MBD Implementation 10 DOs and 10 DON’Ts – Don’t Rely on 2D Drawings as the Master Anymore

My last post on Model-Based Definition (MBD) implementation, “Measure progress” touched upon NIST’s MBD capability assessment, where drawing-centric or model-centric is a key distinction between level 0 and level 1. In this blog, let’s expand this topic a bit further and understand why 2D drawings shouldn’t be the design authority anymore.

Here is a question to you: how often do your 2D drawings mismatch 3D model? I’d love to learn your comments below, but according to my personal experience and conversations with many manufacturers, up to 60% of 2D drawings don’t match 3D model. There are so many sources of discrepancies: After design revisions, designers forget to update all involved 2D drawings used in downstream production; or shop floor just modifies 2D drawings on the fly to speed up manufacturing without even notifying designers; or even if Design and Manufacturing reaches an agreement, changes are just red-lined on a piece of paper drawing instead of being incorporated into 3D models.

Here comes the next question: given these disagreements between 3D model and 2D drawings, which one do you take as the design authority? That is, which one to follow as the master? Again, your feedback will be appreciated in the comment area.

What we found is very encouraging: in a SOLIDWORKS customer base survey in 2015 (sample size: 486), two thirds take 3D as the authority and one third follow 2D. To the 3D group, congratulations! You are not far away from model-based definition (MBD). To the 2D group, let’s see why taking 3D as the authority is better.

1. We live in a 3D world and human cognition is 3D-oriented, so by nature, 3D is easier to communicate than 2D and results in better clarity and less ambiguity.
2. Because of point 1, 3D design has become mainstream today thanks to CAD technology development and will only become more popular as time goes on. Since design is in 3D already, why do we have to project it to 2D plane just to convey design specifications? Why can’t we integrate dimensions, tolerances and other key specifications in one consistent and intuitive 3D model? By the way, this is a very natural thought and majority of SOLIDWORKS users have considered it as reported in the same survey mentioned above.
3. From 3D CAD workflow standpoint, a 2D drawing is a derivative of 3D design. So 3D drives 2D, not the other way around. Taking 2D as the master would have to really reverse this CAD workflow, which would mean lots of additional efforts and unexpected consequences. For example, if 2D contains authoritative manufacturing specifications that don’t exist in 3D, when 3D updates, there could be substantial work just to maintain or even re-apply these 2D specifications.
4. Now if we look at the entire production, 3D dimensions and tolerances can bring even more advantages such as automatically driving CMM and 3D scanning inspection reports.

How to switch from 2D authority to 3D authority?

First it’s a mindset change. Companies need to encourage and cultivate the habit of chasing down 3D design as a single source of truth. Second, build up model-centric processes. Here are several examples, GE Power and Water only allows 3D models to be checked into PLM. Pseudo drawings can be produced on need basis as a transition, but are not allowed in PLM system. Other companies forbid any ad-hoc modifications of 2D drawings without design team’s approval. Even if a change is approved, it must start with 3D model and flow to all related 2D drawing derivatives used by all impacted departments.

Another recommendation is to integrate all specifications into 3D. If key manufacturing information, such as notes and bill of materials (BOMs) tables can only be found in 2D, instead of 3D, it creates a dependency on 2D and invites objections. The good news is SOLIDWORKS MBD supports many manufacturing specifications in 3D already besides dimensions and tolerances, such as BOM, Notes, and Balloons as shown below.

I hope this blog is helpful. In order to implement MBD, please remember: Don’t take 2D drawings as the authority any more. My next blog will move onto Automation, another exciting topic. To learn more about SOLIDWORKS MBD, please visit its product page. Also welcome to discuss with me at Twitter (@OboeWu) or LinkedIn (OboeWu).