In short, MBD is a 3D CAD model which contains all the Product manufacturing information (PMI) including Dimensions, GD&T necessary to manufacture, communicate all in one document thus eliminating the need of separate 2D drawings and documentations and making it easier to maintain a product.
For Many decades, 2D drawings has been the primary way of communication between product devolvement, Supplier and Manufacturing.
Even since computer programs took over manual drawings, the changes started to began.
Initially, Engineers used computer programs create 2D drawings instead of creating the drawings manually and this was transferred to many departments using physical copies.
When 3D CAD modelling became popular and accessible to everyone, Engineers started to create 3D CAD models and then create a 2D drawing based on that and share it with other departments, suppliers.
When computers started to occupy the industry with the development of new technologies like Virtual reliant (VR), Augmented reality (AR), 3D Scanning, High end CNC machines, the need 2D drawings has been constantly decreasing.
The method of manufacturing input to a machine has changed from manual inputs to codes to now just a 3D CAD model. Lets just take an example of 3D Printing.
Instead if giving input parameters like dimensions, positions, etc you have have to just upload a 3D CAD model in a compatible 3D file format like the popular .STL file format.
Here is an example of Model Based Definition.
No matter how complex the CAD model is, You don’t have to give any dimensional input or code except for the basic parameters like boundary, speed etc.
The method of inputting CAD models to manufacturing machines is rapidly increasing from small machines to bigger CNC machines. This eliminates the need of 2D drawings where the engineer needs to understand the drawing and need to input to the machine.
Another reason is drawings are complicated to understand. You need to visualize the 3D model from 2D drawings first to be able to write codes or give the input. Not everyone understands it 100 percent and engineers make mistakes while interpreting the 2D drawings.
On the other hand, 3D CAD models are very easy to understand and you get a very clear idea of the part and the time for analyzing / visualizing is reduced. More importantly, the mistakes are eliminated.
The Model Based Definition (MBD) is a part of Model Based Enterprise (MBE) which is a ecosystem. It has the necessary tools / softwares that enables seamless communication of design data from designer, supplier, management. It also includes revision control where anyone could see the changes in 3D easily.