Friction Stir Welding and Processing IX: Control and Simulation
Sponsored by: TMS Materials Processing and Manufacturing Division, TMS: Shaping and Forming Committee
Program Organizers: Yuri Hovanski, Brigham Young University; Rajiv Mishra, University of North Texas; Yutaka Sato, Tohoku University; Piyush Upadhyay, Pacific Northwest National Laboratory; David Yan, San Jos State University

Thursday 2:00 PM
March 2, 2017
Room: 9
Location: San Diego Convention Ctr

Session Chair: Enkhsaikhan Boldsaikhan, Wichita State University; John Baumann, Boeing Research & Technology

2:00 PM Introductory Comments

2:10 PM  Invited
Depth and Temperature Control during Friction Stir Welding of 5 cm Thick Copper Canisters: Lars Cederqvist1; Olof Garpinger2; 1Swedish Nuclear Fuel and Waste Management Company; 2Alten
    Welding canisters requires variable power to control the probe temperature. By using a cascaded loop that determines the power requirement, the controller wont be dependent on repeatability in the power, and the lagtime in the temperature wont be critical. The cascade controller result in a probe temperature within 5C of the desired value (845C) during full circumferential welds compared with a process window of 60C. A depth controller is adjusting the axial force to control the shoulder depth. The purpose is to eliminate flash and to control the probe tip position, which affects the hook defect. The controller was verified during 13 separate cycles in lid and tubes with different material properties. Although the shoulder depth varied more than 3.3 mm between cycles during the plunge, the controller was able to achieve the desired shoulder depth of 2.2 mm for both these cycles as the joint line was reached.

2:30 PM  
Direct Pin Tool Temperature Measurements in Friction Stir Welding: Xiaoqian Ma1; Stanley Howard1; 1South Dakota School of Mines and Technology
    Friction stir welds were made on 1.27 cm thick 6061 T6 Al plate using three bull nose shaped H13 pin tools. Temperatures at two locations along the pin tool-metal interface were directly measured using transmitting thermocouples inserted in the pin tool. Thermocouples located near the bottom were 17, 24, 21 and 28 K cooler than 0.79 cm away at the side of the pin tool at 200, 400, 600 and 800 RPM. Homologous temperatures of welds made at the four RPMs were within one percent of 0.80, 0.89, 0.91, 0.92 and independent of travel speed (2 to 8 IPM) or the pin tool used. Five welds over the same weld bead showed a 2 and 8 K increase in weld temperature between the first and second pass with nearly constant temperatures thereafter. There was a 2.2 K decrease in side and bottom temperature difference with weld pass number.

2:50 PM  
Effect of Pin Tool Profile on Metal Flow, Torque and Forces during Friction Stir Welding-limiting Friction Cases: Narges Dialami1; Miguel Cervera1; Michele Chiumenti1; Carlos Agelet de Saracibar1; 1CIMNE
    This work studies pin tools with circular, triflute, trivex, and triangular profiles adopting a validated model of FSW process developed by the authors. The effect of rotating tool geometry on the flow behavior and FSW process outcomes is analyzed. The study is carried out for both slip and stick limiting friction cases between pin and workpiece employing Norton’s friction model. To characterize the material behavior during the weld, Norton-Hoff constitutive law is applied. The piecewise linear version of the model developed by the authors greatly facilitates the convergence of the numerical solution. The computational time consumed is further reduced through developing a two-phase speed-up strategy. The study shows that the geometries considered lead to significantly different process outcome and material flow patterns around the pin. The proposed modelling approach can be used to predict and interpret the FSW behavior when using specific pin geometry without the need for experimental trials.

3:10 PM  Invited
Measuring the Advancing Side Separation Forces during Self-reacting FSW of Al: Scott Rose1; John Baumann1; Sean Thuston1; Eric Thomas1; Brian Martinek1; 1The Boeing Company
    When scaling friction stir welding to production, fixturing is often an undervalued or under-engineered part of the design effort, despite its criticality in ensuring proper weld containment and joint fit-up. Reports of weld forces are typically focused on the process forces internal to the weld plate rather than the forces required for fixturing. These fixturing forces were quantified in our previous work. The separation forces on the retreating side of the pin tool were found to be approximately equal to the path normal loads exerted by the tool. The object of this study was to expand on this previous work, with new tools, to measure the fixture separation forces from the advancing side of the pin tool using improved fixturing. When combined with the previous work on the retreating side forces, this study provides a more complete picture of the forces that are required for fixturing friction stir welds.

3:30 PM Break

3:50 PM  
Predicting Lap Shear Strength for Friction Stir Scribe Joining of Dissimilar Materials: Erin Barker1; Piyush Upadhyay1; Yuri Hovanski1; Xin Sun1; 1Pacific Northwest National Lab
    Friction stir scribe technology has been developed to join materials with vastly different properties, most importantly different melting regimes. Specifically lighter, lower temperature materials such as aluminum or magnesium can be joined to higher temperature materials such as steel and titanium. The scribe portion of the modified friction stir welding pin tool creates in situ mechanical interlocks at the material interface. This mechanical interlocking, or hook-like interface morphology, has shown promising joint strength. However, this morphology can vary along a weld length and is sensitive to joining and tooling parameters. The current work seeks to determine the sensitivity of joint strength to the morphology of the hook interface and predict joint strength based on key morphology parameters. Key geometry features of the hooks extracted from joined samples are varied to quantify their impact on simulated lap shear strength. Predictable joint strength is key to wide spread use of this technique.

4:10 PM  Invited
Simultaneous Independent Control of Tool Axial Force and Temperature in Friction Stir Processing: Kenneth Ross1; Glenn Grant1; Jens Darsell1; David Catalini1; 1Pacific Northwest National Laboratory
    Maintaining consistent tool depth relative to the part surface is a critical requirement for many FSW applications. Force control is often used with the goal of obtaining a constant weld depth. When force control is used, if weld temperature decreases, flow stress increases and the tool is pushed up. If weld temperature increases, flow stress decreases and the tool dives. These variations in tool depth and weld temperature cause various types of weld defects. Robust temperature control for FSP maintains a commanded temperature through control of the spindle axis only. Robust temperature control and force control are completely decoupled in control logic and machine motion. This results in stable temperature, force and tool depth despite the presence of geometric and thermal disturbances. Performance of this control method is presented for various weld paths and alloy systems.

4:30 PM  
Prediction of Mechanical Properties of Friction Stir Welds through Microstructural Data: Akbar Heidarzadeh1; Hesam Askari2; 1Azarbaijan Shahid Madani University; 2University of Rochester
    Friction stir welding is an efficient joining process used to join many metallic materials used in aerospace and automotive applications. Different tooling and welding properties results in different microstructures and will ultimately affect the mechanical properties of the weld. We Aim at predicting the behavior of the weld in different loading conditions, using a microstructurally-informed continuum dislocation dynamics model based on experimental data obtained in different zones of the weld. Our model can predict the response of different regions of the weld as well as the overall response of the inhomogeneous microstructure across the welded region. We validate the outputs of our model comparing against tensile tests performed on single weld zones and welded sheets with weld seam oriented at different angles.