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automatically updates itself when model changes occur, which prevents confusion and rework that results from using outdated or mismatched documentation.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
For companies moving toward Industry 4.0, MBD aligns better with the concept of a digital thread — a connected data flow that links every phase of the product lifecycle. MBD is the foundation for Model-Based Enterprise (MBE), enabling full traceability, real-time collaboration, and better data reuse.
The Case for Keeping 2D Drawings
1. Widespread Familiarity and Accessibility
2D drawings are ingrained in the workflows of most manufacturing environments. Many machinists and inspectors still rely on them because they are simple, quick to reference, and don’t require specialized viewing software or training.
2. Regulatory and Documentation Requirements
Some industries — particularly aerospace, defense, and medical devices — still require formal 2D documentation as part of regulatory submissions or quality audits. These drawings are considered legal documents and may be required to be archived in hard copy for years.
3. Lower Technical Barriers
While most companies use 3D CAD, not all shop floor personnel can access MBD-friendly tools. Some CNC machines or inspection systems may not support direct PMI import from models. Smaller suppliers or contract manufacturers may lack the resources to implement MBD infrastructure.
4. Faster Reference for Simple Parts
A clean 2D drawing is easier to read for straightforward components than a multi-featured 3D model. It provides a quick reference without requiring navigation or interpretation, particularly in settings where time is critical.
5. Transitional Costs and Complexity
Implementing MBD demands software updates, training programs, and new operational procedures. The costs, together with the complexity of MBD implementation, can exceed the perceived short-term advantages, especially for small and medium-sized enterprises.
A Divided Perspective: Sales vs. Shop Floor Experience
One of the reasons the MBD vs. 2D drawing debate can feel so polarized is that the strongest voices on each side often come from very different perspectives and with various incentives.
On one hand, many of the most vocal proponents of model-based definition tend to be vendors, consultants, or sales representatives from software companies or digital transformation firms. These individuals are often vested in promoting MBD because they sell the tools, training, or services that support it. Their messaging focuses on long-term benefits like cost savings, efficiency, and alignment with Industry 4.0 initiatives, all valid but often viewed through a strategic or theoretical lens.
On the other side of the conversation are machinists, inspectors, and manufacturing engineers: in other words, the people who work with drawings and CAD files on the shop floor. These professionals understand the practical challenges of interpreting incomplete PMI, navigating cumbersome viewers, or dealing with incompatible file formats. Many value 2D drawings not because they resist change but because drawings remain the most efficient and accessible way to do their jobs in real-world conditions.
This divide highlights an important truth: what works well in a software demo doesn’t always translate cleanly to the shop floor. While MBD may offer technical advantages, it must be implemented to respect the needs and workflows of those who actually machine parts, perform inspections, and manage production schedules.
As one shop veteran said, “We don’t need a digital revolution — we need clear instructions.” That clarity, for many, still comes from a well-made 2D drawing taped to a machine or clipped to a traveler.
Final Thoughts
The future of digital manufacturing, according to MBD, presents an attractive perspective, yet 2D drawings continue to serve essential functions in various operations. The debate becomes more productive when we analyze the specific value points of each method and their potential collaborative use.
Ultimately, the goal is to communicate design intent accurately and efficiently. Whether through pixels or paper, the proper method is the one that best supports your team, your tools, and your customers.
What does DraftAid Support?
Few know this, but DraftAid’s AI is fully capable of generating MBD as well as 2D drawings! The reason we promote our 2D drawing abilities is that, in the thousands of engineering design companies around the world that we have spoken to, they were all interested in MBD; however, when it came time to pay, they only wanted to purchase 2D drawings.
