Inventor 6 strengthens surfaces

31 Dec, 2002 By: Bill Fane

Autodesk’s flagship modeler also introduces new weldment environment.

Highly Recommended Autodesk Inventor Release 6 is the seventh release in just three years (don't forget R5.3) and is billed as the "biggest" since Release 1 in terms of new or improved features. So who should be using Inventor? You probably should, if you design "mechanical" things such as machinery, mechanisms, sheet-metal parts, power-transmission equipment, and so on.

Autodesk refers to Inventor R6 as the customer-driven release, because the "over 200" new and improved features are based primarily on input from customers. That seems like an obvious way of doing business, but over the years I have used a variety of programs from a number of vendors that seem to be driven more by programmers showing off their prowess rather than by what users really need.

Two new capabilities in Inventor R6 in particular should not just improve its operation but should also open it up to many more users.

If you design things that are fabricated by welding smaller pieces into a bigger lump, R6's new weldment capabilities are exactly what you need.

R6 also adds a great many new surfacing and free-form drawing tools that will interest designers of styled objects, including consumer goods such as toasters, hair dryers, portable CD players, and door handles.

We'll start with a review to help you categorize Inventor, then come back to look at some of the specifics. It is a parametric solid modeler, along with such programs as Mechanical Desktop, Pro/ENGINEER, SolidWorks, Solid Edge, thinkdesign, and IronCAD. You create a 3D solid model, and the program then generates the 2D drafting views.

If you change the value of a dimension, the size and shape of the 3D model changes accordingly, and the 2D drafting views update accordingly. You can also create assemblies from these parts, and when a part changes, the assembly updates.

These products are aimed primarily at mechanical designers, and their chief power comes from the ease with which you can incorporate changes and revisions into the design process.

Inventor has two particular strengths that set it apart from other parametric modelers.

First, because of the unique way it handles its data, it is particularly good for very large assemblies.

Second, assemblies can contain adaptive parts. With other modelers, if you change the size of a component part, other parts in an assembly move accordingly. For example, if you change the length of a bracket, the bearing mounted on it moves. With Inventor's adaptivity, however, if you change the location of the crankshaft, the length of the connecting rod changes so things still work properly.

Start by thinking about how a steel weldment is usually physically produced. First, you produce individual components, usually by flame-cutting from flat plate or by cutting from standard structural shapes. Some components may require additional preparation such as chamfering of edges to improve weld penetration. The prepared components are then welded together. Finally, the weldment receives any required post-welding machining operations.

With existing parametric modelers, it is easy enough to replicate the first and third steps. You can produce models of the individual components (figure 1) and assemble them into a single weldment (figure 2). On the other hand, detailing of the edge preparations and of post-welding machining operations can get extremely messy to do, and even messier to revise. When 2D drafting views are created, welding annotations usually need to be added manually.

Figure 1. The individual components of a weldment.
Figure 2. The components in position, waiting to be welded.

Inventor R6 introduces a whole new operating environment for weldments. In it, you create models of individual components and assemble them, much as before. The difference is that you can add weld preparation chamfers from within the assembled model. They show in the assembly drawings but do not reflect back to the individual component drawings.

You then add welds within the assembly model. They can be shown schematically (figure 3, right brace) or pictorially (figure 3, left brace).

Figure 3. Inventor R6 now adds “weld” objects to the assembly.
Figure 4. Machining operations can be performed after welding. . .

You use industry-standard annotations to define what you want within a dialog box. Inventor then creates the weld as a "weld" object within the assembly and attaches a standard annotation to the 3D model. These annotations always face normal to the screen even if you rotate or orbit the model.

I made the braces transparent so you can see the arrow-side and other side welds.

When you create 2D drafting views of the weldment, Inventor R6 automatically generates the weld annotations and pictorial or symbolic representations of the welds themselves.

You can also perform machining operations on the assembled model (figure 4). You can use the usual modeling techniques of creating profiles and then cut-extruding them, and you can apply standard predefined holes. The significant point here is that the machining

operations are applied to the assembly-they don't reflect back to the individual component drawings that you need for the cutting shop (figure 5). You can edit weld definitions any time, and everything updates. If the parts change, the welds change accordingly.

Figure 5. . . . but the machining does not affect the “as cut” component drawing.

Previously, surfacing and free-form curves were not strong points with Inventor, especially compared with certain competitors.

Autodesk startled the industry last year when it announced that it would no longer license the ACIS solid modeling kernel, but had bought the source code and would now develop it independently. Autodesk now calls its version Shape Manager.

Autodesk claims that its control over the modeling kernel has allowed it to greatly improve surface modeling. Autodesk refers to it as a hybrid environment. Unlike many other products, including Autodesk's own Mechanical Desktop, surfacing in Inventor R6 was not developed independently and then added to the basic product. Instead, it was developed as an integral part of the modeling kernel. This makes it much easier to flip back and forth between solids and surfaces and to convert features back and forth.

For example, when creating a solid with a complex free-form shape, normal procedure is to create a solid larger than needed, then create a curved surface. The curved surface is used as a cutting tool to cut part of the solid.

With R6, when a surface is combined with a solid, it not only cuts material off the solid, but it can also add material on if the surface rises above the solid. Figure 6 shows a basic (transparent blue) cube and a separate curved (copper-colored) surface. I used a simple "ribbon" surface, but a compound-curve one also works.

Figure 7 shows the result of combining the solid and surface. As usual, everything remains parametric so that changes to the solid or surface reflect back and drive the other feature.

Figure 6. A simple solid brick and a curved surface.
Figure 7. When the surface is combined with the solid, it adds on as well as cutting off.

Inventor now includes a full set of tools for people who are creating sculpted shapes. These include the extrusion of open profiles, stitching of surfaces, thickening of a surface into a solid, lofting of multiple sections and guide curves, and so on. Applications include the design of plastic and die-cast parts for consumer goods, but "styling" is also being applied more and more to industrial products.

3D paths and profiles can now be generated from the intersection of solid faces and/or surfaces. Among other uses, this can make it easier for designers who are attempting to lay out hydraulic and pneumatic hoses.

You can emboss text and other features on flat or curved faces, and apply scanned decals to parts.

The list of existing and new features in Inventor goes on and on. Autodesk's "What's New" summary runs 52 pages, so obviously everything cannot be covered in a single review. Suffice it to say, Inventor is intended for users in a wide range of design fields. This includes, but is not limited to, designers of manufacturing machinery, earthmoving equipment, kitchen gadgets, racing cars, doorknobs, toasters, portable CD players, and cameras.

The resultant 3D models can be used to generate traditional 2D documentation, but it is becoming more and more common to forego this step when producing component parts. Inventor is able to export data in a variety of file formats that can be imported by the matter replicator.

The matter replicator? So who has been watching too much Star Trek?

No, seriously, the matter replicator exists in two basic forms. CNC machines produce a part, or tooling to make many copies of the part, by starting with a big lump of material. They then cut off everything that does not look like the desired object.

Rapid prototyping processes such as stereolithography create an object by building it up through adding material. The object is produced from the 3D model file. The ultimate strength of parametric modeling, however, lies in the basic fact that design intent can be captured within the model, so that changes automatically reflect through the part and into the assembly, making it simple to explore "what if" scenarios.

This power can also be used to quickly create families of parts and assemblies, such as a basic hydraulic cylinder design that is produced in a variety of bore sizes and stroke lengths. Show me a design that has not changed, and I'll show you a design that's not in production yet.
Highly Recommended.

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