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Heat Control via Torque Control in Friction Stir WeldingIn a proposed advance in friction stir welding, the torque exerted on the workpiece by the friction stir pin would be measured and controlled in an effort to measure and control the total heat input to the workpiece. The total heat input to the workpiece is an important parameter of any welding process (fusion or friction stir welding). In fusion welding, measurement and control of heat input is a difficult problem. However, in friction stir welding, the basic principle of operation affords the potential of a straightforward solution: Neglecting thermal losses through the pin and the spindle that supports it, the rate of heat input to the workpiece is the product of the torque and the speed of rotation of the friction stir weld pin and, hence, of the spindle. Therefore, if one acquires and suitably processes data on torque and rotation and controls the torque, the rotation, or both, one should be able to control the heat input into the workpiece. In conventional practice in friction stir welding, one uses feedback control of the spindle motor to maintain a constant speed of rotation. According to the proposal, one would not maintain a constant speed of rotation: Instead, one would use feedback control to maintain a constant torque and would measure the speed of rotation while allowing it to vary. The torque exerted on the workpiece would be estimated as the product of (1) the torque-multiplication ratio of the spindle belt and/or gear drive, (2) the force measured by a load cell mechanically coupled to the spindle motor, and (3) the moment arm of the load cell. Hence, the output of the load cell would be used as a feedback signal for controlling the torque (see figure).
Document ID
20110020531
Acquisition Source
Marshall Space Flight Center
Document Type
Other - NASA Tech Brief
Authors
Venable, Richard
(Lockheed Martin Corp. Huntsville, AL, United States)
Colligan, Kevin
(Lockheed Martin Corp. Huntsville, AL, United States)
Knapp, Alan
(Lockheed Martin Corp. Huntsville, AL, United States)
Date Acquired
August 25, 2013
Publication Date
September 1, 2004
Publication Information
Publication: NASA Tech Briefs, September 2004
Subject Category
Man/System Technology And Life Support
Report/Patent Number
MFS-31834
Distribution Limits
Public
Copyright
Public Use Permitted.
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