The Friction Stir welding process is now introduced in production plants. More and more applications are developed and the most part of the work is now centered on the mean of production to be used. Institut de Soudure and Arts et Métiers ParisTech are working on this subject since mid of 2005. The results of this work is a recognize knowledge on the methodology for qualifying a Friction Stir Welding Equipment [1]. In the same time, and based on this work, Institut de Soudure has bought a new kind of Friction Stir Welding machine based on a KUKA Robot

BIGOT, Régis

LANGLOIS, Laurent

LAYE, Julien

ZIMMER-CHEVRET, Sandra

English

The Friction Stir welding process is now introduced in production plants. More and more
applications are developed and the most part of the work is now centered on the mean of production to be used. Institut de Soudure and Arts et Métiers ParisTech are working on this subject since mid of 2005. The results of this work is a recognize knowledge on the methodology for qualifying a Friction Stir Welding Equipment [1]. In the same time, and based on this work, Institut de Soudure has bought a new kind of Friction Stir Welding machine based on a KUKA Robot

Name not available

Science Arts & Métiers (SAM)is an open access repository that collects the work of Arts et Métiers ParisTechresearchers and makes it freely available over the web where possible.This is an author-deposited version published in: http://sam.ensam.euHandle ID: .http://hdl.handle.net/10985/8776To cite this version :Sandra ZIMMER-CHEVRET, Julien LAYE, Laurent LANGLOIS, Régis BIGOT - Overview of themean of production used for FSW - In: INTERNATIONAL CONFERENCE ON SCIENTIFIC ANDTECHNICAL ADVANCES ON FRICTION STIR WELDING AND PROCESSING, France, 2010-01-27 - FSWP'2010 - 2010Any correspondence concerning this service should be sent to the repositoryAdministrator : archiveouverte@ensam.eu1 Overview of the mean of production used for FSW  S. Zimmer1, J. Laye2, L. Langlois1, R. Bigot1 1Arts et Métiers ParisTech Metz – LCFC, 4, Rue Augustin Fresnel, 57070 Metz, France  sandra.zimmer@ensam.eu, laurent.langlois@ensam.eu, regis.bigot@ensam.eu 2Institut de Soudure - FSW Center, 2-4 rue Pilâtre de Rozier, 57420 GOIN, France j.laye@institutdesoudure.com   Keywords: Friction Stir Welding, Industrialization, Friction Stir Welding Equipment  Abstract: The Friction Stir welding process is now introduced in production plants. More and more applications are developed and the most part of the work is now centered on the mean of production to be used. Institut de Soudure and Arts et Métiers ParisTech are working on this subject since mid of 2005. The results of this work is a recognize knowledge on the methodology for qualifying a Friction Stir Welding Equipment [1]. In the same time, and based on this work, Institut de Soudure has bought a new kind of Friction Stir Welding machine based on a KUKA Robot.  1. Introduction  The main advantages of friction stir welding (FSW) lie in the fact that it is a solid state welding process [2]. This particularity gives it the availability to weld almost all types of aluminum alloys, even the one classified as non-weldable by fusion welding due to hot cracking and poor solidification microstructure in the fusion zone [3]. To perform FSW, a non-consumable rotating tool, made up of a shoulder and a pin, is inserted into the interface of two workpieces rigidly clamped. Once the shoulder in contact with the surface’s workpieces, a constant down force is applied on the tool and is moved along the joint line, bounding the workpieces together. The thermo-mechanical tool/material interactions generate high forces during the welding operation [4] [5]. The welding equipment must be rigid enough to satisfy them [6]. Furthermore, the machine should be able to weld complex joint geometry to offer a wide range of applications. So, to produce industrial weld, special dedicated machine were developed. These kinds of equipments, as not standard, are generally expensive. Therefore, the industrials are reluctant to adopt this new technology.  The objective of this research work is the industrialization of the friction stir welding process in order to provide tools to industrials to select and qualify a machine for their FSW applications. The industrialization can be split into three aspects the analysis of the product, the process and the resources, these three entities being in interactions.   This paper presents a methodology to determine the Friction Stir Welding equipment adequate to an application. The adequate equipment can be every machine that can perform friction stir welds. Therefore, this paper presents a short review, based on literature survey, of the existing friction stir welding equipments.   2. The existing friction stir equipment  Today, the machine commonly used to perform FSW, industrially and in laboratories, are dedicated FSW machine, modified milling machine, serial and parallel kinematics robots.   a. Modified milling machine Milling and FSW machine have the same general characteristics [7], spindle rotation, travel speed and CNC control process necessary to perform FSW welds. They generally offer high stiffness and a good accuracy. The biggest disadvantage of most the milling machine is unavailability to propose a force controlled operation [5]. But, new milling machines technologies can offer a force controlled process.  2  b. FSW dedicated machine FSW dedicated machine allows a force control operation and generally the possibility to weld with the three tool technologies, conventional, retracting and bobbin tool. Each machine is designed to weld, 2- or 3-dimensional and has a predefined workspace. The main advantages of these machines are their high payload capacity due to high framework stiffness. They generally offer large workspace. The disadvantages of this kind of equipment is its high investments cost and the poor accessibility of the tool.   c. Parallel and serial kinematics robot FSW on Tricept 805 robot has been developed by GKSS research centre. This kind of machine is commonly used for high speed milling applications [8]. Tricept robots are characterized by high stiffness and to assure good position accuracy [6]. This kind of equipment possesses high investments costs and small workspace due to its design [9]. These two characteristics are major obstacles to widespread its industrial used for FSW.   Modern industrial serial robots (Figure 1) ensure flexibility, multidimensionality and lower investments cost than dedicated FSW machine [10]. They also possess a highly developed user interface for rapid programming [9]. Their disadvantage is their lack of force / load capacity due to their lack of stiffness [4] [10]. Therefore, to assure the robot welding capabilities and provide a wide range of applications, the robot must be a high payload robot [4]. Furthermore, the robot must be force controlled during the operation; its stiffness doesn’t allow a position control [11]. Furthermore, their lack of stiffness involves the deviation of the tool according to the seam [10] [12]. Despite these two disadvantages, the industrial robot seems to be a good FSW mean of production. The different publications on the robotic FSW, [4] to [10] show a real development improvement and a real potential for industrial applications. They appear to be a good compromise between complex weld geometry, range of applications, workspace and investments costs.    Figure 1: Serial kinematic robot for FSW application  3. Presentation of the developed methodology   The proposed methodology is based on a global and a local approach (see figure 2). The last one consists of an analysis of the FSW process. It corresponds to the determining of the value of the driving parameters of the FSW process in order to obtain a weld satisfying its functional specifications.    3 These parameters are: - The position and the orientation of the tool relative to the seam. Precisely, they correspond to the distance between tool axes and the seam and two angles determining the orientation of the tool relative to the vector normal of the work pieces and the vector tangent of the seam. - The rotation speed and the travel speed of the tool.  - The down force applied by the tool on the material.    In order to qualify a mean of production it is necessary to determine the tolerances associated to each parameter. Concerning the three main driving parameters, the admissible variations are defined by the process windows.  The tolerances concerning the position and the orientation of the tool relative to the weld seam are important characteristics for serial kinematics robots. These tolerances are also linked to the tolerances for the design of the workpiece work-holding device and the manufacturing of the workpieces to be welded. The tool/material mechanical interactions depend on the processing parameters. So, for parameters of process windows, it is necessary to associate the welding forces and torque generated during the whole welding operation. The description of the tool/workpiece mechanical interactions is discussed in the next part.   Write the FSW mean of production requirements(Machine, workpiece work-holding device) Tool material mechanical interactions determinationTorques and forces associated to each welding stageProcessing parametersdetermination and their tolerancesAnalyze of the caseTool technology and geometryMaterial and thicknessTool / workpiece kinematicsdeterminationSeam geometryTool path determination  Figure 2: Scheme of the methodology used to define the FSW means of production requirements  The global analyze of the welding operation consists in determining the geometry of the weld path. At each point of the seam a local reference frame RMi (Mi, ti, vi, ni) is defined (Figure 3). The vector ti is tangent to the seam line, L, and oriented according to the welding direction. The vector ni is normal to 4 the plane tangent to the workpiece welded surfaces. The third vector vi is chosen in order to form an orthonormal reference frame. The determination of the processing parameters and the weld seam allows the definition of the complete tool path (see figure 3).    Mi itrinrivrSurface formed by joining two piecesworkpiece interfaceMiSeam, LWorkpiece 1Workpiece 2Seam, LyrxrTool rotation axisωOzrFSW ProcessparametersTool pathdefinitionWeld seam definition Figure 3: Definition to the tool position and orientation at each location of the welding path   4. Description of the tool/workpieces mechanical interactions  Generally the FSW operation is described by two main stages, the plunge and the welding stages [13] and [14]. As the tool - workpiece interactions differ according to the welding stage, it is necessary to decompose the whole welding stages. So, the tool kinematics was analyzed leading to the decomposition of the welding stages into six independent sub-stages: plunging, dwell time, acceleration, welding at constant speed, deceleration and pin retracting. The figure 4 presents the tool kinematics and the corresponding stages during FSW.  Tool pentrationTime [s]PlungePenetration depthWelding atconstant speedDwell timeAccelerationDecelerationTool retractingWelding speed[rpm] [mm]Tool weldingspeedvtravelminmmRotational speedTool rotational speed Figure 4: Presentation of the tool kinematics during the welding stage  5 Former research works [1] showed that the analyses of the tool/workpiece mechanical interactions can be reduced to the analysis of the plunging and welding at constant speed stages for the qualification of a FSW means of production and the workpiece work-holding device. According [14] and [15], the plunging stage is characterized by a brief peak of the vertical effort, when the shoulder comes into contact with the surface. The “peak” intensity mainly depends on the penetration velocity [15]. The maximal torque and force are obtained almost simultaneously, at the end of the penetration. In the last 25% remaining penetration, probably when the shoulder touches material displaced upwards by the pin penetration, the curves of the torque and force grow more rapidly until they reach a “peak”. That maximum occurs at the end of the plunge, when the tool shoulder is completely in contact with the plate’s surfaces. The welding stage is force controlled; the down force Fz remains constant. After increasing during the acceleration stage, the travel force and transverse force seems to stabilize. The torque also stabilizes after a few seconds.  Figure 5 shows evolutions of the tool/workpiece mechanical interactions components for to applications.   -7-3159131721252933183 193 203 213 223 233 243 253 263 273 283 293 303 313 323 333 343Time [sec]Forces [kN]050100150200250Torque [Nm]Plunge Welding at constant speedDweel Time Acceleration DecelerationDecelerationFyFxCzFzForces and torque during the welding of a 6000 series aluminum alloy of thickness 5mmForces and torque during the welding of a 7000 series aluminum alloy of thickness 20mm-2-10123456789101112131433 35.5 38 40.5 43 45.5 48 50.5 53 55.5 58 60.5 63 65.5 68 70.5Time [sec]Foce [kN]0102030405060708090Torque [Nm]Plunge DweelltimeWelding at constant speedAcceleration DecelerationTool retractingFyFxCz, TorqueFz Figure 5: Forces and torque during the welding operation according to the time for different aluminium alloys and thicknesses  The mechanical interactions between the tool and the welded material can be represented by two set of force and torque corresponding to: - The maximum torque and force reached at the end of the plunge. - The “stabilized” torque and forces (down force, travel and transverse forces) reached during the welding stage.   6 This knowledge will permit to focus on these two stages processing parameters in order to reduce the forces and torque applied on the tool. Thus, it will enable the FSW on machine with load / rigidity weaknesses. On the other hand, another way to reduce the process forces is to work on the tool geometry [14].   5. Conclusion and perspectives  The presented work focuses on the definition of the functional specification for the choice and/or the design of a FSW machine and the work-holding device. In the case of the use of a low-stiffness machine like serial kinematics robot, the evaluation of the tolerances concerning the position and the orientation of the tool can be a very determinant factor.   Contrary to conventional welding fusion process (GMAW or Laser Welding) mechanical interactions between the tool and the material have to be taken into account. They have to be taken into account for the determination of the forces and torques the FSW machine must apply during the welding operation.   Moreover, thanks a machine stiffness model, it is possible to estimate the tool deviation from the seam in order to compare it to the one admissible by the welding process. It validates the feasibility of the welding operation. The presented methodology must also include the workpieces work-holding device. The applied methodology must be completed by the study of the tool accessibility on the seam and the workpieces assembly and disassembly from the work-holding device. This kind of methodology is commonly used in machining process.  The process windows can be restricted by: - The machines characteristics in terms of down force, rotational speed and travel speed.  - The tool deviation due to a lack of stiffness of the machine. - The machine workspace or its lack of accessibility.  For certain types of machine, like serial kinematics robot, the force capacities and the stiffness depend on the tool position inside the workspace. Then the process windows is not directly restricted by the seam accessibility but by the fact that it is not possible to keep the required stiffness throughout the welding path.   6. Acknowledgment  The authors would like to thank the Region Lorraine, the Moselle department and the French Government for their financial support.   7. References  [1] S. ZIMMER, L. LANGLOIS, J. LAYE, J-C. GOUSSAIN, P. MARTIN, R. BIGOT Methodology for qualifying a Friction Stir Welding equipment 7th International Symposium on Friction Stir Welding, May 2008  [2] W.M. THOMAS, E.D. NICHOLAS, J.C. NEEDHAM, M.G. MURCH, P. TEMPLEMITH, C.J. DAWES Patent Application No. 9125978.8 (December 1991)  [3] R.S MISHRA, Z.Y. MA Friction Stir Welding and processing Materials Sciences and Engineering R 50 (2005) I-78   7 [4] C.B. SMITH   Robotic Friction Stir Welding using a Standard Industrial Robot 2nd International FSW Symposium, June 2000  [5] D. EREINER Prozessmodelle zur statischen Auslegung von Anlagen für das Friction Stir Welding ISBN: 3-8316-0650-1 (September 2006)  [6] A. von STROMBECK, C. SCHILLING, J.F. DOS SANTOS Robotic Friction Stir Welding – Tool Technology and Applications 2nd International FSW Symposium, June 2000  [7] M. PONTE, J. ADAMOWSKI, C. GAMBARO, E. LERTORA Low-cost transformation of conventional milling machine into a simple FSW work station Advanced Manufacturing and Technology, CISM Courses and Lectures No.486, Springer Wien New York, 2005. ISBN: 10-3-211-26537-6 p.357-365 [8]  R. ZETTLER, S. LOMOLINO , J. F. DOS SANTOS, T. DONATH, F. BECKMANN, T. LIPPMAN, D. LOHWASSER A Study on Material Flow in FSW of AA 2024-T351 and AA 6056-T4 Alloys 5th International FSW Symposium, 2004  [9] M. SORON Towards Multidimensionality and Flexibility in Friction Stir Welding Using an Industrial Robot System Recent Advances in Friction Welding and Allied Processes, Dubrovnik, Croatia, 2007  [10] G; VOELLNER, F. ZAEH, J. SILVANUS, O. KELLENBERGER Robotic Friction Stir Welding AeroTech Congress & Exhibition, Los Angeles, California, September 17-20, 2007  [11]  R. CRAWFORD, G. E. COOK, A. M. STRAUSS Modelling of friction stir welding for robotic implementation Int. J. Modelling, Identification and Control, Vol. 1, No. 2, 2006  [12] G. VOELLNER 3-D FSW using a modified high payload robot 6th International FSW Symposium, 2006  [13]  S. SHEIKHI  Herstellung und Bewertung der Umformbarkeit von reibrührgeschweissten Tailored Blanks aus Aluminiumlegierungen Ph.D. Thesis –University of Duisburg-Essen - 2005  [14] M. F. ZAEHL, D. EITEINER, L. PAPADAKIS Friction Stir Welding with modern milling machines. Requirements, Approach and Application 5th International FSW Symposium, 2004  [15] A. SIMAR A multiscale multiphysics investigation of aluminium friction stir welds from thermal modelling to mechanical properties through precipitation evolution and hardening Ph.D. Thesis - UCL – 2006  

Overview of the mean of production used for FSW

SAM : Science Arts et Métiers

A multiscale multiphysics investigation of aluminium friction stir welds from thermal modelling to mechanical properties through precipitation evolution and hardening Ph.D. Thesis - UCL –

BIGOT Methodology for qualifying a Friction Stir Welding equipment th International Symposium on Friction Stir Welding,

Herstellung und Bewertung der Umformbarkeit von reibrührgeschweissten Tailored Blanks aus Aluminiumlegierungen Ph.D. Thesis –University of Duisburg-Essen -

KELLENBERGER Robotic Friction Stir Welding AeroTech Congress & Exhibition,

LERTORA Low-cost transformation of conventional milling machine into a simple FSW work station

MA Friction Stir Welding and processing

PAPADAKIS Friction Stir Welding with modern milling machines. Requirements, Approach and Application th International FSW Symposium,

Prozessmodelle zur statischen Auslegung von Anlagen für das Friction Stir Welding ISBN:

Robotic Friction Stir Welding using a Standard Industrial Robot

STRAUSS Modelling of friction stir welding for robotic implementation

Towards Multidimensionality and Flexibility in Friction Stir Welding Using an Industrial Robot System Recent Advances in Friction Welding and Allied Processes,

VOELLNER 3-D FSW using a modified high payload robot th International FSW Symposium,

SAM;  the Arts et Métiers ParisTech open access repository

Science Arts & Métiers (SAM)
is an open access repository that collects the work of Arts et Métiers ParisTech
researchers and makes it freely available over the web where possible.
This is an author-deposited version published in: https://sam.ensam.eu
Handle ID: .http://hdl.handle.net/10985/8776
To cite this version :
Sandra ZIMMER-CHEVRET, Julien LAYE, Laurent LANGLOIS, Régis BIGOT - Overview of the
mean of production used for FSW - In: International Conference on Scientific and Technical
Advances on Friction Stir Welding and Processing, France, 2010-01-27 - FSWP'2010 - 2010
Any correspondence concerning this service should be sent to the repository
Administrator : archiveouverte@ensam.eu
1 
Overview of the mean of production used for FSW 
 
S. Zimmer
1
, J. Laye
2
, L. Langlois
1
, R. Bigot
1
 
1
Arts et Métiers ParisTech Metz – LCFC, 4, Rue Augustin Fresnel, 57070 Metz, France  
sandra.zimmer@ensam.eu, laurent.langlois@ensam.eu, regis.bigot@ensam.eu 
2
Institut de Soudure - FSW Center, 2-4 rue Pilâtre de Rozier, 57420 GOIN, France 
j.laye@institutdesoudure.com
 
 
 
Keywords: Friction Stir Welding, Industrialization, Friction Stir Welding Equipment 
 
Abstract: The Friction Stir welding process is now introduced in production plants. More and more 
applications are developed and the most part of the work is now centered on the mean of production to 
be used. Institut de Soudure and Arts et Métiers ParisTech are working on this subject since mid of 
2005. The results of this work is a recognize knowledge on the methodology for qualifying a Friction 
Stir Welding Equipment [1]. In the same time, and based on this work, Institut de Soudure has bought 
a new kind of Friction Stir Welding machine based on a KUKA Robot. 
 
1. Introduction 
 
The main advantages of friction stir welding (FSW) lie in the fact that it is a solid state welding 
process [2]. This particularity gives it the availability to weld almost all types of aluminum alloys, 
even the one classified as non-weldable by fusion welding due to hot cracking and poor solidification 
microstructure in the fusion zone [3]. 
To perform FSW, a non-consumable rotating tool, made up of a shoulder and a pin, is inserted into the 
interface of two workpieces rigidly clamped. Once the shoulder in contact with the surface’s 
workpieces, a constant down force is applied on the tool and is moved along the joint line, bounding 
the workpieces together. The thermo-mechanical tool/material interactions generate high forces during 
the welding operation [4] [5]. The welding equipment must be rigid enough to satisfy them [6]. 
Furthermore, the machine should be able to weld complex joint geometry to offer a wide range of 
applications. So, to produce industrial weld, special dedicated machine were developed. These kinds 
of equipments, as not standard, are generally expensive. Therefore, the industrials are reluctant to 
adopt this new technology. 
 
The objective of this research work is the industrialization of the friction stir welding process in order 
to provide tools to industrials to select and qualify a machine for their FSW applications. The 
industrialization can be split into three aspects the analysis of the product, the process and the 
resources, these three entities being in interactions.  
 
This paper presents a methodology to determine the Friction Stir Welding equipment adequate to an 
application. The adequate equipment can be every machine that can perform friction stir welds. 
Therefore, this paper presents a short review, based on literature survey, of the existing friction stir 
welding equipments.  
 
2. The existing friction stir equipment 
 
Today, the machine commonly used to perform FSW, industrially and in laboratories, are dedicated 
FSW machine, modified milling machine, serial and parallel kinematics robots.  
 
a. Modified milling machine 
Milling and FSW machine have the same general characteristics [7], spindle rotation, travel speed and 
CNC control process necessary to perform FSW welds. They generally offer high stiffness and a good 
accuracy. The biggest disadvantage of most the milling machine is unavailability to propose a force 
controlled operation [5]. But, new milling machines technologies can offer a force controlled process.  
2 
 
b. FSW dedicated machine 
FSW dedicated machine allows a force control operation and generally the possibility to weld with the 
three tool technologies, conventional, retracting and bobbin tool. Each machine is designed to weld, 2- 
or 3-dimensional and has a predefined workspace. The main advantages of these machines are their 
high payload capacity due to high framework stiffness. They generally offer large workspace. The 
disadvantages of this kind of equipment is its high investments cost and the poor accessibility of the 
tool.  
 
c. Parallel and serial kinematics robot 
FSW on Tricept 805 robot has been developed by GKSS research centre. This kind of machine is 
commonly used for high speed milling applications [8]. Tricept robots are characterized by high 
stiffness and to assure good position accuracy [6]. This kind of equipment possesses high investments 
costs and small workspace due to its design [9]. These two characteristics are major obstacles to 
widespread its industrial used for FSW.  
 
Modern industrial serial robots (Figure 1) ensure flexibility, multidimensionality and lower 
investments cost than dedicated FSW machine [10]. They also possess a highly developed user 
interface for rapid programming [9]. Their disadvantage is their lack of force / load capacity due to 
their lack of stiffness [4] [10]. Therefore, to assure the robot welding capabilities and provide a wide 
range of applications, the robot must be a high payload robot [4]. Furthermore, the robot must be force 
controlled during the operation; its stiffness doesn’t allow a position control [11]. Furthermore, their 
lack of stiffness involves the deviation of the tool according to the seam [10] [12]. Despite these two 
disadvantages, the industrial robot seems to be a good FSW mean of production. The different 
publications on the robotic FSW, [4] to [10] show a real development improvement and a real 
potential for industrial applications. They appear to be a good compromise between complex weld 
geometry, range of applications, workspace and investments costs.  
 
 
Figure 1: Serial kinematic robot for FSW application 
 
3. Presentation of the developed methodology  
 
The proposed methodology is based on a global and a local approach (see figure 2). The last one 
consists of an analysis of the FSW process. It corresponds to the determining of the value of the 
driving parameters of the FSW process in order to obtain a weld satisfying its functional 
specifications. 
 
 
 
3 
These parameters are: 
- The position and the orientation of the tool relative to the seam. Precisely, they correspond to 
the distance between tool axes and the seam and two angles determining the orientation of the 
tool relative to the vector normal of the work pieces and the vector tangent of the seam. 
- The rotation speed and the travel speed of the tool.  
- The down force applied by the tool on the material.  
 
 
In order to qualify a mean of production it is necessary to determine the tolerances associated to each 
parameter. Concerning the three main driving parameters, the admissible variations are defined by the 
process windows.  
The tolerances concerning the position and the orientation of the tool relative to the weld seam are 
important characteristics for serial kinematics robots. These tolerances are also linked to the tolerances 
for the design of the workpiece work-holding device and the manufacturing of the workpieces to be 
welded. 
The tool/material mechanical interactions depend on the processing parameters. So, for parameters of 
process windows, it is necessary to associate the welding forces and torque generated during the whole 
welding operation. The description of the tool/workpiece mechanical interactions is discussed in the 
next part.  
 
Write the FSW mean of production requirements
(Machine, workpiece work-holding device) 
Tool material mechanical 
interactions determination
Torques and forces associated 
to each welding stage
Processing parameters
determination and their 
tolerances
Analyze of the case
Tool technology and geometry
Material and thickness
Tool / workpiece 
kinematics
determination
Seam geometry
Tool path 
determination
 
 
Figure 2: Scheme of the methodology used to define the FSW means of production requirements 
 
The global analyze of the welding operation consists in determining the geometry of the weld path. At 
each point of the seam a local reference frame RMi (Mi, ti, vi, ni) is defined (Figure 3). The vector ti is 
tangent to the seam line, L, and oriented according to the welding direction. The vector ni is normal to 
4 
the plane tangent to the workpiece welded surfaces. The third vector vi is chosen in order to form an 
orthonormal reference frame. 
The determination of the processing parameters and the weld seam allows the definition of the 
complete tool path (see figure 3).  
 
 
Mi i
t
r
in
r
iv
r
Surface formed by joining two pieces
workpiece interface
Mi
Seam, L
Workpiece 1
Workpiece 2
Seam, L
y
r
x
r
Tool rotation 
axis
ω
O
z
r
FSW Process
parameters
Tool path
definition
Weld seam definition
 
Figure 3: Definition to the tool position and orientation at each location of the welding path 
 
 
4. Description of the tool/workpieces mechanical interactions 
 
Generally the FSW operation is described by two main stages, the plunge and the welding stages [13] 
and [14]. As the tool - workpiece interactions differ according to the welding stage, it is necessary to 
decompose the whole welding stages. So, the tool kinematics was analyzed leading to the 
decomposition of the welding stages into six independent sub-stages: plunging, dwell time, 
acceleration, welding at constant speed, deceleration and pin retracting. The figure 4 presents the tool 
kinematics and the corresponding stages during FSW. 
 
Tool pentration
Time [s]
Plunge
P
e
n
e
tr
a
ti
o
n
 d
e
p
th
Welding at
constant speed
Dwell time
Acceleration
Deceleration
Tool retracting
W
e
ld
in
g
 s
p
e
e
d
[rpm] [mm]
Tool welding
speed
vtravel




min
mm
R
o
ta
ti
o
n
a
l 
s
p
e
e
d
Tool rotational speed
 
Figure 4: Presentation of the tool kinematics during the welding stage 
 
5 
Former research works [1] showed that the analyses of the tool/workpiece mechanical interactions can 
be reduced to the analysis of the plunging and welding at constant speed stages for the qualification of 
a FSW means of production and the workpiece work-holding device. 
According [14] and [15], the plunging stage is characterized by a brief peak of the vertical effort, when 
the shoulder comes into contact with the surface. The “peak” intensity mainly depends on the 
penetration velocity [15]. The maximal torque and force are obtained almost simultaneously, at the 
end of the penetration. In the last 25% remaining penetration, probably when the shoulder touches 
material displaced upwards by the pin penetration, the curves of the torque and force grow more 
rapidly until they reach a “peak”. That maximum occurs at the end of the plunge, when the tool 
shoulder is completely in contact with the plate’s surfaces. 
The welding stage is force controlled; the down force Fz remains constant. After increasing during the 
acceleration stage, the travel force and transverse force seems to stabilize. The torque also stabilizes 
after a few seconds.  
Figure 5 shows evolutions of the tool/workpiece mechanical interactions components for to 
applications. 
 
 
-7
-3
1
5
9
13
17
21
25
29
33
183 193 203 213 223 233 243 253 263 273 283 293 303 313 323 333 343
Time [sec]
F
o
rc
e
s
 [
k
N
]
0
50
100
150
200
250
T
o
rq
u
e
 [
N
m
]
Plunge Welding at constant speed
Dweel Time Acceleration Deceleration
Deceleration
Fy
Fx
Cz
Fz
Forces and torque during 
the welding of a 6000 
series aluminum alloy of 
thickness 5mm
Forces and torque 
during the welding of a 
7000 series aluminum 
alloy of thickness 
20mm
-2
-1
0
1
2
3
4
5
6
7
8
9
10
11
12
13
14
33 35.5 38 40.5 43 45.5 48 50.5 53 55.5 58 60.5 63 65.5 68 70.5
Time [sec]
F
o
c
e
 [
k
N
]
0
10
20
30
40
50
60
70
80
90
T
o
rq
u
e
 [
N
m
]
Plunge Dweell
time
Welding at constant speed
Acceleration Deceleration
Tool retracting
Fy
Fx
Cz, Torque
Fz
 
Figure 5: Forces and torque during the welding operation according to the time for different 
aluminium alloys and thicknesses 
 
The mechanical interactions between the tool and the welded material can be represented by two set of 
force and torque corresponding to: 
- The maximum torque and force reached at the end of the plunge. 
- The “stabilized” torque and forces (down force, travel and transverse forces) reached during 
the welding stage.  
 
6 
This knowledge will permit to focus on these two stages processing parameters in order to reduce the 
forces and torque applied on the tool. Thus, it will enable the FSW on machine with load / rigidity 
weaknesses. On the other hand, another way to reduce the process forces is to work on the tool 
geometry [14]. 
 
 
5. Conclusion and perspectives 
 
The presented work focuses on the definition of the functional specification for the choice and/or the 
design of a FSW machine and the work-holding device. In the case of the use of a low-stiffness 
machine like serial kinematics robot, the evaluation of the tolerances concerning the position and the 
orientation of the tool can be a very determinant factor.   
Contrary to conventional welding fusion process (GMAW or Laser Welding) mechanical interactions 
between the tool and the material have to be taken into account. They have to be taken into account for 
the determination of the forces and torques the FSW machine must apply during the welding 
operation.  
 
Moreover, thanks a machine stiffness model, it is possible to estimate the tool deviation from the seam 
in order to compare it to the one admissible by the welding process. It validates the feasibility of the 
welding operation. The presented methodology must also include the workpieces work-holding 
device. The applied methodology must be completed by the study of the tool accessibility on the seam 
and the workpieces assembly and disassembly from the work-holding device. This kind of 
methodology is commonly used in machining process. 
 
The process windows can be restricted by: 
- The machines characteristics in terms of down force, rotational speed and travel speed.  
- The tool deviation due to a lack of stiffness of the machine. 
- The machine workspace or its lack of accessibility. 
 
For certain types of machine, like serial kinematics robot, the force capacities and the stiffness depend 
on the tool position inside the workspace. Then the process windows is not directly restricted by the 
seam accessibility but by the fact that it is not possible to keep the required stiffness throughout the 
welding path.  
 
6. Acknowledgment 
 
The authors would like to thank the Region Lorraine, the Moselle department and the French 
Government for their financial support. 
 
 
7. References 
 
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7
th
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[2] W.M. THOMAS, E.D. NICHOLAS, J.C. NEEDHAM, M.G. MURCH, P. TEMPLEMITH, 
C.J. DAWES 
Patent Application No. 9125978.8 (December 1991) 
 
[3] R.S MISHRA, Z.Y. MA 
Friction Stir Welding and processing 
Materials Sciences and Engineering R 50 (2005) I-78 
 
 
7 
[4] C.B. SMITH   
Robotic Friction Stir Welding using a Standard Industrial Robot 
2nd International FSW Symposium, June 2000 
 
[5] D. EREINER 
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ISBN: 3-8316-0650-1 (September 2006) 
 
[6] A. von STROMBECK, C. SCHILLING, J.F. DOS SANTOS 
Robotic Friction Stir Welding – Tool Technology and Applications 
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[7] M. PONTE, J. ADAMOWSKI, C. GAMBARO, E. LERTORA 
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[8]  R. ZETTLER, S. LOMOLINO , J. F. DOS SANTOS, T. DONATH, F. BECKMANN, T. 
LIPPMAN, D. LOHWASSER 
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5th International FSW Symposium, 2004 
 
[9] M. SORON 
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System 
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[12] G. VOELLNER 
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Aluminiumlegierungen 
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mechanical properties through precipitation evolution and hardening 
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Overview of the mean of production used for FSW

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