Effect of various process parameters on friction stir welded joint

IJRET: International Journal of Research in Engineering and Technology eISSN: 2319-1163 | pISSN: 2321-7308
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Volume: 02 Issue: 12 | Dec-2013, Available @ http://www.ijret.org 555
EFFECT OF VARIOUS PROCESS PARAMETERS ON FRICTION STIR
WELDED JOINT: A REVIEW
Shrikant G.Dalu1
, M. T. Shete2
1
M.Tech. student, Production Engineering, Govt. College of Engineering, Amravati, (M.S.) India.
2
Asst. Professor, Mechanical Engineering Department, Govt. College of Engineering, Amravati, (M.S.),India
dalushrikant1@gmail.com, mtshete@yahoo.com
Abstract
This paper is a review of research work in the last decade on friction stir welding. Research is going on to investigate the effect of
various process parameters on quality of the welded joint. In this study, the investigation is made on the effect of various process
parameters, such as tool rotational speed, traverse speed, axial force and tool geometry on the quality of the welded joint are
reviewed. Yield strength, ultimate strength, elongation, toughness, microstructure of the joint are evaluated and correlated with
received base material. To compare and validate experimental results, FEA model is the best way to study the quality of welded joint.
Keywords- Friction stir welding, tool rotation and transverse speed, axial force, tool geometry
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1. INTRODUCTION
Friction stir welding (FSW) is a material joining process. It is
a highly important and recently developed joining technology
that produces a solid phase bond. It is particularly appropriate
for the welding of high strength alloys. Its main characteristic
is to join material without reaching the fusion temperature. It
enables to weld almost all types of aluminium alloys, even the
one classified as non-weldable by fusion welding due to hot
cracking and poor solidification microstructure in the fusion
zone. FSW is considered to be the most significant
development in metal joining in a decade and is a ―green‖
technology due to its energy efficiency, environment
friendliness, and versatility. The key benefits of FSW are
summarized in Table 1[1].
Table 1 Key benefits of FSW are summarized below
Metallurgical benefits Environmental benefits
 Solid phase process.
 Low distortion of
work piece.
 Good dimensional
stability &
repeatability.
 No loss of alloying
elements.
 Fine microstructure
 Absence of cracking
 No shielding gas
required.
 No surface
cleaning
required.
 Eliminate
grinding wastes.
 Consumable
materials saving.
Friction stir welding process parameters and welded joint are
analysed by testing welded joint or modeling welding process
using FEA software‘s and simulating it. The FEA software,
such as WELDSOFT, ABACUS, Altair Hyperworks,
DEFORM-3D etc. are more user friendly to the designer such
that modifications of any data is easily done on seeing preview
of the simulated weld conditions. The accuracy of the result
depends upon the assumption made in constructing the model.
The results obtained from FEA simulation are verified by
running a confirmatory experiment [20].
2. FSW PROCESS
The working principle of Friction Stir Welding process is
shown in Fig. 1 The FSW process utilizes a rotating tool to
perform the welding process. The rotating tool consist of small
pin (probe) underneath a larger shoulder. The tool serves three
primary functions, that is, heating of the workpiece, movement
of material to produce the joint, and containment the hot metal
beneath the tool shoulder. In FSW, rotating shouldered tool
plunges into the joining point of plates and the heat is
originally developed from the friction between the welding
tool (including the shoulder and the probe) and the welded
material, which causes the welded material to soften at a
temperature less than its melting point. The tool shoulder
restricts softened material underneath the shoulder is further
leads to movement of material from the front of the pin to the
back of the pin by the rotational and transverse movements of
tool. It is expected that this process will inherently produce a
weld with less residual stress and distortion as compared to the
fusion welding methods, since no melting of the material
occurs during the welding [19].

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Fig. 1: Schematic of Friction Stir Welding.
3. WELDING PARAMETERS
FSW involves complex material movement and plastic
deformation. Welding parameters, Tool geometry and joint
design exert significant effect on the material flow pattern and
temperature distribution, thereby influencing the micro
structural evolution of material [1]. Therefore, welding speed,
the tool rotational speed, the tilt angle of the tool, tool material
and the tool design are the main independent variables that are
used to control the FSW process.
3.1 Tool Rotation
For FSW, two parameters are very important: tool rotation rate
(v, rpm) in clockwise or counter clockwise direction. The
motion of the tool generates frictional heat within the work
pieces, extruding the softened plasticized material around it
and forging the same in place so as to form a solid-state joint.
3.2 Transverse Speed
The welding speed depends on several factors, such as alloy
type, rotational speed, penetration depth, and joint type.
Higher tool rotation rates generate higher temperature because
of higher friction heating and result in more intense stirring
and mixing of material. During traversing, softened material
from the leading edge moves to the trailing edge due to the
tool rotation and the traverse movement of the tool, and this
transferred material, are solidify in the trailing edge of the tool
by the application of an axial force [1].
3.3 Tool Tilt Angle
In addition to the tool rotation rate and traverse speed, another
important process parameter is the angle of spindle or tool tilt
with respect to the workpiece surface. A suitable tilt of the
spindle towards trailing direction ensures that the shoulder of
the tool holds the stirred material by threaded pin and move
material efficiently from the front to the back of the pin. The
tool is usually characterized by a small tilt angle (θ), and as it
is inserted into the sheets, the blanks material undergoes to a
local backward extrusion process up to the tool shoulder.
Further, the plunge depth of pin into the work pieces (also
called target depth) is important for producing sound welds
with smooth tool shoulders [1].
3.4 Tool Design
In order to determine the optimum tool geometry, the two
components of the torque are used for various shoulder
diameters. As the shoulder diameter increases, the sticking
torque, MT, increases, reaches a maximum and then
decreases. This behavior can be examined, which shows that
two main factors affect the value of the sticking torque. First,
the strength of the material is decreases with increasing
temperature due to an increase in the shoulder diameter.
Second, the area over which the torque is applied increases
with shoulder diameter [2].
A three-dimensional heat transfer and visco-plastic model is
used to compute the influence of pin length and diameter on
traverse force during FSW. The total traverse force increases
significantly with increase in pin length [3].
4. PARAMETRIC STUDY OF FSW
Many investigators have performed friction stir welding to
study the effect of various parameters on quality of friction stir
welded joint.
4.1 Aluminium
V. Balasubramanian, et al [4] investigates the effect of
welding speed and tool pin profile on friction stir processing
zone formation in AA2219 aluminium alloy. They found that
the square pin profile tool at a welding speed 45.6mm/min,
produced mechanically sound and metallurgically defect free
welds with maxium tensile strength, higher hardness.
Vivekanandan. P, et al [5] study microstructure and hardness
of aluminium 6035 and 8011. At the rotating speed 550rpm
and welding speed 60mm/min, the fine grain are formed at the
center of the weld, due to dynamic recrystallization, which
result in higher tensile strength of 50N/mm2 with the
maximum hardness of 91HV. M. Abbasi Gharacheh, et al
[6]found that increase in the ratio of rotational speed / traverse
speed results in formation of large weld nugget, because of
increase in heat input easier material flow, therefore
probability of formation of incomplete root penetration defect
is reduced. A. C. S. Kumar, et al [7]focus on optimization of
FSW parameters in different conditions of base material and
the microstructures of the as-welded condition are compared
with the post weld heat treated microstructures welded in
annealed and T6 condition. The result show that in annealed
condition tool rotation speed 800 rpm and welding speed 10
mm/min and 15 mm/min are the optimal parameters. The tool
rotation speed 1000 rpm and welding speed 10 mm/min are
the optimal parameters in ‗T6‘ condition. P. Cavaliere, et al
[8] study mechanical and microstructural properties of
AA6082 joints. The material welded with the advancing speed
of 115mm/min & fixed rotating speeds of 1600rpm exhibited

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the best fatigue properties and the higher fatigue limit. A.
Kumar, et al [9] find optimum mechanical properties of Al
6061-T6 alloy & Mg AZ31B alloy. The joint fabricated using
rotational speed of 1120 rpm, a welding speed of 40 mm/min,
taper thread pin profile, shoulder diameter of 18mm, (D/d)=3
shows higher tensile properties. S. Rajakumar, et al [10] study
tensile strength properties of AA7075-T6 joints produced by
friction stir welding. They found that the joint fabricated at a
tool rotational speed of 1400 rpm, welding speed of 60
mm/min, axial force of 8 kN, using the tool with 15 mm
shoulder diameter,5 mm pin diameter, 45 HRc tool hardness
yielded higher strength properties. Prashant Prakash, et al [11]
found that at rotational speed 1400rpm, welding speed 25
mm/min & pin length 5.7mm maximum tensile strength
obtained is 182MPa, gives 60% joint efficiency. Dr.Ayad M.
Takhakh, et al [12] optimum result gained at 80 mm/min weld
speed and 1500 rpm rotation speed, the efficiency reaches to
89% of the ultimate tensile strength of the alloy 3003 H13. P.
Bahemmat, et al [13] found that the joint is fabricated by four-
flute pin profile at rotational speed of 800rpm have
demonstrated 90% ultimate and yield strength and the tapered
screw thread joint fabricated at the rotational speed of 600rpm
show 84% ultimate strength in AA2024 aluminium. Patil H S,
et al [14] found that the joint fabricated using taper screw
thread pin at welding speed of 70mm/min exhibits superior
tensile strength of 92.30% of base metal ultimate strength and
% elongation of 27.58% in AA6082-0 aluminium.
4.1 High Density Polyethylene
Mustafa Kemal Bilici, et al [15] study the effects of welding
parameters on friction stir spot welding of HDPE sheets to
analyse the strength of the welds of HDPE sheets by means of
experimental techniques. Friction stir spot welding parameters
such as the tool rotation speed, tool plunge depth, plunge rate,
dwell time & tool geometry are found to affect significantly
the weld strength & weld nugget formation.Fabrizio Quadrini
et al[16] studied Friction stir welding of 3mm thick high
density polyethylene (HDPE) sheet with single pass. At high
rotational speeds, a higher amount of heat. Finally they
concluded that welding strength is depends on the optimized
temperature value in the range of 132-140°C. M. K. Bilici
investigate the effect of tool geometry on friction stir spot
welding of polyethylene sheets. They were obtained biggest
tensile strength with threaded tool for 4mm thick sheets with
7.5mm pin diameter, 15̊ pin angle, 5.5mm pin length , 30mm
shoulder diameter and 6̊ shoulder angle, pitch length 0.8mm
[17]. Amir Mostafapour et al They conclude that by utilizing
heat assisted friction stir welding, polyethylene sheets could
be joined with ultimate tensile strength of higher than 95% of
base material strength at welding speed of 25 mm/mim [18].
5. THERMAL EFFECTS ON FSW
Many researchers have developed friction stir welding model
in various analysis software for analyzing the thermal effect
produced in the FSW.C.M. Chen, et al [19] study the thermal
history & thermomechanical process using 3D FEA model.
Prediction & measurement shows that maximum temperature
in longitudinal & lateral direction are beyond shoulder edge.
Longitudinal residual stress is greater than lateral residual
stress. Binnur Gören Kıral et al [20] found that maximum
temperature increases as tool holding time & rotational speed
increases. Temperature decreases as welding speed increases
in aluminum alloys Al6061. Muhsin J. J, et al [21] found that
the maximum temperature measured during FSW at mid
position 629K & numerically value from the simulation is
642K, which is significantly less than the melting temperature
of 7020-T53 aluminum alloy at 916K. Numerical results
(Tmax = 642K) agreement with measured data (Tmax =
629K) in 5mm workpiece(AA 7020-T53) thickness. Abdul
Arif, et al [22] with dissimilar alloys (AA5086 & AA6061)
they found that longitudinal residual stresses are about 30-
45% transverse of the residual stresses. Values of temperature
& residual stresses by FEM are close to real temperature
distribution & residual stresse in weld construction. N.
Rajamanickam, et al [23]study the numerical simulation of
thermal history & residual stresses in friction stir welding of
Al 2014-T6. Difference of maximum temperature at same
location is less than 120K (2% error). Selvamani S.T, et al
[24]model is developed to study the temperature analysis of
tool geometry & material properties. Rotational speed & axial
force is constant & 0.75mm/sec welding speed yield strength,
ultimate strength, elongation & hardness test of Al6061 alloy
is more reliable on retreating side.
CONCLUSIONS
From the above review it is observed that –
 Tool rotation speed, traverse speed, axial force and
tool design are the most significant process
parameters in friction stir welding.
 Modeling of friction stir welded joint can be done
with various FEA software‘s such as WELDSOFT,
ABACUS, Altair Hyperworks, DEFORM-3D etc.
 Values of temperature and residual stresses by finite
element modeling are close to real temperature
distribution and residual stresses in experimental
construction of friction stir welding.
 Yield strength, ultimate strength, elongation and
hardness test are more reliable in both experimental
and proposed model.
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processing‖, Materials Science and Engineering, Vol.50,
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[2]. A. Arora , M. Mehta, A. De, T. DebRoy, ―Load bearing
capacity of tool pin during friction stir welding‖, Int J Adv
Manuf Technol, Vol.61, 2012, 911–920.

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Effect of various process parameters on friction stir welded joint

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