Use of robotic friction stir welding (FSW) has gained in popularity as robotic systems can accommodate more complex part geometries while providing high applied tool forces required for proper weld formation. However, even the largest robotic FSW systems suffer from high compliance as compared to most custom engineered FSW machines or modified computer numerical control (CNC) mills. The increased compliance of robotic FSW systems can significantly alter the process dynamics such that control of traditional weld parameters, including plunge depth, is more difficult. To address this, closed-loop control of plunge force has been proposed and implemented on a number of systems. However, due to process parameter and condition variations commonly found in a production environment, force control can lead to oscillatory or unstable conditions and can, in extreme cases, cause the tool to plunge through the workpiece. To address the issues associated with robotic force control, the use of simultaneous tool interface temperature control has been proposed. In this paper, we describe the development and evaluation of a closed-loop control system for robotic friction stir welding that simultaneously controls plunge force and tool interface temperature by varying spindle speed and commanded vertical tool position. The controller was implemented on an industrial robotic FSW system. The system is equipped with a custom real-time wireless temperature measurement system and a force dynamometer. In support of controller development, a linear process model has been developed that captures the dynamic relations between the process inputs and outputs. Process validation identification experiments were performed and it was found that the interface temperature is affected by both spindle speed and commanded vertical tool position while axial force is affected primarily by commanded vertical tool position. The combined control system was shown to possess good command tracking and disturbance rejection characteristics. Axial force and interface temperature was successfully maintained during both thermal and geometric disturbances, and thus weld quality can be maintained for a variety of conditions in which each control strategy applied independently could fail. Finally, it was shown through the use of the control process model, that the attainable closed-loop bandwidth is primarily limited by the inherent compliance of the robotic system, as compared to most custom engineered FSW machines, where instrumentation delay is the primary limiting factor. These limitations did not prevent the implementation of the control system, but are merely observations that we were able to work around.

References

References
1.
Thomas
,
W. M.
,
Nicholas
,
E. D.
,
Needham
,
J. C.
,
Murch
,
M. G.
,
Temple-Smith
,
P.
, and
Dawes
,
C. J.
,
1991
, “
Friction Stir Butt Welding
,” GB Patent No. 9125978.8.
2.
Mishra
,
R. S.
, and
Ma
,
Z. Y.
,
2005
, “
Friction Stir Welding and Processing
,”
J. Mater. Sci. Eng.
,
R50
, pp.
1
78
.
3.
Threadgill
,
P. L.
,
Leonard
,
A. J.
,
Shercliff
,
H. R.
, and
Withers
,
P. J.
,
2009
, “
Friction Stir Welding of Aluminium Alloys
,”
Int. Mater. Rev.
,
54
(
2
), pp.
49
93
.10.1179/174328009X411136
4.
Fehrenbacher
,
A.
,
Duffie
,
N. A.
,
Ferrier
,
N. J.
,
Pfefferkorn
,
F. E.
, and
Zinn
,
M. R.
,
2011
, “
Toward Automation of Friction Stir Welding Through Temperature Measurement and Closed-Loop Control
,”
ASME J. Manuf. Sci. Eng.
,
133
(
5
), p.
051008
.10.1115/1.4005034
5.
Fehrenbacher
,
A.
,
Duffie
,
N.
,
Ferrier
,
N.
,
Pfefferkorn
,
F.
, and
Zinn
,
M.
, “
Closed-Loop Control of Temperature in Friction Stir Welding and Its Effect on Weld Quality
,”
Int. J. Adv. Manufacturing
(in press).10.1007/s00170-013-5364-4
6.
Cederqvist
,
L.
,
Garpinger
,
O.
,
Hagglund
,
T.
, and
Robertsson
,
A.
,
2012
, “
Cascade Control of the Friction Stir Welding Process to Seal Canisters for Spent Nuclear Fuel
,”
Control Eng. Pract.
,
20
(
1
), pp.
35
48
.10.1016/j.conengprac.2011.08.009
7.
Ross
,
K.
, and
Sorensen
,
C.
,
2011
, “
Investigation of Methods to Control Friction Stir Weld Power With Spindle Speed Changes
,” Friction Stir Welding and Processing VI (TMS Annual Meeting & Exhibition).
8.
Peel
,
M.
,
Steuwer
,
A.
,
Preuss
,
M.
, and
Withers
,
P. J.
,
2003
, “
Microstructure, Mechanical Properties and Residual Stresses as a Function of Welding Speed in Aluminum AA5083 Friction Stir Welds
,”
Acta Mater.
,
51
, pp.
4791
4801
.10.1016/S1359-6454(03)00319-7
9.
Gratecap
,
F.
,
Racineux
,
G.
, and
Marya
,
S.
,
2008
, “
A Simple Methodology to Define Conical Tool Geometry and Welding Parameters in Friction Stir Welding
,” 7th International Friction Stir Welding Symposium, Awaji Island, Japan, TWI, Published on CD.
10.
Simar
,
A.
,
Brechet
,
Y.
,
de Meester
,
B.
,
Denquin
,
A.
, and
Pardoen
,
T.
,
2008
, “
Microstructure, Local and Global Mechanical Properties of Friction Stir Welds in Aluminium Alloy 6005A-T6
,”
Mater. Sci. Eng., A
,
486
(
1–2
), pp.
85
95
.10.1016/j.msea.2007.08.041
11.
Smith
,
C. B.
,
2000
, “
Robotic Friction Stir Welding Using a Standard Industrial Robot
,” 2nd International Friction Stir Welding Symposium, Gothenburg, Sweden, TWI, Published on CD.
12.
Von Strombeck
,
A.
,
Schilling
,
C.
, and
dos Santos
,
J. F.
,
2000
, “
Robotic Friction Stir Welding—Tool Technology and Applications
,” 2nd International Friction Stir Welding Symposium, Gothenburg, Sweden, TWI, Published on CD.
13.
Zäh
,
M. F.
, and
Eireiner
,
D.
,
2004
, “
Friction Stir Welding Using NC Milling Machines
,”
Weld. Cutting
,
3
(
4
), pp.
220
223
.
14.
Oakes
,
T.
, and
Landers
,
R. G.
,
2009
, “
Design and Implementation of a General Tracking Controller for Friction Stir Welding Processes
,”
IEEE
, Piscataway, NJ, pp.
5576
5581
.
15.
Smith
,
C. B.
, and
Hinrichs
,
J. F.
,
2004
, personal communication.
16.
Zhao
,
X.
,
Kalya
,
P.
,
Landers
,
R. G.
, and
Krishnamurthy
,
K.
,
2009
, “
Empirical Dynamic Modeling of Friction Stir Welding Processes
,”
ASME J. Manuf. Sci. Eng.
,
131
(
2
), p.
021001
.10.1115/1.3075872
17.
Melendez
,
M.
,
Tang
,
W.
,
Schmidt
,
C.
,
McClure
,
J. C.
,
Nunes
,
A. C.
, and
Murr
,
L. E.
,
2003
, “
Tool Forces Developed During Friction Stir Welding
,” NASA Marshall Space Flight Center, Technical Report No. 20030071631.
18.
Cole
,
E. G.
,
2009
, “
Investigation of Weld Material and Process parameter Influence of Forge Force in Friction Stir Welding
,” M.S. thesis, University of Wisconsin-Madison, Madison, Wisconsin.
19.
Fehrenbacher
,
A.
,
Schmale
,
J.
,
Zinn
,
M.
, and
Pfefferkorn
,
F.
, “
Measurement of Tool-Workpiece Interface Temperature Distribution in Friction Stir Welding
,” (to be published).
20.
Schmale
,
J.
,
Fehrenbacher
,
A.
, and
Pfefferkorn
,
F.
, “
Modeling and Calibration of Friction Stir Welding Temperature Sensors for Measurement of Tool-Workpiece Interface
,” (to be published).
21.
Reynolds
,
A. P.
, and
Tang
,
W.
,
2012
, “
Thermal Management for Production of Very High Strength alloy 7050 Friction Stir Welds
,” 9th International Friction Stir Welding Symposium, Huntsville, AL, TWI, Published on CD.
22.
Upadhyay
,
P.
, and
Reynolds
,
A. P.
,
2012
, “
Effect of Backing Plate Thermal Property on Friction Stir Welding of 1” Thick AA6061
,” 9th International Friction Stir Welding Symposium, Huntsville, AL, TWI, Published on CD.
23.
Shultz
,
E. F.
,
Cole
,
E. G.
,
Smith
,
C. B.
,
Zinn
,
M. R.
,
Ferrier
,
N. J.
, and
Pfefferkorn
,
F. E.
,
2010
, “
Effect of Compliance and Travel Angle on Friction Stir Welding With Gaps
,”
ASME J. Manuf. Sci. Eng.
,
132
(
4
), p.
041010
.10.1115/1.4001581
You do not currently have access to this content.