MCAD Tech News #141

16 Mar, 2005

Cadalyst MCAD Tech News

CAD vs. CAM 101

Understanding the similarities, differences
of these closely knit technologies

In the normal course of my business, I often get asked, "Are CAD and CAM really that different from each other?" At first glance, CAD (computer-aided design) and CAM (computer-aided manufacturing) seem to be more similar than they are different. But I've found the opposite to be true. Yes, it's true that CAD and CAM do share some similarities: For both, you create something — one digital, one physical. And yes, the industry has made major progress to close the gap between CAD and CAM functionality and interoperability. However, each is still considerably different from the other.

The major differences between CAD and CAM really come down to a few basic things:

  • features

  • interoperability

  • workflow

  • specialized vs. integrated products

In CAD and CAM, two basic kinds of features exist: design features and manufacturing features. Design features are what define a part in a CAD system and can be either additive or subtractive in nature. Feature-based CAD packages display features and operations in history trees, and users can directly manipulate parts and assemblies and modify them using the history trees or directly in the models. History trees can sometimes be a pain to deal with, but they also can provide beneficial overviews to manufacturing because they provide insight into how a design was created with regard to design intent.

Manufacturing features, on the other hand, group geometry for manufacturing processes that will be applied to it, such as machining. Manufacturing features can become complicated quickly, because although some are the direct result of a machining operation, they also could be the indirect result of machining another feature.

CAD/CAM interoperability has seen many advances, but it is still a major issue today. For example, a lot of design intent is often still lost as design data moves from CAD to CAM. Data incompatibility costs the industry tens of billions of dollars annually.

One of the most promising innovations to remedy CAD/CAM data incompatibility is the Super Model Project led by Step Tools.

The goal of the Standard for Product Data Exchange (STEP) is to provide a comprehensive, extensible standard for product data throughout a product's lifecycle. The goal of the Super Model Project is to develop software and databases for an integrated design-to-manufacturing system that allows CNC machine tools to be controlled by product design data. The Super Model database is defined using STEP and STEP-NC, a replacement for the 30-plus-year-old RS274, a language historically used to program numerically controlled (NC) machine tools. RS274 severely restricts the range of design data that can be communicated to a machine tool controller. STEP-NC, on the other hand, has a rich data format that integrates manufacturing processes with manufacturing features, and the geometry used to derive the processes.

By its nature, CAM is generally much more process-oriented than CAD, and the sequence of processes can be critical in the CAM world. In other words, CAD defines a part, whereas CAM defines a part's manufacturing processes and how the part takes shape from rough stock to final product. Therefore, workflow is more important to CAM. Also, the concept of time is an important aspect of CAM that really isn't a factor at all in CAD. This situation is analogous to that of graphics: Time is important in animation, but of no concern to static graphics. Time is especially important on the manufacturing side because a part continually changes with different machining processes over time.

Specialized vs. Integrated Products
Some CAD products today include CAM functions, but more commonly you will find that vendors offer a suite of products, each for handling a specific aspect of the CAD and CAM functions associated with design, management and manufacturing. Products that specialize in a given discipline, whether CAD or CAM, generally are better suited for the task at hand, as opposed to an integrated product that tries to do multiple duty.

Although the situation continues to improve, major compromises still exist in both approaches, either specialized or integrated. On one hand, CAD users don't want to be constrained by having to predict manufacturing processes. On the other hand, CAM users don't want to be forced to produce parts that are too expensive to produce or can't be realistically produced at all. So getting CAD and CAM software products and users to work together remains a great dilemma. More so than for CAD, CAM users also have to carefully weigh whether a product's capabilities are necessary for their applications, because CAM products are often more challenging to use than CAD, and CAM products often offer more capabilities than most machine shops will ever need.

Even though they are so different, the best solution to this problem might be to fully integrate the two. But will CAD and CAM ever join as one? Ultimately, yes — or at least, probably. For now, however, the differences between CAD and CAM will slow their integration, largely because their workflows and final products are so different. Because of how they are used, most CAD and CAM software products look, feel and behave differently, and probably will for some time to come.