Week 3 - 2D meshing for sheet metal

ABSTRACT:

• By using CAE Pre-Processing Tool ANSA & to develop 2D meshing for an Automobile Hood or Bonnet, it usually protects and covers the components mainly Engine, Battery, Radiator, and AC parts which include compressor condenser, etc.
• The Hood or Bonnet these days come with different types of materials and shapes according to the usage the cost constraints. Here we use a sedan Hood to demonstrate and the material mainly used is Steel.

METHODOLOGY:

1. Importing the CAD geometry and Assigning Property ID (PID) for each part
2. Checking out the errors.
3. Extracting Mid-Surface (3D to 2D interpretation)
4. Assigning Quality Criteria
5. Meshing and Improving Mesh Quality.

INTRODUCTION:

Keeping safety, strength, and many design aspects, Hood or Bonnet has to undergo many conditions, and the final CAD outcome is considered for pre-processing in ANSA.

The main parts include in this geometry:

• Outer Panel
• Inner Panel
• Both supporting Hinges (Left and Right)
• Latch

PROCEDURE:

1. Importing CAD Geometry of HOOD or Bonnet in ANSA and Assigning Property ID (PID) for each part:

• For any component, we need to assign Property ID(PID) for each and every part so as to differentiate individual checks in our process in later stages.
• This helps in switching to different parts specified upon user requirement.

2.Checking Out for Errors:

• After successfully importing the Hood CAD geometry we need to perform the geometry check under CHECKS Manager in order to see any geometrical problems of the model such as Unmeshed Macros, Unchecked Faces, Needle Faces, Collapsed Cons, Triple Cons, Overlaps, and Cracks.
• ANSA detects some errors and we need to ensure that these needs to fixed manually or by just running the automatic fix command and confirm that there are no geometry errors there in the model.

• Make sure that the Hood is always Gray which indicates Positive in ANSA where yellow stands as Negative.
• Use the Orient option under Faces in Topo Mode to change the color of the model to Gray if it’s so. (Orient<Visible)

3.Extracting Mid-Surface:

• In order to Mesh the component, it needs to undergo mid-surfacing for all the components/parts as the component becomes a 2D object after extracting Mid-Surface and it will be ideally good for Meshing.
• There are different methods a CAE engineer can use for Mid-Surfacing the component and the best would be Mid-SurfaceModules Buttons in Topo Mode.
• Here I used the Mid-surfacing option in faces as it's easy and much efficient.
• Select the whole surface to extract the mid surface and set the offset distance to each and every part of the material
• Create a separate PID for all the Mid-Surfaces Extracted in the Property ID Manager in order to obtain the results at the end.
• Make sure that all the PID’s are created and remove any Hot Points if any.
• Bulb indicates the part selected in the PID Manager.

OUTER PANEL MID SURFACE :

INNER PANEL MID SURFACE:

LATCH, LEFT HINGE, RIGHT MID SURFACES:

Topological Clean-Up:

• So as to acquire the smooth flow of mesh a CAE engineer should do topological clean-up for each and every corner of the model and examine, remove unwanted CONS by using different options available under Module Buttons, mostly used keys are cut, release, insert & delete.

4. Assigning Quality Criteria:

• Give Average/Target length to all the individual Mid-Surfaces using the Perimeters
• Average length alters the shell element length of the component.
• The remaining values are assigned in the Quality Manager or just tapping the F11 key.
• Each element in the Mesh should qualify the Quality Criteria given.
• After assigning the values given for the quality check, we need to perform the topological clean-up before meshing.

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

• Before meshing mid surface set the length parameter
• Measure the length at every end of the surface to clean up the geometry if any length exceeds or descends

5.Meshing and Improving Mesh Quality.

Meshing:

• After Topological Clean up, consider meshing each and every part separately
• One can use different methods in order the Mesh the surfaces, I used the Best Meshing option under Mesh Generation in Mesh Modules Buttons.
• Best Mesh ensure the user a good Mesh flow across the part and ANSA provides a decent outcome.
• Once the Meshing is done, try to reconstruct the Mesh generated and Smooth it for enhancing the Mesh.

Improving Mesh Quality:

• Once the Meshing is done with the desired quality criteria, we need to ensure there should be no unnecessary rotating Trias or Quad elements in the model.
• In 2D objects, the allowed elements are Triangle (Tria) with 3 Nodes & Quadrilateral (Quad) elements with 4 Nodes.
• Nonlinear Tria & Quads are avoided.

• Trias and Quad elements can be adjusted using the Split & Swap options under Element Option, smooth the elements again and again till the flow is fine and accurate, avoid OFF elements whenever possible.

Hinge and Latch mesh surfaces:

• After Completion of meshing, set quality criteria as a draw as a solid.

• Final Hood model

Learning Outcome:

• Able to analyze the model, extracting the property ID for different parts involved.
• Checking the Geometry and creating Mid-Surface for each part (3D to 2D extraction).
• To assign Quality criteria.
• Generating Mesh & checking the quality of Mesh.

CONCLUSION :

• A 3D Automobile Hood is Meshed successfully converting it into a 2D surface thereby extracting its Mid-Surface giving the quality criteria and performed the Meshing, Improving Mesh Quality using different tools with the help of ANSA.
• As ANSA is a trial and error tool user should follow the steps again and again in order to get the desired output.

Google drive link: https://drive.google.com/file/d/1Osc6RHJ8Qr7O1vQC6J-E8deyYI185ESn/view?usp=sharing