Model-Based Definition (MBD)

Model-Based Definition (MBD) is a product definition approach in which a 3D CAD model, including embedded annotations and product manufacturing information (PMI), serves as the primary and often sole authority for describing a part or assembly. In an MBD approach, dimensions, tolerances, surface finishes, material specifications, and other requirements are attached directly to the 3D model rather than being maintained primarily on separate 2D drawings.

Key characteristics

• 3D model as the authority: The 3D CAD model, with its PMI, is treated as the master reference for design, manufacturing, and quality, often replacing traditional 2D drawings.
• Embedded product manufacturing information (PMI): Geometric dimensions and tolerances (GD&T), notes, callouts, and other attributes are applied directly within the model environment.
• Digital interoperability: The model is intended to be consumed downstream by CAM, CMM, MES, PLM, and other systems to support NC programming, inspection planning, and automated feature extraction.
• Configuration and change control: MBD data typically lives under formal revision control in PDM/PLM systems, similar to drawings, and must align with document control and quality procedures.

Use in industrial and regulated environments

In manufacturing operations, especially in aerospace, defense, and other regulated sectors, MBD commonly appears as:

• Design authority packages: Customers or engineering groups releasing 3D models with embedded PMI as the official definition delivered to suppliers or internal manufacturing.
• Inputs to MES and digital work instructions: MBD models referenced in digital travelers, operation instructions, or visual work instruction tools to show model views and callouts at each operation.
• Inputs to inspection and FAI: MBD used to drive ballooning, characteristic extraction, and CMM programs for First Article Inspection and ongoing inspection plans.
• Source for manufacturing automation: CAM, toolpath generation, and coordinate measuring routines built directly from the model to reduce re-interpretation of requirements.

What MBD includes and excludes

• Includes the 3D geometry and all necessary product definition details (dimensions, tolerances, GD&T, notes, references to standards, and other PMI) required to manufacture and inspect the part.
• May include links to related specifications, materials, and process requirements managed in PLM, QMS, or document control systems.
• Does not automatically include full process plans, routings, or work instructions, although MBD is often referenced by these artifacts.
• Does not replace quality records, FAI reports, DHRs, or other compliance documents, but can serve as a primary data source for generating them.

Operational considerations

When MBD is used on the shop floor and in quality systems, typical considerations include:

• Access and visualization: Ensuring operators, inspectors, and suppliers can view and interrogate 3D models and PMI with appropriate tools and permissions.
• Version governance: Aligning MBD revisions with ERP/MES routings, work orders, inspection plans, and FAI baselines under controlled change processes.
• Integration with other systems: Mapping model features and characteristics into MES, PLM, QMS, and CMM software without manual re-entry where possible.
• Training and interpretation: Ensuring personnel understand 3D PMI, GD&T usage, and how model-based requirements translate into measurement and process controls.

Common confusion

• Model-Based Definition (MBD) vs Model-Based Enterprise (MBE): MBD focuses on using the 3D model as the formal product definition. Model-Based Enterprise refers to a broader organizational approach where model-based data flows through design, manufacturing, quality, and support processes.
• MBD vs 3D CAD models without PMI: A simple 3D model used only for visualization or rough geometry is not typically considered MBD. MBD implies that the model carries the authoritative dimensions, tolerances, and other PMI required to build and verify the part.
• MBD vs digital drawings: PDF or electronic 2D drawings are digital but are still drawing-centric. MBD shifts the source of truth to the 3D model itself rather than to a 2D representation.