Tolerance analysis in manufacturing process planning is critical in assuring the quality of machined components. Its purpose is to analyze the problem of tolerance stackup caused by setup datum changes during machining in order to achieve the goal of "doing things right the first time." Traditional tolerance analysis techniques, although effective in handling dimensional tolerances, are not sufficient in dealing with geometric tolerances. This paper presents a normalization approach based on manufacturing error analysis to convert geometric tolerances into none-type-specific values called normalized tolerances. A normalized tolerance is an angle representing the maximum permissible rotation error when locating the component. Different types of geometric tolerances can be compared after they are converted into normalized tolerances. The smaller the value of a normalized tolerance, the tighter the underlying geometric tolerance is. Tolerance stackup analysis can also be performed on normalized tolerances. The tolerance normalization approach is a mathematically rigorous approach for tolerance analysis that provides a new dimension in achieving total tolerance control. In this paper, the formulae for normalizing parallelism and perpendicularity tolerances are derived. An example is then used to illustrate the procedure for performing stackup analysis on geometric tolerances. Future research directions are also briefly discussed.
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