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Creating MMC for bolting modelisation. Any Tips for effective geometry simplification to help MMC?

Creator
Creator

Hi everybody,

 

I work with models containing polygon bodies, many of them bolts in threaded holes. (NX 9.0.1)

I try to use Mesh Mating Conditions to "glue - coincident" the internal thread to external thread but with "big" models (I cannot put a number on big, sorry) the MMC method seems not very robust: sometimes it can create the MMC, sometimes not.

 

Also, depending on modifications done to the idealised model, MMC done before will not be anymore and other not possible before will happen.Man Sad

 

  • Does anyone have tips for preparing the geometry for this operation?
    Are there any rules to respect during the CAD creation, so that touching cylindrical surfaces will always create clean MMC?
  • I tried to split the contacting surfaces perpendicular to the axis of the boltind but it sometimes doesn't help.
  • Should I split the cylinders of the male and female part on a line parallel to the axis to consistently obtain a MMC?
  • Could Siemens make the MMC more robust so that consistency happens in this process?

yours sincerly,

Cyril
4 REPLIES

Re: Creating MMC for bolting modelisation. Any Tips for effective geometry simplification to help MM

Siemens Legend Siemens Legend
Siemens Legend
Hi cyril,
when using MMC conditions, the polygon faces are splittet to have a common polygon face where the mating condition is applied as a constraint for meshing. Maybe there are small geometries that lead to the problems you are facing.

Did you try to use surface glueing in the Simulation Objects in the SIM file? This will define a mesh independent glue contact to fix the bolts.

Regards
Boris

Re: Creating MMC for bolting modelisation. Any Tips for effective geometry simplification to help MM

Siemens Phenom Siemens Phenom
Siemens Phenom

Cyril,

 

Is it true that your model includes the bolt threads? As Boris indicates, the problem could be related to tiny faces resulting from the imprint of the bolt faces onto the tapped hole faces. Threaded faces being small, I can see why you're model poses a challenge. 

 

If you aren't doing a detailed contact analysis, and all you want is a continuous solid mesh through the tapped hole face into the bolt, then consider removing the threads in the PRT geometry before creating mesh mating conditions. This will simplify the geometry to cylindrical faces. You could also edit the radii to match in the PRT too. This is all possible with synchronous modeling techniques.

 

If problems persist, or if I'm interpretting this incorrectly, you can send me example data and we can proceed offline.

 

Regards,

Mark

 

Mark Lamping

Simulation Product Management

Product Engineering Software

 

Siemens Industry Sector

Siemens Product Lifecycle Management Software Inc.

mark.lamping@siemens.com

Re: Creating MMC for bolting modelisation. Any Tips for effective geometry simplification to help MM

Creator
Creator

Hi Boris, Hi Mark,

 

thank you for your input.

 

I indeed am looking for a continuous mesh for detailed analysis.

Since I will have to create a temperature map, the gluing option is not what I want because I would have to do the gluing conditions twice (because the simulation object surface to surface gluing created in structural solution cannot be used as surface to surface gluing in the thermal solution).

 

The geometry of my bolts (heads and threads) have been already optimized (same diameter for internal and external threads); the MMC under the head are usually not the issue. The most problematic (because not repeatable) is the MMC at the threads (cylindrical face to cylindrical face).

 

As I stated before, sometimes the threads MMC are created in the FEM, then I go back to the PRT to improve some other region, and the next time I go back to the FEM and update it, some threads MMC are lost, some can be done though they could'nt before, and some cannot be done.

 

I checked the NX documentation (can't remember where), the statement about spliting the cylindrical face along on a line parallel to the axis enables to consistently obtain a MMC but it is a long process.

 

So Mark, I consider the problem persists, could you help please?

 

I will send you an email ASAP.

 

Thank you,

Cyril

Re: Creating MMC for bolting modelisation. Any Tips for effective geometry simplification to help MM

Siemens Phenom Siemens Phenom
Siemens Phenom

I'm updating this thread since we've resolved this issue offline. The problem was that after splitting bodies in the PRT, split body MMCs weren't always being created automatically in the FEM. The root cause of the problem was due to the process Cyril used to create/edit the FEM. NX supports 3 options for adding bodies to the FEM:

 

1. All

2. All visible

3. Select

 

The ability to automatically create MMCs from split bodies requires that the bodies are added to the FEM at the same time. Cyril's workflow was based upon the Select option. The FEM was such that one body was already in it and its new version updated that body after a split body operation. However, the second body from the split wasn't added. It had to be selected in a separate Edit FEM operation. That means both bodies from the split were added to the FEM at different times. Therefore the split body MMC wasn't automatically created.

 

This would not have been a problem had the All or All Visible options been used. Development now has a PR for this and will investigate adding logic to the FEM update process with respect to the Select option and split body operations.

 

Regards,

Mark

 

Mark Lamping

Simulation Product Management

Product Engineering Software

 

Siemens Industry Sector

Siemens Product Lifecycle Management Software Inc.

mark.lamping@siemens.com