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Weekly UpdatesMany aerospace component suppliers are seeking ways to improve their productivity and bottom line results in the face of uncertain economic times and the resulting budget tightening.
Spirit AeroSystems in Wichita, KS, a primary supplier to Boeing and other aircraft builders, has been ahead of the curve.
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Through a predictive maintenance program and continuous upgrades to the controls, motors, drives, and other components on the multiaxis gantry mills that produce many of the structures here, Spirit has realized productivity gains without the capital investment of new machine tool purchases.
Credit goes to Ed Fenn and his team of retrofit/machine shop. Under the direction of Fenn, the facilities manager for retrofit/machine shop operations, over 275 retrofits of machine tools have been performed since Fenn helped establish the group shortly after joining the company in 1982.
Every retrofit planned or in progress and every machine tool in the facility, approximately 575 at present, is monitored under a predictive maintenance program. Through this program, all machine parameters of wear, uptime, routine maintenance, and even environmental impact are monitored, with an eye on the day when a planned retrofit or complete overhaul of the machine will be required.
By doing this, Spirit has conserved millions of dollars in new capital expense, while improving the performance of its machine tool fleet.
Gantry mills upgrades
Several Cincinnati (now MAG/ Cincinnati) gantry mills are essential to the manufacturing of large metal aircraft components, as well as materials handling structures such as nacelles, which house jet engines.
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 at Spirit, the gantry mills machine the majority of the metal parts, primarily from grades of aluminum, titanium, and tool steels.
"Because we have periodically upgraded our machine controls, along with the motor and drive packages, gear boxes, spindles, encoders, and column structures on our gantry mills, we have tracked better productivity numbers on all of them," Fenn explained.
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"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 that we utilize," he added. "To be honest, we ask very little from our suppliers, as we maintain a substantial database of information on all available technologies."
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 allows the precise "volumetric compensation machining critical in aerospace part production.
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Since the typical machined metal part in this industry has few, if any, straight lines, there is a continuous need for accurate, 5-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.
Leads the way
Spirit led the way in the implementation of this technology on the machine tools, according to Fenn. This type of technology is found on the Cincinnati and Henri Lind (now Forest Line) 5-axis and 6-axis machines, all of which have been retrofitted at least once by the team.
On some of the largest machines at Spirit used to join the fuselage to the spars and ribs, such as Brotje riveters, all the axis and ancillary equipment control capability of the Siemens Sinumerik 840D comes into play, Fenn said.
Other non-metal cutting equipment such as riveters, hydraulic presses, and robotic materials handling devices often get retrofitted with this CNC, as well as Siemens PLCs and other control gear.
In creating the run simulation programs for evaluation, Fenn typically uses online tools such as WebEx and pcAnywhere for monitoring and vendor communications. This enables his team to predetermine the best solutions for the machine and process involved in a proposed retrofit.
There is also constant evaluation of the machine tool performance at Spirit. Through the onboard CNC, the VLAN and ICS protocols employed, all machine parameters, including vibration and thermal characteristics, are monitored and entered into a database for evaluation.
As an example, the stresses on even a simple component such as a way cover are monitored for predictive maintenance and eventual retrofit. In total, over 25,000 points are monitored throughout the 11-million-sqft campus.
The entire monitoring process is done by seven technicians in a compact control room. In that same room, Spirit also employs another Siemens development, the Apogee building automation systems software to monitor HVAC, lighting, and campus-wide energy consumption as part of the company's ongoing green initiative.
Total metrics off the Siemens CNC architecture are maintained by the campus-wide control system, with constant monitoring of every aspect of machine performance.
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Monitoring of machining processes in real time is possible for further documentation of the machine's performance. This setup has been especially useful in monitoring the newest technologies used at Spirit, namely, the composite fiber tape-laying machines that build up the fuselages for the Boeing 787 and other aircraft structures.
The company houses the fiber tape-laying machine running in a clean-room environment to produce composite sections for the aerospace industry.
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Highly sophisticated reliability and condition monitoring equipment is used on the machine tools throughout the Spirit facilities.
Fenn worked with Siemens engineers in Germany when Siemens was developing its ePS system of predictive maintenance. Siemens sought the input of customers, though the system Fenn currently uses is highly proprietary, dedicated, and integrated for all the control platforms used on the various machine tools throughout the campus.
For cost comparison, the typical retrofit project on a large gantry mill might run $1 million or more, but that amount typically represents only about 30-40 percent of the cost of a new machine.
"We keep the steel and replace everything else," Fenn said, though he noted a recent retrofit of a Z-axis column on a Henri Line 5-axis machine required an investment of about 50 percent of the new machine cost. However, he said the performance was every bit as good as that of a new machine.
10-year goal
The 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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As a precursor to the retrofit process, the retrofit team may engage in ancillary studies or software developments, from adaptive control schemes for a CNC to the material composition of a poured concrete foundation for a machine base, done to enhance stability and reduce vibration.
Fenn noted that the onboard control is the top priority in gaging obsolescence on any machine at Spirit.
"The control technologies have progressed so far and so rapidly in the last 20 years that we would be foolish to remain in a fixed time mode for retrofitting any machine we operate here," he explained.
Following the initial studies, the team assesses the retrofit-versus-buy value proposition. Once the decision to retrofit is made, the team develops a procurement package to submit to corporate purchasing. The scheduling of offline time for a machine tool is a major responsibility, as the building of an aircraft fuselage requires the precise integration of many departments working in concert.
All machines on the campus have a five-year plan attached, with condition coding tags built into the machine's controller. Once a retrofit need is determined, the facility service request (FSR) is submitted and a return on investment is calculated.
When the budget is finally released on the retrofit project, a flow chart is prepared for cost, time, materials, labor, quality checking, and the full turnkey project completion schedule.
The retrofit operations involve a machine shop, motor/ pump repair shop, fabricating/welding shop, inspection area, and materials handling.
This department is not only responsible for affecting the repairs and retrofits, but also provides all paperwork back-up, software validation, environmental impact data, alarm code sequences, product lifecycle management data, and full maintenance record-keeping.
Spirit has implemented Siemens WinCC SCADA software and OPC interfaces to the machine controls to support the internal MDA of the control-monitoring platform and to bring more consistency to the HMI for the operator.
Composites support
As is true throughout the aerospace industry, composites technology is making an impact on machine builders, shop operations, and controls personnel alike. Spirit is no exception and leads the way in advanced composites build-up and machining, according to Fenn.
The retrofit team also plays a key role at this point, because there is a 25-year-old Cincinnati machine tool performing well on hard metal components that support the composite structures, having been retrofitted with a new control system, coolant system, hydraulics, and all-new operator station.
Another Cincinnati machine is on deck for retrofit with new ways, racks, control station, accelerometers, and pressure transducers. The retrofit team also retrofitted the first Ingersoll fiber placement machine, partnering with Ingersoll as this machine produced the first sections of the Boeing 787, a total composite fuselage except for the spars and ribs.
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