Week - 5 - 2D meshing for Plastic components

Objective:

For the given Plastic Bottle Cap model, check for the geometrical errors and take the mid surface by suitable mid surfacing techniques. PID and Thickness assignment has to be done for all the mid surfaces. Mesh the same with the given element Quality criteria. (Refer to the table below for the Quality criteria)

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

The first step after importing the model is to analyze properly and understand the geometry. When a CAD model is imported into the ANSA, there might be several geometrical errors like missing/distorted surfaces, intersecting surfaces, etc. due to the format conversion process or inherent bad model. And, it is important to clear all these errors before starting meshing. So, the next step is to clean up the geometry. To ensure that all the surfaces are connected properly Faces>Topo tool is used for all the edges of each individual component at a time. Next, geometry check is performed by going to Checks>Geometry and running it for parameters as shown in the image below. Another image shows the errors detected.

• MAKE TOPOLOGY

The model has some minor errors which can be fixed automatically fixed. SELECT THE ERRORS > RIGHT MOUSE CLICK > FIX, this will clear the errors, if errors still exist, manual cleanup needs to be carried out by releasing the cons and fixing the damaged face and performing the topo to fix the free edges.

• Mid Surface Extraction

Before mid-surface extraction check the thickness of the component if it has a varying thickness, then the best way to extract the mid-surface is by manual mid-surfacing. When the model has varying thickness ANSA algorithm fails to capture the proper geometry, hence the manual mid-surfacing is carried out.

To measure the thickness go to UTILITIES > MEASURE > select the points.

The given model is a plastic component that has a varying thickness, hence manual mid- surfacing is performed, by extracting individual mid-surface form faces of different thicknesses. It helps in cutting the faces passing through each other; it creates a cut on the faces which are intersecting each other. For parts with varying thickness, cons are used to create the middle curve and using the middle curve mid face is generated using FACES > NEW

After creating the mid surface, divide the mid surface and apply the appropriate property with thickness to both the faces final mid-surface with varying thickness property IDs applied to the mid-surfaces.

Geometry cleanup for meshing the generated mid-surface, Run the geometry check again on the mid-surface and fix the issues

• Create Set PID

After completing the extraction of mid surface create a new property ID by using an option FACES>SET PID and give the property values.

• Quality criteria

After creating the property ID for the midsurface, assign the quality criteria parameters which are given.

Set up the quality criteria for the meshing, go to UTILITIES > QUALITY CRITERIA

• Mesh generation

To start the meshing switch to Mesh module bar in the modules menu bar Using these common parameters repeatedly a 2D mesh passing all the quality can be generated, to start meshing the surface go to MESH GENERATION > BEST and select the surface to be meshed.

After completing the property ID set the geometry parameters and macros for 1mm by using the length in the perimeter option of the mesh tab and if the model is symmetry then delete the half portion in the cad model because when transforming the symmetry of the mesh surface will regenerates along with mesh.

The meshed part can be checked for quality criteria by switching the drawing styles to hidden at some areas where two different triple cons are present the elements fail due to minimum element length which cannot be solved; hence there are some off elements present in the mode.

Drawing shell as solid and checking the applied thickness to the master model.

from the above images it can be seen that the entire geometry has been captured with proper thickness values.

Learning outcomes:
Mid-surfacing of plastic components, manual mid-surfacing, varying thickness application

Conclusion:

Generated mid-surface for the given plastic component and 2D meshing is performed on the midsurface and property cards with different thickness are created and applied to the appropriate faces.