Modern Machine Shop

JUL 2018

Modern Machine Shop is focused on all aspects of metalworking technology - Providing the new product technologies; process solutions; supplier listings; business management; networking; and event information that companies need to be competitive.

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MMS JULY 2018 92 mmsonline.com WORLD'S L ARGEST DIGITAL CAMER A underway and proving to be even more challenging. The housing is a cylindrical 6061 aluminum part the same diameter as the back flange (5.5 feet), but taller (about 2.5 feet high) and with thinner walls. The housing is actually several pieces welded together; the main shell is rolled metal, with forged rings on the top and bottom. Additional side plates are welded in several places, as are gussets all the way around on the inside. Keller performed the welding in house, then sent the part out for initial OD/ID turning on a large vertical turning lathe. That is where the trouble started. The shell, which had a starting thickness of 0.625 inch, needed to be finished down to 0.25 inch or less in some places. Welding causes residual stresses in metal, and as the housing got thinner, those stresses began to show themselves. "We thought we had plenty of mate- rial to machine," says Jorge Martinez, quality department manager, but the wall became so thin that even handling it could make it go out of spec, and the subcon- tractor halted the operation. At that point, Keller sent the housing out for a low-temperature thermal treatment, a controlled process in which metal is heated and cooled gradually to relieve stress while limiting the effect on the aluminum-base-metal properties. The company hoped this process would help stabilize the welded material, but the housing came back from stress relief out of round. To counter the roundness issues, Keller set up the camera housing on its Toshiba Shibaura BF-130B horizontal milling and boring machine. The idea was not to use this machine tool for cutting the part, but rather, to use the Toshiba's large turntable to facilitate on-machine probing to determine where the part was out-of-round and by how much. The machine's open architecture also enabled access for another step: welding. When I visited, the shop was in the process of mechanically straightening the part. "We jacked it out (like you would with a car jack) until it reached the correct dimensions," Mr. Martinez says. Then, the company fabricated a four-spoke support structure from aluminum tubing. This support, called the "spider," was welded inside the camera housing while it sat fixtured on the Toshiba. A second spider was about to be installed at the time of my visit. The housing then went out for thermal stress relief again, this time with the spiders in place to keep it round, and at a higher temperature to ensure removal of internal stresses. Approaching the Big Picture Once the housing returned from stress relief for the second time, Keller removed the spiders and sent it out for turning. The next steps will be to machine the cutouts and finish it on the Parpas gantry machining center. Programmer Scott Steggs already has a CAM program in progress for the part; one benefit to the Mastercam software is that it allows for off line work, so that Mr. Steggs Gussets inside the camera housing (shown here in Mastercam) mean that the upper half of the part cannot be turned, and will need to be milled from the inside with the HSM head. Toolpath simulations with Vericut help to ensure success machining one-offs and other challenging parts such as the camera housing. Images: Keller Technology The LSST camera parts leverage Keller Technology's expertise in machining one- offs. Another example—a diffractometer component for the Department of Energy—in this article: gbm.media/kellerdoe CONFIDENCE IN ONE-OFFS

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