Tolerance allocation in flexible assemblies: a practical case

Flexible mechanical parts can be assembled having the use of their elasticity together with their geometrical shape. In this case the choose of dimensional and geometrical tolerances is difficult and neglecting elasticity effects may lead to produce a lot of rejected conformal components. Flexible assemblies can be found in many mechanical application. In this paper the authors discuss a study of the influence of dimensional errors on the functioning of a flexible assembly. The methodology has been applied to a plastic earphone set of a mobile phone which has to be mounted on a metallic hub. In this case the flexibility of the part is necessary to strictly connect the two parts. On the other hand, excessive dimensions may lead to high internal stresses and damage by fatigue phenomena. The aim is to propose a methodology to improve and optimize the allocation of tolerances in systems which can be assembled with deformation. This approach is based on a Computer Aided parametric model in order to simulate dimensional errors, build up Finite Element Model and perform assembly analysis.