0
Research Papers

Enabling Automation of Friction Stir Welding: The Modulation of Weld Seam Input Energy by Traverse Speed Force Control

[+] Author and Article Information
William R. Longhurst

Department of Mechanical Engineering, Welding Automation Laboratory, Vanderbilt University, VU Station B 351592, 2301 Vanderbilt Place, Nashville, TN 37235-1592russ.longhurst@vanderbilt.edu russlonghurst@comcast.net

Alvin M. Strauss

Department of Mechanical Engineering, Welding Automation Laboratory, Vanderbilt University, VU Station B 351592, 2301 Vanderbilt Place, Nashville, TN 37235-1592al.strauss@vanderbilt.edu

George E. Cook

Department of Mechanical Engineering, Welding Automation Laboratory, Vanderbilt University, VU Station B 351592, 2301 Vanderbilt Place, Nashville, TN 37235-1592george.e.cook@vanderbilt.edu

J. Dyn. Sys., Meas., Control 132(4), 041002 (Jun 15, 2010) (11 pages) doi:10.1115/1.4001795 History: Received May 28, 2009; Revised March 28, 2010; Published June 15, 2010; Online June 15, 2010

Friction stir welding (FSW) joins materials by plunging a rotating tool into the work piece. The tool consists of a shoulder and a pin that plastically deforms the parent materials and then forges them together under the applied pressure. To create the pressure needed for forging, a rather large axial force must be maintained on the tool. Maintaining this axial force is challenging for robots due to their limited load capacity and compliant nature. To address this problem, force control has been used, and historically, the force has been controlled by adjusting the plunge depth of the tool into the work piece. This paper develops the use of tool traverse speed as the controlling variable instead of plunge depth. To perform this investigation, a FSW force controller was designed and implemented on a retrofitted Milwaukee Model K milling machine. The closed loop proportional, integral plus derivative (PID) control architecture was tuned using the Ziegler–Nichols method. Results show that the control of axial force via traverse speed is feasible and predictable. The resulting system is more robust and stable when compared with a force controller that uses plunge depth as the controlling variable. A standard deviation of 41.5 N was obtained. This variation is much less when compared with a standard deviation of 129.4 N obtained when using plunge depth. Using various combinations of PID control, the system’s response to step inputs was analyzed. From this analysis, a feed forward transfer function was modeled that describes the machinery and welding environment. From these results, a technique is presented regarding weld seam input energy modulation as a by product of force control via traverse speed. A relative indication of thermal energy in the welding environment is obtained with the feedback of axial force. It is hypothesized that, while under force control, the controller modulates weld seam input energy according to the control signal. The result is constant thermomechanical conditions in the welding environment. It is concluded that the key enablers for force control are the unidirectional behavior and load dynamics of the traverse motor. Larger bandwidths and more stable weld conditions emerge when using traverse speed instead of plunge depth to control the force. Force control of FSW via traverse speed has importance in creating efficient automatic manufacturing operations. The intelligence of the controller naturally selects the most efficient traverse speed.

Copyright © 2010 by American Society of Mechanical Engineers
Your Session has timed out. Please sign back in to continue.

References

Figures

Grahic Jump Location
Figure 1

Illustration of the FSW process (1)

Grahic Jump Location
Figure 2

Axial force as a function of traverse speed (3)

Grahic Jump Location
Figure 3

FSW machine at Vanderbilt University

Grahic Jump Location
Figure 4

Control diagram of force control via traverse speed

Grahic Jump Location
Figure 6

Treaded pin tool

Grahic Jump Location
Figure 7

Weld sample with no force control

Grahic Jump Location
Figure 8

Weld flaw due to lack of force control

Grahic Jump Location
Figure 9

Weld sample using force control via traverse speed

Grahic Jump Location
Figure 10

Regulation of z force using force control via traverse speed

Grahic Jump Location
Figure 11

Force control response when the controlling variable is plunge depth

Grahic Jump Location
Figure 12

Regulation and step input with PID control

Grahic Jump Location
Figure 13

Regulation and step input with P control

Grahic Jump Location
Figure 14

Regulation and step input with PI control

Grahic Jump Location
Figure 15

Regulation and step input with PD control

Grahic Jump Location
Figure 16

Simulink model of the FSW force control system

Grahic Jump Location
Figure 17

Results of the modeled transient response of the FSW force control system

Grahic Jump Location
Figure 18

Weld using 1/4 in. Trivex tool and force control via traverse speed

Grahic Jump Location
Figure 19

Weld using 1/4 in. threaded tool and force control via traverse speed

Grahic Jump Location
Figure 20

Tensile test data

Grahic Jump Location
Figure 22

Results of the energy model

Grahic Jump Location
Figure 23

FSW preheating experiments under force control (11)

Tables

Errata

Discussions

Some tools below are only available to our subscribers or users with an online account.

Related Content

Customize your page view by dragging and repositioning the boxes below.

Related Journal Articles
Related eBook Content
Topic Collections

Sorry! You do not have access to this content. For assistance or to subscribe, please contact us:

  • TELEPHONE: 1-800-843-2763 (Toll-free in the USA)
  • EMAIL: asmedigitalcollection@asme.org
Sign In