D.H. Lammlein PhD Dissertation - Vanderbilt University

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Figure 145: CFD model axial forces plotted with traverse rate for butted pipe welds made with a 5/8” diameter scrolled shoulder and 6mm diameter threaded probe tool. Efforts were made to ensure that following proper depth and seating of the tool shoulder at the weld initiation site, forces would subsequently fluctuate within an acceptable range during the weld traverse. Figure 146 and Figure 147 show the axial force history of selected experimental welds. Keeping force fluctuations within an acceptable range was done by means of several techniques. The parent pipe sections were machined from their received condition on their inner diameter and outer diameter. After this preprocessing, the wall thickness varied from the approximate thickness of 0.19” by a maximum of 0.005”. This tolerance limit was maintained on each pipe section, and between each pipe section, ensuring near uniform thickness around the circumference of each section and well matched wall thicknesses between pipe sections. The use of the expanding mandrel, described earlier, forced pipe sections into a more perfect circular shape and aligned the inner diameter of the pipe sections. 166
Together, a fine wall thickness tolerance and a tightly adjusted expanding inner mandrel served to align the joint in the geometric configuration most favorable to joining by FSW. With the use of force control and an expanding mandrel it would be possible to allow a greater wall thickness tolerance and the preprocessing step could be eliminated from the welding procedure (Longhurst, <strong>Dissertation</strong>: Force control in friction stir welding, 2009). The shoulder of both of the tools used in the experiment used a scroll to force material inward from the edge of the shoulder during welding as the tool rotates. The scrolled shoulder is shown in Figure 148. This feature increased the tolerance of the tool to tool-work contact variations. Figure 149 and Figure 150 show the superficial appearance of the welds. Preliminary welds performed with an unfeatured shoulder tool showed consistent poor surface quality, producing either surface void defects or flash (material expulsion). It proved to be very difficult to produce superficially acceptable welds without a tool with shoulder features. Finally, the tool was offset 6mm ahead of the geometric center of the work along the traverse direction. This created a plowing effect which reduced tolerance to vertical positioning error. This offset was arrived via experimental trial. It was found that positioning the tool directly over the high point of the pipe (i.e. no offset) resulted in buffeting and an unstable weld condition. Taking these steps meant the experiment could be performed without force control despite the difficulties of system eccentricity and secondary heating present in small diameter pipe FSW. 167
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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
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CHAPTER IV THE FRICTION STIR WELDIN
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applications for its high strength
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Figure 97: Experimental weld sample
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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 and 182: eccentricity, the method of interio
Page 183 and 184: gas tungsten arc welding of small d
Page 185 and 186: Full penetration welds of 4.2” (1
Page 187 and 188: Figure 143: The curvature of the pi
Page 189: Figure 144: Experimental axial forc
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
Page 233 and 234: new FSW process environment is reso
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D.H. Lammlein PhD Dissertation - Vanderbilt University

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