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Using Multi-body modeling

Multi-body modeling, like in-context modeling, is a powerful technique with strengths and weaknesses. If you model what will later turn out to be separate parts together in a single part, you can avoid in-context modeling altogether. You should not replace assemblies with multi-body modeling for a number of reasons, such as limitations of multi-body techniques for common assembly operations such as dynamic assembly motion and interference detection. Used judiciously, multi-body modeling can help you save time making models that hold up well to changes. Master Model techniques are discussed at length in Chapter 19.

Dealing with the Practical Details of In-Context Modeling

Figure 10.9 shows a simple box with the sketch of a simple top for the box. Notice in the FeatureManager that two parts are listed as the top and base. The .050-inch offset is creating a sketch in the top part that is driven by the edges of the base part. This simple assembly demonstrates the in-context process in the sections that follow.

Understanding the in-context process

You can perform in-context modeling using one of two basic schemes. You can build parts from the very beginning in the context of the assembly (using the Insert⇒Component⇒New Part menu option) or you can start them using bottom-up techniques, creating the parts in a separate part window, adding them to the assembly, and then adding additional in-context features later.

Starting out in-context

To start a new part in the context of an assembly, you will first assume that the assembly contains another part. Creating a new part in a blank assembly is not very interesting. This example uses the assembly shown in Figure 10.9. To create the new part, choose Insert⇒Component⇒New Part. This command is also available through a toolbar button (shown to the left) that you can place on the Assembly toolbar. At this point, SolidWorks prompts you to select a face or plane on which to locate the new part. When you select the face or plane to place, SolidWorks places the Front plane of the new part on it, opens a new sketch, and adds an InPlace mate to the assembly. In-context parts start as virtual parts, saved inside the assembly; you can choose to save them as external or internal parts the next time you save the assembly. Virtual part functionality is discussed later in this chapter.

FIGURE 10.9

The top of the box being built in-context

InPlace mate

The mate that SolidWorks automatically adds when a part is created in-context is called an InPlace mate. It works like the Fixed option, although it is actually a mate that is listed with the other mates and may be deleted but not edited.

The InPlace mate clamps the part down to any face or plane where it is applied. It is meant to prevent the in-context part from moving. You will learn later in this chapter why it is so important for in-context parts not to move.

Alternative technique

Instead of using the Insert⇒Component⇒New Part command, you can simply create a blank part in its own window and save it to the desired location. Then insert the blank part into the assembly and mate the origins coincident. You can then edit the part in-context, the same as if you had created it in-context from the beginning. The only difference between parts developed this way and parts created in-context is the InPlace mate. The InPlace mate cannot be edited and is not related to other geometry in the usual sense. Many users feel more secure with real mates to real geometry, which they can identify and change if necessary.

Valid relations

Sketches, vertices, edges, and faces from the other parts in the assembly can be referenced from the in-context part as if they were in the same part as the sketch. Most common relations are concentric for holes, and coincident for hole centers. Converted entities (On-Edge relations) make a line-on-edge relation between the parts, and Offset sketch relations are also often used.

Other types of valid in-context relations include in-context sketch planes and end conditions for