Drawings have been a staple of planning and recording since prehistory. In caves across the world, humans began drawing by marking their interaction with nature across the walls of their fire-lit homes. As human technology progressed, so did our ability to illustrate ideas.
Fast forwarding through the eons, drawing took on many forms. Perspective was first honed by the Greeks, the Romans brought precision to the drafting table and the Middle Ages brought skewed perspectives with oblique visual descriptions of cities, castles and wars. Though drafting would progress, it wasn’t until the Renaissance that technical drawing came into its own. Working in Florence, Italy, a designer named Filippo Brunelleschi ushered in a new theory of drawing that contemporary people would understand as a blueprint. Using linear perspective, the Italian began constructing some of the most wonderful architectural feats that world had ever seen. To guide their construction, Filippo used his diagrams and, in doing so, introduced the world to technical drawings.
Since their invention, technical drawings have evolved. In the late 18th century, Gaspard Monge, a French mathematician, developed his ideas of descriptive geometry, codifying the planar views that manufacturers are familiar with today. In the middle of the 20th century, another seismic development occurred in technical drawing. Geometric dimensioning and tolerancing (GD&T) was created to make manufactured goods more consistent with their technical specifications by more precisely defining required precision and allowable variability.
Most recently, the technical drawing’s path has merged with another transcendent technology—the computer. Since the mid-1970s, technical drawing has moved off of the drafting table and onto the computer screen. Today, designers use CAD to create 2D drawings, 3D models and animations that describe how parts should be made. With CAD, technical drawings have become easier to create and share. However, engineers have started to realize that CAD drawings aren’t necessarily the best way to distribute, correct or archive manufacturing documents. Instead of relying on drawings, engineers have started to look for ways to combine the models they’re creating with the technical drawings that were based on those 2D and 3D forms. This new phase of technical drafting has been called model-based definition (MBD).
What Is MBD?
MBD is essentially a term that describes a 3D model that contains all of the annotation data that would be needed for a part to be manufactured. Aside from dimensions, an MBD model will communicate a component’s GD&T requirements, material information, configuration details, and other data that could be useful for anyone that might have input into the manufacturing of a design.
Who’s Using MBD?
As of now, MBD is still a nascent technical drawing paradigm. However, industrial catalysts like the U.S. Department of Defense (DoD), select companies in the aerospace industry and the automotive sector have started to insist that any vendors working on affiliated projects have to produce 3D MBD models.
One of the biggest factors driving this trend is the lifespan that some DoD and aerospace products see before they’re eventually retired. For the DoD or Boeing, having a machine run for 20, 30 or even 50 years isn’t out of the ordinary. With service lives that stretch out that long, its easy to see that building design information directly into a model can be invaluable. Who’s to say that the designer of a particular system on a legacy aircraft will be around to impart his or her design intent to the younger engineers deputizing the design work when something goes wrong down the road?
Another benefit that MBD offers engineers is the ability to use their models as a verification datum upon which they can automate inspection of manufactured parts. With all of its dimension and definitions built right into the model, MBD components can be used in conjunction with coordinate measuring machines and 3D scanners to ensure that a part meets documented manufacturing standards without having to reference outside drawings. All of the information that would be needed to compare the two parts would be right there attached to the model, making an often painstaking and time-consuming process much easier and quicker, while also enabling more process automation.
Aside from its communication and validation benefits, MBD has also been able to deliver cost-savings to those who have adopted the emerging documentation trend. Since adopting MBD principles, Toyota, Boeing and BAE have demonstrated up to a 50 percent reduction in costs in the product development processes. What’s more, the Naval Air Warfare Center Aircraft Division based in Lakehurst, N.J., has noted that after implementing MBD into its design workflow, the cost of labor used in component fabrication has dropped 30 percent.
Why Adopt MBD?
In the end, MBD is valuable because it preserves the geometry of a 3D model while still delivering all of its manufacturing information that’s usually associated with a 2D technical drawing. Because MBD relies on 3D geometry, it gives manufacturers or anyone interacting with a 3D model greater insight into the design intent of each feature as well as a more natural way to interact with a virtual part. Though that might seem simplistic in its promise, machinists who have to transform raw stock into goods could really benefit from visualizing a part in 3D before deciding on CAM setups and toolpaths.
Furthermore, design teams working across time zones could use MBD models to better understand their colleagues’ design requirements without having to sift through reams of paper drawings and manually searching for minute bits of information.
Finally, as we’ve seen, drawings have been evolving ever since man wanted to communicate an idea down through the ages. While MBD, with its 3D nature and its intrinsic link to computers, might seem completely disconnected from the cave paintings of old, when you take a step back, you notice that both techniques are trying to do the same thing—communicate an idea in the most sophisticated and enduring way possible so that good ideas find fewer ways to be lost.
If MBD is going to be the next evolution in drawing’s long history, the age-old trade could have done worse. With its ability to condense information into an encyclopedic form, MBD appears to be an excellent way forward for technical drawing.
About the Author
Kyle Maxey is a mechanical designer and writer from Austin, TX. He earned a degree in Film at Bard College and has since studied Mechanical and Architectural drafting at Austin Community College. As a designer Kyle has had vast experience with CAD software and rapid prototyping. One day he dreams of becoming a toy designer.