Merge boundaries of two parts

Hello,
I have two solids that are defined by trimmed NURBS surfaces. One
should "sit on top of" the other, ideally. But, as it's happened the
surfaces overlap ever so slightly (the forms are built from anatomical
data, and some overlap occurred at some point in the conversion). I
can subtract one part from the other, or intersect & merge the parts,
but either of those options is undesirable: it creates a lot of
surface boundaries, which interfere later with finite element meshing.
Does anybody know a way to merge the bodies so that the top surface of
one will be coincident with the bottom surface of the other? (without
creating lots of extra boundaries)

Thanks,
Adam

 

There is no clean easy way to merge them with solid operations. Look up
the "curvy stuff" presentations by Ed Eaton at the DiMonte Group web
site:

http://www.dimontegroup.com/Tutorials/SolidWorks_Tutorials.htm

One of those, I can't remember which, has an explanation of what's going
wrong. The example is almost exactly this situation, just not an
anatomical application. I think it's one of the early presentations,
maybe even 101. Your time won't be wasted even if it's in the last
presentation though. Great stuff.

What you need to do is edit the two solid bodies so that you have two
open surface bodies meeting each other where you want to join them. Then
use a surface knit to combine them into a solid.

 

Hi,
Thanks for this response. I downloaded those tutorials, and they
are very good quality. I am not sure if they address this particular
question, though. The issue is that the object intersect in several
different places. It's not the case that there's uniform overlap. So,
when I intersect (Combine "common") the objects, I get a large number
of slivers. (I realize that this wasn't stated in my previous email.)
Then of course there are also small gaps between the objects where
there aren't slivers. Is there a way to merge the surfaces for a
problem like this?

Thanks,
Adam

 

What is not clear to me is whether or not the mating scanned/converted
surfaces have curvature (but I'll assume this),... or maybe they are
closer to a planar, spherical, cylinderical, faceted or other
(combination of) topology?
The slivers tells me it maybe a faceted topology or a set of surface
patches with different curvatures or there maybe overlay issues with
the tessellation of the analysis model?
What I would suggest is to copy (offset copy 0.0 or more if needed)
one of the better surfaces of the two and use that copy surface to
replace (replace face) the other mating surface.
So, to help get past the slivers, create a analytical surface to mate
the two halfs or create a surface interface which best mimics the
topology and replace face both sides?
You should now have a equally mated or offset interface (increase if
tessellation for the analysis is causing the overlap?) for your two
parts.

...

 

I have to agree with Paul. What you're describing could be a range of
different issues. Can you post somewhere before-and-after images of the
problem areas? Paul and other (more so than me) can better tell you what
needs to be done if they can see precisely what the issue is.

 

Thanks Dale and zxys.

Here are my two objects:
http://www.u.arizona.edu/~tabaker/raw.jpg

Here is what happens when the bottom object is subtracted from the
top:
http://www.u.arizona.edu/~tabaker/top-bottom.jpg
(I just noticed that Merge "common" fails.)

The issue is all the extra edges/boundaries it creates.

I attempted the replace face approach. I'm getting various error
messages. It's difficult to see, but the edges in the NURBS surfaces
are not really in convenient places. Also, one surface is not really
"above" another, since the parts are curved. Would you expect the
replace face technique to work in spite of that?

Thanks,
Adam

 

Well,... you got a problem here... but, I think you can still do it if
it's alright to have some extra surface hanging over the edges?
What you could do is create a few cross sections of the two bodies and
try to do a average surface of your own, trim away the area which is
common to both and thicken (mid) your common surface so that the other
bodies are added to the merge?

Another way to creating a surface patch using the fill feature,..
create a 3dsketch which is as close the to common boundary as possible
and then use a few cross sections for your control curves used for
surface fill. Then thicken to merge both.

...

 

Are you sure that the overlaps are a conversion problem? Maybe they are real
and you need to space your two parts slightly to account for the way in
which the high points on the two parts meet.

Jerry Steiger