2D? 3D? How Companies Really Share PMI




For centuries, designers have communicated important manufacturing information using drawings.  GD&T, materials, surface finishes—everything is simply added to the 2D model, and distributed to anybody who needed it. In the modern era, with the introduction of 3D CAD, designers could now automate this 2D process as they generated 2D drawings from the 3D model and then added the product manufacturing information (PMI).  This approach has ensured that downstream stakeholders (think manufacturing, procurement, suppliers) know everything they need to turn those designs into physical products.   

This approach made a lot of sense before everyone had access to 3D CAD tools and viewers, but it has always suffered from a singular flaw….

A drawing with GD&T information

The problem with engineering drawings, and the rise of MBD

Once a drawing leaves the designer, it’s harder to make sure it’s updated when anything changes. And that can lead to errors:

“One of the main problems with the printing of a 2D drawing is that as soon as it is printed, it is obsolete,” writes Brian Wilson, Sr., on the TriStar blog. “There is no control over it and no way to make sure that manufacturing is working with the latest print.”  In fact, he says that it’s quite common find obsolete drawings on shop floors as a result.

That’s one reason many companies are moving away from using 2D drawings for product definitions and toward model-based definition (or MBD). (Another reason is, of course, that 3D viewers are now widely available.)

What is MBD? Lifecycle Insights defines MBD as “a mechanical engineering initiative where a 3D model with Product Manufacturing Information augments or replaces a 2D engineering drawing as design documentation.”

When engineers place the PMI directly on the model, they create a master or “single source of truth” for the product that won’t become disconnected during the development and manufacturing cycle. Problem solved, right? Yes and no.

A 3D model annotated with GD&T information shows an example of MBD

The reality of MBD today

Again, we have used drawings for centuries (seriously, millennia even), and this transition is going to take time. Today some companies use a pure model-based approach, some still rely on drawings, and others use a combination of the two. We talked about this with Jennifer Herron, the founder and CEO of Action Engineering and author of the book Re-Use Your CAD: The Model-Based CAD Handbook about MBD.

“We specifically identified four different data package types,” she said. “One was a drawing and three were variations of what we would call model-based.”

What’s more, her company recently conducted a survey and that found exactly how many companies use fully 2D, fully 3D, or blended data package methods. In general, companies pass on PMI in one of 4 ways:

  • 2D drawing containing PMI
  • 2D drawing containing PMI and an unannotated 3D model
  • 2D drawing containing PMI with a model also annotated with PMI
  • 3D model containing PMI (no drawing)

So, just how popular are each of these methods? Here’s what Herron said:

 

The takeaway

Although some say the goal of MBD is to abandon 2D drawings, only a small number of respondents work in a completely drawing-less environment. You might also be surprised to learn that the data package you work with already falls within something that could be called an MBD approach. What does it all mean? Here’s the takeaway—the world is moving toward pure MBD, but not every company has adopted the all-or-nothing approach (all 3D model based or none at all). We’ll talk about the reasons for that in an upcoming post.

The free eBook

MBD is quickly becoming the preferred approach to design as many of the hurdles to creating a single source authority model for every stage of product development are falling away. To learn more about model-based definition, check out the free eBook from PTC. You’ll find out more about the limits of 2D drawings, how MBD simplifies complexity, and where to get started. Download your copy today.