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CAD model quality in parametric design scenarios largely determines the level of flexibility and adaptability of a 3D model (how easy it is to alter the geometry) as well as its reusability (the ability to use existing geometry in other contexts and applications). In the context of mechanical CAD systems, the nature of the feature-based parametric modeling paradigm, which is based on parent-child interdependencies between features, allows a wide selection of approaches for creating a specific model. Despite the virtually unlimited range of possible strategies for modeling a part, only a small number of them can guarantee an appropriate internal structure which results in a truly reusable CAD model. In this paper, we present an analysis of formal CAD modeling strategies and best practices for history-based parametric design: Delphi's horizontal modeling, explicit reference modeling, and resilient modeling. Aspects considered in our study include the rationale to avoid the creation of unnecessary feature interdependencies, the sequence and selection criteria for those features, and the effects of parent/child relations on model alteration. We provide a comparative evaluation of these strategies in the form of a series of experiments using three industrial CAD models with different levels of complexity. We analyze the internal structure of the models and compare their robustness and flexibility when the geometry is modified. The results reveal significant advantages of formal modeling methodologies, particularly resilient techniques, over non-structured approaches as well as the unexpected problems of the horizontal strategy in numerous modeling situations.

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Revista:Computer-Aided Design Versión / Versió: Preprint Cita bibliográfica / Cita bibliogràfica (ISO 690):CAMBA, Jorge, et al. Extended 3D annotations as a new mechanism to explicitly communicate geometric design intent and increase CAD model reusability. ComputerAided Design, 2014, vol. 57, p. 61-73 AbstractA successful implementation of the Model-Based Enterprise concept (MBE) requires maximizing the potential benefits of annotated 3D models. The foundations of the MBE model are established by digital product definition data practices, which are currently regulated by standards such as ASME Y14. 41-2003 and ISO 16792:2006. At the center of the MBE concept is the notion of CAD model reusability, which relies on the idea that 3D CAD models can be reused both throughout the entire product lifecycle and as a starting point for future development of new products. In this context, a critical aspect of CAD model reuse is the proper identification and understanding of the geometric design intent that is usually expressed implicitly within the CAD model.In this work, we present a method to communicate geometric design intent explicitly by overloading and extending the scope of the current annotation instruments available in the MBE approach. We propose a new broader type of model annotation that we call "extended annotation," where design information is represented both internally within the 3D model and externally, on a separate repository. This structure naturally demands additional mechanisms to support the interaction of users with the information. In order to manage the information stored in these extended annotations effectively, we implemented an annotation manager that automatically synchronizes the dual representation of the annotations. To reduce the visual clutter in the 3D model, the software provides powerful filtering, editing, and visualization capabilities, giving users complete control of the information stored in the model. Finally, a study was conducted with 60 participants to evaluate the performance of the proposed model and the usability of the annotation manager. Results show a statistically significant benefit of using the extended annotation system, suggesting the use of this model as a valuable approach to improve design intent communication.

Design intent is generally understood simply as a CAD model's anticipated behavior when altered. However, this representation provides a simplified view of the model's construction and purpose, which may hinder its general understanding and future reusability. Our vision is that design intent communication may be improved by recognizing the multifaceted nature of design intent, and by instructing users to convey each facet of design intent through the better-fitted CAD resource. This paper reviews the current understanding of design intent and its relationship to design rationale and builds on the idea that communication of design intent conveyed via CAD models can be satisfied at three levels provided that specialized instruction is used to instruct users in selection of the most suitable level for each intent.Keywords: design rationale, design intent, CAD model quality, CAD education. INTRODUCTIONFeature-based parametric CAD is a commonly deployed 3D modeling technology that is widely used in industrial settings. In these systems, the 3D CAD model is created by gradually and sequentially adding geometric features through parent/child relationships, which creates an interconnected structure that, when defined properly, allows for more flexible and reusable models. This process is recorded in a structure known as a design tree, feature tree, or history tree. Parent/child interdependencies are the basic elements that facilitate CAD reusability and alteration of parametric models. When these dependencies are defined properly, changes in the artifact can be performed efficiently, as alterations propagate automatically from parent to child nodes. However, parent/child dependencies can also be the root of numerous regeneration problems, which often forces designers to rebuild the CAD model entirely, costing time and money.Previous researchers have determined that 48% of CAD models fail during design exploration [38] and according to the 2013 State of 3D Collaboration and Interoperability Report, 49% of engineers spend more than 4 hours per week repairing design data with 14% spending more than 24 hours per week [39]. The same report states that 32% of organizations miss deadlines due to design data problems [39]. Gerbino states that data exchange issues result from poor modeling strategies [28]. González-Lluch and colleagues echo these sentiments stating that erroneous CAD models that filter toward downstream applications require effort to rework the models to remove data corruption [29]. Poor understanding and/or communication of design rationale and design intent are commonly argued to cause most of those failures. But the concepts of design rationale and design intent are complex in themselves.Describing the purpose of a design and the justifications for specific decisions made when creating it are essential tasks for engineers and design professionals. Design rationale can be defined as the explicit documentation of the reasons behind the decisions made when designing a system or artifact [52]. Although d...