Feature Data Replacing Geometry as Key to CAD Interoperability
Giving engineers the ability to reuse models with little or no effort requires a different philosophy; one based on the exchange of feature information.
Up until the mid-1980s, product manufacturers, engineers and government officials foresaw the need for an effective means for exchanging product data. In those early days of using computers to design and manufacture products, data obstacles and bottlenecks quickly emerged throughout the process and supply chain. Initially, no critical integration existed between CAD programs or with the complementary design and manufacturing technologies (CAM, CAE, PDM, etc.). Clearly, a lot of model rebuilding occurred in those early days, which led to formal efforts to create a neutral file format that would streamline the movement of data between CAD programs, as well as with complementary systems.
Computer-aided design has come a long way since then. Today, the development of effective data exchange methodologies, both planned and market-driven, has progressed to the point that many of the obstacles to reusing product data, which slowed the design process in the past, are being addressed.
However, even today, a dichotomy exists in the area of CAD integration. Despite government efforts and industry initiatives to provide CAD data exchange standards, which are applied with varying degrees of effectiveness by some design organizations, many engineers continue to rebuild models from many sources - legacy data, customers, suppliers and partners - because they often find it easier, as a result of improved CAD interfaces, to rebuild models than attempt file conversions using standardized file formats and data translation tools.
Of course, nobody really wants to rebuild models. Such a task involves duplicate effort and consumes some of an engineer's time. Engineers have a choice when facing the need to access other CAD data - data translation or model rebuilding - and ultimately base their decision on what is most effective for them.
After 20 years of industry efforts to develop a standardized, neutral file format, the obvious question is why does this dichotomy exist, why do engineers continue to rebuild models rather than employ data translation methodologies? The answer requires the perspective of an engineer. While static geometry represents a starting point for updating designs and may serve the needs of complementary systems, the engineer's needs center on model features. Why? Because engineering is all about changes and trade-offs. Ideally, an engineer wants more than just a static representation of model boundaries. An engineer wants to know how and why the shape was originally made so he or she can modify and refine the model based upon new information. In short, engineers desire feature information, not just geometry data.
The Data Translation Focus
The development of industry product data standards, such as the Initial Graphics Exchange Specification (IGES), which was first introduced in 1980, and the Standard for the Exchange of Product Model Data (STEP), the first and most current international standard, has focused on geometric data exchange and translation - how do I get this geometric representation from CAD system A into CAD system B, or from my CAD system into my analysis, machining or product data management programs?Until now, little progress had been made to share and transfer model feature data, to give the geometric representation some intelligence, and to recognize specific model features, such as holes, cuts, bosses, fillets, chamfers and pockets. Even the effort of the Design and Modeling Applications Council (DMAC) - an industrial consortium created to enhance CAD interoperability through the Microsoft OLE/COM development platform - has focused on embedding objects and links to other software packages, rather than transferring model feature data.
The actual data in an object continues to belong to the sending application. Under this approach, users do not have the ability to edit or manipulate the data without having the application in which the data was created. While IGES and STEP have improved the process of transferring geometric information and fulfill a real data translation need, and OLE for D&M (Object Linking and Embedding for Design and Modeling) provides flexibility in reporting and communication, actual CAD interoperability - the ability to manipulate data from different CAD programs - requires a different approach.
The Purpose of CAD Interoperability
Technically speaking, true CAD interoperability consists of the ability to manipulate not only geometry, but also feature data among different CAD programs. Importing static geometry, whether through standardized file formats (IGES, STEP, etc.), geometry files (Parasolids, SAT, etc.) or translated files (DXF) has provided many benefits to many manufacturing organizations. Even so, giving engineers the ability to reuse models with little or no effort requires a different philosophy - one based on the exchange of feature information.Engineers benefit from model data exchange but even more so from the exchange of feature data. Reusing models saves time and money. Reusing model features can result in even greater time and cost savings, achieving a true degree of CAD interoperability beyond simple geometry exchange.
In an effort to resolve the current CAD interoperability dichotomy, research and development of feature data exchange and recognition technologies has been accelerated while the support of standardized file formats and data translation efforts (IGES, STEP, OLE for D&M, etc.) has continued. By supporting both geometry and feature data exchange, users receive the best of both worlds - facilitating design and engineering efforts for product manufacturers.
Maintaining the intelligence embedded in the model during translation provides engineers with greater flexibility to experiment and make changes without recreating model features manually.
The Emergence of Intelligent Geometry
Feature recognition software introduces new intelligence to a static model or reestablishes the intelligence that went into the creation of a model. It gives engineers the ability to make changes easily, reuse unique features and test their design creativity, spending energy and effort on the design process instead of the translation process.Parametric feature recognition software for CAD users recognizes features from files produced by standard data translation formats, reapplying intelligence to the static geometric data. Keeping model features intact between CAD programs preserves design intent and maintains quality.
An example of such a feature would be a hole. With this parametric feature recognition software, whether the hole was created as a simple, tapered, counter-bored, blind or through-all feature, its essential specification, which may have been lost through the data translation process, is retained. This approach to CAD interoperability leverages past work and provides a tool for reusing rather than redesigning parts.
Steve Carlson, design standards engineer with Barber Colman (Loves Park, IL) - an aircraft equipment and control manufacturer - says his company is deploying parametric feature recognition software in an effort to understand whether it can save time over rebuilding models. "We hope this software will be of some advantage. The speed at which we can create models in it may obviate its usefulness, but we may find it to be essential for leveraging legacy data," he explains.
De Facto Versus Planned Standards
Industry experience has shown that when it comes to standards, most arise as a result of market forces and competitive benefits rather than planned, organized efforts. Consider 3-D solid models. Why are changeable solids rapidly becoming the de facto standard for product design? Because they enable design innovation and shorter product development cycles, making companies capable of producing higher quality products faster and at less cost. In other words, 3-D solids are a product of competitive market forces. Just as Adobe's Portable Document Format (.pdf) for document transfer and Microsoft's Excel files (.xls) for spreadsheets have become de facto standards because they provide solutions to problems framed by market forces, 3-D solids are becoming an industry design standard because they help companies improve their competitiveness.While the future of data translation and exchange most likely will ride the geometry bus, CAD interoperability will continue to rely on the management, transfer or recreation of model feature information. Geometry creation is generally getting easier every day, fueled by the growth of the mid-range solid modeling market. As these models are created, valuable feature information also is established. As the de facto standards emerge, engineers and designers will be more concerned about the retention of model features than with the geometry format because feature information is more useful, preserves design intent, and promotes communication of dynamic design information. No market force is as powerful as the will of the consumer, and engineers will demand hassle-free, intelligent geometry transfer before real CAD interoperability is recognized.
