Model-based definition, or MBD, is the practice of documenting the information necessary to manufacture and inspect parts and assemblies in 3D computer-aided design (CAD) models, as opposed to 2D production drawings.


Image: Example of CAD model with model-based definition created in Creo.

Benefits of MBD

MBD provides numerous benefits to the product development process. According to a study by the National Institute of Standards and Technology (NIST), MBD can reduce the design-to-manufacturing-to-inspection process by a phenomenal 78.4%. That’s like completing all your work for the week before the end of the day on Monday.

Why is MBD more efficient than the traditional 2D drawing method? Because the 3D annotations in the CAD model are semantic, which means that other software can understand them.

Rather than sharing a PDF or a print of a drawing with your supply chain, you share either the original native part file or a CAD-neutral STEP file. When these files are opened in computer-aided manufacturing (CAM) software or inspection software for coordinate measuring machines (CMM), the software recognizes the 3D annotations and their geometric references.
This eliminates the work of translating the information from a drawing to downstream software. This is faster and reduces mistakes.

Pathway to MBD

The roots of model-based definition date back to the first 3D CAD software in 1968. However, today most companies are still drawing-based. They develop a 3D model and then generate a 2D production drawing.

Drawings contain views of the object and product and manufacturing information (PMI), including:

• Dimensions.
• Geometric tolerances.
• Notes.
• Symbols and surface finishes.
• Tables like bills of material (BOM).

Engineering companies and organizations realized they could reap immense benefits and savings by eliminating the drawing and going right from the design to manufacturing. Creating a 2D drawing is a step backward from 3D.

Several people met at Boeing in Wichita, Kansas, in the mid-1990s to propose a new methodology for capturing the PMI directly in the CAD model: MBD. The engineering standards for MBD are captured in ASME Y14.41-2019 and ISO 16792:2015.

Implementing MBD

If CAD users already know how to create 2D drawings, the transition to MBD is easy. The main elements of MBD in the CAD model are the following:

• Annotation planes to define the placement and orientation of the details to be placed in the model.
• 3D annotations for the product and manufacturing information.
• Combination states to organize the 3D annotations for clarity and organization. Combination states also include:
  • Explode states.
  • Cross sections.
  • Simplified representations to reduce the number of components displayed.
  • Appearance states to show components in different colors and textures.
  • Style states to show components in a variety of display modes, such as shaded, transparent, and hidden lines removed.

     

Creating 3D annotations in MBD tends to be easier than creating 2D drawing views and details because MBD allows more flexibility. For example, a dimension can appear in only one drawing view, but a 3D annotation can appear in multiple combination states. Most companies have strict rules on the appearance of details in 2D drawings.

The Deliverable

One common misperception is that MBD is “drawingless” or “paperless.” MBD means the drawing is no longer the primary source of truth. When necessary, you can create a drawing if your supply chain requires it.

Instead of a PDF, the primary deliverable from MBD is the technical data package (TDP). This is a set of electronic files that can include the following:

• The model either in its native format, such as Creo, or the CAD-neutral STEP AP242 format.
• The bill of materials in Excel or CSV format, which can be consumed by other software, as opposed to tables on 2D drawings that must be transcribed into downstream supply chain systems.
• Other related electronic files like notes, schematics, and first article inspection (FAI) documents.

Conclusion

MBD streamlines the product development workflow because it generates content that can be used downstream in manufacturing, supply chain, inventory, and across the enterprise.