Printer Friendly

Building the flying wing.

A computer-controlled "smart" drill, and a milling machine that cuts at 75,000 rpm, are among advanced machine tools making parts for the B-2 Stealth bomber.

From a design standpoint, the US Air Force's B-2 Advanced Technology Bomber-commonly known as Stealth-is a remarkable machine. Flying at low altitudes, its shallow profile and curved composite surfaces enable it to elude detection by conventional radar. Though only 69 ft long, the B-2's long, notched wings stretch 172 ft, giving rise to the nickname "Flying Wing." And it can range over 6000 nautical miles at high altitude without refueling.

Besides being a major coup in design, the B-2 also represents a breakthrough in aircraft manufacturing technology. An impressive array of advanced, special machine tools and methods have been marshalled by general contractor Northrop Corp, Los Angeles, CA, for machining and fabricating the plane's structural components.

One of these production machines is a computer-controlled, adaptive drilling system developed by AllenBradley Co's Rockwell Industrial Tools Div, Columbia, SC. This system senses the hardness of different materials, adjusts cutter speed accordingly, and automatically retracts to allow cuttings to be removed periodically.

As a result of using this system, Northrop has sharply increased the quality of holes drilled through stacked layers of aluminum, titanium, and graphite composites. The costs of scrap and rework have come down accordingly.

Further, average drilling time for a hole through stacked layers was reduced to one-half that formerly needed with conventional drills. Besides reducing production time, this extends tool operating life. For instance, drill bits that had to be resharpened after every 15 holes now can drill 60 or more holes before needing attention.

Called Pro-Spec, the new system integrates a portable, positive-feed drilling machine, sensor technology, and microprocessor control. Included are a drill motor, on-board process controller, and data entry station (drawing).

Software used at the station downloads control parameters into the controller, enabling it to adjust the drill motor to various cutter and kit combinations. Part of the motor, the process controller stores operating logic needed to govern cycles.

The controller processes a number of parameters, including start, shift, Delta, and end thrusts; point delay; dull-cutter warning and disable; and sampling rate, calibration constants, and others.

Control software runs on Compaq 286, IBM PC/AT, and Allen-Bradley industrial PCs. Historical data collected during drilling cycles provide optional capability for later batch analysis.

For full details on Pro-Spec, write to Allen-Bradiey Co, Rockwell Industrial Tools Div, 10138 Two Notch Rd, PO Box 23187, Columbia, SC 29224. Phone (803) 788-1212.

Supermill

Another special machine tool used in B-2 parts production is a high-speed milling machine from Matsuura of Japan. Controlled by computer, the machine's spindle rotates at 75,000 rpm during cutting. This is about three times faster than usual spindle rotation rates for high-speed milling or routing of aircraft structural parts.

The Matsuura machine allows Northrop to mill B-2 parts 20 times faster than previously, and to tighter tolerances. Developed in conjunction with Hughes Aircraft Co, this mill design will soon be released for general use.

Another special machine tool, developed by Northrop Corp itself, cuts composite materials into required shapes three times faster-and much more accurately than has been possible with other composite cutters. The machine uses ultrasonic energy to cut at rates to 1200 ipm, with accuracies of +/-0.01011. This compares favorably with the 400-ipm, +/-0.03211 performance of conventional cutters, Northrop says.

Yet another type of special machine, developed for the B-2 program, automates application and forming of composite tape to contoured tools. (The process is called tape layup.) These are used in fabrication of structural rib stiffeners, known in the industry as stringers. In this operation, hand labor has been reduced by 69 percent.

Machines and software for tape application were developed by Cincinnati Milacron, Cincinnati, OH, and Ingersoll Milling Machine Co, Rockford, IL. Both companies now market their tape-layup systems commercially.

Integrated data

Another advanced manufacturing technique for the B-2 program is an integrated 3-D database developed by Northrop Corp. According to them, the B-2 is the first aircraft built from a 3-D database combining CAD and CAM data.

The 3-D system links Northrop's engineering, manufacturing, and logistics support departments. Also tied into the network are numerous subcontractors and the US Air Force. All have access to the common database that holds a complete B-2 definition. This includes not only geometry but also dimensions, descriptive data, and processing data.

As a result of using this database and network, the B-2 team did not need to build a costly prototype, but went directly from electronic models to a production aircraft. Also eliminated was the need for many mockups and traditional tooling steps.

Northrop says that thanks to their database, the B-2 has been built to tighter tolerances than any other aircraft. For instance, the aircraft's 172-ft wingspan is accurate to within 0.25 ". And parts cut on the Matsuura mill are machined to a level of precision 20 times greater than previously possible.

Major subcontractors in the B-2 program include Boeing , LTV, General Electric, Hug]hes Aircraft, General Dynamics, TRW, Unisys, United Technologies, and Rockwell International. Also contributing to the program are Allen-Bradley Co, Cincinnati Milacron, and Ingersoll Milling Machine Co.

For more information, write to Northrop Corp, Public Relations Dept, 1840 Century Park East, Los Angeles, CA 90067. Phone (213) 553-6262.
COPYRIGHT 1990 Nelson Publishing
No portion of this article can be reproduced without the express written permission from the copyright holder.
Copyright 1990 Gale, Cengage Learning. All rights reserved.

Article Details
Printer friendly Cite/link Email Feedback
Title Annotation:stealth bomber
Publication:Tooling & Production
Date:Jul 1, 1990
Words:886
Previous Article:CMM success: focus on teamwork.
Next Article:Abrasive-belt machine gets wheels.
Topics:


Related Articles
Sneaky, secret bomber shows its face.
The Stealth bomber story you haven't heard; it doesn't work, and it'll probably crash.
MCKEON SEEKS ADDED B-2S AIR FORCE EXPECTED TO BE AGAINST IDEA.
BUILDING BOMBER FLEET MCKEON, OTHERS PUSH BUSH FOR MORE B-2S.
STEALTH PAIR BOUND FOR GUAM; TRAINING WILL BE 1ST FOR B-2S OUTSIDE U.S.
REPORT: NO MORE BOMBERS; PANEL REJECTS CALL FOR ADDITIONAL B-2S.
B-2 TO GIVE DODGERS FANS A BUZZ; VISIT FROM BOMBER SCHEDULED FOR MEMORIAL DAY BALLGAME.
LOCKHEED MARTIN PLANNING TWO DECADES INTO THE FUTURE AVIATION GIANT OFFERS PENTAGON CONCEPT FOR THE B-2'S REPLACEMENT.
'STEALTH' SCHOOL CAMPUS NAMED FOR AVIATION PIONEER.

Terms of use | Copyright © 2017 Farlex, Inc. | Feedback | For webmasters