Week 3 - 2D meshing for Sheet metal

Objective: To perform geometry cleanup, extract mid-surface and perform 2D meshing using the given quality criteria on the given Hood model. 

Procedure: 

The given Hood model falls under the category of sheet metal components. So 2D meshing should be performed on the given component in the pre-processing stage. 

The procedure consists of three steps.

1. Geometry clean up

2. Extraction of mid-surface

3. 2D Meshing

1. Geometry cleanup:            

  

                                          Figure 1: Given Hood Model imported to ANSA

Geometry cleanup is an essential step to ensure a smooth mesh flow in the meshing stage. The CAD model imported to ANSA may consist of topology errors.

The errors may include single cons, needle faces, triple cons, cracks, and unchecked faces. 

Geometry cleanup is performed to rectify these topology errors and ensure that the surfaces are properly stitched, and that there are no discrepancies in the geometry that can affect the mesh flow.

                                                              

                                                   Figure 2: Cad Model after the initial topology 

                                                               

                                    Figure 3: Checks manager showing 106 errors in the geometry    

                                                                   Tools>>Checks>>Geometry

To perform topology, the checks manager is used to know the errors in the geometry. The errors are corrected over a series of steps until the checks manager shows no errors.

i. A few errors are fixed using the autofix option. 

ii. Single cons are pasted using the Cons option. Cons>>Paste

iii. Triple cons are fixed by the release cons option. 

iv. Unchecked faces need to be fixed by generating new faces in the areas where the surface is missing. 

                                                              

                                      Figure 4: Checks manager showing 0 errors in the geometry. 

2. Extraction of Mid-Surface:

Since the given model is a sheet metal component, it is necessary to extract the mid-surface. Mid-surface extraction helps in an accurate representation of the geometry. 
To extract the mid-surface, first measure the thickness of the model.  

Utilities>>Measure

                                                                        

                                                          Figure 5: Thickness of the component 

Since the thickness of the component is 0.75mm, the mid-surface exists at half the distance measured from the top surface and half the distance measured from the bottom surface. 

So the off-set distance is 0.75/2 = 0.375mm

Mid-surface is extracted using the manual mid-surfacing procedure. 

Faces>>Offset

Select the offset option, and select the faces. Input offset distance and offset direction. 

                                                          

                                                                  Figure 6: Mid-surface of the model

After extracting the mid-surface, assign property ID to the mid-surface using assign PID and ensure that the material is defined. 

3. Meshing:

The given hood model is a sheet metal component. Hence, 2D meshing has to be performed on the mid-surface. 
To mesh the component, the element quality criteria have to be defined. 

The element size is given as 5. 

Perimeters >> Length >> Perimeters >> set the length to 5

Using the measure command, measure the distance between the nodes on the perimeter at various locations and ensure that the distance between the nodes meets the defined length. 

Define the element quality criteria as per the model requirement. The element quality criteria can be defined by using the Utilities command. 

Utilities >> Quality Criteria

                                                          

                                                                Figure 7: Element quality criteria 

After defining the element quality criteria, start meshing. 

From the modules panel, switch to the Classic meshing module. This module consists of all the meshing tools. 

In the meshing module, using the mesh generation command start meshing the component. 

Mesh Generation >> Best 

If the obtained best mesh has any issues, the mesh can be reconstructed using the reconstruct command. 

Shell mesh >> Reconstruct

       

                                                               Figure 8: Meshed component

After meshing the component, assign thickness to the meshed component. 

For assigning thickness, select the property ID of the component. 

PID >> Thickness

         

                                                            Figure 9: Thickness assigned 

LEARNING OUTCOME:

1. I have understood the ANSA GUI and various commands in ANSA

2. I have learned to perform geometry cleanup to rectify topology errors.

3. I have learned the manual mid-surfacing procedure for extracting the mid-surface of a sheet metal

4. I have learned about element quality criteria and their importance in obtaining a good-quality mesh. 

5. I have understood the 2D meshing procedure and why 2D meshing is performed on sheet metal components.