Siemens helps Spirit AeroSystems keep gantry mills flying

  • 27-Mar-2009 02:55 EDT

Ed Fenn, head of Spirit AeroSystems' retrofit team, stands next to a Cincinnati gantry mill that is being rebuilt.

Through a systematic predictive maintenance program and continuous upgrades to the controls, motors, drives, and other components on its huge multi-axis gantry mills, Spirit AeroSystems of Wichita, KS, has realized substantial productivity gains without the capital investment of new machine tools.

Under the direction of Ed Fenn, Facilities Manager for retrofit/machine shop operations, more than 275 retrofits of machine tools have been performed since Fenn helped establish the group shortly after joining Spirit (Boeing at the time) in 1982.

Each of the approximately 575 machine tools in the facility is monitored under a predictive maintenance program. Wear, uptime, routine maintenance, and even environmental impact are monitored to determine when a planned retrofit or complete overhaul of the machine will be required. Spirit has conserved millions of dollars in new capital expense because of the program, while improving machine tool performance, according to Fenn.

Several Cincinnati (now Mag/Cincinnati) gantry mills are key to the manufacture of the large metal aircraft components Spirit produces, as well as material-handling structures such as nacelles, which are also made in-house. Originally equipped with Siemens ACRAMATIC controls, the forerunner to the advanced SINUMERIK 840D CNC platform that is now used on most of the machine tools here, the gantry mills machine the majority of the metal parts made, primarily from various grades of aluminum, titanium, and tool steels.

“Because we have periodically upgraded our machine controls, along with the motor and drive packages, gearboxes, spindles, encoders, and column structures on our gantry mills, we have tracked better productivity numbers on all of them,” Fenn said. “This is the result of newer controls, which have faster processing speeds, as well as the higher-accuracy positioning drives, linear motors, and encoder technologies we use.”

To further increase machine accuracies, Spirit was the first company in the industry to run a NURBS control, which is the basis for Transformation Orientation (TRAORI), the machine tool process that enables highly precise volumetric-compensation machining so critical in aerospace part production. Since the typical machined metal part in this industry has few, if any, straight lines, there is a continuous need for extremely accurate, five-axis simultaneous transformations across the workpiece surface. This ensures a to-spec part with acceptable finish characteristics, executed and monitored for accuracy in real time. This type of technology is found on all of the Cincinnati and Henri Liné (now Forest Liné) five-axis and six-axis machines at Spirit, and all of them have been retrofitted by the team here—some of them several times.

“On some of the largest machines at Spirit, such as our Brötje riveters used to join the fuselage to the spars and ribs, all the axis and ancillary equipment control capability of the Siemens SINUMERIK 840D comes into play,” Fenn said in regards to the power and flexibility of the CNC technology currently used for nearly all his group’s retrofits. Other nonmetal cutting equipment such as riveters, hydraulic presses, and robotic material-handling devices often get retrofitted with this CNC, as well as Siemens PLCs and other control gear.

Since Fenn maintains all necessary documentation for each machine tool on the resident CNC, the individual operators can always access the documentation on any machine. This protocol further closes the loop on what Fenn sees as a critical requirement. “Unless we have input from everyone, including the operators, the retrofit program would suffer,” he said. “My team greatly benefits from knowing what works and what does not work on a machine, in every area, from the control setup to the access ways surrounding the electrical cabinet and even the part fixturing.”

Through the onboard CNC, the VLAN, and ICS protocols employed at Spirit, all machine parameters, including vibration and thermal characteristics, are monitored and entered into a database. As an example, the stresses on even a simple component such as a way cover are monitored. More than 25,000 points are monitored throughout the 11,119,000 ft² campus.

Total metrics off the Siemens CNC architecture are maintained by the campus-wide control system, with constant monitoring of every aspect of all machine performance, conducted by a relatively small group of highly skilled IT technicians in the master control room. Monitoring of machining processes in real time is possible for further documentation of the machine’s performance, as needed.

Highly sophisticated reliability and condition monitoring equipment is used on the machine tools throughout Spirit facilities and has been for more than 10 years, according to Fenn. He worked with Siemens engineers in Germany, when Siemens was developing its now popular ePS system of predictive maintenance.

The typical retrofit project on a large gantry mill at Spirit might run $1 million or more, but that amount typically represents only about 30-40% of the cost of a new machine. Said Fenn, “We keep the steel and replace everything else,” though he noted a recent retrofit of a Z-axis column on a Henri Liné­ fi­ve-axis machine required an investment of about 50% of the new machine cost. However, “the performance we are getting is every bit as good as a new machine’s.” Strategically, the Spirit retrofit team has a goal of making a machine work at peak efficiency for 10 years following the retrofit unless newer available technology or machine damage mandates an earlier date for repair or replacement of onboard components.

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