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Through the Tool Tracking for Friction Stir Welding
Friction Stir Welding (FSW) is increasingly gaining ground in a variety of critical welding applications. Utilizing force sensors mounted on the friction stir welding tool, Vanderbilt inventors have developed a technique to keep a weld tool on track. This technology is especially beneficial in real time corrections for deviations in travel in the case of robotic FSW or "blind" welds. The technique is cost-effective in that no additional sensors such as cameras, thermocouples, acoustic emission receivers, etc. are required.
FSW was developed in 1991 by the Welding Institute in the UK. It is a solid state process where welding is accomplished via mechanical stirringbelow the melting point of the material. In FSW the welding tool consists ofa shoulder and a pin, or probe, and the tool is rotated while traversing the weld line. The shoulder applies pres- sure and heat to the surface of the material while the probe plunges into the material and induces material flow. Vanderbilt research has led to the development of a misalignment detec- tion system for FSW. This technology detects misalignment by monitoring the forces recorded by a dynamometer attached to the tool itself. A straightforward application of misalignment detection is as a means of verification that the FSW tool is properly aligned. This could alert an operator if a misalignment is detected, which could have serious effects on the weld quality. Another compelling use for misalignment detection is as part of a greater system called "Through the Tool Tracking." In this system, misalignment detection is used as a feedback signal for a closed loop lateral position control system. In Through the Tool Tracking, a closed loop control system is established using the previously discussed mis- alignment detection algorithm.
In Through the Tool Tracking, the estimated lateral offset is input into a controller block, which then uses this information to control the positioning motors. The weld controller is a standard feedback control system that strives to maintain some desired state, and this system is then used to actively maintain some lateral posi- tion. This is very useful when either the actual lateral position is difficult to obtain precisely through other means (T-joints) or when the joint line is not a straight line, as might be the case in robotic FSW. Through the Tool Tracking thus represents a means of automatic joint line tracking for FSW. This technology is in use in other welding methods, such as arc welding where the electrical arc signals are used rather than force signals, but not yet in FSW.
The use of Through the Tool Tracking to enable joint line tracking in FSW is an important development for FSW. This technology is expected to improve the robustness of the FSW process by enabling fidelity of compli- cated weld-seams not only in visible tracks, but also in "blind" tracks, as in T-joints. System cost and complexity does not increase substantially due to the need for only tool mounted force sensors.
At the present time it is not possible to define the market size. Suffice it to say that as FSW gains acceptance in the welding of critical components and an ever-increasing range of applications, the need to precision and control will increase. This technology will provide an enabling basis for the stringent requirements loom- ing on the horizon.
The adoption of this technology should present few barriers. The hardware modifications required for adoption are insignificant, and the components used can be readily found off-the shelf. The software algorithms used for implementa- tion will require a modest degree of customization depending on the specific circumstances. The technol- ogy should lend itself rather well to adoption in robotic welding.
Vanderbilt seeks a commercializa- tion partner who would be willing to commit to commercialization of the technology via some development work in conjunction with Vanderbilt, as well as licensing of the intellectual property embodying this technology.
Intellectual Property Status
Inventors:Paul FlemingDavid LammleinGeorge CookDon WilkesAlvin StraussDavid DeLappDaniel Hartman