SIMPLIFICATION OF SELECTIVE ASSEMBLY.

Selective assembly is used whenever the tolerances which have to be allowed for the components are so large that the natural build up with random assembly will not satisfy functional requirements. The traditional method divides the more variable components into a number of zones of equal width and then specifies what combinations of grades may be assembled so as to produce sufficient uniformity in the final product. Theoretically there is no limit to the number of grades which can be used, but there is a serious organisational problem of having only the specified categories available at one time, and another control problem to ensure that components are correctly graded. Further, a large proportion of components may not be usable through mismatching of quantities and this can increase costs considerably. These difficulties can be reduced by suitable quality control schemes which are additional to the grading operation. The method proposed in this paper is that components should be balanced by quantities rather than by size. It depends upon knowledge of all process capabilities and requires a quality control scheme to ensure that the mean size produced for every component coincides with the objective mean. The grading operation itself gives rise to a simple quality control scheme which is based on the balancing quantities. The same scheme is applicable to all components. Mismatching is impossible as long as control is maintained and all components are used in a reasonable period of time. It is shown that many applications can be made with only three grades and that even extreme sized components can be used. Methods are given to compute the variation which will be obtained from product to product when selective assembly is only applied to some types of component and the remainder are assembled at random. Thus, it is possible to design a procedure which will give sufficient uniformity at minimum cost and avoid the complexity of excessive numbers of categories. Err... [ABSTRACT FROM AUTHOR]