How Bodies Can Help

Bob M. asked a great question, to paraphrase: What are some practical applications of bodies?

This is an incomplete list, because it’s really just limited by your imagination and your current needs.

Bridge

If you were modeling an old telephone, you might make the earpiece and mouthpiece first, then make the handle between them. There are other ways to do this, but if order truly doesn’t matter, then you shouldn’t have to construct things in such an order that it always has a single body.

If you want to create a part that can be flexible, you can build two bodies, and loft between them.

Indentations on the sides that carry into the middle were done using tool bodies, and an indent feature.

Tools

Solid bodies can be used as tools. You can add or subtract them to make an enclosure around a circuit board, or find the range of motion of an operator. Insert one part into another as a reference to avoid interpart assembly references. If you have to use a complex shape several times, make it once and copy/pattern the body rather than remaking the same thing. You can import an entire engine as a multibody to build a frame to fit it.

In the red part shown here, tool bodies were used to create the indentations on the sides. This could have been done in another way, but it would have been much more difficult.

This was to be molded from plastic. Making the water ways and valve bodies was done as separate bodies.

Piecewise geometry

Some types of geometry, like shells (thin walls) can be tough to combine without using multibodies.This molded manifold was impossible to shell, so it had to be modeled using other methods. I created the waterways as positive geometry, and made thin walled manifold passage ways from that.

Material breaks

Multi-shot molded parts, dipped, or overmolded, inseparable assemblies, purchased assemblies where you have to show all the geometry, but you don’t need BOM, or motion.

Complex shape across parts (master model)

If you need to create a complex shape that is continued between multiple parts, multibody modeling is probably the best way to do it. You build the shape as a single part, then break it up into multiple bodies, and publish it to multiple parts. There are other ways to do it, but this is one of them.

Patterning

Sometimes its faster to pattern a large chunk of a model than patterning features.

Lazy Assembly modeling

I consider it bad practice to model an assembly as a multibody part. That’s a left over prejudice that comes from history-based modeling, and will probably diminish as I do more with ST.

Endless workarounds

I’ve used multi-bodies for endless workarounds. When you can’t get a shell or a fillet or some other shape, split the part into sections, make the features, then put it back together. On very complex parts I’ve built sections of parts separately and then joined them together. This was really a history-based performance workaround to avoid having too many features in a single part.

surfacing is all multibody until the end, when it all comes back together.

Surfacing

Face it. Surfacing IS multi-body modeling. In solids, everything tries to combine into a single body, but in surfaces, you are working by default in a multi-body world. After developing surface modeling habits, you never look at CAD modeling the same way again.

In history-based modeling, you have to be more careful, and there are a lot of reasons for NOT doing multi-body modeling. In direct edit, in the end, its more about the organization of your model.

Updated: August 1, 2012 — 10:22 am

1 Comment

  1. Thanks Matt,

    In all my years of using CAD I’ve tended to stay away from making models this way. Probably a combination of the type of work I do, as well as the fact that I started with 3D CAD  back in the early days of Wire Frame modeling where stuff like this was only imagined.

    The examples you presented forced me to stop and really think about them, since my old school thinking went a completely another way. But like you I think Solid Edges/ST5′s MB capabilities seems like an great opportunity to learn some new tricks.

     

    Again thanks for all the examples.

     

    Bob

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