A New Method for Integrated Design and Tolerancing

Abstract

The dimensional and geometrical tolerancing of machine elements is an important step in the design and manufacturing of a product. Unfortunately, tolerancing takes place late in the current design processes. Generally, it is only in the detail drawings of the parts that the tolerances are determined qualitatively and quantitatively. Some design problems appear which could have been detected upstream if the tolerances had been introduced from the very start. In the proposed design process, the mechanism is defined from a minimal kinematics structure to a detailed geometry. The tolerancing method is directly integrated into this design process. There is an inevitable growing complexity of the mechanical structure. Some technical choices are carried out at each level and it would be interesting to evaluate their geometrical influence on the expressed conditions. Therefore, we propose to deal with the problem of tolerance in an integrated manner with the process of design. The recursive top-down design and tolerancing process is general. The different design solutions, and technological choices, directly influence the dimensional and geometrical tolerances. We present a graph tool, which allows definition of the topology of the mechanism, during all phases of its design. The tolerancing graph is translated into ISO standards conforming tolerances. Different views are possible depending on the detail level needed by the designer. During the design process, the graph is simultaneously updated. An example is studied with the different steps to illustrate this integrated method. The influence of different possible design solutions on the tolerances is compared in order to validate these choices.