Tolerance analysis is a name given to a number of approaches used today in product design to understand how imperfections in parts as they are manufactured,and in assemblies as they are put together, affect the capability of a product to meet customer expectations. Tolerance analysis is a way of understanding how sources of variation in part dimensions and assembly constraints propagate across parts and assemblies, and how that
total variation affects the capability of a design to achieve its design requirements within the process capabilities of manufacturing organizations and supply chains.
Tolerancing directly influences the cost and performance of products. For example, in electrical devices, safety requires that the power supply be located a certain minimum distance from adjacent components, such as another sheet-metal part, in order to eliminate electrical short circuits across that distance. Tolerance analysis will show whether the nominal clearances the engineer specifies will meet or violate the safety requirement, given manufacturing and assembly variability impact on the minimum clearance.
The biggest misunderstanding in the market today is trying to equate true three-dimensional tolerance analysis with the widespread practice of using a spreadsheet to simplify the problem to a series of one-dimensional or two-dimensional studies and assuming all the tolerances are in the worst-case conditions for analyzing the behavior of parts and assemblies. This simplistic practice does not properly comprehend variation because it involves no statistical techniques and does not consider real world three-dimensional behavior in parts and assemblies that may be significantly different than the simplified tolerance model. Simplifications of tolerance models involve significant user judgment in how close the tolerance model represents true physical contact behavior and then about how to set tolerances based on their sensitivity to the assembly and part behavior. Guesswork such as this rarely ensures that engineers will meet critical design requirements while using the least-expensive manufacturing processes.