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Optimized Design for a Device to Measure Thermal Contact Conductance During Friction Stir Welding Daniel Ellis1   · Matthew Goodson1 · Michael Miles2 · Troy Munro1 Received: 17 September 2020 / Accepted: 26 September 2020 © Springer Science+Business Media, LLC, part of Springer Nature 2020

Abstract Friction stir welding (FSW) is a solid-state welding process that is finding increasing use in a variety of industries, owing to its ability to create high-quality welds with less heat input than fusion welding. While the modeling of FSW has been an active effort for at least 15 years, two input parameters, namely the friction coefficient and the heat transfer coefficient, are still adjustable quantities that are difficult to measure. This lack of information compromises the predictive capability of FSW models. While the modeling of friction between the tool and workpiece remains a complex task, the measurement of heat transfer should be possible, but has not been adequately addressed because of the difficulty of accessing the relevant interface with thermocouples. This paper presents a multi-layered frequency-domain thermoreflectance (FDTR) method and transducer design to measure the heat transfer coefficient between the spinning tool and the workpiece. Due to constraints of the welding process, a multi-layered structure is needed for a useable measurement to maximize the heat flow from the modulated heating surface through the heat transfer interface into the welded workpiece. An analytical 2D thermal quadrupole model is shown to be useful in determining layer properties. A multi-layered structure for a specific tool design is validated using COMSOL and optimized. This process can be used to determine the ideal transducer structure to maximize the signal from an FDTR measurement during a friction stir welding process. Keywords  Thermal quadrupoles · FDTR · FSW · Heat transfer coefficient

Electronic supplementary material  The online version of this article (https​://doi.org/10.1007/s1076​ 5-020-02746​-0) contains supplementary material, which is available to authorized users. * Troy Munro [email protected] 1

Department of Mechanical Engineering, Brigham Young University, Provo, UT, USA

2

Department of Manufacturing Engineering, Brigham Young University, Provo, UT, USA



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International Journal of Thermophysics

(2021) 42:6

1 Introduction 1.1 Friction Stir Welding Overview Friction Stir Welding (FSW) is a solid-state joining process that mechanically joins two metals through a combination of frictional heating and plastic deformation. A non-consumable tool with a pin spins, heats, and compresses the material with sufficient force (3 kN − 8.4 kN) [1] in a manner that facilitates joining, as shown in Fig. 1a. When the temperature of the workpiece is high enough, the tool can translate across the joint and create a high-quality bond [2]. FSW has proven to be effective with aluminum alloys in shipbuilding and marine industries, aerospace, automotive and rail industries [3].