Identification of the main contributors in the 3D tolerances assessment in mechanical transmissions

The management of spatial dimensional variations and 3D tolerance stacks is a key issue to achieve high performance and robust solutions. The state of the art in 3D tolerance analysis addresses two main difficulties: On the one hand, the issue about the dimensioning and tolerancing methods, and the related annotation transfer from 2D drawings to 3D parts. On the other hand, the lack of integration of design methods for 3D tolerance stacks calculation in the design process and, moreover, the restricted application fields in which tolerance methods are applied, as in aerospace or automotive fields. In this scenario, we propose a Computer-Aided Tolerancing (CAT)-based approach, integrated within the embodiment design of the product development and able to support the analysis and the design of 3D tolerance stacks in mechanical assembly, by simulating the 3D effects of both the dimensional and geometrical tolerances. Focusing on a gearbox assembly, the CAT-based approach aims to identify the main contributors (sources) of variation within the tolerance stacks, by means of a statistical and sensitivity analysis. After defining the design inputs (involved parts, tolerances definition, assembly sequence, and required measurements), we follow a bottom-up approach, starting from the part tolerances as set by the designers, up to the assembly tolerances. The CAT software simulates how the tolerances vary within their ranges. Finally, we are able to identify the main contributors to variation, which may require tightening their tolerance values, in order to improve the performance of the gearbox assembly.