Effective Maintenance and Upgrades Keep Gantry Mills Flying
Like most manufacturers, aerospace component suppliers are seeking ways to improve their productivity and bottom line results in tough times. Spirit AeroSystems in Wichita, KS, is a primary supplier to Boeing and other aircraft builders, and has been following this strategy for decades. Ed Fenn, facilities manager for retrofit/machine shop operations, and his team of retrofit and machine shop s...
Like most manufacturers, aerospace component suppliers are seeking ways to improve their productivity and bottom line results in tough times. Spirit AeroSystems in Wichita, KS, is a primary supplier to Boeing and other aircraft builders, and has been following this strategy for decades. Ed Fenn, facilities manager for retrofit/machine shop operations, and his team of retrofit and machine shop specialists have created a systematic program of predictive maintenance and continuous upgrades to the controls, motors, drives, and other components on the huge multi-axis gantry mills that produce many aircraft structural components. As a result, Spirit has realized substantial productivity gains without the capital investment of new machine tool purchases.
Under Fenn’s direction, the team has performed over 275 retrofits of various machine tools since 1982. Fenn helped establish the team originally at Boeing, and stayed with it after the business was spun off to form Spirit. 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 Continuous Quality Improvement (CQI) in place, which gave me further insights into methods 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.”
He characterizes the process as a grass-roots standards development, beginning with the key people on his team. Rich Henley, lead mechanical technician, and Mike Spencer, lead electrical technician, work with Ed’s assistant, Nicole Jay, to keep the process as streamlined as possible. Every one of the 575 machine tools currently in the facility is monitored under a predictive maintenance program. Through this program, all machine parameters are closely monitored, until the day when a 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.
Keeping mills turning
Several Cincinnati (now MAG/Cincinnati) gantry mills are key to manufacturing large metal aircraft components and materials handling structures such as nacelles, which are 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 higher accuracy positioning drives, linear motors, and encoder technologies we utilize. To be honest, we ask very little from our suppliers, as we maintain a substantial data base of information on all available technologies.”
Given the odd shapes and complex curves of aircraft components, CNC mills for this industry require sophisticated programming capability to create those contours.
Few straight lines
To further increase machine accuracies, Spirit was the first company in the industry to run a NURBS (Non-Uniform Rational B-Spline) control, which is the basis for Transformation Orientation (TRAORI), the process that allows precise volumetric compensation machining critical in aerospace part production. Since a typical metal aircraft part has few, if any, straight lines, there is a 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. Spirit led the way, according to Fenn, in the implementation of this technology. Today, it’s on all the Cincinnati and Henri Line (now Forest Line) five-axis and six-axis machines at Spirit, all of which have been retrofit by the team here, some of them several times.
“On some of the largest machines at Spirit, such as our Brötje riveters [which are] 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,” says Fenn about the CNC technology currently used for nearly all his group’s retrofits. Other equipment such as riveters, hydraulic presses, and robotic materials handling devices equipment often get retrofitted with this CNC, as well as 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.
Aggressive for new technology
Boeing has been especially aggressive in encouraging its parts suppliers and machine builders to use this technology for process improvement strategies. Since Fenn maintains all necessary documentation for each machine tool on the resident CNC, individual operators can always access the documentation on any machine. This protocol 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 control set-up to 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 and the Spirit crew retrofitted the third without external assistance, but following common-sense solutions developed through interaction between builder, control supplier, other vendors, and especially the Spirit machine operators.
Spirit rigorously monitors machine tool performance, including vibration and thermal characteristics, collecting data for evaluation by the CBM team engineers. In total, over 25,000 points are monitored throughout this 11,119,000 square-foot campus. This monitoring program has been especially useful while integrating the newest technologies used at Spirit, the composite fiber tape laying machines that build up the fuselage for Boeing 787 and other aircraft structures made here. Spirit houses the fiber tape-laying machine running in a clean-room environment to produce composite sections for the aerospace industry. This massive machine tool required 610 cubic yards of concrete to be poured for the base. Then, the building was erected around the installed machine.
Still less than new
Assembling aircraft fuselages requires lots of open space under roof.
A typical retrofit on a large gantry mill might run $1 million or more, but that’s only about 30-40% of the cost of a new machine. “We keep the steel and replace everything else,” says Fenn, although he noted a recent retrofit of a Z-axis column on a Henri Line five-axis machine reached about 50% of a new machine. Still, he believes the performance from a rebuilding is as good as a new machine. The Spirit retrofit team has a goal of making a rebuilt machine work at peak efficiency for 10 years, but technology advances or machine damage can shorten that. “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,” Fenn adds.
As a precursor to the retrofit process, the team at Spirit might engage in a variety of ancillary studies, considering software developments, adaptive control schemes for CNC, or even material composition of a machine foundation to enhance stability and reduce vibration.
If the value of a retrofit wins over replacing a given machine, the team develops a procurement package and initiates the buys through corporate purchasing. Scheduling 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.
When the budget is finally released on a retrofit project, Nicole Jay prepares the flow chart for cost, time, materials, labor, quality checking, and the full turnkey project completion schedule. The 40-person crew of the department, begins the process with weekly status meetings to monitor progress.
Large supporting cast
To support retrofit operations, a machine shop, motor/pump repair shop, fabricating/welding shop, and inspection area are available. Moreover material handling equipment is on site to move huge machines through the shop. Fenn says his team members pride themselves on their ability to work in the most complex hardware and software arenas, as well as the world of heavy metal machining and fabrication, without losing site of their customers. Recently they devised a system of labeling I/O modules inside the electrical cabinets that simplified a rather tedious job for their maintenance crew.
This department also provides all paperwork back-up, software validation, environmental impact data, alarm code sequences, product lifecycle management data, and maintenance record-keeping.
As is true throughout the aerospace industry, composites technology is rapidly making a huge 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. The retrofit team plays a key role here, because it reconfigured a 25-year-old Cincinnati machine tool to handle hard metal components that support composite structures. Changes included a new control system, coolant system, hydraulics, and all-new operator station. 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.
Fenn reflects, “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.”
Don Trotter is an account manager for Siemens Aerospace. Reach him at firstname.lastname@example.org .
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