What is Model-Based Definition?
Model-based methods are a hot topic with far-reaching benefits. Model-based definition (MBD) may have several meanings. Products and processes can be defined using model-based methods, thus MBD includes Model-Based Product Definition and Model-Based Process Definition; however, MBD is mainly used to mean Model-Based Product Definition. Note, too, that MBD is typically only used if product or process geometry is represented as 3D data.
MBD is the system and techniques used to define a product as completely as possible using 3D data. The main component in MBD is an annotated 3D model that includes 3D geometry, product, and manufacturing information (PMI), metadata, and other data elements. PMI includes dimensions, tolerances, surface texture symbols, notes, GD&T, welding symbols, and other annotations, attributes, and data.
Most products cannot be completely defined by 3D data. Additional data may be presented in lists, schematics, matrices, and other 2D documents. Along with the 3D annotated model, these files and documents are used as a Technical Data Package (TDP). A TDP is a set of one or more files or documents that contains all of the information needed to completely define a product and its requirements. TDPs are created by the design organization and used by other departments within the supply chain, such as manufacturing, inspection, and quality, assembly, service, technical publications, etc. A TDP is generally a combination of 2D and 3D data. Today, with MBD, the move is toward 3D TDPs.
Model-Based Definition and Model-Based Enterprise
Note that some organizations use the term MBD to represent Model-Based Design and the term MBE to represent Model-Based Engineering. As is true with many new technologies, different groups develop different terms with similar or overlapping meanings. For the purpose of this discussion, MBD means Model-Based Definition and MBE means Model-Based Enterprise.
Why MBD? Why MBE?
MBD is the next revolution in CAD/CAM/CAE, where annotated 3D models and 3D TDPs are used as the single source for all design information, eliminating the need for 2D Drawings.
When MBD is implemented at the beginning of the product lifecycle and re-used throughout an enterprise and its supply chain, it enables rapid, seamless and affordable development and deployment of products from concept to disposal. This environment is referred to as a Model-Based Enterprise (MBE). MBE is the environment in which MBD is the primary product definition or design authority. It is important to understand that simply switching from 2D drawings to 3D MBD is not sufficient. To realize the benefits of MBD, an MBE environment must be optimized to use the 3D dataset as much as possible throughout the enterprise and supply chain.
Having an optimized and effective 3D-centric product lifecycle process that satisfies the needs of downstream users creates a lean environment with less waste. Error rates and re-work are reduced, as is labor in the data and document creation process. The cost of drawing maintenance is also greatly reduced.
Considerations for Implementing MBD
Many things need to be considered by an enterprise planning to migrate from a 2D/3D environment to a 3D MBD environment. Key areas such as legacy data migration and MBD data re-use across the engineering supply chain are often ignored but are key to a successful MBD implementation.
The development of new standards and processes for 3D model annotation is a key driver in the trend toward MBD. Technical Data Packages must be in a format compatible with all CAD systems and all uses of the dataset. For a model to be the single source for a part, it must be able to be consumed by many different parties along the supply chain, regardless of the CAD formats used.
Ensuring quality and true design intent in the model and TDP is also critical. For MBD to truly be faster and more efficient, everyone who views the model must receive the same dimensions and work rules in the TDP. This allows for collaboration without having to ask questions and without the risk of downstream manufacturing issues.
ITI has an extensive range of engineering data interoperability solutions, several of which can be deployed to address these issues and those identified below, helping your company successfully implement MBD.
MBD Authoring System Validation
MBD Authoring System Validation includes model comparison and verification for engineering, manufacturing, and sustainability applications. With the objective of replacing 2D engineering drawings with a complete 3D product model master, model validation can be integrated into all phases of the product lifecycle. A 3D MBD model includes:
- Annotations (aka 3D PMI, GD&T, FT&A, etc.)
- Model attributes
- Domain-specific data
Why MBD Model Validation?
If the model is the master, then downstream modifications must be reconciled with the product design model. If you integrate all phases of the product lifecycle, then the design model must be re-usable in simulation, manufacturing, support, etc. There is a need for MBD validation in the following scenarios:
- Simulation validation – Unacceptable differences and unsynchronized changes undermine MBD integration of design and simulation.
- Design change validation – Geometry and feature parameter changes must be clearly communicated to downstream users.
- Manufacturing validation – Defects and translation differences undermine MBD integration of engineering and manufacturing.
- Legacy migration validation – Unacceptable differences introduced during migration undermine MBD re-use of legacy data.
- Product lifecycle transition validation – MBD processes are undermined if the model is not validated at critical transitions in the product lifecycle.
3D PMI Quality Checking
How can you ensure that the 3D PMI entities contained in an MBD part meet your company MBD guidelines and standards, and are stable and usable for all downstream MBD applications across the supply chain?
In the same way that model geometry requires verification against accepted standards and criteria, the 3D PMI entities require quality checking against a set of rules and criteria.
CADIQ can be used to check the quality of both the 3D CAD model geometry and the PMI entities.
MBD Engineering Change Control
With no 2D drawings to mark up and edit in the MBD environment, how will the enterprise manage engineering change control?
Users need to be able to clearly identify, document and communicate design changes for all consumers of the MBD part.
The CADIQ solution accurately compares two revisions of the same CAD model and automatically generates 3D PDF report documentation that clearly highlights the changes in model geometry and 3D PMI between the model revisions.
MBD Supply Chain Collaboration
Not all companies in the supply chain will use the same CAD system as the OEM. You may need to export the 3D CAD model, complete with 3D PMI data, to a neutral format such as STEP or JT. How do you know that the exported STEP or JT file is a true and accurate representation of the source model and that no unexpected errors or deviations have been introduced?
A deviation in the geometry or PMI in an exported STEP or JT file presents the potential for significant downstream tooling errors and re-work.
As part of a fully validated and certified automatic supplier data delivery process, CADIQ can be used to accurately compare the 3D geometry and PMI in the exported JT or STEP neutral file to the source native CAD part, and generate a 3D PDF report that identifies any unexpected deviations.
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