Design and Implementation of a Nonlinear Axial Force Controller for Friction Stir Welding Processes


In Friction Stir Welding (FSW) processes the axial force provides a forging action that affects the part's microstructure and, hence, its mechanical properties. Controlling this force provides good, consistent welding quality. The aim of this paper is to provide a systematic method to design and implement axial force controllers for FSW processes. The axial force is modeled as a nonlinear function of the measured FSW process parameters (i.e., plunge depth, traverse rate, and rotation speed) and the equipment is modeled as a pure delay from the commanded to the measured process parameters. Based on these dynamic models, a nonlinear feedback controller for the axial force is designed using Polynomial Pole Placement. This controller is implemented in a Smith Predictor-Corrector structure to compensate for the inherent equipment delay and the controller parameters are tuned to achieve the best closed-loop response given the equipment limitations. Experimental implementations verify the controller is able to maintain a constant axial force, even when gaps are encountered during the welding process.

Meeting Name

2007 American Control Conference, ACC (2007: Jul. 9-13, New York, NY)


Mechanical and Aerospace Engineering

Keywords and Phrases

Axial flow; Dynamic models; Dynamic programming; Electric welding; Force control; Friction; Friction welding; Gas welding; Heat affected zone; Lithography; Mechanical properties; Welding; (PL) properties; Axial forces; Closed loops; Controller parameters; Friction STIR welding; Friction Stir Welding (FSW); Non linear functions; Nonlinear feedback controllers; Polynomial pole placement; Process Parameters; Pure delay; Rotation speeds; Smith predictors; Systematic methods; Traverse rate; welding processes; Welding quality; Process control

International Standard Book Number (ISBN)


International Standard Serial Number (ISSN)


Document Type

Article - Conference proceedings

Document Version


File Type





© 2007 Institute of Electrical and Electronics Engineers (IEEE), All rights reserved.

Publication Date

01 Jul 2007