ToleranzStackUp

ToleranzStackUp, also known as tolerance stack-up analysis, is a systematic evaluation of how dimensional tolerances on individual parts accumulate in an assembled product and influence the final dimensions and function. In practice, it seeks to determine the possible range of an assembly dimension resulting from the variability of manufacturing processes and part tolerances. The goal is to ensure that the assembled product will still meet its functional requirements and fit with mating components.

Tolerances can be linear or angular and originate from manufacturing processes, material properties, or design allowances. The stack-up is influenced by how tolerances are allocated and how many parts contribute to the critical dimension. The analysis helps identify whether a design will function across the expected production variance and where adjustments are needed.

Common methods include worst-case analysis, which assumes all tolerances are at their extremes to guarantee function, and statistical approaches such as root-sum-square (RSS) or Monte Carlo simulations, which model variability as distributions and estimate the probability of meeting specifications. The choice depends on accuracy requirements and the cost/complexity trade-off.

A typical workflow: identify the critical assembly dimension, define tolerances with allowances, build a stack-up model, perform calculations or simulations, verify that the functional requirement is satisfied for the intended production variance, and iterate by tightening tolerances, changing geometry, or re-allocating tolerances.

Standards and practice: tolerance analysis is used alongside geometric dimensioning and tolerancing (GD&T) per ISO and ASME Y14.5, and is supported by specialized software for complex assemblies.