technology in action
tolerances and rigid specifications. As an example, some blades must meet weight tolerances reaching three deci- mals in grams in addition to strict dimensional requirements. Because turbine engine manufacturers continually raise the operating temperatures of their products to reduce emissions and increase efficiency, the blades often feature complex contours and internal coring engineered to manage heat. The acute contours and coring increase the challenges of grind- ing and fixturing the blades. Form Grind fills a mid-range production niche. Vice Presi- dent and General Manager Gary Treichler said, “Although some blade programs are as large as 100,000 pieces yearly, at the end of the day we are a job shop. Most of our runs are 500 to 1000 blades at a time.”
CNC technology enables the shop to handle the varying volumes efficiently. While the shop’s first manual machines required constant skilled attention, today’s CNC equipment permits setting up multiple machines that can be tended by one operator after production runs begin. “We don’t do strictly untended operation, but certainly
there are jobs where cycle times may be 10 or 15 minutes and an operator can load and watch multiple machines,” Treichler said. “The CNC equipment basically allows us to work smarter. We’ve had around 50 employees for the last 10 years, and with additional Mägerle grinders we have doubled our output over that decade with the same workforce.” Quick turnover is crucial in the job shop environment. The shop may set up a job in a day, run it for two to five days, then take it off the machine to make room for the next job. Some of Form Grind’s jobs repeat on a monthly, quarterly, yearly, or even longer basis. For example, the shop recently brought back previously used tooling to again refurbish com- ponents for B-52 bombers.
Tooling Fabrication
A key contributor to Form Grind’s responsiveness and flexibility is its in-house design and fabrication of workhold- ing tooling. “We are able to maximize efficiency by loading many parts into holding fixtures,” Treichler said. “We want to maximize efficiency where we get as many parts as close together as possible to get the best bang for the buck.” For smaller blades in 1 to 3" (25–76-mm) sizes, the shop uses guillotine-type six point nest fixtures that hold 20 blades for an operation. The fixturing is engineered to position the parts so the wheel is not grinding air and operating at shallow depths of cut, maximizing wheel usage. When two sets of multi-piece fixturing are built for a job, one is always on the machine and the grinder can run
continuously. Treichler pointed out that continuous, accurate output is largely dependent on grinding machine capabili- ties, and noted that the Mägerle machines, some with 20” (508 mm) diameter wheels and 100-hp (75-kW) water-cooled AC spindle drives, run 20 hours a day, six days a week. “To compete in a global environment you have to have a really strong piece of equipment that can continuously grind parts,” he said. He added that the grinders’ rigidity and strength also come into play when grinding the tough nickel-base alloys that comprise most gas turbine blades.
Form Grind has a long history with United Grinding. The shop has bought new machines (the most recent a Mägerle MFP 125), acquired machines from other grind shops, and had its legacy machines rebuilt. Through collaboration with United Grinding’s Customer Care Team and the efforts of Form Grind’s in-house maintenance staff, Treichler said, “We have machines that are 30 years old and are still making money on them. In fact, we just sent a machine to the United Grinding facility in Miamisburg, OH, for rebuild. Once re- turned, the machine will give us another lifetime of precision grinding production.”
The complexity and permanence of the Form Grind’s custom-fabricated tooling depends on job requirements. Typically, a blade-grinding program of 100,000 blades a year will employ elaborate, high-capacity tooling. Initial tooling costs will be significant but will be more than recovered over the high-volume run. A blade program that has 500 to 1000 pieces per year, on the other hand, may use fixtures that hold six to 10 parts as opposed to 20 at a time and tooling costs will better match the program’s return.
Fir Tree Precision Treichler said the first steps in grinding a blade usually focus on establishing the dimensions of the critical blade root mounting feature called a fir tree. So called because of its shape, the fir tree becomes a reference point for further op- erations such as grinding end face or shroud features. To build fixtures for the critical grinding operations, where in some cases the tolerances are ± 0.0002" (0.005 mm), the shop uses an iterative alignment method to establish target points on a blade and build a six-point nest for holding the part.
Process Strategies
Depending on factors such as blade size, workpiece material, and tolerance requirements, Form Grind establishes different grinding processes for different blades. “For some larger blades we might want to creep feed grind and reduce the reciprocation at the end of the process,” Treichler said.
104 — Aerospace & Defense Manufacturing 2015
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