Dear community,
I am trying to mesh a part in Moldflow. I plan to have the part, two mold inserts, and two 3D cooling structures in the model. In order to get good results, I have to apply different mesh densities for all aforementioned elements and I would like to use the "Precise Match" function for meshing.
However, the latter is where the problem arises. Applying the mesh densities works fine. Meshing the part with the default setting of "Ignore contact" also works fine and the mesh looks like intended by the different mesh densities. If I choose "Precise Match" instead of "Ignore contact" for the part mesh, the mesh is completed, but the mesh densities that I have set are not applied. Moreover, the analysis log gives me some information that there were two meshing attempts and something went wrong with the meshing. Hence, an alternative method had to be used. Please find the complete analysis log below. I have no clue why there the software needs two attempts (for "Ignore Contact" only one) and what happens using this alternative meshing method.
Has anybody experience the same? Any suggestions or ideas how to solve the problem?
I appreciate all help, since I have right now no way to proceed with that problem!
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Copyright Autodesk, Inc. All rights reserved.
(C)2009 2010 2011 2012 2013 2014
Portions of this software are covered by U.S. Patent Numbers 5,287,408 and 6,096,088.
Version: ami2015-promethium_compile_windows-x64 (Build 14104-714)
64-bit build
Mesh running on host: XXX
Operating System: Windows 7 Service Pack 1
Processor type: GenuineIntel Intel64 Family 6 Model 42 Stepping 7 ~3392 MHz
Number of Processors: 8
Total Physical Memory: 16340 MBytes
Mesh with the following settings:
Mesh Type: 3D
3D Mesher: Advancing Front
Global edge length: 0.5000 mm
Merge tolerance: 0.0100 mm
Enable chord angle control: Yes
Chord angle: 10.0 deg
Percentage of minimum curvature size vs global size: 20.0000
Growth rate: 0.0000
Mesh on assembly contact faces: Precise Match
Sliver Removal: No
Minimum number of elements through the thickness: 10
Maximum edge length in thickness direction: 0.5000 mm
Use surface mesh optimization: Yes
Use surface mesh matching: Yes
Automatic tetra aspect ratio control: Yes
Even distribution without biasing: No
Bias ratio: 1.2000
Mesh smoothing: Smooth all nodes
Extra refinement near gates: Yes
Relative edge length around gates: 20.0 %
This process will not mesh mold blocks or 3D cooling channels.
If you wish to mesh mold blocks or 3D channels, please include Cool(FEM) in analysis
sequence and then click Create 3D Mold Mesh or Create 3D Channel Mesh.
Generating CAD mesh
First attempt:
Second attempt:
Trying to recover from previous error(s).
Retrying the mesh process using a fallback tessellation method.
Mesh density defined on faces will not be used by this approach.
Start region: 2
Percent 5 done ....
Percent 10 done ....
Percent 20 done ....
Percent 25 done ....
Percent 30 done ....
Percent 35 done ....
Percent 40 done ....
Percent 45 done ....
Percent 50 done ....
Removing disconnected nodes
Removing disconnected nodes
Meshing Stopped
A surface mesh has been created. Please check the mesh by diagnostic tools and
make sure it has no free edges, no non-manifolding edges and no intersections.
A 3D mesh can be generated by launching meshing again.
Meshing complete
Removing disconnected nodes
Removing disconnected nodes
Execution time
Mesh commenced at Mon Jul 21 10:19:13 2014
Mesh completed at Mon Jul 21 10:19:31 2014
CPU time used 11.64 s
Total elapsed time: 17.54 s
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Background information:
OS: Win 7
Moldflow: Synergy/Insight 2015
Analysis type: Cool(FEM)+Fill+Pack+Warp
Elements: not available, since meshing does not work properly
Hardware: i7-2600 3.4 GHz, 16 GB RAM, AMD Radeon HD6450, 500 GB 7200rpm HDD
Hi Maxmar,
When you select "Precise Match" that means you advice software to use global edge length same for all parts.
Please use Cool(FEM) for 3D. do not use Cool(BEM).
You can manually remesh the areas where you need to have different mesh densities to compensate for no. of elements.
Which import format you are using? have you tried with CADoctor first for any problem areas to heal?
Some more info you may need:
Mesh on assembly contact faces options
Regards,
Mayur
When you see "Second attempt", it means the CAD model could not be meshed with the current settings (precise match).
When 'precise match' is selected, the assembly model will be converted into a non-manifolding model, while the contact interface is shared by 2 bodies.
When the model has no problems on the interface, this will give you matched triangles on both bodies. Local mesh density will be used.
However, when the 2 bodies are not matched properly on the interface, this process will fail, and meshing cannot go ahead.
"Second attempt" means the CAD model was actually meshed as an STL model. In this case, only a global edge length will be used, while local mesh densities defined on CAD entities will be ignored.
To avoid this problem, you can go to CAD system and fix the original model with focus on contact interfaces.
Shoudong Xu
Moldflow Meshing Team
Hi Mayur,
"When you select "Precise Match" that means you advice software to use global edge length same for all parts.
Please use Cool(FEM) for 3D. do not use Cool(BEM)."
I use Cool(FEM) and have never touched Cool(BEM). I am not sure about the differences and advantages, so I go for the stuff I know.
Anyways, you are saying that "Precise Match" means that the software uses the same global edge length for all parts. That would mean setting different mesh densities (for part, mold, channels or within one of these domains) and the mesh density tool become useless?!
My expectation was that I mesh the part first with the desired mesh densities assigned to the faces of the imported CAD model. Then, I mesh the cooling channels likewise. Finally, I mesh the mold where I do not have to assign mesh densities, because the software will automatically mesh the mold in a way that the mesh will match the one of the part or channels at the contact areas.
"You can manually remesh the areas where you need to have different mesh densities to compensate for no. of elements.
Which import format you are using? have you tried with CADoctor first for any problem areas to heal?"
I believe if I remeshed the areas where I need higher mesh density, I would destroy the mesh match at the contact interfaces again. Or how do you mean that exactly?
Anyhow, I prefer not to remesh, because I made bad experiences with that. Sometimes the remeshing does not give me any effect or I loose geometrical accuracy and edges of my original shape. I think it is also problematic, because starting with a larger global edge length will inevitably lead to a loss in geometrical accuracy, because the mesh will not catch small and round features of the original shape. By starting with a very fine mesh and then reduce the size is usually not an option for me, since the number of elements will shoot through the roof.
I use different file types, usually direct import of SolidWorks (.sldprt, .sldasm), Inventor (.ipt), or Step (.stp) files. In this particular case, I imported a Solidworks assembly (.sldasm) which contains the part, two mold inserts, and two cooling structures. The two inserts are in .sldprt format, derived from .stp. The part and cooling structure I prepared myself by applying boolean operations on the two inserts.
Because of that reason, I assumed a perfect match between the CAD models of the part, mold, and channels, and I did not use CADoctor to check. I cannot see any problems in Solidworks. Where do I get the CADoctor from? If I google it, I find several different versions and providers.
"Some more info you may need:
Mesh on assembly contact faces options
I am aware of the three different types for meshing on contact interfaces. I think what you write ressembles the help of Autodesk Moldflow. Still, thanks the information. It is good to have it here to make more people aware of it.
Best regards,
maxmar
Hi xusho,
I find your post very helpful to get some insight on what happens "behind the curtains" while meshing. According to your explanation, it seems that the problem stems from the CAD model I am having. However, I cannot see any problems in the CAD model in Solidworks (compare to my previous post). Do you have any suggestions how to check the match of the interfaces within SolidWorks or an alternative software? Do you think CADoctor will do the job and where do I get it from?
Best regards,
maxmar
Hi Maxmar,
Please refer attached image, when you have multi-body in contact, at that time you should have a same edge length, otherwise how could you expect to match the nodes on both the bodies, this is a general criteria while meshing in contact surfaces, so you will need 'Precise Match' with global edge length same, you cann't alter Edge length for all surfaces, thats why i ask you to remesh the required areas (If your geomtery is simple, no major features, then you may not need fine mesh at this region, it won't be useful, as for e.g. suppose you got some plaine surface at this region,assuming you will not get weld lines, ait traps, no need to fine mesh here.)
CADoctor is a Autodesk tool, to heal geomtery, which creates a *.UDM file to import into synergy.
Regards,
Mayur
Ok ,
meshing of assemblies is and still keeps a gamble.
I have tried to mesh very often assemblies some with good results and some with no chance.
1. the error message: Fallig back to tesselation, always comes when there is a problem in the cad mesh and you can not mesh it with precise match. But if you have inserts and you want to simulate core shift thenodes should be matched at contact faces. To use precise match you need to import the assembly
2. How to solve the errors in the cad
Well fist problem is to find the errors. One solution is to open the assembly in fusion and to validate the faces. It shows you where the errors are. So you have perhaps a possibility to correct it. Also good solution is to use caddoctor. Sometimes I use both simulatniously. Try not to do import export the cad to often. You get more and more errors. And I also had bad experience with importing assemblies of solidworks.
3. one possibiliy is also to mesh in a external mesher. We did some goog try with hypermesh. Worked very finde. I imported the bdf files from hypermesh in moldflow.
4. I hope you meshed the cooling channels with channel mesh and the mold with mold mesh. But to use precise match with part and mold you have to use in dual domain the standard mesher. This also works and then use the mold mesher for the mold.
5. If precise mesh wil absolutely not work you can give the contact face the same mesh density. But if you have a complex part this is much work.
Ther are always several ways in moldflow.
Greetings philipp
If the parts are not too complicated I use NX Advanced FEM for meshing.
It handles contact good, gives better results regarding trinagle aspect ration and "deletes" small features by choosing the right mehs length.
What is can´t do is mehs matching, so for DD you´re kind of busted if Moldflow doesn´t work.
The 2nd attempt of meshing is often so bad that i stopp it immidiatley.
Better mesh your part outside Moldflow to an STL, this gives you (in most cases) more control over the process.
Everything else: Good luck.
Regards
Harald
The process to convert assemblies into non-manifloding models is very sensitive to gaps on contact interfaces. That is the reason we do not use it as default option.
When this happens, I would suggest: do not use precise match.
Moldflow solvers have been improved in recent years, and "precise match" does not make big differences as before.
With "Ignore contact", you can define same edge length on both faces. Triangles on interfaces do NOT have to be matched.
Shoudong Xu
Dear all,
thank you very much for your lively contribution and feedback! I would like to wrap up and point out some things for all readers and the Autodesk people and come up with some new questions to discuss.
SolidWork assemblies might cause trouble when using "Precise Match" for meshing
It seems to me that the problem was caused by this particular assembly of SolidWorks. If you are having the same problem, try to diagnose thecontact surfaces with:
I could not investigate the issues in that way, since we do not have that in house and I do not have access to our Autodesk subscription center. Consequently, I do have neither software to my disposal right now. Nonetheless, I tried the whole meshing process with another assembly that I made in SolidWorks. The meshing worked without any problems and the assembly could be meshed in the first attempt, accepting the assigned mesh density.
"Precise Mesh" can be used if the faces to be matched have the same mesh density
The same local edge length/mesh density must be given to the faces of a CAD assembly where the mesh is to be matched. It is not enough to set only the mesh size on one of the faces. The software will not automatically copy the mesh to the other face (why actually not?).
External meshers might help you out
Any automatic second attempt will give you most likely bad meshing results. You can try external software instead:
Going with the default "Ignore contact" might give you decent results, since the Moldflow solver has evolved a lot and the difference between the two settings decreased.
"Precise Match" option seems to conflict with mesh refinement at injection location
Since Moldflow 2015, it is possible to let the software refine the mesh at the injection location (given that the injection location is placed on the CAD bodies prior to the meshing step). I think this feature is very handy. In a recent study, I have figured out though that the mesh refinement at the injection location does not work, if the "Precise Match" option is selected.
It does not always happen. I have run the meshing with another part (similar size and meshing settings). The mesh refinement was carried out both with "Precise Match" and "Ignore Contact".
Please have a look at the attached pictures where I made a comparison between "Precise Match" and "Ignore Contact" for both studies.
Anyone seen the same? Any ideas where this could come from?
Best regards,
Max
Hi Max,
Good job pulling together the relevant information.
Here are some additional considerations from an Autodesk support case that I went through in June 2013 regarding achieving perfect match with assemblies for Cool(fem); hopefully they are of some use.
Firstly, as you have noted, precise matching between CAD bodies is ideal, but often not obtainable. The solvers are said to be tolerant of imperfect matching between bodies.
Next, the "precise match" option refers only to mating CAD geometry, and it ignores previously created elements. One of the primary recommendations was to mesh all components simultaneously with the default mesher (as if they were part (3D) components). After meshing, the element definition could be changed to mold block (3D) or mold insert (3D) as desired. If you mesh the mold components after the plastic components, the "precise match" option is ignored for those interfaces.
Also, I learned some history on the Cool(fem) mesher. Prior to Design Link being included in the normal software release, users needed a way to achieve good mesh matching between CAD bodies when they were unable to import assemblies. As a general rule, when possible, the regular mesher should be used to mesh all CAD geometries in a single step (except 3d cooling channels). This Cool(fem) mesher accounts for previously created elements (and ignores CAD geometry on those surfaces).
Apart from the support case, I also have the following tips from experience:
Hope this helps.
Matt
I could add another tipp to this topic:
Meshing with Open Source.
I didn´t believe myself at first.
I had some difficulties to mesh a large part with a special cold runner with 40(!) gates. Gate shape is a half cone with a radii of 0.3mm.
The whole part is about Ø 200 mm.
Whether Moldflow 2015 nor NX in that case serves me well.
I could have tried Altair HM, but I´m lazy. And since I´ve used Cadmould a lot I know that they use Netgen internally.
So did I!
I had to use GMESH also to get the mesh as surface mesh from Netgen to Moldflow (as *.bdf/nas).
And imagine my surprise when looking for the quality. Of course no matching!
But since I´ll do 3D in most cases anyway...
Meshratio was 4:1 on the bad side!
Netgen and Gmesh do not mesh touching parts, - so no help for that. But with the tolerant behavior of the solver we should get away meshing every single part.
Though I would expect some of the characteristics of this open source mesher in the next Moldflow release.
Cheers
Harald
Hi Matt,
thanks for your additional information. I think you point out some very precious details which are not obvious:
I would like to comment moreover on your thoughts at the end of your post:
Best regards,
Max
Gmesh is a powerful tool, and I use(d) to to analyse meshes.
In this case I use Netgen to mesh, and it was somewhat of a journey to find the right settings.
I could have used Gmesh directly, but I didn´t find the parameter in there. At least I found it more difficult.
For 3D Meshes Gmesh uses Netgen anyway (There are to famous 3D Netgenerators out there, beside Netgen it´s Tetgen)
So to make it easy if you´re going to test it I attach a PNG that might be helpful for first tests.
May the force be with you.
Harald
Hi,
Gmsh is a very nice tool 🙂 thanks for the tip.
After a while of testing and learning, its very good to handle. I've meshed directly in gmsh, there is a good option to remesh the geometry by defining number of nodes (Mesh--> Define--> Transfinite--> Line) But one think I'm searching:
Is it possible to define the minimum number of layers?
It would be very nice, if its possible to directly import the 3d-mesh without remeshing (refining) in Moldflow.
Markus
Markus,
I'm not sure what Gmesh can do (or Netgen, which is what Gmesh uses at last).
I got pretty good meshes the way I described above. So taking the surface mesh and let Moldflow do the rest seems better for me,
since I'm thinking the Moldflow can care about the mesh it needs (or maybe a biased mesh).
Maybe Netgen will do the trick, but I don't think so.
If you get the meshing done in Gmesh alone, you might tell us (me?) how to? So we have something up our sleeves.
On the other hand I should retry it with the current release as well as with upcoming ones, there are always slight or bigger
improvements found in every new release of Moldflow.
Harald
Moldflow has specific requirements for it's 3D mesh.
I don't think a standard mesher can give us the nice tetra inside the thickness we requires.
If you get a good surface mesh, Moldflow shouldn't have any issues to generate your 3D mesh.
Remember to pay attention at the number of layer you generate. If you want a higher number of layer, it is better to have a small enough edge length on the surface to avoid high aspect ratio on tetra.
Hi,
thats the way i've gone to generate a mesh:
1. Open CAD-Model
2. Review a first 3D- Mesh
3. Optimize the 3D-Mesh
4. Place more nodes
Do this for every line you want to optimize and you'll get a nice mesh 🙂
There are also other ways to refine but i didn't test it till now.
Hope this helps.
Markus