Maximum material condition in process planning

Abstract

Appropriate and cost effective assignment and interpretation of dimensional and geometrical tolerances, in conjunction with tolerancing principles such as the maximum material condition (MMC), constitute a major area of concern for manufacturing SMEs. This is particularly true for the process planning stage, where production operations and parameter values establish the final product quality and cost. A frequently used geometrical tolerance is the position tolerance. It allows at least 57% more space for feature allocation without affecting product quality and is very useful for accurate specification of multiple-hole assemblies. Feature allocation becomes further relaxed in case a position tolerance is assigned to the MMC. This assignment is mainly exploited during inspection, because it permits fewer rejections. In terms of cost, it is advantageous to systematically integrate the MMC tolerance bonus into the position tolerance at the process planning stage. A methodology that allows a new MMC-adapted position tolerance to be calculated is presented in this paper. The new, increased, position tolerance can then be taken into consideration early in the process planning stage, in order to achieve lower production cost, without affecting the quality.