Meshing of an automotive hood for structural analysis

Title:- Geometry cleanup and meshing of an automotive hood for structural analysis

Objective:

1. Perform geometry cleanup of automotive hood (both inner and outer panel).
2. Perform mid-surface extraction of both the panels and Hem both the surfaces .
3. Perform shell meshing/grid generation of the following model and maintain the mesh flow and necessary quality criteria.

Element Quality Criteria:

Model:

The Hood model before geometry cleanup.

Fig:-1

Fig:-2

The geometry check shows that model has almost 166 errors which are all single cons that need to be fixed.

After topology correction, the hood model is as follows:

Fig:-3 (Inner panel)

Fig:4 (Outer panel)

Mid-Surface Extraction:

Mid-surface extraction is very useful for meshing when it comes to thick components such as sheet metal components and plastic components.

• Accuracy of the end result can be way off with solid mesh elements.
• The solid mesh approach, which needs 3 to 4 elements across the thickness, results in huge amount of elements and long running times.
• Meshing nasty geometry with solid mesh elements needs preparation too.
• The shell mesh approach creates a fast running accurate simulations.

The mid-surface extraction in this case is done manually using "offset" option instead of going through "casting" option. The inner panel and outer panel has a thickness of 0.75 mm. So, the mid-surface extraction is done at "0.375 mm"

Fig:-5 (Mid-Surface Extract of inner and Outer panel hemmed together)

Hemming:-

• Hemming is a process where the edge of the component is rolled over itself.
• Hems are usually given to reinforce edge, hide rough edges etc.
• Hems are commonly used in automotive components such as hoods, back doors, side doors etc.

Hemming in ANSA is done by first projecting the hem outer edge of the outer panel into the surface of the inner panel as well as outer panel.

Then deleting the ham surface (curve surface) of the outer panel.

Now, joining the edge of the inner panel with the projected curve in the outer panel using "paste" option. In turn a triple con is formed which shows both the inner and outer panel has been hemmed.

Fig:- 6 (Shadow view of the Hammed section)

Fig:- 7 (Wireframe mode of the Hemmed section)

Meshing:-

For structural analysis, usually mixed mode (both Quads and trias) are commonly preferred due to better mesh pattern (restriction : total trias % <5). Sometimes for structural analysis ofr for convergence and better result for non-linear analysis pure qualdrilateral element meshing option is selected.

For the given geometry, we have selected "spot mesh" and "map mesh" to maintain the quality of the element as well as "mesh flow".

Fig:-8 ( Shell Mesh)

Fig:-9 (Shell Mesh)

Fig:-10 (Shell Mesh Converted to solid mesh)

The mesh model obtained has a preety good mesh flow and total trias are 2091 out off 90887 elements which is = 2.30% of the total element (< 5%) which meets the industry standards.