D.H. Lammlein PhD Dissertation - Vanderbilt University

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Figure 140: A closeup view of a tool used in the experiment and the butted weld specimens used in the experiment. The pipe sections are shown mounted in the welding apparatus. The experiment is started from this position. The tool probe was position was calibrated, or zeroed, against the surface of the work. The tool rotation is started and the probe is plunged into the material until the desired contact is achieved with the shoulder on the cylindrical surface of the work. The circular nature of the weld path in a butted pipe configuration results in a secondary heating at the end of the weld. To complete a full, circumferential weld, the tool must cross over the weld initiation site which remains warm for a small diameter pipe. This additional heat affects the steady state portion of the weld and the weld termination. The highly coupled nature of the thermal and mechanical phenomena in FSW means this thermal effect can affect the weld mechanical properties. In this work, welds are observed by thermal camera and the effect of secondary heating is seen in the thermal data and the CFD model contours. The shank temperature is observed to increase throughout the weld. A similar problem is observed by Kou et al. in autogenous 158
gas tungsten arc welding of small diameter Al-6061 pipe (Kou & Le). The authors conclude that computer model and experiment show a uniform fusion zone girth during seam welding and a continually increasing fusion zone girth under the same conditions in circumferential welds on small diameter pipe. The authors propose a preprogrammed reduction in weld power during the weld to reduce fusion zone growth during the process. Lee et al. used a state-space optimization method of process parameters to successfully maintain weld pool geometry around the circumference of small diameter Al-6061 pipe (Na & Lee). Weld pool geometry was maintained but it was noted that the 450°C isotherm continued to expand. In a butted pipe configuration, the cylindrical work must be rotated about its axis and this presents three issues which complicate the ability to maintain a constant contact condition between the work and shoulder. Eccentricity in the rotation of the pipe combined with eccentricity in the circumference of the pipe sections and variations in pipe thickness result in varying height of the work surface at the tool contact location. If this variation is significant, it can be accounted for by mapping the system eccentricity prior to welding by touching the tool to the work surface at various locations around the circumference. A mapped height path can then be followed during welding. Additionally, process force feedback control can be used to compensate for system eccentricity by adjusting vertical tool position or weld parameters based on axial force, torque, or both (Longhurst, Strauss, Cook, Cox, Hendricks, & Gibson, Investigation of force controlled friction stir welding for manufacturing and automation, 2010) (Longhurst, Strauss, & Cook, Identification of the key enablers for force control of friction stir welding) (Longhurst, Strauss, & Cook, Enabling Automation of Friction Stir Welding: The Modulation of Weld Seam Input Energy by Traverse Speed Force Control, 2009) (Longhurst, Strauss, Cook, & Fleming, Torque control of friction stir welding for manufacturing and automation, April 28, 2010). In this work an expandable inner mandrel is used to support and locate the pipe sections during welding. A photo of this setup is shown in Figure 141. Screws force an interior plug with an outer diameter taper into the ring anvil which has an inner diameter taper. A gap cut in the ring anvil allows the ring (or c-shape) to expand against the interior of the pipe sections. An expandable mandrel, as opposed to a press fit or 159
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FRICTION STIR WELDING OF SPHERES, C
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TABLE OF CONTENTS TABLE OF FIGURES
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Appendix ..........................
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Figure 16: Left(FE streamline), Mid
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Figure 51: A thermal camera image t
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for a similar conventional weld (3/
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Figure 102: Tapered retraction proc
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setting are indicated. Note that st
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Unsupported welds of this kind with
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Figure 157: A thermal camera image
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ottom sample is a tungsten inert ga
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N - newton (force unit) n - visco-p
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INTRODUCTION Friction Stir Welding,
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educed conduction lengths. In small
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CHAPTER I LITERATURE REVIEW: COMPUT
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frictional condition at the interfa
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contact. The contact area can inclu
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For horizontal sections, a heat inp
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(1.11) where r p is the probe (pin)
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This efficiency term, η pd , is kn
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The heat input on the tool surface
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The added complication of these met
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Figure 5: Lateral cross sections of
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Flow stress in aluminum alloys is d
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Figure 8: Three flow fields a) rota
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and post-weld cool-down. This model
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Williams et al. [60] use a 2D-axisy
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Figure 16: Left(FE streamline), Mid
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Figure 18: Temperature contour over
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Figure 22: Temperature distribution
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Figure 24: Lateral velocity contour
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Figure 26: Experimental(white) vers
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Figure 28: Top view schematic of tu
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[5] Taylor RE, Groot H, Goerz T, Fe
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[41] Heinz B., Skrotzki B., Eggler
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CHAPTER II COMPUTATIONAL ANALYSIS O
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Figure 30: Blind t-joint setup with
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Figure 33: Process forces and later
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Figure 35: Experimental Welds, Axia
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Figure 37: FEA boundary conditions
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A 4500 N axial force is applied eve
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axial force with lateral offset dur
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Figure 42: Contour plot of von Mise
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Figure 44: Deformation contour for
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Figure 46: Quarter-plate model for
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Figure 49: Contour plot of deflecti
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where P is the weld power (W), Q is
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Figure 52: Fluent CFD model zones.
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Figure 55: Thermal contour of weld
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Figure 59: Thermal contour of weld
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Figure 61: Velocity vectors for 0.0
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Figure 65: Contour of velocity magn
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CHAPTER III THE APPLICATION OF SHOU
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Figure 66: A shoulder-less, conical
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Figure 68: Typical axial(Z-axis) fo
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Figure 71: 90° conical tool macros
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Figure 75: Run 3, 80° conical tool
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Figure 79: (90º tool) Ultimate ten
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Figure 83: (90º tool) Lateral forc
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Figure 87: (80º tool) Lateral forc
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The Eulerian, finite volume, CFD so
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Figure 92 shows the increasing elem
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Figure 91: CFD model geometry consi
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Figure 95: Lateral cross-section of
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Figure 96: Attempts a probe tapered
Page 131 and 132: CHAPTER IV THE FRICTION STIR WELDIN
Page 133 and 134: applications for its high strength
Page 135 and 136: Figure 97: Experimental weld sample
Page 137 and 138: Figure 99: Split protrusion type de
Page 139 and 140: with a cupped recess. It is however
Page 141 and 142: of tapered retraction (i.e. move th
Page 143 and 144: The adjustments in vertical positio
Page 145 and 146: manners the assigned depth was main
Page 147 and 148: Figure 108: Lateral macrosections f
Page 149 and 150: Figure 110: (Supported, cupped tool
Page 155 and 156: apparent strength of 26% parent whi
Page 157 and 158: with a 100º conical tool (0.025”
Page 159 and 160: Figure 119: Macrosection view of an
Page 161 and 162: and tooling. Torque is highly depen
Page 163 and 164: locally in proportion to the local
Page 165 and 166: Figure 126: (threaded tool) Contour
Page 167 and 168: Figure 128: (conical tool) Geometry
Page 169 and 170: Figure 131: (threaded tool) Lateral
Page 171 and 172: The results presented here show tha
Page 173 and 174: Figure 136:(from left: Tapered retr
Page 175 and 176: [8] Metallurgical analysis of ablat
Page 177 and 178: CHAPTER V FRICTION STIR WELDING OF
Page 179 and 180: Collaboration between Advanced Meta
Page 181: eccentricity, the method of interio
Page 185 and 186: Full penetration welds of 4.2” (1
Page 187 and 188: Figure 143: The curvature of the pi
Page 189 and 190: Figure 144: Experimental axial forc
Page 191 and 192: Together, a fine wall thickness tol
Page 193 and 194: Figure 147: Axial force history for
Page 195 and 196: The weld macrosections show complet
Page 197 and 198: Figure 154: Macrosections of welds
Page 199 and 200: Figure 157: A thermal camera image
Page 201 and 202: Figure 159: Average tool shank temp
Page 203 and 204: 471,146 faces. The meshes are fine
Page 205 and 206: Figure 162: A closeup view of mesh
Page 207 and 208: 4 2 3 4 5 16 " 1.745 2 0.24
Page 209 and 210: applied heat locally in proportion
Page 211 and 212: Figure 164: Modeled temperature con
Page 217 and 218: Figure 172: Model pathlines for the
Page 219 and 220: Figure 174: Model pathlines for the
Page 221 and 222: later speed setting, the tool welds
Page 223 and 224: Figure 178: Zoom view of a macro ta
Page 225 and 226: Figure 180: The superficial appeara
Page 227 and 228: Figure 182: The rotary welding appa
Page 229 and 230: Figure 185: A diagram illustrating
Page 231 and 232: CONCLUSION AND FUTURE WORK Conclusi
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new FSW process environment is reso
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D.H. Lammlein PhD Dissertation - Vanderbilt University

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