59. Application of Statistics to Vendor Casting Weights

Paper

Abstract

The manufacturing of aircraft castings is usually subcontracted to vendor companies who work from furnished engineering drawings which include dimensions and tolerances for making the parts. Since the weight analyst assumes that the vendor will, on the average, manufacture these castings to the nominal dimensions, his calculations are made on this basis. From past experience, it has usually been found that a comparison of the actual casting weights as received from the vendor and the calculated castings weights based on engineering drawings are seldom in close agreement. The difference between actual and calculated weights are due mostly to the complexity of the parts which does not permit an accurate weight analysis, and to vendor manufacturing techniques. However, since most casting drawings do permit an accurate analysis of the weight, two questions present themselves: (a) Is there a significant difference between the nominal weights of castings as calculated from engineering drawings and the actual weight of castings as received from the vendors? (b) Do some vendors produce lighter weight castings than others?
The purpose of this paper is to show how a solution to this problem may be obtained with the use of statistical methods. The data and conclusions shown herein, although obtained from a real case, are for example purposes and for this reason may or may not be representative of industry experience.