Aerospace Materials 170,000 ſt2 (15,810 m2 ) CMC factory near Asheville, NC, which
will make a high-pressure turbine shroud for the LEAP engine, marking the first time CMCs will be used for a commercial application. Te LEAP, a product of CFM International, a joint company of GE and France’s Snecma SA, will enter airline service in 2016 and will power the Airbus A320neo, Boeing 737 MAX and China’s Comac C919. In other words, as Billy Ocean might put it; CMCs are
finally getting out of our dreams and into our planes. Which makes this a good time to ask two questions:
First, just how does this stuff work? And second, just what happened in the two decades between its groundbreaking discovery and the groundbreaking ceremony for the Asheville production facility? Jeff Wessels, GE Aviation’s plant leader for the Newark, DE, CMC microfactory, recently spoke to Manu- facturing Engineering Media to answer both questions and to walk us through how CMCs are made at GE.
The Recipe According to Wessels, the process for making CMC
components begins in Japan at a Tokyo-based company called NGS Advanced Fibers—a joint venture of GE, Safran, and Nippon Carbon Co. that makes silicon carbide (SiC) con- tinuous fiber or Nicalon. GE, at its Newark, DE, facility, puts
cess. But then we go on to a couple of extra steps to fully densify the component, and really turn it into a ceramic matrix.” Te next step is pyrolysis, which burns off all of the organic
constituents that are still leſt inside aſter the autoclave process. What’s leſt behind is a porous lattice made from the ceramic- coated silicon-carbide fibers in the shape of the desired part. Tis is then followed by what Wessels terms the melt-infiltra- tion process: “Tis is where we use another furnace to basically melt
silicon in contact with the part,” Wessels explained. Te silicon wicks its way into the lattice, turning all of the constituents that were leſt over in that matrix into silicon carbide. “Where previously you had a porous carbon matrix, you end up with a silicon-carbide matrix—it’s all silicon carbide but now it’s a fiber within a matrix. And that,” he said, “is what imparts the toughness to these materials.” “Te beauty of what GE’s been able to develop is that we get
very close to full density on these parts—maybe 98% density or more, without losing the properties of the fiber,” he noted. Te final step in creating a CMC part is finishing it with
five-axis CNC milling machines. Te CMC material is ex- tremely hard and durable—too tough for traditional cutting tools, Wessels said. “Rather than conventional cutting tools, we have to use diamond-coated tools. Tey’re the one thing we
“It’s all silicon carbide but now it’s a fiber within a matrix. And that’s what imparts the toughness.”
several layers of “a very proprietary” coating onto the fiber via chemical vapor deposition. Tis coating does two things, Wessels says: “It provides the toughness needed later on in the process, when the silicon carbide fiber needs to slide within a matrix, and it provides protection that the fiber will need in downstream processes, which will involve a lot of high tem- peratures.” Others at GE refer to it as “the secret recipe.” Tat coated fiber is then turned into a prepreg tape, in a
process that will sound familiar to those who work with car- bon composites. “We put the fiber through a slurry compound that has all of the matrix constituents in it, including carbon, silicon carbide. It goes onto the fiber, and the fiber is wound onto a drum, with very close spacing between the fibers that is surrounded by this matrix material. We dry it, and what we end up with is a piece of tape, about 15" wide by 50" long by 0.007–0.008" thick [381 × 1270 × 0.17–0.20 mm].” Tis tape is provided to a layup team, who again follow a
process identical to that of more traditional composite layup: “Tey cut it into different shapes and lay those pieces over and on top of each other in a tool that imparts the final shape of the part that we’re looking to make,” Wessels said. “Te next step is to use an autoclave to bake at temperature and pressure—all very similar to PMC—the polymer matrix composite-type pro-
140 Aerospace & Defense Manufacturing 2014
have that cuts through this material effectively on a bulk scale. But other than the use of diamond-encrusted tools, the rest of the process is typical machining. We use the same kind of five- axis programming that’s used throughout the industry.”
Size Matters Te first part to be manufactured at Asheville is a turbine
shroud that’s about 5" (127-mm) in circumferential length, but CMC components can be much larger and smaller. Te pyroly- sis and melt-infiltration processes aren’t affected at smaller sizes, Wessels said, but he noted that “when going small, the handling of the plies becomes more complex.” At somewhat larger sizes, in contrast, the plies become easier to handle when laying up the part. “But when you get too large,” he noted, “you end up needing a lot of silicon to infiltrate the part. “We’ve been able to make pretty large parts, though. We’ve
made a combustor liner from this material, a part that’s about 32" [813-mm] diam and with an axial length of 8–10" [203–254 mm].”
The Refinement In the popular imagination, there is no intermediary step between the creation of a new material and its implementation
Page 1 |
Page 2 |
Page 3 |
Page 4 |
Page 5 |
Page 6 |
Page 7 |
Page 8 |
Page 9 |
Page 10 |
Page 11 |
Page 12 |
Page 13 |
Page 14 |
Page 15 |
Page 16 |
Page 17 |
Page 18 |
Page 19 |
Page 20 |
Page 21 |
Page 22 |
Page 23 |
Page 24 |
Page 25 |
Page 26 |
Page 27 |
Page 28 |
Page 29 |
Page 30 |
Page 31 |
Page 32 |
Page 33 |
Page 34 |
Page 35 |
Page 36 |
Page 37 |
Page 38 |
Page 39 |
Page 40 |
Page 41 |
Page 42 |
Page 43 |
Page 44 |
Page 45 |
Page 46 |
Page 47 |
Page 48 |
Page 49 |
Page 50 |
Page 51 |
Page 52 |
Page 53 |
Page 54 |
Page 55 |
Page 56 |
Page 57 |
Page 58 |
Page 59 |
Page 60 |
Page 61 |
Page 62 |
Page 63 |
Page 64 |
Page 65 |
Page 66 |
Page 67 |
Page 68 |
Page 69 |
Page 70 |
Page 71 |
Page 72 |
Page 73 |
Page 74 |
Page 75 |
Page 76 |
Page 77 |
Page 78 |
Page 79 |
Page 80 |
Page 81 |
Page 82 |
Page 83 |
Page 84 |
Page 85 |
Page 86 |
Page 87 |
Page 88 |
Page 89 |
Page 90 |
Page 91 |
Page 92 |
Page 93 |
Page 94 |
Page 95 |
Page 96 |
Page 97 |
Page 98 |
Page 99 |
Page 100 |
Page 101 |
Page 102 |
Page 103 |
Page 104 |
Page 105 |
Page 106 |
Page 107 |
Page 108 |
Page 109 |
Page 110 |
Page 111 |
Page 112 |
Page 113 |
Page 114 |
Page 115 |
Page 116 |
Page 117 |
Page 118 |
Page 119 |
Page 120 |
Page 121 |
Page 122 |
Page 123 |
Page 124 |
Page 125 |
Page 126 |
Page 127 |
Page 128 |
Page 129 |
Page 130 |
Page 131 |
Page 132 |
Page 133 |
Page 134 |
Page 135 |
Page 136 |
Page 137 |
Page 138 |
Page 139 |
Page 140 |
Page 141 |
Page 142 |
Page 143 |
Page 144 |
Page 145 |
Page 146 |
Page 147 |
Page 148 |
Page 149 |
Page 150 |
Page 151 |
Page 152 |
Page 153 |
Page 154 |
Page 155 |
Page 156 |
Page 157 |
Page 158 |
Page 159 |
Page 160 |
Page 161 |
Page 162 |
Page 163 |
Page 164 |
Page 165 |
Page 166 |
Page 167 |
Page 168 |
Page 169 |
Page 170 |
Page 171 |
Page 172 |
Page 173 |
Page 174 |
Page 175 |
Page 176 |
Page 177 |
Page 178 |
Page 179 |
Page 180 |
Page 181 |
Page 182 |
Page 183 |
Page 184 |
Page 185 |
Page 186 |
Page 187 |
Page 188 |
Page 189 |
Page 190 |
Page 191 |
Page 192 |
Page 193 |
Page 194 |
Page 195 |
Page 196 |
Page 197 |
Page 198 |
Page 199 |
Page 200 |
Page 201 |
Page 202 |
Page 203 |
Page 204 |
Page 205 |
Page 206 |
Page 207 |
Page 208 |
Page 209 |
Page 210 |
Page 211 |
Page 212 |
Page 213 |
Page 214 |
Page 215 |
Page 216 |
Page 217 |
Page 218 |
Page 219 |
Page 220 |
Page 221 |
Page 222 |
Page 223 |
Page 224 |
Page 225 |
Page 226 |
Page 227 |
Page 228 |
Page 229 |
Page 230 |
Page 231 |
Page 232 |
Page 233 |
Page 234 |
Page 235 |
Page 236 |
Page 237 |
Page 238 |
Page 239 |
Page 240 |
Page 241 |
Page 242 |
Page 243 |
Page 244 |
Page 245 |
Page 246 |
Page 247 |
Page 248 |
Page 249 |
Page 250 |
Page 251 |
Page 252 |
Page 253 |
Page 254 |
Page 255 |
Page 256 |
Page 257 |
Page 258 |
Page 259 |
Page 260 |
Page 261 |
Page 262 |
Page 263 |
Page 264 |
Page 265 |
Page 266 |
Page 267 |
Page 268 |
Page 269 |
Page 270 |
Page 271 |
Page 272 |
Page 273 |
Page 274 |
Page 275 |
Page 276 |
Page 277 |
Page 278 |
Page 279 |
Page 280 |
Page 281 |
Page 282 |
Page 283 |
Page 284 |
Page 285 |
Page 286 |
Page 287 |
Page 288 |
Page 289 |
Page 290 |
Page 291 |
Page 292 |
Page 293 |
Page 294 |
Page 295 |
Page 296 |
Page 297 |
Page 298 |
Page 299 |
Page 300 |
Page 301 |
Page 302 |
Page 303 |
Page 304 |
Page 305 |
Page 306 |
Page 307 |
Page 308 |
Page 309 |
Page 310 |
Page 311 |
Page 312