Application of robust design principles on the example of tolerance allocation for a spool type pressure relief valve

The functional properties of a mechanical product are usually defined by the geometrical specifications of its inherent subcomponents. Therefore, any deviation from the design’s nominal assigned values, can potentially lead to loss of functionality and failure to meet quality criteria. In order to ensure
product functionality such deviations have to be limited by the assignment and allocation of tolerances.
The conventional product development process described in VDI 2221, however does not sufficiently emphasize the importance of tolerance design principles in the early stages of product development. This shortcoming has been met by integrating Taguchi’s robust design methodology alongside the VDI
guidelines, thus introducing the tasks of tolerance design and process planning to the product development engineer. In this contribution a use case for the application of such wholistic tolerancing
approaches is being proposed. A spool type pressure relief valve thereby serves as a function assembly for studying the relationship of the valve’s geometrical properties and its resulting functional performance.
Functional testing, geometrical inspection and mathematical modelling of the transfer function, are the methodologies used for allocating appropriate tolerance values to the parts.