VariMod: A Structured Approach to Variability in 3D Modelling

Today's manufacturing industry is confronted with an increasing demand for product variability that stems from product customisation needs and the engineering process. Different customer demands and the mass-customisation of physical products require designing multiple variants of products, and additional requirements may be introduced when the product reaches subsequent stages (simulation, manufacturing, assembly...) in its engineering process. The state-of-the-art 3D modelling software deals with variability in a mostly ad-hoc fashion. Designing products typically involves creating digital 3D models using Computer-Aided Design (CAD) software, and implementing variability requires duplication of entire models or parts thereof that then require changes without any identification of or distinction between the different requirements that caused them. Parametric CAD approaches do enable designing 3D models that contain modifiable parameters, but designers must still ensure that the 3D model with updated parameter values satisfies all requirements. It is therefore difficult or impossible with current approaches and tools to design variants of products in a structured and efficient manner. In this work, we present VariMod, a 3D modelling approach that distinguishes between invariant requirements that each variant of a 3D model must satisfy, and variant-specific requirements that individual variants must satisfy. Hereby, VariMod enables the specification of 'generic' 3D models that satisfy invariant requirements, of which the parameter values can be optimised so that they also satisfy variant-specific requirements. To this end, VariMod represents both types of requirements as bidirectional constraints that are solved to find optimal parameter values that satisfy all constraints. VariMod features a constraint-solving process that aims to minimise the modifications made to parameter values when optimising a 3D model, thereby preventing unexpected modifications to the 3D model. We use PrintTalk, a programmatic CAD language for parametric 3D modelling, as a vehicle for implementing and validating VariMod by demonstrating how it can be used for designing variants of 3D models in a structured and efficient manner.