The Drawing vs MBD Debate

published on 27 May 2025

What is Model-Based Definition (MBD)?

Model-based definition refers to using a 3D CAD model, enriched with all relevant product manufacturing information (PMI), as the authoritative design data source. This data includes dimensions, tolerances, material specs, surface finishes, GD&T (Geometric Dimensioning and Tolerancing), and more.

Instead of generating a separate 2D drawing, the design intent is embedded directly into the model. This model can be used across the product lifecycle, from design to simulation, machining, quality assurance, and beyond.

The Traditional Role of 2D Drawings

2D drawings have been the language of engineering for centuries. They remain widely used in many industries — from aerospace to medical to automotive. A 2D drawing provides a simplified, standardized way to convey manufacturing details using orthographic views, section cuts, and annotations.

The Case for Model-Based Definition (MBD)

1. Single Source of Truth

The MBD system removes the need to maintain both 3D models and 2D drawings. The benefit reduces the possibility of discrepancies between them. The PMI system automatically updates itself when model changes occur, which prevents confusion and rework that results from using outdated or mismatched documentation.

2. Better Support for Automation

The MBD system allows for smooth digital workflow operations. The 3D model allows CAM software and CMM programming and simulation tools to extract PMI directly which reduces manual data entry and speeds up programming times.

3. Improved Clarity and Visualization

3D models provide a more intuitive understanding of part geometry than 2D views. Rotating, zooming, and cross-sectioning a model is much easier than interpreting complex multi-view drawings.

4. Cost and Time Savings

MBD can shorten design cycles and reduce engineering costs by eliminating the time spent creating, revising, and reviewing 2D drawings. It also helps identify design issues earlier in the process through better visualization and simulation tools.

5. Better Fit for Smart Manufacturing

The Case for Keeping 2D Drawings

3. Lower Technical Barriers

4. Faster Reference for Simple Parts

5. Transitional Costs and Complexity

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Final Thoughts

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