Week - 4 - 2D meshing for Plastic components

Aim

To check for the geometrical errors and take the mid surface by suitable mid surfacing techniques, PID and Thickness assignment for all the mid surfaces and to mesh the same with the given element Quality criteria, for the given plastic bottle Cap model using ANSA.

Procedure

Imported the CAD geometry using the open option on ANSA. As ANSA supports the .igs, .stp, .stl files hence the challenge .stp file is successfully opened.

Checked the property ids, and defined the material for the hood by going to the material tab and ticking the define tickbox.

Geometry checkup for the whole component is performed using checks > geometry > execute and errors are generated. Then selected all the errors and performed auto fix on them and fixed them and lastly again executed the checks geometry for any further errors. Hence in this way geometry cleanup is done.

Now as done with the geometry cleaning measurements were taken for the sheet metal component for its uniform thickness for all the property ids and viewed them all by turning on the measurement tab in the database panel. (Used F12 to turn on database panel)

Now it's time for the mid surface to be generated as it reduces complexity during analysis by simplifying CAD and gives better simulation results in a shorter time. Like sheet metal components auto mid surface generation can here also be carried out carried out using the mid surface option under faces tab. But this time casting will be used instead of skin option(Faces>midsurface>Casting>Give the thickness>Give target length>set handle as single solid>ok). This will take some time if the compponent is complex, depends on the processing efficiency and no. of cores in the system. Now important thing is that in the skin option(for sheet metal components) the midsurface generated deletes the original geometry until the 'keep geometry' in the option list is crossed out, and then we would have to mesh it and then release the elements after meshing to remove FEA associativity with the CAD. But here after doing midsurface casting it itself removes the FEA associativity with the midsurface CAD and deletes the midsurface Cad geometry. That's why we cannot segregate it from the parent geometry and we are only left with the FEA which can be individually seen when geometry is off and only FEA viewing is on. To see that FEA as a different property id the property option and part option in the automidsurface should to changed to 'create new'.

The 21273 combine2 is the one, which later has been renamed as Auto midsurface.

But it is seen that for this automidsurface is not perfectly captured.

It can be rectified with functions like align, move free, element delete, but the the features which are not captured fully can be very hard to rectify as there is not FEA CAD assiociativity. So for these reason for complex CADs manual midsurfaciing is much preffered and after that we can compare that with the the auto mid. Now as the measurements are done in the previous to previous step. But here the thickness is varying in almost every area, Offset faces method cannot be used for the whole component only. In some places Faces>Middle is also used.

Now for the curves features, teeth, threads normal midurfacing will give poor results hence Curve>Middle option from the TOPO deck to map out the curves in the middle of the feature cons and then by using those curves we can generate surfaces by projecting them to the adjacent walls. In some cases, where the features are at some angle there the CONS>Project will not give preferred results as projection of hot points and CONS are perpendicular from the point to be projected. In such cases FACES>EXTEND option is used.

Curves used in this challenge are:

Features which are captured:

Final manual mid surface generated. Triple CONS are there where three surfaces are meeting.

The SetPID under the Faces tab had to be used to assign the new midsurface as a new property and further assign thickness to the midsurface. Renamed the new property ids and under T thickness is also visible.

Now quality criteria is given in the question only which is as under:

S.No	Quality Criteria	Value
1	Target/Average length	1
2	Minimum Length	0.5
3	Maximum Length	3
4	Aspect	3
5	Warpage	15
6	Skewness	45
7	Jacobian	0.7
8	Minimum Quad Angle	45
9	Maximum Quad Angle	135
10	Minimum Tria Angle	30
11	Maximum Tria Angle	120
10	Tria Percentage	15

Now quality criteria is provided for quality checks so that the component is devoid of quality issues so that boundary conditions and loads can be applied further. Using the F11 key opened the quality criteria table and ticked the required quality parameters and provided the above mentioned values, hid the inactive parameters and clicked on apply. Then went to the presentation parameters and ticked the Elements% and under detail & demand effect slides the cursor and selected all details. Then pressed apply an ok to make those changes.

Then provided the mesh parameters such as Target length and Min length.

As all the quality parameters are given, we can go for meshing so switching to MESH deck. All the functions from now on are used from the MESH deck. All the elemental perimeter length should be equal to or nearby the Target Length hence used the Length option to redesignate the element to element distance.(MESH Deck>Perimeter>Length>Selected the whole component>Middle Click>Provided the target length>ok). After the operation, manually checked the node distance whether the change has been applied or not. Also checked for the number of edges for the holes and found odd then changed edge number using the Number option to give the nearer even no(MESH Deck>Perimeter>Number>Selected the whole component>Middle Click>Provided the required no of edges>ok). Also NUM+/- can be used to increase or reduce the no of edges as it is a hybrid button(MESH Deck>Perimeter>NUM+/->Right click/Left click on the edges>ok).

Now before going to mesh the components are defeatured by removing unnecessary surfaces, edges, otherwise bad mesh will be generated. Here the Cut option is used to join and create new surfaces as it can perform both the operations with left and right mouse click respectively(MESH Deck>Macros>Cut>Left click/Right click). Now meshed the part using the BEST (MESH Deck>Mesh generation>Best>Select>Select the parts to Mesh>Middle Click)Mesh, as it gives better mesh results among all the other algorithms. Then turned on the hidden mode to see the quality criteria and the elements which are failing to meet quality. Then Reconstruct(MESH Deck>Shell Mesh>Select the elements>Middle Click x3), Smooth(MESH Deck>Shell Mesh>Select the elements>Middle Click x3) reconstruct and smoothen the mesh flow respectively and also used these to reduce quality issues. The trias near the perimeter are removed using Split(MESH Deck>Elements>Select the edges/nodes>Left click/Right click>Middle Click). Paste(MESH Deck>Grids>Select the grids>Middle Click) are used to reduce the quality issues. Now for better mesh flow, segregating the surfaces using Project cut and normal Macro>Cut alternatively and when the meshing is done joining them by changing mesh>reconstruct to keep in options list otherwise the cuts will be permanent on the CAD geometry (where not required also) and the mesh will be intact respectively.

Now checked the meshed midsurface with the parent geometry in PID mode with transparency on.

Finally drawing the shell as solid(Quality criteria>Presentation parameters>Tick draw shell as solid>apply>ok) which will enable the elements to gain the PID thickness.

These are viewed with perimeter option off.

Now the elements can be released by using Elements>Release(It deletes the FEM-CAD associativity) or we can export it as it is.

Learning Outcomes

At the end of this challenge I am more familiar with the curve usage, extending the surfaces hence can generate mid surface for plastic and casting components, can perform defeaturing, can improve the mesh and resolve quality issues.

Conclusion

Hence the geometry cleanup, mid surface generation with assigning thickness, meshing with quality checks has been successfully done.