Energy and Force Analysis of Ti-6Al-4V Linear Friction Welds for Computational Modeling Input and Validation Data
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LINEAR friction welding (LFW) is a solid-state welding process that is used to manufacture highperformance aerospace components,[1,2] with the titanium alloy Ti-6Al-4V being commonly used.[2–4] The process has many advantages over traditional fusion welding methods, including excellent mechanical properties, avoidance of melting, and very low defect rates. During LFW, one workpiece is oscillated relative to another whilse under a large applied force, as shown in Figure 1. The process is said to occur over four phases:[3,5,6] Phase 1—Initial phase. During this phase asperity
contact exists between the two surfaces to be joined and heat is generated due to friction—see Figure 1(a). The asperities soften and deform, increasing the true area of contact between the workpieces. Negligible axial shortening (burn-off) in the direction perpendicular to oscillation is observed during this phase. Phase 2—Transition phase. During this phase the material plasticizes, so the true area of contact
ANTHONY R. McANDREW, Research Student, PAUL A. COLEGROVE, Senior Lecturer, and ADRIAN C. ADDISON, Senior Research Fellow, are with Cranfield University, Cranfield, Bedfordshire MK43 0AL, U.K. Contact e-mail: a.r.mcandrew@cranfield.ac.uk BERTRAND C.D. FLIPO, Senior Project Leader, is with TWI Ltd, Granta Park, Great Abington, Cambridge CB21 6AL, U.K., and also with Friction and Forge Processes Department, TWI Ltd, Granta Park, Great Abington, Cambridge CB21 6AL, U.K. MICHAEL J. RUSSELL, Section Manager, is with Friction and Forge Processes Department, TWI Ltd. Manuscript submitted April 5, 2014. Article published online September 26, 2014 6118—VOLUME 45A, DECEMBER 2014
increases to 100 pct of the cross-sectional area—see Figure 1(b). The heat conducts back from the interface plasticizing more material and the burn-off begins to register due to viscous material expulsion. Phase 3—Equilibrium phase. During this phase the interface force, thermal profile, and the rate of burnoff reach a quasi-steady-state condition. Significant burn-off occurs through the rapid expulsion of the plasticized material. Phase 4—Deceleration phase. Once the burn-off reaches the pre-set value, the relative motion is ramped down and the workpieces are aligned. In some applications, an additional forging force may also be applied. To understand how the process works, researchers have studied the evolution of the process forces with time,[5,6] used computational models to predict the temperature and deformation,[1,7–10] and have examined the weld microstructures.[4,8,11,12] Computational models are particularly useful as they provide a means of predicting what happens at the weld interface in the rapidly evolving process. However, the models are limited by a lack of data[13]—in particular, the interface force, friction coefficient, and steady-state burn-off rate as a function of the process inputs for the different phases of a weld. This paper addresses these issues using a systematic design of experiments to determine the effects of the process inputs on the average v
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