Investigation on pin-hole connection in flexible assembly

In some kind of mechanical products, the correct assembly is obtained considering also the deformations of every single element; sometimes this condition ensures the respect of design functionality. In this case, the calculation and allocation of dimensional and geometric tolerances is particularly difficult. In fact, with common GT&D method, the single parts are considered as rigid and the functional tolerancing method does not take into account deformations. The only reference standard is UNI ISO 10579 for flexible assembly. Moreover, its prescriptions are only general indications useful only for dimensional check. In such event, it must be held in consideration also the deformability of every part together with the imposed tolerances and together with the stress level due to the assembly process. This paper proposes a methodology to estimate the combined effects of geometric errors and admissible deformations, for assigning tolerances that ensure the respect of functional requirements of the assemblies. A simple pin-hole connection has been proposed as an example; the case examined is composed of two cylindrical pins and their relative holes. The assessment of multiple effects of geometric tolerances and pin deformations, and the possibility of connections with respect to functional conditions are been investigated. First of all, all possible assembly configurations have been estimated considering the bodies as rigid. Subsequently, all not mountable assemblies have been analyzed including pin deformations. The percentage of reject parts has been carried out with a statistical method (Montecarlo method) while the stress analysis has been performed using Finite Elements Model.