CATIA V5R1531 Dec, 2005 By: Jeffrey Rowe
A Lot to Learn, but a Lot to Like
Let me say this at the outset: I have not reviewed a CAD product like CATIA since the last time I reviewed CATIA a few years ago. It has a breadth and depth that I don't often encounter in other CAD products. It also has a pretty steep learning curve—not that it's overly difficult, but it does several basic things differently from what I'm used to—but more about that later. Overall, this is a whopper of a CAD application that, once mastered, has endless potential for mechanical design and engineering. It's not without some trouble spots, though, and I'll cover those, too.
There is so much to CATIA that it's going to be very difficult to cover everything here. To keep it somewhat simple, I'll cover some basic modeling techniques and tasks that CATIA 5 supports. Another reason to cover only the basics is that the more complex jobs get, the more combinations of supplemental CATIA products can enter the mix.
CATIA V5 R15
I looked at CATIA V5 R15. IBM/Dassault has since released V5 R16, which features 64-bit Windows support and enhancements to simulation, electrical, shipbuilding and modeling functionality. With that said, let's get started.
All About Workbenches
CATIA is a parametric, feature-based modeler that provides its basic design capabilities through various workbenches—different environments with tools for performing specific sets of tasks. This concept isn't really all that different from most other CAD applications, but is implemented in a definitive and disciplined manner. The basic design workbenches covered in this review include:
Part Design. This is where users create solid models from sketches by converting sketches into features. Additional features, such as chamfers and fillets, are known as dress-up features in CATIA vernacular (figure 1). This workbench is also where materials are assigned to a model.
Figure 1. CATIA V5 provides extremely robust fillet creation.
Wire-frame and Surface Design. The tools in this workbench are much like those found in the Part Design workbench, except users create, edit and manipulate surfaces into shapes.
Assembly Design. CATIA supports two approaches for assembling components—top-down and bottom-up. Top-down lets users create component parts contained in an assembly from within the Assembly workbench. Bottom-up lets users constrain together previously created parts in an assembly to maintain their design intent.
Drafting. CATIA provides two methods for documenting parts and assemblies—generative and interactive drafting. Each has its place, depending on needs and workflow.
Because of its sheer magnitude, CATIA is not an application that can be put to work right out of the box. Plan on investing in a good training class or series of classes to become familiar and proficient with CATIA before expecting to do productive work. A couple of good third-party reference books won't hurt, either. The documentation included with CATIA helps users get acquainted with the basics, but that's about it.
Sketch and Create Base Features
As with most contemporary CAD systems, parts are usually constructed by combining different types of features—sketched and placed. Sketched features require users to create a sketch that defines a 2D shape (figure 2). Placed features are created without drawing a sketch, such as a fillet. What's being created is known as a base sketch, from which a solid model will later be created.
Figure 2. We captured the design intent of the exhaust manifold by fully constraining the profile sketch to the geometry.
These fundamental steps take place in CATIA's Sketcher workbench. The first 2D sketch users draw is the base sketch. It's then used as the profile to create a base feature that eventually becomes a 3D model. This is an easily learned technique, but as users become more familiar with CATIA, most will probably prefer to use a derived feature or derived part as the base feature. Derived features and parts are those that come from previously created entities and are real timesavers. But for beginners, sketching is the way to go.
Sketching to create a base feature is easy enough, but the next step, constraining the sketch, proves more challenging. Constraining sketches is a necessary evil—it stabilizes their shape, size and position, so it's almost always recommended. This is important so surprises aren't encountered later as the design becomes more complex. Two types of constraints need to be applied—geometric, which are applied while drawing a sketch (although some are automatically applied), and dimensional, which are usually applied after all geometric constraints are in place. Constraints can be unclear for new CATIA users. After constraints are applied, a sketch exists in one of these five states: iso-constrained, underconstrained, overconstrained, inconsistent and not changed. Usually the best state to be in is the first one, iso-constrained—the term fully constrained would be a better term.
Fancy Features and Editing
Once users create a few base features, it's time to create some advanced features for the part. These dress-up features include such things as holes, chamfers, shells, fillets and drafts. Most are easily applied to base features, but some of the dialog boxes are too vague or too complicated. Once users get the hang of them, though, the features are a powerful tool set. Some of them could be streamlined and made more straightforward.
No part is ever perfect the first time around, so the ability to edit a part is a crucial aspect of the design process. There are different ways to edit models, but probably the most common method uses the Definition option. Users can choose the feature to change from the feature history tree (specification tree in CATIA lingo) or from the graphic window (geometry area) and right-click it. Select Definition from the contextual menu, and a dialog box connected to the selected feature displays. Modify the feature's parameters, exit and the feature updates. Again, this sounds easy, but isn't always as easy as it sounds.
Surface capabilities really set the CATIA core product apart from the competition. While this is the most interesting aspect of CATIA for me (I'm an industrial designer), it's also probably the most complex aspect of the application. Although CATIA offers more advanced ways of creating surfaces, we'll stick with the Wire-frame and Surface Design workbench.
The first step in using this workbench is creating wire-frame construction elements, such as circles and splines, to assist in creating surfaces. Sketches from the Part Design workbench can also be used. Users can create relatively simple surfaces, such as extruded, revolved and offset, as well as more advanced ones, such as sweep and blends. CATIA provides a lot of surface options, and it's helpful when users have at least a basic understanding of some of the math and geometric techniques that underlie the surfacing capabilities (figure 3). Surfaces can be extensively modified to produce some complex surface models—important if designers deal with stylized product design.
Figure 3. The exhaust manifold s complex surfaces were created using design-in-context so the mating surfaces always align.
Build Assemblies, and Document a Design
In CATIA's Assembly Workbench, users bring parts in and assemble them by applying parametric assembly constraints. Like part constraints, assembly constraints ensure that every part stays put in relation to the other parts in the assembly. As I said earlier, there are two different types and approaches for assemblies. CATIA encourages and I recommend using the bottom-up approach because it focuses a designer's attention on creating better individual parts, then on assembling them. Keep in mind that users can create an assembly using a combination of both approaches, but that's usually reserved for more advanced users with unique design requirements.
CATIA provides two ways to generate drawing views of parts and assemblies—generative and interactive. Generative drafting is more efficient because it automatically generates drawing views of parts and assemblies as you go, as well as BOMs (bills of materials) and drawing view balloons (figure 4). Interactive drafting requires users to create individual drawing views by sketching them and adding dimensions. This can be time-consuming compared with the generative technique.
Figure 4. With a simple click, a part from the exhaust manifold is associated to the multiple views and section cuts within the drawing.
Some Final Thoughts
As I said, I've just barely scratched the surface of what CATIA is capable of. If users take the time to learn the tricks, techniques and nuances that CATIA has to offer, they will be able to design almost anything. I doubt that many users will outgrow its myriad capabilities.
Jeffrey Rowe is an independent mechanical design and technical communications consultant. With offices in Colorado and Michigan, he can be reached at 719.539.8549 or firstname.lastname@example.org.