Week 7- Meshing of Backdoor Challenge

Week 7- Meshing of Backdoor Challenge

Objective :

• Make a proper geometric clean up on the surfaces if there is any damaged surfaces. To extract a proper mid surface from the parent components manually. Maintain a Proper mesh flow with less tria concentration. To achieve exact quality criteria as given.

Procedure :

Phase 1 - Importing

a. Hence we are importing a given CAD geometry into hypermesh.
b. There are file formates like IGES,STEP,Parasolid where we can import these file formats into any CAD,CAE Softwares.
c. 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.

IGES,STEP,These two are standard file formats which are used most in industries.But now a days in industries,they are aslo using parasolid file format's.

Figure 1

Phase 2 - Examining

• Before working on the model.We have to check the geometry if there are any errors like

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

• By assessing the Car Backdoor CAD model.We can see there are three components in the Model.

• Inner Panel
• Upper Body
• Lower Body

Figure 2- Inner Body

Figure 3- Upper Body

Figure 4- Lower Body

Phase 3 - Extracting Midsurface

3:1 How to Extract Mid Surface ?

• Before extracting the mid surface,Delete the solids and then extract the midsurface cause we are not going to mesh on the solid
  model.We are going to mesh on the surface.Ensure whether you have deleted the solids or not.
• In Geometry>>Mid Surface>>Auto Mid Surface.
• Extraction Options>>Use Skin Offset.This option will be able to capture the features properly.

3:2 How to Extract Mid Surface Manually ?

• In Geometry>>Surface Edit>>Offset>>Surface>>Offset.

Figure 5-Extracting midsurface manually

3:3 Why to Extract Mid Surface ?

• Before extracting the mid surface for every component,We should measure the thickness of the component and then we have to proceed
  to extract the mid surface.
• If the component thickness is less than 6mm then we will come to know it is a sheet metal component.
• For sheet metal and plastic components,Mid Surface extraction is must.

3:4 Assigning a property and Material for 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.

Figure 6-Assigning Property

3:5 Checking symmetry for the component's.

• By examining the components,we have only two symmetric components called

• Lower Body
• Upper Body

• Other one called Inner Panel.In this component some region's are symmetry and some are not.

3:6 Why checking symmetry is necessary for the component's ?

• Cause we can save the time.
• 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.

3:7 How to reflect ?

• First cut the component surface into half using delete tool.

Figure 7-Selecting the surfaces which we want to delete according to symmetry

Figure 8-Half of the surface has been deleted according to symmetry

Phase 4 - Manual Clean Up

• Manual clean up is necessary to achieve a things like

• Proper mesh flow.
• Feature capturing.
• To eschew 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.

4:2 Toggling Edges and Purpose of it.

• 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.

Figure 9-After toggling the lines

Phase 5 - Perform Mesh on the surfaces.

5:1 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.

Target Element size - 5 Units

S.N	Quality Criteria	Value
1	Aspect Ratio	5
2	Skewness	45
3	Warping	15
4	Taper	0.5
5	Min. Length	3 Units
6	Max. Length	7 Units
7	Min angle Quad	45
8	Max angle Quad	135
9	Min angle Tria	30
10	Max angle Tria	110
10	Tria %	15

5:2 Conditions to be followed while meshing.

1. Feature Capturing.

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

Figure 10-Feature Capturing.

• Tria Management

• Avoig higher number of trias.

• Important Parameter's in tria management

• No trias in corner's or edge's.
• No opposite trias.
• No back to back trias.
• No trias in fillets or hemmings(We can have minimum but anyhow try to avoid).
• No rotational quads.
• No trias should share a boundary with feature line.
• Connectivity between elements.
• Split and perform the mesh.
• Use mixed type mesh for irregular shaped surfaces and quads only for rectangular/square surfaces(Opposite sides should be parallel and equal).

5:3 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.
8	Combine Tria Element	To combine two tria elements, left-click on their shared edge. HyperMesh combines the two tria elements into one quad element.

5:4 Manual Clean Up

• Distance
• Translate
• Align Nodes

• 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.

Figure 11-Before

Figure 12-After

• Translate

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

• 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.

Phase 6 - Reflecting the component.

• Once the mesh is done completley,we need to reflect the component.
• Tool → reflect → select the element's as duplicate → current component → select y axis (In which direction we want to reflect it) →
  base node → reflect.

Final Cad Model Image

Result :

• Hence the mid surface for every individual component has been extracted manually and every component has been meshed with proper good mesh flow and attained the quality criteria as per given.
• Every tria conditions has been followed in this model and completed successfully.

Conclusion and Learning Outcome :

• In this week 7 challenge.I came to know how to extract midsurface manually and mesh a component properly with proper mesh flow.
• Proper feature capturing,avoid trias as much as,
• Avoid rotational quads(rotational quads in hemming regions),
• Attain quality criteria and do manual clean up,
• Check for the duplicates,nodes,normals,and tria percentage.