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aerospace manufacturing Specialized Machining


While the machine capabilities at Triumph Structures– Wichita were clearly substantial, it was determined that a need existed for a particular machine that could be used to serve multiple purposes. First, the machining of very long parts with volumetric compensation to manage material expansion and the tool tip position over a very long cutting cycle, often multiple days, was required. Triumph Struc- tures–Wichita has extensive experience in this area, given its market focus. However, it was posited that a single machine might also be capable of running multiple smaller parts or


“We had a variety of machine styles available, but the best solution was a head with three rotary axes, A-B-C integrated in a forked milling head. This provided simultaneous six- axis cutting in a very compact design, with no pole position, less overall axis rotation, a constant feed rate capability and improved surface quality.”


The individual head machining time scenario was further detailed. If the maximum time was achieved using an A and C head with infi nite C axis, the alternative A-B-C integrated rotary axis head could accomplish the same work in 25% of that time.


In designing the fi nal work envelope and machine struc-


ture, Zimmermann engineers determined the best solution was a removable break wall built into the midpoint of the machine bed, which would allow completely independent operation of the entire machine, literally running as two machine tools in one. When removed, the machine bed could accept parts up to 960" (24.4 m) in length and process them using the twin heads working in tandem and monitored for total collision avoidance by the two CNCs onboard. Owing to the unique volumetric compensation feature of the Siemens CNC, where the execution of the machining is based upon the actual tool tip position, the point of intersection for the twin heads was found to be an easily addressed and resolved issue. Surface integrity on the workpiece would be preserved, while machine and operator safety would remain paramount. This machine was built over a period of 18 months. Parts


were sent to Zimmermann to be fully tested prior to being erected onsite at Triumph Structures–Wichita.


The machine’s twin gantries each have a Siemens Sinumerik 840D SL CNC and can operate independently or in tandem to machine a variety of workpieces or a single structure up to 960” in length.


operate in twin fashion, occasionally using the entire machine bed with both heads working the same part in tandem. Clearly, the latter scenario would demand extremely close attention to collision avoidance between the gantries, as well as the consistency of surface machining at the points where the twin machining heads intersected. For the requirements presented by Triumph Structures– Wichita, the optimal machine necessitated that Zimmermann, a longtime partner and portal machine supplier to Triumph, modify its popular FZ100 machine with twin gantries, each equipped with a three-axis rotary head and independent Siemens Sinumerik 840D sl CNC. As Zimmermann Inc. President Matthias Tockook notes,


The Machine in Action In operation, according to Harry Thurmond, the Zim- mermann head design provides signifi cant advantages in speed on the typical peaks and pockets found in aerospace structure machining, working in tandem with the look- ahead feature on the CNC. “It slows down and speeds up in anticipation of the next required surface contour. Over long run times, this can translate into an improvement of 35% or better, because there is no deburring or polishing required,” he said. “We routinely get better than a 125 rms fi nish on inside pocket surfaces and up to a 32 rms on the outside of the Series 7000 aluminums we run. Combined with the fl ex- ibility of the machine to work a single structure or individual workpieces simultaneously, we have been quite satisfi ed with the results to date.”


On longer runs, Thurmond adds, the chilled coolant used on the Zimmermann is helpful in minimizing thermal expan- sion of the material, a critical factor in long-run machining


74 — Aerospace & Defense Manufacturing 2015


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