Patternless casting, portable coordinate measuring create successful combo.
Managed by Princeton Univ., Princeton, N.J., NCSX is a joint effort of the Princeton Plasma Physics Laboratory (PPPL) and the Oak Ridge National Laboratory, Oak Ridge, Tenn., both of which are units of the U.S. Dept. of Energy. Poured in June, the steel casting was like nothing ever done at Waukesha Kramer because of:
* Complex geometry--The casting was an open ring (inner diameter of more than 4 ft.) with two flanges running around the exterior of the part and a T-shaped feature "roller-coastering" around the inside diameter. Two large irregularly shaped wings required a drag and two copes so the mold had two parting lines. Eight cores were required.
* Size and weight--Measuring 128 x 108 x 70 in., the prototype was one of the biggest molds (60,000 lbs.) ever built at Waukesha. The raw casting weighed 7,500 lbs. while the finished version tipped the scales at 5,500 lbs. The metal was a proprietary nonmagnetic stainless steel similar to AISI 316.
* Patternless casting--A first for Waukesha, this is a time-and money-saver when large castings are to be poured only once or twice. Chemically bonded sand is allowed to set up into blocks for the cope and drag. The reverse of the shape of the part to be cast is machined into the sand, usually with a 5-axis CNC router.
Successful innovation takes more than courage and capability, however. It also takes an exhaustive amount of inspection. Waukesha Kramer performed hundreds of dimensional checks with a portable coordinate measuring machine (PCMM) from Romer CimCore, Farmington Hills, Mich. The PCMM, a System 3000i, is sold with PowerInspect, developed by Delcam PLC, Windsor, Ontario, Canada. "Without the portable System 3000i, there would have been no way to inspect something that big other than 'hand' methods such as measuring tapes, templates and height gauges," said Bill Norris, vice president of product development for Waukesha Kramer.
"And those methods would have been unacceptable to the NCSX program managers," added John Puhl, president of J.P. Pattern, Butler, Wis., who was Waukesha's customer on the project.
The Romer arm is valued for its infinite rotation in all its major axes. This means users never get wound up (literally) in a complicated inspection job, such as inside a large tool or special casting. If they did, they would have to unwind the arm and back out. The original setup may be lost and, if so, the inspection would have to be repeated.
"During measurement of the mold and the casting, the Romer users had a lot of twisting and turning and going back and forth from one side to the other," Puhl said. "There was a lot of stretching out to surfaces while standing in the middle of the molds and, later, in the casting. That would have been a major nuisance to do without the Romer arm's infinite rotation and portability."
The key strengths of PowerInspect are that it instantly compares each inspected point with the original CAD file or solid model that was used and generates a report on tolerances over, under and right-on.
Select No. 001 at www.moderncasting.com/info
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|Title Annotation:||Case History; Waukesha Kramer Inc.; National Compact Stellarator Experiment|
|Date:||Sep 1, 2004|
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