Recent advances in the quantitative understanding of friction stir welding
Friction stir welding (FSW) is a relatively new welding process and its comprehensive understanding is still developing. While the process is commercially used for aluminum and other soft alloys, its commercial application for the welding of hard alloys will require development of cost-effective a...
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De, A. DebRoy, T. 2016-06-14T17:52:15Z 2016-06-14T17:52:15Z 2013 Recent advances in the quantitative understanding of friction stir welding / A. De, T. DebRoy // Автоматическая сварка. — 2013. — № 10-11 (726). — С. 43-47. — Бібліогр.: 22 назв. — англ. https://nasplib.isofts.kiev.ua/handle/123456789/103215 621.791.14 Friction stir welding (FSW) is a relatively new welding process and its comprehensive understanding is still developing. While the process is commercially used for aluminum and other soft alloys, its commercial application for the welding of hard alloys will require development of cost-effective and durable tools. Here we review the recent progress made in numerical modeling heat transfer and material flow with particular emphasis on optimizing tool dimensions and selection of welding conditions for maximizing tool durability. en Інститут електрозварювання ім. Є.О. Патона НАН України Автоматическая сварка Пленарные доклады Международной конференции Recent advances in the quantitative understanding of friction stir welding Последние достижения в сварке трением с перемешиванием Article published earlier |
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Recent advances in the quantitative understanding of friction stir welding De, A. DebRoy, T. Пленарные доклады Международной конференции |
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Recent advances in the quantitative understanding of friction stir welding |
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recent advances in the quantitative understanding of friction stir welding |
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De, A. DebRoy, T. |
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De, A. DebRoy, T. |
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Пленарные доклады Международной конференции |
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Friction stir welding (FSW) is a relatively new welding process and its comprehensive understanding is still developing. While
the process is commercially used for aluminum and other soft alloys, its commercial application for the welding of hard alloys
will require development of cost-effective and durable tools. Here we review the recent progress made in numerical modeling
heat transfer and material flow with particular emphasis on optimizing tool dimensions and selection of welding conditions for
maximizing tool durability.
|
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https://nasplib.isofts.kiev.ua/handle/123456789/103215 |
| citation_txt |
Recent advances in the quantitative understanding of friction stir welding / A. De, T. DebRoy // Автоматическая сварка. — 2013. — № 10-11 (726). — С. 43-47. — Бібліогр.: 22 назв. — англ. |
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AT dea recentadvancesinthequantitativeunderstandingoffrictionstirwelding AT debroyt recentadvancesinthequantitativeunderstandingoffrictionstirwelding AT dea posledniedostiženiâvsvarketreniemsperemešivaniem AT debroyt posledniedostiženiâvsvarketreniemsperemešivaniem |
| first_indexed |
2025-11-24T04:05:21Z |
| last_indexed |
2025-11-24T04:05:21Z |
| _version_ |
1850841309782212608 |
| fulltext |
4310-11/2013
UDC 621.791.14
RECENT ADVANCES IN THE QUANTITATIVE
UNDERSTANDING Of fRICTION STIR WELDING
A. De1 and T. DebRoy2
1 Indian Institute of Technology, Bombay, India
2 The Pennsylvania State University, University Park, USA. E-mail: amit@iitb.ac.in
friction stir welding (fSW) is a relatively new welding process and its comprehensive understanding is still developing. While
the process is commercially used for aluminum and other soft alloys, its commercial application for the welding of hard alloys
will require development of cost-effective and durable tools. Here we review the recent progress made in numerical modeling
heat transfer and material flow with particular emphasis on optimizing tool dimensions and selection of welding conditions for
maximizing tool durability. 22 Ref., 6 figures.
K e y w o r d s : friction stir welding, numerical modeling, heat transfer, material flow, welding conditions, tool durability
Introduction
In the last two decades, the applications of friction
stir welding (fSW) in aerospace, shipbuilding, trans-
portation and other industries have grown significant-
ly, particularly for the welding of aluminum and other
soft alloys [1–3].General reviews of the fSW process
are available in the literature [1–3].Because melting
of the parts is avoided, the process offers several im-
portant benefits compared to the conventional fusion
welding processes. As a result, there is considerable
commercial interest in the friction stir welding of
steels and other hard alloys [4–6]. The fSW process
involves several simultaneous physical phenomena
that affect the durability of the tool and the structure
and properties of the welded material. Heat is gener-
ated due to both the interfacial friction between the
tool and the work piece and the plastic deformation
of work piece material. The work piece material is
softened close to the tool and the plasticized material
flows due to rotation and the linear movement of the
tool.
fSW is a relatively new process, and because of
the complexity of the process a comprehensive under-
standing of the process is still evolving [7–13]. There-
fore, it is useful to undertake a review of the current
status of quantitative understanding of the process.
Here we review our recent research on numerical
modeling of heat transfer and material flow in fSW
and how it can be used for the solution of two impor-
tant contemporary problems. first, the application of
the heat transfer and material flow model to estimate
the optimum tool dimensions is discussed. Second,
we show that the model can be used to enhance lon-
gevity of the fSW tools, particularly for the welding
of hard alloys.
Optimum shoulder diameter
The diameter of the tool shoulder is important be-
cause the shoulder generates most of the heat, and its
grip on the plasticized material largely establishes the
material flow field [14, 15]. Both the heat generation
rate and the material flow are important for the fSW
process. With the increase in the shoulder diameter,
the temperature increases and the work piece mate-
rial is softened. for a good fSW practice, the mate-
rial should be adequately softened for flow, the tool
should have adequate grip on the plasticized material,
and the total torque and power should not be exces-
sive [15]. Experimental investigations have shown
that only a tool with an optimal shoulder diameter
results in the highest strength of the AA6061 fSW
joints [16]. Although the need to determine an opti-
mum shoulder diameter has been recognized in the
literature, the search for an appropriate principle for
the determination of an optimum shoulder diameter is
just beginning [14, 15].
We recently proposed [14, 15] a method to deter-
mine the optimal shoulder diameter for the fSW of
aluminum alloys by considering the sticking (MT) and
sliding (ML) components of torque. The main engine
for the calculations is a steady three dimensional heat
transfer and material flow model which was validat-
ed for friction stir welding of aluminum alloys, steels
and a titanium alloy [7, 8, 10]. The torques were cal-
culated based on the tool geometry, flow stresses in
work piece, and the axial pressure (PN) as [14, 15]
( )1T A
A
M r dA= × - δ t×∫
(1)
L A f N
A
M r P dA= × δµ ×∫
(2)
where rA is the distance of any infinitesimal area ele-
ment, dA, in work piece material from the tool axis, d
and mf are spatially variable fractional slip and coeffi-
cient of friction between the tool and the work piece,
respectively, and t is the shear stress at yielding. The © A. De, T. DebRoy, 2013
44 10-11/2013
tool rotation speed and the radial distance from tool
axis affect the local values of d and mf . The total
torque, M is the sum of sticking and sliding torques.
The required spindle power (P) can be calculated
from the total torque as [14]:
( ){ }1 f N A
A
P P r dA= - δ t + δµ ω∫ (3)
where w refers to the angular speed in rad/s.
figure 1 shows that for the fSW of AA6061, the
sliding torque continuously increases with shoulder
diameter because of the larger tool-work piece inter-
facial area. However, the sticking torque increases,
reaches a maximum and then decreases. This behav-
ior can be understood from equation (1) that includes
the two important factors that affect the sticking
torque. first, with the increase in shoulder diameter-
the area, A, increases, the temperature rises and the
shear stress at yielding, t, decreases. The product of
these two opposing factors lead to a maximum value
of sticking torque in the plot of sticking torque versus
shoulder diameter. This value of sticking torque indi-
cates the maximum grip of the shoulder on the plas-
ticized material [14, 15]. The calculated results show
that any further increase in the shoulder diameter will
result in decreased grip of the tool on the plasticized
material, higher total torque and higher spindle power
requirement. for these reasons, the optimum shoulder
diameter should correspond to the maximum sticking
torque for a given set of welding parameters and work
piece material [14, 15].
figure 2 shows the variation of sticking torque
with shoulder diameter for various tool rotational
speeds for the fSW of 7075 aluminum alloy. The
shoulder diameter at which the maximum sticking
torque is attained depends on tool rotational speed-
whenall other welding variables aremaintained con-
stant. for the rotational speeds indicated in the fig-
ure, the optimum values of the shoulder diameter are
in the 20 to 30 mm range for the various parameters
used in the experiments. Since the 7075 alloy is hard-
er than the 6061 aluminum alloy, the computed larg-
er optimum shoulder diameters compared with those
estimated for the fSW of 6061 is consistent with the
larger heat demand for the fSW of 7075 alloy. The
results show that the principle of optimizing shoulder
diameter by maximizing tool’s grip on the plasticized
material can be applied to different alloys. Since tool
durability and cost-effectiveness are crucial issues for
successful commercial application of fSW to steels
and other hard alloys, a general principle for the opti-
mum design of shoulder diameter based on scientific
principle such as the one discussed here is important.
Pin geometry
Since tool pins often fail during welding of hard
alloys, a systematic investigation of the various tool
materials and their load-bearing abilities are impor-
tant [17]. In particular, the pin being the structural-
ly weakest section of the fSW tool, an estimation of
the load bearing ability of the tool pin is required for
efficient functioning of the fSW process. Although
some measurements and calculations of the forces on
the tool have been reported in the literature, a proce-
dure to calculate the load bearing ability of the tool
pins of different shapes is of interest [18, 19]. Such a
methodology has beendiscussedrecently based on the
calculation of maximum stresses experienced by the
tool pin resulting from a combination of torsion due
to torque and bending due to traverse force [18, 19].
figure 3(a) shows a schematic force distribution,
q(z), on a straight cylindrical tool pin in fSW. It can
be noted that the force distribution, q(z) would be in
adirection opposite to the welding direction. figure
3(b) depicts a transverse cross-section of the tool pin
along S-S in fig. 3(a). The bending moment (My) ex-
perienced at any point A on the tool pin profile can be
figure 1. Variation in sliding (ML), sticking (MT) and total
torques with shoulder diameter for fSW of 6 mm thick AA6061
at a tool rotational speed of 1200 rpm and welding speed of
1.25 mm/s [15]
figure 2. Variation of sticking (MT) torque with shoulder di-
ameter for fSW of 3.5 mm thick AA7075at a welding speed of
0.67 mm/s [14]
4510-11/2013
estimated as [18]:
1
( )
L
y
z
z q z dzΜ = ∫
(4)
where L is the length of pin, z1 is the distance of the
point A from the root of the pin, q(z) is the force on
an infinitesimal part, dz, of the pin at a distance (z+z1)
from the root of the pin. The normal stress due to
bending, sB, and the shear stress due to torsion, tT, and
also due to bending, tB, on any point A on the pin pro-
file can be estimated further as [18]:
y
B
yy
M x
I
s =
,
(5)
z
J
T
T
M r
t =
(6)
and
B
yy
VQ
I g
t =
(7)
where yyI and ZJ are the second moment and polar
moment of inertia for the pin structure, respectively,
yM and TM are the bending moment and sticking
torque, respectively, V is the shear force and Q is the
first moment of inertia of the section beyond chord
AB (in fig. 3b) about the neutral axis, x is the normal
distance between the neutral axis and the chord AB, r
is the pin radius and g is the length of the chord AB.
These components of stresses can be used to compute
the resultant maximum shear stress, tMAX,experienced
by the tool pin as [18]
( )
2
2 2
max sin ( cos )
2
B
B T T
s t = + t + t θ + t θ
.
(8)
It follows that tMAX times a safety factor, f, should
be lower than the shear strength of the tool material at
the prevailing working temperature to avoid prema-
ture shear failure of the tool pin in the operating range
of process parameters.The pin length depends on the
thickness of the work piece. The geometry of the pin
must be determined based on its load bearing ability,
i.e., the ability to withstand the maximum shear stress.
The traverse force on the pin increases with in-
crease in the pin length as shown in fig. 4. As the
plate thickness increases, pins of longer lengths are
required. A longer pin experiences higher resultant
maximum shear stress and a larger cross-sectional
area of the pin becomes necessary to avoid pin fail-
ure. However,as the pins of large diameters move for-
ward, plasticized alloys must fill up the void space
left behind by large pins. Any disruption of the flow
of plasticized material or a small reduction in tem-
perature will enhance the occurrence of defects such
as worm-holes.The traverse force on the tool can be
measured using a dynamometer, and the values can
be used to monitor defect formation during fSW be-
cause the large forces indicate sluggish material flow.
Thus, the lower limit for the tool pin diameter can be
prescribed from the calculation of the maximum shear
stress on the tool pin and the upper limit for the pin di-
ameter can be estimated considering the weld quality.
The load bearing abilities of pins with circular,
square and triangular cross-sections have been com-
pared19under similar welding conditions. for compar-
figure 3. (a) Schematic distribution of force on a typical straight cylindrical tool pin and (b) cross-section of pin profile along section
S-S.18
figure 4. A comparison of computed and corresponding estimat-
ed values of traverse force on tool pin in fSW of AA6061 at tool
rotational speed of 650 RPM, welding velocity of 3.33 mm/s and
pin diameter of 7.6 mm [18, 20]
46 10-11/2013
ison of the three cross-sections, the triangular cross
section is considered to be of equilateral shape and
thetriangular and the square cross-sections are con-
sidered to have dimensions that fit within the circular
pin profile. It is found that the lowest and the highest
values of the maximum shear stress are experienced
by the circular and the triangular pin cross-sections,
respectively. During one complete rotation, the tri-
angular pin cross-section experiences the largest fluc-
tuation of the maximum shear stressfollowed by the
square and the circular pin profiles. Figure 5 shows
the typical fluctuation of various stresses during rota-
tion expressed as a function of angle with the welding
direction. The large fluctuation of maximum shear
stress during rotation makes the triangular cross sec-
tion susceptible to fatigue failure.
Durabilityof FSW Tool
Since the tool pin is structurally the weakest sec-
tion of FSW tool, itsdegradation due to plastic defor-
mation or wear as well as its ability to withstand the
torsion and bending stresses are of significant con-
cern. A review of the currently used and potential tool
materials is available in the literature [17]. The mate-
rial to be used for FSW tool should be cost effective
and have high strength, hardness and good toughness,
and high melting and softening temperatures [17].
Furthermore, the geometry of the tool pin for a given
material should also be assessed for its low suscepti-
bility to premature failure for various values of FSW
variables. Recently, a tool durability factor has been
proposed that can indicate whether the thermo-me-
chanical environment experienced by a tool pin for a
given FSW condition is safe enough to avoid a prema-
ture shear fracture [21, 22]. The tool durability factor
does not consider vbration and other abrupt causes of
tool degradation. However, the progressive degrada-
tion of the tool pin may be minimized by focusing
on the relative severity of maximum shear stress it
experiences for various welding conditions. The tool
durability factor is defined as the ratio of the shear
strength of the tool material at the peak temperature
and the resultant maximum shear stress experienced
by the tool pin due to bending and torsion.
Figure 6 shows a typical tool durability mapfor
various tool shoulder radius and rotational speed for
the FSW AA7075 alloy. A comparison of the solid and
dashed lines in Fig. 6(a) shows how the tool durability
index or the factor of safety for the tool pin changes
with the change in plate thickness. During FSW of
thick plates, there is considerable decrease intempera-
ture away from the tool shoulder and the pin encoun-
Figure 5. Variation of fluctuating stress components — normal
stress for bending, σB, shear stress due to bending, τB, shear
stress due to torsion, τT, and the maximum shear stress, τmax for
one completerotation of the tool during FSW of AA7075-T6
usingtriangular pin profile [19]
Figure 6. Tool durability indices as function of shoulder radius and rotational speed in FSW of AA 7075 using a tool pin diameter of 4
mm and axial pressure of 18 MPa. (a) shows the effect of plate thickness with the solid and dashed lines referring to thinner (2.9 mm)
and thicker (5.7 mm) plates, respectively, at a welding speed of 1.0 mm/s, (b) shows the effect of welding speed with the solid and
dashed lines depicting the lower (1.0 mm/s) and higher (4.5 mm/s)speeds, respectively for a plate thickness of 2.9 mm [22]
4710-11/2013
terscooler and stronger workpiece material near the
lower part of the pin. As a result, tools encounter large
stresses during welding of thick plates and the tool
durability decreases with increase in plate thickness.
Similarly, a comparison of the solid and the dashed
lines in fig. 6(b) shows that an increase in welding
speed reduces the value of tool durability index. Sim-
ilarly an increase in the welding speed reduces the
rate of heat generation per unit length of weld result-
ing in relatively colder material around the tool pin.
As a result, the tool durability index decreases with
increase in welding speed.
Concluding remarks
Because fSW is a new and complex process, its
comprehensive understanding is still developing.
Unlike other welding processes, its existing
knowledge base cannot be relied upon for solving
important contemporary problems such as extending
its reach to harder materials such as steels and
titanium alloys. Well tested heat transfer and
material flow models provide a recourse to address
the important issues based on solid scientific
principles. The examples reviewed here show how
the quantitative understanding of heat transfer and
material flow offer new insights about optimizing tool
design. Both the optimization of shoulder diameter
and the consequences of alternative tool pin shapes
can be examined based on well tested numerical
models.In the past, the sophisticated numerical
models of heat transfer and materials flow in welding
have not been widely used in industry.In recent years,
the modeling results for fSW have been presented
as easy to use process maps,enabling practicing
engineers to select welding conditions based on
scientific principles to extend tool life. Apart from
revelingsignificant insight about the fSW process, the
numerical models of heat transfer and materials flow
can also providesignificant competitive technological
advantage.
1. Mishra, R.S., Ma, z.Y. (2005) friction stir welding and
processing. Mater. Sci. Eng. R, 50(1/2), 1–78.
2. Nandan, R., DebRoy, T., Bhadeshia, H.K.D.H. (2008) Recent
advances in friction-stir welding — process, weldment
structure and properties. Prog. Mater. Sci., 53(6), 980–1023.
3. Threadgill, P. L., Leonard, A. J., Shercliff, H. R. et al. (2009)
Withers: friction stir welding of aluminum alloys. Int. Mater.
Rev., 54(2), 49–93.
4. Bhadeshia, H.K.D.H., DebRoy, T. (2009) Critical assessment:
friction stir welding of steels. Sci. Technol. Weld. Joining,
14(3), 193–196.
5. DebRoy, T., Bhadeshia, H.K.D.H. (2010) friction stir
welding of dissimilar alloys — a perspective. Ibid., 15(4),
266–270.
6. Heideman, R., Johnson, C., Kou, S. (2010) Metallurgical
analysis of Al/Cu friction stir spot welding. Ibid., 15(7), 597–
604.
7. Nandan, R., Roy, G. G., DebRoy, T. (2006) Numerical
simulation of three-dimensional heat transfer and plastic flow
during friction stir welding. Metallurgical and Materials
Transact. A, 37A, 1247–1259.
8. Nandan, R., Roy, G. G., Lienert, T. J. et al. (2007) Three-
dimensional heat and material flow during friction stir
welding of mild steel. Acta Materialia, 55, 883–895.
9. Colegrove, P. A., Shercliff, H. R., zettler, R. (2007) A model
for predicting the heat generation and temperature in friction
stir welding from the material properties. Sci. Technol. Weld.
Joining, 12(4), 284–297.
10. Nandan, R., Lienert, T. J., DebRoy, T. (2008) Toward reliable
calculations of heat and plastic flow during friction stir
welding of Ti-6Al-4V alloy. Int. J. of Materials Research,
99(4), 434–444.
11. Arora, A., Nandan, R., Reynolds, A. P. et al. (2009) Torque,
power requirement and stir zone geometry in friction stir
welding through modeling and experiments. Scr. Mater., 60,
13–16.
12. Arora, A., zhang, z., De, A. et al. (2009) Strain and strain
rates during friction stir welding. Ibid., 61, 863–866.
13. Arora, A., DebRoy, T., Bhadeshia, H.K.D.H. (2011) Back
of the envelope calculations in friction stir welding —
velocities, peak temperature, torque, and hardness. Acta
Mater., 59(5), 2020–2028.
14. Mehta, M., Arora, A., De, A. et al. (2011) Tool geometry for
friction stir welding-optimum shoulder diameter. Metall.
Mater. Transact. A, 42A(9), 2716–2722.
15. Arora, A., De, A., DebRoy, T. (2011) Toward optimum
friction stir welding tool shoulder diameter. Scripta Mater.,
64(1), 9–12.
16. Elangovan, K., Balasubramanian, V. (2008) Influences of
tool pin profile and tool shoulder diameter on the formation
of friction stir processing zone in AA6061 aluminium alloy.
Mater. Des., 29(2), 362–373.
17. Rai, R., De, A., Bhadeshia, H.K.D.H. et al. (2011) Review:
friction stir welding tools. Sci. Technol. Weld. Joining, 16(4),
325–342.
18. Mehta, M., Arora, A., De, A. et al. (2012) Load bearing
capacity of tool pin during friction stir welding. Int. J. Adv.
Manuf. Technol., 61, 911–920.
19. Mehta, M., De, A., DebRoy, T. (2013) Probing load bearing
capacity of circular and non-circular tool pins in friction stir
welding. In: Proc. of 9th Int. Conf. on «Trends in Welding
Research» (Chicago, USA, June 04-08, 2012) 563–571.
20. Sorensen, C. D., Stahl, A. L. (2007) Experimental
measurement of load distribution on friction stir weld pin
tools. Metall. Mater. Transact. B, 38B, 451–459.
21. Manvatkar, V. D., Arora, A., De, A. et al. (2012) Neural
network models for peak temperature, torque, traverse force,
bending stress and maximum shear stress during friction stir
welding. Sci. Technol. Weld. Joining, 17(6), 460–466.
22. DebRoy, T., De, A., Bhadeshia, H.K.D.H. et al. (2012) Tool
durability maps for friction stir welding of an aluminum
alloy. Proc. of the Royal Society A, 468, 3552–3570.
Received 21.06.2013
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