Abstract

In friction stir welding, the temperature of the process zone affects the properties of the resulting weld and has a dramatic effect on tool life in PCBN (polycrystalline cubic boron nitride) tools. Therefore an active control system that changes process parameters to control weld temperature is desirable. Mayfield and Sorensen proposed a two-stage control model that contains an inner loop that controls the spindle speed to keep power constant and an outer loop for setting the desired power based on weld temperature. This work contains the analysis and implementation of a temperature control method based on their work. This research shows that power input to the stir zone leads tool temperature. Due to the inertia associated with the spindle, power control is best achieved by commanding torque rather than spindle speed. Heat transfer in the tool and stir zone is explored and analytical models are developed. It is shown that the temperature response to power is nonlinear. Nevertheless a first-order approximation with time delay is sufficient to select functional controller gains for a PID controller. Standard manual PID tuning techniques can be used to achieve a desired rise time, settling time and overshoot. Gains for an H-13 tool steel FSW tool were tuned to produce a rise time of approximately 7 seconds, settling time of approximately 30 seconds and overshoot of approximately 30%. Welds were run using these gains in various plate thicknesses, commanded temperatures, backing plates and feed rates. In all cases temperature control functioned properly and the commanded temperature was held with a standard deviation of less than one degree Celsius. Similar results are presented for welds run using PCBN tools.

Degree

MS

College and Department

Ira A. Fulton College of Engineering and Technology; Mechanical Engineering

Rights

http://lib.byu.edu/about/copyright/

Date Submitted

2012-03-08

Document Type

Thesis

Handle

http://hdl.lib.byu.edu/1877/etd5039

Keywords

friction stir, welding, temperature, power, control

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