Constant innovation is essential to maintaining a competitive edge in aerospace manufacturing. Lead time and cycle time reductions must be achieved while simultaneously improving quality levels across all manufacturing processes. To that end, Boeing has been using high-speed machining cells to manufacture window belt frames faster and more effectively than ever before.
Window belt frames, which are machined from aluminum and titanium forgings, wrap around the airplane's cockpit section once assembled. Simple to describe, the frames were proving complex to manufacture.
Machining cells help eliminate the stacks of parts waiting to be used by assembly.
Om Tandon, the Boeing equipment engineer responsible for the new cells, explains. "Each window belt frame is made up of compound angles with more than 100 holes," he says. "Each hole must be incredibly accurate, within a few thousandths of an inch tolerance, to line up with other parts. It can be a tough part to machine using conventional methods. Multiple setups were required across dedicated machinery. This not only impacted cycle time, but heat from these multiple processes could warp the part's elaborate aluminum shape, compromising part integrity and accuracy."
Tandon opted to move from dedicated machinery to three high-speed machining cells to increase part quality and throughput while decreasing cycle time. The cells include a total of nine Makino MC1816-5X high-speed, horizontal machining centers. This move not only eliminated dedicated machinery and consolidated part finishing and hole drilling operations, it now allows Tandon and his team to create more parts of higher quality, 30 percent faster than ever before.
High-Tech Support Cuts Out Time
Part of this cycle time reduction is made possible by the cells material handling support. Each cell is equipped with a Makino modular machining complex (MMC) and Makino's A2 cell control system. The MMC's shuttle delivery system reduces machine setup time dramatically by automatically retrieving and delivering parts to each machine.
"In the past," says cell operator James McDaniel, "we spent a lot of time on setup. We had to stop the machine every time we set up a new job. With this shuttle system, spindle utilization has been increased. Since the machining centers are not waiting for another part, we literally run these machines constantly across three shifts, five days a week for nearly constant uptime. And the cell control dynamically schedules production to optimize workflow and eliminate the chance for operator error. It frees me up to deal with other work on the shop floor."
Machining cells reduced cycle time for one window belt frame more than 30 percent.
The MC1816-5Xs are as flexible as they are efficient. Supported by the A2 cell control and standardized tooling, the cells are capable of producing each of the 24 different window belt frame models for the 737 Next Generation, 767 and 777 airplanes.
Flexible Cell, Rigid Application
We equipped the MC1816-5Xs with standardized tooling to support an array of window belt frames," says cell manager Gerald Helten. "This cell makes it possible to changeover quickly. An operator can machine a different part number in minutes, by merely changing the part program. It's a fast and fairly simple procedure that does not impact spindle uptime. It also allows us to easily incorporate the latest engineering changes to a part."
Boeing does ensure, however, that one aspect of this cell is extremely inflexible. Throughout the application, high rigidity standards are required of the tooling, machining center, spindle and toolholders.
"We use Makino's Jet 50 spindle and HSK tool holders," says Helten. "Combined with the rigid machine construction and our tooling package, we have an extremely sturdy application. It's a necessity when creating such close tolerances on precise holes."
High-Speed Hole Drilling
Since moving hole drilling operations from a jig to the MC1816-5Xs, hole accuracy has gone from hundredths of an inch to a few thousandths of an inch in tolerance. The machining centers' trunnion-style, five-axis table provides access to the window frames' various angles.
"We also use an 18-inch drill extension to eliminate runout," says Helton. "Insert drill cutters and endmills are used to mill holes at 10,000 rpm using high-speed cutting techniques that eliminate heat warpage problems encountered with conventional methods."
High-speed machining cells are capable of producing each of the 24 different window belt frame models for the 737 Next Generation, 767 and 777 airplanes.
Makino's proprietary Super Geometric Intelligence software allows the MC1816-5Xs to interpolate boring and compensate for machine tool behavior on the fly, reducing tool path error. This provides accurate interpolations at high feed rates and boring operations at multiple diameters with a single end mill.
Far Reaching Results
This approach has brought Boeing impressive results. The cycle time for one window belt frame has been reduced more than 30 percent. Seven MC1816-5Xs currently manufacture about 21 complete window units per month, each unit consisting of six window belt frames.
The team plans on increasing throughput to 24 units per month. And since the machining centers provide more throughput than expected, the team currently utilizes the remaining two machining centers to pull in work from other areas within Boeing.
"This flexibility supports our assembly operations' new pull system," says Tandon. "Based on assembly's perceived demand for parts, they actually order parts from manufacturing. We have been able to eliminate the stacks of parts waiting to be used by assembly and assembly is no longer held up by a lack of parts."
Part quality has also impacted the time and cost of window belt frame assembly. Part quality is so high that the need for shims has been eliminated. Shims are used during assembly to eliminate minor gaps between the airplane's aluminum skin and the window frame-gaps caused by part inaccuracy.
The conventional assembly of these parts required literally hundreds of shims; each shim had to be custom made. This negatively impacted assembly time, cost and ultimately the weight of the window unit. Now only one shim is needed, and it has been purposely engineered into the assembly.
Machining Center As CMM
The impressive accuracy provided by the window belt frame cell has proven reliable over time. In fact, the FAA-certified cell no longer requires a coordinate measuring machine (CMM). The MC1816-5X's probing apparatus measures the parts before the machining process to track part accuracy and ensure no human error has been made during setup. Boeing Wichita's quality assurance teams then rely on machining center data, reducing time spent on part inspection dramatically -- from hours to minutes.
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