Shell meshing a plastic bottle cap having various thickness using ANSA preprocessor

Google Drive link for the Bottle cap model:

https://drive.google.com/file/d/1yeHqBkcsxJwkbn5jJ8uE8C9Qcs9VLp6o/view?usp=sharing

Aim:

Obtain a 2D shell mesh from the bottle cap component following the given criteria.

Target/Average length	1
Minimum length	0.5
Maximum length	3
Aspect ratio	3
Warpage	15
Skewness	45
Jacobian	0.7
Minimum Quad angle	45
Maximum Quad angle	135
Minimum Tria angle	30
Maximum Tria angle	120
Tria Percentage	15

Objective:

• Clear the geometry errors of the parent model.
• Extract the mid surface from the parent model.
• Generate the shell mesh from the mid surfaces according to the given criteria.

Procedure:

• The IGES format file of the plastic bottle cap model is imported into the ANSA workspace.

• The model is refined to make the features clearer.

• The missing connections between the surfaces are rearranged to remove the geometrical errors. Features available in the topo module are made used.

• Orientations of the surfaces are managed accordingly as shown above.
• Geometry check is done and if errors are found, they are addressed accordingly.
• The lock views are created and managed as required.
• Auto mid surface from the casting mid surface selection with appropriate options is tried and the obtained mid surface is found to be not correct. So manual mid surface extraction is opted to obtain the final mid surface.

• Some features are approximated since the model is a plastic model which is having various thicknesses at various positions.

• The mid surface is generated by offsetting the surfaces with appropriate offset distance.

• The connections are made accordingly by checking with the parent component. The intersection and extend options are used to edit the surfaces accordingly.

• The thread patterns are created from creating the middle curve and sweeping the appropriate con or curve over the middle curve. The obtained surface is projected on to the middle surfaces.

• In case of threads on the outer cylinder, the surface created by sweeping along the middle curves crosses the stiffener like sections as shown in the image below. Since this type of intersection is not happening in the parent component, approximations are made to the thread and the surface of thread is edited to avoid this type of intersection.

• Some surfaces are created using middle option and the parent surfaces are retained and these parent surfaces are placed in a separate part.

• The tooth is created from the curves and 35 more instances are created from the original tooth by rotating fo 10-degree angle instance.

• The surfaces of the mid component are divided accordingly and separate properties are assigned for varying thickness sections. The measurements of these various thickness sections are stored for the reference.
• The perimeters of the edges are refined accordingly.
• The quality criteria and mesh parameters are inserted into the software.
• The surfaces are cut into small surfaces to control the mesh flow. The best mesh algorithm is used to create the primary mesh.
• If required the generated mesh is reconstructed to obtain the better mesh flow and quality.
• The trias are handled to get better mesh by swapping the edges and splitting the adjacent quads. Example of handling the tria to eliminate quality failure is shown in the below image.
• The mesh elements are edited accordingly to improve quality. As in below case, the tria element in the middle of mesh is manipulated to eliminate the failing condition of jacobian (Blue colour element)

• The best possible mesh is created by using all the features of the mesh module.
• The generated mesh is smoothened at regular intervals to have better mesh flow representation.

• To control the generation of shell mesh, the meshed surfaces are hidden using the unmeshed option.

• To check the quality, the hidden modes are used. The elements are allowed to fail in critical areas without compromising on capturing the features.

Conclusion:

Out of various possible ways for shell generation, the best possible mesh is obtained. Averaging the thickness at different positions to match the plastic model is tried. Smoothness at the feature areas is compromised to obtain the 2D shell mesh.