., 2011).
One of the reasons for the need of multiple sheet welding
is the continuous attempt to reduce the weight of vehicles
in order to improve fuel efficiency and to reduce CO2
www.bayerojet.com
26
emission by developing new materials with higher
strength-to-weight ratio and better performance. Another
reason is design complexity. As the design of modern
automobile becomes more complex, multiple sheet
joining becomes inevitable (Choi et al., 2007; Ma &
Murakawa, 2010). Some of the complex structures in
which multiple sheet spot welding is applied include
front longitudinal rails, A, B, and C pillars, and the
bulkhead to inner wing and at cross-member intersection.
The multiple sheets welding leads to improvement of
design flexibility, lower cost and higher productivity
ISSN : 1597-5835
Manladan, S.M et al /(JET) Journal of Engineering and Technology Vol. 10 (2) 2015 ,20-37
compared to two sheet joining of automobile body panels
(Mori et al., 2014; Tavasolizadeh et al., 2011).
However, RSW of multiple sheets is very challenging.
Compared to two-sheet spot welding, joining three sheets
is significantly more complicated due to the addition of
extra interfaces. Welding current flow throughout the
joints is also complicated. The use of different material
combinations and different sheet thicknesses further
complicates the process (Nielsen et al., 2011). The weld
nugget quality has become a major concern. There is
insufficient growth of the weld nugget, which has a
detrimental effect on the crashworthiness of the vehicle.
Moreover, the failure mechanism of three-sheet
resistance spot welds is not well understood (Kang et al.,
2010; Pouranvari & Marashi, 2012c; Shen et al., 2011).
Despite the importance of multiple sheet spot welding,
reports in the literature dealing with their welding
behavior and mechanical behavior are limited.
Pouranvari and Marashi (2012c) investigated the failure
behavior of 1.25/1.25/1.25 mm three-sheet low carbon
steel resistance spot welds. It was found that fusion zone
size along sheet/sheet interface is the most important
controlling factor of peak load and energy absorption.
Kang et al. (2010) studied the fatigue characteristics of
spot welds for three equal thickness sheet stack-ups of a
Dual Phase (DP600) and mild steel. The results of the
www.bayerojet.com
27
study showed a scatter in the plot of the maximum
applied loads versus cycles to failure of spot welds and
this is attributed to the weld sizes and also the strength of
the base metal. Lei et al. (2011) built a two dimensional
finite element (FE) model for RSW process of mild steel
with three sheets assemblies. The temperature
distribution changes of the three sheets assemblies were
obtained and the thermal characteristics were analyzed.
The results of their work revealed that the highest
temperature starts at two faying surfaces between the
workpiece-workpiece symmetric to the centre of the
sheets. This was due to contact resistance and equal
thickness of the metal sheet used which differs from
temperature distribution of the assembly of two metal
sheets. Tavasolizadeh et al. (2011) studied the weld
nugget growth, mechanical performance and failure
behavior of three thickness low carbon steel resistance
spot welds. They concluded that increasing welding time
leads to increase in peak load and energy absorption of
the joints. Shen et al. (2011) developed a model to
predict the weld nugget formation process of resistance
spot welding of a sheet stack made of 0.6 mm thick
galvanized SAE1004, 1.8 mm thick galvanized SAE1004
and 1.4 mm thick galvanized dual-phase (DP600) steel.
The results of their work revealed that the model
underestimated the weld sizes in all interfaces.
ISSN : 1597-5835
Manladan, S.M et al /(JET) Journal of Engineering and Technology Vol. 10 (2) 2015 ,20-37
Figure 7: Specimen geometry for (a) CT, (b) TS and (c) CP tests (Pouranvari & Marashi, 2013)
2.2.3 Mechanical Properties of Resistance Spot Welds
In an automotive structure, spot welds experience both
shear loading due to the relative displacement or rotation
of the adjacent sheets and tensile loading due to the
separating forces applied between adjacent sheets in a
direction normal to the sheets (Rathbun et al., 2003).
2.2.4 Testing the Mechanical Performance of Resistance
Spot Welds
The mechanical performance of spot welds is normally
considered under quasi-static and dynamic loading
conditions. Tensile-shear (TS), cross-tension (CT) and
coach peel (CP) tests are examples of tests conducted
under quasi-static loading conditions. Impact and fatigue
tests are examples of tests conducted under dynamic
loading conditions (Pouranvari & Marashi, 2013).Figure
8 schematically illustrates sample geometry for TS, CT
and CP tests.
Due to simplicity in preparing samples for tensile–shear
(TS) test , it is widely used to determine the strength of
resistance spot welds (Babu et al., 2012). In this test,
load bearing capacity (peak load) and failure energy are
the two most important parameters used to describe the
performance of the joint. The peak load and failure
energy are extracted from the load–displacement curve
obtained from the test. (Pouranvari & Marashi, 2013).
Figure 8 shows a typical load–displacement curve
obtained
TS
test
Figure 8: Typical load displacement-curve obtained from TS test (Kianersi et al., 2014)
www.bayerojet.com
28
ISSN : 1597-5835
Manladan, S.M et al /(JET) Journal of Engineering and Technology Vol. 10 (2) 2015 ,20-37
2.2.5 Failure Mode of Resistance Spot Welds
Failure mode of resistance spot welds is a qualitative
measure of mechanical properties and an indicator of
their load-bearing capacity and energy absorption
capability. There are three types of failure mode:
Interfacial, partial interfacial and pull out failure mode
(Pouranvari & Marashi, 2012a; Zhang et al., 2014).
Figure 10 shows a schematic diagram of these failure
modes.
.
www.bayerojet.com
29
Interfacial Failure Mode (IF)
In this failure mode, the joint fails through the weld
nugget centerline and the fracture surface is relatively
smooth. Cracks usually initiate from a sharp notch and
then propagate through the weld nugget. IF mode is
accompanied by little plastic deformation and has a
detrimental effect on the crashworthiness of the vehicles
(Zhang et al., 2014). Plate 2 shows the surfaces of a
resistance spot weld in an austenitic stainless steel which
failed
in
IF
mode
ISSN : 1597-5835
Manladan, S.M et al /(JET) Journal of Engineering and Technology Vol. 10 (2) 2015 ,20-37
Figure 9: Schematic representation of three failure modes observed in tensile shear test: (a) interfacial, (b) partial
interfacial, and (c) pullout (Yao et al., 2014).
Plate 2: Interfacal failure mode resistance spot-welded metastable austenitic stainless steel (Liu et al. 2012)
Partial Interfacial Failure (PIF) Mode
As shown in Figure 10, in PIF mode a fraction of
the weld nugget is removed. The crack first
propagates in the weld nugget, then redirects
perpendicularly to the centerline towards one of
the sheets.
Pullout Failure (PF) Mode
PF occurs by withdrawal of the weld nugget
from one sheet, as shown in Figure 10 and
Figure 12. Fracture may initiate in the base metal
(BM), HAZ or HAZ/FZ, depending on the
metallurgical and geometrical characteristics of
the weld zone and the loading conditions. Spot
welds that fail by PF mode have higher peak
loads and energy absorption levels than those
that fail through IF or PIF failure modes. PF is
the most preferred failure mode and hence
process parameters should be adjusted so that the
pullout failure mode is established(Babu et al.,
2012; Pouranvari & Marashi, 2013)
The amount of force required to cause failure is
equal to the product of the strength of the
material and the failed area of cross section.
Based on this, the following equations were
derived to predict failure loads, FPO and FIF, for
pullout and interfacial failure modes,
respectively (Radakovic & Tumuluru, 2008):
𝐹𝑃𝑂 = 𝑘𝑃𝑂 . 𝜎𝑈𝑇 . 𝑑. 𝑡
--(2)
𝐹𝐼𝐹 = 𝑘𝐼𝐹 . 𝜎𝑈𝑇 . 𝑑 2
--(3)
where
𝑘𝑃𝑂 ~2.2 and 𝑘𝐼𝐹 ~0.6 𝑎𝑟𝑒 constants; 𝜎𝑈𝑇
is the ultimate tensile shear strength of the base
material, d is nugget diameter, t is the sheet
thickness.
2.2.6 Critical Weld Nugget Diameter (Fusion
Zone Size)
The weld nugget diameter controls the
mechanical performance and failure mode of
resistance spot weld. Small nugget diameter
often results in interfacial failure (IF) mode
while a large one normally leads to pullout
failure (PF) mode (Zhang et al., 2014)
The transition from IF mode to PF mode is
generally related to the increase in the size of the
FZ above a minimum value. The minimum FZ
size is a function of sheet thickness,
BM/HAZ/FZ material properties and loading
conditions (Dancette et al., 2011)
Plate 3: Pull out failure mode of resistance spot weld in dissimilar DP780 and DP600 steels (Zhang et al., 2014)
www.bayerojet.com
30
ISSN : 1597-5835
Manladan, S.M et al /(JET) Journal of Engineering and Technology Vol. 10 (2) 2015 ,20-37
A critical nugget size exists which determines the
transition from IF to PF modes.
Chao (2003) derived a relationship for critical
weld nugget size (DC) in the cross-tension (TS)
test:
Dc = 0.86
τ HAZ
2
3
K FZ
c
4
t3
---
(4)
Where t is the sheet thickness, τHAZ is the shear
strength of the HAZ and K FZ
is the fracture
c
toughness of the fusion zone.
For the tensile shear loading condition, Chao
(2003) proposed the following equation:
4
Dc = 3.41t 3
--(5)
Where t is the sheet thickness.
Pouranvari and Marashi (2012a) developed the
following equation to predict the critical FZ size
(FZs) required to ensure pullout failure mode
during the cross-tension test of AISI 304 spot
welds:
t ×H
FZs CT = 4t H FL
--(6)
FZ
Where t is sheet thickness, HFL and HFZ are
hardness of failure location and fusion zone
respectively.
2.2.7 Effect of Welding Parameters on
Mechanical Performance of Resistance Spot
Welds
parameter and it is essential for heat generation.
If the welding current is too small, the heat input
is inadequate to form the weld nugget and the
strength of the weld joints is low. If the welding
current is too large, expulsion occurs. Expulsion
refers to the drifting away or loss of molten
metal from the fusion zone (Zhang et al., 2014).
Figure 13 shows a defect-free and a surface in
which expulsion occurred.
Podržaj et al. (2006) observed that increasing
welding current generally indicated better weld
quality for resistance spot welded mild steel
sheets. However, very high welding currents lead
to expulsion and subsequent loss of mechanical
properties. Kianersi et al. (2014) optimized the
welding current and time in RSW of the
austenitic stainless steel sheets grade AISI
316L.The welding current was varied from 4kA
to 9kA, in steps of 1kA, at constant welding
time. As illustrated in Plate 4, it was observed
that increasing welding current lead to increase
in weld nugget diameter. Moreover, it was
observed that the load bearing capacity also
increased with increased welding current from
4kA to 8kA. However, it was noted that
increasing the current from 8kA to 9kA led to
reduction in load bearing capacity (Figure 7).
This was attributed to expulsion.
Effect of Welding Current
Welding current is the most important process
Plate 4: Spot welded specimens (a) at lower heat inputs (defectless), (b) at higher heat inputs (expulsion phenomenon)
(Razmpoosh et al., 2015)
www.bayerojet.com
31
ISSN : 1597-5835
Manladan, S.M et al /(JET) Journal of Engineering and Technology Vol. 10 (2) 2015 ,20-37
Figure 6: Variation of weld nugget diameter with welding current(Kianersi et al., 2014)
Figure 7: Variation of load bearing capacity with welding current(Kianersi et al., 2014)
Aslanlar et al. (2007) found that welding current
had a significant influence on tensile-shear and
tensile-peel failure behavior for galvanized
chromate steel sheets. Small weld nugget
diameters and lower tensile strengths were
obtained with small welding currents. Decrease
in load bearing capacity and nugget diameter
were observed by increasing the current above
10kA.
Similarly, Lang et al. (2008) investigated the
effect of welding parameters on the
microstructure and mechanical properties of
AZ31 magnesium alloy. The results showed that
increasing the welding time (1–16 cycles) and
welding current (15–23 kA) led to an increase in
nugget diameter and consequently joint strength.
It was, however, noted that welding currents
higher than 25kA resulted in excessive heat
generation, leading to metal expulsion and
consequently reduction in joint strength.
However, Moshayedi and Sattari-Far (2014)
noted that welding current has slight effect on
micro-properties of DP600 spot welds.
Expulsion and unsatisfactory partial interfacial
failure mode were observed at 12kA. The
experimental results were found to be in good
agreement with results predicted by finite
www.bayerojet.com
element modelling.
Effect of Welding Time
Welding time has a significant influence on the
mechanical performance of spot welded joint.
Increasing welding time leads to increase in heat
input and larger weld nugget diameter(Kocabekir
et al., 2008).
Tavasolizadeh et al. (2011) observed that, for
three thickness resistance spot welded low
carbon steel, increasing the welding time leads to
better weld nugget formation (Plate 5). This
leads to an increase in peak load and energy
absorption of the joint and transition of
interfacial failure mode to pullout failure mode,
primarily due to the enlargement of weld nugget
size along sheet/sheet interface. In another study,
however, it was noted that longer welding time
is required to ensure sufficient weld nugget
growth along the sheet/sheet interface of sheets
compared to the required time for nugget growth
along geometrical centre of the joint(Harlin et
al., 2003; Pouranvari & Marashi, 2012c).
Effect of Electrode Force
Electrode force influences the properties of
resistance spot welded joints (Qiu et al., 2010),
primarily because of its effects on contact
32
ISSN : 1597-5835
Manladan, S.M et al /(JET) Journal of Engineering and Technology Vol. 10 (2) 2015 ,20-37
resistance and contact area. Generally, increasing
the electrode force leads to reduction in the
contact resistance(Liu et al., 2010). Very high
electrode force could lead to severe indentation,
sheet separation and distortion (Liu et al., 2010).
On the other hand, very low electrode force
would result in high contact resistance, excessive
heat generation and consequently expulsion,
surface marking and poor joint quality (Liu et al.,
2010). Lang et al. (2008) investigated the effect
of electrode force on mechanical properties of
AZ31 magnesium alloy (in the range of 1.5– 4.5
kN) at a welding current and welding time of
23kA and 8 cycles, respectively. The results
showed that the electrode force had a manifest
effect on the weld nugget size and thus the
strength of the joint. Lowering the electrode
force within this range enhanced the weld nugget
diameter and improved the joint strength.
However, very low electrode force (1.5 kN)
caused expulsion.
Zhao et al. (2013) investigated the effects of
electrode force on microstructure and mechanical
behavior of the resistance spot welded DP600
joint. The results indicated that varying the
electrode force has effect on weld nugget sizes.
They noted that there is a critical electrode force
that gives maximum weld nugget size and best
mechanical properties. However, it was noted
that the electrode force has little effect on the
micro-hardness and martensite content of the
welded joint, although it alters the microstructure
and grain size.
Harlin et al. (2003) found that increasing the
electrode force from 2.1kN to 6kN leads to a
shift in the position of weld nugget formation
from sheet/sheet interface to the center of the
middle sheet in three thickness zinc-coated steel
resistance spot welds.
Plate 5: Macrostructure of weld nugget for spot weld made at welding time of a 0.18 s, b 0.22 s and c
3. ANALYSIS OF FINDINGS
Analysis of Findings
Vehicle
crashworthiness,
environmental
pollution and fuel economy are the major
concerns in the automotive industry. Vehicle
manufacturers are constantly under pressure to
improve fuel efficiency and thus reduce
greenhouse gas emissions. Therefore, a lot of
research efforts and investments are directed
towards developing lightweight materials with
excellent strength-ductility combination for the
automotive industry. Although conventional
mild steel is the least expensive of all the
automotive sheet materials, weight saving
requirements does not favour its use. AHSS
which
possess
high
strength-ductility
combination, especially DP and TWIP steels,
www.bayerojet.com
have great potential for vehicle weight reduction
and enhanced crashworthiness and should
therefore be used extensively in vehicle
manufacturing.
Light alloys, with superior specific strength,
excellent recyclability and other remarkable
properties, such as aluminum alloys and
especially magnesium alloys are ideal candidates
for next generation vehicles. However, due to
their low bulk resistivity and high thermal
conductivity, their RSW is significantly more
challenging than RSW of steels. Large welding
current and therefore electrode degradation,
porosity and formation of columnar dendritic
zones in the FZ and HZ are major concerns
during RSW of these alloys. Although RSW has
33
ISSN : 1597-5835
Manladan, S.M et al /(JET) Journal of Engineering and Technology Vol. 10 (2) 2015 ,20-37
been perfected to produce good quality joints in
steels, to successfully incorporate magnesium
and aluminum alloys into the automotive
structure, significant research efforts are required
to perfect the RSW of these alloys.
Cost effectiveness is also a major consideration
in vehicle construction. AHSS and other newly
developed light alloys, like magnesium alloys,
are more expensive than conventional mild steel.
Therefore, an effective strategy to improve
overall crashworthiness and fuel economy would
be the dissimilar welding of the various
automotive sheet materials to form hybrid
structures. For example, dissimilar joining of
AHSS to conventional mild steel or to
magnesium alloys.
3
Nugget diameter is the most critical factor that
determines the overall mechanical performance
and failure mode of spot welds. Large nugget
diameter leads to high strength and better energy
absorption. Resistance spot welding process
parameters such as welding current, welding
time and electrode force greatly influence the
weld nugget size, load bearing capacity, energy
absorption and transition from interfacial failure
mode to pullout failure of resistance spot welds.
For both similar and dissimilar materials
combination, the welding parameters should be
optimized to produce large nugget size and pull
out failure mode in order to ensure higher peak
load and energy absorption.
CONCLUSION
Significant progress has been made in
developing suitable materials for the automotive
industry. Materials with high strength to weight
ratio, improved formability and better
performance such as advanced high strength
steels, aluminum and magnesium alloys are
increasingly being used in the automotive
industry to offer weight savings, improved fuel
efficiency and passenger safety. However, among
the materials been used in automotive industry
.
TWIP has shown a very good ductility – strength
property.
Process parameters (welding current, welding
time and electrode force) are very important in
determining the quality of weld produced. The
process parameters of RSW should therefore be
optimized to get optimum nugget diameter size
to avoid interfacial failure and also to ensure
quality
REFERENCES
Alizadeh-Sh, M., Marashi, S., & Pouranvari, M.
(2014). Resistance spot welding of AISI 430
ferritic stainless steel: phase transformations and
mechanical properties. Materials & Design, Vol.
56, pp. 258-263.
Babu, N. K., Brauser, S., Rethmeier, M., &
Cross, C. (2012). Characterization of
microstructure and deformation behaviour of
resistance spot welded AZ31 magnesium alloy.
Materials Science and Engineering: A, Vol. 549,
pp. 149-156.
Alizadeh-Sh, M., Pouranvari, M., & Marashi, S.
(2015). Welding metallurgy of stainless steels
during resistance spot welding Part II-heat
affected zone and mechanical performance.
Science and Technology of welding and joining,
pp. 1-10.
Chao, Y. (2003). Failure mode of spot welds:
interfacial versus pullout. Science and
Technology of welding and joining, Vol. 82, pp.
133-137.
Aslanlar, S., Ogur, A., Ozsarac, U., Ilhan, E., &
Demir, Z. (2007). Effect of welding current on
mechanical properties of galvanized chromided
steel sheets in electrical resistance spot welding.
Materials & Design, Vol. 281, pp. 2-7.
Charde, N., Yusof, F., & Rajkumar, R. (2014).
Material characterizations of mild steels,
stainless steels, and both steel mixed joints under
resistance spot welding (2-mm sheets). The
International
Journal
of
Advanced
www.bayerojet.com
34
ISSN : 1597-5835
Manladan, S.M et al /(JET) Journal of Engineering and Technology Vol. 10 (2) 2015 ,20-37
Manufacturing Technology, Vol. 751-4, pp. 373384.
Chen, L., Zhao, Y., & Qin, X. (2013). Some
aspects of high manganese twinning-induced
plasticity (TWIP) steel, a review. Acta
Metallurgica Sinica (English Letters), Vol. 261,
pp. 1-15.
Choi, B. H., Joo, D. H., & Song, S. H. (2007).
Observation and prediction of fatigue behavior
of spot welded joints with triple thin steel plates
under tensile-shear loading. International journal
of fatigue, Vol. 294, pp. 620-627.
Cole, G. (2007). Magnesium vision 2020-a north
american automotive strategic vision for
magnesium. Paper presented at the IMA
Proceedings, pp. 13
Cui, L. H., Qiu, R. F., Shi, H. X., & Zhu, Y. M.
(2014). Resistance Spot Welding between
Copper Coated Steel and Aluminum Alloy.
Paper presented at the Applied Mechanics and
Materials, pp. 19-22
Dancette, S., Fabrègue, D., Massardier, V.,
Merlin, J., Dupuy, T., & Bouzekri, M. (2011).
Experimental and modeling investigation of the
failure resistance of advanced high strength
steels spot welds. Engineering Fracture
Mechanics, Vol. 7810, pp. 2259-2272.
Dutta, K., & Ray, K. (2013). Ratcheting strain in
interstitial free steel. Materials Science and
Engineering: A, Vol. 575, pp. 127-135.
Goodarzi, M., Marashi, S., & Pouranvari, M.
(2009). Dependence of overload performance on
weld attributes for resistance spot welded
galvanized low carbon steel. Journal of materials
processing technology, Vol. 2099, pp. 43794384.
Hadzima, B., Janeček, M., Estrin, Y., & Kim, H.
S. (2007). Microstructure and corrosion
properties of ultrafine-grained interstitial free
steel. Materials Science and Engineering: A, Vol.
4621, pp. 243-247.
www.bayerojet.com
Han, Q., Asgari, A., Hodgson, P. D., & Stanford,
N. (2014). Strain partitioning in dual-phase steels
containing tempered martensite. Materials
Science and Engineering: A, Vol. 611, pp. 90-99.
Harlin, N., Jones, T., & Parker, J. (2003). Weld
growth mechanism of resistance spot welds in
zinc coated steel. Journal of materials processing
technology, Vol. 143, pp. 448-453.
Kang, H.-T., Accorsi, I., Patel, B., & Pakalnins,
E. (2010). Fatigue performance of resistance spot
welds in three sheet stack-ups. Procedia
Engineering, Vol. 21, pp. 129-138.
Khan, M., Kuntz, M., Biro, E., & Zhou, Y.
(2008).
Microstructure
and
mechanical
properties of resistance spot welded advanced
high strength steels. Materials Transactions, Vol.
497, pp. 1629-1637.
Kianersi, D., Mostafaei, A., & Amadeh, A. A.
(2014). Resistance spot welding joints of AISI
316L austenitic stainless steel sheets: Phase
transformations, mechanical properties and
microstructure characterizations. Materials &
Design, Vol. 61, pp. 251-263.
Kim, J., Hong, S., Anjabin, N., Park, B., Kim, S.,
Chin, K., Lee, S., & Kim, H. (2015). Dynamic
strain aging of twinning-induced plasticity
(TWIP) steel in tensile testing and deep drawing.
Materials Science and Engineering: A, Vol. 633,
pp. 136-143.
Kocabekir, B., Kacar, R., Gündüz, S., & Hayat,
F. (2008). An effect of heat input, weld
atmosphere and weld cooling conditions on the
resistance spot weldability of 316L austenitic
stainless steel. Journal of materials processing
technology, Vol. 1951, pp. 327-335.
Koyama, M., Tasan, C. C., Akiyama, E.,
Tsuzaki, K., & Raabe, D. (2014). Hydrogenassisted decohesion and localized plasticity in
dual-phase steel. Acta Materialia, Vol. 70, pp.
174-187.
Kuziak, R., Kawalla, R., & Waengler, S. (2008).
Advanced high strength steels for automotive
industry. Archives of civil and mechanical
engineering, Vol. 82, pp. 103-117.
35
ISSN : 1597-5835
Manladan, S.M et al /(JET) Journal of Engineering and Technology Vol. 10 (2) 2015 ,20-37
Lang, B., Sun, D., Li, G., & Qin, X. (2008).
Effects of welding parameters on microstructure
and mechanical properties of resistance spot
welded magnesium alloy joints. Science and
Technology of Welding & joining, Vol. 138, pp.
698-704.
Lei, Z., Kang, H., & Liu, Y. (2011). Finite
element analysis for transient thermal
characteristics of resistance spot welding process
with three sheets assemblies. Procedia
Engineering, Vol. 16, pp. 622-631.
Li, D., Feng, Y., Song, S., Liu, Q., Bai, Q., Ren,
F., & Shangguan, F. (2015). Influences of silicon
on the work hardening behavior and hot
deformation behavior of Fe–25wt% Mn–(Si, Al)
TWIP steel. Journal of Alloys and Compounds,
Vol. 618, pp. 768-775.
Liu, L., Feng, J., & Zhou, Y. (2010). 18 Resistance spot welding of magnesium alloys. In
L. Liu (Ed.), Welding and Joining of Magnesium
Alloys: Woodhead Publishing, pp. 351-367e
Ma, N., & Murakawa, H. (2010). Numerical and
experimental study on nugget formation in
resistance spot welding for three pieces of high
strength steel sheets. Journal of materials
processing technology, Vol. 21014, pp. 20452052.
Mori, K., Abe, Y., & Kato, T. (2014). Self-pierce
riveting of multiple steel and aluminium alloy
sheets. Journal of materials processing
technology, Vol. 21410, pp. 2002-2008.
Moshayedi, H., & Sattari-Far, I. (2014).
Resistance spot welding and the effects of
welding time and current on residual stresses.
Journal of materials processing technology, Vol.
21411, pp. 2545-2552.
Palanivel, S., Nelaturu, P., Glass, B., & Mishra,
R. (2015). Friction stir additive manufacturing
for high structural performance through
microstructural control in an Mg based WE43
alloy. Materials & Design, Vol. 65, pp. 934-952.
www.bayerojet.com
Podržaj, P., Polajnar, I., Diaci, J., & Kariž, Z.
(2006). Influence of welding current shape on
expulsion and weld strength of resistance spot
welds. Science and Technology of Welding &
Joining, Vol. 113, pp. 250-254.
Pouranvari, M., Alizadeh-Sh, M., & Marashi, S.
(2015). Welding metallurgy of stainless steels
during resistance spot welding Part I: fusion
zone. Science and Technology of welding and
joining, pp. 1-4.
Pouranvari, M., & Marashi, S. (2012a). Failure
mode transition in AISI 304 resistance spot
welds. Welding Journal, Vol. 91, pp. 303-309.
Pouranvari, M., & Marashi, S. (2012c). Weld
nugget formation and mechanical properties of
three-sheet resistance spot welded low carbon
steel. Canadian Metallurgical Quarterly, Vol.
511, pp. 105-110.
Pouranvari, M., & Marashi, S. (2013). Critical
review of automotive steels spot welding:
process, structure and properties. Science and
Technology of welding and joining, Vol. 185,
pp. 361-403.
Qiu, R., Shi, H., Yu, H., Zhang, K., Tu, Y., &
Satonaka, S. (2010). Effects of electrode force on
the characteristic of magnesium alloy joint
welded by resistance spot welding with cover
plates. Materials and Manufacturing Processes,
Vol. 2511, pp. 1304-1308.
Qiu, R., Zhang, Z., Zhang, K., Shi, H., & Ding,
G. (2011). Influence of welding parameters on
the tensile shear strength of aluminum alloy joint
welded by resistance spot welding. Journal of
Materials Engineering and Performance, Vol.
203, pp. 355-358.
Radakovic, D., & Tumuluru, M. (2008).
Predicting resistance spot weld failure modes in
shear tension tests of advanced high-strength
automotive steels. Welding Journal, Vol. 874,
pp. 96.
Rathbun, R. W., Matlock, D., & Speer, J. (2003).
Fatigue behavior of spot welded high-strength
36
ISSN : 1597-5835
Manladan, S.M et al /(JET) Journal of Engineering and Technology Vol. 10 (2) 2015 ,20-37
sheet steels. Welding Journal, Vol. 828, pp. 207218.
Razmpoosh,
M.,
Shamanian,
M.,
&
Esmailzadeh, M. (2015). The microstructural
evolution and mechanical properties of resistance
spot welded Fe–31Mn–3Al–3Si TWIP steel.
Materials & Design, Vol. 67, pp. 571-576.
Rossini, M., Spena, P. R., Cortese, L., Matteis,
P., & Firrao, D. (2015). Investigation on
dissimilar laser welding of advanced High
strength steel sheets for the automotive industry.
Materials Science and Engineering: A.
Shen, J., Zhang, Y., Lai, X., & Wang, P. (2011).
Modeling of resistance spot welding of multiple
stacks of steel sheets. Materials & Design, Vol.
322, pp. 550-560.
Spena, P. R., D’Aiuto, F., Matteis, P., &
Scavino, G. (2014). Dissimilar Arc Welding of
Advanced High-Strength Car-Body Steel Sheets.
Journal of Materials Engineering and
Performance, Vol. 2311, pp. 3949-3956.
Tamarelli, C. (2011). AHSS 101: the evolving
use of advanced high strength steels for
automotive
applications.
Steel
Market
Development
Institute
(AUTOSTEEL),
Washington, DC, USA.
Tavasolizadeh, A., Marashi, S., & Pouranvari,
M. (2011). Mechanical performance of three
thickness resistance spot welded low carbon
steel. Materials Science and Technology, Vol.
271, pp. 219-224.
Vural, M., & Akkus, A. (2004). On the
resistance spot weldability of galvanized
interstitial free steel sheets with austenitic
stainless steel sheets. Journal of materials
processing technology, Vol. 153, pp. 1-6.
tensile shear load in resistance spot welded joints
of AZ31 Mg alloy. Science and Technology of
Welding & joining, Vol. 128, pp. 671-676.
Yao, Q., Luo, Z., Li, Y., Yan, F., & Duan, R.
(2014). Effect of electromagnetic stirring on the
microstructures and mechanical properties of
magnesium alloy resistance spot weld. Materials
& Design, Vol. 63, pp. 200-207.
Zhang, C., Hu, X., Lu, P., & Zhang, G. (2013).
Tensile overload-induced plastic deformation
and fatigue behavior in weld-repaired highstrength low-alloy steel. Journal of materials
processing technology, Vol. 21311, pp. 20052014.
Zhang, H., Qiu, X., Xing, F., Bai, J., & Chen, J.
(2014). Failure analysis of dissimilar thickness
resistance spot welded joints in dual-phase steels
during tensile shear test. Materials & Design,
Vol. 55, pp. 366-372.
Zhang, H., & Senkara, J. (2011). Resistance
welding: fundamentals and applications: CRC
press.
Zhao, D., Wang, Y., Zhang, L., & Zhang, P.
(2013). Effects of electrode force on
microstructure and mechanical behavior of the
resistance spot welded DP600 joint. Materials &
Design, Vol. 50, pp. 72-77.
Zhao, Y., Lu, Z., Yan, K., & Huang, L. (2015).
Microstructural characterizations and mechanical
properties in underwater friction stir welding of
aluminum and magnesium dissimilar alloys.
Materials & Design, Vol. 65, pp. 675-681.
Zheng, R., Lin, J., Wang, P.-C., Zhu, C., & Wu,
Y. (2015). Effect of adhesive characteristics on
static strength of adhesive-bonded aluminum
alloys. International Journal of Adhesion and
Adhesives, Vol. 57, pp. 85-94.
Wang, Y., Mo, Z., Feng, J., & Zhang, Z. (2007).
Effect of welding time on microstructure and
www.bayerojet.com
View publication stats
37