3D TETRA MESHING OF PLASTIC COMPONENTS

Aim :

• Make a proper geometric clean up on the surfaces if there is any damaged surfaces.
• To create a 2D mesh on the model surface.
• Maintain a Proper mesh flow with less tria concentration.
• To achieve exact quality criteria as given in the question with clean up tools to get proper mesh flow.
• To convert the 2D mesh into 3D Tetramesh.
• Obtained 3D tetramesh using 'Quick tetra' and 'Volume tetra' command.

Procedure :

1. TetraMesh Generation Method 2D to 3D Conversion :

Step 1 - Geometry Import

• Importing a given CAD geometry into hypermesh.
• There are file formates like IGES, STEP, Parasolid where we can import these file formats into any CAD,CAE Softwares.
• But in hypermesh we can only import three file formates like IGES [Initial Graphics Exchange Specification], STEP [Standard for the Exchange of Product Model Data], Solidworks as shown in the figure below.

Step 2 - Examining

• Before working on the model.We have to organize the many components to single individual components, so that it's easy to work on and then check the geometry if there are any errors. some of the geometrical errors are as follows.

1. Damaged Geometry.
2. Free edges in unnecessary areas.
3. Unnecessary points on the lines.
4. Unnecessary Connections and connectivity error.

Step 3 - Extracting Midsurface

• Since 3D tetramesh is to be created, the whole thickness of the model is considered for the final 3D tetramesh.

Step 4 - Assigning material property to the components

• To assign a property,Right click on the feature tree panel/right click>">>>create>">>>property.
• Do the same thing for the material also.
• After creating property and material.Select the property and give the material which you have created and thickness to the property.
• And then go and assign the property to the component which you have exracted the mid surface from it.

Assigning Property

• If we have symmetry in the components.We can cut into half and we can reflect the surface and mesh on the other side.By doing like
  this,we can save lot of time instead of doing both sides.
• Since the model is not perfectly symmetric, meshing is done for the whole model.

Step 4 - Manual Clean Up

Manual clean up is necessary to achieve a things like

• Proper mesh flow.
• Feature capturing.
• To correct the elements failing for the minimum length.
• For surface deformations.
• For connectivity errors.

4:1 Extracting the midline for Upper Body.

• We have to toggle all the split lines which are less than minimum length.
• We have to go [Midline option>">>>geom>">>>lines>">>>midline].
• We have to select two fillet edges on the hemming portion and then create a mid line.

[Note : If it is necessary to extract the midline in the hemming regions.You can extract or it's fine.]

Extracting Midline in hemming region

• If there is any unnecessary lines,We can toggle that edges to get a proper mesh flow.
• In this component.In the fillet region,there some unneccessary shared edges so,toggle that edges also.If we
  mesh without toggling the edges,the element's will fail.

Step 5 - Perform Mesh on the surfaces.

• Enter the quality criteria what they given for the component's.
• Tool bar → preferences → criteria file settings → checks for the element criteria →Enter values → apply → ok.
• Save the criteria file settings for that component as it facilitates easy loading of the required criteria for analysis.

S.N	Quality Criteria	Value
1	Target length	5
2	Min length	2
3	Max length	7
4	Tet collapse	0.15

Try to achieve the quality criteria mentioned above in the table.

Conditions to be followed while meshing.

• Feature Capturing.
• Feature capturing is must while meshing. All the nodes must be connected to the shared edges.

Feature Capturing

• Mesh Flow

Mesh Flow

• Quality Criteria

Quality Criteria

• Since the mesh is a 3D tetra mesh. Only the given 3 quality criteria has to be met.

Begin meshing the surfaces

• Start meshing from the centre regions or from least free edges.You will get proper mesh density and proper mesh flow.
• If the mesh is not proper since remesh or rebuild the mesh by using this two tools.

Using quality index clean up tools

SI.NO	Tool Name	Purpose of the Tool
1	Place Node	Move the node along the plane or curvature of the surface or away from surface.
2	Swap Edge	Each time if we click an edge, it switches to the next valid configuration.
3	Element Optimize	To move the midnodes attached to the element we are optimizing, enabled the with attached midnodes checkbox.
4	Smooth	It is used to improve the element quality of the surface.
5	Split/Collapse Edge	To use the split edge tool, left-click on an edge. HyperMesh splits the elements that share the selected edge in a way that will achieve the optimum quality.
6	Drag Tria Element	To use the drag tria element cleanup tool, left-click on a tria element and drag it to a desired location. HyperMesh highlights the selected tria element in pink.Drag both trias to combine when they are facing opposite direction.
7	Split Quad Element	To split a quad element, left-click on the quad element you wish to split. HyperMesh splits the quad element into two tria elements.

Other Clean Up tools

• Distance
• Translate
• Align Nodes
• rebuild mesh

a. Distance

• Geometry → Distance → two nodes → enter the value.
• The Distance panel to determine the distance between two nodes/points or the angle between three nodes/points, or to change
  distances or angles.

b. Translate

• Tool → Translate → Nodes → N1,N2,N3 → Translate +/-
• This tool is used to fix the warpage.

c. Align Nodes

• Geometry → Node edit → align mode → 1st node → 2nd node → 3rd node → align.
• Select a node that defines one end of the imaginary line.
• Select a node that defines the other end of the imaginary line.
• Once both nodes are selected, now we can pick the nodes that we wish to align.

Check Nodes

• Tool → Count → Nodes → right click select all → press selected ( no of nodes will be displayed)

Check Normals

• Top side of surface must be in blue colour.
• Bottom side of surface must be in red colour.

Check dependency

• Check whether the nodes dependent on multiple nodes as this can cause issue during the analysis, So there must 0 nodes containing multiple dependency.

Check tria percentage

• Check whether the tria percentage is within the given tria concentration in the quality criteria. Tria concentration is not the required quality criteria in this model.

Check for equivalence and duplicates

2. TetraMesh Generation Using Quick tetra method :

3D tetra mesh is created for the Model 2 using the 'Quick tetramesh' option. The option is selected in the Utility option in the drop down menu. Here the required quality criteria is mentioned and the only trias are selected. This option produces a 3D tetramesh which is usually preferred to get a rough mesh on the selected Model.

The final mesh obtained from the 'Quick tetra' option is shown in the figure below.

3. TetraMesh Generation Using Volume tetra method :

3D tetramesh can be obtained using the volume tetramesh option as well. The parameters required for the 3D mesh is set in the Tetramesh parameter command and the volume tetramesh option is selcted. The solid for which the mesh is required is selected and the mesh button is clicked. The 3D tetramesh obtained is shown in the figure below.

Conclusion :

• Obtained 3D tetramesh using the 2D to 3D trai conversion method.
• Obtained 3D tetramesh using the Quick tetra utility.
• Obtained 3D tetramesh using the Volume tetra option and selecting the required solids.

(MODEL 1 ) https://drive.google.com/file/d/1KvBYkEXOmQs61rTTekMbN6QEzv2XFbWL/view?usp=drive_link

(MODEL 2) https://drive.google.com/file/d/1Ym0Qmo8BkssnhAdENza8C5IkLZK2aZ9O/view?usp=drive_link

(MODEL 3) https://drive.google.com/file/d/18mSEF-aICjkzwXxSbbfEoUMBIi8Kq05w/view?usp=drive_link