Meshing Hood for Structural Analysis

Objective :-

• To Clean up the Hood geometry and perform hemming on it.
• And mesh the geometry with the Target element size of 5 mm
• Set Quality criteria for shell as shown in table below

What is Hemming ?

Hemming is a forming operation in which the edges of the sheet are folded or folded over another part in order to achieve a tight fit. Normally hemming operations are used to connect parts together, to improve the appearance of a part and to reinforce part edges.

In car part production, hemming is used in assembly as a secondary operation after deep drawing, trimming and flanging operations to join two sheet metal parts (outer and inner) together. Typical parts for this type of assembly are hoods, doors, trunk lids and fenders.

The accuracy of the hemming operation is very important since it affects the appearance of the surface and surface quality. Material deformations, which occur during the hemming process, can lead to dimensional variations and other defects in parts. Typical hemming defects are splits or wrinkles in the flange, material overlaps in the corner areas or material roll-in. This is why it is important to use simulation tools in order to, on the one hand, better understand the hemming process and, on the other hand, significantly reduce the number of “trial and error” loops during tryout and production.

Various Steps that are followed by me to cleanup the geometry, Meshing and then Hemming the model in ANSA :-

Step 1 : Import the model

• Import the model to the ANSA. File - Open -Select - Import
• Check if the model is only showing by its edges then it is in wireframe mode so click on the below shadow icon to convert it into solid mode.
• When we are importing the model by default it is in entity mode so we convert it into PID(Property ID) mode.
• If edges showing the same color as the modle so to change it go to Quality criteria - Presentation parameters and check the Draw CONS in PID, MID...mode like in ENT mode in Visualization option.

Fig : Hood model

Fig : Inner part of Hood

Fig : Outer part of Hood

Step 2 : Check for the geometry error

• After all the above step done, Now we can check for any error so click the tick mark icon above And then open for geometry checkup and click on Execute.
• If it gives green check mark in status column so it means our geometry has no error but in our case it shows various of error so we have to clear all this before meshing.

Fig : Check for geometry error in Hood by Geometry check tool.

• So by the above figure we observe that, we have many errors in our geometry so first of all clean all the errors using TOPO module.

Step 3 : Clean up the geometry

• In this first of all we are using the inbuild function of ANSA to Automatic fix the gemotry error. For this right click on error in geometry check and then select Fix option. So ANSA try to clear for the error as much as possible.
• If some error left then we are using the TOPO Modules Buttons tools of ANSA to manually fix the error we patches the cons and clear all the intersection error so we can generate the mesh properly.
• We have various tool to patch the single cons and intersection.
• For this model we generally use Coons, delete face, topo, project, new faces and intersects command.

Fig : Cleaned geometry of inner part of Hood

Fig : Cleaned geometry of outer part of Hood

Step 4 : Midplane Extraction

• Midplane is extracted for the geometries consisting the sheet metal of thicness less than 6 mm.
• For extracting mid plane we are using Offset tool in Faces and giving the offset value to 75/2 mm

Step 5 : Symmetry check

• For checking symmetry we are using the tool Rm.Dbl in Faces option to find the geometry is symmetry or not.
• After that we are deleting half of the hood part and copy the left one to the other side using transform-copy-symmetry tool by defult symmetry plane.

Step 6 : Hemming

• Hemming is the process to join the inner hood part to the outer hood part.
• To calculate the thickness of the hemming is 2*Outer thickness + inner thickness.
• For hemming process in ANSA first of all we are projecting the hem end edge to the inner and outer part of hood and delete the extra curved region.
• After that join the inner panel with the outer panel using paste tool and it appears as triple con.

Step 7 : Assigning the PID, MID and thickness

• For setting up the PID and MID first we have to ensure that in visualization Cross Hatches mode is ON so by that we can select the face for naming.
• So, now go to Modules Buttons - Faces - Set PID and select for Faces/Shells, now click on the faces that we want to give name and then click the middle mouse button for property help.
• In property help go to New and Give the name for the faces and then click on OK.
• Now name the property and give the MID and thickness to the component.
• So now in the property help double click on the face that we have named to assign the name to that face.
• At last we go to the property and check all the faces are named correctly or not.

Fig : We provided seperate PID for all component.

Fig : MID is same for all component.

Step 8 : Mesh generation

• For creating the mesh on the model first of all we have to switch the module from TOPO to MESH.
• So, now go to Modules Buttons - Perimeters - length and select for perimeters, now select the edges or directly left click and drag a box around the body so all the edges directly selected.
• After that click the middle mouse button for open the length parameters dialog box and provide the length as 5 mm and then click on \'ok\' to apply.
• So, now for mesh generation go to Modules Buttons - Mesh generation - Best mesh and select \'mixed\' in element type, now left click and drag a box around the body that we have to mesh.
• After that click the middle mouse button to apply.

Fig : Model after meshing

Step 9 : Make mesh check to find the error and correct them.

• For check the mesh error go to the check manager tool and double click on the surface mesh check.
• So surface mesh check box open so now click on the execute key to check for the error.
• Now check is compleated and it indicates warning in our mesh so first of all correct them.

So now we have remove all the error and cross check again for the mesh error and now it shows green tick mark in all so it means our mesh is fine.

Step 10 : Setting up for the quality criteria in shells

• For this go to the quality criteria tool and tick on parameters like skewness, min length, max length etc. as shown in above table and set the failed criteria for it.

• No we have various of skewness and length error so by the use of tool (MV surf, Split, Swap, Reconstruct, Cut, etc) we remove all the error.

• In the above fig Off indicates the quality criteria error.

Fig : Quality criteria error.

Fig : Model after all the quality criteria error solved.

Final Model after all the geometry error, mesh error and quality Criteria error Solved.

Fig : Inner side

Fig : Outer side

Google drive Link for the final model :-

https://drive.google.com/open?id=1BtsbMHZrI6yVZr2dtqN3-C81C-vUw8Lx