Week 3 - 2D meshing for sheet metal

Aim

To take the mid surface for all the components after checking the geometrical errors and mesh the mid surface with the given element Quality criteria, for the given Hood 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, viewed the component without shadow mode using Ctrl + Shift shortcut 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. Now as the measurements are done in the previous step only we have the half thickness value for the mid surface generation using the Offset faces method present in the faces tab under the classic TOPO deck. But for this challenge auto mid surface generation is carried out using the mid surface option under faces tab. For mid-surface using the offset method after the mid-surface generation, 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. But in the auto skin process by the SetPID method PID and thickness both are assigned automatically. (Faces>midsurface>Skin>select the entity>middle click). Skin is used for sheet metal components where thickness is uniform. Renamed the new property ids and under T thickness is also visible. The parent CAD has been removed as in the auto midsurface option automatically. But we can keep the parent CAD by turning off the Delete Face option in the option list when the auto mid surface option is on.

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

S.No	Quality Criteria	Value
1	Target/Average length	5
2	Minimum Length	2
3	Maximum Length	7
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. Now saved the quality parameters as “.ansa_qual” file for repeated use. 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 and saved the parameter file as “.ansa_mpar” for repeated use.

• As all the quality parameters are given, we can go for meshing so switching to MESH deck. But before that in this challenge we can see that the components are symmetric about z-x plane using the function RmDbl (TOPO module>Faces>RmDbl>untick “Replace selected faces with symmetry links>ok”). After that half of the symmetric face will be generated. In the inner hood component one part is not falling under symmetry hence will not be deleted after the RMDbl operation. Now very less area to mesh hence less hectic. At last, again checked for geometry before proceeding to mesh.

• Now changed to the MESH deck to view the component. 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. Especially the filets are to be defeatured to meet the quality (MESH Deck>Macros>Cut>Left click/Right click).

becomes

• 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). As Split function is a hybrid function performs split,join and split with left,right click respectively. Right click is also used here to swap. The above function also reduced quality issues to some extent. Also, Move free(MESH Deck>Grids>Right click to choose shell with the local coordinate>Middle Click) and Paste(MESH Deck>Grids>Select the grids>Middle Click) are used to reduce the quality issues and to fix the cracks(Can be seen by turning the perimeter view and turing on the bounds).

Now as the parts are meshed hence we can generate the other symmetrical halves of the parts using transform(Transform>Select the whole half>middle click>Symmetry>Apply the default deck>ok ).

• Showing when all the property Id is switched 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.

• 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 ANSA workflow, can perform topology cleanup, can generate mid surface for complex sheet metal, 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.