Week 3 - 2D meshing for sheet metal

AIM: - 2D meshing for sheet metal (given Hood model).

OBJECTIVE: -

• To Take the mid surface for all the components.
• To check the geometrical errors and fix that error.
• Mesh the mid surface with the given element Quality criteria.

Given Quality Criteria:

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
12.	Tria Percentage	15

PROCEDURE/STEPS:-

• import cad geometry file

Here we have five sub components Hood upper body, hood inner body, two hinges and one central lock. We work on all the sub components one by one.

command:- File>>Open>>Hood model_1

a.) Upper Hood body

b.) Hood inner body

c.) Both hinges

d.) Central lock

• Geometry Clean up :-

Very first we need to analyse and the geometry, when a CAD model is imported into the ANSA, there might be several geometrical errors like intersecting surfaces, missing/distorted surfaces etc. due to the format conversion process or inherent bad model. And, it is important to clear all these errors before starting meshing. So, the next step is to clean up the geometry. To ensure that all the surfaces are connected properly we use command Faces>>Topo is used for all the edges of each individual component at a time.

next we go Tools>>Checks>>Geometry>>Execute>>rightclick on errors>> fix

after Execution

Most of the errors are fixed by right-clicking on the error.

• Mid surface:-

The next, step is to extract the mid surfaces for each component and keep them in separate property id. Mid surfaces are extracted using the manual method i.e., offsetting the. First, the thickness of each component is measured using the Measure tool from Utilities>>Measure>>Nodes>>left click on hot points (between two hot points and distance will genearate in mm).

here we measure thickness for hinge.

similarly we measure for,

Hood inner body (0.75) mm

Hood outer body (0.75) mm

Central Lock/Latch (1.2) mm

of uniform thickness.

The mid surface is extracted using the Offset tool by and selecting all the surfaces on one face. half of the thickness is given as the offset value, the direction is checked and offset.

command: Faces>>Offset>>select faces by left mouse click >> middle mouse click >> OFFSET value (half of thickness) >> OK >> Delete original faces NO

To view only mid surface use !NOT command and select mid plane as shown in the figure….

then press midle mouse click, after that press right click and selecting the part of mid plane in selecting window and reapeat process again and again then finaly mid plane is visible. now the time is set new PID.

a.) Hinge mid surface (right hinge) :-

Command for new PID generation : Faces >> SetPID >> macros/shells >> selecting the entire mid surface (by left click window) >> press midle mouse click for confirmation >> Property card will open (PSHELL) >> right click on PSHELL >> selecting New PSHELL

and edit the PSHELL card .....

similarly we can generate mid surface and their PID for all the sub components.

b.) Hood inner part mid surface:

c.) Hood outer part mid surface:

d.) second hinge (left hinge) mid surface :

e.) central lock / Latch mid surface :-

After that we check manually the mid surface if mid surface is proper then we go further process.

• Setting Quality Parameters: -

quality parameters are configured by using command Utilities >> Quality Criteria

After setting all given quality Criteria hit Apply and press OK.

we set Detail on Demand effect at its lowest value point

After that we hit Apply and press OK.

Next we open Utilities >> mesh parameters.

Here we edit some parameters and we mention their appropriate values in red box.

After that we go Classical mesh >> Perimeters >> Length >> Perimeters >> selecting full component by using left mouse click >> hit middle mouse click.

and select length 5

• Meshing:-

next step is to prepare the mid surfaces for meshing follows these steps

• All the areas are checked for minimum element length and altered where elements might fail for minimum length.
• CONS that are not essential to define a feature are removed by joining the surfaces using Macros >> Join >> selecting CONS and press left click ( this will work in Classic mesh mode) in Topo mode we use Faces >> cut >> selecting CONS by right click. for generating CONS we use Macros >> cut >> selecting CONS and press left click in Classic mesh mode and in Topo Faces >> cut >> selecting and press left click.
• All the holes are rotated using Perimeters >> Slide >> Hotpoints >> Mark/Un tool to ensure the CONS are parallel to the nearby CON.

meshing is done using the Mesh generation >> Best tool. This tool generates the mesh using the best algorithm applicable in selectes area.

created mesh is refined by using command Shell Mesh >> Reconstruct . It is ensured that there are no rotating quads. Also, trias are kept as low as possible.

Things need to be ensured while meshing

• Avoid back-to-back triangle.
• Avoid opposite trias.
• Avoid triangle element at the edges.
• To fix Elements quality Criteria and trias are removed using >>Split, >>Swap, >>Join (Elements Tab), >>Smooth (Shell mesh tab), >>Paste (Grids), and >> Num +/- (perimeter tab).

Mesh results:

a.) Hood inner body

b.) Hood outer part

c.) central lock / Latch

d.) Both Hinges

• Mesh Cleaning :-

To deal with trias elements, the following tools/Commands are used

• Grid >> Paste to paste the nodes and move the triangle element backward
• Elements >> Split to split an element and move tria forward
• Elements >> Swap to move the tria left or right
• Elements >> Join to join two trias to make a quad After modifying the mesh,
• Shell Mesh >> Smooth tool is used to smoothen the flow of the mesh.
• Any elements failing for quality criteria are also fixed by either re-meshing or smoothing the elements.

Finally, the shell element representation is changed by going to Utilities >> Quality Criteria >> Presentation parameters and tick Draw shell as solid.

hit Apply and press OK.

CONCLUSION:

Here we done Geometry clean-up, mid-surface extraction, and 2D meshing of the given hood model. And all the elements pass the quality criteria. All the features in the model are captured properly with good mesh flow.

Learning outcome: -

How to clean up the geometry of simple components.

How to Extract Mid – Surface and assign property and thickness.

Basics of ANSA Software tools and GUI.

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