Week - 4 - 2D meshing for Plastic components

2D Meshing for plastic component [Bottle Cap]

AIM-

• Preprocessing on Bottle cap using ANSA as preprocessor software.

Objective-

• Clearing all geometrical glitch over the CAD of this Bottle cap.
• Extracting the midsurface for the component.
• After extracting midsurface we will perform 2D meshig over the midsurface based upon the given quality criteria.
• Assigning PID's and the thickness for the mesh on the component since here is different different thickness so we need to set the PID's individually.

Procedure:

Stage-1

Importing the model:

• Here we will be importing the CAD file into ANSA.
• Here is many types of file format supported by ANSA for CAD model like IGES,STEP and somtimes Parasolid also depending upon the requirment of industries.

For importing the model

we will go on pull down tab >> File >> open >> select the all format >> select the model from folder

• Here is the Bottle cap model which we need to open on ansa GUI.
• As we can see here is many type of format we can import in ANSA.

Imported Model:

• This is the imported bottl cap CAD model.
• Since we use to import the CAD models in different different formats so due to softwares algorithm some geometrical changes are found after importing.

Here first we need to manullay check the properties ID [PID's] available in the model and also properties in the same way,

Go to the Model browser on tool bar menus,

Here we can see only main PID is usefull, so other one we need to delete.

• In simmilar way we also need to check for Model browser also,

Here in the model browser one unnecessary model is present which we will delete.

Stage-2

Manual Geometric Check and cleanup:

So after extracting the model we have to clean all the geometrical glitch and errors like,

1. Unconnected surfaces.
2. Uneccessary cons and surfaces.
3. Damaged surfaces.
4. Triple cons.
5. Free edges.

For detecting the geometrical errors we will Go to tool bar >> Check >> Geometry.

• When we click on the geometry a new tab will open.
• Do not forget to check on type of geometry (according to image shown below) we need to fix.

• On that tab we can see a execute option will click on that.
• Then we can see all the gepmetrical errors will display.
• Now we will clear the gemetrical glitches autometically and manually also.
• For that will slelect all the errors and right click and fix.

• After fixing the gemetrical errors we will rerun the execution adn we can see all the errors are get fixed.

[Note: we can fix all the geometrical errors manually also if auto fix not worked]

Stage-3

Midsurface Extration:

• Before midsurface extraction we will change the perimeter and macros length as 1mm.
• We are doing it just because to get a proper and finished surface while extracting midsurface.
• For giving the perimeter and macros length.
• Go to mesh module >> Length >> perimeter >> select region by box drag >> middle click >> put 1mm

• will do it same for the acros also as we did for perimeter.

Model after applying the perimeter ans macros length as 1 mm:

• As we can see due to length and parimeter as 1 mm surface as more finer nd smooth as compare to before.

Midsurface extraction:

Why we need midsurface extraction?

As we know we have to mesh this 2D component, and as we can the real CAD model is not perfect 2D. Its having some thickness at every part in the whole component.

• If model is having thickness less than 6 mm then its may be sheet metal or plastic component.
• And for sheet metal and plastic component midsurface is neccessary for meshing purpose

And since we are going to apply trias and quads elements so we need to change this model ito perfectly 2D as sheet.Then we can apply Trias and quads elements on the sheet. For that we can choose multiple option for extracting the mid surface like,

• Automesh
• Casting
• Offset the surface
• Use of middle line

By these methodes we can extract midsurface for this particular component.

• Here we will start extarcting midsurface from complex areas like cap top surface as shown below.
• In this methode we have uses offset surface at middle.
• Go Topo module >> faces >> offset >> put distance.

• In simmilar way it start extracting midsurface for circular regions also.

• For such geometry we can use offset and middle surface methode both.

Now will see the ribs kind of part using middle surface method.

• Go topo >> Faces >> Middle >> multi >> uncheck boxes as shown >> select the red,green and blue surfaces

• Here red color is showing inner surface, green is showing outer surface and blue is the surface for middle refrence.
• In simillar way we will do for all the ribs.

Final midsurface:

Stage-4

Meshing:

Once geometry cleanup cleanup is completed it means there should not be any ustitched surfaces, unwanted free edges etc. Meshing meshing is next step

Mesh module >> Mesh generation >> Best >> select component and mesh

1. In 2D meshing with ANSA preprocessor easiest way of meshing is by Best mesh option.
2. After giving mesh to the surface usually we will be using Reconstruction (Recon.) from shell mesh for better mesh flow.
3. Uses of some other tools also like smooth,split,swap,cut,join,projcut etc. For better mesh flow

Given Quality criteria for this model:

Target Element Length = 1 Unit

S.N. Quality criteria Functions Values

1 Aspect Ratio Ratio of max lenth/min legth 5

2 Skewness Deviation from ideal shape 45

3 jacobian Transformation of coordinate system 0.7

4 Warping Angle between the two planes of the same element(quad) 15

5 Min.Length shortest length of any given element 0.5

6 Max.Length largest length of any given element 3

7 Min. angle quad Minimum angle in any given quad element 45

8 Max. angle quad Maximum angle in any given quad element 135

9 Min. angle tria Minimum angle in any given tria element 30

10 Max. angle tria Maximun agnle in any given tria element 120

11 Tria % percentage of tria in meshef surface 15

• So before start meshing we will set all the quality criteria in ANSA using shortkey F11.
• Quality criteria tab open >> shell >> put all the values and apply >> ok, and set presentation parameters also in the same tab .
• In Graphics do check tick on the % Elements and All details arrow on left corner side.

• Now start giving mesh in every region-

Some thumbrule while meshing for better mesh flow-

1. Feature capturing is must while meshing it means all shared edges should have better nodes connectivity.
2. Try to keep less number of trias.
3. Avoid trias on feature line and edges should swap it.
4. Avoid opposite trias, use split option and combine them.
5. Try to keep less number of trias on fillets, use split or swap tool.
6. Avoid rotational quads, Recons. or split into trias and move them.
7. Use mixed type of elements on complex geometry means trais and quads for this 2D meshig

Assigning thickness and PID's-

• Since here every part is having different thickness so now we will assign PID's indivisually and also assign the thickness for every part.

• Final check-

• For final check we will first on the 2D visibility of elements.
• so that we can visually chack that every part is having its own thickness elements or not.
• For that go to Quality table >> Presentation parameter >> check on Draw shell as solid.

Final Meshed Bottle Cap-

Result-

• We have achive zero surface error in the model
• Succesfully extracted midsurface for each component.
• Feature line have connected properly and surfaces have good connectivity.
• A good mesh flow have been achived with zero elemental failure.
• We have achive minimum tria concentration below than 3%.

What we learned ??

• In this challenge we have perform all geometry cleanup for the hood component.
• Then we have extraced the midsurface using auto midsurface extraction.
• How to generate a good mesh flow.
• How to achive less tria concentration.