SolidWorks 2011 Assemblies Bible - Matt Lombard [10]
Modeling parts in place
In-context design is discussed in more detail in Chapter 10, but here you will get some idea of what to look forward to, and why this book isn't just about in-context design by itself. Modeling parts in the context of an assembly that contains other parts enables you to make relationships between the parts. Those relationships are managed by the assembly. The parts have to be arranged spatially with respect to one another, and the references to the files must also be managed.
When you see a sales demonstration, the technique of using edges of other parts from the assembly to make a new part looks very compelling, especially when you make a change to the other part and the new part updates as well. It's hard to argue with that kind of functionality. But the price you pay for that sort of associativity is that you have to manage the relationship between three files: the parent part, the child part, and the assembly. And further, within the assembly, the relationships are made between specific instances of the parts, so if you have multiple instances of each, you have to do something to remember which pair of parts is the driving pair.
Also, model history with parts does not work the same with assemblies. The relationship between the parts does not have any memory, so if you started the in-context relationships before the parent part was complete, and then put fillets over the edges that you had referenced, your in-context references would fail.
Take another look at the robot arm and the model car examples. Using in-context methods, you could certainly design the robot arm, but again you might run into some problems with getting it to move correctly while maintaining the references. However, with the model car, getting the parts in the right place wouldn't be any problem because you would be modeling the parts in-place. On the other hand, you might be able to get the shape to flow smoothly, but it is still doubtful. In-context modeling can copy 3D surfaces between parts, but for an improved workflow for this type of work, you will have to read further into this chapter.
An example of a part where modeling in-context works well is a table with legs, as well as a fixture that sits on the table, as shown in Figure 1.3. The in-context work lines the holes up between the parts. There is no relative movement between the parts, and the individual parts are not likely to be used in other assemblies.
FIGURE 1.3
Using the in-context method to its best advantage
The ideal situation to use in-context techniques is when two parts are assembled face-on-face, the shape of the contact faces are the same or offset, and there is a set of holes used for fasteners. Complex shapes are generally not a good candidate for in-context methods. The main point is that there is no relative motion between the two parts.
Modeling parts as multi-bodies
Another method you can use to model parts is to start the models in a multi-body part. It is not recommended to use this method for creating finished parts as multi-bodies, but getting some of the major parts on an assembly started as a single part and then breaking them out into individual parts for details can be a very effective method.
Say you are modeling a riding lawn mower, and you need to create the plastic cowling on the front of the mower. The cowling is made up of multiple pieces because some of them are different colors, and some are transparent. The complex shapes of the cowling encompass multiple parts. If you were to model one part, and then try to model another part independently that shared some of the same shape, it would be very difficult or impossible to get the shapes to match acceptably.
One answer to this problem is to create