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Flexible cell doubles Boeing wing output.

Flexible cell doubles Boeing wing output

Automation in the relatively short-run aircraft industry reached new heights at Boeing Military Airplanes in Wichita, KS. Key to the operation is a four-profiler flexible machining group (FMG) primarily used to machine hinge fittings, wing folds, and wing end ribs for the A-6 navy attack fighter.

Heart of the cell includes four 5-axis bridge-type profilers specially designed for Boeing by Cincinnati Milacron, Cincinnati, OH, each sporting four vertical spindles with 120 mm bearing support. Each profiler is valued at about $2.5 million. Considered a first for the air frame industry and Cincinnati Milacron, it was installed in May 1988. Increased stiffness needed to cope with high torque (up to 1/3 hp per rpm) and high horsepower cuts (up to 30 per spindle) in stainless, inconel, and titanium is achieved using a stationary bridge (rather than a moving gantry). That configuration also facilitates an automated pallet-type transfer system.

"The FMG, which currently processes about 100 different part numbers, has helped improve productivity two times on parts made from tough-to-machine metals. And because a computer directs most facets of its operation, we're seeing parts of high quality and tight tolerance come off the machines," says Gary Bonhoff, general supervisor of the machining spar shop at Boeing-Wichita. He adds: "We're using statistical process control to monitor the machining. This has helped us find problems before they damage quality or interrupt component scheduling."

The A-6, a 1950s-designed plane has wings reaching the limits of their operational lives. Rather than replace the entire plane, the navy has decided to simply replace the wings. Although the plane is still being built by Grumman, the wing program was developed by Boeing. The original wing was all metal. The new one is a combination of titanium and graphite-epoxy, considered to be stronger and longer lasting. One family of parts manufactured in the new manufacturing cell is the right-and left-hand wing hinge fittings (the A-6 wings fold for storage on board an aircraft carrier) made from titanium. Boeing reports each formerly took 220 hours to complete but now are made four-at-a-time in 30 percent less time.

Another complex part manufactured on the new machines are "pi" fittings (so-called because they resemble the Greek symbol) used on the common strategic rotary launch project. The fittings secure short-range attack missiles to aircraft such as the B-1 bomber. Mr Bonhoff explains that fittings are cut four-at-a-time, each starting out as a 93 lb stainless steel forging. Within 24 hr four completed components roll off the machine--that's after roughing, boring, contour milling, and finish machining removes about 75 percent of the metal in 45 percent less time than the previous method.

16 spindles with 480 horses

Each spindle provides a full 50 deg of tilt and rotary motion in the A and B axes. By combining the two servo-controlled spindle axes with the machine's three linear movements--113" in the X; 68" in the Y; and 28" in the Z--Boeing can cut the compound angles required on their complex parts. DC servodrives are used on all five axes and provide enough torque to drive any combination of axes through a continuous 30 hp cut. That equals a total of 120 spindle horsepower per machine. Each machine can also run in a two-spindle mode. For example, the spindles can simultaneously cut four 30" wide or two 60" wide parts.

To reduce downtime, each spindle is equipped with its own automatic toolchanger, permitting four tools to be replaced simultaneously. Each ATC can store 20 tools. Control of tool changing and selection is by a computer-control resident stationed at each machine. Each machine can perform activities in process as directed by the NC program, such as fixture offset checking. The probe can be stored in the ATC matrix and automatically retrieved and placed into the spindle for use, the same as any cutting tool.

Boeing estimates the group of machines will generate about 100,000 lbs of chips annually. To handle chip removal, a combination in-floor coolant and chip conveyor system was built into the group.

Material handling payload

An automated pallet-changing system services all four machines in the group. Located behind the units, the system employs an electric, self-propelled, 28 ft long shuttle car capable of carrying two 10 ft long X 6 ft wide pallets from machine to machine. Maximum payload is 70,000 lb. The system is presently programmed manually but could be upgraded at a later date for full computer control.

Eight pallets are used in the cell--one on each machine and four in queue, permitting a minimum of 10 hours worth of machining to be held for immediate transfer to the machines. Six off-line workstations, located side by side and adjacent to the shuttle car path are used for loading and unloading.

Here's the typical part-flow through the cell: While machines are in production, a worker loads raw parts on a prefixtured pallet located at one of the six workstations. When machining is complete on any of the profilers, the shuttle car is activated. Traveling at 50 ipm, it picks up and transports a pallet of uncut parts to the proper machine where it is exchanged automatically. Complete pallet change takes about 10 minutes.

Part-making is virtually uninterruptable within the cell should any one machine have to be shut down. The group runs on a CNC married to each profiler, permitting the four machines to function independently, thus adding to its flexibility and its 92 percent uptime. Boeing, however, desiring to fuse all management of data and manufacturing instructions on computers, thus saving labor and improving productivity, has placed the group under full management of the company's distributed numerical control (DNC) network.

PHOTO : A total of 16 cutting spindles insures rapid and heavy metal removal--about 100,000 lbs of

PHOTO : chips annually. A combination in-floor coolant and chip conveyor system removes chips with

PHOTO : a 95 percent efficiency and ensures a continuous supply of coolant.

PHOTO : "Pi" fittings start out as 93 lb stainless steel forgings (right) and end up as a 22 lb

PHOTO : finished part twice as fast as used to be the case thanks to Cincinnati Milacron

PHOTO : four-spindle, five-axis profilers at Boeing-Wichita.

PHOTO : A cell of 4, five-axis profilers puts 16 spindles to work cutting tough, complex titanium,

PHOTO : Inconel, and stainless steel complex parts. Each spindle has its own automatic 20-tool

PHOTO : changer.
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Copyright 1990 Gale, Cengage Learning. All rights reserved.

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Publication:Tooling & Production
Date:Mar 1, 1990
Words:1064
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