SolidWorks 2011 Assemblies Bible - Matt Lombard [11]
Multi-body modeling has advantages over in-context modeling in that it reduces external references (although saving bodies out as parts creates an external reference), but it also has some drawbacks. If you were to take all the features of individual parts and stack them into a single feature tree in a single part, you would probably be unhappy with the result. By making all of the features for all parts within a single part file, you make troubleshooting much more difficult, and rebuild times are dramatically increased. Add to this the inability to reuse parts, do individual revision management, or perform simple assembly operations such as dynamic motion, exploded views, or BOMs, and following the multi-body method through to finished parts becomes very unattractive.
The best option for using multi-bodies to create parts for an assembly is to start the parts in multi-body mode, and then as soon as the inter-body references are no longer needed, transition the bodies to separate parts.
Multi-body modeling may not do so well when parts are repeated, or where purchased components represent a large percentage of the total parts. While you do have mate-like functionality for placing bodies within a multi-body part, it is probably not the best use of this method. Figure 1.4 shows a product that is designed as a multi-body part but involves many difficulties because of reused parts and hardware.
FIGURE 1.4
Reusing parts is not a strength of multi-body methods.
Revisiting the test for each method, you would find that the robot arm is well suited to being designed as a multi-body part and then reassembled with mates in an assembly. In fact, the multi-body method is probably the best method for this type of work, maintaining references between parts, and then assembling the parts into an assembly mechanism with motion.
The model car, with its shape that flows between parts, would still be awkward, although it could be done as individual parts. You will now look at the last method to see if this helps with the car model.
Inserting a master model
You will learn about the master model technique in Chapter 19. In a nutshell, a master model is a single part where you place sketches, reference geometry, surfaces, and maybe some solids, and then insert that part into other parts to use a reference to build each individual part. Using this technique makes in-context work unnecessary, and eliminates some of the dangers of creating too many features in a multi-body part.
You assemble parts in this manner the same as with the multi-body part method. Take each part, and drop it into the FeatureManager of the assembly. This aligns the part origin with the assembly origin, and because each part was built from the same master model, all parts share the same origin.
Take another look at the robot arm and model car examples. The robot arm may be a little awkward using this method, but it works. The multi-body method is probably best for this type of design.
On the other hand, the master model method brings real power to projects such as the model car. You can design the entire outside of the car as if it were a single part, and then break it up into individual parts. In Figure 1.5, notice how some parts that will be manufactured as a single part can be easily pulled off of the master model. Sketches within the master model can help define breaks between parts and even if there is relative motion — for example, with the doors.
FIGURE 1.5
Pulling parts off of the master model
Excluding