When history-based, parametric modeling systems hit the market in 1985, it seemed that the product design process would forever be changed. History-based modeling is in principal the idea of modeling something based on the software sequentially rebuilding geometry from a recipe (design intent).
Parametric, history-based modelers leverage a history tree to bring control and intelligence to the process of building CAD models. The parametric modeling process requires users to anticipate and define feature constraints, relations, and dependencies to ensure that any design change will update all related downstream geometry in a predefined manner.
History-based modeling garnered popularity over the traditional direct modeling approach, in part because it was seen as being a more powerful and automated way to create complex models, especially for large assemblies that use families of parts. These systems are ideal when designers are held to strict criteria, such as specific design aesthetics, performance metrics, and manufacturing criteria.
Over the past several years, however, there has been a rising tide of interest in direct modeling approaches as more users question the inflexibility of history-based parametric modeling systems and the complexities involved with editing fully parametric assemblies. Some users encounter problems resulting from the complexity of the history tree as well as the inflexibility of the tools for doing conceptual design and making last-minute design changes.
Several new direct modeling CAD tools have hit the market in the last several years that address many of the common complaints and weaknesses of history-based systems. Perhaps in response, history-based CAD vendors have introduced variations of direct modeling tools, including some new hybrid tools touted to offer users the best of both worlds.
To be or not to be (history-free). Is that the question?
CAD systems are either history-based or history-free. In history-based systems, the design’s modeling history is tracked and features are ordered with parent/child relationships. Because direct modeling CAD systems don’t have the overhead of history-based systems, users can directly manipulate model geometry without regard to how that geometry was created.
The main advantage of direct modeling systems seems to be ease of use along with a significantly shorter learning curve, which opens up CAD to non-specialists who are now important members of the extended design team. Designed to be flexible and intuitive, direct modeling tools enable users to simply grab, pull, and drag geometry to edit or make changes.
Collaborative design efforts are greatly facilitated when members of the design team who are non-engineers are provided with design tools that don’t require specific 3D CAD expertise. Rather than remaining in the realm of specialists, anyone who wants or needs to visualize concepts or new ideas in 3D can do so using direct modeling tools. By deploying the use of direct modeling tools, organizations can foster greater innovation and fuel product concept pipelines with the help of those outside of the engineering department.
By providing a common CAD platform, direct modeling systems also make dealing with CAD data in multiple formats easier. This is a big benefit to most companies with multi-CAD environments who must juggle CAD data from partners and suppliers that was created in various CAD systems.
Reuse of existing designs without unnecessary rework is also more easily accomplished using direct modeling tools since importing design data from any source is easier. Designers can leverage all types of available content—such as sketches, surfaces, single parts, or entire assemblies—without data interoperability problems since STEP and IGES are viewed as native CAD data to direct modeling.
Another area that can greatly benefit from the use of direct modeling tools is conceptual design. Direct modeling tools offer the freedom and flexibility to quickly and intuitively iterate various concept ideas without having to “lock in” on one design. Designers can also use direct modeling techniques to prepare models for analysis.
Looking into the future, there is little doubt that there will be room for both CAD design paradigms in the design of new products that will only increase in complexity and functionality. Vendors will strive to create tools that boost the strengths of both approaches, however, the hope is that both of these modeling techniques will eventually merge and morph into more intelligent design systems that truly represent the best of both.
For more extensive information on the benefits of direct modeling, download the free eBook “5 Ways You Can Benefit from the Simplicity of Direct Modeling”.
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