Week 4 - 2D Meshing for Sheet Metal

AIM :

To Check for the geometrical errors, take mid-surface and mesh with the given element Quality Criteria for the given Component and perform suitable connections.

OBJECTIVE :

For the given CCB CAD model, Check for the Geometry cleanup (if required),

Take the mid surface, and

Mesh it with the below 2D element Quality criteria.

S.No	Quality Criteria	Value
1	Target/Average length	5
2	Minimum Length	3
3	Maximum Length	7
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

A cross-car beam (CCB) or an instrument panel(IP) support integrates the cross-car structure, steering column, air conditioning module and airbag system, electrical components, and plastic enclosure into one beam. Moreover, it plays a vital role in absorbing the energy of accidents. The cross car beam is the backbone of the instrument panel. From a structural perspective, the ends are mounted to the body walls and the firewall.

Adopted method:

1. Importing model and Geometry cleanup

Import the CAD model of a CCB assembly into ANSA interface. Uploaded CCB is not connected/stitched. This can be resolved using Topo option. 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.

Perform an initial geometry check and fix the errors if any.

Visually check the orientation and rectify if any discrepancies arise.

2. Preparing the model for mid surface

Thickness of each component should be measured, the thickness of each component is measured using the Measure tool from Utilities→Measure. The thickness is uniform hence the component is sheet metal.

Prepare the mid surfaces for meshing. For that, switch to the Mesh module. First, the shell element length is altered by going to mesh →Perimeters→Length and all the CONS are selected and target element length 5 is fed as length value. The same is done for all the Macros (surfaces).

The next, step is to extract the mid surfaces for each component and keep them in separate property ID. Midsurfaces are extracted using the manual method i.e. offsetting the surfaces of either face to the middle. Or by midsurface → skin option.

Here the more number of components are present in this module, midsurface → skin option is used to save time.

The property is assigned to the extracted mid surface by going to Faces>Set PID and assigning to the respective property.

In the mesh interface, quality criteria and mesh attributes are assigned as required. Length command is used to assign average length in to the model.

We obtained the Mid Surface for the whole CCB assembly as shown in the image given below.

Command used were offset→faces and mid surface →skin options.

Mid surfacing has to be achieved manually. After creating a Mid-Surface, Click Faces--> Set PID option and create New PID for Each component in the properties. The mid surface generated is isolated and saved as a new PID.

3. Meshing

Best command is used to generate mesh. Quality check is performed on the generated mesh. Mesh is adjusted accordingly such that it obeys the required quality criteria.

Mesh cleanup is done using the combination of the following commands as and when required:

1. Reconstruct, smooth operation under the option shell mesh
2. Delete nodes and
3. cut option under the option Macros
4. Split, swap option under elements.
5. Paste command under grid options

In the mesh, the following things should be observed for good mesh flow and better analysis at later part

1. The mesh should be smooth and clean
2. Back to Back trias should be avoided
3. Two opposite trias nearer to each other should be avoided
4. Tria elements in the fillets should be avoided
5. Tria elements in adjacent to outer edges should be removed
6. Tria elements attached to the hole edges should be avoided

Challenges in the project:

• CCB assemby has many a component which are made of metal, sheet metal, and plastic component as well. This requires assigning each component with different material, thickness.
• Creating the mid surface for each component and assigning PID.
• Sheet metal components are meshed in this exercise which has many different shapes, configuration.
• Features are positioned at different angles,getting mesh flow was challenging.
• In Manual Meshing, we need to use the offset option and manually select the faces and also need to define its offset value as well as direction.
• The time taken is too high because we need to mesh it area by area using the batch/spot meshing option. The Quality issue is very high due to human error.

Learning outcomes:

• Learnt to work on CCB assembly which had many components each component had different feature, configuration.
• Learning on improving mesh flow since mesh flow is something that cannot be absolutely perfect in components such as this.
• Learnt to check all the areas for minimum element length and to alter where elements might fail for minimum length. Similarly, CONS which are not essential to define a feature are removed by joining the surfaces

Conclusion

Importing the geometry, geometry cleanup, mid surface extraction for individual component and assigning PID for component, and 2D meshing of the given CCB model were successfully done. All the features in the model are captured properly with good mesh flow.