Meaning
Statistical modeling identifies the total variation possible when multiple manufactured components are combined into a single assembly. Through tolerance stackup analysis, engineers determine if a machine will function correctly even if every individual part is at its maximum or minimum size limit. This study prevents the production of assemblies that cannot be put together due to physical interference.
Design Verification
Geometric dimensioning provides the data points for calculating the worst case scenario of a fit. While tolerance stackup analysis is usually performed during the design phase, it also helps in troubleshooting failures in the field. Root cause investigations often find that parts which are individually within spec create a collective failure.
Error Accumulation
Dimensional drift occurs when the variations of a bolt, a washer and a bracket all lean in the same direction. Performing a tolerance stackup analysis allows the engineering team to relax certain non critical dimensions while tightening others to maintain the overall clearance. This optimization reduces the cost of manufacturing by allowing for wider margins where they do not matter.
The mathematical model usually employs either a simple arithmetic sum or a root sum square approach. Arithmetic sums represent the most conservative estimate of risk. Root sum square methods assume a normal distribution of parts and offer a more realistic view of high volume production.
Assembly Risk
Interference between moving parts leads to premature wear or total mechanical seizure. Managing the results of a tolerance stackup analysis ensures that the gap for lubrication remains open.
