September 27, 2010
3D Model-Based Design: Setting the Definitions Straight
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Jeff Rowe - Managing Editor

by Jeff Rowe - Contributing Editor
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Editor's Note: We were recently approached by Jennifer Herron, an enterprising mechanical engineer, with an intriguing idea of what really constitutes a 3D CAD design. She rightly posits that it's a 3D model, not a 2D drawing. Her thesis is the fact that there is a major disconnect between a perceived CAD workflow and actual workflow, largely due to a lack of standardized language, methods, and practices, regardless of CAD software used. In addition, she questions why are we still using 2D drawings to convey 3D designs when 3D models do a much better job? Below is her take on making standardization more practical through the use of a common language for interaction and collaboration throughout the design process with what she calls model-based design.

There is a lot of ongoing confusion among CAD designers on how to take advantage of CAD software capabilities and consequently, Model-Based Design (MBD) is not winning any popularity contests. Adoption of MBD is stalled by the lack of methods and practices that standardize the design engineer's workflow. Designers are stuck when setting up, creating and delivering CAD models. They need a comprehensive set of clear standards and processes to maximize their software ROI and to collaborate and communicate with other members of their team using CAD models.

To that end, I suggest that we, the CAD community, go back to the basics and re-clarify the language we commonly use. In doing so, my goal is to facilitate the transition using discipline and organization to span the gap between 2D detailed drawings for manufacture and the 3D CAD revolution.

I invite those involved in the CAD community, to help me edit the definitions for MBD, in hopes of developing clear language for building hardware from 3D CAD.

Instructions for editing a definition

To provide an edit or comment for a definition, click on the send comment link under each definition. This will generate an email and send it to me. Please make your language as clear and plain as possible.

Click here to edit and comment the MBD Definitions


Model Based Design (MBD)
- A development approach, for the design engineer, that declares the 3D CAD as the design authority as opposed to the 2D Drawings. The idea is to make the CAD models the source of the design database. This pushes a shift in the engineer's mindset to think of 3D CAD as THE deliverable document. 3D CAD models are no longer just a means to creating a 2D drawing. Rather, the 3D CAD model is the source of the design database and is the authority which all other outputs flow from (i.e. Finite Element Meshes (FEM), production drawings, bill of materials, etc.). While most will still use drawings for the manufacturing stage, the practice of MBD lends itself more readily to collaboration and interoperability, a future in digital prototyping and additive manufacturing and 3D digital work instructions.

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Model Based Enterprise (MBE) - NIST and the DOD define it as - A fully integrated and collaborative environment founded on 3D product definition detailed and shared across the enterprise; to enable rapid, seamless, and affordable deployment of products from concept to disposal. More information is available at the Model Based Enterprise website.

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Model - A mathematically correct three-dimensional representation of a person or thing or of a proposed structure.

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Computer Aided Design (CAD) - The use of computer technology for the design of objects.

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2D Drawing - Two-dimensional flat orthogonal representations of a three-dimensional object; used to convey detailed information such as dimensions, tolerance, materials, and construction techniques related to how an object is to be built. Both engineering and architecture organizations have standardized this communication method.

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2D CAD - The use of CAD software to create 2D drawings, resulting in either printed paper or digital PDF. In many engineering environments the 2D drawings produced by CAD Software are the official specifications (design authority or record of authority) for finished products and are often generated from and linked to the 3D CAD.

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3D CAD - The use of Computer Aided Design Software to create and view objects in three dimensions, i.e. a geometrically correct digital model of the object. The results of the process are saved in a digital computer file referred to as a 3D CAD Model. Most modern 3D CAD software applications are capable of generating the orthographic projections required for a 2D drawing and from the 3D CAD, changes can be pushed to the drawing as well.This model may or may not include PMI (Product and Manufacturing Information) data.

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Drawing Standard - A drawing standard defines how to translate 3D data into a 2D format in a standardized method, so that all members of the team can effectively understand the drawing. This communication method includes: orthographic views, dimensions, tolerances, materials, revision history, company information, etc. This standard is well defined and used across many industries as the ASME Y14.5.

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MBD CAD Modeling Standard - A standard that specifies procedures and techniques for building CAD models that enable effective implementation of Model Based Design to all forms of hardware products. The modeling standard is analogous to using ANSI Y14.5 for creating 2D drawings, but is instead applied to 3D CAD. In short, it is a standardized communication method for 3D CAD models, encompassing what to include in the model from fillets and threads to model translation techniques for analysis or digital manufacturing.

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Add Definition - Don't see a critical definition? Feel free to add one with recommended title and definition. Click on the Send Comment link below.

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Commentary By Jeffrey Rowe, Editor

We applaud and support Ms. Herron's effort for a consistent language that includes definitions of what 3D CAD and associated models are really all about. She's really only gotten started with it, but your input could prove invaluable to her effort and the larger CAD community.

A lot of what she proposes are extensions of efforts put forth by some of the standards organizations, such as NIST, as well as the DoD. Although it may seem a bit formal at first, it begins to make sense when you consider how vital communication is for collaborative design and engineering projects conducted by teams literally around the world.

Contrary to what we've been hearing for the past 10+ years, drawings (whether digital or on paper) aren't going totally away any time soon. But, isn't it about time that we exploit and capitalize on 3D models for what they are - the true end product from the 3D design process on the way to manufacturing that product in 3D.

Of the above concepts and definitions, I find one of the most interesting to be the Model-Based Enterprise (MBE) that is based on a product definition referred to as the Model-Based Definition (MBD). The MBD can be viewed as an annotated 3D CAD model that contains all the information needed to define a product. This annotated model is what replaces a traditional drawing. In this context, then, a 2D drawing is created as an exception not as a standard byproduct of the 3D design process. This makes even more sense in the context of collaboration and communicating a design further upstream as part of the comprehensive product manufacturing information (PMI) package.

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-- Jeff Rowe, Contributing Editor.

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