One element of tolerance analysis is the formula used to relate product tolerances to component tolerances. This paper discusses deficiencies with traditional tolerancing, outlines a simple procedure for converting process capability information into an improved tolerancing formula tailored to a specific class of products, and describes how this analysis can contribute to substantive improvements in profits by improving tolerancing of future products and helping to identify improvement opportunities in production of current products.
Key Words: Manufacturing Cost, Pareto, Tolerance Limits
By Spencer Graves, Productive Systems Engineering, San José, CA 95126
Tolerancing requires the achievement of a balance between the cost of greater manufacturing precision and the costs associated with products whose components do not mate well. This paper describes a simple modification to traditional statistical tolerancing that can improve its ability to contribute to that balance in any manufacturing organization. The following four sections describe traditional tolerancing formulae and a proposed improvement. The improvement adds a "tolerance inflation factor" to statistical tolerancing which may assume different values for different situations. A subsequent section describes how a hypothetical company uses their own manufacturing process capability data to prioritize improvement opportunities and to estimate a tolerance inflation factor tailored to their organization, thereby reducing production costs while developing a tool to make tolerancing easier and more accurate for future products.
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