Is the CAD Interoperability Problem Over?
Opening a 3D CAD file designed in one vendor’s CAD in another system without a format conversion process has historically resulted in inconsistent or sometimes broken geometry and loss of design intent. Each 3D CAD model springs from an underlying mathematical kernel that created it, and each will interpret geometry differently. Compounding the problem, most manufacturing firms, on average, use at least three different CAD software products for their product design needs.
Manufacturers cite various reasons for using multiple CAD vendors. For instance, a company may have a history of mergers and/or acquisitions of other companies that have resulted in a mix of CAD platforms. Sometimes a company chooses a secondary CAD vendor that offers specialization in certain areas (i.e. plastics, sheet metal design, styling, etc.). Other factors include cost, retraining or maybe even a policy to not rely on a single vendor. Larger automotive and aerospace manufacturers, in particular, tend to continuously face the issue of working with multiple CAD formats for different projects across their entire supply chains. In such cases, the large manufacturers historically impose requirements on their suppliers to work with their chosen CAD system or format. The ability to seamlessly exchange various CAD formats directly impacts a project’s schedule.
CAD Neutral Formats
Over time, CAD systems have evolved to include more than just geometric and dimensioning information in 3D models. They now encompass rich data such as material information, styling, annotations, manufacturing process data, cost and hooks as well as other features across the design files, including product structure. Such rich design and manufacturing details embedded in the 3D model are valuable across the entire life cycle of a product. However, this complexity can result in a closed, proprietary file format absolutely incompatible with other CAD systems.
Designers heavily use IGES, STEP, STL and JT Open for exchanging files in a neutral format. Although every designer would prefer a universal CAD format, the issue with neutral formats is that, to some extent, they strip off much of the rich data embedded in the native CAD format. Converting native files to a neutral format also commonly results in geometric errors, tolerance issues and loss of metadata associated with the design. Each CAD-neutral format is very different and has its own value and strength for specific applications. From a designer’s perspective, it is advisable to use DWG or DXF for 2D drawings, IGES for surfacing and STEP for exchanging solid geometry. These three neutral formats are supported by almost all CAD systems. The quality or richness of existing 3D models also depends on the number of times a model is exchanged or converted. The final model will have the quality and precision of the least accurate system in the translation chain.
Design Approaches to Solve Interoperability
Feature-Based and Direct Modeling
Direct modeling, PTC Creo Direct. (Image courtesy of PTC.)
The feature-based design approach involves a history tree and a well-structured methodology of creating constraints that assure changes made to a design will also update the related parts or subassemblies. Such feature histories cannot be completely interpreted when a 3D model is brought in directly from one CAD format to another. In the past, this would often result in costly remodeling in order to make changes. Modern direct modeling eliminates such issues by making interoperability between different formats easier and less error prone. Direct-modeling CAD systems have been universally accepted in conceptual design, but the importance of feature-based design is still very well recognized for detailed designing. Some of the notable CAD products that feature direct-modeling capabilities specifically targeting the issues associated with interoperability include:
- ANSYS SpaceClaim
- Autodesk Inventor
- Dassault Systèmes—CATIA Live Shape and SOLIDWORKS Direct Model Editing
- Kubotek KeyCreator Direct CAD
- PTC Creo Direct
- Siemens NX and Solid Edge with Synchronous Technology
Direct CAD Translation Software
The need for 1) editing and reusing an existing 3D model in another non-native CAD system, 2) conducting CAE simulation and 3) using the data across other enterprise software has created opportunities for various third-party companies to develop or provide services for CAD translation. Such vendors offer toolkits or libraries for direct 3D model translation, repair of geometry, comparison, etc. Many CAD software vendors include libraries for CAD translation software from these third-party service providers via partnership agreements. Despite functions such as CAD neutral format translation, 3D BREP conversion, feature-based conversion, model-based definition translations and consolidation of 2D and 3D format by translators, the converted models often require manual intervention to convey the correct design intent. Depending on the translator used and the formats involved, there can be loss of assembly attributes, features, manufacturing information, layers, user-defined views and other elements. However, although not 100 percent foolproof, they can come in handy when working with most 3D models. There are several translator developers and service providers that specialize in one or more CAD systems to provide nearly error-free interoperability.
Non-Native Format Import and Modification
Autodesk AnyCAD multi-CAD format support. (Image courtesy of Autodesk.)
The interoperability issues associated with designing in multi-CAD environments are here to stay. Recognizing this, the big CAD software vendors provide reliable modules that provide one-way import of non-native CAD formats for further modification of design. The objective of importing non-native CAD files is to preserve design intent of the non-native CAD format without resorting to geometry repair. Lately, all the major CAD players have either introduced or are enhancing their functionality to support CAD interoperability in this fashion. The support for non-native formats that is offered by big CAD players are listed below:
- Autodesk AnyCAD in Inventor 2016 supports import of CATIA, SOLIDWORKS, Pro/ENGINEER and Creo, NX, Alias, STEP, IGES, Rhino, SAT and Parasolid binary files.
- PTC Creo with Unite Technology supports import of CATIA V4, CATIA V5, Siemens NX or Unigraphics NX, JT, CADDS 5, STEP, Autodesk (Inventor, DXF and AutoCAD Drawing), Solid Edge, Rhino and STEP.
- Siemens offers productivity tools for CAD interoperability. Supported formats include IGES, STEP, JT, STL and DXF. Siemens also offers various translators and other partner-developed software to natively import files from CATIA, Pro/ENGINEER, AutoCAD and SOLIDWORKS.
- Dassault Systèmes’ SOLIDWORKS provides over 30 translators that support direct import of popular native formats from Pro/ENGINEER, AutoCAD, Solid Edge, Rhino, etc. Dassault Systèmes also has a many partners and service providers that offer CATIA V5 and CATIA V6 Multi-CAD Plug-in for PTC Creo, JT, NX, etc.
Modern CAD systems have evolved considerably beyond just conveying design intent and now include improving collaboration across the enterprise—yet vendors have not been able to solve the interoperability issue completely. Designers should not expect a fully seamless conversion of design data between various CAD systems. And it’s not going away anytime soon. As CAD system features continue to be added to solve complex industry-specific design challenges, an unfortunate result will be the complication of CAD interoperability.
The user is still far from a totally interoperable and seamless multi-CAD environment. The best approach at present is still to choose a good translator service, product or process that caters to the company’s specific interoperability needs along with a CAD company that is committed to ongoing support for CAD interoperability.
About the Author
Sanjeev Pal is an analyst and software architect with his firm, Neovion Group. He has more than 20 years of experience in the field of product development (CAD/CAM/CAE-PLM) and enterprise technologies. Previously, he worked as a research manager with IDC, in services and R&D at Dassault Systèmes and as a design professional at Timex watches.