Autodesk Mechanical Desktop: Integrating Toolbodies into Your Design Flow By Bill Fane
Seems to me that the toolbodies capability in Mechanical Desktop? software has been overlooked by a lot of users and that's unfortunate; it's a powerful, easy-to-use function, as you'll soon see, that you can use to create models of molds, patterns, and other tooling directly from the model of the part you want the tooling to produce. You can also use toolbodies to create complex parts that would be difficult or impossible with normal modeling techniques. First, let's review the basics. Building a part in Mechanical Desktop is normally a sequential process. Once you create a part's basic shape ("the basefeature"), you begin adding other features. Each succeeding profile needs two additional dimensions or constraints to tie it to the existing part.
When working in an assembly file, you can always start a new, independent part that subsequently assembled with and constrained to the other parts in the assembly.
On the other hand, a new part file can only ever contain a single part and, therefore, all subsequent features must be directly constrained back to the existing part—except when you use toolbodies.
Figure 1: Create a drawing of the casting core first.
Figure 2: To produce the core box, subtract the core (as a toolbody) from the block.
Take a look at Figure 1, which shows a core (in magenta) to be used in the production of a sand casting. Of course it requires a core box, which is basically a mold into which you pack the special sand used to make the core. Figure 2 shows the core box in yellow.
Figure 3: A gold brick is the base part, the red object is created as a toolbody.
There are two ways to build the model of the core box.
The first, most-often used way is to design the core and then subtract the core's five features (the magenta part), one at a time, to arrive at the core box. This obviously involves a duplication of effort and takes some messy work with parameter files to keep the model of the core box in step with any changes made to the model of the core. The other way—the toolbody way—is to design the core and then use it as a toolbody to create the core box. This requires just two features, and is automatically linked to the core model. Let's work through a simple example together, and then I'll show you a few more samples and give you a few tips.
1. Open a new drawing file, and sketch a simple part, a rectangle. 2. Profile and dimension it. 3. Extrude it into a brick.
You're now ready to create a toolbody.
1. Use one of the following commands to start the operation. Not surprisingly, you have at least three ways to start. You can
Type in amnew at the command prompt. From the main menu, double-click Toolbody and then click New Toolbody. Click on the hammer-and-wrench icon in the main toolbar. The Toolbody Modeling shortcut menu appears. Click the hammer-and-wrench icon again in the flyout. 2. Once the command has started, press Enter to accept the default name, <Toolbody1>, which appears after each of the above command sequences, or name it as you choose. 3. Press Enter.
Nothing much seems to happen. Mechanical Desktop simply drops back to the command prompt. Closer inspection reveals that a Toolbody1_1 entry has appeared in the browser; right-clicking it indicates that it is active. You can now proceed as if you were working on a new, independent part.
Figure 4: The toolbody is constrained to the base part using assembly constraints.
Figure 3 shows the original gold brick and a new toolbody, in red. I built the toolbody by revolving a profile and then adding a rectangular extrusion to one end, as if I was building a new, independent part. Its profiles did not need to be constrained to the existing part.
4. Build the toolbody in any way you choose.
5. Suitably constrain the toolbody using 3D constraints. Once again, there are several ways to start this operation:
From the menu bar, pick Toolbody then 3D Constraints.
From the Toolbody Modeling toolbar pick 3D Toolbody Constraints, which is the little red c-clamp icon.
Figure 5: The toolbody can be subtracted from the base part.
If you're now thinking, "Hey, that looks exactly like the assembly constraints toolbar!", you're right. Figure 4 shows the result of using these constraint tools to mate the center line of the revolution to the edge of the brick: the square peg is mated face-to-face with an offset from the end of the brick, and an angle constraint between an edge of the peg and an edge of the brick keeps everything square. Just like a normal assembly.
Now comes the cunning part. Once the toolbody is constrained you have to combine it with the existing part. 6. Go to the Part pull-down menu or the Part Modeling toolbar and select Placed Features then Combine to start the AM_COMBINE command. 7. You are now offered the three Boolean operations: Cut, Intersect, or Join. Let's start with the default, which is Cut. 8. Select the toolbody to be used for cutting by clicking on it in the graphics window, and Mechanical Desktop will produce figure 5 for you. This is why they are called toolbodies; they are 3D bodies that act like cutting tools to cut away the existing part.
Figure 6: Toolbodies can also be joined to the base part.
Actually, the preceding definition of a toolbody is a little misleading, because you are not restricted to using them as cutting tools. Figure 6 shows a toolbody that was joined to the base part. You can also use them to perform an intersect Boolean.
Figure 7: Making a casting requires a pattern.
Start With an Existing Part In practice, the sequence followed in our example—build the core shape, then the desired part as a toolbody—is not usually the way a design like this happens. Quite often the part exists first, and you want to build the tooling for it.
Not a problem. One of the options under the Toolbody menu or Toolbody toolbar is Toolbody Catalog. This looks and works exactly like the Assembly Catalog. It enables you to attach any existing Mechanical Desktop part file as an externally referenced toolbody.
A little-known trick is that you can copy an existing toolbody, even an external one, and then constrain and combine it to suit your current design. Which is how I arrived at the model in Figure 6.
You can even nest toolbodies; a part that uses a toolbody can in turn be used as a toolbody in a higher-level part. If you subsequently change the external file then all insertions of it in all other part files automatically update.
Toolbodies are not limited to just cutting out a mold cavity. They can also be used to help build complex parts that would be difficult or impossible by the usual means.
Take a look at Figures 7 through 10 and study their captions. This complete series was built from a single casting drawing and one core drawing, externally referenced as toolbodies as required. The entire assembly is totally parametric.
Figure 8: Sand is packed around the core, and then the core is removed.
Figure 9: The core is placed in the mold.
Figure 10a: The finished casting.
Figure 10b: The core produced the magenta surfaces in the casting. To produce a model like the one in this figure, create a basic casting and a core, add the core to the casting to get the pattern, then subtract another core to get the finished casting. Suppress or unsuppress the "combines" to see the variants.
Conclusion And that's all there is to it! As you have seen, it is very easy to create models for patterns and molds that will automatically follow any changes that are made to the model of the part that they are to produce. You can also create complex parts that would be difficult or impossible with normal modeling techniques.