Retrofitting to Increase Productivity

Systematic predictive maintenance and controls upgrades yield big results in cost savings and productivity.

In the face of these economic times and the resulting budget tightening, many aerospace component suppliers are seeking ways to improve their productivity and bottom line results. At Spirit AeroSystems in Wichita, KS, the strategy to accomplish those goals has been in place for decades. Ed Fenn and his team of retrofit/machine shop specialists are among the many reasons for this situation. Spirit has realized substantial productivity gains through a systematic predictive maintenance program and continuous upgrades to the controls, motors, drives, and other components on the huge multiaxis gantry mills that produce many of the structures.

Under the direction of Fenn, the facilities manager for retrofit/machine shop operations, more than 275 retrofits of various machine tools have been performed since 1982. As he explains, "I was at Sony for five years and saw the way they operated, with an ever-watchful eye on process standards and quality. When I joined this company, Boeing had the Continuous Quality Improvement (CQI) in place, which gave me further insights into the methods we could employ to get more systematic in our machine evaluation processes." Fenn proudly refers to the evolution of that process as "a lump of coal becoming a diamond, which is what our company's process has become today." Every retrofit planned or in progress and every machine tool in the facility - approximately 575, currently - is monitored under a predictive maintenance program. Through this program, all machine parameters of wear, uptime, routine maintenance and even environmental impact are closely 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 in new capital expense, while actually improving the performance of its machine tool fleet.

Several Cincinnati (now MAG/Cincinnati) gantry mills are key to the manufacture of the large metal aircraft components, as well as materials handling structures such as nacelles, which are also made in-house at Spirit. 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, these 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, gear boxes, spindles, encoders and column structures on our gantry mills, we have tracked better productivity numbers on all of them," Fenn explains.

"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 utilize." 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 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, 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. Spirit led the way, according to Fenn, in the implementation of this technology, on the machine tools here. Today, this type of technology is found on all the Cincinnati and Henri Liné (now Forest Liné) 5-axis and 6-axis machines at Spirit, all of which have been retrofit, 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 says in regards to the power and flexibility of the CNC technology currently used for nearly all his group's retrofits.

Boeing has been especially aggressive in encouraging its parts suppliers and machine builders to engage in the use of this technology for overall process improvement strategies. 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. 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," Fenn explains.

He demonstrated the result of this vital exchange on three identical gantry mills in one of the plants here. One of the mills was newly built, while another was retrofitted by an outside contractor, Fenn retrofitted another, and his Spirit crew had done the most recent one. Crediting his team entirely, Fenn notes the retrofit design work, component selection and "common sense solutions" employed in their work product were the result of this interaction between builder, control supplier, other vendors and especially the Spirit machine operators.

In process, there is also constant evaluation of the machine tool performance at Spirit. Through the onboard CNC, the VLAN and ICS protocols employed here, all machine parameters, including vibration and thermal characteristics, are monitored and entered into a data base for evaluation by the CBM team engineers. 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, more than 25,000 points are monitored throughout the 11,119,000ft2 campus.

Total metrics off the Siemens CNC architecture are maintained by the campuswide control system at Spirit, with constant monitoring of every aspect of all machine performance. 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 these 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 ePS system of predictive maintenance. This vendor sought out the input of customers such as Spirit, 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, including the new, recently installed, and older legacy systems.

For cost comparison, the typical retrofit project on a large gantry mill at Spirit might run $1,000,000 or more, but that amount typically represents only about 30% to 40% of the cost of a new machine.

Retrofitting control systems onto machines to enable systematic predictive maintenance has helped Spirit Aerosystems to streamline their operations.

According to Fenn, "We keep the steel and replace everything else," though he notes that a recent retrofit of a Z-axis column on a Henri Liné 5-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," he notes. 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.

As a precursor to the retrofit process, the team at Spirit might engage in a variety of ancillary studies or software developments.

Following the initial studies, a comprehensive assessment of the retrofit versus buy value proposition is conducted. Upon the decision to retrofit, the team develops a procurement package and initiates the buys through corporate purchasing. The scheduling of offline time for a machine tool at Spirit 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 Spirit 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.

As Fenn observes, "We generate much better machine evaluations because we constantly assess the performance and condition of all machine components." When the budget is finally released on the retrofit project, Fenn's assistant, prepares the flow chart for cost, time, materials, labor, quality checking and the full turnkey project completion schedule for presentation to the 40-person crew of this department, who have weekly status meetings to monitor progress.

Fenn says his team members pride themselves on their ability to work in the most complex hardware/software arenas, as well as the world of heavy metal machining and fabrication.

They also recently devised a simple system of labeling I/O modules inside the electrical cabinets for easier and consistent identification on any machine tool at Spirit, simplifying a rather tedious job for their maintenance crew.

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 developed here and to bring more consistency to the HMI for the operator. Fenn's team is constantly striving to find simpler solutions for the translation of condition tags to their work orders, he notes.

As final testimony to the merit of this unique group of individuals, the Spirit retrofit team was actually considered for outside contracting to other local aerospace companies, as Wichita is home to numerous world players in aerospace, all producing parts for the industry. Though these plans never materialized, Fenn says it gave his team a great sense of worth and accomplishment to know their work was so much admired by the other aerospace companies in the area. "There is no denying that it gave us all a little bit of extra pride in what do here."

Fenn concludes by observing, "We pull the talent out of people and we always learn from our mistakes. Our only limitation is our imagination and, when tempered with rules, a better system always results."

Spirit Aerosystems Wichita, KS spiritaero.com

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Elk Grove Village, IL
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