Convert Assembly to Single Solid

Is there a way to convert an assembly to a single solid which then
allows the application of Cosmos Express.

I have been able to use Combine bodies IF all the parts are in
physical contact with assemblies and weldments. However when there
are any gaps between parts then this approach does not work.

I have tried Joining Parts, Combining Solid Bodies, Converting
Assembly to a part, Exporting to STEP and Parasolid then importing
back.

Did not SolidWorks in an earlier version like 2001PLUS convert an
assembly to a dumb solid (i.e. one piece)?

Kman

 

If there are gaps between the components how would the FEA give any
kind of realistic answer?

TOP

 

I would be satisfied if there is a method by which these small gaps
between parts are filled and then apply Cosmos Express. This would at
least get me in the ball park (poor man's version of Cosmos)

Would it be possible to convert an assembly to a single part (using
the surfaces only option) and then make this into a solid? Thinking
out loud.

I thought Cosmos (full version) does analyize assemblies. Even those
with gaps?

Kman

 

Make ur assembly

then while save it or saves as choose part from the file type, u can
choose either of three option i.e. 1 to have surface only, 2 all parts
and 3 outer parts and then your assembly (the saved part) will be a
single part.

Then u can check for small gaps and fill that gap with solid or
surface modeling.


Hope this works for you


Deepak

 

Just how many components in this assembly? Why not fill the gaps in
the assembly?

SW sometimes gets it write and sometimes not when exporting as a
part.

Here is a pretty bizarre thought.

1. In your assembly, insert part and extrude a block around the entire
assembly.
2. Use the assembly components to cut a cavity into the block
3. Use delete and patch face to remove the slivers
4. Take the resulting cavity and turn it into a solid by repeating
step 1 above
alt 4. In the part with the cavity make a second block identical to
the first as a second body. Then do a combine subtract operation on
the solids.

TOP

 

The assembly has 86 parts of which 28 have clearances between them.
That is alot of clean up work.
Kman

 

Gotta say something about common sense engineering here.

How can you expect to get Cosmos to give you an answer when the
assembly you have does not describe reality? You can't make a
physical assembly with gaps and have any structural integrity until
part touch and fasteners or joints take loads.

Reality must prevail. Some rethinking of the overall structure is
needed.

Bo

 

I was thinking that once the assembly was converted to a joined part,
then export as a parasolid it would be solved as a single solid part
(apparently not). I have run Cosmos Express on the parasolid and
received the following message after running the analysis: "Failed
Faces (0), Failed Surfaces (0), surface mesh successful, volume mesh
failed, try the following -reduce element size (<12.551mm)

Whatever that message means. And Cosmos Express does not graphically
display what the probelm is with the part.

Anyone know how to get Join to join all the parts in an assembly (not
just some of the parts)?

How does the full version of Cosmos handle assemblies with motion
between mating parts (i.e. clearances)? Does it close the gaps before
performing the analysis? And if it does, then it is not a realistic
model.

Kman

 

How are the different parts attached to eachother.

If they are welded, you should after saving the assembly as a 3d-part
(not surfaces, or use the guide which TOP described), Extrude the
weldments.

Your best opportunity is to make the model as close to the final
product.

Also Cosmos (both express and the full version) have some difficulties
if you use thin-plate elements on big parts, the minimum thinkness
compared to the total size.


Would like some more info on the what it is you are making, and what
you need the Cosmos Express calculation for (deflection? stress
analyses?).

You should keep in mind that there are a lot of things that can go
wrong using Cosmos Express. Do you have any experience using FEM ?

 

About how the full version of Cosmos works, it builds elements just
like the express version, you just have a whole lot of options on how
these elements are build, where the Express version comes with a
standard set of options.

In both cases the program wont make anything up, it is analysing what
you have made. Which means you have to put in bolts or weldments if
thats the way its assemblied, if you want the right result.

If you want to "cheat" and do less work, simplify the area you want to
analyse. You should have a good idea on where the problems would accur
already (if you dont, then the Express version is a "no go" anyways).

So issolate the place where you think the worst stresses / deflection
are and constrain it in a proper way getting it as close to reality as
possible. This would give you a better result than running the express
version on the whole model, cause you are controlling more of the
unknows.

Even with the full version, its a lot of work getting the elements
build in a proper way and making sure they are connected in the right
way also.

 

The assembly is an equalizing roll clamp and tensioning mechanism.
Lift consists of RH-LH core clamp, each of the core clamp sub-
assemblies slide independently on a common pair of guide shafts, the
roll core cones RH-LH rotate independently.

Interested in both deflection and stress analysis. Areas of interest
are the deflection/twist/stress of the guide rods supporting the RH-LH
roll clamp sub-assemblies. Twisting of thte RH-LH clamp sub-assembly
side plates (load is cantileverd off the side plates).

FEM? none

 

Purchasing full version is not an option.

What about clearances between bearings, slides etc... (the way it is
assembled)
How does Cosmos handle component clearances? If I understand you
correctly, it does not. That would mean in order to do an analysis
one would have to make a new assembly just for this purpose. We are a
small company and do not have the resources or time to develop mock
assemblies for the purpose of analysis.

I recall a time when we hired an engineer with FEA background via one
of our VARS to calculate the deflection of a machine base section for
an automotive transfer and assembly line. The deflection results were
off by 100%. We paid alot of money for that one simulation and the
results were useless. The engineer was provided the actual model and
loading conditions.

Simplification: One method being, calculate a beam of equivalent
inertia for each RH-LH sub-assembly, attach the beam to the guide rods
and run a simulation. It is unfortunate SolidWorks/Cosmos can't close
the gaps to make a solid of the assembly. This result would be much
more accurate and take considerable less time.

Simplifying and using beam calculations is reasonable for some of the
components. Determining the multitude of deflections and stress on
the guide shafts is not so straight forward. The load on the roll
cones RH-LH is both cantilevered and eccentric. Ideally, the loads
are symmetrical on both side.

I would think the results will be less accurate. When you say
"controlling more of the unknowns", to me, means making assumptions to
simplifying the model. I really would have preferred Cosmos Express
(for parts) to simulate an assembly. If SolidWorks JOIN command
worked as marketed then this may have been possible. Or maybe, the
complexity is still too much for Cosmos to simulate as previously
mentioned.

That is disappointing news. The Cosmos (full version) demonstration
I witnessed a couple years back didn't mention any shortcommings,
grin.

 

I don't use Cosmos, but I'm sure that Cosmos works the same as Ansys. You
have to put in contact pairs at every clearance between components that you
expect to touch. The system applies the loads and restraints that you want,
and then works out when and how the parts contact one another. This makes
the analysis non-linear and usually makes it take much longer to solve, if
it solves at all.

If your loads aren't too high, you might be able to get away with building a
version of your assembly with the parts rotated and moved into the
approximate positions that they will take when you apply your loads. You can
then bond the parts together and try an analysis. If you are lucky, make
good assumptions, and things behave well, the results won't be too far off.
But if any of your assumptions are incorrect or your loads are high enough
to cause the parts in contact to deflect appreciably, you will get
essentially meaningless results.

You will probably be lucky to get that close.


Jerry Steiger
Tripod Data Systems
"take the garbage out, dear"

 

I hear ya. Like many others we download commercial parts from OEM's
and distributors whenever possible. And we get what they give us so
to speak. Configurations seems to be the best of both realities for
now. Thanks everyone for your input!

Kman

 

Bonding is one of the issues. Join, doesn't work. Creating a part
from assembly doesn't work. Manually modifying an assembly as you
also mention seems to be the only way this can be accomplished.

 

In my expirience when it comes to assemblies, remaking it as a part is
much faster than adjusting the assembly (making cuts and weldments).
I always make another model to make the FE analysis on.

It is a lot of work with assemblies with more than a few parts. But
the program aint better than the data you put into it, and there is no
such things as Yoda-fields

So you would have to make the weldments / bolt-connections or however
it is kept together.


If you save your assembly as a jpeg and send it to me, I might be able
to have a look and give some pointers on how to rebuild as a part.

Also I need to know exactly what result you are after. Max
Deflection / von Mises stresses in a particular place. If the material
stays with the plastic deformation area, if you only allow a certain
deflection basicly what you need the result for.

 

Ronni,

Unfortunately, I am not at liberty to share this information. I do
appreciate your offer to help with this problem.

Regards,
Kman