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Research Papers

Measurement of Tool-Workpiece Interface Temperature Distribution in Friction Stir Welding

[+] Author and Article Information
Axel Fehrenbacher, Joshua R. Schmale, Michael R. Zinn

Department of Mechanical Engineering,
University of Wisconsin—Madison,
Madison, WI 53706

Frank E. Pfefferkorn

Department of Mechanical Engineering,
University of Wisconsin—Madison,
Madison, WI 53706
e-mail: pfefferk@engr.wisc.edu

1Corresponding author.

Manuscript received September 10, 2012; final manuscript received November 20, 2013; published online January 16, 2014. Assoc. Editor: Robert Gao.

J. Manuf. Sci. Eng 136(2), 021009 (Jan 16, 2014) (8 pages) Paper No: MANU-12-1272; doi: 10.1115/1.4026115 History: Received September 10, 2012; Revised November 20, 2013

The objective of this work is to develop an improved temperature measurement system for friction stir welding (FSW). FSW is a solid-state joining process enabling welds with excellent metallurgical and mechanical properties, as well as significant energy consumption and cost savings compared to traditional fusion welding processes. The measurement of temperatures during FSW is needed for process monitoring, heat transfer model verification and process control, but current methods have limitations due to their restricted spatial and temporal resolution. Previous work showed that temperatures at the tool shoulder-workpiece interface can be measured and utilized for closed-loop control of temperature. Adding an additional thermocouple at the tool pin-workpiece interface and performing a calibration of the measurement to gain better insight into the temperature distribution in the weld zone improved the method. Both thermocouples were placed in through holes right at the interface of tool so that the sheaths are in direct contact with the workpiece material. This measurement strategy reveals dynamic temperature variations at the shoulder and the pin within a single rotation of the tool in real-time. It was found that the highest temperatures are at the shoulder interface between the advancing side and the trailing edge of the tool, closer to the advancing side. The temperature distribution was mostly affected by travel speed and the temperature difference within one tool rotation was found to be between 10 °C and 50 °C, depending on the process parameters. The dynamic temperature measurements obtained with the current system are of unmatched resolution, fast, and reliable and are likely to be of interest for both fundamental studies and process control of FSW.

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References

Figures

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Fig. 1

Schematic of the FSW process

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Fig. 2

Schematic of through hole locations for the thermocouples on the FSW tool (not to scale, section view). The thermocouples are exposed at the tool-workpiece interface.

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Fig. 3

Schematic illustrating the main components of the wireless DAQ system used for FSW

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Fig. 4

Photograph of assembled instrumented tool holder for FSW

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Fig. 5

Close-up view of FSW tool showing the exposed thermocouples at the shoulder-workpiece and pin-workpiece interfaces

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Fig. 6

Average temperatures during weld traverse at (a) shoulder and (b) pin interface for various spindle speeds and travel speeds for 6061-T6

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Fig. 7

Measured temperatures for shoulder and pin location during welding of 6061-T6 (solidus temperature 582 °C) at 1100 rpm and 400 mm/min

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Fig. 8

Measured temperature amplitudes obtained from FFT over time during welding of 6061-T6 at 1100 rpm and 400 mm/min. A moving window of 100 samples (0.4 s or 7.3 tool rotations) was applied.

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Fig. 9

Measured temperature (°C) and calculated tool-workpiece interface temperature distributions at the shoulder and pin (1300 rpm, 400 mm/min, 6061-T6)

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Fig. 10

Amplitudes of measured interface temperature for different plunge depths. Constants: 1200 rpm, 200 mm/min, 6061-T6.

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Fig. 11

Average measured interface temperatures for different plunge depths. Constants: 1200 rpm, 200 mm/min, 6061-T6.

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Fig. 12

Amplitudes of interface temperature at shoulder interface during the weld traverse (6061-T6) for various spindle speeds and travel speeds. Plunge depth 4.9 mm (constant).

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Fig. 13

Amplitudes of interface temperature at pin interface during the weld traverse (6061-T6) for various spindle speeds and travel speeds. Plunge depth 4.9 mm (constant).

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