Relaxed Manufacturing Design Tolerance Concepts. Volume I. Discussion and Summary

摘要

This report describes the work on a program designed to relax design requirements on milled airframe parts. In addition, numerical control (NC) programming methods are optimized to decrease cutting time. Traditional design dimensional tolerances, and geometric details such as corner radii, are analyzed as to cost effectiveness, and cost/weight trade-off data is developed. Guidelines for relaxation of specific detail design requirements are recommended for aluminum and titanium milled parts. Measured surface roughness is shown by component test to have no correlation with fatigue life, and revised surface roughness inspection guidelines are proposed. Hand-finishing of milled parts is shown to have little or no value in extending fatigue life. Geometric stress concentrations such as notches or fastener holes are shown to dictate fatigue life. NC programming guidelines are developed by conducting stiffener machining tests and NC programming development tests. Design guidelines are incorporated into F-16 production airframe drawings from the beginning of production. Cost records show 22% reduced hand-finishing in the factory, and a 14% total cost reduction for milled aluminum parts for 1000 F-16 aircraft is conservatively projected.