To do so, however, the user has to anticipate and define feature constraints, relations and dependencies to ensure that changes will update all related downstream geometry in a predefined manner. Users became frustrated when the resulting complexity of the history tree resulted in modeling road blocks. The inflexibility of parametric feature-based modeling made it a difficult tool for conceptual design and for last-minute changes.
The more direct route
To overcome some of the challenges parametric design tools raised, vendors began introducing a new modeling paradigm, the direct modeling approach. SpaceClaim brought North American attention to direct modeling in 2007 with the launch of their direct modeler. Early in 2008 PTC acquired direct modeler CoCreate, and now many history-based CAD vendors including Siemens PLM Software, and Autodesk have direct modelers.
With direct modeling, users can quickly define, capture and manipulate geometry, making the approach ideal for early concept development. Direct 3D modeling tools don't rely on complicated network or interdependent features, and there aren't as many constraints that dictate how users manipulate a model's geometry. As a result, users can focus on creating geometry, not on building features, constraints and design intent into their models.
Making changes is easier and more intuitive with direct modeling. Changes are made to models by push/pull/drag interactions using geometry handles. Modifications are made to explicitly selected and/or inferred sets of geometry, as opposed to parametric, feature-based CAD tools in which modifications are made through existing feature definitions.
With 3D direct modeling tools, 2D users can continue to design the way they did using their 2D tools, allowing their designs to evolve without having to plan their creation in advance. Training time is greatly reduced because the way they interact with the model is so similar to the way they did using 2D design tools. There is no need to understand the model's history or design intent in order to be productive using direct modeling tools.
Synchronous modeling offers best of both
Can you have the best of both worlds, or in this case, the best of both 3D modeling techniques? With the introduction of Siemens' Synchronous Technology, the answer appeared to be a resounding “yes.” This modeling paradigm overcame the order dependencies of history-based tools, enabling users a way to interact intuitively and directly with parametric, history-based models without being confined to the way the model was constructed.
Synchronous technology, offered in the company's Solid Edge and NX products combines the convenience and flexibility of direct modeling with a greater ability to import data from other systems more openly, a key feature in today's multi-CAD environments. When users make a change to the model's geometry, only the operations directly related to the edit are solved simultaneously and dynamically in real-time.
With the third iteration of the technology, dubbed ST3, users can now switch back and forth between feature-based modeling and synchronous modeling. When users directly manipulate a model, synchronous technology simultaneously solves the remembered geometric operations, recalculating the entire model in real time.
One of the most common struggles among engineers is the reality of having to use CAD data created in other CAD systems. One of the biggest benefits of ST is that it allows users to reuse data from other CAD systems without remodeling. Using a technique called “suggestive selection,” the modeler automatically infers the function of various design elements without the need for feature or constraint definitions.
Recognizing the benefits that both paradigms offered users, Autodesk introduced Inventor Fusion 3D CAD software touted to give users the ability to switch between parametric and direct workflows—when needed. Fusion software provides direct modeling features as well the ability to directly edit imported 3D models using direct manipulation operations.
What the future holds for engineers who increasingly demand more functionality, more power, more intelligence but also more flexibility and speed, is hard to predict. For users, however, it's quickly changing from an “either/or” proposition to wanting the best of both modeling paradigms, and the CAD vendors are listening.
Siemens has sponsored promotion of their design solutions on ENGINEERING.com. They have no editorial input to this post - all opinions are mine. Barb Schmitz