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Aviation History
1988
1988 - 2646.PDF
A robot removes burrs from a machined bulkhead for a General Dynamics F-16 McMahon says that the productivity of direct labour, which now accounts for less than 20 per cent of product cost, could be improved by 20 per cent, but that the appli cation of existing manufacturing systems technology could double indirect labour productivity. General Dynamics is nearing the end of a four-year, $40 million project, backed by the US Air Force, to produce a computerised network linking the engineering, order generation and control, process planning, and quality assurance departments. It will support a "paperless" and unmanned machine shop, and could subsequently be expanded to cover other shop-floor tasks. The project represents the first vertical integration of the firm's engineering func tions. The company expects higher produc tivity of direct and indirect labour, shorter product lead-times, and timely information for production control and management. Integration is still some way off. The F-16 was designed on paper, not with a computer- aided design (CAD) system. According to McMahon, some 80 per cent of F-16 parts could, if defined in a CAD system, be built on automated machine tools without manual change to the CAD data. Wing spars are already built in this more efficient fashion. General Dynamics says that it is at least two years away from having 80 per cent of F-16 parts in an integrated system. Upon integration, design changes would be accommodated much more quickly, because of direct links with the shop floor and the ability to design a part "con currently". At present, designs pass from aerodynamics to structures, to systems, and back to structures in an iterative fashion, and it can take 168 days for a design change to be embodied in a product. General Dynamics' integrated manu facturing system ties in with a shop-floor flexible machining system (FMS) similar to LTV's. Machine-tool utilisation is boosted by this flexible manufacturing system at LTV's Dallas factory The FMS, which automatically makes 80 different parts and runs ten shifts a week, is the first of its kind to use distributed computer processing to distribute and update manufacturing data, to employ artificial intelligence for scheduling, and to control all activities for a completely unmanned cell automatically, claims General Dynamics. Although the FMS incorporates only six machining centres, compared with the LTV system's eight, it has artificial vision-guided robots and other technical features not found in the LTV system. Billets pass from the automatic storage and retrieval system to the field of view of a vision system. This tells the robot how to grasp the part and which end effector it must select to bolt the part to a fixture. After the robot bolts the part to a fixture, the assembly is taken by automated guided vehicles to a waiting station and then to the machine tools. Other vehicles take cutting tools to the machine tools for loading on to the machine by robot. A probe on each machine tool monitors tool condition, and tools are automatically replaced after a pre-set period of use. An electronically-erasable, programmable, read only memory chip on each toolholder tells the machine tool control that it has been the correct tool for the job. Even though tools should be in perfect condition throughout the machining process, completed parts are nevertheless sent to a measuring machine which uses touch or laser sensors to check final dimensions. Scheduling such a complex group of machines by hand would be cumbersome, so General Dynamics has resorted to "artificial intelligence" for this job. Digital Equipment Corporation VAX computers running the FMS are equipped with the Automated Reasoning Tool, a piece of software that acts as an expert system and uses programmed rules to work out the best strategy for passing billets through the system. Operators will interrogate consoles to determine production status, and though the scheduler will reveal what it is doing, it will not necessarily be programmed to tell why. So General Dynamics staff rely on extensive testing to ensure that the Automated Reason ing Tool acts sensibly. Staff claim far more information is avail able to them via the consoles than by visual inspection. Operators can delve into the status of each individual card in each machine tool's computer numerical control ler, and can rapidly diagnose faults anywhere in the FMS, though the scheduler auto matically reorganises production to accom modate the failure. General Dynamics' effort is just one of a number supported by the US Air Force at various US Defence contractors, and there are many systems in use or being developed outside the USA. Together they signal a change for management, engineering, and shop floor staff alike. B 40 FLIGHT INTERNATIONAL, 17 September 1988
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