With the advent of commercial solid modelling systems some fifteen years ago, the opportunity for three-dimensional parametric geometry was opened to industry. Today solid modelling systems are the dominating CAD tool among advanced engineering companies, but despite the time and money saving implications, industry has been slow to exploit the parametric capabilities of these systems (Amen and Sunnersjö, 1996).

One reason for the slow adoption of parametric modelling is that originally many solid modellers suffered from lack of stability under parametric changes. This situation is now changed and if a model in a modern CAD system collapses, this is usually due to modelling deficiencies rather than numerical failures. Straightforward dimensional variations rarely cause any problems. However, to fully exploit the parametric capability for complex features with a variable topology, there is a need for a systematic approach to build stable and purposeful parametric models.

The purpose of this work is to discuss how different modelling approaches relate to the ease of use and robustness of the CAD model in terms of creating variants and product families. We use the term Design for Variability, DFV, for a modelling approach that ensures that parametric models are well suited for variation design.