Hi,
I am new to Solidworks and I have gone through several of the Tutorial designs, including that for an assembly. To create an assembly, one needs to arrange two or more seperate part bodies. What then, is a multi body part?
Tom tom_cip snipped-for-privacy@hotmail.com
Before multibody parts there were more limits to the techniques you could use to create a part. Multibody makes it really easy to create a weldment quickly and then split it off into separate parts and even an assembly of those parts.
An assembly on the other hand is a collection of parts used to build well... an assembly of course, it gives you the ability to quickly check how parts will interact with eachother in the real world.
keep in mind that there are many other things that each are used for.
Corey
An assembly file is a grouping of components, consisting of subassemblies and parts. An assembly file cannot contain bodies outside of a component. A part model is a grouping of geometry describing an individual item. That individual item may not be geometrically continuous, resulting in a multi- body part. It may be easier to see the logical difference if you ignore the possibility of multibody parts.
Practically, part files have lousy tools for moving bodies and relating them to each other as bodies; they cannot simulate mechanisms. Also, part files have no facility for creating a list of bodies as components (except for weldments, which are a special case). That is, you can't make a bill of materials from a part file.
An example: A machine can be thought of as an assembly of parts. The individual parts that make up the machine would be modeled as part files, and the machine would be modeled in an assembly file containing all the part files and their relationships to each other. Weldments can be handled either way, and thinking about them right now will just cause confusion.
I just re-read, the original question, and I don't think I addressed it very well.
If something is in a part file it is not necessarily one lump of geometry, but it is a single logical entity.
Sometimes SW steps outside this paradigm for expediency. A multi-body part is a part whose features don't happen to be connected, geometrically speaking, and may represent a weldment, a single part, or just a collection of mathematical entities like lines, arcs, and planes.
A multi body part is a single part that has "non-contiguous" geometry, like what you would get if you drew two circles that didn't overlap and extruded them. If you made a multibody part in a machine shop, you would have two parts. All of the geometry is in a single part file. In an assembly, there are many files.
Multibody parts are usually a stepping stone to something else. Don't get in the habit of modeling using multibody parts, it should be used sparingly and for specific reasons. You would not be happy trying to model more than a few parts in a multibody anyway.
There are a lot of things you can't do in a multibody part that you may want to do with an assembly:
- bill of materials on a drawing
- item number balloons
- exploded views
- mixing sheet metal parts with other parts
- dynamic motion
- easily positioning or moving parts
- ability to suppress parts
- organizing data so that it is more easily used by downstream apps like CAM
- reuse a single part later on
- color, visibility and naming of bodies is extremely clumsy for bodies in parts when compared to parts in an assembly
On the other hand, there are some specific times when multibody is useful
- most surfacing work requires multiple (surface) bodies
- plastic parts where you design an overall shape which is later split into several individual parts
- as a work around when making a feature in another way doesn't work
- ocaisionally for "inseperable subassemblies" like weldments, captive hardware
matt
"Teece" wrote in news: snipped-for-privacy@giganews.com:
You forgot FEA, CG analysis, mass properties, interfernce detection, the list goes on,,,
We have one guy who modeled a whole project as a multibody. Thought he'd found a real shortcut. Couldn't understand why his model was so sluggish, and his machine kept crashing. Very stubborn though, so I let him plod along.
In order to actually "do" anything with the data, we had to completely re-model it. The features were so intertwined and convoluted even he couldn't figure it out. This guy is a really talented designer, in the artistic sense, but completely right brained. If I were to give him a simple model of a 1/4" dia. cylinder 1" long, and asked him to make it 3/4" long, he'd cut 1/4" off of one end, rather than change the number driving the lenght
I don't know how his boss handled having to tell the client that we had to do it again the "right" way. Most likely we ended up eating the hours.
Some lessons are best learned the hard way,,
Use the tool the way it was designed to be used. Just because SW will let you do something, doesn't mean that it's OK.
Regards
Mark
Tom,
Multi bodies allows you more flexibility in the "way" you model. It should not be confused with, or used as a substitute, for assemblies. The end result should still be a single body part. All solid modelling systems work best when the design reflects the real world. That is, after all, the place where it's going to be manufactured
The one exeption to this are purchased parts. For instance, I'm working on a design that employs a Kerk leadscrew. The lead nut consists of a main body, a collet, and a spring. I modelled these as a single part.
Regards
Mark
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